Electromagnetic Interference (EMI) Mitigation in Pulse Width Modulation (PWM) Inverters Using Learning-Based Frequency Modulated Carrier

Abstract

A controller is provided for generating a carrier signal to control a pulse-width modulation (PWM) inverter that drives an electric actuator. The controller includes an interface configured to connect to a victim circuit via a sensor, the victim circuit including an electric power system or an electric actuator, or a combination of an electric power system and an electric actuator. The sensor is configured to measure an electromagnetic interference (EMI) spectrum. The controller further includes a memory configured to store a modulation frequency range, measured electromagnetic interference (EMI) spectrum data of various frequency carriers, a desired EMI spectrum, and a learning-based carrier design program. The processor, together with the memory, is configured to execute generating a frequency modulated (FM) carrier signal by solving an optimization problem generated by the learning-based carrier design program with respect to a sweep time for a predetermined frequency. A PWM generator configured to generate a PWM signal based on the FM carrier signal.

Description

[Technical Field]

[0001] The present invention relates to electromagnetic interference (EMI) mitigation in pulse width modulation (PWM) inverters, and more particularly to reshaping the EMI spectrum of a PWM inverter by using learning methods to design a frequency modulated carrier. [Background technology]

[0002] Pulse-width modulation (PWM) inverters are widely used in modern motor drive systems due to their high efficiency and wide adjustable output frequency range. However, switching devices have large dv / dt and di / dt during their operation, which can cause serious electromagnetic interference (EMI) problems, such as violating EMC regulations, interfering with other nearby equipment, or even causing the system itself to malfunction. With the development of high-power density, high-voltage, and high-switching-frequency semiconductor devices, such as wide-bandgap devices (WBGs), there is a growing need and interest in mitigating EMI in power electronics devices to meet the rapidly growing markets of electric vehicles, electric aircraft, and renewable energy.

[0003] To reduce the EMI level in power electronics equipment, various methods have been researched and verified in the power electronics community, including soft switching, EMI filters (both passive and active), and circuit layout design, etc. All of these techniques aim to reduce the time-domain magnitude of EMI, and as a result, also reduce the overall EMI spectrum level.

[0004] In recent years, frequency modulation (FM)-based methods have attracted much attention for reducing the EMI spectrum level of PWM inverters. PWM drive signals are typically generated by comparing a reference signal at a desired drive frequency with a periodic carrier signal, such as a sinusoidal or triangular signal. Research has shown that the EMI spectrum of PWM inverters contains strong harmonic components of the carrier frequency, which contribute to a large number of frequency components exceeding EMC regulations. Therefore, it is useful to modulate the frequency of the carrier signal so that the harmonic energy can be spread over a relatively wide frequency range. While using an FM carrier signal does not reduce the overall EMI energy, it has proven effective in reducing the harmonic peaks of the EMI frequency spectrum to meet EMC regulations.

[0005] Following this concept of frequency modulation, many frequency modulation methods have been proposed to reduce the EMI level of PWM inverters. For example, random FM methods have been proposed to randomize switching times so that carrier harmonic energy is spread within a corresponding frequency range, resulting in a lower EMI spectrum level. However, due to its random nature, random carrier FM works well statistically, but is relatively difficult to implement in hardware. Recently, sinusoidal frequency modulation methods have been proposed, in which the frequency of the carrier signal varies within a range following a sinusoidal pattern. A more general frequency modulation method can be found in U.S. Patent No. 1,125,8357, which proposes an adaptive frequency modulation method to reduce received carrier harmonic EMI by taking into account EMI propagation characteristics. This adaptive frequency modulation method mainly focuses on the first harmonic, which is on the order of several hundred kilohertz, or only a small portion of the conducted EMI frequency band (150 kHz to 30 MHz). Therefore, there is a need to develop controllers and signal processors to reduce EMI levels in power electronics equipment across the entire EMI frequency band (150 kHz to 30 MHz). Summary of the Invention

[0006] The present disclosure provides a novel controller and signal processor for generating a carrier signal that controls a pulse width modulated (PWM) inverter that drives an electric actuator.

