Three-Level Inverter Pulse Delay Compensation System and Method Based on Ripple Prediction

Abstract

The present invention discloses a three-level inverter pulse delay compensation system and method based on ripple prediction. First, a current sampling module is used to collect the low-frequency current i of each phase leg of the three-level inverter x , and then the high-frequency ripple current i in each segment of the current switching period is predicted by a phase leg current ripple prediction module ripple (k). Then, a phase leg voltage edge delay calculation module superimposes i x and i ripple (k), and filters out the phase leg current i corresponding to the rising edge moment of the phase leg voltage from the superimposed result rise and the phase leg current i corresponding to the falling edge moment fall . After substituting them into the phase leg voltage switching edge delay function, the rising edge delay compensation time #imgabs0# and the falling edge delay compensation time #imgabs1# of the phase leg voltage are calculated. Finally, a control signal compensation module online corrects the initial positions of the edges of the PWM signals of each phase within the current switching period according to #imgabs2# and #imgabs3#, so as to realize the pulse delay compensation of the three-level inverter

Description

Technical Field

[0001] The present invention belongs to the technical field of three-level inverters. More specifically, it relates to a three-level inverter pulse delay compensation system and method based on ripple prediction. Background Art

[0002] Compared with two-level inverters, three-level inverters can output more levels, and the voltage borne by each switching device is only half of the DC bus voltage. They have the characteristics of good sinusoidal output waveform, high voltage-bearing level, low switching loss, high operating efficiency, and long service life, and are increasingly widely used in high-voltage and high-power fields such as aerospace and electric vehicles.

[0003] In practical applications, in order to prevent shoot-through of the bridge arm, a dead time needs to be inserted into the control signals of the complementary switching devices in the same phase of the three-level inverter. Coupled with the influence of non-ideal factors such as the turn-on and turn-off processes of power devices, there is a delay between the actual output bridge arm voltage pulse of the inverter and the PWM (pulse width modulation) digital signal, resulting in distortion of the output current, reduction of the fundamental component, and increase of low-order harmonics, thereby increasing the motor loss and deteriorating the system control performance. Therefore, it is necessary to compensate for this pulse delay.

[0004] Most of the existing compensation technologies are for two-level inverters. The compensation method based on current polarity judgment does not consider the influence of current high-frequency ripple, resulting in errors in current polarity judgment near the zero-crossing point and affecting the compensation effect; the compensation method based on a disturbance observer requires obtaining an accurate motor model and is easily affected by changes in motor parameters. Moreover, the existing technologies mainly correct the average voltage or duty cycle within the switching period and pay less attention to the specific delay time of the rising and falling edges of the bridge arm voltage pulse, resulting in inaccurate compensation. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a three-level inverter pulse delay compensation system and method based on ripple prediction, which can accurately compensate for the edge delay of the bridge arm voltage pulse of the three-level inverter without additionally increasing complex hardware circuits to meet more refined control requirements.

[0006] To achieve the above object of the invention, the present invention provides a three-level inverter pulse delay compensation system based on ripple prediction, including a three-level inverter and a load. It is characterized in that it further includes: a current sampling module, a bridge arm current ripple prediction module, a bridge arm voltage edge delay calculation module, and a control signal compensation module;

[0007] The input end of the current sampling module is connected to the output end of the three-level inverter and is used to collect the low-frequency current i of each phase bridge arm of the three-level inverter x , where x = a, b, c represents three phases;

[0008] The arm current ripple prediction module includes a duty cycle calculation unit, a segmented time calculation unit, and a current high-frequency ripple prediction unit that are connected in sequence;

[0009] Among them, the duty cycle calculation unit performs current feedback control on the received low-frequency current i x to obtain the modulation voltage u of each phase x , and then calculates the real-time duty cycle d of each phase of the three-level inverter according to the modulation voltage u x ; x

