Power conversion system using high-frequency injection, control method, and readable medium

Abstract

A power conversion system includes an inverter and a controller configured to: measure a motor speed of an IPM motor in response to startup of the system; generate an inverter switch control signal to perform high frequency injection (HFI) in response to the motor speed being less than a threshold; determine a measured angle of the IPM motor during HFI; generate an inverter switch control signal to provide an injection current to the IPM motor during HFI; detect acceleration or deceleration of the IPM motor in response to the injection current; selectively determine an electrical angle as half of the measured angle or as 180 degrees plus half of the measured angle based on the detected acceleration or deceleration of the IPM motor; and generate an inverter switch control signal to drive the IPM motor to a reference frequency in a normal operation mode of the inverter in response to determining the electrical angle.

Description

Technical Field

[0001] The subject matter disclosed herein relates to power converters. Background Art

[0002] Motor drives are sometimes used to drive outdoor fans or pumps in wells. In these applications, when the drive is turned off, the blades of the driven fan or pump may rotate due to the flow of wind or the pumped fluid in the well. Starting the drive when the rotor of the driven motor is rotating (referred to as a flying start) can cause high current spikes in the drive. Summary of the Invention

[0003] In one aspect, a power conversion system includes an inverter and a controller configured to: measure a motor speed of an interior permanent magnet (IPM) motor in response to startup of the system; generate an inverter switch control signal to perform high frequency injection (HFI) in response to the motor speed being less than a threshold; determine a measured angle of the IPM motor during HFI; generate an inverter switch control signal to provide an injection current to the IPM motor during HFI; detect acceleration or deceleration of the IPM motor in response to the injection current; selectively determine an electrical angle as half of the measured angle or as 180 degrees plus half of the measured angle based on the detected acceleration or deceleration of the IPM motor; and generate an inverter switch control signal to drive the IPM motor to a reference frequency in a normal operation mode of the inverter in response to determining the electrical angle.

[0004] In another aspect, a method includes: measuring a motor speed of an IPM motor in response to startup of a power conversion system; generating an inverter switch control signal to perform high frequency injection (HFI) in response to the motor speed being less than a threshold; determining a measured angle of the IPM motor during HFI; generating an inverter switch control signal to provide an injection current to the IPM motor during HFI; detecting acceleration or deceleration of the IPM motor in response to the injection current; selectively determine an electrical angle as half of the measured angle or as 180 degrees plus half of the measured angle based on the detected acceleration or deceleration of the IPM motor; and generating an inverter switch control signal to drive the IPM motor to a reference frequency in a normal operation mode of the inverter in response to determining the electrical angle.

[0005] In another aspect, a non-transitory computer-readable medium has computer-executable instructions that, when executed by a processor, cause the processor to perform the following operations: measure the motor speed of an IPM motor in response to startup of a power conversion system; generate an inverter switch control signal to perform high-frequency injection (HFI) in response to the motor speed being less than a threshold; determine a measured angle of the IPM motor during HFI; generate an inverter switch control signal to supply an injection current to the IPM motor during HFI; detect acceleration or deceleration of the IPM motor in response to the injection current; selectively determine an electrical angle as half of the measured angle or as 180 degrees plus half of the measured angle based on the detected acceleration or deceleration of the IPM motor; and generate an inverter switch control signal to drive the IPM motor to a reference frequency in a normal operation mode of the inverter in response to determining the electrical angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of a motor drive power conversion system.

[0007] Figure 2 is a flowchart of a method.

[0008] Figure 3 is a graph.

[0009] Figure 4 is a graph.

[0010] Figure 5 is a graph. DETAILED DESCRIPTION

[0011] Referring now to the drawings, several embodiments or implementations will be described hereinafter in conjunction with the drawings, in which like reference numerals are always used to refer to like elements, and in which the various features are not necessarily drawn to scale.

