Hybrid device with segmented waveform converter

An apparatus includes a controlled field alternator or utility source of electrical power, a segmented waveform converter, and a controller. The source of electrical power is configured to generate a polyphase signal. The synchronous inverter includes multiple switches connected between the polyphase signal of the source of electrical power and an output filter. The controller is configured to provide a control signal for the switches based on measured electrical quantities associated with the output filter and may provide a field control signal to the controlled field alternator. The apparatus may be applied to a vehicle, a lawnmower, a zero turn radius lawnmower, or another type of machine.

FIELD

This application relates to the field of variable speed generators, and more specifically, an alternating current (AC) to AC converter for controlling the output of a controlled-field synchronous alternator on a variable-speed generator.

BACKGROUND

An engine-generator set, which may be referred to as a generator or a genset, may include an engine and an alternator or another device for generating electrical energy or power. One or more generators may provide electrical power to a load through a power bus. The power bus, which may be referred to as a generator bus or common bus, transfers the electrical power from the engine-generator set to a load. In many examples, the electrical load on the engine-generator set may vary over time.

The frequency of the output of a synchronous generator is based on the speed of the engine and the number of poles in the generator. In order to provide a constant output frequency, the prime mover may have to operate at a fixed speed. The engine may not need to operate at the fixed speed in order to provide enough power to supply the load, but does so to maintain frequency.

Although allowing the engine speed to decrease at light loads may reduce wear, fuel consumption, and sound emissions from the generator, converting the frequency is required in order to allow the engine speed to decrease from rated speed.

DETAILED DESCRIPTION

An alternating current (AC) to AC converter converts an AC signal or waveform to another AC signal having a different or changed electrical property. The changed electrical property may be voltage, frequency, or another property. Example types of AC to AC converters include cycloconverters, matrix converters, and hybrid converters. A cycloconverter converts the input waveform to a lower frequency output signal by synthesizing segments of the input waveform without a direct current link. Cycloconverters may use silicon controlled rectifiers (SCRs) as switches to synthesize the inputs. Matrix converters utilize a network of transistors to similarly synthesize segments in a piecewise manner in order to generate the desired output waveform. Hybrid converters may combine a combination of the two approaches. Although frequency converters or cycloconverters may allow for correction of the frequency, they operate to control the output of the generator without control of the input.

Any of these examples may be referred to collectively as a segmented waveform converter. The segmented waveform converter may generate a single phase output from a multiple phase input. The output of the segmented waveform converter may be a four-quadrant output as the segmented waveform converter can transfer both real power and reactive power in either direction through the segmented waveform converter. The segmented waveform converter generates the output waveform one segment at a time by directly passing a combination of one or more of the input signals. Appropriate filtering of the input waveform may be used to remove high-frequency ripple, switching noise, and undesirable distortion of the output. The output waveform is created from sequential piecewise sampling of the input voltage. The frequency of the sampling defines the length of the segments. The frequency of the sampling may be significantly higher than the frequency of the input waveform and the output waveform. For example, an input frequency of 200 Hz and an output frequency of 60 Hz may require a sampling and switching frequency of 20 kHz in order to provide acceptable output power quality.

An additional advantage realized from the segmented waveform converter, as opposed to conventional inverters, is that lower rated components may be used. The segmented waveform converter uses more switching elements between the source and load than conventional rectifiers. Thus, on average, less current must go through each of the switching elements, and the switching elements may have a smaller current or power rating. Lower rated components may be much less costly. The segmented waveform converter may be electrically connected to one or more filters and configured to provide a filtered output to a variety of loads. Such a segmented waveform converter may be referred to as a synchronous inverter herein.

It is preferred to allow the cycloconverter to control the input voltage and frequency in addition to the output voltage in order to optimize efficiency and provide protection for components in the cycloconverter. In addition, many cycloconverters generate total harmonic distortion (THD) on the output voltage due to switching and commutation noise. This THD can be undesirable depending on the application.

FIG. 1Aillustrates an example engine-generator set10aincluding a synchronous inverter11, an engine12, and an alternator13. The synchronous inverter may include at least one controller (i.e., microprocessor) for controlling a network of switches of a segmented waveform converter. The alternator13may be a controlled field alternator in which a field current is actively controlled by a generator controller (field current controller) to adjust the output of the alternator13. The synchronous inverter controller and the field current controller may be the same device or different devices. The output device14of the synchronous inverter provides the output waveform to a load or another device.

The controlled field alternator13is configured to generate a poly-phase signal through operation of the engine12. The controlled field alternator13may include an exciter armature for generating a field current. As the exciter armature is rotated in a magnetic flux, a time varying voltage is induced in the windings of the exciter armature. The output from the exciter armature is connected to the main field portion of generator. The connection may be made with or without brushes and slip rings. The field current of the output of the exciter provides a magnetic field in rotor field of the generator. As the field portion of the alternator is rotated relative to the stator, a magnetic flux is passed through and across the alternator stator windings producing time varying voltage. The field current from the exciter armature output may be rectified or otherwise controlled.

The output of the alternator13may be a three phase signal. The phases of the poly-phase signal may be offset one another by a predetermined angle (e.g., 120degrees or 2*Pi/3 radians). The poly-phase signal may vary with respect to amplitude and frequency.

The controlled field alternator13provides the poly-phase signal to the segmented waveform converter of the synchronous inverter11, which may include a matrix cycloconverter. The segmented waveform converter includes a network of switches that selectively controls passing a combination of the components of the poly-phase signal to the output14. For example, consider an example in which the poly-phase signal includes two components, A and B. The network of switches could provide several combinations of the two components to the output, which may include only the A component, only the B component, an additive signal of A+B, a subtracted signal of A-B or B-A, and 0 or a null signal, which may be achieved by A-A or B-B.

Before the output14, the synchronous inverter11may include an output filter and electrical quantities may be measured by the controller at the output filter by one or more sensors. The controller of the synchronous inverter11may be configured to provide a control signal for the network of switches based on measured electrical quantities associated with the output filter and provide a field current control signal to the controlled field alternator.

The controller may receive the electrical quantities from at least one sensor. The controller may perform a calculation or consult a lookup table to determine a combination of the components of the poly-phase signal to pass to the output14. In one example, a lookup table relates combinations of available voltages to different settings for the plurality of switches. The available voltage may change over time. In one example, the available voltages vary according to a time-based schedule of expected values. In another example, the available voltages vary according to measured values.

FIG. 1Billustrates another example engine-generator set10bincluding two synchronous inverters11aand11b, an engine12, and an alternator13. The two synchronous inverters11aand11bmay be connected through a synchronization path15.

Both synchronous inverters11aand11bare fed by alternator13and are configured to synchronize their output waveforms using the sync signal on the synchronization path15between synchronous inverters11aand11b. The sync signal may include a digital signal which may indicate a peak, a positive-going or negative-going zero-crossing on the target voltage waveform, or another element of the internal target signal. The sync signal may include an analog signal, indicating a target waveform, a phase angle indicator, or another element of the target output waveform.

The sync signal may be a communications signal communicating a target voltage, target frequency, real load, reactive load, apparent load, zero-crossing timestamp, time synchronization signal, or other information related to the measured output waveform, the target output waveform, or the input to the inverter from the alternator. In one example, one of the synchronous inverters11adetects a zero crossing and slope of the output of synchronous inverter11a, which is sent to the other synchronous inverter11busing the sync signal. The other synchronous inverter11bmay introduce a delay in order to synchronize with the synchronous inverter11a. Various techniques may be used to synchronize the synchronous inverters.

The supplies from the alternator13to the synchronous inverters11aand11bmay be magnetically isolated from each other to allow connection of the inverters in series, the two inverters may allow for connection in a center-tap configuration, allowing 120 or 240 output voltage as desired.FIG. 2illustrates an example synchronous inverter11including segmented waveform converter20. The segmented waveform converter20includes a network of switches SW1-6and at least one energy storing device. The example shown inFIG. 2includes an inductor21and a capacitor23. The inputs, A, B, and C, to the segmented waveform converter20are components of the poly-phase AC waveforms.

In one example, the segmented waveform converter20is configured to supply a control signal to each of the switches for any combination of two or fewer of the components of the poly-phase input waveform. The control signal may include A, B, C, A-B, A-C, B-C, B-A, C-B, C-A, and 0. Other switch configurations may be configured to provide other combinations, such as additive combinations A+B, B+C, and A+C, using a switch configuration other than that illustrated. In another example, the segmented waveform converter20is configured to supply a predetermined set of outputs based on combinations of the components of the poly-phase input waveform. The predetermined set of outputs may include a subtractive combination of exactly two of the components, including A-B, A-C, B-C, B-A, C-B, and C-A. The predetermined set of outputs may include 0, any single component (A, B, or C) or any subtractive combination of exactly two of the components.

The controller may access a target output level as a function of time. For example, the target output may be an AC waveform at a specific frequency and/or a specific amplitude. The target output level may be stored as a series of time based target values. For example, time values are associated with target output levels (e.g., {time1, output1}, {time2, output2}). The target output level may follow a sinusoidal function, and the target output levels may be computed based on a specified voltage and frequency for the output.

The controller may calculate a target electrical parameter for the output filter. In one example, the controller calculates a target current for the inductor21, and in another example, the controller calculates a target voltage for the capacitor23. The controller may calculate a desired change in the electrical parameter based on a measured quantity (e.g., voltage or current) at the output filter. The controller may calculate a change value (delta) based on the difference between the target output level and the current measured quantity. The controller may compare the change values to the available output segments from the combinations of components and selects the closest combination.

Different switch combinations correspond to different output ranges. For example, at time interval 3 on Table 1, combination C-A provides 24V, which is closest to the target at time interval 3 (18). In another example, at time interval 2, combination C-B provides 135, which is the closest to the target at time interval 2 (168). For each time interval, the controller selects one of the possible combinations. Only six combinations are shown, but more combinations are possible. A lookup table based on a single phase measurement may be used. Alternatively, each phase may be measured and compared. The controller may compare the possible combinations to the target value and select the closest combination. The controller generates a field current control signal for the selected combination. The controller may output an individual control signal for each of the switches SW1-6. Each switch SW1-6may be either on or off. Each of the combinations represents different current paths through the segmented waveform converter.

As another example, the controller may select the switch combination that provides that largest voltage to the output and determine a pulse width modulated (PWM) duty cycle to operate between that switch combination and a free-wheeling state. The PWM duty cycle may be chosen based on a ratio between the target voltage and the available voltage, a predetermined sequence, a closed-loop output voltage controller, a model-based control of the output, or a similar technique.

The controller may determine whether the closest available combination is within a threshold difference to the target. When the closest available combination is farther away from the target than the threshold, the controller may apply PWM control to adjust the signal. For example, a PWM duty cycle may be applied to the closest combination to approach the target. In another example, when the closest available combination is farther away from the target than the threshold, the controller first selects the available combination that is greater than the target. Then, the controller applies a PWM duty cycle to adjust the selected combination to approach the target. The PWM duty cycle may be calculated according to Equation 1.
PWM Duty Cycle=Target/Selected Combination Output  Eq. 1.