[0010] The segmented time calculation unit first determines the initial position of the edge of the PWM signal of each phase of the three-level inverter according to the real-time duty cycle d x , and then segments the current switching cycle based on the initial position of the edge of the PWM signal of each phase to obtain the action time t of each segment k , where k represents the number after segmentation of the current switching cycle;

[0011] The current high-frequency ripple prediction unit calculates the current ripple slope within each segment according to the voltage value and inductance value acting on the inductor L of each phase x , and then predicts the high-frequency ripple current i within each segment of the current switching cycle according to the action time t of each segment k and the current ripple slope ripple (k);

[0012] The first input end of the arm voltage edge delay calculation module is connected to the current sampling module, and the second input end is connected to the output end of the arm current ripple prediction module; the high-frequency ripple current i within each segment ripple (k) is superimposed with the low-frequency current i x , and then the arm current i corresponding to the rising edge moment of the arm voltage and the arm current i corresponding to the falling edge moment are selected from the superimposed result rise and fall , and then i rise and i fall are substituted into the arm voltage switch edge delay function to calculate the rising edge delay compensation time and the falling edge delay compensation time

[0013] The control signal compensation module online corrects the initial position of the edge of the PWM signal of each phase within the current switching cycle according to the rising edge and falling edge delay compensation times of the arm voltage, so as to realize the pulse delay compensation of the three-level inverter.

[0014] The present invention also provides a three-level inverter pulse delay compensation method based on ripple prediction, which is characterized by including the following steps:

[0015] (1) Establish the edge delay function of the bridge arm voltage switch;

[0016]

[0017]

[0018] Among them, and are the delay compensation times of the rising edge and falling edge of the bridge arm voltage respectively, T d is the dead time, t on and t off are the turn-on and turn-off times of the bridge arm respectively, i rise and i fall are the bridge arm currents corresponding to the rising edge moment and falling edge moment of the bridge arm voltage;

[0019] (2) Collect the low-frequency current i x of each phase bridge arm of the three-level inverter through the current sampling module, where x = a, b, c represents three phases;

[0020] (3) Perform current feedback control on the low-frequency current i x through the duty cycle calculation unit to obtain the modulation voltage u x of each phase, and then calculate the real-time duty cycle d x of each phase of the three-level inverter according to the modulation voltage u x ;

[0021] (4) Determine the initial position of the PWM signal edge of each phase of the three-level inverter according to the real-time duty cycle d x , mark the zero moment, the end moment of the current switching cycle, and the rising edge moment and falling edge moment of each phase PWM signal, sort all the marked moments in ascending order, and take the interval between two adjacent moments after sorting as a segment to obtain the action time t k of each segment, where k represents the number after segmentation of the current switching cycle;

[0022] (5) Calculate the current ripple slope within each segment according to the voltage value and inductance value acting on each phase inductor L x ;

[0023]

[0024] Among them, f k represents the current ripple slope within the kth segment, U Lx (k) represents the voltage value acting on the x-phase inductor within the kth segment, L x represents the inductance value of the x-phase, v xO(k) represents the arm output voltage of the x-th phase within the k-th segment, v x represents the load voltage of the x-th phase within the current switching period, v NO (k) represents the common-mode voltage within the k-th segment;

[0025] (6), predict the high-frequency ripple current within each segment of the current switching period;

[0026] i ripple (k) = i ripple (k - 1) + f k t k

[0027] wherein, i ripple (k) represents the high-frequency ripple current at the end moment of the k-th segment, and the high-frequency ripple current value at the initial moment of each switching period is 0, t k is the action time of the k-th segment;

[0028] (7), superimpose the high-frequency ripple current i ripple (k) within each segment with the low-frequency current i x , and select the arm current i rise corresponding to the rising edge moment of the arm voltage and the arm current i fall corresponding to the falling edge moment from the superimposed result;

[0029] (8), substitute i rise and i fall into the arm voltage switching edge delay function established in step (1) to calculate the delay times and

[0030] (9), insert the dead time T d at the initial position of the edge of each phase PWM signal, then move the switching positions of the first half cycle forward as a whole and move the switching positions of the second half cycle forward as a whole to compensate for the delay between the arm voltage power pulse and each phase PWM signal caused by the dead time and the device turn-on and turn-off times, so as to realize the synchronous control of all arm voltage pulses.

