Modulation unit of motor simulator with common DC bus structure and its application

Abstract

The present application provides a modulation unit of a motor simulator with a common DC bus structure and its application, wherein the modulation unit includes a common-mode voltage calculation module for calculating in real time the common-mode voltage output by the motor controller and the motor simulator; a DC component tracking module for tracking the DC component of the zero-sequence circulating current existing in the motor drag test platform; a zero-sequence component calculation module for tracking the low-frequency component of the zero-sequence circulating current, and generating a real-time changing zero-sequence component based on the DC component and the low-frequency component; a modulation algorithm generation module for injecting the real-time changing zero-sequence component into the modulation wave generated by the sinusoidal pulse width modulation algorithm to obtain the actual switching signal for controlling each branch of the motor simulator. The modulation unit provided in the present application can generate in real time a compensation term for injecting SPWM to suppress the circulating current, and has the advantages of low structural complexity, low cost and low current harmonic content.

Description

Technical Field

[0001] The present application belongs to the technical field of electric drive control for electric vehicles, and specifically provides a common DC bus structure motor simulator modulation unit and the application of the modulation unit. Background Art

[0002] The automotive motor-to-motor test platform with a common DC bus structure uses a single power supply to simultaneously power the motor controller (Motor Control Unit, MCU) and the motor simulator (Electric Machine Emulator, EME), which can reduce the number of power supplies in the power-level hardware-in-the-loop simulation system, simplify the complexity of the system, reduce the system cost, and is conducive to large-scale industrial applications.

[0003] However, the use of a common DC bus structure will form a zero-sequence conductive path with extremely low impedance in the test platform system. The zero-sequence current generated by it will act as a disturbance to the motor controller under test, introduce additional load to the switch of the power device, increase system loss, and reduce system life. In addition, the existence of zero-sequence current will deteriorate the sinusoidality of the system's three-phase current, making it difficult to output high-quality current waveforms, affecting the system test accuracy.

[0004] Most existing circulating current suppression solutions require modifications to the motor controller algorithm, or use hardware common-mode inductor structures to increase system complexity, which is inconsistent with the actual application scenarios of motor simulators. Summary of the invention

[0005] The purpose of the present application is to provide a novel common DC bus structure motor simulator modulation unit, which is used to modulate and control the motor simulator in a common DC bus structure motor pair test platform, and can effectively suppress the zero-sequence circulating current existing in the test platform. The modulation unit includes:

[0006] A common mode voltage calculation module, used for calculating in real time the common mode voltage output by the motor controller and the motor simulator, wherein the motor controller and the motor simulator are powered by a single power supply and connected via a coupling network;

[0007] A DC component tracking module is used to track the DC component of the zero-sequence circulating current in the motor drag test platform;

[0008] A zero-sequence component calculation module, used for tracking the low-frequency component of the zero-sequence circulating current, and generating a real-time changing zero-sequence component based on the DC component and the low-frequency component;

[0009] The modulation algorithm generation module is used to inject the real-time changing zero-sequence component into the modulation wave generated by the sinusoidal pulse width modulation algorithm to obtain the actual switching signal of each branch of the control motor simulator.

[0010] Furthermore, the control model of the motor-to-motor test platform with a common DC bus structure includes a motor controller, a motor simulator, a coupling network and a single power supply; the inverters of the motor controller and the motor simulator are both three-phase two-level topology structures; the coupling network includes a three-phase inductor connected to the three-phase line between the motor controller and the motor simulator; the single power supply simultaneously supplies power to the motor controller and the motor simulator through a common DC bus structure.

[0011] Furthermore, the DC component tracking module tracks the DC component of the zero-sequence circulating current based on PI control and generates a DC component compensation term

[0012] Furthermore, the zero-sequence component calculation module tracks the low-frequency component of the zero-sequence circulating current based on the following formula, and generates a zero-sequence component that changes in real time based on the DC component and the low-frequency component:

[0013]

[0014] in, is the zero-sequence component that changes in real time, T s is the switching cycle of the power device, V tp is the triangular carrier amplitude, U dc is the output voltage of a single power supply, U min , U max are the minimum phase voltage and the maximum phase voltage respectively, e is the common mode voltage modulation factor, e1 is the compensation term for eliminating the low frequency component of the zero sequence circulating current, is a compensation term for eliminating the DC component in the zero-sequence circulating current, are the action time of the two non-zero voltage vectors of the motor controller, are the action times of the two non-zero voltage vectors of the motor simulator.

[0015] Preferably, the motor controller is modulated by a space vector pulse width modulation algorithm, which synthesizes the target voltage through two zero vectors and six non-zero voltage vectors with the same amplitude and equally spaced within a period, and the modulation wave generated by the space vector pulse width modulation algorithm has a saddle waveform.

[0016] Furthermore, the ratio of the amplitude of the third harmonic component in the low-frequency component to the amplitude of the phase current fundamental wave is greater than 18%.

[0017] Preferably, the common DC bus structure motor simulator modulation unit further includes a high-frequency component suppression module for suppressing high-frequency components in the zero-sequence circulating current.

