Three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode

Abstract

The invention discloses a three-phase hybrid rectifier model predictive current control method based on a variable exponential sliding mode. An inner ring active rectifier adopts a rapid optimal three-vector model predictive controller; the inner ring passive rectifier adopts a three-order extended state observer-model prediction controller; and a voltage outer loop adopts variable exponential reaching law sliding mode control. According to the method, the variable exponential reaching law sliding mode control can effectively restrain violent buffeting caused by large gain. The fast optimal three-vector model predictive controller can determine the optimal vector combination through only two times of optimization, so that the calculation complexity is greatly reduced. According to the input voltage observation method based on the third-order extended state observer, the number of used sensors is reduced, and meanwhile the input current quality is improved. The research of the method has important significance for improving the reliability of the industrial equipment power supply.

Description

Technical Field

[0001] The invention relates to the technical field of three-phase hybrid rectifier control, and in particular to a three-phase hybrid rectifier model prediction current control method based on variable exponential sliding mode. Background Art

[0002] Three-phase hybrid rectifiers have attracted widespread attention due to their simple structure, unity power factor operation, high power density and low harmonic content. Compared with single active rectifiers, three-phase hybrid rectifiers can load larger power and are more efficient, reliable and economical.

[0003] The three-phase hybrid rectifier is composed of an active rectifier module and a passive rectifier module in parallel. When the three-phase hybrid rectifier is running, the input current of the passive rectifier module (Three-phase Diode Rectifier, TDR) and the active rectifier module (Three-phase Active Rectifier, TAR) are combined into a sinusoidal current synchronized with the grid voltage. The load power is shared by the two rectifier modules, which not only reduces the rated load and loss of each device, but also reduces the system volume by sharing the DC side capacitor, thereby improving efficiency and power density.

[0004] In the traditional single vector model predictive control, the current values ​​corresponding to the six non-zero switching vectors are calculated by traversing, and the switching vector with the smallest error is selected to act on the system using the cost function. However, the problem with this method is that the error between the selected action vector and the reference voltage vector is large, which affects the control effect. In addition, when the prediction equation is used for control in the actual control system, a one-step delay problem will occur. This problem will cause errors in the model prediction and affect the control effect. Summary of the invention

[0005] In order to improve the stability and dynamic performance of the three-phase hybrid rectifier, the present invention provides a three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode. Among them, the variable exponential reaching law sliding mode control can effectively suppress the violent jitter caused by large gain. The fast optimal three-vector model predictive controller can determine the optimal vector combination by only two optimizations, which greatly reduces the computational complexity. The input voltage observation method based on the third-order extended state observer reduces the number of sensors used and improves the quality of the input current. The research on this method is of great significance to improving the reliability of the power supply for industrial equipment.

[0006] The technical solution adopted by the present invention is:

[0007] Model predictive current control method for three-phase hybrid rectifier based on variable exponential sliding mode,

[0008] The inner loop active rectifier uses a fast optimal three-vector model predictive controller;

[0009] The inner loop passive rectifier adopts a third-order extended state observer-model predictive controller;

[0010] The voltage outer loop adopts variable exponential reaching law sliding mode control.

[0011] The fast optimal three-vector model predictive controller includes the following calculation steps:

[0012] Step (1): Calculate the corresponding optimal voltage vector through the reference current, as shown in the following formula:

[0013]

[0014] Where: u d (k) is the optimal voltage vector of the d-axis in the dq coordinate system at time k; u q (k) is the optimal voltage vector of the q axis at time k; i d1 (k) and i d1 (k+1) are the calculated values ​​of the active rectifier d-axis current at time k and k+1, respectively. d1 (k+1) Use the outer loop control signal instead; i q1 (k) and i q1 (k+1) are the calculated values ​​of the active rectifier q-axis current at time k and k+1, respectively. q1 (k+1) is set to 0; T S is the sampling period; u gd (k) and u gq (k) are the grid voltages of the d-axis and q-axis respectively; ω is the grid angular frequency; L 1 Represents the filter inductance at the front end of the active rectifier;

[0015] Step (2): Transform the optimal voltage vector to the αβ coordinate system. The transformation formula is:

[0016]

[0017] Where: θ is the phase information of the grid voltage; u α (k) and u β (k) is the value of the voltage vector calculated in step (1) transformed into the αβ coordinate system; u d (k) and u q (k) is the optimal vector in the dq coordinate system calculated in step (1).

