Patent Description:
A distributed DC bus system supplies DC power to multiple loads from a single DC source. One application for a distributed DC bus is found in industrial control. A controlled machine or process may have multiple axes of motion, where each axis is controlled by a motor. A single rectifier front end is provided to convert, for example, a three-phase AC voltage from a utility supply to a DC voltage. The three-phase AC voltage may be, for example, <NUM> VAC or <NUM> VAC and the resulting DC voltage supplied on the distributed DC bus may be <NUM> VDC or <NUM> VDC, respectively. The power rating of the rectifier front end is sufficient to supply enough current at the corresponding DC voltage level to multiple motor drives via the distributed DC bus. A first set of conductors is provided to supply the DC bus voltage from the rectifier front end to each motor drive in the system. Each motor drive receives the DC voltage and supplies a controlled AC voltage, having a variable amplitude and variable frequency, to a motor connected to the motor drive to achieve desired operation of the motor.

However, in addition to the DC bus voltage required to generate the AC voltage used to control rotation of the motor, each motor drive requires a control voltage to supply power to control circuits such as a microprocessor executing within the motor drive, logic circuits, gate drive circuits, analog-to-digital converters, digital-to-analog converters, communication circuits, and the like. The control voltage is commonly at or below <NUM> VDC, which is considered a safe voltage that does not require further guarding against accidental contact, and is similarly distributed to the motor drives. In many applications, it is desirable to have the control voltage present without having the DC Bus voltage present. During commissioning, for example, the control voltage is required to enable a technician to set parameters on the motor drive that will define how the motor controlled by the motor drive will operate. Consequently, the control voltage is supplied independently of the DC bus voltage. Either a separate power supply generates the control voltage or the rectifier front end is configured to supply the control voltage via an output separate from the DC bus voltage. A second set of conductors is provided to connect the control voltage to each of the motor drives. However, because the current and power rating of the control voltage is much less than the current and power rating required to supply power to control rotation of the motor, the size of the wires utilized for distributing control power to the motor drives is correspondingly less than the size of the wires or than the bus cross-section utilized for distributing DC bus voltage to the motor drives.

Use of the smaller size wire to distribute control power to motor drives is not without certain drawbacks. Smaller wire has a greater resistance per unit length than a larger wire. Thus, wire used to distribute control power has a greater resistance than wire used to distribute the DC bus voltage when run the same distance. If the control power is also distributed from the rectifier front end to each motor drive, this resistance per unit length can generate a voltage drop on the control power conductors that may limit the distance that a motor drive may be located from the rectifier front end.

Thus, it would be desirable to provide a system for distributing DC bus voltage and control power to multiple motors with an increased distance that the motor drive may be positioned from the rectifier front end.

Additionally, a motor may require external devices connected to the motor which, in turn, require control power to operate. The motor may include a brake and/or a fan which operate from the control power to the motor. A brake requires a significant current to energize the brake coil to release the brake. The system must be configured to supply the current required during operation if each brake coil is energized in tandem. The current required by the brakes may limit the number of brakes and, therefore, limit the number of motors that may be connected to a single power supply. The total power drawn from the control power supply is equal to the amplitude of the voltage times the amplitude of the current. If the power supply must be able to supply power to control components within the motor drive as well as to supply power to external components connected to the motor, the number of motors receiving control power from a single power supply is reduced. Additional power supplies may, therefore, be required either within a central control cabinet or distributed around the controlled machine or process to provide the required control power.

Thus, it would be desirable to provide a system capable of supplying control power to an increased number of motor drives, reducing the number of power supplies required within an application.

In order to supply both DC bus voltage and control power from the rectifier front end, cables are required for each. Additionally, the rectifier front end commonly requires communication with the motor drive, requiring still another cable for communication. One method of providing the DC bus voltage, control power, and communications between the rectifier front end and each motor drive is to supply three separate cables. A first cable supplies the DC bus voltage, a second cable provides the control power, and a third cable transmits data packets between the devices. The first cable includes three conductors and may include a shield within a jacket or housing, where the three conductors are for the positive DC bus voltage, the negative DC bus voltage, and a ground connection. The second cable includes two conductors and a shield within a jacket or housing, where the two conductors are for the positive control voltage and the negative control voltage. The third cable includes a pair of transmit conductors, a pair of receive conductors, and a shield within a jacket or housing. Each of the three cables must be routed between the rectifier front end and a motor drive.