[0007] Some embodiments of the present disclosure are based on the recognition that a learning-based method can provide a customized FM carrier signal for generating a PWM drive signal to achieve a desired EMI spectral envelope. Given EMI spectrum data for a PWM inverter, or a type of PWM inverter operating with various periodic carrier signals at various frequencies, the carrier design problem is formulated as a constrained optimization problem, where an objective function is formed according to the desired EMI spectrum and constraints are imposed on the weights of various frequency components so that the total EMI energy remains unchanged. Once the weights are determined, we design an FM carrier signal whose frequency modulation time is proportional to the corresponding weight. The expected EMI spectrum is expressed as a linear combination of the EMI spectra according to the various weighted periodic carrier signals corresponding to the various frequencies. Compared to other empirical frequency-modulated carrier designs, our method is more customized and optimized for various devices. Simulation and experimental results demonstrate that the desired spectral envelope can be achieved using the designed FM carrier.

[0008] According to some embodiments of the present disclosure, a controller for generating a carrier signal to control a pulse-width modulation (PWM) inverter that drives an electric actuator is provided, the controller including an interface configured to connect to a victim circuit via a sensor, the victim circuit including an electric power system or an electric actuator, or a combination of an electric power system and an electric actuator, the sensor configured to measure an electromagnetic interference (EMI) spectrum, the controller further including: a memory configured to store a modulation frequency range, measured electromagnetic interference (EMI) spectrum data of various frequency carriers, a desired EMI spectrum, and a learning-based carrier design program; a processor configured to execute, in conjunction with the memory, generating a frequency modulated (FM) carrier signal by solving an optimization problem generated by the learning-based carrier design program with respect to a sweep time for a predetermined frequency; and a PWM generator configured to generate a PWM signal based on the FM carrier signal.

[0009] Some embodiments of the present disclosure further recognize that a signal processor is provided for generating modulation parameters used by a pulse-width modulation (PWM) modulator that generates a carrier signal to control an inverter that drives an electric actuator, the signal processor comprising: an interface configured to connect to the PWM modulator and a sensor configured to measure an electromagnetic interference (EMI) spectrum; a memory configured to store a modulation frequency range, measured electromagnetic interference (EMI) spectrum data for various frequency carriers, a desired EMI spectrum, and a learning-based carrier design program; and a processor configured, together with the memory, to: generate a frequency modulated (FM) carrier signal by solving an optimization problem generated by the learning-based carrier design program with respect to a sweep time for a predetermined frequency; and transmit the generated FM carrier signal to a signal modulator configured to generate a PWM signal based on the generated FM carrier signal. [Brief explanation of the drawings]

[0010] Embodiments of the present disclosure are further described hereinafter with reference to the accompanying drawings, in which the drawings are not necessarily to scale, emphasis generally being placed upon illustrating the principles of embodiments of the present disclosure.

