Apparatuses, systems, and methods of variable frequency drive operation and control

An exemplary system includes a compressor, a condenser, an expander, and an evaporator fluidly coupled to form a vapor-compression circuit, and an electric motor configured to drive the compressor. An inverter having a plurality of switching elements is configured to provide an output voltage to the electric motor through operation of the switching elements. A waste heat recovery circuit is configured to transfer waste heat from the inverter to a load. A controller is configured provide switching commands to the switching elements of the inverter. The controller is further configured to sense a condition of the system, determine a heat production requirement based at least in part upon the system condition, and to vary the number of switching commands per unit time based at least in part upon the heat production requirement.

BACKGROUND

The present application relates generally to apparatuses, systems, and methods of variable frequency drive operation and control. Variable frequency motor drives offer a number of potential benefits for applications such as driving compressors or other loads for heating, ventilation, air-conditioning, or refrigeration (HVACR) systems, including potential for enhanced efficiency, power density, and speed control precision. Such motor drives present unique challenges with respect to waste heat and control of the same. Conventional designs often seek to minimize waste losses under all operating conditions to the extent possible in light of other operational targets. Some proposals have been made for recapture of part of the waste heat generated by variable frequency drive operation. These approaches suffer from a number of disadvantages and shortcomings including those respecting control and beneficial use of waste heat. Such motor drives also present unique challenges with respect to audible noise and control of the same. Conventional designs often seek to minimize audible noise under all operating conditions, for example by setting the switching frequency as high as the motor load will allow. These approaches suffer from a number of disadvantages and shortcomings including those respecting system efficiency and generation of waste heat. There remains a significant need for the unique and inventive apparatuses, methods and systems disclosed herein.

DISCLOSURE

For the purposes of clearly, concisely and exactly describing exemplary embodiments of the invention, the manner and process of making and using the same, and to enable the practice, making and use of the same, reference will now be made to certain exemplary embodiments, including those illustrated in the figures, and specific language will be used to describe the same. It shall nevertheless be understood that no limitation of the scope of the invention is thereby created, and that the invention includes and protects such alterations, modifications, and further applications of the exemplary embodiments as would occur to one skilled in the art.

SUMMARY

A number of non-limiting exemplary embodiments are summarized below. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings.

One exemplary embodiment is a system comprising: a compressor, an expander, a first heat exchanger, and a second heat exchanger, fluidly coupled to form a vapor-compression circuit; an electric motor configured to drive the compressor; an inverter comprising a plurality of switching elements, the inverter configured to provide an output voltage to the electric motor through operation of the switching elements; a waste heat recovery circuit configured to transfer waste heat from the inverter to a selected component of the system; and a controller including a system conditions module structured to sense a condition of the system, a heat production module structured to determine a heat production requirement based at least in part upon the system condition, and an inverter operation module structured to provide switching commands to the switching elements of the inverter, wherein the controller is configured to vary the number of switching commands per unit time based at least in part upon the heat production requirement.

In some forms the controller is configured to vary the number of switching commands per unit time by changing the switching frequency of a PWM signal. In some forms the controller is configured to vary the number of switching commands per unit time by changing between a continuous PWM signal and a discontinuous PWM signal. In some forms the condition comprises a system start-up condition. In some forms a working fluid of the vapor-compression circuit comprises a refrigerant and an oil; and wherein the waste heat recovery circuit is structured to transfer heat from the inverter to the working fluid such that the refrigerant boils and is separated from the oil. In some forms the waste heat recovery circuit is configured to exchange heat with a compressor-lubricating oil. In some forms the the selected component is a suction line of the compressor, and wherein the condition comprises a temperature of a refrigerant in the suction line. Some forms further comprise a reversing mechanism operable to reverse the flow direction of a refrigerant in the vapor-compression circuit. In some forms the selected component is at least one of the first and second heat exchangers, and wherein the condition comprises the reversal of flow direction. Some forms further comprise a temperature sensor configured to sense an inverter temperature; and wherein the inverter operation module is further structured to reduce the number of switching commands per unit time in response to the inverter temperature being greater than a reference temperature.

One exemplary embodiment is a system comprising: a refrigerant loop including a compressor, a condenser, an expander, and an evaporator; a motor configured to drive the compressor; a variable frequency drive including an inverter configured to drive the motor; a cooling circuit configured to receive heat generated by operation of the inverter; a controller configured to provide switching commands to the inverter; wherein the controller is configured to vary the rate of switching commands to selectively increase the heat generated by the inverter based upon one or more first criteria for increased heat transfer to the cooling circuit, and selectively decrease the heat generated by the inverter based upon one or more second criteria.

In some forms the controller is configured to vary the rate of switching commands by not providing a switching command for a predetermined duration or a predetermined time. In some forms the cooling circuit is further configured to transfer heat to the refrigerant loop between a refrigerant inlet of the evaporator and the compressor, and wherein the first criteria comprises a temperature of a working fluid between the refrigerant inlet of the evaporator and the compressor being below a predetermined superheat temperature. In some forms the cooling circuit is further configured to transfer heat to the evaporator, and wherein the first criteria comprises a detection of frost on the evaporator. Some forms further comprise an oil line configured to supply oil from to the compressor, and wherein the cooling circuit is further configured to transfer heat to the oil line.

One exemplary embodiment is a method comprising: providing a pulse width modulation (PWM) pattern to an inverter, the PWM pattern transitioning between a first signal magnitude and a second signal magnitude greater than the first signal magnitude; operating the inverter based upon the PWM pattern to provide a voltage output to drive a motor, wherein heat is generated as a byproduct of operating the inverter, and wherein the amount of heat generated correlates to the number of transitions between the first signal magnitude and the second signal magnitude; driving a compressor of a refrigeration system with the motor, the refrigeration system comprising a compressor, a condenser, and an evaporator; transferring heat between the inverter and a component of the refrigeration system using a heat transfer circuit thermally coupled to the inverter and the component; determining if additional heat is desired at the component; and modifying the PWM pattern in response to the determining such that the PWM pattern transitions between the first signal magnitude and the second signal magnitude more frequently.

Some forms further comprise determining if heat is no longer desired at the component, and ceasing the transferring heat based upon the determining. In some forms the component comprises the evaporator, the transferring heat between the inverter and the evaporator heats a working fluid within the evaporator, the working fluid comprising a refrigerant and a lubricant. Some forms further comprise separating the lubricant from the refrigerant by boiling the refrigerant with the transferred heat and returning the lubricant to the compressor. Some forms further comprise determining if less heat generation is desired and modifying the PWM pattern in response to the determining such that the PWM pattern transitions between the first signal magnitude and the second signal magnitude less frequently. In some forms the modifying the PWM pattern comprises providing only one of the first and second signal magnitudes at a predetermined time corresponding to one of a peak and a trough of a current waveform in the motor for a predetermined duration of at least ten percent of a period of the current waveform. In some forms the current waveform comprises a synthesized sinusoid. In some forms the determining if less heat generation is desirable comprises determining if a temperature of the inverter is higher than a threshold temperature.

One exemplary embodiment is a system comprising a compressor, a condenser, an expander, and an evaporator fluidly coupled to form a vapor-compression circuit; a controller comprising: an audible noise module configured to determine a target audible noise profile comprising a target maximum level of audible noise generated by the system; a schedule selection module configured to select a switching schedule based at least in part upon the target audible noise production profile; an inverter operation module configured to provide an inverter command comprising a plurality of switching commands according to the selected switching schedule; an inverter comprising a plurality of switching elements responsive to the switching commands, the inverter being configured to output a voltage signal in response to the inverter command; and a motor drivingly coupled to the compressor, and responsive to the voltage signal.