[0018] Preferably, when the carrier modulating the motor controller and the carrier modulating the motor simulator have a non-time-varying phase difference, the high-frequency component suppression module suppresses the high-frequency component in the zero-sequence circulating current by synchronizing the carrier modulating the motor controller and the carrier modulating the motor simulator.

[0019] The present application also provides a motor-drag test platform, including a motor controller, a motor simulator, a coupling network and a single power supply. The motor controller and the motor simulator are powered by a single power supply and form a common DC bus structure. The coupling network is connected between the motor controller and the motor simulator. The motor-drag test platform uses the aforementioned common DC bus structure motor simulator modulation unit to modulate the motor simulator.

[0020] The common DC bus structure motor simulator modulation unit provided in the present application adopts a modulation algorithm based on the improved SPWM modulation strategy to control the motor simulator in the motor-to-motor test platform of the common DC bus structure. There is no need to intervene in the modulation strategy on the motor controller side. It only needs to perform routine collection of the voltage and current signals measured by the motor controller and the motor simulator to generate in real time the compensation item for injecting SPWM to suppress the circulating current. It has the advantages of low structural complexity, low cost and low current harmonic content. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The schematic diagram is a schematic diagram of the architecture of a common DC bus motor towing test platform;

[0022] Figure 2 A circuit diagram of a low-impedance zero-sequence current path existing in a motor-to-motor test platform with a common DC bus structure;

[0023] Figure 3 A schematic diagram of the architecture of a modulation unit of a motor simulator with a common DC bus structure provided according to an embodiment of the present application;

[0024] Figure 4 A schematic diagram of the circuit principle of a motor pair test platform with a common DC bus structure provided according to an embodiment of the present application;

[0025] Figure 5 Schematic diagram of the principle of synthesizing the target voltage vector in sector IV through the SVPWM algorithm;

[0026] Figure 6 This is a schematic diagram of the switching sequence of sector IV;

[0027] Figure 7 This is a waveform diagram of the three-phase modulation wave finally output by the SVPWM algorithm;

[0028] Figure 8 It is a schematic diagram of the duty cycle of the A phase and the duty cycles of two non-zero vectors under the SVPWM modulation algorithm on the motor controller side;

[0029] Fig. 9 A schematic diagram of the common mode voltage difference and low frequency circulating current caused by using SVPWM algorithm modulation on the motor controller;

[0030] Fig.10a Schematic diagram of generating PWM modulation signal for SPWM algorithm modulation;

[0031] Fig.10b A schematic diagram of establishing similar triangles when deriving SPWM expressions;

[0032] Fig.11a Schematic diagram of generating PWM modulation signal for SVPWM algorithm modulation;

[0033] Fig.11b A schematic diagram of establishing similar triangles when deriving SVPWM expressions;

[0034] Fig.12 It is a schematic diagram of the modulation waveform after the zero-sequence component is injected into the SPWM modulation wave;

[0035] Fig.13 This is a schematic diagram of the change of zero vector action time after the common mode voltage modulation factor e is introduced;

[0036] Fig.14 It is a schematic diagram of the system circulating current in the specific embodiment 1 of the present application;

[0037] Fig.15 It is a schematic diagram of the three-phase modulation wave on the motor simulator side before the low-frequency circulating current suppression is turned on in the specific embodiment 1 of the present application;

[0038] Fig.16 This is a schematic diagram of the three-phase current of the system before low-frequency circulating current suppression is enabled in the specific embodiment 1 of the present application;

[0039] Fig.17 It is a schematic diagram of the three-phase modulation wave on the motor simulator side after the low-frequency circulating current suppression is turned on in the specific embodiment 1 of the present application;

[0040] Fig.18 This is a schematic diagram of the three-phase current of the system after low-frequency circulating current suppression is turned on in the specific embodiment 1 of the present application;

[0041] Fig.19 This is a schematic diagram of the change of the zero vector allocation coefficient after low-frequency circulating current suppression is turned on in specific embodiment 1 of the present application. DETAILED DESCRIPTION

[0042] Hereinafter, the present application will be further described based on preferred embodiments with reference to the accompanying drawings.

[0043] In order to clearly explain the technical solution of the present application, the cause of the generation of zero-sequence current in a motor pair test platform using a common DC bus structure is first explained.

[0044] The electric motor simulator (EME) can simulate the port characteristics of an automotive motor when it is working. It replaces the motor body and the loading motor in the traditional three-electric architecture test to achieve high-speed simulation of the motor in the forward and reverse directions. It has been widely used in many test scenarios such as functional testing, fault testing, and life testing of automotive motor controllers.

[0045] The common DC bus structure is a new type of automotive motor drag test platform architecture that has emerged in recent years. This architecture can reduce the number of system power supplies and only requires one battery simulator to perform power level drag tests, which helps reduce system complexity, optimize system costs, and is conducive to large-scale industrial applications.