[0018] Step (3): Through u α (k) and u β (k) Determine the sector position of the optimal voltage vector:

[0019] Assume that the angle between the optimal voltage vector and the α axis is η:

[0020]

[0021] Counting counterclockwise from 0°, there is one sector every 60°, for a total of 6 sectors.

[0022] Step (4): Calculate the three voltage vectors V at the sector where the optimal voltage vector is located i , V j and V 0 The duration of action;

[0023]

[0024] Where: S xi ,S xj ,S x0 is the voltage vector V i , V j and V 0 The rate of change of current during action, x = d, q; t i , t j and t 0 are the action time of the three voltage vectors respectively; i dr and i qr are the d-axis and q-axis current reference values ​​respectively; T s is the sampling period. Step (5): Perform switch control through SVPWM modulation.

[0025] The weight function of the third-order extended state observer-model predictive controller is:

[0026]

[0027] Where: F is the weight function; is the predicted inductor current reference value of the passive rectifier at the k+1th moment; i D (k+1) is the predicted value of the inductor current of the passive rectifier at the k+1th moment; ζ is the weight coefficient of the duty cycle, which is 0.6 here; d(k+1) is the duty cycle at the k+1th moment; d prev (k+1) is the duty cycle reference value at the k+1th moment. The weight function calculates the difference between the inductor current and the reference value under two switching conditions of the passive rectifier, and determines the switching state of the passive rectifier at the next moment in combination with the duty cycle weight coefficient.

[0028] In the third-order extended state observer-model predictive controller:

[0029] The predicted value of the inductor current of the passive rectifier at the k+1th moment i D (k+1) is calculated by the following formula:

[0030] i D (k+1)=T S / L 22 ×(0.5U D (k)-R 22 i D (k)-0.5(1-d)u dc (k))+i D (k);

[0031] Where: L 22 is the boost inductance value of the passive rectifier; R 22 is the equivalent resistance of the boost inductor; U D (k) is the grid voltage after the uncontrolled rectifier bridge, which is obtained from the third-order extended state observer get;i D (k) is the inductor current of the passive rectifier; d is the duty cycle of the passive rectifier; u dc (k) DC side voltage sampling value.

[0032] The equation of the third-order extended state observer is:

[0033]

[0034] Where: are the observed value of the passive rectifier inductor current, the observed value of the input voltage and the bounded disturbance respectively; l 1 , l 2 , l 3 is the third-order extended observer gain; L 22 is the boost inductance value of the passive rectifier; R 22 The equivalent resistance of the passive rectifier boost inductor. dc Indicates the DC side voltage. d indicates the duty cycle. i D Inductor current.

[0035] The third-order extended observer gain is:

[0036]

[0037] Where: ω is the observer cutoff angular frequency, ω = 628 rad / s.

[0038] In the voltage outer loop variable exponential reaching law sliding mode control:

[0039] The sliding mode controller is designed as:

[0040] i=u dc / R L +C(-k 0 S-((2 |S| / (2|S| +1)-0.5)ε 0 +λρ)sign(S)-e) / λ

[0041] Where: i represents the output signal of the sliding mode controller. dc is the DC side voltage sampling value. L is the load resistance value. C is the DC side capacitance value. k 0 is the exponential gain, ε 0 is the switching gain. λ is the control gain. 0<ρ<1 is the error boundary. e is the difference between the DC voltage and the reference voltage;

[0042] sign(S) is the sign function, S represents the sliding surface, when S ≥ 0, sign(S) = 1, when S ≤ 0, sign(S) = 0. The output of the sliding mode controller is multiplied by the control coefficient k 1 and k 2 As the reference value of the current inner loop.

[0043] The variable exponential reaching law is:

[0044]

[0045] in: represents the derivative of S; k 0 , ε 0 Both represent control gain, k 0 >0,ε 0 >0; e is the difference between the DC bus voltage and the reference voltage; S is the sliding surface; sign(S) is the sign function, if the variable in the brackets is greater than 0, sign(S) = 1; if the variable in the brackets is less than 0, sign(S) = -1; if the variable in the brackets is equal to 0, sign(S) = 0.