For example, consider the example at time interval 2, combination C-B provides 135, which is the closest to the target at time interval 2 (168). The controller may revert to the next largest output (215) from combination (C-A). Using Equation 1, the PWM duty cycle would be (168/215)=0.78 or 78%. In one example, the PWM duty cycle may be finely tuned (e.g., every 1%). In another example, a few examples are available and the closest PWM duty cycle is selected. For example, when five duty cycles are available, the options may be 20%, 40%, 60%, 80%, and 100%. In the example above, when equation 1 provides 78%, the PWM duty cycle of 80% is selected.

Table 2 illustrates example control signals for each of the switches in order for the segmented waveform converter20to provide the various output levels or combination of components of the poly-phase signal. The controller may include an output pin for each of the switches to provide the individual control signals to the switch. In another example, the segmented waveform converter20may include a switch controller that receives a bitwise signal according to rows of Table 2. For example, each series of bits corresponds to a set of control signals in the format {SW1, SW2, SW3, SW4, SW5, SW6}.

The controller may calculate a target electrical parameter for the output filter. In one example, the controller calculates a target current for the inductor21, and in another example, the controller calculates a target voltage for the capacitor23. The controller may calculate a desired change in the electrical parameter based on a measured quantity (e.g., voltage or current) at the output filter. The controller calculates a change value (delta) based on the difference between the target output level and the measured quantity. The controller compares the change values to the available output segments from the combinations of components and selects the closest combination.

The filter components Inductor21and capacitor23may be selected to minimize THD on the output of the inverter. They may also be selected based on a target switching frequency of the segmented waveform converter. The filter components may be replaceable or integral to the design. The filter components may be different based on target output voltages and frequencies from the inverter. As an example, the inductor21may be decreased in size when the output frequency increases. As another example, the capacitor may be increased in size for a lower voltage application. The filter components may vary by application, such as decreased filter size when feeding a motor load or increased filter size when feeding a sensitive load.

The filter components may also enable the inverter to control short-circuit current by limiting the rate that the current through the switch can rise. The current control may provide a sinusoidal, trapezoidal, saw-tooth, triangular, DC, square-wave or otherwise shaped output current into a short circuit. The frequency of the output current into a short circuit may differ from nominal frequency. The current control may provide a high level of output current slowly decreasing to a lower level of output current. As an example, the current control may provide 300% of rated generator current into a short circuit for 2 seconds, then decrease the output current to 100% of rated current over the next 5 seconds. As another example, the current control may provide 300% of rated generator current into a short circuit for 5 seconds, then stop sourcing current.

FIG. 3Aillustrates example switches SW1-6for the segmented waveform converter20. The switches SW1-6include a pair of transistors25(e.g., metal-oxide-semiconductor field-effect transistors or MOSFETs) which are controlled by a gate driver27through one or more gate resistors26. The sources of the transistors25may be directly electrically connected. The switches may also utilize a plurality of transistors connected in parallel in order to increase the current rating or to decrease the losses in the power conversion.

The switches are configured such that they block current traveling in either direction. This allows the segmented waveform converter to switch between two AC waveforms. The body diode, if present, on each transistor can conduct when the transistor is conducting in one direction, so the voltage drop across one transistor is typically lower than the other. The gate driver circuit provides the necessary isolation to allow the sources of the switches to float relative to the input and output of the converter, while providing a voltage or current referenced to the sources to trigger the switch. The gate drivers pass a digital signal from the controller to the actual switch.

FIG. 3Billustrates another example switches SW1-6for the segmented waveform converter20. The switches SW1-6include a pair of transistors29(e.g., insulated-gate bipolar transistor (IGBT) or another three-terminal power semiconductor device.) The emitters of the transistors29may be directly electrically connected. The switches may also utilize a plurality of transistors connected in parallel in order to increase the current rating or to decrease the losses in the power conversion. The emitters may be connected using paralleling resistors if the thermal characteristics of the IGBTs are not conducive to paralleling.

The switches are configured such that they block current traveling in either direction. This allows the segmented waveform converter to switch between two AC waveforms. The body diode on each transistor can conduct when the transistor is conducting in one direction, so the voltage drop across one transistor is typically lower than the other. The gate driver circuit provides the necessary isolation to allow the emitters of the switches to float relative to the input and output of the converter, while providing a voltage or current referenced to the emitters to trigger the switch. The gate drivers pass a digital signal from the controller to the actual switch.

FIG. 4illustrates an example network30aof segmented waveform converters. The inputs to the network30ainclude S1, S2, and S3for the first segmented waveform converter, T1, T2, and T3for the second segmented waveform converter, and U1, U2, and U3for the third segmented waveform converter. The outputs of the network30include one output line (L1, L2, L3) for each of the segmented waveform converters. The energy storing devices33, which may be inductors, in combination with energy storing devices34, which may be capacitors, combine to form an output filter. The measurement points37, for current, and39, for voltage, illustrate example locations on the network30where electrical quantities may be measured for controlling the segmented waveform converters. Other voltage and current measurement locations may be utilized. A circuit35includes a field current power supply for generating a field current (DC+, DC−) that is transmitted back to the field coils of the alternator.

InFIG. 4each of the segmented waveform converters share the neutral connection (N). Thus, each of L1and L2and L3can be connected only in parallel or in a three-phase wye configuration.FIG. 5illustrates another example three phase segmented waveform converter in which each of the segmented waveform converters are independent and can be connected in any configuration.

Each of the converters is capable of providing a single-phase AC output, but the phase between the outputs may be fixed such that the network of converters produces a poly-phase AC output. For example, the output of the three converters, between1and4,2and5, and3and6, may be fixed at 120 electrical degrees apart, providing three phase power. As another example, the three outputs, between1and4,2and5, and3and6, may all produce voltage at the same phase angle, allowing them to be connected in parallel to provide increased current sourcing capability in a single-phase application. In yet another example, one of the three outputs,3and6, could produce voltage at 180 electrical degrees from the other two,1and4,2and5, allowing center-tap single-phase output voltages such as 120/240. In this case, one of the output lines from the generator has double the current rating of the other output line because two converters are connected in parallel. In another example, outputs1and4may be 180 electrical degrees from2and5with3and6at the same phase angle as1and4with twice the magnitude. This enables center-tap single-phase output voltages with balanced line current ratings but only half the line current is available from the neutral connections. This final configuration may require higher voltage switches for the converter,31, connected to inputs U1, U2, U3.

FIG. 6Aillustrates an example pin diagram for a circuit package or integrated circuit for a network of segmented waveform converters30a. The inputs to network30a, which are S1, S2, S3, U1, U2, U3, T1, T2, and T3, are on one side of the circuit package, and the line outputs L1, L2, and L3, neutral line N, and field current outputs DC+, DC− are on the other side of the circuit package. The controller area network (CAN) provides a control input to the circuit package in order to set the output. The control input may be the bitwise switch settings describe above (e.g., {SW1, SW2, SW3, SW4, SW5, SW6}) or the control input may be a target output, and the switch settings are controlled internal to the circuit package.

FIG. 6Billustrates an example pin diagram for a similar circuit package or integrated circuit for the network of segmented waveform converters30b. The inputs to network30b, which are S1, S2, S3, U1, U2, U3, T1, T2, and T3, are on one side of the circuit package, and the differential outputs 1, 2, 3, 4, 5, and 6, and field current outputs F+, F− are on the other side of the circuit package. As described above the CAN control input to the circuit package sets the output with either bitwise switch settings or a target output level.

FIG. 6Cillustrates an example power supply40for controlling the field current. The field current power supply40may be used in combination with the circuit ofFIG. 5or in lieu of circuit35inFIG. 4. The power supply40includes an array of transistors41and a switching power supply for stepping up the voltage.

The network of waveform converters provides an output to control the field on the alternator13, allowing the converters to control supply voltage(s). The field on the alternator13may be supplied by a high-voltage DC bus, generated from battery voltage by a DC-DC converter. Control of the supply voltage may allow for improved efficiency, decreased stress on components, broader output voltage range, and improved control under short-circuit conditions, among other benefits.

In any of the examples above, the synchronous inverters may be connected to provide two equally-rated (e.g., 120V) power supplies or the synchronous inverters may be connected in a variety of configurations. The inverters are in communication via a synchronization signal between them to allow the inverters to provide synchronized output voltage. In this case, the two inverters provide a very versatile range of output voltages, allowing a single generator package to be used in a variety of applications.

FIGS. 7A and 7Billustrate example single phase wiring diagrams for synchronous inverters that may be achieved by the segmented waveform converters of eitherFIG. 4orFIG. 5.FIG. 7Aillustrates circuitry as a means for connecting a low voltage (e.g. 120 VAC), single-phase output.FIG. 7Billustrates circuitry as a means for connecting a nominal voltage (e.g. 220 or 240 VAC) for a single-phase configuration.

FIG. 8Aillustrates circuitry as a means for connecting a Low Wye (e.g. 120/208 VAC) three-phase configuration that may be achieved by the segmented waveform converters of eitherFIG. 4orFIG. 5.FIG. 8Billustrates circuitry as a means for connecting a High Wye (e.g. 230/400 or 277/480 VAC) three-phase configuration that may be achieved by the segmented waveform converters ofFIG. 5.FIG. 9illustrates circuitry as a means for connecting a center-tap Delta (e.g. 120/240/208 VAC) three phase configuration that may achieved by the segmented waveform converters ofFIG. 5.

FIG. 10illustrates an example engine-generator set including an engine51, a battery52, a controlled field machine (CFM)55, two segmented waveform converters53, and a generator controller50. Each of the segmented waveform converters53includes a power stage54, a microprocessor56, and a cranking switch58. The engine51includes or is electrically connected with an engine control module (ECM)57and a crank angle sensor59. The power stage54includes the array of switches for receiving the CFM outputs61that feed into the segmented waveform converters53and the field current line63to supply field current back to the CFM55. The CFM55may be an alternator or another rotary device that is controlled by an electrical field. Additional, different, or fewer components may be included in the genset.

The synchronous inverter53may be used to initiate engine rotation (crank the engine51). The synchronous inverter53receives battery power from battery52on the normal AC output and provides an AC voltage waveform on the alternator stator windings, generating a rotating magnetic flux in the stator. The rotating magnetic flux on the stator may generate a torque on the rotor. The generated torque causes the engine to spin, causing air and fuel to be compressed in the cylinders and allowing the engine to initiate combustion (start).