Routing three cables, however, requires additional cost, space, and wiring time during assembly of the controlled machine or process. To facilitate assembly, it is known to provide a bundled cable. In one option, the DC bus voltage cable and the control power cable are bundled into a single cable, and the communication cable is routed separately. The bundled DC bus voltage and control power cable includes the five conductors within the jacket, where two conductors are provided for DC bus voltage, one conductor is a ground conductor and two conductors are provided for the control voltage such that both the DC bus voltage and the control power and included within a single cable. In another option, all three of the previously discussed cables (e.g., DC bus voltage cable, control power cable, and communication cable) may be bundled into a single cable. While the number of cables that must be routed and assembled is decreased, the number of conductors remains the same. The single bundled cable includes nine conductors where each of the three separate cables similarly require nine conductors total between the three cables. The number of connections is not reduced, the weight per unit length of the cable increases, and the flexibility of the cable decreases as an increased number of conductors must be bent at the same time.

Thus, it would be desirable to provide a system for distributing DC voltage and control power in a distributed DC bus system that simplifies wiring without incurring the disadvantages of the bundled cables. <CIT> discloses that a rectifier stage is used to charge a DC link stage to a first (low) voltage. Next, the main SMPS circuit is started. Thus, the voltage output by the rectifier stage in the step must be sufficient to enable the SMPS circuit to function. Then the control <NUM> is turned on. In order for the control module to be turned on, the main SMPS circuit needs to be outputting a sufficient voltage. Finally, the rectifier is used to charge the DC link voltage to a second, higher level. This second higher level is the normal operating level of the system. <NPL> discloses on pages <NUM> and <NUM> a smart line module and an the active line module, respectively, each of which comprise an internal power supply powered by <NUM> Volt DC Line to provide power to a braking module over the DC bus in cases when the main power is interrupted. <CIT> discloses an exemplary embodiment of a distributed motor control system <NUM> including a power interface module, a pair of <NUM> , and a pair of integrated motor drives. A first communication cable is connected between the power interface module and a first communication connector on the first integrated motor drive. A second communication cable connects a second communication connector from the first integrated motor drive to the first communication connector on the second integrated motor drive. A first power cable is connected between the power interface module and a first power connector on the first integrated motor drive. A second power cable connects a second power connector from the first integrated motor drive to the first power connector on the second integrated motor drive. <NPL>, relates to an applicability assessment regarding power line communication through power converter's DC bus. An analysis is provided of the applicability of Power Line Communication, when used for data transmission between the supervisory system and remote systems, in an application based on static frequency converters, using the converter's DC link as a transmission medium. It is the object of the present invention to provide an improved system for distributing a DC bus voltage and a control voltage. This object is solved by the subject matter of claim <NUM>.

The subject matter disclosed herein describes a system for distributing DC bus voltage and control power to multiple motors that is not limited in length by a smaller control wire. A rectifier front end receives AC voltage as an input and converts the AC voltage to a DC bus voltage. The rectifier front end also receives a control voltage which it may first convert to a desired DC control voltage or pass directly on to other devices if the control voltage received is at the desired DC control voltage. Both the DC bus voltage and the DC control voltage are distributed via a common set of conductors. Consequently, the system distributes DC bus voltage and control power without incurring the disadvantages of bundled cables. Diodes are operatively connected between the DC control voltage and the DC bus such that the diodes are forward biased when the DC control voltage is present and the DC bus voltage is not present, and the diodes are reverse biased when the DC control voltage is present and the DC bus voltage is present. The diodes allow forward conduction of the DC control voltage and distribution of control power to distributed devices when the DC bus voltage is not present. Once the DC bus voltage is present, the diodes block conduction of the DC control voltage. Each of the distributed devices are configured with an internal power supply that is operative to generate an internal control voltage from either the DC control voltage or the DC bus voltage. Because the external devices on the motor are not required to operate without DC bus voltage present, the distributed device may draw DC bus voltage to power the external devices, and the system no longer requires control power for operation of external devices on the motor.

According to a first embodiment of the invention, a distributed DC bus system includes a first input configured to receive an AC input voltage, a rectifier section operative to convert the AC input voltage to a DC bus voltage having a first amplitude, a DC bus electrically connected to the rectifier section and operative to receive the DC bus voltage, and a pair of diodes operatively connected between a DC control voltage and the DC bus. The DC control voltage is less than the DC bus voltage, and at least one motor drive is operatively connected to the DC bus. The pair of diodes are operatively connected to be forward biased when the DC control voltage is present in the distributed DC bus system and the DC bus voltage is not present on the DC bus, and the pair of diodes are operatively connected to be reverse biased when the DC control voltage is present in the distributed DC bus system and the DC bus voltage is present on the DC bus. Each motor drive includes an inverter section electrically connected to the DC bus to receive the DC bus voltage as an input and to provide an AC voltage as an output and a power supply electrically connected to the DC bus. The power supply is operative to output a motor drive control voltage from either the DC bus voltage or the DC control voltage present on the DC bus.