[0046] In the voltage outer loop variable exponential reaching law sliding mode control:

[0047] When the difference between the load voltage and the reference voltage increases, the parameter k 0 The main function of k is to make the DC load voltage quickly approach the reference value; when it reaches the reference value, k 0 S is approximately 0, then the variable exponential reaching law Play a leading role.

[0048] Since 2 in the second part of the variable exponential reaching law |S| / (2 |S| +1)-0.5 is variable. When the error between the DC load voltage and the reference voltage is zero, the variable exponential approach law Therefore, the variable exponential reaching law can reduce the jitter in the output signal of the voltage outer loop sliding mode controller, especially in the gain ε0 The present invention provides a three-phase hybrid rectifier control method based on current model prediction-sliding mode control, and the technical effects are as follows:

[0049] 1) The hybrid rectifier control method of the present invention can reduce the change of DC voltage when the load changes suddenly to a certain extent when dealing with load disturbances, and has a faster response speed, so that the DC side output voltage can quickly return to a stable state.

[0050] 2) The hybrid rectifier control method of the present invention can effectively reduce the THD of the total input current on the AC side and enable the system to operate stably at a unity power factor.

[0051] 3) In the present invention, the fast optimal three-vector model predictive control can effectively reduce the computational loss.

[0052] 4) In the present invention, the third-order extended state observer can reduce the use of sensors and effectively reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention will be further described below in conjunction with the accompanying drawings and examples;

[0054] Figure 1 This is the topological structure diagram of the three-phase hybrid rectifier.

[0055] Figure 2 Process diagram for fast optimal three-vector model predictive control of active rectifier.

[0056] Figure 3 This is the principle block diagram of the sliding mode controller.

[0057] Figure 4 A block diagram of the current control prediction for a three-phase hybrid rectifier model based on variable exponential sliding mode.

[0058] Figure 5 A schematic diagram of the operating power factor of an example implementation of the present invention.

[0059] Figure 6 A schematic diagram of an input current waveform implemented in an example of the present invention.

[0060] Figure 7 This is a schematic diagram of the DC side load sudden voltage waveform implemented in an example of the present invention. DETAILED DESCRIPTION

[0061] Figure 1 is the topological structure diagram of the three-phase hybrid rectifier. ga ,u gb ,u gc is the three-phase input voltage on the grid side; i a ,i b ,i cis the three-phase input current on the grid side; L 1 is the filter inductor at the front end of the active rectifier, R 1 is the equivalent resistance of the filter inductor; S j (j=1,2,...,6) is the switch tube of the active rectifier; L 21 is the filter inductor at the front end of the passive rectifier, R 21 is the equivalent resistance of the filter inductor; L 22 is the boost inductor of the passive rectifier, R 22 is the equivalent resistance of the boost inductor; S 7 It is the switch tube of the passive rectifier; u dc is the DC side load voltage; i dc is the DC side load current; R L is the load resistance; C is the DC side filter capacitor.

[0062] The active rectifier is connected to the power grid through three inductors. According to Kirchhoff's voltage law, the mathematical model of the active rectifier can be obtained by writing the loop equation:

[0063]

[0064] Convert equation (1) to the two-phase rotating coordinate system:

[0065]

[0066] In formula (2): i d1 ,i q1 i a1 ,i b1 ,i c1 On the dq0 axis there is the input current of the active rectifier; u gd ,u gq u ga ,u gb ,u gc The grid voltage on the dq0 axis; u d =S d u dc ,u q =S q u dc ω is the grid angular frequency.

[0067] The mathematical model of the passive rectifier in the three-phase stationary coordinate system is:

[0068] L 22 d D / dt=0.5U D -R 22 i D -0.5(1-d)u dc (3);

[0069] In formula (3), U D is the equivalent DC power supply output by the diode rectifier bridge; i D is the output current of the uncontrolled rectifier bridge; d is the duty cycle.

[0070] The common capacitance on the DC side can be obtained from Kirchhoff's current law.