[0011] [Figure 1] FIG. 1 is a schematic diagram illustrating a PWM inverter drive system according to some embodiments of the present disclosure. [Figure 2] FIG. 1 is a schematic diagram illustrating a PWM inverter drive system using a learning-based frequency modulated carrier, in accordance with some embodiments of the present disclosure. [Figure 3] 1 is a flowchart illustrating a learning-based frequency modulation carrier design method according to some embodiments of the present disclosure. [Figure 4] 1A and 1B show EMI spectrum data maps of A and B using periodic triangular wave carriers at various frequencies from 50 kHz to 150 kHz with a step size of 1 kHz, in accordance with some embodiments of the present disclosure. [Figure 5] 1A-1C illustrate various frequency modulation functions of a carrier signal using various existing methods and a learning-based design method in accordance with some embodiments of the present disclosure. [Figure 6A] 1A-1C illustrate EMI spectra using a periodic carrier signal, a random FM carrier, a linear FM carrier, an adaptive FM carrier, and a learning-based carrier, respectively, using the proposed method, in accordance with some embodiments of the present disclosure. [Figure 6B] 1A-1C illustrate EMI spectra using a periodic carrier signal, a random FM carrier, a linear FM carrier, an adaptive FM carrier, and a learning-based carrier, respectively, using the proposed method, in accordance with some embodiments of the present disclosure. [Figure 6C] 1A-1C illustrate EMI spectra using a periodic carrier signal, a random FM carrier, a linear FM carrier, an adaptive FM carrier, and a learning-based carrier, respectively, using the proposed method, in accordance with some embodiments of the present disclosure. [Figure 6D] 1A-1C illustrate EMI spectra using a periodic carrier signal, a random FM carrier, a linear FM carrier, an adaptive FM carrier, and a learning-based carrier, respectively, using the proposed method, in accordance with some embodiments of the present disclosure. [Figure 6E] 1A-1C illustrate EMI spectra using a periodic carrier signal, a random FM carrier, a linear FM carrier, an adaptive FM carrier, and a learning-based carrier, respectively, using the proposed method, in accordance with some embodiments of the present disclosure. [Figure 7A] FIG. 10 illustrates exemplary results of minimizing overall conducted EMI levels using a learning-based carrier (#2), in accordance with some embodiments of the present disclosure. [Figure 7B] 10A-10C illustrate exemplary results of minimizing EMI levels in various frequency ranges in accordance with EMC regulations, according to some embodiments of the present disclosure. [Figure 8] 10A-10C illustrate exemplary results of aggregating EMI levels over various frequency ranges, in accordance with some embodiments of the present disclosure. [Figure 9] FIG. 2 is a schematic diagram illustrating an example configuration of a controller for generating a carrier signal that controls an inverter that drives an electric actuator, according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following description provides exemplary embodiments only and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the following description of exemplary embodiments will provide those skilled in the art with an enabling description for implementing one or more exemplary embodiments. Various changes are contemplated that may be made in the function and arrangement of elements without departing from the spirit and scope of the disclosed subject matter as set forth in the appended claims.

[0013] In the following description, specific details are provided to provide a thorough understanding of the embodiments. However, those skilled in the art will understand that the embodiments may be practiced without these specific details. For example, systems, processes, and other elements in the disclosed subject matter may be shown as components in block diagram form in order to avoid obscuring the embodiments in unnecessary detail. In other instances, well-known processes, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. Furthermore, like reference numbers and names in the various drawings indicate like elements.

[0014] Also, particular embodiments may be described as a process that is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. While a flowchart may describe operations as a sequential process, many of the operations can be performed in parallel or simultaneously. Additionally, the order of operations may be rearranged. A process may terminate when its operations are completed, but may include additional steps not described or included in the diagram. Moreover, not all operations in any specifically described process may be performed in all embodiments. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, the end of the function may correspond to a return of the function to the calling function or the main function.

[0015] Furthermore, embodiments of the disclosed subject matter may be implemented, at least in part, either manually or automatically. Manual or automatic implementations may be performed or at least assisted by the use of machines, hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, program code or code segments to perform the necessary tasks may be stored on a machine-readable medium. A processor may perform the necessary tasks.

[0016] In a PWM inverter, the PWM control signal is generated by comparing a sinusoidal reference signal of the desired frequency with a high frequency carrier signal, such as a sine wave or a triangular wave, to generate a train of rectangular pulses of varying widths that control the operation of the switching devices. The reference signal frequency, which is also the desired frequency of the inverter output, is called f r In the following part, we will analyze various carrier signals from the EMI point of view, ignoring other side effects such as total harmonic distortion, heat loss, vibration, etc.

[0017] 1 shows a schematic diagram illustrating a PWM inverter drive system 100 according to some embodiments of the present disclosure. The PWM inverter drive system 100 includes a power supply / EMI victim 110, a PWM converter / EMI source 120, a controller 130, and a load 140. The controller 130 obtains one or more sensor information of position, speed, and motor current using one or more sensors, and uses the information to control a modulated signal frequency to a desired operating frequency 132, which is compared with a carrier signal 133 a at a given carrier frequency 150 to generate a PWM signal(s) 134 to control the switching operation of the PWM inverter. Periodic Carrier