According to another embodiment of the invention, a distributed DC bus system includes a first input configured to receive an AC input voltage, a rectifier section operative to convert the AC input voltage to a DC voltage having a first amplitude, a DC bus electrically connected to the rectifier section and operative to receive the DC bus voltage, and a pair of diodes operatively connected between a DC control voltage and the DC bus, where the DC control voltage is less than the DC bus voltage. The pair of diodes are operatively connected to be forward biased when the DC control voltage is present in the distributed DC bus system and the DC bus voltage is not present on the DC bus, and the pair of diodes are operatively connected to be reverse biased when the DC control voltage is present in the distributed DC bus system and the DC bus voltage is present on the DC bus. The DC bus is configured to be electrically connected between the rectifier section and at least one motor drive. Each motor drive includes an inverter section operative to output an AC output voltage from the DC bus voltage received as an input, and each motor drive includes a power supply operative to output a motor drive control voltage from either the DC bus voltage or the DC control voltage present on the DC bus.

According to still another embodiment of the invention, a distributed DC bus system includes a DC bus electrically connected to a rectifier front end and operative to selectively receive either a DC bus voltage or a DC control voltage and at least one motor drive operatively connected to the DC bus. Each motor drive includes an inverter section electrically connected to the DC bus to receive the DC bus voltage as an input and to provide an AC voltage as an output and a power supply electrically connected to the DC bus. The power supply is operative to output a motor drive control voltage from either the DC bus voltage or the DC control voltage present on the DC bus.

These and other advantages and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings are given by way of illustration and not of limitation, the scope of the invention being defined by the appended claims.

Turning initially to <FIG>, an exemplary motor control system <NUM>, which may be used in conjunction with the various embodiments of the invention disclosed herein, is illustrated. According to the exemplary embodiment, the motor control system <NUM> includes a front-end rectifier <NUM> and a motor drive <NUM>. Although illustrated as separate components, it is contemplated that some embodiments will include a front-end rectifier and motor drive as a single component. The front-end rectifier <NUM> is configured to receive a three-phase AC voltage <NUM> at an input to a rectifier section <NUM>. The rectifier section <NUM> may include any electronic device suitable for passive or active rectification as is understood in the art. With reference also to <FIG>, the illustrated rectifier section <NUM> includes a set of diodes <NUM> forming a diode bridge that rectifies the three-phase AC voltage to a DC voltage on the DC bus <NUM>. Optionally, the rectifier section <NUM> may include other solid-state devices including, but not limited to, thyristors, silicon-controlled rectifiers (SCRs), insulated-gate bipolar transistors (IGBTs), power metal-oxide semiconductor field-effect transistors (MOSFETs), or other transistors or solid-state devices to convert the input power <NUM> to a DC voltage for the DC bus <NUM>. The DC voltage is present between a positive rail <NUM> and a negative rail <NUM> of the DC bus <NUM>.

The front-end rectifier <NUM> also includes a DC bus capacitance <NUM> connected between the positive and negative rails, <NUM> and <NUM>, to reduce the magnitude of the ripple voltage resulting from converting the AC voltage to a DC voltage. It is understood that the DC bus capacitance <NUM> may be a single capacitor or multiple capacitors connected in parallel, in series, or a combination thereof. According to one embodiment of the invention, the positive rail <NUM> is at a voltage potential generally equal to or boosted above the magnitude of the peak of the AC input voltage and the negative rail <NUM> is at a voltage potential at zero volts, where the negative rail <NUM> may be a floating common or tied to an earth ground. According to the another embodiment of the invention, the DC bus capacitance <NUM> may be arranged in a split-bus configuration, such that a first portion of the DC bus capacitance <NUM> is connected between the positive rail <NUM> and a ground connection, and a second portion of the DC bus capacitance <NUM> is connected in series with the first portion of the DC bus capacitance between the ground connection and the negative rail <NUM>. The total voltage potential across the DC bus <NUM> in the split bus configuration remains generally equal to or boosted above the magnitude of the peak of the AC input voltage, but the voltage potential across each portion of the capacitance <NUM> is one-half of the total DC bus voltage.

Similarly, the front-end rectifier <NUM> may also receive a control voltage <NUM> for distribution to each of the motor drives <NUM>. According to the embodiment illustrated in <FIG>, the control voltage is a <NUM> VDC input voltage. The front-end rectifier <NUM> includes a control power supply <NUM>, which is a switched mode power supply. A switch <NUM>, which may be implemented by a transistor, is selectively opened and closed to establish conduction through a transformer <NUM>. The inductive nature of the transformer, in combination with the diode <NUM> and capacitor <NUM> work in combination with the switch <NUM> to boost the <NUM> VDC at the input <NUM> to a <NUM> VDC control voltage at the output of the control power supply <NUM>. In addition, the transformer <NUM> provides electrical isolation between the control voltage at the input <NUM> and the control voltage at the output of the power supply <NUM>. A pair of diodes <NUM>, <NUM> are connected between the output of the control power supply <NUM> and the DC bus <NUM>. As will be discussed in more detail below, the pair of diodes <NUM>, <NUM> allow the <NUM> VDC control voltage to be present on the DC bus <NUM> when the DC bus voltage output from the rectifier section <NUM> is not present and disconnect the control power supply <NUM> from the DC bus <NUM> when the DC bus voltage output from the rectifier section <NUM> is present.