[0046] Figure 1 A schematic diagram of a motor pair test platform with a common DC bus structure is shown. Figure 1 As shown, the towing test platform includes a motor controller (represented by MCU in the figure), a motor simulator (represented by EME in the figure), a coupling network and a single power supply.

[0047] Among them, U dc It is the output voltage of a single power supply, which provides a constant DC voltage to the motor controller and the motor simulator at the same time. In some specific embodiments, for the convenience of analysis, the battery simulator in the traditional motor simulator test system can be simplified, and the DC power output by the inverter can be used as the system power supply to provide a relatively constant battery voltage and achieve a power isolation effect.

[0048] The coupling network is located between the motor controller and the motor simulator, and includes a three-phase inductor structure connected to the three-phase line between the motor controller and the motor simulator, which is used to isolate the voltages on both sides and also plays a role in current filtering.

[0049] The core hardware structure of the motor controller and motor simulator is an inverter unit with a three-phase two-level topology. Each phase of the inverter unit includes two upper and lower power devices. Figure 1 The control algorithm on the motor controller side and the current tracking control algorithm on the motor simulator side generate PWM high-frequency switching signals, which are used to control the switches of each power device in the two inverter units, thereby inverting DC power into AC power and outputting power to the outside in the form of voltage, thereby realizing control of the motor controller and motor simulator.

[0050] In such Figure 1 In the single-power-supply common DC bus motor pair test platform shown in the figure, after the three-phase inductance is applied to the inverter parallel structure, a circuit such as Figure 2 The low impedance zero-sequence current path shown in FIG. 1 is used to generate a zero-sequence current. Therefore, the generated zero-sequence current can circulate in the inverters on both sides through the common DC bus. The voltage source in the zero-sequence circuit is the inverters on both sides. L is the zero-sequence inductance, R L is the three-phase winding resistance.

[0051] and They are the common-mode voltages generated by the inverters on both sides of the towing test platform with a common DC bus motor structure. The common-mode voltage difference provided by the above two inverters forms a zero-sequence voltage U0, which is the average value of the sum of the voltages on both sides of the three-phase inductor. Its expression is as follows:

[0052]

[0053] Furthermore, define Indicates the switching status of each phase power device of the inverter on each side of the motor controller and the motor simulator. The upper bridge arm power device corresponding to the xth phase is turned on; when When the corresponding x-phase lower bridge arm power device is turned on, and It can be expressed as:

[0054]

[0055] when and When they cannot be completely offset, the difference in common-mode voltage between the motor controller and the motor simulator will cause the zero-sequence voltage to no longer be zero. The generation of zero-sequence voltage can generate zero-sequence current in the zero-sequence equivalent circuit, which is reflected at the DC end as the circulating current on the common DC bus side. The above-mentioned circulating current, as a disturbance of the motor controller under test, will introduce additional load to the switch of the power device, increase the loss of the system, and reduce the life of the system. In addition, it will also deteriorate the sinusoidality of the three-phase current of the system, making it difficult to output high-quality current waveforms, affecting the system test accuracy.

[0056] The following factors need to be considered for suppressing the above zero-sequence current: First, since the motor controller is the device under test during the motor drag test, its modulation strategy is pre-determined and cannot be intervened. Therefore, the modulation algorithm on the motor simulator side can only be improved based on the real-time voltage and other information output by the motor controller to achieve the suppression of zero-sequence current. Secondly, when improving the modulation algorithm on the motor simulator side, it is necessary to ensure that the motor simulator side has good output performance to improve voltage utilization, and to avoid tedious calculation steps such as law sector judgment as much as possible, so as to effectively improve the calculation speed of the control system and reduce resource occupation.

[0057] To this end, an embodiment of the present application provides a common DC bus structure motor simulator modulation unit to effectively suppress the zero-sequence circulating current caused by the common DC bus structure on the basis of good modulation of the motor simulator.

[0058] Figure 3 The schematic diagram of the architecture of the motor simulator modulation unit of the common DC bus structure and the motor pair test platform of the common DC bus structure provided in the embodiment of the present application is as follows: Figure 3 As shown, the modulation unit includes:

[0059] A common mode voltage calculation module, used for calculating in real time the common mode voltage output by the motor controller and the motor simulator, wherein the motor controller and the motor simulator are powered by a single power supply and connected via a coupling network;

[0060] A DC component tracking module, used for tracking the DC component of the zero-sequence circulating current existing in the motor-to-motor test platform;

[0061] A zero-sequence component calculation module, used for tracking the low-frequency component of the zero-sequence circulating current, and generating a real-time changing zero-sequence component based on the DC component and the low-frequency component;

[0062] The modulation algorithm generation module is used to inject the real-time changing zero-sequence component into the modulation wave generated by the sinusoidal pulse width modulation algorithm to obtain the actual switching signal of each branch of the control motor simulator.