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[0019] FIG. 2 is a schematic diagram illustrating a PWM inverter drive system 200 using a learning-based frequency-modulated carrier, according to some embodiments of the present disclosure. The PWM inverter drive system 100 includes a power supply / EMI victim 110, a PWM converter / EMI source 120, a controller 130, and a load (victim circuit) 140. The controller 130 acquires position, speed, and motor current information from one or more sensors and controls the modulation signal frequency 132 using the information. An EMI spectrum 210 generated by the PWM inverter / EMI source 120 using a carrier signal 133a of various frequencies within a carrier frequency range 150b is measured as a training data set. Given EMI regulations for the EMI spectrum 220, a learning-based FM carrier design program (algorithm) 230 is executed to generate / design a frequency-modulated carrier signal 133b. A PWM generator 134 compares the modulation signal 132 with the frequency-modulated carrier signal 133b to generate a PWM signal. The PWM generator 134 is configured to control the switching operation of the PWM inverter with the generated PWM signal.

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[0027] From Section II, we see that the performance of EMI mitigation using various FM carriers depends on the frequency modulation method. The sweep time of each carrier frequency determines the contribution of the corresponding EMI spectrum to the overall EMI spectrum. The longer the frequency sweep time, the greater the partial weight of the same frequency carrier to the EMI spectrum. Since different devices have different EMI propagation characteristics, it is desirable to optimize the FM carrier so that the overall EMI spectrum can meet EMC regulations with the maximum margin, in other words, achieve the lowest possible EMI level according to EMC limits.

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[0029] Figure 4 shows the EMI spectrum data map for A using periodic triangular carriers at different frequencies from 50 kHz to 150 kHz with a step size of 1 kHz. Each column represents the EMI spectrum using the corresponding frequency carrier, and different gray levels represent different magnitudes in dB scale, as shown in the grayscale bar on the right.

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[0035] 5 illustrates various frequency modulation functions of a carrier signal using various existing methods and learning-based design methods according to some embodiments of the present disclosure. For linear frequency modulation (FM), the modulation function is a straight line, meaning that the carrier frequency increases linearly over time from the minimum carrier frequency to the maximum carrier frequency for each sweep duration. For random FM, the modulation function is an irregular curve, indicating that the carrier frequency increases in random steps from the minimum carrier frequency to the maximum carrier frequency. For adaptive FM and learning-based FM, the frequency adaptively increases over time, or the frequency follows a pattern learned from the measured EMI spectrum, so that the EMI spectrum can achieve a desired level.

[0036] Figures 6A-6E show the EMI spectra using the proposed method with a periodic carrier signal, a random FM carrier, a linear FM carrier, an adaptive FM carrier, and a learning-based carrier, respectively. In Figure 6A, we r = 200Hz and f cAn example plot of the PWM frequency spectrum using = 50 kHz is shown. We can observe that the EMI spectrum contains strong harmonics of the carrier frequency, especially the first harmonic.

[0037] For the random FM carrier, adaptive FM carrier, and learning-based carrier, a sweeping frequency range of [50, 150] kHz is considered. While the random carrier frequency modulation in Figure 6B significantly reduces the EMI level by approximately 10 dB overall compared to the periodic triangular wave carrier in Figure 6A, the first harmonic level from 50 kHz to 150 kHz is not sufficiently suppressed. When a linear frequency modulation carrier is employed (Figure 6C), the first harmonic and conducted EMI are further reduced by approximately 2.5 dB, but the results are not flat. In Figure 6D, when an adaptive FM carrier based on the first harmonic is employed, the first harmonic is reduced by another 2.3 dB. However, the maximum conducted EMI level simultaneously increases. In the case of our learning-based carrier (#1) (Figure 6E), which aims to reduce the first harmonic, the first harmonic level is reduced to a minimum level of 68.78 dB, the lowest among the various carriers.

[0038] Figure 7A plots an example result of minimizing the total conducted EMI level using the learning-based carrier (#2). The overall level of the combined EMI is reduced to 76.8 dB, which is also the lowest among the various FM carrier levels.

[0039] FIG. 7B plots exemplary results of minimizing EMI levels for various frequency ranges according to EMC regulations, where the upper dashed line represents the EMC regulations and the lower dash-dot lines represent the maximum levels for a particular frequency range for different conducted EMI frequency ranges of [10 kHz, 1 MHz] and [1 MHz, 30 MHz], respectively.