According to another embodiment of the invention, as shown in <FIG>, it is contemplated that the control voltage <NUM> is a single-phase AC input, such as <NUM> VAC. The front-end rectifier <NUM> may further include a voltage regulator <NUM> that converts the AC input to the <NUM> VDC control voltage. A capacitor <NUM> is provided at the output of the voltage regulator <NUM> to help smooth any ripple of the DC voltage and/or to provide some ride through due to the loss of the AC input. Optionally, the capacitor <NUM> may be incorporated within the voltage regulator <NUM>. Once again, a pair of diodes <NUM>, <NUM> are connected between the output of the voltage regulator <NUM> and the DC bus <NUM>. As will be discussed in more detail below, the pair of diodes <NUM>, <NUM> allow the <NUM> VDC control voltage to be present on the DC bus <NUM> when the DC bus voltage output from the rectifier section <NUM> is not present and disconnect the voltage regulator <NUM> from the DC bus <NUM> when the DC bus voltage output from the rectifier section <NUM> is present.

According to still another embodiment of the invention (not shown) it is contemplated that a <NUM> VDC voltage may be supplied as a control voltage <NUM> input to the rectifier <NUM>. If the <NUM> VDC voltage is referenced to the negative potential on the DC bus voltage, the front-end rectifier <NUM> may include just the pair of diodes <NUM>, <NUM> to selectively connect the control voltage input <NUM> to the DC bus <NUM> as a function of whether the DC bus voltage output from the rectifier section <NUM> is present. Alternately, an isolation transformer <NUM> may be provided which provides a one-to-one turns ratio while also establishing electrical isolation between the control voltage input and the control voltage output. The output of the isolation transformer is then connected to the pair of diodes <NUM>, <NUM> to selectively connect the <NUM> VDC to the DC bus <NUM>. Various other sources of <NUM> VDC as a control voltage may be provided for selectively connecting to the DC bus <NUM> via the diodes <NUM>, <NUM> without deviating from the scope of the invention. Similarly, it is contemplated that the control voltage may be selected at other DC voltage levels, such as 24VDC, where the magnitude of the control voltage is less than the magnitude of the DC bus voltage level, without deviating from the scope of the invention.

The front-end rectifier <NUM> further includes a control circuit used to control operation of the rectifier. According to the illustrated embodiment, the control circuit includes a processor <NUM> and a memory <NUM>. One or more modules are used to control operation of the front-end rectifier <NUM>. The modules may be programs stored in the memory <NUM> and executed on the processor <NUM>, logic circuits, or a combination thereof. The memory <NUM> is configured to store data and programs, which include a series of instructions executable by the processor <NUM>. It is contemplated that the memory <NUM> may be a single device, multiple devices, or incorporated, for example, as a portion of another device such as an application specific integrated circuit (ASIC). The processor <NUM> is in communication with the memory <NUM> to read the instructions and data as required to control operation of the front-end rectifier <NUM>. The processor <NUM> receives input signals from input terminals, communication circuits, such as an industrial network, and the like, which include, for example, an enable signal, a disable signal, or other command signals defining desired operation of the rectifier <NUM>. The processor <NUM> similarly receives feedback signals from sensors indicating the present operation of the rectifier <NUM>. The feedback signals may include, but are not limited to, the magnitude of voltage and/or current present at the input power <NUM>, the control voltage input <NUM>, or on the DC bus <NUM>. The processor <NUM> executes a control module responsive to command signal(s) and the feedback signals to generate control signals, if necessary, for an active rectifier or for the switched mode control power supply <NUM>.