Based on the layout of the segmented waveform converter, the switches allow for bi-directional power flow. Given this configuration, it may be possible to provide a signal that allows the alternator to act as a motor to rotate the engine. The alternator may act as an induction machine using damper windings in the rotor, induced current in the rotor field winding, reluctance variation between the rotor and stator, magnetic hysteresis in the rotor, or eddy currents generated in the rotor steel or laminations. The alternator may also act as a synchronous machine by exciting the rotor field, by rectifying induced voltage in the rotor field, or providing a permanent magnet rotor. The rotor field may be excited by an AC voltage, a DC voltage, or a combination of AC and DC voltage. The rotor field supply may couple through the exciter armature when the rotor is stationary.

The generator controller50is configured to provide a start signal to the segmented waveform converter53. In addition to the start signal, the segmented waveform converter53may receive a position signal of the rotational components relative to the stationary components to determine the speed and position of the engine. In some cases, the position signal may provide information to the segmented waveform converter53that allows the synchronization of the AC voltage applied to the alternator stator. The segmented waveform converter may also determine engine position by measuring back electromagnetic fields (EMF) from the stator windings, stator impedance, stator current, or another signal. In some cases, the output of the crank angle sensor59(an angle) may be fed directly into the synchronous inverter53. In other cases, the crank angle sensor59may be read by the ECM57or generator controller50and the information communicated to the synchronous inverter53.

The engine cranking may be performed by one or more of the segmented waveform converters. The converters may share the cranking load simultaneously, share the cranking load by switching converters occasionally, or some combination of the two techniques. The converter to supply the cranking current may be chosen based on a temperature of each converter, the time that the converter has supplied the current, in order to assess functionality of the components on each converter, or for another reason.

The engine cranking may also be performed by a separate converter or a three-phase inverter. The separate inverter may be part of the segmented waveform converters or a separate converter. The separate converter may connect to a dedicated set of windings on the alternator. The dedicated set of windings on the alternator may be galvanically isolated from the windings connected to the segmented waveform converters. The dedicated set of windings may have a different number of turns than the main windings. The dedicated set of windings may be used to recharge the battery that supplies the cranking current.

The engine cranking may be performed by controlling the frequency and amplitude of the applied voltage. The engine cranking may be performed by controlling the voltage and phase angle between the rotor and stator. The engine cranking may be performed by controlling the torque applied to the engine51. The torque applied to the engine can be measured from the phase angle between the current and voltage, the amplitude of the current, the amplitude of the voltage, the engine speed, or other characteristics of the stator or rotor.

FIG. 11Aillustrates a chart for engine gross torque for an example engine-generator set including a synchronous inverter. As shown by plot110, the engine provides increasing torque as the speed increases for most of the operating speed of the engine. Due to the torque output limitations of the engine, it may be difficult to accelerate the engine quickly from a lower speed. In addition, accelerating from a lower speed may take longer because of the infrequency of combustion events.

The engine torque produced may be significantly less than is indicated inFIG. 11A, depending on the torque demanded by the alternator. The engine output torque may be controlled by controlling the fuel supply to the engine. The engine output torque may be controlled by controlling the air supply to the engine. The torque demanded by the alternator may increase with increasing electrical load. The engine speed may decrease if the alternator torque exceeds the engine torque produced. The engine speed may increase if the engine torque exceeds the alternator torque. The alternator torque may have to be limited to a level slightly below the engine torque in order to allow the engine to accelerate.

FIG. 11Billustrates a chart for engine power for an example engine-generator set including a synchronous inverter. As shown by plot112, the engine speed may increase in order to provide enough power to meet the load demand. The engine speed may be controlled by controlling the torque output of the engine. In order to allow the engine speed to increase, the synchronous inverter may have to reduce output voltage temporarily. If the engine is unable to provide enough power to supply the load, the inverter may have to reduce output voltage temporarily.

The engine may operate at a fixed speed, with the output voltage controlled by adjusting the field current. The engine may operate at a variable speed with the output voltage controlled by adjusting the engine speed. The engine may operate at a combination of fixed speed and variable speed, with the output voltage controlled by a combination of adjusting the speed and adjusting the field current. The output frequency of the alternator may be controlled by adjusting the engine speed. The synchronous inverter may increase the frequency of the output voltage from that of the alternator. The synchronous inverter may decrease the frequency of the output voltage from that of the alternator. Different alternator and engine types require different means of controlling the input voltage to the synchronous inverter.

The synchronous inverter may control the output from the alternator in order to control the input voltage to the segmented waveform converter. Control of the alternator output may provide improved protection for switches in the converter, decreased THD on the output, improved efficiency, better durability, and improved response.

FIG. 12Aillustrates a chart114for rotor and stator losses in an alternator on an example engine-generator set including a synchronous inverter. The example design uses a wound-field alternator to produce the voltage supply to the synchronous inverter and an ECM that allows adjustment of the engine speed. The rotor losses in the alternator may be at a maximum at low speed because the alternator is operating in saturation at low speed in order to allow maximum voltage generation at a minimum speed. The stator losses may increase due to increasing copper losses from current due to increasing load. The total losses may be at a maximum at no load because the system efficiency is not important at no load. The system losses may be at a minimum at 30% load because 30% load is the most common operating point for the generator.

FIG. 12Billustrates a chart116for total system losses for an example engine-generator set including losses from the synchronous inverter. The example generator set may be rated to produce 10 kW. The total system losses may be approximated by the sum of the alternator and inverter losses. The total efficiency may be computed as the ratio between the total power provided by the alternator to the total power produced by the engine. The example generator set may have an efficiency approaching 90%.

As illustrated inFIG. 12B, the engine speed increases with increasing generator load. This may allow the engine to provide sufficient power to supply the load and may also improve fuel consumption, sound and air pollutant emissions, and system longevity. The engine speed may remain constant, decrease or increase in a different example. The alternator voltage produced by the system may increase with increasing load, remain constant, or decrease with increasing load. Increasing alternator voltage with increasing load may help to minimize THD, constant voltage with changing load may simplify inverter control, and decreasing voltage with increasing load may help to minimize stress on components in the segmented waveform converter.

FIG. 13illustrates an example wound-field alternator to provide voltage to the synchronous inverter. The example alternator is configured with the exciter field lying in a common plane with the main machine. The example alternator topology may provide additional voltage control and improved speed range over a permanent magnet alternative. The example alternator topology may provide a similar size profile and efficiency to a permanent magnet alternative. The example alternator topology may be integral to the flywheel of the engine. In this example, the output shaft of the engine may drive a coolant pump, a fan, a fuel pump, another device, or be removed from the shaft casting. The output seal may also be removed from the end-plate casting of the engine.

FIG. 13illustrates a shaft222that supports a rotor frame223. A stator frame221is supported by a fixed member that provides the frame of reference for the rotating rotor. The fixed member may be an engine block or skid or other fixed member. The rotor frame223rotates with the shaft. The rotor frame223supports a rotor field device and an exciter armature device224d. Thus, the rotor field device224aand the exciter armature device224dmay be rigidly mounted together or integrally formed. The stator frame221supports an exciter field device224c, and a main stator device224b. Thus, the exciter field device224cand the main stator device224bare rigidly mounted in the same frame of reference relative to the rotor or may be integrally formed. Either or both of the stator side and the rotor side may be formed of cast iron or steel or laminated silicon steel or other magnetically permeable materials. The outermost component may be designed to act as a shield for electromagnetic interference due to high frequency switching of a power electronic device or devices interior to the outermost component. Also, this may be designed to minimize radiated electromagnetic interference conducted to the alternator from an external power electronic device such as a synchronous inverter.

An exciter air gap225ais maintained between the exciter field device224cand the exciter armature device224d. The exciter field device224cis energized by a voltage regulator or another power source to generate an exciter magnetic field in the exciter air gap225a. The exciter armature device224dis configured to rotate with respect to the exciter field device224cand impart a first time varying voltage in a set of coils in the exciter armature across the exciter air gap225a. In one alternative, the exciter field device224cmay include permanent magnets. In another alternative, the exciter field device may include coils or another magnetic field generating device.

A main air gap225bis maintained between the rotor field device224aand the main stator device224b. The main stator device224bincludes a second set of coils. The rotor field device224ais configured to be energized by the first current in the first set of coils and generate a main magnetic field that imparts a second time varying voltage in the coils of the main stator device224bacross the main air gap225b.

As illustrated inFIG. 13, the main stator device224band the exciter field device224clie in on a common plane normal to an axis of rotation of the shaft222. In a first embodiment, only the main stator device224band the exciter field device224clie in on the common plane with the rotor field device24aand the exciter armature device224dlying in an adjacent plane. In this example, the adjacent plane including the rotor field device224aand the exciter armature device224dare axially spaced from the main stator device224band the exciter field device224c. In this embodiment, the main air gap225band the exciter air gap225alie in adjacent planes or a common plane normal to the shaft. In this first embodiment, magnetic flux travels parallel to the axis of shaft rotation across the main airgap225band the exciter airgap225a. In a another embodiment, the main stator device224b, the exciter field device224c, the rotor field device224aand the exciter armature device224dlie in the common plane. In this embodiment, the main air gap225band the exciter air gap225amay be concentrically aligned parallel to the axis of the shaft222with all or part of the cylindrical exciter air gap225acontained within the cylindrical main air gap225b. The exciter armature device224dis inwardly spaced from the exciter field device224c, main stator device224b, and the rotor field device224a. In other words, the exciter armature device224dis closer to the shaft222than the exciter field device224c, the main stator device224b, and the rotor field device224a. In this second embodiment, magnetic flux travels normal to the axis of shaft rotation across the main airgap225band the exciter airgap225a. Note combinations of the first and second embodiments are possible and contemplated.

FIG. 14illustrates a block diagram for an example synchronous inverter system. The example synchronous inverter contains three segmented waveform converters205a,205band205cwhich may provide the potential to produce three-phase output power through the filter circuits207a,207b, and207c. The segmented waveform converters205a,205band205cmay be supplied with controlled voltages S1, S2, S3, T1, T2, T3, U1, U2and U3from the alternator13through the input filters201a,201b, and201c. The input voltages S1, S2, S3, T1, T2, T3, U1, U2and U3may be adjustable using the field current control device216. The field current control device216may be circuitry or a device configured to receive a command or control signal from the microcontroller200and generate a field current in response to the command. The control signal or command for field current control device216may be generated by the microcontroller200. The segmented waveform converters may be controlled based on the input metering203a,203band203cand the output metering209a,209band209c. The segmented waveform converters may be controlled by the microcontroller200.

The cranking battery voltage may be applied to the segmented waveform converters205a-cthrough the filters207a-cby switching output contractors202a-c. The synchronous inverter may provide engine cranking capability using the segmented waveform converters205a-cto provide a three-phase AC voltage on the alternator windings. Voltages S1, S2and S3, T1, T2and T3and U1, U2and U3may be galvanically isolated from each other. Voltages S1, S2and S3, T1, T2and T3and U1, U2and U3may be connected to separate windings in the alternator13.