In some forms the target audible noise profile includes a profile of acceptable magnitudes of a plurality of frequencies. In some forms the audible noise module is configured to determine the target audible noise profile based at least in part upon one or more of a user selection and a time of day. In some forms the controller further comprises a pulse width modulation (PWM) schedules module configured to provide a set of PWM patterns, and wherein the schedule selection module is configured to select the switching schedule from the set of PWM patterns. In some forms the controller further comprising a conditions module configured to determine one or more conditions selected from the group consisting of a temperature of the inverter, an electrical noise level of an electrical current in the motor, and current ripple; and wherein the schedule selection module is further configured to select the switching schedule based upon the one or more conditions. In some forms the schedule selection module is further configured to determine a subset of PWM patterns that do not violate the audible noise profile, and to select the switching schedule from the subset. In some forms the schedule selection module is further configured to determine a subset of PWM patterns that do not violate a predetermined parameter of the sensed condition, and to select the switching schedule from the subset. In some forms the system further comprises a sensor configured to sense the condition, and to transmit information relating to the condition to the conditions module. In some forms the motor is a surface mounted permanent magnet machine.

One exemplary embodiment is a system comprising: a refrigerant loop including a compressor, a condenser, and an evaporator; a motor configured to drive the compressor; a variable frequency drive including an inverter configured to drive the motor; and a controller configured to provide switching commands to the inverter according to a pulse width modulation (PWM) schedule based at least in part upon a carrier frequency and a PWM technique; wherein the controller is configured to determine a target audible noise level based upon one or more criteria, and to vary at least one of the carrier frequency and the PWM technique based at least in part upon the target audible noise level.

In some forms the controller is further configured to vary at least one of the carrier frequency and the PWM technique based upon at least one of electrical noise production and current ripple. In some forms the motor is a surface mounted permanent magnet motor. In some forms the controller is further configured to vary the switching commands such that the inverter does not overheat. Some forms further comprise a user interface operable to change the target audible noise level. In some forms the controller is further configured to vary the switching commands such that a selected component is not excited at its natural frequency for longer than a first predetermined duration.

One exemplary embodiment is a method comprising: determining a target audible noise profile based on or more criteria, the target audible noise profile comprising a target audible noise level for an HVACR system including an inverter; selecting a first pulse width modulation (PWM) schedule based at least in part upon the audible noise profile; providing a first series of switching commands according to the first PWM schedule to a variable frequency drive comprising an inverter, generating an inverter waveform in response to the first series of switching commands; powering a motor with the inverter waveform such that the motor drives a compressor of a vapor-compression circuit.

In some forms the determining is based upon at least one of a user selection and a time of day. In some forms the selecting includes comparing the audible noise profile to an acoustic noise generated by the HVACR system when operated according to each of a plurality of PWM schedules. Some forms further comprise: determining a natural frequency of a component of one of the variable frequency drive, the motor, and the compressor; selecting a second PWM schedule based at least in part upon the natural frequency of the component; the providing the first series of switching commands is for a first predetermined time; the method further comprising providing a second series of switching commands according to the second PWM schedule for a second predetermined time. In some forms the audible noise profile is a first selection criterion, and the selecting is further based upon a second selection criterion, each of the selection criteria being assigned a weighting value. In some forms the second selection criterion is selected from the group consisting of inverter temperature, electrical noise generation, and system efficiency. In some forms at least one of the plurality of selection criteria is a critical selection criterion, and wherein the first PWM pattern is selected such that the critical selection criterion is satisfied. In some forms the second selection criterion is a maximum operating temperature of the inverter, and wherein the maximum operating temperature is a critical selection criterion.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

With reference toFIG. 1there is illustrated an exemplary HVACR system100which includes a refrigerant loop comprising a compressor110, a first heat exchanger120, an expander125, and a second heat exchanger130. HVACR system100may further comprise a reversing mechanism configured to reverse the flow direction of the working fluid. In the present embodiment, the reversing mechanism is illustrated as four-way valve140. It is also contemplated that other reversing mechanisms may be utilized, such as separate two-way valves. Furthermore, in certain exemplary embodiments such as large chiller units, it is contemplated that the compressor110may be directly in flow series with second heat exchanger130and first heat exchanger120, and the valving which permits the system to operate in reverse, i.e., as a heat pump and a cooler, may be omitted. In such embodiments first heat exchanger120may be configured as a dedicated condenser and second heat exchanger130may be configured as a dedicated evaporator.

Four-way valve140is configured to receive compressed refrigerant from compressor110and direct the compressed refrigerant to either first heat exchanger120or second heat exchanger130. Four-way valve140has a first configuration in which refrigerant lines are connected as shown by the solid lines and refrigerant flows in the direction of the solid arrows, and a second configuration in which refrigerant lines are connected as shown by the dashed lines and refrigerant flows in the direction of the dashed arrows. First heat exchanger120is a condenser when the flow is in the direction of the solid arrows, and an evaporator when the flow is in the direction of the dashed arrows. Second heat exchanger130is an evaporator when flow is in the direction of the solid arrows, and a condenser when flow is in the direction of the dashed arrows. The following description will be made with reference to HVACR system100when four-way valve140is in the first configuration, corresponding to solid lines and arrows. One having skill in the art will readily understand that HVACR system100operates in a similar fashion when four-way valve140is in the second configuration.

In the first configuration of four-way valve140, refrigerant flows through system100in a closed loop from compressor110to first heat exchanger120to expander125to second heat exchanger130and back to compressor110. A waste heat recovery circuit180transfers heat generated by variable frequency drive155to second heat exchanger130. Variable frequency drive155may be a variable frequency motor drive200(FIG. 2) having an inverter module280, described below. Various embodiments of system100may also include additional refrigerant loop elements including, for example, valves for controlling refrigerant flow, refrigerant filters, economizers, oil separators and/or cooling components and flow paths for various system components.

Compressor110is driven by a drive unit150including a permanent magnet electric motor170which is driven by a variable frequency drive155. In the illustrated embodiment, variable frequency drive155is configured to output a three-phase PWM drive signal, and motor170is a surface magnet permanent magnet motor. Use of other types and configurations of variable frequency drives and electric motors such as interior magnet permanent magnet motors, reluctance motors, or inductance motors are also contemplated. It shall be appreciated that the principles and techniques disclosed herein may be applied to a broad variety of drive and permanent magnet motor configurations.

First heat exchanger120is configured to transfer heat from compressed refrigerant received from compressor110. In the illustrated embodiment first heat exchanger120is a water cooled condenser which receives cooling water at an inlet121, transfers heat from the refrigerant to the cooling water, and outputs cooling water at an outlet122. It is also contemplated that other types of condensers may be utilized, for example, air cooled condensers or evaporative condensers. It shall further be appreciated that references herein to water include water solutions comprising additional constituents unless otherwise limited.

Expander125is configured to receive refrigerant from first heat exchanger120, and to expand the received refrigerant to decrease its temperature. In the illustrated embodiment, expander125is a throttle valve. It is also contemplated that other types of expanders may be utilized, for example, capillary tubes. It is further contemplated that expander125may be formed integrally with second heat exchanger130.