[0012] Motor drives are sometimes used to drive outdoor fans or pumps in wells. In these applications, when the drive is turned off, the blades of the driven fan or pump may rotate due to the flow of wind or the fluid being pumped in the well. Starting the drive when the rotor of the driven motor is rotating (referred to as "capture restart") can result in high current spikes in the drive. Before actively driving the motor, the back electromotive force (CEMF, also referred to as back EMF) can sometimes be used to measure the speed and position (e.g., angle) of the rotor, and the drive output voltage and speed can be matched to the corresponding CEMF and rotor rotation to avoid high current spikes. However, the CEMF is low at low speeds, and the estimated rotor position obtained may have large errors. Static offset tests can inject pulses to estimate the rotor position before starting the drive, but this technique is not very suitable for rotating motors and may result in large errors in the estimated rotor position. Using inaccurate position angle information to start the active driving of a rotating motor may result in incorrect north pole and south pole identification, leading to large drive currents and overcurrent faults that may trip the drive.

[0013] Figure 1 An example electrical system with a motor drive power conversion system 100 is shown, which converts power to drive a motor load. In one example, the system 100 achieves intelligent capture restart by applying high frequency injection (HFI) when the motor shaft (e.g., rotor) speed is low, and then injecting a reference current (e.g., the torque-producing q-axis injection current IQREF, such as 10% of the rated inverter output current) into the motor to facilitate the identification of the shaft's response to motor acceleration or deceleration. The system 100 detects the response acceleration or deceleration, sets the electrical angle according to the corresponding south pole / north pole identification, and increases the drive output voltage and frequency in a ramp manner to match the CEMF of the rotating motor, and finally resumes or starts normal operation without causing current spikes or tripping the drive. This example capture restart device and technique can be used to start a rotating motor with minimal impact on the load or speed of various applications such as fan / pump systems and resume normal operation as soon as possible.

[0014] The motor drive power conversion system 100 receives single-phase or polyphase AC input power from an external power source 102. The example shown receives three-phase input. In other examples, single-phase or other polyphase implementations are possible. The motor drive 100 converts the input power from the power source 102 to deliver output power to drive the motor load 104. In one example, the motor load 104 is an interior permanent magnet (IPM) motor. The motor drive 100 includes a three-phase input filter circuit 120, such as an LC filter or an LCL filter. The motor drive 100 also includes a rectifier 130, a DC bus or DC link circuit 140, and an output inverter 150.

[0015] The rectifier 130 and the inverter 150 are operated by a controller 160. The controller 160 includes a processor 162, an electronic memory 164 or other non-transitory computer-readable medium storing data and program instructions, and a rectifier controller 132 and an inverter controller 152. The controller 160 and its components can be implemented as any suitable hardware, processor-executed software, processor-executed firmware, logic, and / or a combination thereof, where the illustrated controller 160 can be implemented as processor-executed software or firmware that provides various control functions by which the controller 160 receives feedback and / or input signals and / or values (e.g., set points), and provides a rectifier switch control signal 134 and an inverter switch control signal 154 to operate the switching devices S1 to S6 of the rectifier 130 and the switches S7 to S12 of the inverter 150 to convert the input power for providing AC output power to drive the IPM motor 104. Additionally, the controller 160 and its components 132, 152 can be implemented as a single processor-based device (e.g., a microprocessor, a microcontroller, an FPGA, etc.), or one or more of the controller 160 and its components 132, 152 can be separately implemented by two or more processor devices in a unified manner or in a distributed manner.

[0016] In one example, the motor drive 100 provides an active front end (AFE) including a switched rectifier (also known as a converter) 130 that receives three-phase power from a power supply 102 through a filter circuit 120. The active rectifier 130 includes rectifier switches S1 to S6, which can be insulated gate bipolar transistors (IGBTs) or other suitable forms of semiconductor-based switching devices capable of selectively conducting current when energized according to corresponding rectifier switch control signals 134. Additionally, diodes are connected across each of the IGBTs S1 to S6. In operation, the switching of the rectifier switches S1 to S6 is controlled according to the pulse-width modulated rectifier switch control signals 134 from a rectifier switch controller 132 to provide active rectification of the AC input power from the power supply 102, thereby providing a DC bus voltage Vdc across the DC bus capacitor C4 in the DC link circuit 140.