The cranking battery218may be charged from the inputs C1, C2and C3from the alternator13. The voltage generated on C1, C2and C3may be galvanically isolated from the voltage generated on S1, S2, S3, T1, T2, T3, U1, U2, and U3. The voltage provided to C1, C2and C3may be generated by a separate winding in the alternator13. The battery charger213may receive a rectified DC voltage from C1, C2and C3through the rectifier211. The battery charger213may be controlled based on a fixed sequence. The fixed battery charging sequence may include a bulk charge mode where the voltage is maintained at a higher level until the current drops below a threshold, a float mode where the voltage is maintained at a low enough level to avoid overcharging the battery and an equalize mode where the voltage is increased for a short duration to ensure that the charge in all cells in the battery is equal. The battery charger213may be controlled based on the battery metering215. The battery charger213may be controlled by the microcontroller200. The microcontroller200may be powered by the board power supply217. All components on the synchronous inverter may be switched at the same frequency to minimize electromagnetic interference (EMI) due to aliasing of the signals.

The input filters210a-cmay provide protection to the switches in the segmented waveform converters205a-cin addition to the snubber circuits provided with the switches. In addition, the input filters201a-cmay provide a bypass path for the current flowing through the inductance of the output windings supplying S1, S2, S3, T1, T2, T3U1, U2and U3, allowing the current to be switched as necessary to minimize the THD of the output voltage.

The output filters207a-cmay provide a bypass for the high-frequency switching noise from the segmented waveform converters205a-c. The microcontroller200may determine the voltage on the output and the current in the filter inductor using the output metering209a,209band209c. The microcontroller200may determine the output current from the inverter based on the filter inductor current, the voltage on the filter capacitor, the switching position, past information from a variety of signals, and system parameters such as the capacitance of the filter capacitor and the inductance of the filter inductor. The microcontroller200may determine the capacitance value of the filter capacitor over time. The microcontroller200may learn the inductance of the filter inductor over time. The output metering209a,209band209cmay include measurement of the output current.

The microcontroller200may determine a real and reactive droop characteristic based on the computed or measured output current from each inverter. The real and reactive droop characteristic may be used to operate seamlessly in parallel with a standard generator. The real and reactive droop characteristics may allow for parallel operation with another generator using a synchronous inverter. The output of the generator may be protected outside the four-quadrant capability curve for the generator by opening all switches, closing all switches, some combination thereof, or some other function of microcontroller control.

FIG. 15illustrates an example synchronous inverter topology that provides a segmented waveform converter on C1, C2and C3to crank the engine. The example is similar to that illustrated inFIG. 14with the addition of the fourth segmented waveform converter205d, as well as corresponding input filter201d, input meter203d, output filter207d, and output metering209d, and the removal of output contractors202a-c. The additional segmented waveform converter205dmay provide the capability of sourcing AC output voltage from the generator without running the engine if a magnetic flux is applied to the stator without exciting the rotor field. The magnetic flux applied to the stator through windings C1, C2and C3may generate a voltage on windings S1, S2, S3, T1, T2, T3, U1, U2, and U3of the alternator13. This capability may require different alternator topology such as the ability to disconnect the rotor field from the exciter armature or rectifier and the removal of any damper or induction windings in the rotor.

When cranking battery voltage is applied to segmented waveform converters205a-c, the synchronous inverter may crank the engine. The crank sequence may be initiated by a digital signal, a communications signal, a state of existing inputs and outputs, or by the presence of cranking battery voltage on the outputs as detected by the output metering209a,209band209c. Cranking may be controlled by the microcontroller200. Cranking may be performed by measuring a phase angle of the alternator rotor and moving a magnetic flux to a position at a given angle away from the rotor position. Cranking may be controlled by measuring a speed of the alternator rotor and rotating a magnetic flux at a given difference in speed, also called slip frequency. Cranking may my controlled by providing a fixed rotation frequency in a known direction without feedback from the engine.

Combining the control of input voltage and frequency within the same synchronous inverter that provides the output voltage and frequency may provide various advantages. As an example, the synchronous inverter may provide 139 VAC line to neutral in order to produce 240 VAC line to line in a low-wye configuration or 480 VAC line to line in a high wye configuration. Providing this additional voltage may require increased input voltage from the alternator, but such increased voltage may be unnecessary when providing 120 VAC line to neutral to produce 208 VAC line to line. Including control of the engine speed may allow the synchronous inverter to improve the efficiency of the system by minimizing the engine speed or improve efficiency by providing a frequency that is an integer multiple or simple ratio to the desired output frequency. In addition, control of the engine speed may allow the synchronous inverter to adjust voltage outside the range otherwise provided by adjusting the field current. As an example, the alternator may only be able to produce 90 VAC at 1000RPM, but 100 VAC may be required to produce 139 VAC line to neutral. In this case, the synchronous inverter may increase the engine speed to 1100RPM in order to provide 100 VAC.

The alternator field current may be provided by a battery, the AC output of the generator, a dedicated coil on the alternator, or a combination of sources. The synchronous inverter may control the field current using a half bridge supply or a full bridge supply. The half bridge supply may be capable of providing positive voltage to the field and allowing it to decay naturally. The full bridge supply may be able to provide a negative and positive voltage to the field, increasing and decreasing the current more quickly. The half-bridge driver may be provided with battery voltage or with a higher voltage generated from the battery voltage or another source. The full-bridge driver may be provided with battery voltage or with a higher voltage generated from the battery voltage or another source.

Combining engine starting capability into the synchronous inverter may allow the total system complexity to be reduced by utilizing the same components for both operations and eliminating the need for a separate starting motor. Starting using the alternator may provide quieter starting operation by removing the power transfer through spur gears on the starter motor and flywheel, lower current draw on the cranking battery by improved efficiency, reduced wear on the system due to minimized side loading while cranking, higher cranking speed due to lower loss connection, decreased package size and lower cost due to removal of the dedicated starting motor, and galvanic isolation due to the use of separate windings in the alternator from the battery charging windings.

Integrating battery charging in the inverter may decrease total package size by eliminating the battery charging alternator, improve reliability of the system by removing the drive mechanism for the battery charging alternator, reduce system complexity by eliminating one controller, provide galvanic isolation between the battery and the generator outputs by using a separate winding, and provide a high-voltage supply for the field from the battery charging windings.

The alternator13may have inductance in the stator which may cause voltage spikes on the input to the segmented waveform converter. The voltage spikes that are generated by the inductance may be minimized by the input filter, by control algorithms for the segmented waveform converters, and by control of the alternator field and engine speed.

The output of the synchronous inverter may be used to operate a motor, similar to a variable frequency drive operation. The segmented waveform converter topology may allow for bi-directional power transfer from the motor, allowing regenerative breaking from the motors. If multiple motors are being driven by a given generator, power may be transferred from one motor to the other.

The alternator may have slightly varying characteristics with temperature and manufacturing tolerance stackup. The microcontroller in the inverter may adapt to the changing characteristics to allow for consistent operation between all products utilizing the synchronous inverter configuration. The engine performance characteristics may also vary with atmospheric conditions, manufacturing tolerances, fuel types and maintenance items. The microcontroller may be able to adapt to the engine characteristics in order to provide expected power quality over the entire load range.

The microcontroller200may control the output voltage using closed-loop feedback from the output metering. The microcontroller200may control the output voltage as a function of the input voltage. The voltage may be controlled with a combination feedback and feed-forward system, with feed-forward tables that may provide adaptive learning capability.

In a short circuit condition, the microcontroller200may control the output current using closed loop feedback from the output metering. The output filter inductor may limit the rise rate of the output current, potentially protecting the switches from damage when sourcing into a short-circuit condition. The short circuit current may be controlled by the switches in the segmented waveform converters, the excitation level in the alternator, or a combination of the two. In addition the output current may be controlled in a scenario where the inverter is connected to a motor in order to limit motor torque.

In cases were multiple inverters are used, the inverters may communicate a synchronizing signal in order to match phase angle across different inverters. The synchronizing signal may be provided over communications, a digital signal, and analog signal, or by observation of the input voltage from the alternator, among other techniques. The sync signal may provide loading information, target information, control mode, connection information, etc. If multiple inverters are used, only one inverter may have control of the field current. That said, the other inverter(s) in the system may want to adjust their supply voltage, so the inverters may communicate a desired input voltage over the communications network, a digital signal or an analog signal.

If multiple inverters are used in parallel, the inverters may need to share loading information in order to equalize the load on each inverter. This may be provided by communications, digital signals, analog signals, or simple droop handling.

The output voltage from different inverters may be tied in parallel with other inverters, or even multiple output stages from a single inverter may be connected together. The configuration of the output of the inverter may be user-adjustable or it may automatically detect that outputs are connected together in order to determine how to control the voltage. Automatic connection detection could involve a specific power up sequence where one inverter stage observes voltage on the input, it could involve current monitoring for abnormalities, it could involve transmission of a special signal on the outputs to be received by another device, or another technique.

FIG. 16illustrates an example generator controller91. The generator controller91may include a processor300, a memory352, and a communication interface353. The generator controller91may be connected to a workstation359or another external device (e.g., control panel) and/or a database357for receiving user inputs, system characteristics, and any of the values described herein. Optionally, the generator controller91may include an input device355and/or a sensing circuit311. The sensing circuit311receives sensor measurements from as described above (e.g., alternator output SWC output). Additional, different, or fewer components may be included. The processor300is configured to perform instructions stored in memory352for executing the algorithms described herein. The processor300may be compatible with a variety of engine and alternator combination and may identify an engine type, make, or model, and may look up system characteristics, settings, or profiles based on the identified engine type, make, or model.FIG. 17illustrates a flow chart for the operation of the generator controller ofFIG. 16. Additional, different of fewer acts may be included.

At act S101, the processor300accesses from memory352or from real time measurement (e.g., sensing circuit311), a measured electrical quantity at an inverter output. The inverter output may be an actual power signal applied to a load under a specification. The specification may be a target value for a sinusoidal signal at time intervals. Alternatively, the target value may specify an amplitude range or root mean squared range for the inverter output. The target value may specify a variance or quality (e.g., THD) level for the inverter output.

At act S103, the processor300calculates a change value for based on the measured electrical quantity and the target value. In other words, the processor300determines the difference between the target value and the actual value of the inverter output. The change value may be either positive or negative.

At act S105, the processor300compares the change value to available inverter inputs. One set of available inverter inputs is shown on each row of Table 1 above. The available inverter inputs depend on either the expected or actual values of outputs of the alternator. For example, in a three phase alternator having outputs A, B, and C, the set of outputs may be A, B, C, A-B, B-C, A-C, B-A, C-B, and C-A. Each of the set of outputs has a value, which changes on each time interval (e.g., sampling interval).

At act S107, the processor300selects a closest available inverter input combination (alternator output) based on the comparison. In one embodiment, the closest available inverter input combination is used without modification. In another embodiment, the closest available inverter input combination is modified to more closely achieve the target value using PWM.

At act S109, the processor determines a switch setting for a switch array of a segmented waveform converted corresponding to the selected inverter input combination. The switch setting is a digital signal or series of bits that describes which of the switches of the segmented waveform converter should be turned on and off in order to provide the selected inverter input combination.