As illustrated in <FIG>, a single motor drive <NUM> is connected to the front-end rectifier <NUM> to receive the DC voltage present on the DC bus <NUM>. A pair of bus bars <NUM>, <NUM> conduct the voltages present on the positive and negative rails <NUM>, <NUM> between the rectifier <NUM> and the drive <NUM>. It is understood that still additional motor drives <NUM>, may be mounted adjacent to the illustrated motor drive and the bus bars <NUM>, <NUM> may extend from the front-end rectifier <NUM> to each of the adjacent motor drives, extending the DC bus <NUM> to the additional motor drives <NUM>. Each motor drive <NUM> connected to the DC bus <NUM> receives the DC voltage present on the bus and uses the DC voltage to control one or motors <NUM> connected to the corresponding motor drive <NUM>. According to the embodiment illustrated in <FIG>, a DC bus connection member <NUM> includes a housing <NUM> in which the bus bars <NUM>, <NUM> are mounted. Terminals <NUM> on the upper surface of each motor drive <NUM> are configured to receive the bus bars <NUM>, <NUM>. Each pair of terminals <NUM> on one motor drive <NUM> are connected to the positive rail <NUM> and negative rail <NUM> of the DC bus <NUM> within the corresponding drive. DC bus connection members <NUM> of varying length may be supplied to connect terminals <NUM> between adjacent motor drives <NUM> according to the width of the corresponding drives <NUM>.

The motor drive <NUM> may also include a DC bus capacitance <NUM> connected between the positive and negative rails, <NUM> and <NUM>, to reduce the magnitude of the ripple voltage resulting from converting the AC voltage to a DC voltage and to provide some ride through in the event of variation in the voltage level present on the DC bus <NUM>. It is understood that the DC bus capacitance <NUM> in the motor drive <NUM> may be a single capacitor or multiple capacitors connected in parallel, in series, or a combination thereof. Optionally, all or a portion of the DC bus capacitance <NUM> may be provided in the front-end rectifier <NUM>. The DC bus <NUM> is connected in the motor drive <NUM> to an inverter section <NUM>. Referring also to <FIG>, the inverter section <NUM> consists of switching elements, such as transistors, thyristors, or SCRs as is known in the art. The illustrated inverter section <NUM> includes IGBTs <NUM> and a free-wheeling diode <NUM> connected in pairs between the positive rail <NUM> and each phase of the output voltage as well as between the negative rail <NUM> and each phase of the output voltage. Each of the IGBTs <NUM> receives gating signals <NUM> to selectively enable the transistors <NUM> and to convert the DC voltage from the DC bus <NUM> into a controlled three phase output voltage to the motor <NUM>. When enabled, each transistor <NUM> connects the respective rail <NUM>, <NUM> of the DC bus <NUM> to an electrical conductor <NUM> connected between the transistor <NUM> and the output of the motor drive <NUM>. The electrical conductor <NUM> is selected according to the application requirements (e.g., the rating of the motor drive <NUM>) and may be, for example, a conductive surface on a circuit board to which the transistors <NUM> are mounted or a bus bar connected to a terminal from a power module in which the transistors <NUM> are contained. The output of the motor drive <NUM> may be connected to the motor <NUM> via a cable <NUM> including electrical conductors connected to each of the output terminals <NUM>.

One or more modules are used to control operation of the motor drive <NUM>. The modules may be stored programs executed on a processor, logic circuits, or a combination thereof. The modules used to control operation of the motor drive <NUM> will be referred to herein generally as a control circuit. According to the illustrated embodiment, the control circuit of the illustrated motor drive <NUM> includes a motor interface circuit <NUM>, a non-transitory storage device, or memory <NUM>, a processor <NUM>, and a switch mode power supply (SMPS) <NUM>. It is contemplated that the control circuit may include additional devices, such as a dedicated processor or gate driver circuit <NUM> (as shown in <FIG>) to generate gate signals <NUM>, buffers, analog-to-digital converters, and the like as may be needed to control operation of the motor drive. The non-transitory storage device, or memory <NUM>, is configured to store data and programs, which include a series of instructions executable by the processor <NUM>. It is contemplated that the memory <NUM> may be a single device, multiple devices, or incorporated, for example, as a portion of another device such as an application specific integrated circuit (ASIC). The processor <NUM> is in communication with the memory <NUM> to read the instructions and data as required to control operation of the motor drive <NUM>. The processor <NUM> receives feedback signals from sensors indicating the present operation of the motor drive <NUM>. The feedback signals may include, but are not limited to, the magnitude of voltage and/or current present on the DC bus <NUM> or at the output <NUM> of the inverter section <NUM>, as supplied to the motor <NUM>. The feedback signals may also include position feedback, temperature feedback, or brake status signals from the motor <NUM> received at the motor interface circuit <NUM>. Optionally, the motor drive <NUM> may also transmit, for example, a brake release signal via the motor interface circuit <NUM> to the motor <NUM>. It is contemplated that the motor drive <NUM> may utilize one of many various methods of controlling operation of the motor <NUM> as is understood in the art without deviating from the scope of the invention,.