[0040] Figure 8 plots exemplary results summarizing EMI levels in various frequency ranges, where the frequency range [50 kHz, 150 kHz] corresponds to the first harmonic and [10 kHz to 30 MHz] corresponds to conducted EMI.

[0041] 9 is a schematic diagram illustrating an example configuration of a controller 900 for generating a carrier signal to control an inverter that drives an electric actuator, according to some embodiments of the present disclosure. The controller 900 is configured to generate a PWM signal to control the inverter circuit 120 that drives the electric actuator 140 (or motor). The controller 900 includes a carrier frequency modulation unit (circuit module) 133b and a PWM signal generator 134. The carrier frequency modulation unit 133b is configured to execute a process 910 including steps for generating a frequency-modulated carrier signal. The carrier frequency modulation unit 133b includes an interface (interface controller) 920 configured to connect to a sensor 131 connected to the inverter circuit 120 to measure EMI spectrum data A210 (measured electromagnetic interference (EMI) spectrum 210) using the sensor 131, a processor 910, and a memory unit 930. The memory unit 930 is configured to store the measured electromagnetic interference (EMI) spectrum 210, the carrier frequency range 150b, and a desired EMI spectrum 220b according to the EMC regulation 220. Here, the desired EMI spectrum 220b may be lower than the allowable EMI level according to the EMC regulation 220 by a constant. The processor 910 is configured to perform calculation of a PWM reference signal. The carrier frequency modulation unit 940 is configured to calculate a sweep time of each discrete frequency in each sweep period using the learned weights according to 231, and modulate the carrier frequency based on the sweep time of each frequency. The controller 900 further includes a PWM signal generator 134 configured to generate a PWM signal based on the frequency-modulated carrier signal and the reference signal. The PWM signal generator 134 can send the PWM signal to the inverter circuit 120.

[0042] In some cases, the measured EMI spectrum 210 is obtained based on a linear frequency modulated (LFM) carrier, where the frequency modulation may be performed by a periodic sawtooth signal. Furthermore, the modulation frequency may be performed as a function of EMC regulations. The measured EMI spectrum 210 may be obtained from the frequency response of the victim circuit using a LISN when a linear frequency modulated carrier signal is used to generate the PWM signal for the inverter circuit 120.

[0043] In another embodiment, processor 910 may be a signal processor 910 that may be configured to generate modulation parameters used by PWM signal generator 134 to generate a PWM signal that controls inverter circuit 120, which drives electric actuator 140. Signal processor 910 is connected to an interface 920 that is configured to connect a memory unit 930 configured to store measured electromagnetic interference (EMI) spectrum 210 and desired EMI spectrum 220b to PWM signal generator 134. In this case, signal processor 910 is configured to calculate weights associated with sweep frequency durations across a frequency range, the weights being determined by EMC regulations of victim circuit 1000, which includes at least power system 110, or at least electric actuator 140, or a combination of power system 110 and electric actuator 140. Furthermore, signal processor 910 is configured to calculate the sweep time of each frequency in each sweep period according to the weights. The signal processor 910 is configured to modulate the frequency of the carrier signal according to the sweep time of each frequency to generate a frequency-modulated carrier wave, and transmit the frequency-modulated carrier wave to the PWM signal generator 134. After receiving the frequency-modulated carrier wave, the PWM signal generator 134 generates a PWM signal based on the frequency-modulated carrier wave and the reference signal of the signal processor 910, and transmits the PWM signal to the inverter circuit 120 so that the EMI level for the victim circuit 1000 satisfies the EMC regulations.

[0044] The above-described embodiments of the present invention can be implemented in any of numerous ways. For example, these embodiments may be implemented using hardware, software, or a combination thereof. If implemented in software, the software code may be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers. Such a processor may be implemented as an integrated circuit, with one or more processors in an integrated circuit component. However, a processor may be implemented using circuitry in any suitable format.

[0045] Also, embodiments of the invention may be embodied as methods, examples of which are provided. Acts performed as part of a method may be ordered in any suitable manner. Thus, while exemplary embodiments are shown as sequential operations, embodiments may be constructed in which operations are performed in a different order than shown and may include performing some operations simultaneously.