[0071] i=i 1 +i 2 =Cdu dc / dt+u dc / R L (4);

[0072] Figure 2 This is the process diagram of the fast optimal three-vector model predictive control of the active rectifier. After discretization of equations (2) and (3), we get:

[0073]

[0074] i D (k+1)=T S / L 22 ×(0.5U D (k)-R 22 i D (k)-0.5(1-d)u dc (k))+i D (k) (6);

[0075] Where: T s is the sampling time. In addition, the sampling period is much smaller than the grid voltage period, so the discrete values ​​of the grid voltage in adjacent periods are approximately equal;

[0076] u g (k+1)=u g (k) (7);

[0077] In formula (5), i d1 (k) and i q1 (k) is the sampled value of the active rectifier input current after dq transformation. In this process, the main function of the active rectifier is to control its input current to be sinusoidal and in phase with the grid voltage. However, the input current of the passive rectifier is a rectangular wave. At this time, the total input current can be expressed by equation (8):

[0078] i x =i x1 +i x2 (8);

[0079] The total input current will be significantly distorted after the input currents of two parallel rectifiers are superimposed. In order to solve this problem, the present invention adjusts the current sampling value of the active rectifier to the total input current, thereby changing its control target to achieve sinusoidalization of the total input current. That is, it is ensured that after the input current of the active rectifier is superimposed with the input current of the passive rectifier, the total input current can still maintain an ideal sinusoidal waveform.

[0080] For active rectifiers, three-vector model predictive control can significantly reduce the error between the output control voltage vector and the reference voltage vector within one control cycle, thereby improving the control accuracy and performance of the system.

[0081] The u in formula (5) d (k) and u q (k) Move to the left side of the equation:

[0082]

[0083] In formula (9), u d (k) is the optimal voltage vector of the d-axis in the dq coordinate system at time k, u q (k) is the optimal voltage vector of the q axis at time k. d1 (k) and i d1 (k+1) are the calculated values ​​of the active rectifier d-axis current at time k and k+1, respectively. d1 (k+1) is replaced by the outer loop control signal. Similarly, i q1 (k) and i q1 (k+1) are the calculated values ​​of the active rectifier q-axis current at time k and k+1, respectively. q1 (k+1) is set to 0. T S is the sampling period, u gd (k) and u gq (k) are the grid voltages of the d-axis and q-axis respectively, and ω is the grid angular frequency.

[0084] By transforming equation (9) to the αβ coordinate system, we can solve u α (k) and u β (k) can be compared once to get the sector where the optimal vector is located, and get two non-zero voltage vectors. When the three vectors act, it is necessary to solve the action time of the three vectors. Suppose the two constant vectors are V i and V j , the zero vector is V 0 , the action time is t i , t i , t 0 The formula for predicting current is:

[0085]

[0086] In formula (10), S xi ,S xj ,S x0 (x=d,q) is the vector V i , V j and V 0 The current change rate during action. Substituting the three vectors into equation (2) and connecting them in parallel with equation (10) can give the action time of the three vectors.

[0087]

[0088] Finally, combining modulation for switch control can effectively reduce the calculation time.

[0089] In formula (6), U D (k) is the rectified voltage of the three-phase uncontrolled rectifier bridge, so the prediction model of the passive rectifier requires information about the input voltage. Therefore, a third-order extended state observer is designed to observe the input voltage and reduce the use of additional sensors. The third-order extended state observer equation is:

[0090]

[0091] Where: are the observed value of the passive rectifier inductor current, the observed value of the input voltage and the bounded disturbance. 1 , l 2 , l 3 is the observer gain, and the observer gain is:

[0092]

[0093] Where: ω is the observer cutoff angular frequency.

[0094] After discretizing equation (12), the inductor current prediction formula after the observer can be obtained from equation (6) and equation (12).

[0095]

[0096] The weight function of the passive rectifier is:

[0097]

[0098] Where: ζ is the weight coefficient of the duty cycle, which is 0.6 here. D is the predicted inductor current for the passive rectifier.

[0099] In addition, when using prediction equations for control in actual control systems, there will be a one-step delay problem. This problem will cause errors in model prediction and affect the control effect. In order to solve this delay problem, the k+2th prediction value obtained by the model is usually used instead of the k+1th prediction value.