Second heat exchanger130is configured to receive refrigerant from expander125, and transfer heat from a medium to the refrigerant. In the illustrated embodiment second heat exchanger130is configured as a water chiller which receives water provided to an inlet131, transfers heat from the water to the refrigerant, and outputs chilled water at an outlet132. It is contemplated that a number of particular types of evaporators may be utilized, including dry expansion evaporators, flooded type evaporators, bare tube evaporators, plate surface evaporators, and finned evaporators among others.

HVACR system100further includes a controller160which outputs control signals to variable frequency drive155to control operation of the motor170and compressor110. Controller160also receives information about the operation of drive unit150. In exemplary embodiments, controller160receives information relating to the temperature of various components of HVACR system100. In further embodiments, controller160receives information relating to motor current, motor terminal voltage, and/or other operational characteristics of the motor.

With reference now toFIG. 8, further details of an illustrative embodiment of controller160will be described. Exemplary controller160includes a sensor module, a criteria evaluation module, a commands module, and a data storage module800. Controller receives160information from at least one sensor, for example temperature sensors provided to various components of HVACR system100, and may further receive information from a user interface. Controller160provides commands to at least variable frequency drive155, and may further provide commands to other components of HVACR system100. Controller160may also output information to a user interface.

Data storage module800is a non-transitory computer readable medium configured to store data for use by other modules of controller160. Data storage module800may store, for example, sensor data such as sensor calibration data, parameters such as acceptable operating temperature ranges for various components of HVACR system100, switch patterns such as a plurality of PWM schedules, and/or valve settings such as the information of Table 1 below.

The sensor module of controller160receives information from at least one sensor, and may interpret the information according to data received from data storage module800. For example, the sensor module may convert analogue information from a sensor to digital information using the sensor data.

The commands module of controller160issues switching commands to variable frequency drive155. The commands may be based on one of a plurality of switch patterns stored on data storage module800, such as PWM patterns. Exemplary PWM patterns are described with respect toFIGS. 5 and 6below. The commands module may also provide additional commands, such as valve commands according to valve settings stored on data storage module800.

The criteria evaluation module evaluates information, such as input from the sensors and/or user interface, and determines what commands the commands module will issue. In one aspect, the criteria evaluation module evaluates sensor information received by the sensor module. The criteria evaluation module may compare the sensor data to parameters stored on data storage module800. In an exemplary embodiment, the criteria evaluation module compares a received temperature of a component of HVACR system100to an acceptable range of temperatures, and determines whether to change the pattern of the switching commands issued by the commands module. Further detail regarding the comparison and determination will be described below. The criteria evaluation module may determine other commands to be issued by the commands module, such as valve position commands. The valve position commands may relate to four-way valve140, and may relate to valves in waste heat recovery circuit180, as described with respect toFIG. 7below.

It shall be appreciated that the controls, control routines, and control modules described herein may be implemented using hardware, software, firmware and various combinations thereof and may utilize executable instructions stored in a non-transitory computer readable medium or multiple non-transitory computer readable media. It shall further be understood that controller160may be provided in various forms and may include a number of hardware and software modules and components such as those disclosed herein.

Returning toFIG. 1, it shall be further appreciated that waste heat recovery circuit180is configured to transfer heat from variable frequency drive155to a cooling medium, for example as described below with respect toFIG. 3. In the illustrated embodiment, waste heat recovery circuit180is configured as a closed loop cooling circuit configured to circulate a cooling medium, such as a working fluid, between variable frequency drive155and second heat exchanger130. It shall be appreciated that the cooling medium performs both cooling of variable frequency drive155and heating of a load such as evaporator. The cooling medium may be circulated by a pump (not shown) which may be controlled by controller160or by other another device or system.

Waste heat recovery circuit180may alternatively be a non-fluid based transfer device, for example, a heat sink thermally coupling the variable frequency drive155and second heat exchanger130. It is also contemplated that waste heat recovery circuit180may be formed integrally with the refrigerant loop or may be in selectable fluid communication with the refrigerant loop. That is, the cooling medium may be the refrigerant circulated in the refrigerant loop. Additionally or alternatively, waste heat recovery circuit180may be configured to transfer heat from variable frequency drive155to a different portion of the HVACR system100, for example, a suction line of compressor110, or a lubricant supply line. In further embodiments waste heat recovery circuit180may be configured to transfer heat to a load external to system100, for example, an external apparatus, device or system which may be related to but not part of system100or may be dedicated to one or more functionalities not related or not directly related to those of system100.

FIG. 7is a schematic illustration of an alternative embodiment of waste heat recovery circuit180. Waste heat recovery circuit780comprises a pump702, an inverter heat exchanger704, a first coolant heat exchanger706, a second coolant heat exchanger708, and a plurality of valves710,712,714,716, and718.

Pump702circulates a cooling medium to inverter heat exchanger704, through first coolant heat exchanger706and/or second coolant heat exchanger708, depending on the state of valves710,712,714,716, and718.

Inverter heat exchanger704is configured to receive the cooling medium from pump702, and discharge the cooling medium toward coolant heat exchangers706and708. Inverter heat exchanger is thermally coupled to an inverter or other switching device of variable frequency drive155, either in direct contact with a drive structure such as a heat sink or inverter board base structure, or through intermediate thermally conductive elements, and transfers heat from variable frequency drive155to the cooling medium.

First coolant heat exchanger706is configured to transfer heat between the cooling medium and a first component of HVACR system100. For example, first coolant heat exchanger706may be configured to transfer heat between the cooling medium and first heat exchanger120. First coolant heat exchanger706includes an inlet port706a, an outlet port706b, and an inlet/outlet port706c.

Second coolant heat exchanger708is configured to transfer heat between the cooling medium and a second component of HVACR system100. For example, second coolant heat exchanger708may be configured to transfer heat between the cooling medium and second heat exchanger130. Second coolant heat exchanger708includes an inlet port708a, an outlet port708b, and an inlet/outlet port708c.

Each of the plurality of valves is configured to provide selective fluid coupling between various components of waste heat recovery circuit780. Valve710controls flow to inlet port706a. Valve712controls flow from outlet port706b. Valve714controls flow to inlet port708a. Valve716controls flow from outlet port708b. Valve718controls flow between inlet/outlet port706cand inlet/outlet port708c. Each of the plurality of valves may be an open/close valve, for example a solenoid valve, or may be a variable flow valve. The plurality of valves may be controlled by controller160, a separate controller, or other control devices or systems.

The flow of the cooling medium in waste heat recovery circuit780, and therefore the heat transfer between the components, can be controlled by the open or closed state of the plurality of valves. The valves can be set such that the cooling medium flows only through first coolant heat exchanger706, only through second coolant heat exchanger708, to both first and second coolant heat exchangers706and708in parallel, from first coolant heat exchanger706to second coolant heat exchanger708, or from second coolant heat exchanger708to first coolant heat exchanger706.

For example, when heat transfer is desired only to first coolant heat exchanger706, valves710and712are set to an open state, and valves714,716, and718are set to a closed state. Additional exemplary configurations are detailed in Table 1 below, with “O” representing an open state of the valve, and “X” representing a closed state of the valve.