[0017] The inverter 150 includes switches S7 to S12 that are coupled to receive power from the DC bus 140 and provide AC output power to the IPM motor 104. The inverter switches S7 to S12 can be any suitable form of high-speed switching device, including but not limited to IGBTs that operate according to switch control signals 154 from an inverter switch control component 152 of a drive controller 160. The inverter 150 converts DC power into AC power to drive the IPM motor 104. Each of the inverter switch devices S7 to S12 selectively couples a corresponding AC node to a respective one of a first DC node and a second DC node of the DC bus circuit 140 according to a corresponding inverter switch control signal 154.

[0018] In some examples, the controller 160 receives various input signals or values, which include setpoint signals or values for a desired output operation (e.g., motor speed, position, torque, etc.) and feedback signals or values representing the operating values of various parts of the motor drive 100 and electrical system components of the drive 100. Additionally, in some examples, the controller 160 receives one or more voltage feedback signals or values and / or current feedback signals or values from sensors to indicate the DC bus voltage Vdc, line-to-line AC input voltage values, motor line-to-line voltage values, and / or current, etc. A memory 164 stores motor control program instructions 166 (e.g., speed control, torque control, etc.) and capture restart program instructions 168 stored in the memory 164.

[0019] Figure 2FIG. 200 is a flow chart of a method 200 for capture restart of an IPM motor 104 implemented by a controller 160, which is implemented, for example, by a processor 162 executing capture restart program instructions 168 stored in a memory 164. The motor drive power conversion system 100 is started, for example, by a user or by a system component (such as a thermostat that determines the need for fan cooling) at 202. In response to the start of the system 100, the controller 160 measures the motor speed of the IPM motor 104 at 204 and compares the motor speed with a threshold TH at 206. In one example, the threshold TH is a non-zero value that is 10% or less of the rated speed of the inverter 150, for example, approximately 5 Hz in one implementation. If the motor speed is greater than or equal to the threshold TH (at 206, "NO"), the method 200 proceeds to 224 and 226, and the controller 160 obtains the shaft position and speed by measuring the Cemf voltage at the inverter output, matches VHz at 224 to catch up with the electrical angle of the inverter output waveform and the rotor speed, and matches the inverter output voltage with the Cemf voltage. At 226, the controller 160 transfers to normal operation, for example, generating an inverter switch control signal 154 to implement open-loop pulse width modulation (PWM) control of the IPM motor speed.

[0020] In response to the motor speed being less than the threshold TH (at 206, "YES"), at 208, the controller 160 generates an inverter switch control signal 154 to perform high-frequency injection (HFI) to obtain the rotor angle of the IPM motor 104, for example, thereby generating a high-frequency inverter output voltage at a frequency above the normal operating frequency of the IPM motor (e.g., greater than twice the inverter output frequency at which the IPM motor 104 is driven at its rated maximum motor speed). At 210, the controller 160 determines the measured angle of the IPM motor 104. The advantage of HFI is that it generates an estimate of the rotor position at low speeds, but the value of the measured angle during HFI is twice the actual rotor angle of one pole (north or south) (e.g., 2*THETA).

[0021] To eliminate the ambiguity of the measured angle determined at 210, before adjusting the inverter electrical angle for VHz matching at 224 and normal operation at 226, the controller 160 uses the injected reference current to perform north / south pole identification to identify whether the actual rotor position is at THETA or at THETA + 180 degrees. At 212, the controller 160 supplies an injected current IQREF to the IPM motor 104. In one example, the controller 160 starts the injected current IQREF as a percentage of the inverter rated current (e.g., 5% or 10% of the rated current of the inverter 150).