At act S111, the processor300provides a waveform to the inverter output corresponding to the switch setting. In one example, the processor300calculates a difference between the closest available inverter input combination and the target value, and modifies the waveform using a pulse width modulated signal with a duty cycle that is based on the difference between the closest available inverter input and the target value.

FIG. 18illustrates an example system including an engine401, an alternator403, two synchronous inverters or segmented waveform converter405aand405b, an output device400, and a battery413. One of the synchronous inverters405ais coupled with a motor407a, a brake409a, and a wheel411a, and the other of the synchronous inverters405bis coupled with a motor407b, a brake409b, and a wheel411b. Either or both of motors407aand407bare examples of an output drive mechanism for the system. The motors407aand407bmay be referred to individually and interchangeably as motor407, the brakes409aand409bmay be referred to individually and interchangeably as brake409, and the wheels411aand411bmay be referred to individually and interchangeably as wheel411. The engine401may directly drive the output device400. Additional, different, or fewer components may be included.

The alternator403is mechanically coupled with the engine401. As described in earlier embodiments, the rotation of an output shaft of the engine401rotates an exciter portion and a main field portion of the alternator403. The exciter portion includes an exciter armature for generating a field current to induce a time varying magnetic flux in the armature windings, generating voltage. The induced voltage in the windings of the exciter armature is connected to the main field portion of generator. The corresponding field current of the output of the exciter provides a magnetic field in rotor field of the main field portion of the generator. As the main field portion of the alternator is rotated relative to the stator, a magnetic flux is passed through and across the alternator stator windings producing an alternator output signal in bus402. Alternate forms of field control are included herein as well (e.g. brushes and slip rings, flux weakening coils, direct axis current injection).

The alternator output signal may include multiple components that are selectively controlled by the synchronous inverters405aand405b. The derivation of the output of the synchronous inverters405aand405b, or the conversion of the alternator output signal to the output of the synchronous inverters405aand405bmay be performed by generator controller50, generator controller91, or microcontroller200(any one referred to individually as “controller”) in the examples described previously. The controller may consult a lookup table or a configuration value that is specifically tailored to a particular type of motor application of the motor, or feedback based on the current operation of the motor. The controller may determine switch settings for multiple settings that set the output of the synchronous invertors as combination of the multiple components of the alternator output signal. One of the components may be passed or multiple components may be added or subtracted. The controller may apply the switch settings to at least one segmented waveform converter including multiple switches connected between the alternator403and the output drive mechanism (e.g., motors407aand/or407b).

The motors407aand407bmay be AC motors comprising a stationary stator including coils supplied with alternating current by the synchronous inverters405aand405b(referred to individually or as synchronous inverter405). The coils induce a rotating magnetic field that causes a rotor and attached to an output shaft of the AC motor to rotate. The stator and rotor may be housed in a casing, and the stator may be mechanically coupled to the casing. The output shaft may be rotatably mounted to the casing using a bearing.

The output of the synchronous inverter405may include a drive frequency that causes the output shaft of the motor to rotate at a particular speed. In one example, the speed of the output shaft in rotations per second is the same as the drive frequency in cycles per second or related by a predetermined ratio. In other examples, as with induction motors, the drive frequency and shaft speed may not be related by a predetermined ratio. The predetermined ratio may depend on the numbers of poles in the rotor and/or the number of poles of the stator.

The output of the synchronous inverter405may be selected, via switch settings, to cause the speed of the output shaft to change in time. The changes in the speed of the output shaft may be within a time interval that is less than a single rotation of the output shaft or even less than a cycle of the output of the synchronous inverter405, which may be referred to as electrical subcycle torque control. Electrical subcycle torque control applies in torque changes to the output shaft in less than an electrical cycle of the output of the synchronous inverter405. Electrical subcycle torque control may be on the order of 1 to tens of milliseconds. In this way, very quick changes may be applied to the output shaft. The shaft may rotate at multiple speeds within just a few rotations or even a single rotation.

The controller may select the output of the synchronous inverter405based on a feedback signal for the rotation of the output shaft, an input signal, or both. The input signal may be from an input device for setting the speed of the rotor. The feedback signal may be generated by a sensor such as a rotation sensor. The rotation sensor may magnetically, optically or mechanically measure the rotation of the output shaft. Thus, the feedback signal may be indicative of the speed of the output shaft.

Also, the feedback signal could be derived from the output of the synchronous inverter405. The controller may calculate shaft output characteristics such as speed or torque as a function of the synchronous inverter output voltage or current. The controller may compare the feedback signal to the input signal. When the input signal indicates a speed or torque for the output shaft that is greater than a speed or torque target, the controller decreases the frequency, voltage, or current output of the synchronous inverter405. Likewise, when the input signal indicates the speed for the output shaft that is less than the target, the controller increases the frequency, voltage, or current output of the synchronous inverter405.

Through the synchronous inverter405, the speed of engine401and alternator403may be independent of the frequency applied to the motors407and accordingly, independent of the speed of the wheels411. Therefore, the engine401and alternator403may be controlled only to optimize the output device400(e.g., speed of the output device) and the synchronous inverters405control the speed of the motors407. Only the alternator403power or voltage output is controlled to sufficiently supply the synchronous inverters.

The speed of the engine401and the output of the synchronous inverters405may be independent within an operating range of the engine401. Through the operating range, the output device400speed may be adjusted without interrupting the speed applied to the motors407and the wheels411. In other words, when the engine401is operated within a predetermined power range or rotational speed range, the speed of wheels411may be operating in any predetermined speed range in which the power requirements are met by the predetermined power range of the engine401.

The battery413is connected to the synchronous inverter405to act as a source and sink of power. The synchronous inverter405may be configured to charge the battery413or utilize the battery413as a source of power to crank the engine401via the alternator403. The synchronous inverter405may also use the battery413in a limited capacity to deliver power to the motor407or actuate the brake409. The system is capable of transferring power between components without use of the battery. The battery capacity may not be sufficient to provide full power to all components.

Power may also travel in the reverse direction, from the motor407to the synchronous inverter405. For example, a reverse torque may be applied to motor407a, which induces a reverse current though the synchronous inverter405ato the alternator403. Through the power bus402, the reverse current may contribute to the power drawn by the synchronous inverter405band applied to motor407b.

In one example, the system illustrated inFIG. 18is applied to a vehicle such as a forklift, a loader, a golf cart, or a lawnmower such as a zero turn radius lawnmower. A zero turn radius lawnmower may be a lawnmower in which at least two wheels are individually controlled. While the term “lawnmower” may be used in some of the following embodiments, substitutes may be made for other types of vehicles. Aside from the deck and mower apparatus, the drive systems and synchronous inventors may be applied to other types of vehicles. Thus, each wheel411aand411bare individually controlled by the outputs of the synchronous inverters405aand405b. A first segmented waveform converter405ais associated with a first wheel411aof a vehicle and a second segmented waveform converter405bis associated with a second wheel411bof the vehicle. The first wheel411aand/or the second wheel411bis coupled to a drive train, which is the output drive mechanism (primary drive system), to propel the vehicle. In alternative embodiments, only a single wheel is controlled, multiple wheels are connected to a single motor, or three or more motors for multiple wheels are controlled.

Advantages of electrical control using the synchronous waveform converters may be realized over hydraulic or other mechanical systems. For example, in addition to the increased granularity of torque control, electrical drive is more efficient than hydraulic systems. The efficiency improvements save in fuel costs and a smaller engine may be selected. Electrical systems have other advantages over hydraulic systems including the elimination of hydraulic fluid spills, which may damage equipment or vegetation.

The lawnmower may also include a mowing system. The mowing system includes one or more blades configured to cut grass or other vegetation. The mowing system may correspond to output device400. A shaft, belt or other drive train may mechanically connect the engine401to the output device400. The output device400and the engine401may respond to the power requirements of cutting depending on the specific local requirements (e.g., thickness of the vegetation, water content, or other factors).

In operation, when the vehicle is traveling generally in a straight line the speed of the wheels is the same. However, when making turns, the inner wheel with respect to the curve or turn experiences a lower average speed or number of revolutions than the outer wheel with respect to the curve or turn. For the slower wheel to reduce speed, a brake409may be applied to the wheel411. In addition, a power transfer (e.g., negative torque, reverse torque, rear facing torque) may be made from the inner wheel to the outer wheel. The kinetic energy of the rotating mass of the inner wheel is consumed to deliver power to the outer wheel, thereby effecting a braking force on the inner wheel while effecting an accelerating force on the outer wheel without drawing power from or as supplement to power delivered by the engine. As an example, the kinetic energy of the rotating mass of the inner wheel411ais used to drive the motor407ato generate power, controlled by synchronous inverters405a, which is delivered via bus402to synchronous inverters405bfor drive of the outer wheel411b. In a further embodiment, the power delivered by the inner wheel synchronous inverters405amay be used to charge battery413or battery505.

In one example, the controller is configured to generate and provide a magnetic field control signal to the controlled field alternator403. The magnetic field control may adjust the field current. Alternatively, an armature reaction technique such as adjustment of current on flux weakening coils or a mechanical technique such as changing a linkage path of the magnetic path may be used to modify the magnetic flux or the magnetic field control signal. In other examples, a DC output from at least one of the segmented waveform converter may be applied to the controlled field alternator403as a field current. The DC output may be generated by circuit35described in other embodiments. The magnetic field control may be provided by one or more of the synchronous inverter DC outputs. Alternatively, the magnetic field control may be provided by another device with or without a signal from the synchronous inverters405.

The DC output of the other synchronous inverter may be applied to a release mechanism for the brakes409. The primary function of the brakes is to slow the wheels411when activated. However, the brakes409may include a safety mechanism (e.g., a spring) that defaults to biasing the brakes409to stop the vehicle. The safety mechanism may be released by an actuator (e.g., solenoid) when so signaled by the DC output of the synchronous inverter. This causes the brakes to be applied when the engine401or the synchronous inverter is off and to be released when the engine401or the synchronous inverter is running and applying the DC output.

The DC output of the other synchronous inverter may be applied to another purpose such as a control panel, safety mechanism, or status indicator. The control panel may include an interface for setting the output of the synchronous inverter. The safety mechanism may be a circuit to measure an electrical quantity of the synchronous inverter and compare to a threshold and identify an error with the threshold is exceeded. The status indicator may include one or more lights or displays that indicates the synchronous inverter. In another embodiment, the DC output of the other synchronous inverter may be used to power an accessory outlet or lighting of a configurable AC or DC nature.

FIG. 19illustrates an example alternator and three synchronous inverters for a lawnmower. Similar components illustrated previously are consistent withFIG. 19. Additional, different or fewer components may be included.