An illustrative example of an implementation of waste heat recovery circuit780in connection with HVACR system100will now be described. Inverter heat exchanger704is thermally coupled to variable frequency drive155. First coolant heat exchanger706is thermally coupled to first heat exchanger120. Second coolant heat exchanger708is thermally coupled to second heat exchanger130. In this and other embodiments, first and second coolant heat exchangers706and708may be formed integrally with the corresponding heat exchangers120and130. HVACR system100is initially operated with four-way valve140in the first configuration, wherein the refrigerant flows in the direction of the solid arrows. In this first configuration, first heat exchanger120acts as a condenser and becomes relatively hot, and second heat exchanger130acts as an evaporator and becomes relatively cold. In other exemplary embodiments, such as large chiller units, first heat exchanger may be a dedicated condenser, second heat exchanger130may be a dedicated evaporator, and valving for permitting reversible operation may be omitted and the system may operate in only one direction, rather than reversibly.

In reversible systems, determination is made, for example by controller160or by a user, that the system should be reversed. The determination may be based, for example, on a desire to provide chilled water at outlet122, or heated water at outlet132. Controller160commands four-way valve to the second configuration, wherein the refrigerant flows in the direction of the dashed arrows. In this second configuration, second heat exchanger130acts as the condenser, and first heat exchanger120acts as the evaporator. Because first heat exchanger120is still relatively hot, it will be unable to chill water flowing from inlet121to outlet122for a period of time. Similarly, because second heat exchanger130is still relatively cold, it will be unable to heat water flowing from inlet131to outlet132for a period of time.

Controller160determines that additional heat exchange is desired, and sets the plurality of valves as shown in the “706to708” entry in Table 1 above. That is, valves710,716, and718are set to an open state, and valves712and714are set to a closed state. The cooling medium flows from pump702to inverter heat exchanger704, where it accepts heat from variable frequency device155, to first coolant heat exchanger706where it accepts additional heat from first heat exchanger120, to second coolant heat exchanger708where it rejects heat to second heat exchanger130, and back to pump702. Waste heat recovery circuit780may further include additional coolant lines and valves (not shown) such that in an additional configuration, the cooling medium flows from pump702to first coolant heat exchanger706where it accepts heat from first heat exchanger120, to inverter heat exchanger704where it gains additional heat from variable frequency drive155, to second coolant heat exchanger708where it rejects heat to second heat exchanger130, and back to pump702. Controller may further determine whether additional heat is desired, and adjust the command signal provided to variable frequency drive155such that variable frequency drive155generates additional heat, as described in detail with reference toFIGS. 4-6below.

With reference toFIG. 2there is illustrated an exemplary circuit diagram for a variable frequency motor drive200. Drive200is connected to a power source210, for example, a 400/480 VAC utility power supply which provides three-phase AC power to line filter module220. Line filter module220is configured to provide harmonic damping to mitigate losses which can arise from harmonic feedback from drive components to power source210. Line filter module220outputs three-phase AC power to a rectifier290which converts the AC power to DC power and provides the DC power to a DC bus291. DC bus291is preferably a film capacitor-cased bus which includes one or more film capacitors electrically coupled between positive and negative bus rails. DC bus291is connected to inverter280. Waste heat recovery circuit181is thermally coupled to inverter280and another component of the HVACR system100, shown generally as HVACR component182.

For clarity of illustration and description, rectifier290, DC bus291, and inverter280are shown as discrete elements. It shall be appreciated, however, that two or more of these components may be provided in a common module, board or board assembly which may also include a variety of additional circuitry and components. It shall be further understood that, in addition to the illustrated 6-pulse rectifier, other multiple pulse rectifiers such as 12-pulse, 18-pulse, 24-pulse or 30-pulse rectifiers may be utilized along with phase shifting transformers providing appropriate phase inputs for 6-pulse, 12-pulse, 18-pulse, 24-pulse, or 30-pulse operation.

Inverter module280includes switches285,286, and287which are connected to the positive and negative rails of DC bus291. Switches285,286, and287are preferably configured as IGBT and diode based switches, but may also utilize other types of power electronics switching components such as power MOSFETs or other electrical switching devices. Switches285,286, and287provide output to motor terminals275,276, and277. Current sensors281,282, and283are configured to detect current flowing from inverter module280to motor270and send current information to identification (ID) module293. Voltage sensors are also operatively coupled with motor terminals275,276, and277and configured to provide voltage information from the motor terminals to ID module293.

Waste heat recovery circuit181is thermally coupled to inverter module280, and a cooling medium flowing in waste heat recovery circuit181receives heat generated in inverter module280by the operation of switches285,286, and287. A pump (not shown) circulates the heated cooling medium to HVACR component182, which accepts heat from the cooling medium. HVACR component182may be, for example, second heat exchanger130, or a suction line of compressor110.

In embodiments in which the refrigerant loop circulates a refrigerant-oil mixture, HVACR component182may be configured to heat the mixture or the oil using the transferred heat. In such embodiments, HVACR component may heat the mixture or the oil using only the transferred heat, or may use the transferred heat in combination with an additional heating device. HVACR component182may be an oil separator, configured to boil the refrigerant, such that the oil is separable from the refrigerant. HVACR component182may be an oil purifier configured to boil off refrigerant dissolved in the oil. HVACR component182may be an oil heater, configured to heat the oil to a predetermined temperature.

ID module293includes burden resistors used in connection with current sensing to set the scaling on current signals ultimately provided to analog to digital converters for further processing. ID module293tells the VFD what size it is (i.e. what type of scaling to use on current post ADC) using identification bits which are set in hardware on the ID module293. ID module293also outputs current and voltage information to gate drive module250and also provides identification information to gate drive module250which identifies the type and size of the load to which gate drive module250is connected. ID module293may also provide current sensing power supply status information to gate drive module250. ID module293may also provide scaling functionality for other parameters such as voltage or flux signals in other embodiments.

Gate drive module250provides sensed current and voltage information to analog to digital converter inputs of digital signal processing (DSP) module260. DSP module260processes the sensed current and voltage information and also provides control signals to gate drive module250which signals gate drive module250to output voltages to boost modules251,252and253, which in turn output boosted voltages to switches285,286, and287. The signals provided to switches285,286, and287in turn control the output provided to terminals275,276, and277of motor270.

Motor270includes a stator271, a rotor273, and an air gap272between the rotor and the stator. Motor terminals275,276, and277are connected to windings provided in stator271. Rotor273includes a plurality of permanent magnets274. In the illustrated embodiment magnets274are configured as surface permanent magnets positioned about the circumference of rotor273. The rotor is typically constructed using the permanent magnets such that an essentially constant magnetic flux is present at the surface of the rotor. In operation with rotation of the rotor, the electrical conductors forming the windings in the stator are disposed to produce a sinusoidal flux linkage. Other embodiments also contemplate the use of other magnet configurations such as interior magnet configurations as well as inductance motor configurations, reluctance motor configurations and other non-permanent magnet configurations.

Turning now toFIG. 3, one non-limiting arrangement of a portion of inverter module280is schematically illustrated. Inverter module280includes a switching device285positioned on and in thermal communication with a thermally conductive base or substrate302. Switching device285includes one or more internal switching junctions and in one non-limiting embodiment is in the form of one or more insulated gate bipolar transistors (IGBT's). In another form, switching device285is a power MOSFET or another type of switching device. Base302may be formed from a variety of different thermally conductive materials or combinations of materials. For example, in one particular but non-limiting form, base302is formed from copper or an alloy thereof. A thermal pad304is positioned between base302and a heat sink306, although forms in which thermal pad304is omitted and base302is positioned directly on heat sink306are also contemplated. It should further be understood that forms in which one or more additional components are positioned between switching device285and base302and/or between base302and heat sink306are possible.