[0022] At 214, during HFI, the controller 160 determines the acceleration or deceleration of the IPM motor 104 based on the measured angle (2*THETA) injected according to HFI (e.g., in response to the injected current IQREF). If not (No at 214), the controller increases the injected current IQREF at 216 (e.g., starting from an initial value of 5% of the rated inverter current) in response to not detecting acceleration or deceleration of the IPM motor 104 in response to the injected current IQREF. Once the controller 160 detects acceleration or deceleration of the IPM motor 104 in response to the injected current IQREF (e.g., Yes at 214), the controller 160 verifies whether the identified rotor pole is north or south based on the detected acceleration or deceleration of the IPM motor 104, and determines the electrical angle THETA as half of the measured angle (e.g., (2*THETA) / 2) or 180 degrees plus half of the measured angle (e.g., 180+(2*THETA) / 2).

[0023] At 218, the controller 160 determines whether the IPM motor 104 accelerates in response to the injected current IQREF based on the measured angle (2*THETA) injected according to HFI. In one example, at 218, the controller 160 verifies acceleration or deceleration by based on the change in the electrical angle based on the measured angle (2*THETA) injected according to HFI. If so (Yes at 218), then at 220, the controller 160 sets the electrical angle THETA to half of the measured angle 2*THETA / 2 in response to detecting acceleration of the IPM motor 104. Otherwise (e.g., detecting motor deceleration, No at 214), at 222, the controller 160 sets the electrical angle THETA to 180 degrees plus half of the measured angle in response to detecting deceleration of the IPM motor 104.

[0024] Before driving the IPM motor 104 to the reference frequency in the normal operation mode of the inverter 150 at 226, at 224, in response to determining the electrical angle THETA at 220 or 222, the controller 160 generates the inverter switch control signal 154 at 224 to match the voltage and frequency of the inverter 150 with the motor voltage and motor speed, respectively.

[0025] Figure 3 A graph 300 of signals in the system 100 in an example implementation of the capture restart method 200 performed by the controller 160 is shown. The graph 300 includes a curve 301, and the curve 301 shows the states of the state machine implemented by the controller 160 when executing the capture restart program instruction 168, where Figure 3Shows several example capture restart states labeled "State 1", "State 6", "State 4", and "State 5". Graph 300 also shows curve 302 of the electrical angle THETA and curve 303 of the actual rotor position. Figure 3 Curve 304 in [reference] shows a first implementation IqRef1 of the injected current IQREF, and curve 305 shows a second implementation IqRef2 of the injected current IQREF in another example. Figure 3 Curve 306 in [reference] shows an example inverter output phase current at the output of inverter 150 during the capture restart procedure. Graph 300 shows an example of curves 301, 302, 303, 304, 305, and 306 for drive system 100 using a 10 - pole IPM motor 104 rated at 400V, 40.7A, 250Hz, 3000rpm, and 29.5Kw. This example shows the capture restart when the rotor of IPM motor 104 rotates at 60rpm (e.g., 5Hz).

[0026] In capture restart state 1, controller 160 measures the rotor speed and position. In capture restart state 6, controller 160 sets the d - axis reference current IdRef and q - axis reference current IqRef used in motor control (e.g., Figure 1 motor control command 166 in [reference]) to zero during the first half period. Thereafter, controller 160 sets the q - axis reference current IQREF that generates torque to 10% of the rated current of inverter 150. In capture restart state 4, controller 160 adjusts the north / south pole based on the detected acceleration or deceleration of IPM motor 104 (e.g., as indicated by ThetaE not being adjusted due to acceleration in graph 300). In capture restart state 5, controller 160 completes the capture restart. In this example, controller 160 applies HFI from the start of state 6, and HFI continues until normal operation. In this example, controller 160 keeps IdRef1 at zero. In one example, controller 160 controls IqRef1 to rise from zero to 10% of the motor - related current in the middle of state 6 and sets IqRef1 back to zero at the end of state 6. In another implementation, controller 160 raises IqRef2 to 10% in the middle of state 6, then if no acceleration or deceleration is detected, increases IqRef2 in a ramp (e.g., at Figure 2 216 in [reference]), and finally reduces IqRef2 to zero in response to the detected acceleration or deceleration.