FIG. 19includes a third synchronous inverter405cthat controls a third motor407cfor the mower410(e.g., mower deck). Thus, the output drive mechanism (secondary drive system) coupled with the synchronous inverter405cdrives the mower410. In this embodiment, the engine401only drives the alternator403. Control of engine speed and torque may be made solely on total power requirements of the system, which may be balanced and allocated by the synchronous inverters405. In other words, cutting speed for the mower410is independent of engine speed and the speed of each of the wheels411is independent of the engine speed. As well, the cutting speed for the mower410may be independent of the speed of each of the wheels411(e.g., wheel411ais independent of mower410, wheel411bis independent of mower410, and wheel411ais independent of wheel411b). In the embodiment ofFIG. 19, any of the DC outputs of the synchronous inverters405may supply the field current to the alternator403. In one example, the magnetic field control is provided by synchronous inverter405cthat drives the mower410.

FIG. 20illustrates an example lawnmower implementing a synchronous inverter for battery charging. The engine401in the embodiment ofFIG. 20directly drives the mower410. Similar components illustrated previously are consistent withFIG. 20. Additional, different or fewer components may be included.

A synchronous inverter503(supplemental segmented waveform converter), which may also be configured and operated by the controller, applied power from battery505to the power bus402, and accordingly, to synchronous inverters405and the motors407. Power may also flow in the reverse direction. That is, when braking or otherwise slowing one of the wheels411, the motor407may act as a generator and provide power back to synchronous inverter503to charge the battery505. Therefore, either of synchronous inverters405aand405bmay charge the battery505.

A switch501, which may be implemented as a relay or an addition synchronous inverter, connects and disconnects the alternator403to the power bus402. The switch501may also be operated by the controller.

At accessory output507provided by the synchronous inverter503may power other electrical systems or accessories of the lawnmower. The other accessories may include headlights, gauge panels, turn signals, horns, radios, or other devices.

FIG. 21illustrates an example lawnmower implementing three synchronous inverters in addition to a synchronous inverter for battery charging. Similar components illustrated previously are consistent withFIG. 21. Additional, different or fewer components may be included.

In this embodiment, synchronous inverter405cprovides power to motor407c, which drives mower410. In addition, the DC output of the synchronous inverter405cmay set the height of deck610of the mower410. The controller may receive a user input for deck height (e.g., distances from the ground) and in response, control the switch settings of synchronous inverter405cto raise or lower the deck610using another motor or drive mechanism.

FIG. 22illustrates an example lawnmower implementing three synchronous inverters and a utility source. Similar components illustrated previously are consistent withFIG. 22. Additional, different or fewer components may be included.

The embodiment ofFIG. 22includes a utility source that may also provide power to the power bus402through synchronous inverters613aand613b. Any number of synchronous inverters may be coupled to the utility source615. The utility may be an AC source provided to the lawnmower through a variety of delivery mechanisms. In one example, an electrical cord may extend to the vehicle from the utility (e.g., electrical outlet). Alternatively, an inductive or other wireless coupling may provide the utility source615. For example, one or more inductive coils may be buried or otherwise placed beneath a driving surface. The inductive coils induce a voltage on one or more receiving coils in the lawnmower and provide power to the synchronous inverters613aand613b, which are configured and operated by the controller.

FIG. 23illustrates an example lawnmower implementing synchronous inverters for the drive of the motion of the lawnmower, mowing of the lawnmower, and supplemental synchronous inverters for charging the battery505and the utility source615. Similar components illustrated previously are consistent withFIG. 23. Additional, different or fewer components may be included.

Depending on the circumstances or current settings, the utility source615, the battery505and/or the alternator403may provide power to the wheels411aand411bthrough synchronous inverters405aand405band/or the mower410and/or deck610through the synchronous inverter405c. Also depending on the circumstances or current settings, the utility source615and/or the alternator403may charge the battery505through the synchronous inverter603.

FIG. 24illustrates an example lawnmower and a utility source and no engine. Similar components illustrated previously are consistent withFIG. 24. Additional, different or fewer components may be included.

Depending on the circumstances or current settings, the utility source615and/or the battery505may provide power to the wheels411aand411bthrough synchronous inverters405aand405band/or the mower410and/or deck610through the synchronous inverter405c. Also depending on the circumstances or current settings, the utility source615may charge the battery505through the synchronous inverter603.

The battery505may also provide power to an external device such as a light tower. For example, at some times the utility source615charges the battery505when the utility (e.g., induction coils) are nearby, and when the lawnmower is remote from the utility source615, the battery505provides power to the external device.

FIG. 25illustrates an example vehicle including synchronous inverters. Two synchronous inverters405are shown, but more or fewer can be used to power motor707. In the case of more than one synchronous inverter405, they would be operated in parallel to increase power capacity, increase voltage, increase redundancy, or for improved controllability. Similar components illustrated previously are consistent withFIG. 25. Additional, different or fewer components may be included. The embodiment ofFIG. 25may be a lawnmower but is not a zero turn radius lawnmower. The vehicle includes the engine401, the alternator403, one or more synchronous inverters405aand405b, a motor707coupled with wheels711, a manual brake703, an emergency brake705, and an output710. The wheels may be connected to the motor directly or via a torque converter (e.g. gear reduction, differential). A steering mechanism turns wheels711together. As described in earlier embodiments, power transfer may occur in a forward direction from the alternator403, through the synchronous inverters405, to the motor707, and ultimately to wheels711. An output of one of the synchronous inverters405may provide the output710, which may be converted from DC to AC (e.g., 120 V convenience output).

FIG. 26illustrates an example vehicle including synchronous inverters in addition to a synchronous inverter for battery charging. Similar components illustrated previously are consistent withFIG. 26. Additional, different or fewer components may be included.

As described in earlier embodiments, bidirectional power transfer may occur in a forward direction from the alternator403, through the synchronous inverters405, to the motor707, and in a reverse direction from the wheels711in response to either emergency brake705or manual brake703being applied, through the synchronous inverters405and603ato the battery505.

Rather than the manual brakes in the embodiment ofFIG. 25, a brake805provides stopping capability in addition to the stopping capability provided in a regenerative control scheme. In the regenerative mode, the motor707supplies power through the synchronous inverter405to the alternator403, the battery505, either output710or507, or any combination thereof.

FIG. 27illustrates an example vehicle including synchronous inverters and the utility source615. Depending on the circumstances or current settings, the utility source615, the battery505and/or the alternator403may provide power to the wheels711through synchronous inverters405aand405b. Also depending on the circumstances or current settings, the utility source615and/or the alternator403may charge the battery505through the synchronous inverter603.

FIG. 28illustrates an example generator system including a synchronous inverter system. Similar components illustrated previously are consistent withFIG. 28. Output710is a DC output and output721is an AC output. Through the synchronous inverters405aand405b, the engine401may run at variable speeds while providing a constant AC output721.

FIG. 29illustrates an example generator system including a synchronous inverter system for providing power from the generator in addition to a synchronous inverter for providing power from a battery. Similar components illustrated previously are consistent withFIG. 29. Each synchronous inverter system may provide a DC output. Synchronous inverters603aand603bprovide DC output810b, and synchronous inverters403aand403bprovide DC Output810a.

FIG. 30illustrates another example generator system with synchronous inverter. Similar components illustrated previously are consistent withFIG. 30.

The capacitor bank823may adapt the single phase utility from utility source615for the synchronous inverters. The capacitor bank823generates a poly-phase signal from the single phase utility through phase shifting the single phase source. The difference in phase is utilized to provide poly-phase input to the synchronous inverter403. The capacitor bank823may include two or more capacitors, or two or more sets of capacitors to convert single phase source to a three phase signal. The single phase utility source may be designated as phase A, the output of a first capacitor or first set of capacitors may be designated as phase B, and the outputs of a second capacitor or second set of capacitors may be designated as phase C.

FIG. 31illustrates a flow chart for the operation of the generator controller ofFIG. 16. Additional, different of fewer acts may be included.

At act S201, the processor300identifies a polyphase signal at a controlled field alternator (e.g., alternator403). The polyphase signal may be detected by the sensing circuit311.

At act S203, the processor300determines determining an output control signal for at least one synchronous inverter to control switches connected between the polyphase signal of the controlled field alternator and at least one output device. The output control signal determines the output of the at least one synchronous inverter.

At act S205, the processor300determines an output torque for the at least one output device. The output device may be a wheel, a drive mechanism, a mowing system, a deck height system, or a generator. In an alternative embodiment, the processor300may determine an output speed, position, or other target for the at least one output device. Additionally, the controlled field alternator may be utilized as the electrical power source or electrical power may be supplied by an alternative source (e.g. utility, battery, wind, solar, nuclear).

Referring toFIGS. 14 and 15, one or more segmented waveform converters205including a plurality of switches connected to the polyphase signal of the controlled field alternator and configured to generate produce three-phase output power through an output filter circuit including at least one output filter207. The output power may be referred to as a drive signal, which may drive at least one motor, as described in the examples ofFIGS. 24-31. An input circuit to the segmented waveform, which may include input filter201, includes an input coupled to a controlled field alternator and configured to receive a polyphase signal from the controlled field alternator. At least one output filter207is configured to modify the drive signal based on at least one setting for the motor. The controller200is configured to generate a control signal to set states of the switches to generate the drive signal for the at least one motor. The control signal may be based on sensor data.

Referring toFIG. 32A, an example engine-generator assembly70includes a synchronous inverter11, an engine12, an alternator13, and an output filter74and is coupled to a load device65. The synchronous inverter11may include an input coupled to a controlled field alternator configured to receive a polyphase signal from the controlled field alternator and at least one controller (i.e., microprocessor) for controlling a network of switches of a segmented waveform converter connected to the polyphase signal of the alternator13and generate a drive signal for at least one load device75. In addition, the alternator13may be a controlled field alternator in which a field current is actively controlled by a generator controller (field current controller) to adjust the output of the alternator13.

Electrical noise from the alternator, in which the waveform deviates from an ideal sinusoidal, becomes mechanical noise (audio) as the waveform powers the motor. In AC to AC converters, noise is typically not a design concern. On heavy equipment such as mining equipment, mechanical noise from electrical motors may be acceptable with respect to cost, because other noise in the environment often exceeds that of the electrical motors. Other applications may require that less noise is produced by the electric motors. In some examples, the sound from the hydraulics may exceed that of the engine. Sounds becomes a priority in some applications such as carts or lawnmowers that are used in quiet environments such as golf courses. The output filter74reduces noise on the waveform output from the alternator12, which may include audible noise and electromagnetic interference. The output filter74may also reduce heating in the motor because the filtered waveform more closely matches the physical characteristics of the motor.

The output filter74is configured to modify the drive signal based on at least one setting for at least one load device75. The output filter74may include one or more active components include an SCR, a field effect transistor (FET), and an insulated gate bipolar transistor (IGPT), and one or more passive components such as capacitors, inductors, and resistors. The at least one setting may include physical parameters of the load device75, a tilt setting for traveling on an incline, a decline, or along an incline, a turn setting for low radius turns, a load setting for the motor, a fuel efficiency setting, or a configuration setting. The following sections each of these examples in more detail. As shown inFIG. 32B, the at least one load device75may be a motor such as a direct current (DC) motor, an AC induction motor, a synchronous AC motor, a brushless DC motor, a brush-type DC motor, or a combination of multiple of the foregoing designs.