[0063] The DC component tracking module tracks the DC component of the zero-sequence circulating current based on PI control and generates a DC component compensation term

[0064] Furthermore, the zero-sequence component calculation module tracks the low-frequency component of the zero-sequence circulating current based on the following formula, and generates a zero-sequence component that changes in real time based on the DC component and the low-frequency component:

[0065]

[0066] in, is the zero-sequence component that changes in real time, T s is the switching cycle of the power device, V tp is the triangular carrier amplitude, U dc is the output voltage of a single power supply, U min , U max are the minimum phase voltage and the maximum phase voltage respectively, e is the common mode voltage modulation factor, e1 is the compensation term for eliminating the low frequency component of the zero sequence circulating current, is a compensation term for eliminating the DC component in the zero-sequence circulating current, are the action time of two non-zero voltage vectors of the motor controller, are the action times of the two non-zero voltage vectors of the motor simulator.

[0067] Figure 4 FIG. 1 shows a circuit schematic diagram of a motor pair test platform with a common DC bus structure provided according to a specific embodiment of the present application. Figure 4 As shown, the motor simulator in this embodiment uses the above-mentioned motor simulator modulation unit to generate switching signals for controlling the power devices of each branch of the motor simulator, wherein the difference between the MCU common-mode voltage on the motor simulator side and the EME common-mode voltage on the motor simulator side forms e1, and the PI controller tracks the loop current collected by the coupling network, and outputs e2 according to the target current value (0A) of the loop current and the actual loop current difference, and the two respectively represent the compensation items for low-frequency component compensation and DC component compensation of the zero-sequence circulating current. Furthermore, a modulation factor is generated according to e1 and e2 to further obtain the real-time changing zero-sequence component It is injected into the modulation wave generated by the traditional sinusoidal band pulse width modulation algorithm (SPWM), and finally the switching signal of each branch power device of the motor simulator is obtained.

[0068] The following uses the space vector pulse width modulation algorithm (SVPWM) of the motor controller as an example to explain the mechanism of the modulation unit for zero-sequence current suppression. Figure 1 During the towing test on the test platform shown, the motor controller, as the device under test, needs to determine the control algorithm for its internal inverter unit in advance, and its modulation method cannot be interfered with during the test.

[0069] SVPWM is a common motor controller modulation algorithm that uses the volt-second balance principle to synthesize the target voltage through two zero vectors U0 and U7 and six non-zero voltage vectors U1-U6 with fixed amplitudes and 60° intervals. The algorithm modulates the motor controller through the generated saddle waveform modulation wave, which can maintain the modulation wave in the high-voltage area for a longer time, thereby increasing the voltage utilization rate. Therefore, it has been widely used in the control of motor controller power devices.

[0070] by Figure 5 Taking the target voltage of sector IV as an example, if the output amplitude is U out The target voltage vector is determined by the volt-second balance principle. It is only necessary to specify each switching cycle T s The action time T1 and T3 of the two non-zero vectors U1 and U3 can synthesize the target voltage vector. By modifying T1 and T3, the actual output voltage size and direction can be controlled. For each switching cycle T s The remaining time, the zero vector action time T can be used zero Fill it.

[0071] After calculating the non-zero vector action time, the switching sequence and the action time of the power device can be designed according to the seven-segment algorithm. Figure 6 shows the switching sequence defined by the PWM waveform in sector IV, as Figure 6 As shown in the figure, at each switch state change, only one phase of the switch device performs the action, thereby reducing the number of switches as much as possible and reducing high-order harmonics. This distribution method is the software-based seven-segment SVPWM algorithm. Figure 7 The waveform of the three-phase modulation wave finally output by the SVPWM algorithm (ie, the waveform at the switching moment of the three-phase bridge arm) is shown. As shown in the figure, its shape is a saddle wave form.

[0072] Take the three-phase two-level inverter receiving the [1 0 0] control command as an example to analyze the output voltage, which generates 2U on the α axis. dc / 3 voltage component, the voltage component generated on the β axis is 0. Since the common DC bus structure introduces a zero-sequence path, the common-mode voltage output by the system is U dc / 3, and so on. Under the modulation of the SVPWM algorithm, the voltage vector distribution of all 8 switching states is shown in Table 1, among which the six non-zero vectors can generate both the voltage fundamental frequency and the common-mode voltage component, while the two zero vectors can only generate the common-mode voltage component.

[0073] Table 1 Voltage vector distribution of eight switching states of three-phase two-level inverter

[0074]

[0075] If the time of the two non-zero vectors in each switching cycle is evenly distributed, and the time of the two zero vectors is evenly distributed, the common-mode voltage is 0. However, in the process of modulating the motor controller using the SVPWM algorithm, in order to generate a saddle-shaped modulation wave, the inverter has only two zero vectors in each switching cycle that are evenly distributed in time. The distribution of the action time of the two non-zero vectors is basically impossible to be equal, and their duty cycle is not evenly distributed.