Heat sink306is formed of a thermally conductive material and is in thermal communication with base302and a cooling medium308. Cooling medium308may be a liquid cooling medium circulated in a conduit307of waste heat recovery circuit181. In this arrangement, heat sink306is configured to absorb heat created by switching device285during operation of inverter module280and transfer the heat to cooling medium308. Cooling medium308may be in any form suitable for absorbing and moving heat away from heat sink306, examples of which include air, water, glycol or a refrigerant, just to provide a few possibilities. In one particular but non-limiting form, cooling medium308is refrigerant of the refrigerant loop that includes compressor110, first heat exchanger120, and second heat exchanger130, and heat is transferred away from heat sink306by the refrigerant. In another form, cooling medium308could be part of a separate heat transfer system that includes a closed loop of cooling medium308and a heat exchanger configured to release heat from cooling medium308to HVACR component182.

Inverter module280also includes a number of sensors positioned at different locations and configured to measure temperatures and provide sensed temperature values to controller160. More particularly, inverter module280includes sensor322configured to measure temperature of base302and provide a sensed temperature value of base302to controller160, sensor326configured to measure temperature of heat sink306and provide a sensed temperature value of heat sink306to controller160, and sensor328configured to measure temperature of cooling medium308and provide a sensed temperature value of cooling medium308to controller160. In the illustrated embodiment, inverter module280includes a single sensor at each separate location. In other non-illustrated forms however, inverter module280includes a plurality of sensors at each location such that a plurality of sensed temperature values are provided to controller160for each of base302, heat sink306and cooling medium308. Forms in which inverter module280does not include a sensor at one or more of these locations, or includes sensors at locations in addition to or in lieu of these locations, are also possible.

The schematic flow diagram ofFIG. 4and related description which follows provides an illustrative embodiment of performing procedures for modifying the heat generation of an inverter in a system such as that shown inFIG. 2. Operations illustrated are understood to be exemplary only, and operations may be combined or divided, and added or removed, as well as re-ordered in whole or part, unless stated explicitly to the contrary herein. Certain operations illustrated may be implemented by a computer executing a computer program product on a non-transitory computer readable storage medium, where the computer program product comprises instructions causing the computer to execute one or more of the operations, or to issue commands to other devices to execute one or more of the operations.

The exemplary procedure400includes providing a switching pattern402to inverter module280such that switch285changes between a first state and a second state according to the switching pattern. Switch285generates heat as a byproduct of each change of state, a portion of which is transferred to HVACR component182by waste heat recovery circuit181.

Procedure400further includes checking heat production criteria404, which may include receiving temperature values from a temperature sensor, for example a temperature sensor thermally coupled to HVACR component182and/or at least one of temperature sensors322,326and328. Checking heat production criteria404may further include determining if more heat is desired406and determining if less heat is desired410.

Determining if more heat is desired406may include comparing a temperature of HVACR component182to a desired temperature, and determining whether additional heat transfer to HVACR component182is desired. If more heat is desired406Y, the number of switches in the switching pattern is increased, leading to increased heat generation by switch285. It shall be appreciated that increases in the number of switches in the switching pattern may be accomplished through a number of techniques, including increasing the carrier frequency or switching frequency, altering particular regions within the PWM pattern to increase the number of switching events, transitioning from discontinuous to continuous PWM or from more discontinuous to less discontinuous PWM, and combinations of these techniques, among other techniques.

Determining if less heat is desired410may include comparing a temperature of at or near switch285, for example as sensed by temperature sensor322,326, and/or328, and comparing the temperature to a maximum operating temperature of switch285. If less heat is desired410Y, the number of switches in the switching pattern is decreased412, leading to decreased heat generation by switch285. It shall be appreciated that decreases in the number of switches in the switching pattern may be accomplished through a number of techniques, including decreasing the carrier frequency or switching frequency, altering particular regions within the PWM pattern to decrease the number of switching events, transitioning from continuous to discontinuous PWM or from less discontinuous to more discontinuous PWM, among other techniques. Determining if less heat is desired410may of course be performed prior to or concurrently with determining if more heat is desired406.

Increasing408and decreasing412the number of switches in the switching pattern may include selecting a new switching pattern to provide to the inverter module. Exemplary switching patterns will now be described.

FIGS. 5A, 5B, 6A, and 6Billustrate exemplary pulse width modulation (PWM) switching patterns for a three-phase inverter. In each of the figures, the vertical axis is the magnitude of the PWM signal, and the horizontal axis is time.

FIG. 5Aillustrates symmetric/continuous PWM switching patterns510,520, and530corresponding to a switching frequency (sometimes referred to as a carrier frequency) of 2 kilohertz (kHz), though it shall be appreciated that various different switching frequencies may utilized. PWM patterns, such as PWM pattern510, may be generated, as a simple example, by providing modulating signal518to one input of a comparator, and providing a carrier signal (not shown) to another comparator input to output the illustrated pattern510. The carrier signal may be, for example, a sawtooth or triangular waveform, though other carrier signals are contemplated. In embodiments utilizing a carrier signal, the frequency of the carrier signal is the switching frequency. It is also contemplated PWM patterns, such as PWM pattern510, may be generated by a number of additional or alternate PWM generation techniques such as delta, delta-sigma, space vector modulation, statistical techniques, direct torque control, or time proportioning techniques, among others. Regardless of the technique which is utilized the switching frequency is correlated to the number of switching events per unit time.

PWM pattern510comprises signals of a first magnitude512, signals of a second magnitude514, and transition regions516. When provided to a switching device, such as switch285, first magnitude signals512command switch285to a first state, second magnitude signals514command switch285to a second state, and transition regions516correspond to a change between the first and second states. Each change between the first and second states generates heat. When inverter module280is configured to supply power to motor170, a synthesized current waveform is produced in motor170.

For three-phase operation of inverter module280, PWM pattern520may be provided to switch286based upon modulating signal528, and PWM pattern530may be provided to switch287based upon modulating signal538. Modulating signals518,528and538are preferably sinusoidal waveforms of the same frequency with a phase separation of 120° which, under normal system operation, are effective to provide corresponding synthesized sinusoidal current waveforms with a phase separation of 120° in the motor. It is also contemplated that other multi-phase systems could be utilized.

FIG. 5Billustrates symmetric PWM switching patterns550,560, and570corresponding to a switching frequency of 4 kHz. In the illustrated embodiment, switching patterns550,560, and570are obtained by comparing modulating signals558,568, and578to a carrier signal having a 4 kHz frequency, though they may also be generated using the other techniques described above. PWM pattern550comprises signals of a first magnitude552, signals of a second magnitude554, and transition regions556. When PWM pattern550is provided to inverter module280, a synthesized current waveform is produced in motor170. PWM pattern550has a greater number of transition regions than PWM pattern510, and therefore produces more waste heat.

For three-phase operation of inverter module280, PWM pattern560may be provided to switch286based upon modulating signal568, and PWM pattern570may be provided to switch287based upon modulating signal578. Modulating signals558,568and578are preferably sinusoidal waveforms of the same frequency with a phase separation of 120° which, under normal system operation, are effective to provide corresponding synthesized sinusoidal current waveforms with a phase separation of 120° in the motor. It is also contemplated that other multi-phase systems could be utilized.