[0031] The invention object of the present invention is realized as follows:

[0032] The three-level inverter pulse delay compensation system and method based on ripple prediction of the present invention first collect the low-frequency current i x of each phase arm of the three-level inverter through the current sampling module, and then predict the high-frequency ripple current i ripple within each segment of the current switching period through the arm current ripple prediction module(k), and then the bridge arm voltage edge delay calculation module superimposes i x and i ripple (k), and filters out the arm current i rise corresponding to the rising edge moment of the bridge arm voltage and the arm current i fall corresponding to the falling edge moment from the superimposed result. After substituting them into the bridge arm voltage switch edge delay function, the rising edge delay compensation time of the bridge arm voltage and the falling edge delay compensation time are calculated. Finally, the control signal compensation module corrects the initial positions of the edges of the PWM signals of each phase within the current switching period according to and online, so as to realize the pulse delay compensation of the three-level inverter.

[0033] Meanwhile, the three-level inverter pulse delay compensation system and method based on ripple prediction of the present invention also have the following beneficial effects:

[0034] (1), by predicting the high-frequency ripple current of the bridge arm, the present invention solves the problem of error in judging the current polarity near the zero-crossing point when only considering the filtered low-frequency current;

[0035] (2), the present invention comprehensively considers the dead-time freewheeling delay time, as well as the relationship between the turn-on and turn-off delay times of the power devices in the three-level inverter and the arm current polarity and amplitude, and establishes a bridge arm voltage switch edge delay function, which can accurately compensate the rising edge and falling edge delays of the bridge arm voltage pulses, reduce the distortion of the output current waveform, and improve the performance of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the schematic diagram of the three-level inverter pulse delay compensation system based on ripple prediction of the present invention;

[0037] Figure 2 is Figure 1 the schematic diagram of the arm current ripple prediction module shown;

[0038] Figure 3 is the schematic diagram of the switching period segmentation;

[0039] Figure 4 is the schematic diagram of the flowing direction of the arm current within the dead time when the modulation voltage is greater than 0 and less than 0;

[0040] Figure 5 is the comparison diagram of the control signals of each switch tube, the ideal waveform and the actual output waveform of the bridge arm voltage when the modulation voltage is greater than 0 and less than 0;

[0041] Figure 6It is the rising and falling edge delay time curves of the three-level inverter leg voltage under a 2us dead time;

[0042] Figure 7 It is a comparison diagram of the actual current ripple and the predicted current ripple of the three-level inverter leg;

[0043] Figure 8 It is the phase A current curves of no compensation, traditional fixed-time dead time compensation, and the pulse delay compensation method provided by the present invention under the same working conditions;

[0044] Figure 9 It is a comparison diagram of current harmonics under different compensation methods. Detailed implementation manners

[0045] The following describes the detailed implementation manners of the present invention with reference to the accompanying drawings so that those skilled in the art can better understand the present invention. It should be particularly noted that in the following description, when the detailed descriptions of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0046] Embodiment

[0047] Figure 1 It is the schematic diagram of the three-level inverter pulse delay compensation system based on ripple prediction of the present invention.

[0048] In this embodiment, as Figure 1 shown, the present invention provides a three-level inverter pulse delay compensation system based on ripple prediction, including a three-level inverter, a load, a current sampling module, a leg current ripple prediction module, a leg voltage edge delay calculation module, and a control signal compensation module;

[0049] The input end of the current sampling module is connected to the output end of the three-level inverter, and is used to collect the low-frequency current i x of each leg of the three-level inverter, where x = a, b, c represents three phases;

[0050] As Figure 2 shown, the leg current ripple prediction module includes a duty cycle calculation unit, a segmented time calculation unit, and a current high-frequency ripple prediction unit connected in sequence;