[0076] Figure 8 The figure shows the duty cycle of phase A and the duty cycle of the two non-zero vectors under the SVPWM modulation algorithm on the motor controller side. It can be seen from the figure that the duty cycle of phase A after SVPWM modulation is in the form of a standard saddle wave, and the fundamental frequency of the saddle wave is consistent with the fundamental frequency of the phase current. The action time (duty cycle) of the two non-zero vectors is not equal outside the intersection point, and the frequency is three times the fundamental frequency, which will cause it to generate a common-mode voltage component related to the third harmonic of the fundamental frequency. Fig. 9 This is a schematic diagram of the common-mode voltage difference and low-frequency circulating current between the motor controller and the motor simulator. It can also be seen from the figure that although there is a phase difference between the common-mode voltage difference and the circulating current on the DC side of the common bus due to inductance, they are still positively correlated, which proves the correctness of the circulating current mechanism analysis.

[0077] In order to analyze the degree of distortion of the phase current waveform caused by the circulating current, the Fast Fourier Transformation (FFT) was used to perform harmonic analysis on the system A phase current. At this time, there were odd harmonics in the system phase current, especially the third harmonic, which had a large amplitude of 18.6% of the fundamental amplitude, and the total harmonic distortion (THD) was 19.02%, proving that the common-mode voltage difference caused by the uneven distribution of non-zero vector time will produce a circulating current mainly containing a frequency component three times the fundamental.

[0078] Furthermore, due to the common DC bus structure of single power supply, there is a Figure 2 The low-impedance zero-sequence current path shown, therefore, when the unequal distribution of this non-zero vector causes the common-mode voltage generated by the two inverter units to be unable to completely offset, the difference in common-mode voltage on both sides of the motor controller and the motor simulator will cause the zero-sequence voltage to no longer be zero, and the generation of zero-sequence voltage can generate zero-sequence current in the zero-sequence equivalent circuit, which is reflected at the DC end as the circulating current on the common DC bus side. Obviously, due to the working mechanism of the SVPWM modulation algorithm, the third harmonic component content of the phase current is the highest. In this application, the circulating current with the third harmonic as the main component caused by the characteristics of the modulation algorithm itself is called low-frequency circulating current.

[0079] As a disturbance to the motor controller under test, low-frequency circulating current will introduce additional load to the switch of the power device, increase the loss of the system, and reduce the system life. In addition, it will also deteriorate the sinusoidality of the system's three-phase current, making it difficult to output high-quality current waveforms, affecting the system test accuracy. However, when formulating a strategy to suppress it, there are the following factors that need to be considered:

[0080] 1) As analyzed above, in the motor-to-motor test, the modulation strategy on the motor controller side is pre-established and cannot be intervened. Therefore, the modulation algorithm on the motor simulator side can only be improved based on the real-time voltage output by the motor controller and other information to achieve the suppression of low-frequency circulating current;

[0081] 2) When improving the modulation algorithm on the motor simulator side, it is necessary to ensure that the motor simulator side can output the same saddle-shaped modulation waveform as the SVPWM on the motor controller side to improve voltage utilization, and to avoid tedious calculation steps such as SVPWM algorithm sector judgment as much as possible to effectively improve the calculation speed of the control system and reduce resource occupation.

[0082] In order to solve the above problems, the present application deduces the relationship between the SVPMW algorithm on the motor controller side and the traditional sinusoidal pulse width modulation algorithm (Sinusoidal Band Pulse Width Modulation, SPWM) algorithm, and establishes a unified model including the two, from which a unified expression of the zero-sequence component injected into SPWM is obtained; and based on the mechanism of low-frequency circulating current generation, a common-mode voltage modulation factor that can be determined in real time by the output information of the motor controller is constructed, and the zero-sequence component is adjusted using the modulation factor to obtain a zero-sequence component that can compensate for the common-mode voltage difference between the two inverters in real time. The zero-sequence component is injected into the modulation wave of SPWM, thereby achieving effective control of the zero-sequence current while modulating the motor simulator.

[0083] From the previous analysis, it can be seen that the emergence of low-frequency circulating current is due to the inherent characteristics of the modulation algorithm such as SVPWM adopted on the motor controller side. Obviously, in order to introduce the correct component for suppressing low-frequency circulating current based on the existing SPWM algorithm, it is necessary to first establish the relationship between the two algorithms through step S2.

[0084] (1) Step S21, derivation of the expression of the traditional SPWM algorithm

[0085] Although the modulation wave is a sinusoidal waveform in macroscopic terms, the modulation wave of each phase can be Treat it as a constant for mathematical derivation.

[0086] Fig.10a The generation process of SPWM modulated PWM signal is shown, where V tp is the triangular carrier amplitude, and the Fig.10b The similar triangles shown in the figure can give the relationship between the duty cycle and the modulation wave as shown in the following formula:

[0087]

[0088] In the above formula, T on is the on-time of the switch tube, from which the duty cycle can be obtained as:

[0089]

[0090] Analyze the output voltage of each phase in any switching cycle. The external output voltage of each phase in one switching cycle is:

[0091]

[0092] Among them, U dc is the voltage of a single power supply. Substituting the expression of duty cycle into the above formula, we can get the relationship between output voltage and modulation wave:

[0093]

[0094] Therefore, the phases under the SPWM algorithm can be obtained The waveform expression is:

[0095]