FIG. 6Aillustrates discontinuous PWM switching patterns610,620, and630corresponding to a switching frequency of 2 kilohertz (kHz). PWM pattern610comprises signals of a first magnitude612, signals of a second magnitude614, and transition regions616. When PWM pattern610is provided to inverter module280, a synthesized current waveform is produced in motor170. PWM pattern610includes an extended first magnitude signal613and/or an extended second magnitude signal611. Extended first magnitude signal613corresponds to a trough618bof modulating signal618, and extended second magnitude signal611corresponds to a peak618aof modulating signal618. Each of the extended signals611and613is of a duration corresponding to a predetermined percentage of the period of modulating signal618, for example ten to twenty percent. The predetermined percentage may vary according to heat generation criteria and acceptable distortion of the synthesized sinusoidal current waveform seen in the motor. PWM pattern610has fewer transition regions than PWM patterns510and550, and therefore produces less waste heat.

For three-phase operation of inverter module280, PWM pattern620may be provided to switch286based upon modulating signal628, and PWM pattern630may be provided to switch287based upon modulating signal638. Modulating signals618,628and638are preferably sinusoidal waveforms of the same frequency with a phase separation of 120° which, under normal system operation, are effective to provide corresponding synthesized sinusoidal current waveforms with a phase separation of 120° in the motor. It is also contemplated that other multi-phase systems could be utilized.

FIG. 6Billustrates discontinuous PWM switching patterns650,660, and670corresponding to a switching frequency of 4 kHz. PWM pattern650comprises signals of a first magnitude652, signals of a second magnitude654, and transition regions656. When PWM pattern650is provided to inverter module280, a synthesized current waveform is produced in motor170. PWM pattern650includes an extended first magnitude signal653and/or an extended second magnitude signal651. Extended first magnitude signal653corresponds to a trough658bof modulating signal658, and extended second magnitude signal651corresponds to a peak658aof modulating signal658. Each of the extended signals651and653is of a duration corresponding to a predetermined percentage of the period of modulating signal658, for example ten to twenty percent. The predetermined percentage may vary according to heat generation criteria and acceptable distortion of the synthesized sinusoidal current waveform seen in the motor. PWM pattern650has more transition regions than PWM pattern610, and fewer transition regions than PWM pattern550.

For three-phase operation of inverter module280, PWM pattern660may be provided to switch286based upon modulating signal668, and PWM pattern670may be provided to switch287based upon modulating signal678. Modulating signals658,668and678are preferably sinusoidal waveforms of the same frequency with a phase separation of 120° which, under normal system operation, are effective to provide corresponding synthesized sinusoidal current waveforms with a phase separation of 120° in the motor. It is also contemplated that other multi-phase systems could be utilized.

While the switching patterns have been illustratively described as PWM patterns corresponding to carrier frequencies of 2 kHz and 4 kHz, the invention is not so limited. PWM patterns of any suitable carrier frequency are contemplated, as is variation among and between the different switching frequencies and patterns disclosed herein as well as other switching frequencies and patterns. While four exemplary switching patterns have been described, any number of switching patterns may be available to choose between, so long as the set of available switching patterns includes switching patterns having a different number of switches per unit time.

Furthermore, in a three-phase power inversion system, different switching patterns may be provided to each of the switches. Temperature sensors may sense the temperature of each switch, and controller160may alter the switching pattern of one or more sensors based on the sensed temperatures. Discontinuous PWM patterns may employ extended signals of varying durations.

With reference to the above-described systems and methods, a number of non-limiting, illustrative examples will now be described.

In certain exemplary embodiments, controller160provides a 2 kHz symmetric PWM pattern510to an inverter module280of variable frequency drive155. HVACR component182is a suction line of compressor110, and waste heat recovery circuit181transfers heat to suction line182. A temperature sensor senses a temperature of a refrigerant in suction line182. Controller160compares the sensed temperature to a predetermined superheat temperature of the refrigerant. If the sensed temperature is not greater than the predetermined superheat temperature, controller160changes the PWM pattern to a 4 kHz symmetric PWM pattern550, increasing the heat generated by variable frequency drive155and transferred to suction line182through waste heat recovery circuit180.

In certain exemplary embodiments, a refrigerant loop circulates a working fluid mixture comprising a refrigerant and an oil of a higher density than the refrigerant. During system idle time, oil settles in the bottom of second heat exchanger130. Oil-rich working fluid is transferred from the bottom of second heat exchanger130to an oil separator defining HVACR component182. The system is started, and controller160provides a 4 kHz symmetric PWM pattern550to variable frequency drive155. Heat is transferred from variable frequency drive155to the oil separator by waste heat recovery circuit181. The transferred heat boils the refrigerant portion of the working fluid. The boiled refrigerant is discharged from the oil separator to the compressor suction line, and the separated oil is transferred to an oil intake of compressor110. After a predetermined time has elapsed, controller160changes the PWM pattern to a 2 kHz symmetric PWM pattern510.

In certain exemplary embodiments, an oil supply line182provides a lubricating oil to compressor110. Controller160provides a 2 kHz discontinuous PWM pattern610to inverter module280. Heat is transferred by waste heat recovery circuit181from inverter module280to an oil supply line defining HVACR component182. A temperature sensor senses the oil temperature. Controller160determines that the oil temperature is too low, resulting in elevated oil viscosity. Controller160changes the PWM pattern to a 2 kHz continuous PWM pattern510to increase the heat generated by inverter module280and transferred to the oil supply line.

In certain exemplary embodiments controller160provides 2 kHz symmetric PWM patterns510,520, and530to switches285,286, and287, respectively, inverter module280thereby providing three-phase power to motor170. Heat is transferred by waste heat recovery circuit181from inverter module280to HVACR component182. Controller160determines that additional heat is desired at HVACR component182, the temperatures of switches285and286are within an acceptable range, and the temperature of switch287is near a failure temperature. Controller160provides 4 kHz symmetric PWM patterns550and560to switches285and286, and provides 2 kHz discontinuous PWM pattern630to switch287.

With reference toFIG. 9there is illustrated an exemplary HVACR system1100which includes a refrigerant loop1101comprising a compressor1110, a condenser1120, an expander1125such as an expansion valve, and an evaporator1130. Refrigerant flows through refrigerant loop1101from compressor1110to condenser1120to expander1125to evaporator1130and back to compressor1110. Variable frequency drive1155may be configured as a variable frequency motor drive200having an inverter module280as described above in connection withFIG. 2. Various embodiments of refrigerant loop1101may also include additional elements including, for example, valves for controlling or reversing refrigerant flow, refrigerant filters, economizers, oil separators and/or cooling components and flow paths for various system components.

Compressor1110is driven by a drive unit1150including a permanent magnet electric motor1170which is driven by a variable frequency drive455. In the illustrated embodiment, variable frequency drive1155is configured to output a three-phase PWM drive signal, and motor1170is a surface mounted permanent magnet motor. Use of other types and configurations of variable frequency drives and electric motors such as interior magnet permanent magnet motors, reluctance motors, or inductance motors are also contemplated. It shall be appreciated that the principles and techniques disclosed herein may be applied to a broad variety of drive and motor configurations.

Condenser1120is configured to transfer heat from compressed refrigerant received from compressor1110. In the illustrated embodiment condenser1120is a water cooled condenser which receives cooling water at an inlet1121, transfers heat from the refrigerant to the cooling water, and outputs cooling water at an outlet1122. It is also contemplated that other types of condensers may be utilized, for example, air cooled condensers or evaporative condensers. It shall further be appreciated that references herein to water include water solutions comprising additional constituents unless otherwise limited.