[0051] Among them, the duty cycle calculation unit performs current feedback control on the received low-frequency current i x to obtain the modulation voltage u x of each phase, and then calculates the real-time duty cycle d x of each phase of the three-level inverter according to the modulation voltage u x ;

[0052] The segmented time calculation unit first calculates according to the real-time duty cycle d xDetermine the initial positions of the PWM signal edges of each phase of the three-level inverter, and then segment the current switching cycle based on the initial positions of the PWM signal edges of each phase to obtain the action time t of each segment k , where k represents the number after segmentation of the current switching cycle;

[0053] The current high-frequency ripple prediction unit calculates the current ripple slope within each segment according to the voltage value and inductance value acting on each phase inductor L x , and then predicts the high-frequency ripple current i k within each segment of the current switching cycle based on the action time t ripple of each segment and the current ripple slope;

[0054] The first input terminal of the bridge arm voltage edge delay calculation module is connected to the current sampling module, and the second input terminal is connected to the output terminal of the bridge arm current ripple prediction module; superimpose the high-frequency ripple current i ripple (k) within each segment with the low-frequency current i x , and then select the bridge arm current i rise corresponding to the rising edge moment of the bridge arm voltage and the bridge arm current i fall corresponding to the falling edge moment from the superimposed result, and then substitute i rise and i fall into the bridge arm voltage switching edge delay function to calculate the rising edge delay compensation time and the falling edge delay compensation time

[0055] The control signal compensation module online corrects the initial positions of the PWM signal edges of each phase within the current switching cycle according to the rising edge and falling edge delay compensation times of the bridge arm voltage, so as to realize the pulse delay compensation of the three-level inverter.

[0056] Next, we describe the specific process of delay compensation for the pulse delay system of the three-level inverter based on ripple prediction, including the following steps:

[0057] S1. Establish a bridge arm voltage switching edge delay function;

[0058]

[0059]

[0060] Among them, and are the rising edge and falling edge delay compensation times of the bridge arm voltage respectively, T d is the dead time, t on and t off are the turn-on and turn-off times of the bridge arm respectively, i riseand i fall are the arm currents corresponding to the rising edge and falling edge moments of the arm voltage;

[0061] S2. Collect the low-frequency current i of each phase arm of the three-level inverter through the current sampling module x , where x = a, b, c represents three phases;

[0062] S3. Perform current feedback control on the low-frequency current i x to obtain the modulation voltage u of each phase x , and then calculate the real-time duty cycle d of each phase of the three-level inverter according to the modulation voltage u x ; x ;

[0063] S4. Determine the initial positions of the edges of the PWM signals of each phase of the three-level inverter according to the real-time duty cycle d x , mark the zero moment, the end moment of the current switching cycle, as well as the rising edge moment and falling edge moment of each phase PWM signal, sort all the marked moments in ascending order, and take the interval between two adjacent moments after sorting as a segment to obtain the action time t of each segment k , where k represents the number after segmentation of the current switching cycle;

[0064] In this embodiment, Figure 3 shows a schematic diagram of the switching cycle segmentation when d a > d b > d c , where Ts is the switching cycle duration.

[0065] S5. Calculate the current ripple slope within each segment according to the voltage value and inductance value acting on each phase inductor L x ;

[0066]

[0067] Among them, f k represents the current ripple slope within the kth segment, U Lx represents the voltage value of the inductor on the xth phase, L x represents the inductance value of the xth phase, v xO (k) represents the arm output voltage of the xth phase within the kth segment, v x represents the load voltage of the xth phase within the current switching cycle, v NO (k) represents the common-mode voltage within the kth segment;

[0068] S6. Predict the high-frequency ripple current within each segment of the current switching cycle;

[0069] i ripple (k) = iripple (k - 1)+f k t k

[0070] Wherein, i ripple (k) represents the high-frequency ripple current at the end moment of the k-th segment. The high-frequency ripple current value at the initial moment of each switching period is 0, and t k is the action time of the k-th segment;