[0096] (2) Step S22, derivation of the expression of SVPWM algorithm

[0097] Taking the IV sector as an example, the mathematical expression of the SVPWM modulation wave is derived. Fig.11a The generation process of SVPWM modulated PWM signal when the carrier ratio is 100. Under the conventional SVPWM seven-segment rule, the switch tube combination conduction time in this cycle is:

[0098]

[0099] Among them, T a , T b , T c are the conduction duration of the three-phase power devices, and are the control zero vector action time T zero The two zero vectors U0 and U7 are not evenly distributed. To unify the expression in the subsequent design of the circulating current suppression algorithm, the switch tube conduction combination time is redefined as:

[0100]

[0101] Where k∈[0,1] is the zero vector allocation coefficient, which is used to redistribute the action time of the two zero vectors to implement subsequent algorithms such as circulation suppression. At this time, the action time of U7 is kT zero , U0 action time is (1-k)T zero , if k≠1 / 2, the two zero vectors are no longer evenly distributed.

[0102] Establish as Fig.11b The similar triangles shown in Figure 1 are c For example, according to the similarity relationship between △BAC and △BDE, the modulation wave can be obtained The relationship between the three-phase modulation wave and the action time of each vector is obtained by analogy:

[0103]

[0104] The action time of two adjacent non-zero voltage vectors can be expressed in the α-β coordinate system as follows: The inverse transformation based on Clark transformation is expressed in the three-phase stationary coordinate system and substituted into the above formula to obtain the relationship between the three-phase modulation wave and the three-phase voltage as follows:

[0105]

[0106] In order to Arranged with and The unified form, in Add the right side of the equation Then subtract, and finally get the standard mathematical expression of SVPWM three-phase modulation wave:

[0107]

[0108] After obtaining the standard mathematical expressions of SPWM and SVPWM modulation waves, in order to facilitate subsequent comparison and calculation, the modulation coefficient s can be defined as shown in the following formula:

[0109] s=2V tp / U dc ,

[0110] Then the modulation waves of SPWM and SVPWM can be simplified as follows:

[0111]

[0112]

[0113] By subtracting the above two equations, it can be clearly seen that there is a common difference between the modulation waves generated by the SPWM algorithm and the SVPWM algorithm:

[0114]

[0115] The above common items can be expressed as:

[0116] U * =(k-1)sU a -ksU c +(2k-1)V tp ,

[0117] Among them, U * It is called the zero-sequence component, and the expression of each phase modulation wave of the SPWM algorithm and the SVPWM algorithm is simplified to:

[0118]

[0119] The relationship between the two modulation algorithms can be obtained from the above formula: The SPWM algorithm injects the zero-sequence component U * The standard SVPWM waveform can be obtained, which also corresponds to the third harmonic component carried by the SVPWM saddle-shaped modulation waveform.

[0120] According to the corresponding relationship between the maximum phase voltage, minimum phase voltage and zero-sequence component expression of each sector, it can be found that in order to ensure that the waveform of SPWM is consistent with SVPWM after the injection of zero-sequence component, the phase voltage of coefficient k should be consistent with the maximum phase voltage U max Correspondingly, the phase voltage of k-1 should be equal to the minimum phase voltage U min Correspondingly, the statistical model of SPWM and SVPWM based on zero-sequence component injection is finally obtained as shown in the following formula:

[0121]

[0122] In the existing SPWM algorithm based on zero-sequence component injection, k = 1 / 2 is generally used, that is, the mean zero-sequence injection method. This method can achieve the same saddle waveform as SVPWM after injecting zero-sequence components into SPWM (such as Fig.12 As shown in the figure, it is impossible to track the common-mode voltage changes caused by SVPWM in real time. Therefore, it is necessary to redistribute the zero vector action time on the motor simulator side to actively generate a common-mode voltage corresponding to the common-mode voltage on the motor controller side, so as to obtain a modulation algorithm that can suppress the zero-sequence voltage U0 in real time.

[0123] Specifically, a zero-sequence voltage model causing low-frequency circulating current is first established as shown in the following formula:

[0124]

[0125] In the above formula, and are the real-time common-mode voltages of the motor controller and the motor simulator, U' a , U b '、U c ' are respectively the real-time voltage differences on both sides of the three-phase inductance;

[0126] Then, the common-mode voltage modulation factor e is determined based on the zero vector redistribution strategy as shown in the following equation:

[0127]

[0128] Among them, T s is the switching period of the power device, e1 is the compensation term used to eliminate the third harmonic component in the low-frequency circulating current, This is a compensation term used to eliminate the DC component in the low-frequency circulating current. Among the above compensation terms, the PI controller can only suppress the DC component in the zero-sequence circulating current, but cannot completely eliminate the third harmonic component. Therefore, it is necessary to introduce a compensation term corresponding to the common-mode voltage difference between the motor controller side and the motor simulator side represented by e1 to form a complete common-mode voltage modulation factor.