A controller71configured to generate a control signal to set states of the plurality of switches to generate the drive signal for the at least one motor. The control signal may be based on sensor data. Examples of sensor data include lever steering sensor data, load sensor data, or orientation sensor data.

The power system apparatus includes a synchronous inverter and at least one motor driven by the synchronous inverter. In one example, the synchronous inverter drives one or more wheels of a vehicle. The power system may include multiple synchronous inverters each electrically coupled with a different electric motor. In addition, the power system may include multiple motors driven by a single inverter.

The power system apparatus may include an electric hybrid power system for a lawnmower or another vehicle. The electric hybrid power system may include a synchronous invertor and electric motor for each of multiple drive wheels. The electric motors and drive wheels may be driven independently according to the techniques described herein. The hybrid power system may include at least one battery that is charged by the alternator at one time or part of a power cycle and later powers at least one motor at a second time or part of the power cycle.

FIG. 33illustrates an example vehicle80including a synchronous inverter and at least one motor. The vehicle80includes the engine12, alternator13, and synchronous inverter11. The vehicle80may also include the output filter74. The vehicle80includes a motor81, a gear transmission82, a wheel linkage83, one or more idle wheels84, one or more driven wheels85, a flywheel88on a driveshaft89(FIG. 35), and a subframe including a support frame86and a gear frame87. The motor81may be a direct current (DC) motor controlled by voltage or an alternating current (AC) motor controlled by frequency. Additional, different, or fewer components may be included.

The synchronous inverter and at least one motor are an example alternative to replace a hydraulic propulsion system such as used on zero turn radius (ZTR) lawnmowers. The hydraulic propulsion system independently operates two driving mechanisms and drive wheels. Traditional ZTR lawnmowers may include hydraulic valves to control hydrostatic transmissions driven by belts from an internal combustion engine, which may be fueled by gasoline, diesel fuel, liquefied petroleum (LP), compressed natural gas (CNG), or another type of combustible fuel. The hydrostatic transmissions require regular maintenance to maintain performance and durability. In addition, hydraulic fluid may leak, causing damage to the environment (e.g., harm grass or stain garage floors).

On the other hand, a similar lawnmower using electric propulsion eliminates these challenges and enables new benefits and features. The lawnmower using electric propulsion and the synchronous inverter may include traction control to prevent one or both wheels from damaging turf, zero radius turning techniques that prevent one wheel from damaging turf, optimization of engine speed for a given ground speed as load changes (e.g., uphill, downhill, or in sand), and/or optimization of engine speed (and fuel consumption) for power take off load changes when used in conjunction with electric motor drives.

FIG. 34illustrates an example subassembly for the vehicle ofFIG. 33.FIG. 35illustrates a reverse view of the example subassembly ofFIG. 34.FIG. 36illustrates a top view of the example subassembly ofFIG. 34.

The subassembly may include the subframe including the support frame86and the gear frame87. The support frame86is secured to the gear frame87using one or more connectors. The term connectors as used throughout may include any combination of bolts, screws, rivets, or welded joints. Alternatively, the support frame86and the gear frame87may be integrally formed. The gear frame87is mechanically coupled using one or more connectors to the gear transmissions. The support frame86is mechanically coupled using one or more connectors to the engine12, the alternator13, which may include the synchronous inverter11, and the one or more motors81.

The subassembly may be pre-assembled as a hybrid power system module. The support frame86may be coupled to the chassis of the vehicle using support bars91. The support frame86may include a bracket that slides onto the support bars91and the assembly may be secured to the chassis of the vehicle using one or more connecters. Thus, any combination of the engine12, the alternator13, the synchronous inverter11, one or more motors81, one or more gear transmissions82, one or more wheel linkages83, the support frame86, and the gear frame87may be coupled to vehicle80at the same time using the subassembly. In one example, the only mechanical connections between the subassembly and the vehicle80is made through the support bars91.

The subassembly may also connect to the vehicle through electrical connections. The electrical connections may include accessories for the vehicle80. That is the subassembly, including the alternator12or the synchronous inverter11, may provide a DC output for running the accessories for the vehicle80such as lights, a radio, a mower deck lift, gauges, a control panel, or other features. In one example, high voltage circuitry associated with the alternator12or the synchronous inverter11are isolated from the electrical connections between the subassembly and the vehicle80. The subassembly may be installed without exposure to any high voltage areas. The subassembly may be installed by a user or technician that is not trained in high voltage installations.

The controller71determines a drive signal for the load device75and generates a control signal for the switches of the synchronous inverter11. The synchronous inverter11outputs the drive signal, which may be modified by the output filter74. The drive signal may include a frequency that specifies a speed of the motor81. The motor81rotates a shaft in the gear transmission82at an input speed, and the gear transmission82changes the input speed to an output speed. The gear transmission82may include a series of gears of different gear ratios in order to convert from the input speed to the output speed. Alternatively, the motor may be directly coupled to the wheel without a transmission.

The gear transmission82may be a right-angle gearbox that transfers the mechanical output of electric motor81to a drive wheel85of the vehicle80. The gear transmission82may include a worm gear for transferring the direction of rotation of the drive shaft of the motor81to the direction of rotation of the wheel linkages83. The wheel linkages83are coupled to the drive wheel85and apply a rotational force to the drive wheel85.

Optionally, when the gear transmission82includes a worm drive gear reduction system, a brake system is not needed because the output shaft is naturally locked unless the input shaft turns. In addition, an override clutch may be included in the gear transmission82to take one or more gears out of mesh. When the override clutch is engaged, the drive wheels85are free to operate independently of the gear transmission82. Thus, when the override clutch is engaged, the vehicle80may be moved or pushed manually or in tow without the motors81rotating the gear transmission82. In another example, the gear transmission82may include one or more limited to set a maximum speed for the drive wheels. Alternatively, the motor may incorporate a spring-applied and electrically-released brake to prevent unintended movement of the vehicle80.

FIG. 37illustrates a perspective view of the vehicle80as a zero turn radius (ZTR) lawnmower. The lawnmower includes drive wheels85, idle wheels84, a mower deck95, and one or more control levers93. The subassembly ifFIGS. 34-36may include a mechanical link to one or more control levers93to transfer a user input level as at least one setting for the motor91. One or both of the control levers may be interchangeable with a joystick or another steering mechanism.

Either or both of the control levers93may be matched with a position sensor. The position sensor may include an optical sensor, a potentiometer or resistive sensor, a displacement sensor, or a rotation sensor. As a control lever93is rotated forward or backward, the position sensor determines a direction and amount of the rotation. The position sensor may generate an output that is proportional to the rotation of the control lever93. The output of the position sensor for each control lever93is analyzed by the controller71to generate a control signal for the synchronous inverter11, which output a drive signal for motor81and corresponding drive wheel85. The controller71may determine a position of the control lever93from the sensor data.

The controller71may include a lookup table that relates positions of the position sensor to respective speeds of the motor81, drive signal levels that correspond to respective speeds of the motor81, or settings for the synchronous inverter11that correspond to the respective speeds of the motor81. The lookup table may be based on the responsiveness of a hydraulic systems. That is, the lookup table may be selected to cause the controller71to mimic a hydraulic system. That is, if a 10 degree rotation in a control lever93would result in a 0.5 second delay before applying a target rotation of 20 revolutions per minute in a hydraulic system, the lookup table may instruct the synchronous inverter11to delay for 0.5 seconds before creating a drive signal that causes the motor81to rotate at 20 revolutions per minute. Alternatively, the lookup table may be selected to specify the torque applied to the drive wheel85, which may mimic a hydraulic system.

The controller71may provide a variety of additional controls for transferring the positional sensor data of the control levers93to the drive signal from the synchronous inverter11for driving the motor81. The additional controls may include a turn setting for turf protection, an incline setting for safety, a steering setting for inclined surfaces, an optimized mowing setting, and a traction control setting.

The turn setting for turf protection may prevent the drive wheels85from damaging the turf when one wheel is driven and the other is held stationary. When one wheel is held stationarity, that wheel may spin in place when the other wheel moves forward. The wheel spinning in place may damage the turf, pulling grass away from the ground.

The controller71may identify this situation and reduce the risk of damage. The controller71may identify this type of turn (e.g., potentially turf damaging turn) when one control lever93is pushed forward or backward past a threshold position and the other control lever93is maintained in a substantially stationary position. An outer wheel of the vehicle80corresponds to the control lever93is pushed forward or backward past the threshold position, and an inner wheel of the vehicle80corresponds to the control lever93maintained in the substantially stationary position. The substantially stationary position may be a position deflection of 0 degrees or within a predetermined range of 0 degrees. Examples for the predetermined range may include within 5, 10, or 15 degrees. Examples of the threshold position to be indicative of forward or backward may be 30, 40, or 50 degrees.

When a potentially turf damaging turn is identified, the controller71adjusts the control signal for the synchronous inverter11and the corresponding drive signal for the drive wheel85. The controller71may pass the control signal for the one control lever93is pushed forward or backward past the threshold position under normal conditions. The controller71may modify the control signal for the wheel in the substantially stationary position. The controller71may generate the control signal for the synchronous inverter11and the corresponding drive signal for the drive wheel85to introduce a nominal adjustment, a feathering, or multiple directional control. The nominal adjustment may include a speed increment or decrement added to the inner wheel associated with a substantially stationary position. The speed increment or decrement may be an adjustment in the speed of the inner wheel by the nominal amount (e.g., 1 revolution per minute, or 1 inch per second). Feathering or multiple directional control may include a series of adjustments to the inner wheel associated with the substantially stationary position. The controller71may cause the inner wheel to be advanced forward for a first time, rotated backward for a second time, and repeated between forward and backward motion. In addition, the controller71may include a hysteresis control so that if the user adjusts the control of the inner wheel, which would normally provide the nominal speed or feathering control of the inner wheel, the controller71maintains the automated speed increment or decrement to the inner wheel rather than that supplied by the user, until the user input exceeds a threshold set by the hysteresis control.

The controller71may provide an incline setting for safety. The controller71may receive orientation data from an inertial sensor coupled to the vehicle80. The inertial sensor may include any combination of an accelerometer, a magnetic sensor, or a gyroscope. The orientation data may describe up to three angles such as roll, pitch, and yaw of the vehicle. The orientation data may include a total angular value that describes a sum of the angular difference from the horizontal (e.g., sum of roll angle and pitch angle).

The controller71may determine whether the vehicle80is traveling uphill or downhill based on at least one of the angles (e.g., pitch angle). The controller71may adjust a speed or braking mechanism of the vehicle80to reduce the risk of tipping the vehicle80or bringing one or more of the wheels away from the driving surface. The vehicle80may be determined to be driving uphill or downhill when the orientation data indicates the pitch angle of the vehicle80exceeds a threshold (e.g., greater than a positive angle threshold or less than a negative angle threshold).