The SMPS <NUM> is configured to operate over a wide range of input voltages. The SMPS <NUM> may receive the control voltage, for example at 48VDC from the control power supply <NUM> or, alternately, may receive DC bus voltage at <NUM> VDC or greater. The SMPS <NUM> converts the input voltage to control voltages such as <NUM> VDC, <NUM> VDC, or any other DC voltage required by control circuits within the motor drive <NUM>. The SMPS includes a switch <NUM>, which may be implemented by a transistor that is selectively opened and closed to establish conduction through a transformer <NUM>. The transformer <NUM> includes a primary winding <NUM> and at least one secondary winding <NUM>. The transformer provides electrical isolation between the primary winding <NUM> and each secondary winding <NUM>. The switch <NUM> may be controlled and operative in combination with a turns-ratio between the primary <NUM> and one of the secondary windings <NUM> to supply each of the desired control voltages (e.g., <NUM> VDC or <NUM> VDC) within the motor drive <NUM>. The control voltages are used to power, for example, the memory <NUM>, the processor <NUM>, and other logic, control, or electronic elements within the control circuit. Turning next to <FIG>, a second exemplary motor control system <NUM>, which may be used in conjunction with the various embodiments of the invention disclosed herein, is illustrated. In a manner similar to the motor control system illustrated in <FIG>, the motor control system <NUM> in <FIG> includes a front-end rectifier <NUM> and a motor drive <NUM>. The front-end rectifier <NUM> is configured to receive a three-phase AC voltage <NUM> at an input to the rectifier <NUM>, and to provide a DC voltage on a DC bus <NUM> as an output of the rectifier <NUM>. The rectifier <NUM> may include any electronic device suitable for passive or active rectification as is understood in the art. The magnitude of the DC voltage between the negative and positive rails, <NUM> and <NUM>, is generally equal to or boosted above the magnitude of the peak of the AC input voltage. One or more motor drives <NUM> may be connected to the DC bus <NUM> to receive the DC voltage present on the bus and to use the DC voltage to control one or motors connected to each motor drive <NUM>.

Unlike the motor control system <NUM> illustrated in <FIG>, the motor drive <NUM> illustrated in <FIG> is mounted to the motor <NUM>. Just as with <FIG>, a single motor drive <NUM> is shown in <FIG> being connected to the front-end rectifier <NUM>. A DC bus cable 50A extends between the front-end rectifier <NUM> and the integrated motor drive <NUM>. With reference also to <FIG>, the DC bus cable <NUM> includes a first conductor <NUM> and a second conductor <NUM> which serve as the positive and negative rails <NUM>, <NUM> of the DC bus <NUM>. A third conductor <NUM> may also be provided which establishes a ground connection between the front-end rectifier <NUM> and each motor drive <NUM>. The DC bus cable <NUM> include an outer jacket <NUM> to insulate the cable <NUM> and may include a shield <NUM> surrounding the conductors. The first and second conductors <NUM>, <NUM> provide the positive and negative rails <NUM>, <NUM> of the DC bus <NUM> from the rectifier <NUM> to the motor drive <NUM>. Optionally, an additional DC bus cable 50B may connected to the motor drive <NUM> to form a daisy chain connection and pass the DC bus <NUM> on to an additional motor drive <NUM>, not shown. Other than the mounting location, the motor drive <NUM> is configured in a manner similar to the motor drive shown and discussed above with respect to <FIG>. Because the motor drive <NUM> is mounted to the motor <NUM>, connections between the motor drive <NUM> and the motor <NUM> may be made via short leads or bus bars internal to the housings of the drive and motor.

In operation, the DC bus <NUM> is operative to provide either control voltage or DC bus voltage from a source, such as the front-end rectifier <NUM>, to one or more loads, such as the motor drives <NUM> or <NUM> over a shared set of conductors. By providing both control voltage and DC bus voltage over a single set of conductors, the total wire count is reduced, which, in turn, simplifies the interconnection between devices, cost of materials, and reduces the potential for errors in wiring. Further, because the number of conductors within the cable is reduced, the weight of the cable is reduced and the flexibility of the cable is increased, which again simplifies the interconnection between devices and may improve routing of cables.

In a first operating mode, the front-end rectifier <NUM> supplies control power to each of the motor drives <NUM> or <NUM> without having the DC bus voltage present. This may be desirable, for example, during installation or commissioning. The motor drive <NUM> requires control power to energize the processor <NUM> and memory <NUM>. Similarly, if a user interface, network interface, or other communication interface is present, the interface similarly requires control power. A technician is able to configure operation of the motor drive <NUM> via the interface, for example, by pressing buttons to directly adjust parameters displayed on a user interface, by downloading a set of parameters, or by interacting with an application executing on a mobile computing device connected to or located proximate the motor drive <NUM>. Optionally, a technician may be in a location or facility remotely located from the motor drive <NUM> and connected via one or more suitable networks, such as the Internet, an intranet, or a dedicated industrial network. The control power enables the processor <NUM> to execute instructions stored in the memory <NUM> and to read and/or adjust parameter settings stored in memory <NUM>.