[0129] The core idea of ​​​​low-frequency circulating current suppression through e is to redistribute the zero vector action time in each switching cycle of the motor simulator, and adjust the zero vector distribution coefficient to make the two zero vector action times T0 and T7 of U0 and U7 unequally distributed, thereby actively generating a common-mode voltage to offset the common-mode voltage difference of the system itself, thereby suppressing the zero-sequence current in the power-stage hardware-in-the-loop test system, without making any changes to the modulation algorithm on the motor controller side under test.

[0130] like Fig.13 As shown, taking the IV sector as an example, after introducing the common-mode voltage modulation factor e, the action time of the three-phase bridge arm power device can be expressed as follows:

[0131]

[0132] in, is the action time of the three-phase power device. When e﹥0, its compensation effect makes the zero vector action time T0 extend by e seconds, and the zero vector action time T7 shortens by e seconds; when e﹤0, the zero vector action time T0 will be shortened by e seconds, and the zero vector action time T0 will be extended by e seconds. By real-time redistribution of the action time of the two zero vectors T0 and T7, the uneven distribution of the zero vector is actively controlled, thereby generating a new common-mode voltage, offsetting the common-mode voltage difference that originally existed in the system, so that the zero-sequence voltage of each switching cycle in the system is kept approximately zero, achieving the purpose of suppressing the circulating current of the system.

[0133] When modulation is performed in the form of a common-mode voltage modulation factor e, SVPWM modulation is still required to calculate the switching moments. The sector judgment and calculation of the intermediate process greatly occupy the limited computing resources of the FPGA, limiting the ultimate operating speed of the motor simulator control system. Therefore, the SPWM algorithm based on zero-sequence component injection can be further adjusted according to the common-mode voltage modulation factor e to obtain an adjusted SPWM algorithm based on zero-sequence component injection, thereby reducing the FPGA resources occupied by the algorithm operation and improving the execution speed of the motor simulator control system.

[0134] Specifically, the real-time value of e can be obtained by real-time acquisition and calculation of the common-mode voltage difference between the motor controller and the motor simulator generated by the non-zero voltage vector in each switching cycle. Then, k is adjusted by the following formula to obtain the adjusted real-time changing zero vector allocation coefficient k0:

[0135]

[0136] At this time, the zero-sequence component changes in real time The final modulated wave can be expressed as follows:

[0137]

[0138] Table 2 below shows the parameters of a motor pair test platform with a common DC bus structure provided according to a specific embodiment of the present application. The architecture and circuit of the pair test platform are shown in Figure 3 and Figure 4 .

[0139] Table 2 Test platform experimental parameters

[0140] Parameter name Parameter Value unit <![CDATA[Bus voltage (U dc )]]> 30 V <![CDATA[Switching frequency (f s )]]> 10 kHz <![CDATA[Average dead time (t d )]]> 3 μs <![CDATA[Number of pole pairs (n p )]]> 4 - Stator resistance (R) 0.08 Ω <![CDATA[Permanent magnet flux linkage (Ψ f )]]> 0.366 Wb <![CDATA[d-axis inductance (L d )]]> 0.25 mh <![CDATA[q-axis inductance (L q )]]> 0.5 mh

[0141] The motor controller is tested using the test platform. At the beginning of the test, the circulating current suppression is not performed. The system circulating current, the three-phase modulation wave on the motor simulator side, and the system three-phase current are respectively as follows: Fig.14 , Fig.15 and Fig.16 As shown, from Fig.14 It can be seen that when the circulating current is not suppressed, the maximum absolute value of the circulating current is 1.99A, which seriously affects the sinusoidality of the three-phase current. Fig.15 As shown in the figure, although the modulation wave is still a standard saddle wave, due to the existence of circulating current, Fig.16 The three-phase current in the system is no longer a standard sinusoidal waveform, and the steady-state signal generated by the motor simulator is of poor quality.

[0142] At 6.1 seconds, the circulation begins to be suppressed, such as Fig.17As shown in the figure, the modulation wave shape is no longer a standard saddle wave, indicating that the action time of the zero vector has been modified, and the common mode voltage difference of the system is compensated in real time. Table 3 compares the low-frequency circulating current in the two cases. As shown in Table 3, after the circulating current is suppressed, the maximum value of the system circulating current is 0.58A, which is 70.9% lower than 1.99A before the circulating current suppression. Its amplitude is 26.4% of the phase current amplitude, and the impact on the phase current is smaller.

[0143] Table 3 Comparison of the amplitude of low-frequency components of system circulating current

[0144] Circulation suppression Circulating current amplitude Decline Phase current sinusoidality none 1.99A - Difference have 0.58A 70.9％ good

[0145] Fig.18 The three-phase current of the system after the circulating current is suppressed is shown. Fig.16 Compared with traditional 3D printing, the sinusoidal degree has been greatly improved, which enables the motor simulator to generate higher quality steady-state signals and simulate the characteristics of real permanent magnet synchronous motors more accurately.