[0027] Figure 4A graph 400 is shown to illustrate another example where the controller 160 detects rotor deceleration. The graph 400 includes the curves 301, 302, 303, 304, 305, and 306 as described above for the example drive system 100 using a 10 - pole IPM motor 104 rated at 400V, 40.7A, 250Hz, 3000rpm, and 29.5Kw. This example shows a capture restart when the rotor of the IPM motor 104 rotates again at 60rpm (e.g., 5Hz). In capture state 6, the controller 160 sets IdRef and IqRef to 0 for the first half period and then sets IDQREF to 10% of the torque current. In capture restart state 4, the controller 160 adjusts the N / S poles due to the detected deceleration (e.g., sets THETA to half of the measured angle + 180 degrees). In capture restart state 5, the controller 160 completes the capture restart.

[0028] Figure 5 A graph 500 is shown having the above - mentioned curves 301, 302, 303, 304, 305, and 306 for the example drive system 100 using a 10 - pole IPM motor 104 rated at 400V, 40.7A, 250Hz, 3000rpm, and 29.5Kw. In this example, the rotor initially rotates in the opposite direction at - 60rpm. In capture restart state 1, the controller 160 measures the rotor speed. In capture restart state 6, the controller 160 sets IdRef and IqRef to 0 for the first half period and then sets IQREF to 10% of the torque current. In capture restart state 4, the controller 160 adjusts the N / S poles due to the detected deceleration (e.g., sets THETA to half of the measured angle + 180 degrees). In capture restart state 5, the controller 160 completes the capture restart.

[0029] Various embodiments have been described with reference to the accompanying drawings. Modifications and changes can be made thereto without departing from the broader scope of the invention as set forth in the appended claims, and additional embodiments can be implemented. Accordingly, the specification and drawings are to be regarded as illustrative rather than restrictive. The above examples merely illustrate several possible embodiments of the various aspects of the present disclosure, where equivalent changes and / or modifications will occur to those skilled in the art upon reading and understanding the specification and drawings. Additionally, while a particular feature of the present disclosure may be disclosed with respect to only one of several implementations, such a feature can be combined with one or more other features in one or more other implementations, which may be desirable and advantageous for any given or particular application. Further, insofar as the terms "comprising", "including", "having", "has", "with", or variants thereof are used in the detailed description and / or the claims, such terms are intended to be inclusive in a manner similar to the term "including".

Claims

1. A power conversion system, comprising: An inverter configured to convert DC power into AC power to drive an interior permanent magnet (IPM) motor, the inverter including inverter switching devices each configured to selectively couple a respective AC node to a respective one of a first DC node and a second DC node in accordance with a respective inverter switch control signal; A controller configured to: Measure a motor speed of the IPM motor in response to startup of the power conversion system; Generate the inverter switch control signal to perform high frequency injection (HFI) in response to the motor speed being less than a threshold; Determine a measured angle of the IPM motor during the HFI; Generate the inverter switch control signal to provide an injection current to the IPM motor during the HFI; Detect acceleration or deceleration of the IPM motor in response to the injection current; Based on the detected acceleration or deceleration of the IPM motor, selectively determine an electrical angle to be half of the measured angle or 180 degrees plus half of the measured angle; And Generate the inverter switch control signal to drive the IPM motor to a reference frequency in a normal operation mode of the inverter in response to determining the electrical angle, wherein the controller is further configured to: Generate the inverter switch control signal to match the voltage and frequency of the inverter with the motor voltage and the motor speed, respectively, before driving the IPM motor at the reference frequency in the normal operation mode of the inverter in response to determining the electrical angle.