[0071] S7. Superimpose the high-frequency ripple current i ripple (k) within each segment with the low-frequency current i x , and select the arm current i rise corresponding to the rising edge moment of the arm voltage and the arm current i fall corresponding to the falling edge moment from the superimposed result;

[0072] S8. Substitute i rise and i fall into the arm voltage switching edge delay function established in step S1 to calculate the delay times and

[0073] S9. Insert the dead time T d at the initial position of the edge of each phase PWM signal, then move the switching positions of the first half cycle forward as a whole and move the switching positions of the second half cycle forward as a whole to compensate for the delay between the arm voltage power pulse and each phase PWM signal caused by the dead time and the device turn-on and turn-off times, so as to realize the synchronous control of all arm voltage pulses.

[0074] The following analysis takes a typical diode-clamped three-level inverter as an example to illustrate the delay compensation. As Figure 4 shown, wherein, Figure 4 (a) and Figure 4 (b) show the flowing directions of the arm current within the dead time when the modulation voltage is greater than 0 and less than 0.

[0075] Taking phase A as an example, when the modulation voltage is greater than 0, as Figure 4 (a) shown, when the arm current i a ≥0, the current during the dead time period flows through D z1 and S a2 , and the arm output voltage is 0; when i a <0, the current during the dead time period flows through the anti-parallel diode D a1 and D a2 for freewheeling, and the arm output voltage is V dc / 2. When the modulation voltage is less than 0, asFigure 4 (As shown in (b), when the arm current i a ≥0, during the dead time period, the current flows through the antiparallel diodes D a3 and D a4 for freewheeling, and the output voltage of the arm is -V dc / 2; when i a <0, during the dead time period, the current flows through D z2 and S a3 for conduction, and the output voltage of the arm is 0. This results in a delay in the edge of the arm voltage, and the influence of the dead time effect on this delay is only related to the polarity of the arm current, and has nothing to do with the amplitude. In addition, the parallel stray capacitance of the inverter switching tubes will affect the turn-on and turn-off times of the arm edges, thus bringing about a delay in the arm edges. When i a ≥0, the turn-on time remains a small constant, and the turn-off time decreases with the increase of the current amplitude; when i a <0, the turn-on time decreases with the increase of the current amplitude, and the turn-off time remains a small constant. Therefore, the turn-on and turn-off processes of the arm are related to both the polarity and direction of the arm current. In summary, the control signals of each switching tube when the modulation voltage is greater than 0 and less than 0, as well as the comparison between the ideal waveform and the actual output waveform of the arm voltage, are as shown in Figure 5 (a) and Figure 5 (b).

[0076] In this embodiment, when the dead time is set to 2 μs for testing, the rise time and fall time delays of the three-level inverter arm voltage are as shown in Figure 6 . For the rise time delay curve, when i rise <-5 A and i rise >0, they can be respectively fitted with straight lines. When -5 A < i rise <0, a polynomial can be used for curve fitting; similarly, for the fall time delay curve, when i fall >5 A and i fall <0, they can be respectively fitted with straight lines. When 0 < i fall <5 A, a polynomial can be used for curve fitting. Thus, a functional relationship between the switching edge delay of the arm voltage and the arm current at the corresponding edge moment is established.

[0077] From the above analysis, it can be seen that the edge delay of the pulse is related to the direction and amplitude of the current at the edge moment. Therefore, to compensate for the pulse edge delay, it is necessary to obtain the arm current at the rise edge and fall edge moments in real time. The arm current contains high-frequency ripple, and only the low-frequency current can be obtained through the sampling circuit. Therefore, it is necessary to predict the arm current ripple to obtain the amplitude and direction of the current at the accurate rise edge and fall edge moments.

[0078] In this embodiment, the prediction result of the arm current ripple of the three-level inverter is predicted by the arm current ripple prediction module as Figure 7 shown. The predicted current ripple is consistent with the actual current ripple, laying a foundation for the accuracy of the arm current polarity judgment.