[0146] Fig.19 After the circulation suppression is performed, the distribution coefficient used for zero vector redistribution changes from Fig.19 It can be seen that when using the modulation algorithm provided by the method of the present application, the zero vector distribution coefficient k that originally maintained a fixed value becomes a modulation coefficient k0 that changes with 1 / 2 as the reference and three times the base frequency. This proves that the modulation algorithm on the motor simulator side is changing the waveform of the zero-sequence component injected in the SPWM modulation through real-time adjustment of k0, thereby changing the modulation wave waveform and redistributing the action time of the two zero vectors. It also shows that the method proposed in the present application is providing accurate amplitude and angle for common-mode voltage suppression, thereby providing the motor simulator with efficient circulating current low-frequency component suppression capability.

[0147] In some preferred embodiments, the common DC bus structure motor simulator modulation unit further includes a high-frequency component suppression module for suppressing high-frequency components in the zero-sequence circulating current.

[0148] Since in the present application, the principle of suppressing the low-frequency circulating current component is to distribute the zero vector action time from the angle of changing the modulation wave waveform, its action mechanism cannot suppress the high-order harmonics near the switching frequency. For this reason, in an embodiment of the present application, when the modulation method of the motor controller and the motor simulator use a carrier of the same frequency (that is, the two have a non-time-varying phase difference), the high-frequency component suppression module synchronizes the carrier of the modulated motor controller and the carrier of the modulated motor simulator to suppress the high-frequency component in the zero-sequence circulating current.

[0149] The above is a detailed introduction to the specific implementation methods of the present application. For those skilled in the art, several improvements and modifications may be made to the present application without departing from the principles of the present application. These improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A motor simulator modulation unit with a common DC bus structure, used to modulate and control a motor simulator in a motor pair test platform with a common DC bus structure, characterized in that: include: A common mode voltage calculation module, used for calculating in real time the common mode voltage output by the motor controller and the motor simulator, wherein the motor controller and the motor simulator are powered by a single power supply and connected via a coupling network; A DC component tracking module, used for tracking the DC component of the zero-sequence circulating current existing in the motor-to-motor test platform; A zero-sequence component calculation module, used for tracking the low-frequency component of the zero-sequence circulating current, and generating a real-time changing zero-sequence component based on the DC component and the low-frequency component; A modulation algorithm generation module, used for injecting the real-time changing zero-sequence component into the modulation wave generated by the sinusoidal pulse width modulation algorithm to obtain the actual switching signal of each branch of the control motor simulator; The DC component tracking module tracks the DC component of the zero-sequence circulating current based on PI control and generates a DC component compensation term The zero-sequence component calculation module tracks the low-frequency component of the zero-sequence circulating current based on the following formula, and generates a zero-sequence component that changes in real time based on the DC component and the low-frequency component: in, is the zero-sequence component that changes in real time, T s is the switching cycle of the power device, V tp is the triangular carrier amplitude, U dc is the output voltage of a single power supply, U min , U max are the minimum phase voltage and the maximum phase voltage respectively, e is the common mode voltage modulation factor, e1 is the compensation term for eliminating the low frequency component of the zero sequence circulating current, is a compensation term for eliminating the DC component in the zero-sequence circulating current, T1 mcu , are the action time of the two non-zero voltage vectors of the motor controller, T1 eme , are the action times of two non-zero voltage vectors of the motor simulator respectively; The motor controller is modulated by a space vector pulse width modulation algorithm, which synthesizes a target voltage through two zero vectors and six non-zero voltage vectors with the same amplitude and equally spaced within a period, and the modulation wave generated by the space vector pulse width modulation algorithm has a saddle waveform.

2. The common DC bus structure motor simulator modulation unit according to claim 1 is characterized in that: The control model of the motor pair test platform with a common DC bus structure includes: Motor controllers, motor simulators, coupling networks and single power supplies; The inverters of the motor controller and the motor simulator are both three-phase two-level topology structures; The coupling network includes a three-phase inductor connected to a three-phase line between the motor controller and the motor simulator; The single power supply simultaneously supplies power to the motor controller and the motor simulator through a common DC bus structure.

3. The common DC bus structure motor simulator modulation unit according to claim 1, characterized in that: The ratio of the amplitude of the third harmonic component in the low-frequency component to the amplitude of the phase current fundamental wave is greater than 18%.

4. The common DC bus structure motor simulator modulation unit according to claim 1, characterized in that: It also includes a high-frequency component suppression module, which is used to suppress the high-frequency components in the zero-sequence circulating current.

5. The common DC bus structure motor simulator modulation unit according to claim 4 is characterized in that: When the carrier modulating the motor controller and the carrier modulating the motor simulator have a non-time-varying phase difference, the high-frequency component suppression module suppresses the high-frequency component in the zero-sequence circulating current by synchronizing the carrier modulating the motor controller and the carrier modulating the motor simulator.

6. A motor-to-motor test platform, comprising a motor controller, a motor simulator, a coupling network and a single power supply, wherein the motor controller and the motor simulator are powered by a single power supply and form a common DC bus structure, and the coupling network is connected between the motor controller and the motor simulator, characterized in that: The motor simulator is modulated using the common DC bus structure motor simulator modulation unit described in claim 1.

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