Similarly, it may be desirable for the motor drive <NUM> to initially power-up with just control power present prior to having DC bus voltage present on the DC bus <NUM>. At power-up, the motor drive <NUM> may perform initial diagnostic tests on the motor drive <NUM> to verify that the motor drive is properly configured or that the electronic components of the motor drive <NUM> are operating normally. After completing the initial diagnostic tests, the motor drive <NUM> may set a flag or transmit a message to the front-end rectifier <NUM> indicating it is ready to receive the DC bus voltage. In either event, the control power is required to power the control circuit and other control elements present in the motor drive <NUM>.

During this first operating mode, the control power supply <NUM> or voltage regulator <NUM> receives the control voltage <NUM> and is operative to provide the control voltage at its respective output. For discussion purposes, a <NUM> VDC voltage will be output from the control power supply <NUM> or voltage regulator <NUM>. Optionally, an external power supply may provide the <NUM> VDC control voltage directly to the input <NUM> of the front-end rectifier. It is contemplated that various other control voltages, such as <NUM> VDC may be output from the power supply <NUM> or voltage regulator <NUM> without deviating from the scope of the invention. The positive output terminal from the power supply <NUM> or regulator <NUM> is connected via a first diode <NUM> to the positive rail <NUM> of the DC bus <NUM>. The first diode <NUM> is connected such that it is forward biased when the <NUM> VDC is present on the positive output terminal of the control power supply <NUM> or voltage regulator <NUM> and no DC bus voltage is present on the DC bus <NUM>. The anode of the first diode <NUM> is connected to the power supply, voltage regulator <NUM>, or directly to the input control voltage <NUM> and the cathode of the first diode <NUM> is connected to the positive rail <NUM> of the DC bus <NUM>. The negative terminal from the power supply <NUM> or regulator <NUM> is connected via a second diode <NUM> to the negative rail <NUM> of the DC bus <NUM>. The second diode <NUM> is connected such that is also forward biased when the <NUM> VDC is present on the positive output terminal of the control power supply <NUM> or voltage regulator <NUM> and no DC bus voltage is present on the DC bus <NUM>. The anode of the second <NUM> is connected to the negative rail <NUM> of the DC bus <NUM> and the cathode of the second diode <NUM> is connected to the power supply, voltage regulator <NUM>, or directly to the input control voltage <NUM>. With no DC bus voltage present, the first and second diodes <NUM>, <NUM> are forward biased and allow the power supply <NUM> or voltage regulator <NUM> to supply control power to each motor drive <NUM> connected via the DC bus <NUM>.

During this first operating mode, it is anticipated that each motor drive <NUM> requires only sufficient power to energize the control circuits within the motor drive <NUM>. Because there is no DC bus voltage present, the motor drives <NUM> will not be controlling operation of their respective motors. As a result, external devices mounted on the motors, such as motor brakes and/or fans, will not need power for operation either. For example, the opening and holding current required to energize a brake coil is not necessary, reducing the power requirements of each node connected to the DC bus <NUM>, where the node includes a motor drive <NUM>, a corresponding motor <NUM>, and external devices connected to the motor. The reduced power requirements of each node allow more nodes to be connected to a single front-end rectifier than if the control power is required to energize motor brakes and the like.

Additionally, the control power is supplied via the DC bus <NUM> connection between the front-end rectifier <NUM> and each motor drive <NUM>. As shown in <FIG>, this connection may be made via a DC bus connection member <NUM> which includes a pair of bus bars <NUM>, <NUM> as shown in <FIG>. Alternately, this connection may be made via a DC bus cable 50A or 50B, as shown in <FIG>, where the DC bus cable <NUM>, as shown in <FIG>, includes a pair of conductors <NUM>, <NUM>. The cross section of the bus bars <NUM>, <NUM> or the wire size for the conductors <NUM>, <NUM> is selected appropriately to handle the current rating required to supply power to each motor <NUM> and motor drive <NUM> combination that is connected for the DC bus <NUM>. The power requirements for the motor <NUM> are substantially greater than the requirements for control power and, therefore, the cross-section or the size of the wire are selected accordingly. As a result, during the first operating mode, the cross-section of the bus bars <NUM>, <NUM> or the size of the wire required for the conductors <NUM>, <NUM> is substantially greater than a corresponding conductor that previously would have been selected if the conductor were dedicated to conducting control power. The value of the resistance per unit length of these bus bars <NUM>, <NUM> or conductors <NUM>, <NUM> is similarly reduced in comparison to a corresponding conductor that previously would have been selected if the conductor were dedicated to conducting control power. The voltage drop along the DC bus bars <NUM>, <NUM> or conductors <NUM>, <NUM> sized to conduct the current for operation of the motors <NUM> is less than conductors that previously would have been selected just to conduct current for the control power and, therefore, this also allows additional nodes to be connected to the DC bus <NUM> and to receive control power from the front-end rectifier <NUM>.