2. The power conversion system according to claim 1, wherein, The controller is configured to: Set the electrical angle to be half of the measured angle in response to detecting acceleration of the IPM motor; and Set the electrical angle to 180 degrees plus half of the measured angle in response to detecting deceleration of the IPM motor.

3. The power conversion system according to claim 2, wherein, The threshold is 10% or less of the rated speed of the inverter.

4. The power conversion system according to claim 2, wherein, The controller is configured to: Increase the injection current in response to not detecting acceleration or deceleration of the IPM motor in response to the injection current.

5. The power conversion system according to claim 1, wherein, The threshold is 10% or less of the rated speed of the inverter.

6. The power conversion system according to claim 1, wherein, The controller is configured to: Increase the injection current in response to not detecting acceleration or deceleration of the IPM motor in response to the injection current.

7. A control method for a power conversion system, comprising: Measure a motor speed of the IPM motor in response to startup of the power conversion system; Generate the inverter switch control signal to perform high frequency injection (HFI) in response to the motor speed being less than a threshold; Determine a measured angle of the IPM motor during the HFI; Generate the inverter switch control signal to provide an injection current to the IPM motor during the HFI; Detect acceleration or deceleration of the IPM motor in response to the injection current; Based on the detected acceleration or deceleration of the IPM motor, selectively determine an electrical angle to be half of the measured angle or 180 degrees plus half of the measured angle; And Generate the inverter switch control signal to drive the IPM motor at a reference frequency in a normal operation mode of the inverter in response to determining the electrical angle, Wherein, the method further includes: In response to determining the electrical angle, generating the inverter switch control signal to match the voltage and frequency of the inverter with the motor voltage and the motor speed respectively before driving the IPM motor at the reference frequency in the normal operation mode of the inverter.

8. The method according to claim 7, further comprising: In response to detecting an acceleration of the IPM motor, setting the electrical angle to half of the measured angle; And In response to detecting a deceleration of the IPM motor, setting the electrical angle to 180 degrees plus half of the measured angle.

9. The method according to claim 8, wherein, The threshold is 10% or less of the rated speed of the inverter.

10. The method according to claim 8, further comprising: In response to not detecting an acceleration or deceleration of the IPM motor in response to the injected current, increasing the injected current.

11. The method according to claim 7, wherein, The threshold is 10% or less of the rated speed of the inverter.

12. The method according to claim 7, further comprising: In response to not detecting an acceleration or deceleration of the IPM motor in response to the injected current, increasing the injected current.

13. A non-transitory computer-readable medium having computer-executable instructions that, when executed by a processor, cause the processor to perform the following operations: Measure the motor speed of the IPM motor in response to the startup of the power conversion system; In response to the motor speed being less than the threshold, generating an inverter switch control signal to perform high-frequency injection (HFI); During the HFI, determining the measured angle of the IPM motor; During the HFI, generating the inverter switch control signal to provide an injected current to the IPM motor; Detecting an acceleration or deceleration of the IPM motor in response to the injected current; Based on the detected acceleration or deceleration of the IPM motor, selectively determining the electrical angle as half of the measured angle or as 180 degrees plus half of the measured angle; And In response to determining the electrical angle, generating the inverter switch control signal to drive the IPM motor to the reference frequency in the normal operation mode of the inverter, Wherein, the computer-executable instructions further cause the processor to perform the following operations: In response to determining the electrical angle, generating the inverter switch control signal to match the voltage and frequency of the inverter with the motor voltage and the motor speed respectively before driving the IPM motor at the reference frequency in the normal operation mode of the inverter.

14. The non-transitory computer-readable medium according to claim 13, having computer-executable instructions that, when executed by the processor, cause the processor to perform the following operations: Set the electrical angle to half of the measured angle in response to detecting acceleration of the IPM motor; and Set the electrical angle to 180 degrees plus half of the measured angle in response to detecting deceleration of the IPM motor.

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