Expander1125is configured to receive refrigerant from condenser1120, and to expand the received refrigerant to decrease its temperature. In the illustrated embodiment, expander1125is a throttle valve. It is also contemplated that other types of expanders may be utilized, for example, capillary tubes or any other device configured to provide expansion (preferably controllable expansion) of refrigerant. It is further contemplated that expander1125may be formed integrally with evaporator1130.

Evaporator1130is configured to receive refrigerant from expander1125, and transfer heat from a medium to the refrigerant. In the illustrated embodiment evaporator1130is configured as a water chiller which receives water provided to an inlet1131, transfers heat from the water to the refrigerant, and outputs chilled water at an outlet1132. It is contemplated that a number of particular types of evaporators may be utilized, including dry expansion evaporators, flooded type evaporators, bare tube evaporators, plate surface evaporators, and finned evaporators among others.

HVACR system1100further includes a controller1160which outputs control signals to variable frequency drive1155to control operation of the motor1170and compressor1110. Controller1160also receives information about the operation of drive unit1150. In exemplary embodiments, controller1160receives information relating to the temperature of various components of HVACR system1100. In further embodiments, controller1160receives information relating to motor current, motor terminal voltage, motor speed, and/or other operational characteristics of the motor.

With reference now toFIG. 10, further details of an illustrative embodiment of controller1360will be described. Exemplary controller1360includes a sensor module1310, a criteria evaluation module1320, a commands module1330, and a data storage module1340. Controller receives1360information from at least one sensor, for example temperature sensors provided to various components of HVACR system1100, and may further be in communication with a user interface. Controller1360provides commands to at least variable frequency drive1155, and may further provide commands to other components of HVACR system1100.

It shall be appreciated that the controls, control routines, and control modules described herein may be implemented using hardware, software, firmware and various combinations thereof, and may utilize executable instructions stored in a non-transitory computer readable medium or multiple non-transitory computer readable media. Likewise, while various functionalities are referred to in connection with individual modules, it shall be understood that references to individual modules does not exclude or prevent the individual modules from being implemented in a common module with multiple sub-functionalities or distributed across multiple discrete modules operating in concert. It shall further be understood that controller1360may be provided in various forms and may include a number of hardware and software modules and components such as those disclosed herein.

Data storage module1340is configured to store data on one or more non-transitory computer readable media for use by other modules of controller1360. Data storage module1340may store, for example, sensor data such as sensor calibration data, parameters such as audible noise profiles, acoustic noise profiles, switch patterns, and a clock. Data storage module1340may further store schedules for target audible noise profiles1452. For example, a schedule may indicate that a first audible noise profile is to be used during day-time hours when cooling demand is high, and a second audible noise profile is to be used during night-time hours, when quiet operation is desired. Schedules may further include weighting factors1456, discussed below. The schedules may be adjustable by the user-interface. Data storage module1340may further include resonance information, for example relating to the natural frequencies of one or more components of variable frequency drive1155, motor1170, and compressor1180.

In the illustrated embodiment, sensor module1310receives information from at least one sensor, and may interpret the information according to data received from data storage module1340. For example, sensor module1310may convert analogue information from a sensor to digital information using the sensor data. Sensor module may receive information regarding temperature of a component, electrical noise, feedback, and acoustic noise. It is also contemplated that, in certain embodiments, controller1360may not include sensor module1310, and certain conditions may be determined by other methods. For example, data storage module1340may include look-up tables relating each switching pattern1480to one or more conditions.

Criteria evaluation module1320is configured to evaluate information—for example according to the procedure described with respect toFIG. 11below—and select a switching pattern based on the evaluation of information. In the illustrated embodiment, criteria evaluation module1320evaluates information stored on data storage module1340, as well as sensor information received by sensor module1310. Criteria evaluation module1320may compare the sensor data to parameters stored on data storage module1340. It is also contemplated that controller1360may not include sensor module1310, and that criteria evaluation module1320may select a switching pattern based only on data stored in data storage module1340. Criteria evaluation module1320may determine other commands to be issued by commands module1330, such as valve commands for valves in system1100.

Commands module1330is configured to generate and output switching commands according to the switching pattern selected by criteria evaluation module1320. The switching commands are provided to inverter module280, thereby operating switches285,286, and287to provide output to terminals275,276, and277of motor270, as described above in connection withFIG. 2. Commands module1330may also provide additional commands, such as valve commands for valves in system1100. It is contemplated that another controls module, such as one implemented through a separate controller, may also be utilized.

The schematic flow diagram ofFIG. 11and related description which follows provides an illustrative embodiment of performing procedures for modifying the audible noise generation of an inverter in a system such as that shown inFIG. 2. Operations illustrated are understood to be exemplary only, and operations may be combined or divided, and added or removed, as well as re-ordered in whole or part, unless stated explicitly to the contrary herein. Certain operations illustrated may be implemented by a computer executing a computer program product on a non-transitory computer readable storage medium, where the computer program product comprises instructions causing the computer to execute one or more of the operations, or to issue commands to other devices to execute one or more of the operations.

The procedure generally includes determining1450an optimal switching pattern1490selected from a switching pattern set1400, determining1450being based at least in part upon a target audible noise profile1452and other factors1454, and issuing1460switching commands to inverter module1280according to selected pattern1490.

Switching pattern set1400includes a plurality of switching patterns1480. In the illustrated embodiment, set1400includes switching patterns generated by different PWM generation techniques1402,1404,1406, and1408, at different carrier frequencies1410,1420,1430, and1440.

In the illustrated embodiment, the PWM techniques include intersective continuous1402(illustrative examples of which are described with respect toFIGS. 5A and 5Babove), intersective discontinuous1404(illustrative examples of which are described with respect toFIGS. 6A and 6Babove), delta modulation1406, and delta-sigma modulation1408. It is contemplated that fewer, additional, or alternative techniques may be employed to generate set1400. For example, set1400may include switching patterns1480generated by techniques such as space vector modulation, statistical techniques, direct torque control, or time proportioning techniques, among others. In the illustrated embodiment, only the intersective technique employs discontinuities. It is also contemplated that discontinuities may be employed in fewer, additional, or alternative techniques, and that the duration of the discontinuities may be modified. Regardless of which technique is utilized, the carrier frequency is correlated to the rate of switch commands, and thus the acoustic noise produced (discussed below).

In the illustrated embodiment, carrier frequencies include 2 kHz1410(illustrative examples of which are described with respect toFIGS. 5A and 6Aabove), 4 kHz1420(illustrative examples of which are described with respect toFIGS. 5B and 6Babove), 8 kHz1430, and 10 kHz1440. It is contemplated that fewer, additional, or alternative carrier frequencies may be employed to generate set1400. In the illustrated embodiment, the carrier frequencies are discrete values. It is also contemplated that a continuum of frequencies may be available to criteria evaluation module1320, for example in the form of a frequency slider.

Determining1450a switching pattern (hereinafter determining1450) may include selecting an acceptable audible noise profile1452, and selecting a switching pattern based at least in part on audible noise profile1452. Determining1450may further take into account other factors1454, and may weigh the importance of the audible noise profile1452and other factors1454according to weighting factors1456.

The selection of the acceptable audible noise profile may itself be based on one or more factors, such as day, time, and user selection. For example, if HVACR system1100is in a commercial building, quieter operation during the day may be desired, whereas in a residential building, quiet operation may be desired at night. Additionally, zoning ordinances may limit the acceptable noise generation during certain hours. In any case, audible noise profile1452sets a target maximum audible noise level upon which determining1450is at least partly based.