In a second operating mode, the AC voltage <NUM> is present at the front-end rectifier <NUM> and the rectifier section <NUM> is operative to supply DC bus voltage on the DC bus <NUM>. The magnitude of the DC bus voltage between the negative and positive rails, <NUM> and <NUM>, is generally equal to or boosted above the magnitude of the peak of the AC input voltage. If passive rectification occurs in the rectifier section <NUM>, the magnitude of the DC bus voltage is approximately equal to the peak value of the AC input voltage. For example, a <NUM> VAC input voltage yields a DC bus voltage of about <NUM> VDC and a <NUM> VAC input voltage yields a DC bus voltage of about <NUM> VDC. If the rectifier section <NUM> has an active rectifier, it may be desirable to boost the DC bus voltage slightly above the peak value of the AC input voltage, such that the DC bus voltage may be, for example, <NUM> VDC or <NUM> VDC for a <NUM> VAC or <NUM> VAC input voltage, respectively. Regardless of whether the DC bus voltage is supplied via passive or active rectification, the amplitude of the DC bus voltage is substantially greater than the <NUM> VDC output from the control power supply <NUM> or voltage regulator <NUM>. When the DC bus voltage is present on the DC bus <NUM>, therefore, the first and second diodes <NUM>, <NUM> become reverse biased, preventing current flow through the control power supply <NUM> or voltage regulator <NUM>.

Because the control power is no longer supplied via the DC bus <NUM> to the motor drives <NUM>, each motor drive <NUM> must be able to utilize the DC bus voltage at, for example, <NUM> VDC or <NUM> VDC in addition to the control voltage at <NUM> VDC to generate internal motor drive control voltages within the motor drive <NUM>. Each motor drive includes a SMPS <NUM> configured to operate over a wide range of input voltages. The SMPS provides the internal control voltages, such as <NUM> VDC or <NUM> VDC, for the motor drive <NUM> to power the processor <NUM>, memory <NUM>, and the like. The input of the SMPS <NUM> is connected to the DC bus <NUM> and, therefore, during the first operating mode, the SMPS <NUM> receives the <NUM> VDC control voltage and in the second operating mode, the SMPS <NUM> receives the <NUM> VDC or <NUM> VDC bus voltage. In either operating mode, the SMPS is configured to supply the necessary control voltage (e.g., <NUM> VDC or <NUM> VDC) for operation of the motor drive <NUM>.

According to still another aspect of the invention, it is contemplated that communication between the front-end rectifier <NUM> and each motor drive <NUM> may additional be performed via the DC bus conductors. Both the front-end rectifier <NUM> and the motor drive <NUM> may include a transceiver in their respective control circuits, where the transceiver is configured to communicate via a power line. The transceiver may, for example, modulate a carrier signal on top of the control voltage or on top of the DC bus voltage at a transmitting device and the receiving device is configured to receive and decode the modulated signal. Data packets may be passed between the two devices via the DC bus conductors, thereby further reducing the wiring between the front-end rectifier <NUM> and each motor drive <NUM>.

Claim 1:
A distributed DC bus system, comprising:
a first input (<NUM>) configured to receive an AC input voltage;
a rectifier section (<NUM>) operative to convert the AC input voltage to a DC bus voltage having a first amplitude;
a DC bus (<NUM>, <NUM>; 50A) electrically connected to the rectifier section and operative to receive the DC bus voltage;
a control power supply configured to output a DC control voltage, wherein the DC control voltage is less than the DC bus voltage;
a pair of diodes (<NUM>, <NUM>) operatively connected between the output of the control power supply and
the DC bus, wherein:
the pair of diodes are operatively connected to be forward biased when the DC control voltage is present in the distributed DC bus system and the DC bus voltage is not present on the DC bus to provide the DC control voltage to the DC bus, and
the pair of diodes are operatively connected to be reverse biased when the DC control voltage is present in the distributed DC bus system and the DC bus voltage is present on the DC bus to prevent the DC control voltage from being provided to the DC bus; and
at least one motor drive (<NUM>) operatively connected to the DC bus, wherein each motor drive includes:
an inverter section (<NUM>) electrically connected to the DC bus to receive the DC bus voltage as an input and to provide an AC voltage as an output; and
a power supply (<NUM>) electrically connected to the DC bus, wherein the power supply is operative to output a motor drive control voltage from either the DC bus voltage or the DC control voltage present on the DC bus.