When the vehicle is traveling uphill, when the angle exceeds an uphill threshold, the controller71may adjust the speed for the motor81by increasing the speed of the motor81or the speed of the engine12by adjusting the control signal for the synchronous inverter11and the corresponding drive signal for the drive wheel85. When the vehicle is traveling downhill, when the angle exceeds a downhill threshold, the controller71may adjust the speed for the motor81by decreasing the speed of the motor81or the speed of the engine12by adjusting the control signal for the synchronous inverter11and the corresponding drive signal for the drive wheel85.

In addition, the controller71may selectively remove current from the electrical release mechanism of the brake on the wheel (if equipped). The controller71may also apply a counter-rotating field to the motor to provide reversing torque. This may be used to load the engine12to prevent an engine overspeed condition.

The controller71may provide a steering setting for inclined surfaces. The controller71may receive orientation data from the inertial sensor coupled to the vehicle80. For the inclined surfaces steering, the orientation data may describe the roll angle. When the vehicle travels along an incline, the roll angle is substantially nonzero and substantially constant. A vehicle traveling along an incline has one set of wheels (e.g., right side) higher in elevation than the other set of wheels (e.g., left side). The controller71may determine that the roll angle is greater than a minimum incline value (e.g., 10 degrees or 5 degrees) and consistent with a predetermine variance (e.g., 10% or another percentage) for a time period. A vehicle traveling along an incline may be a lawnmower traveling perpendicular to a hill.

A ZTR lawnmower traveling along an incline may be particularly difficult to maintain in a forward direction. Due to gravity, the vehicle80may tend to veer in the downhill direction. Operators of ZTR lawnmower may develop a skill to hold the downhill wheel's control lever at slightly more of a forward direction than the uphill wheel's control lever. The controller71may supplement this control. The controller71may identify when a user input for forward travel occurs when the roll angle is greater than a minimum incline value and consistent with a predetermined variance for a time period. In response, the controller71may adjust the speed of the downhill motor to be greater than the speed of the uphill motor. For example, the controller71may adjust the control signal for the synchronous inverter11and the corresponding drive signal for the drive wheel85of the downhill motor.

When the vehicle80is traveling on an incline the controller71may adjust the control signal for the synchronous inverter11, and effectively the drive signal for the drive wheels85in response to the incline.

The controller71may provide an optimized mowing setting based on sensor data for the turf. The sensor data may include a moisture sensor that detects when wet grass is present. The controller71may increase a speed of the engine12in response to the need for increased power required heavier loads like to cut grass that is tall, thick, or wet grass. Thus, the alternator13provides a higher output voltage (if DC motor) or frequency and/or voltage (if AC motor) to maintain mower blade speed. Conversely at light loads, the controller71would decrease engine speed. The controller71causes the synchronous inverter11to maintain the electrical output to maintain the selected motor speed.

The controller71may provide a traction control setting based on sensor data from slippage of the drive wheels85. For example, each of the drive wheels85may be associated with a speed sensor or position sensor that tracks the movement of the device wheels85and generates data indicative of the speed or position of the drive wheels85. The controller71compares the speeds and/or positions of the drive wheels85to determine if one is traveling significantly faster or slower than the other. The controller71may compare the difference in speed of the wheels to a traction threshold to determine if slippage is occurring. Slippage may occur because of a wet surface (e.g., wet trailer ramps, wet pavement, wet grass), mud, or an unstable surface (e.g., loose stones). In response to determining slippage, the controller71may apply traction control by generating a command for a brake for applying a braking force to one or more of the drive wheels85. In one example, the brake force may be applied to the faster (e.g., slipping) wheel.

The controller71may adjust the control signal for the synchronous inverter11based on characteristics of the motor81. In one example, physical characteristics may include the structural dimensions of the motor81or the amount of metal that makes up the motor81. Electrical characteristics may include the pitch, the number of poles or the number of windings for the motor81. The characteristics of the motor81may define the harmonics produced by the motor81or a resonant frequency for noise or vibrations produced by the motor81, adjusting the control signal for the synchronous inverter11may include adjusting a target waveshape to minimize generated harmonics in the motor.

The controller71may receive data indicative of the characteristics from a sensor such as a vibration sensor. The controller81may receive data indicative of the characteristics from a user input such as a setting for the model or manufacturer of the install motor81. The controller81may access data indicative of the characteristics from a memory that includes a table of motor models with characteristics.

The characteristics of the motor81may be associated with an ideal waveform. The ideal waveform may include a frequency that is tuned to the particular motor81. The frequency may be spaced by a set amount from the resonant frequency in order to reduce vibration. The frequency may be selected to reduce harmonics. Using the ideal waveform causes the motor81to produce less internal heat, which improved the efficient of the system.

The controller71may adjust the control signal for the synchronous inverter11so that the ideal waveform is applied to the motor81. The subassembly may be assembled before the controller71and synchronous inverter11are calibrated according to the characteristics of the motor81. In this manner, the harmonics and resonant frequencies for the subassembly are measured before installation in the vehicle80, which further reduced the manufacturing burden in assembling the vehicle80. The calibration eliminates or dampens vibration or harmonics internally by the subassembly.

A typical inverter (DC to AC or AC to AC) regulates to a root mean squared (RMS) voltage and not a sinusoidal target. Regulating to a sinusoidal target allows a subcycle (much faster) response to changes in load on the generator or vehicle. The synchronous inverter11may respond much more quickly to the changes. The term subcycle refers to a change that occurs in less than a cycle of the drive signal that is outputted from the synchronous inverter11.

The controller71may implement optimal operation sequences for the engine12, alternator13, and synchronous inverter11based on the demands placed by the vehicle80. For example, the controller71may implement a hybrid algorithm that switches between power produced at the alternator13and energy stored in one or more batteries.

In one example, the controller71implements a charging cycle for a battery and the optimal operating characteristic of the least one motor81. The optimal operating characteristics for the engine12may be a predetermined percentage (e.g., 80%) of the output of the engine12or the speed of the engine12. Even when less is demanded by the load, the engine12is operating at optimal capacity and any excess is stored in the batteries. The controller71may determine when the one or more batteries read full charge, or a specific level of charge, and turn off the engine12and alternator13and this point. The synchronous inverter11is then run from the stored energy in the battery until the battery reaches a minimum level. At this point, the engine12is started again and run at the optimal level. The sequence repeats.

The controller71may determine an electrical configuration of the synchronous inverter11based on the load connected to the synchronous inverter11. The electrical configuration may be indicative of a single phase load or a three phase load. The electrical configuration may be a load characterization indicative of the type of load connected to the synchronous inverter11.

The controller71may determine whether the load is single phase or three phase based on a test signal. For example, consider three outputs for the synchronous inverter (A, B, C). The controller71may send a test voltage to one of the outputs (A) and measure the resulting voltage on one or more of the other outputs (B, C). When the other outputs (B, C) are measured at a level substantially similar to the test voltage, the controller71determines that the load is single phase. Otherwise, the controller71determines that the load is three phase.

The controller71also may determine the type of load based on a test signal. Example types of load include resistive, nonlinear, capacitive, inductive, and reactive. Example nonlinear loads include battery chargers, uninterruptible power system (UPS), or variable frequency drives (VFD). The controller71is configured to adjust the gains of the synchronous inverter11through the states of the switches in the control signal in response to a load characterization of a load of the segmented waveform converter.

The controller71may identify subcycle load changes based on the type of load. For example, nonlinear loads may include a load spike that occurs at a particular time in the cycle. The load spike may occur when a SCR fires at a particular subcycle position (e.g., 60 degrees). The controller71may modify the control signal for the synchronous inverter11so that the output of the synchronous inverter increases at a predetermined time (e.g., a set number of milliseconds) or a set position in the cycle before the predicted load spike. The pre-emptive change in output may reduce the dip in power that could occur after the load spike. A similar control may be applied to the reduction of a load, avoiding the overshoot in power.

As described above in associated withFIGS. 19-28, multiple synchronous inverters may be linked together to provide power to a load in parallel (providing increased current output) or in series (providing increased voltage output). The synchronous inverters may also communicate with one another using a synchronizing signal in order to match phase angle across different inverters, adjusting their supply voltage using the communications network. In addition or in the alternative, the controller71may generate a communication signal that is modulated on the output drive signal of the synchronous inverter11by a communication interface. The communication signal may be a high frequency signal encoded with data using frequency modulation or pulse width modulation. The modulated communication may be high enough in frequency so as to not interrupt the operation of the motors or other load but still detectable by controllers for the other synchronous inverters in the system.

The synchronous inverters may communicate in order to equalize loading and ensure equal wear among a group of connected synchronous inverters11. For example, for a 25 kW load and four synchronous inverters, the inverters may communicate their loads so that each synchronous inverter converges to supplying 6.26 kW to the load.

FIG. 38illustrates a flow chart for the operation of the controller71, which may be implemented by the generator controller ofFIG. 16. Additional, different or fewer acts may be included.

At act S301, the processor300is configured to receive, at an input coupled to a controlled field alternator, a feedback signal. The feedback signal may be indicative of the current output of the controlled field alternator. The processor300may access a target output from memory352or receive the target output from communication interface353from workstation359or another synchronous inverter.

At act S303, the processor300generates a drive signal for at least one motor at a segmented waveform converter or synchronous inverter including switches connected to the feedback signal of the controlled field alternator. At act S305, the processor300modifies the drive signal based on at least one setting for the motor. At least one setting may include physical parameters of the load motor, a tilt setting for traveling on an incline, a decline, or along an incline, a turn setting for low radius turns, a load setting for the motor, a fuel efficiency setting, or a configuration setting.

The processor300may include a general processor, digital signal processor, an application specific integrated circuit (ASIC), field programmable gate array (FPGA), analog circuit, digital circuit, combinations thereof, or other now known or later developed processor. The processor300may be a single device or combinations of devices, such as associated with a network, distributed processing, or cloud computing.

The memory352may be a volatile memory or a non-volatile memory. The memory352may include one or more of a read only memory (ROM), random access memory (RAM), a flash memory, an electronic erasable program read only memory (EEPROM), or other type of memory. The memory352may be removable from the network device, such as a secure digital (SD) memory card.

In addition to ingress ports and egress ports, the communication interface303may include any operable connection. An operable connection may be one in which signals, physical communications, and/or logical communications may be sent and/or received. An operable connection may include a physical interface, an electrical interface, and/or a data interface.

The communication interface353may be connected to a network. The network may include wired networks (e.g., Ethernet), wireless networks, or combinations thereof. The wireless network may be a cellular telephone network, an 802.11, 802.16, 802.20, or WiMax network. Further, the network may be a public network, such as the Internet, a private network, such as an intranet, or combinations thereof, and may utilize a variety of networking protocols now available or later developed including, but not limited to TCP/IP based networking protocols.