Target audible noise profile1452may be selected from a set of predetermined audible noise profiles, or may be generated at the time of determining1450. An audible noise profile may include sound pressure levels of a plurality of frequency ranges (for example in dB SPL), or may be a single measurement, for example a weighted measurement such as A-weighted decibels (dBA). For example, a first audible noise profile may set a maximum dB SPL of a first frequency range and a second frequency range, while a second audible noise profile may only include a maximum dB SPL of the first frequency range, and be silent as to amplitudes of other frequency ranges.

Determining1450includes evaluating other factors1454, including switching pattern effects. When provided to inverter module280, each switching pattern1480will have a different effect on the system. For example, in addition to changing the acoustic noise profile (discussed below), changing the switching pattern may change electrical noise generation, heat generation, inverter efficiency, current ripple, and the quality of the synthesized current waveform seen in the motor. These effects are often competing concerns, in that changing the switching pattern to reduce a first negative effect may have the result of increasing a second negative effect. For example, increasing the switching frequency may reduce audible noise and current ripple, while increasing electrical noise and heat generation. These effects, as well as other factors1454, may be assigned weighting factors1456according to their relative importance. For example, surface mounted permanent magnet motors require relatively high quality synthesized current waveforms. In systems using such motors, electrical noise reduction may be given greater weighting factor1456than in other systems.

Each of the switching pattern effects may be calculated based on known parameters, or may be measured when the switching pattern is used. Each switching pattern1480may be associated with a corresponding switching pattern effects profile. For example, data storage module1340may include look-up tables with empirically derived data relating to the effects of one or more switching patterns1480.

The effects to be considered as one of other factors1454, including at least the acoustic noise profile, are included in a switching pattern effects profile (EFFECTS). Other factors1454may further include a temperature. For example, the inverter temperature may be considered as one of other factors1454, and optimal pattern may be selected such that inverter module280does not overheat. Other factors1454may include motor information, such as motor speed and motor load. For example, a higher quality of the synthesized current waveform may be required at certain motor speeds. Other factors1454may further include natural frequencies of one or more components, as discussed below.

Operation of inverter module280according to the selected switching pattern1490results in acoustic noise production by one or more of the inverter, the motor, and the compressor. The operation of switches285,286, and287changes the electromagnetic field in motor270. Varying electromagnetic fields can cause magnetically susceptible components of motor270to vibrate at a frequency corresponding to the switching rate, resulting in acoustic noise at the frequency of vibration. The changing electromagnetic field also creates variations in the torque generated by motor270. The varying torque can result in vibration of one or more components of motor270and compressor1110at a frequency corresponding to the switching rate, which in turn results in acoustic noise at the frequency of vibration.

When the operation causes a frequency of vibration at or near a natural frequency of a component of variable frequency drive1155, motor1170, or compressor1110, the acoustic noise becomes much more pronounced. Furthermore, this can be a cumulative effect, in that continued excitation of the component at its natural frequency causes increasingly higher amplitudes of vibration. In certain circumstances, this may even cause damage to the component or its surroundings. Determining1450may include considering the natural frequencies of one or more components as one of other factors1454.

Acoustic noise at other frequencies—for example, due to the rotation of rotor273, or harmonics of the frequency of vibration—may also be produced. The set of acoustic noises produced by the system is referred to herein as an acoustic noise profile. An acoustic noise profile may include sound pressure levels of a plurality of frequency ranges (for example in dB SPL), or may be a single measurement, such as A-weighted decibels.

When the vibration frequency is in the human audible range, the acoustic noise is audible. The average human adult ear has an audible range of about 16 Hz to 16 kHz, and is most sensitive to frequencies of about 2 kHz to 5 kHz. Generally speaking, tones of relatively higher frequencies are less readily perceived by the human ear than a tone of the same decibel level having a relatively lower frequency. For example, according to ISO 226:2003, a 10 kHz tone at 65 dB SPL is perceived as being roughly the same loudness as a 3 kHz tone at 45 dB SPL.

In certain embodiments, determining1450includes selecting the switching pattern1490from a subset1401that includes only switching patterns1480that do not violate a critical condition. For example, when quiet operation of HVACR system1100is of the highest importance, weighting factors1456may indicate target audible noise profile1452as a critical condition. In such a case, determining1450includes creating subset1401to include only switching patterns1480corresponding to acoustic noise profiles that do not violate target audible noise profile1452. Determining1450may then select the optimal pattern1490based on other factors1454, for example using other weighting factors1456. Alternatively, one or more other factors1454may be set as critical conditions, and optimal pattern1490may be selected from subset1401to comply with target audible noise profile1452.

In other embodiments, determining1450includes evaluating audible noise profile1452and other factors1454simultaneously according to weighting factors1456. For example, in certain cases it may be more important to meet the load requirements than to meet target audible noise profile1452. In such a case, the load criterion would be given a higher weighting factor1456than audible noise profile1452, and optimal pattern1490may be selected such that the acoustic noise profile violates audible noise profile1452by only an amount needed to meet the load requirements. In certain cases, weighting factors1456may result in selected pattern1490not meeting any of the criteria, but having the optimal balance (with respect to weighting factors1456) between the competing criteria. Weighting factors1456may themselves be based on a number of conditions, such as for example, day, time, user selection, temperatures and load requirements.

Once optimal switching pattern1490has been selected, optimal switching pattern1490is provided1460to inverter module280. Providing1460may be performed, for example, by commands module1330. Furthermore, optimal switching pattern1490may comprise a plurality of different switching patterns1480, such that a number of criteria may be satisfied. For example, it may be determined that a first switching pattern1412and a second switching pattern1424provide an optimal balance of audible noise and other factors, except for the fact that first pattern1412excites a first component at its natural frequency, and second pattern1424excites a second component at its natural frequency. In such a case, optimal pattern1490may include one or more cycles of first pattern1412followed by one or more cycles of second pattern1424. The first component would be excited at its natural frequency for only the duration of the commands according to first pattern1412, and would be dampened to vibration of a lower amplitude during the commands according to second pattern1424. Similarly, the second component would be excited at its natural frequency for only the duration of the commands according to second pattern1424, and would be dampened to vibration of a lower amplitude during the commands according to first pattern1412.

In certain exemplary embodiments, a first schedule includes weighting factors1456indicating target audible noise profile1452is a critical condition, and a high weighting factor is assigned to system efficiency. A second schedule includes weighting factors1456indicating a predetermined temperature of inverter module280is a critical condition, a high weighting factor is assigned to target audible noise profile1452, and a lower weighting factor is assigned to electrical noise generation.

In certain exemplary embodiments, the quality of the synthesized current waveform is given a lower weighting factor1456for a first range of motor speeds, a higher weighting factor1456for a second range of motor speeds, and is considered a critical condition at a third range of motor speeds.

It shall be understood that the exemplary embodiments summarized and described in detail above and illustrated in the figures are illustrative and not limiting or restrictive. Only the presently preferred embodiments have been shown and described and all changes and modifications that come within the scope of the invention are to be protected. It shall be appreciated that the embodiments and forms described below may be combined in certain instances and may be exclusive of one another in other instances. Likewise, it shall be appreciated that the embodiments and forms described below may or may not be combined with other aspects and features disclosed elsewhere herein. It should be understood that various features and aspects of the embodiments described above may not be necessary and embodiments lacking the same are also protected. In reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.