[0079] After predicting the current ripple in each segment, we can calculate the delay time of the rising edge and falling edge of the arm voltage through the arm voltage edge delay calculation module and Then, insert the dead time T at the initial position of the edge of each phase PWM signal d , and then move the switching positions of the first half cycle forward as a whole The switching positions of the second half cycle are moved forward as a whole To compensate for the delay between the arm voltage power pulse and each phase PWM signal caused by the dead time and the device turn-on and turn-off time, so as to realize the synchronous control of all arm voltage pulses.

[0080] In this embodiment, taking phase A as an example, as Figure 5 shown, based on the initial PWM signal, when the modulation voltage is greater than 0, for the first half switching cycle, delay the rising edge of the control signal of S a1 by the dead time T d , and then move the switching positions of the control signals of S a1 and S a3 forward as a whole For the second half switching cycle, delay the rising edge of the control signal of S a3 by the dead time T d , and then move the switching positions of the control signals of S a1 and S a3 forward as a whole When the modulation voltage is less than 0, for the first half switching cycle, delay the rising edge of the control signal of S a2 by the dead time T d , and then move the switching positions of the control signals of S a2 and S a4 forward as a whole For the second half switching cycle, delay the rising edge of the control signal of S a4 by the dead time T d , and then move the switching positions of the control signals of S a2 and S a4 forward as a whole

[0081] In this embodiment, it is assumed that the DC bus voltage is 200V, the load inductance is 0.55mH, and the dead time is 3us. Figure 8 (a)- Figure 8(c) are the phase A currents under this working condition without compensation, the traditional fixed-time dead zone compensation method, and the pulse delay compensation method of the present invention, respectively. Figure 9 is a comparison chart of current harmonics under different compensation methods. According to Figure 8 and Figure 9 it can be seen that when there is no compensation, the current distortion is serious, and the amplitudes of the 5th and 7th harmonics are relatively large, which are 0.24 A and 0.11 A respectively. After compensation, the fundamental wave amplitude of the current increases, the harmonic amplitude decreases, and the sinusoidality improves. Among them, the amplitudes of the 5th and 7th harmonics after compensation by the traditional fixed-time dead zone compensation method are 0.05 A and 0.03 A respectively, and the amplitudes of the 5th and 7th harmonics after compensation by the pulse delay compensation method based on ripple prediction provided by the present invention are 0.02 A and 0.009 A respectively, indicating that the pulse delay compensation method based on ripple prediction provided by the present invention is significantly superior to the traditional fixed-time dead zone compensation method and has a good compensation effect.

[0082] Although the above-described illustrative specific embodiments of the present invention have been described to facilitate the understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the concept of the present invention are within the scope of protection.

Claims

1. A three-level inverter pulse delay compensation system based on ripple prediction, Characterized in that, Comprising: A current sampling module, a bridge arm current ripple prediction module, a bridge arm voltage edge delay calculation module, and a control signal compensation module; The input end of the current sampling module is connected to the output end of the three-level inverter and is used to collect the low-frequency current \(i_{x}\) of each phase leg of the three-level inverter, where \(x = a, b, c\) represents three phases. x , where \(x = a, b, c\) represents three phases. The bridge arm current ripple prediction module includes a duty cycle calculation unit, a segmented time calculation unit, and a current high-frequency ripple prediction unit connected in sequence; Among them, the duty cycle calculation unit performs current feedback control on the received low-frequency current i x to obtain the modulation voltages u of each phase x , and then calculates the real-time duty cycle d of each phase of the three-level inverter according to the modulation voltage u x ; x ; The segmented time calculation unit first determines the initial positions of the edges of the PWM signals of each phase of the three-level inverter according to the real-time duty cycle d x and then segments the current switching period based on the initial positions of the edges of the PWM signals of each phase to obtain the action time t of each segment k , where k represents the number after segmentation of the current switching period; The current high-frequency ripple prediction unit calculates the current ripple slope within each segment based on the voltage value and inductance value acting on each phase inductor L x and then predicts the high-frequency ripple current i k (k) within each segment of the current switching period according to the action time t ripple of each segment and the current ripple slope; The first input terminal of the bridge arm voltage edge delay calculation module is connected to the current sampling module, and the second input terminal is connected to the output terminal of the bridge arm current ripple prediction module; the high-frequency ripple current i ripple (k) within each segment is superimposed on the low-frequency current i x , and then the bridge arm current i rise corresponding to the rising edge moment of the bridge arm voltage and the bridge arm current i fall corresponding to the falling edge moment are screened out from the superimposed result. Then, i rise and i fall are substituted into the bridge arm voltage switch edge delay function to calculate the rising edge delay compensation time and the falling edge delay compensation time The control signal compensation module online corrects the initial positions of the edges of the PWM signals of each phase within the current switching period according to the delay compensation times of the rising edge and the falling edge of the bridge arm voltage, so as to realize the pulse delay compensation of the three-level inverter.