[0046] The use of ordinal terms such as "first," "second," etc. in the claims to modify claim elements does not, by itself, imply any priority, precedence, or order of the elements of one claim relative to elements of another claim, or any chronological order in which method actions are performed, but is merely used as a label to distinguish one claim element having a certain name from another element having the same name (except when ordinal terms are used) to distinguish between claim elements.

[0047] Although the invention has been described by way of examples of preferred embodiments, it is to be understood that various other adaptations and modifications can be made within the spirit and scope of the disclosure.

[0048] Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.

Claims

1. a controller for generating a carrier signal that controls a pulse width modulated (PWM) inverter that drives an electric actuator, an interface configured to connect to a victim circuit via a sensor, the victim circuit including an electrical power system or an electrical actuator, or a combination of the electrical power system and the electrical actuator, the sensor configured to measure an electromagnetic interference (EMI) spectrum, and the controller further comprising: a memory configured to store a modulation frequency range, a measured electromagnetic interference (EMI) spectrum, a desired EMI spectrum, and a learning-based carrier design program; a processor, the processor, together with the memory, The controller is configured to generate a frequency modulated (FM) carrier signal by solving an optimization problem generated by the learning-based carrier design program regarding a sweep time for a predetermined frequency, and the controller further comprises: A controller comprising a PWM generator configured to generate a PWM signal based on the FM carrier signal.

2. The controller of claim 1 , wherein the PWM generator modulates the frequency of a carrier signal based on a sweep time learned from EMI spectrum data.

3. The controller of claim 1 , wherein the PWM generator monotonically increases the carrier frequency based on a learned frequency modulated carrier.

4. The controller of claim 1 , wherein the PWM generator monotonically decreases the carrier frequency of the PWM signal based on a learned frequency modulated carrier.

5. 2. The controller of claim 1, wherein the FM carrier signal is a sawtooth carrier.

6. The controller of claim 1 , wherein the PWM generator modulates the FM carrier signal as a function of EMC regulations.

7. The controller of claim 1 , wherein the measured EMI spectrum is obtained from the frequency response of the victim circuit using learned frequency modulation.

8. The controller of claim 1 , wherein the victim circuit is an electrical power system or an electrical actuator.

9. 8. The controller of claim 7, wherein the learned frequency modulation is performed by a linearly modulated sine wave or a triangular wave.

10. The controller of claim 1 , wherein the PWM inverter operates with at least three phases.

11. The controller of claim 1 , wherein the PWM inverter is connected to an electric actuator, and the PWM signal is transmitted to the inverter through the interface.

12. a signal processor for generating modulation parameters used by a pulse width modulation (PWM) modulator that generates a carrier signal that controls an inverter that drives an electric actuator, an interface configured to connect to a PWM modulator and a sensor configured to measure an electromagnetic interference (EMI) spectrum; a memory configured to store a modulation frequency range, measured electromagnetic interference (EMI) spectrum data of various frequency carriers, a desired EMI spectrum, and a learning-based carrier design program; a processor, the processor, together with the memory, generating a frequency modulated (FM) carrier signal by solving an optimization problem generated by the learning-based carrier design program with respect to sweep time for a predetermined frequency; transmitting the generated FM carrier signal to a signal modulator configured to generate a PWM signal based on the generated FM carrier signal.

13. 13. The signal processor of claim 12, wherein the PWM modulator modulates the frequency of the carrier signal based on a sweep time learned from EMI spectrum data.

14. 13. The signal processor of claim 12, wherein the PWM modulator monotonically increases the carrier frequency based on a learned frequency modulated carrier.

15. 13. The signal processor of claim 12, wherein the PWM modulator monotonically decreases the carrier frequency of the PWM signal based on a learned frequency modulated carrier.

16. 13. The signal processor of claim 12, wherein the generated FM carrier signal is a sawtooth carrier.

17. 13. The signal processor of claim 12, wherein the PWM modulator modulates the FM carrier signal as a function of EMC regulations.

18. 13. The signal processor of claim 12, wherein the measured EMI spectrum is obtained from the frequency response of the victim circuit using learned frequency modulation.

19. 20. The signal processor of claim 18, wherein the victim circuit is an electrical power system or an electrical actuator.

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