2. A three-level inverter pulse delay compensation method based on ripple prediction, Characterized in that, Comprising the following steps: (1), Establish a bridge arm voltage switch edge delay function; Among them, and are the delay compensation times of the rising edge and the falling edge of the arm voltage respectively, T d is the dead time, t on and t off are the turn-on time and the turn-off time of the arm respectively, i rise and i fall are the arm currents corresponding to the rising edge time and the falling edge time of the arm voltage; (2) The low-frequency current \(i\) of each phase leg of the three-level inverter is collected through the current sampling module, where \(x = a, b, c\) represents three phases. x ​ (3) The low-frequency current i is subjected to current feedback control by a duty cycle calculation unit x to obtain the modulation voltage u of each phase x . Then, based on the modulation voltage u x the real-time duty cycle d of each phase of the three-level inverter is calculated x ; (4) Determine the initial positions of the edges of the PWM signals of each phase of the three-level inverter according to the real-time duty cycle d x Determine the initial positions of the edges of the PWM signals of each phase of the three-level inverter, mark the zero moment, the end moment of the current switching period, as well as the rising edge moment and the falling edge moment of each phase PWM signal, sort all the marked moments in ascending order, and take the interval between two adjacent moments after sorting as a segment to obtain the action time t of each segment k , where k represents the number after segmentation of the current switching period; (5) Calculate the current ripple slope within each segment based on the voltage value and inductance value acting on each phase inductor L x ; Among them, f k represents the current ripple slope within the k-th segment, represents the voltage value acting on the inductor of the x-th phase within the k-th segment, L x represents the inductance value of the x-th phase, v xO (k) represents the bridge arm output voltage of the x-th phase within the k-th segment, v x represents the load voltage of the x-th phase within the current switching period, v NO (k) represents the common-mode voltage within the k-th segment; (6), Predict the high-frequency ripple current in each segment of the current switching period; i ripple (k) = i ripple (k - 1)+f k t k where i ripple (k) represents the high-frequency ripple current at the end of the k-th segment. The high-frequency ripple current value at the initial moment of each switching period is 0, and t k is the operating time of the k-th segment; (7) Superimpose the high-frequency ripple current i ripple (k) within each segment on the low-frequency current i x , and select the arm current i rise corresponding to the rising edge moment of the arm voltage and the arm current i fall corresponding to the falling edge moment from the superimposed result; (8), Substitute i rise and i fall into the bridge arm voltage switch edge delay function established in step (1) to calculate the delay times of the rising edge and falling edge of the bridge arm voltage and (9) Insert a dead time T at the initial position of the edges of each phase PWM signal d , and then move the switching positions in the first half cycle forward as a whole Move the switching positions in the second half cycle forward as a whole to compensate for the delay between the bridge arm voltage power pulse and each phase PWM signal caused by the dead time and the device turn-on and turn-off time, so as to realize the synchronous control of all bridge arm voltage pulses.

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