[0100] Fast optimal three-vector model predictive control by directly solving u α (k) and u β (k) The number of optimization searches of the system is reduced, and the optimal vector can be obtained through only two optimization searches. In addition, the three vectors acting on the control can synthesize vectors in any direction, which is superior to the single-vector model predictive control in terms of the number of optimization searches and the control effect of the voltage vector, greatly reducing the calculation loss. The third-order extended state observer model predictive control can reduce the use of sensors and improve the quality of the input current to a certain extent.

[0101] Figure 3 The schematic diagram of the sliding mode controller is shown in Figure 2. The control variable is defined as the DC bus voltage error, and the sliding surface expression is as follows:

[0102] e=u dc -U dc.ref (16);

[0103] S V =a 1 e+a 2 ∫edt (17);

[0104] Where: U dc.ref is the DC side voltage reference value. When reaching the sliding surface, we can get:

[0105] S V =λe+∫edt=0 (18);

[0106] Where: λ = a 1 / a 2 , and λ is a positive constant, which can adjust the control performance such as the time to reach steady state, steady state error and overshoot.

[0107] By taking the derivative of formula (17), we can get:

[0108]

[0109] Where: λ = a 1 / a 2 ;

[0110] From formula (4), we can get:

[0111]

[0112] Where: d represents udc The uncertain perturbation in . Let d be bounded by |d|≤ρ<1, where ρ is a given positive constant.

[0113] In order to reduce the chattering near the sliding surface, the sliding mode controller is designed using the variable exponential reaching law:

[0114]

[0115] When the system is far away from the sliding surface, the parameter k 0 The main function of is to make the system quickly approach the reference value. When it reaches the reference value, k 0 S is approximately 0, and the second term plays a leading role. Since the parameter of the second term is variable, when the system error is zero, the parameter of the second term will also be equal to zero. Therefore, the variable exponential reaching law can prevent the system from chattering near the sliding surface.

[0116] Therefore, the sliding mode controller can be set as:

[0117] i=u dc / R L +C(-k 0 S-((2 |S| / (2 |S| +1)-0.5)ε 0 +λρ)sign(S)-e) / λ (22);

[0118] Where: ε 0 represents the control gain, and ε 0 >0; sign(S) is the sign function, when S≥0, sign(S)=1, when S≤0, sign(S)=0.

[0119] Figure 4 The current control block diagram of the three-phase hybrid rectifier model prediction based on variable exponential sliding mode. The circuit parameters tested by the present invention are mainly: the front-end filter inductance of the active rectifier is 5mH; the front-end filter inductance of the passive rectifier is 0.4mH, and the DC side boost inductance is 20mH; the DC side reference voltage is 700V, the capacitor is 1100μF, and the load is 120Ω. The equivalent resistance value of each inductor is small. The power distribution of the present invention is multiplied by the control coefficient k after modifying the output of the outer loop sliding mode control 1 ,k 2 to make modifications.

[0120] Figure 5 The schematic diagram of the operating power factor of the embodiment of the present invention is as follows: The method of the present invention can make the three-phase hybrid rectifier operate continuously under the condition of power factor cosφ≥0.998.

[0121] Figure 6This is a schematic diagram of an input current waveform implemented in an example of the present invention. a is the total input current, which is composed of the input current of the active rectifier and the passive rectifier; i a1 is the input current of the active rectifier; i a2 is the input current of the passive rectifier. Connecting a filter inductor in series at the front end of the passive rectifier can effectively suppress the periodic current spikes of the passive rectifier input current.

[0122] Figure 7 This is a schematic diagram of the DC side load sudden voltage waveform implemented in the example of the present invention. At t = 0.3s, the load changes from 120Ω at the beginning of the simulation to 60Ω, at which time the bus voltage drops by about 12V and returns to a stable state after 0.6s. At t = 0.5s, the load changes from 60Ω to 120Ω, the voltage increases by 12V, and returns to a stable state after 0.6s.

[0123] The present invention discloses a model predictive current control method for a three-phase hybrid rectifier based on a variable exponential sliding mode. The model predictive control can effectively improve the control accuracy, stability and robustness of the system by predicting the future behavior of the system and optimizing the control strategy. The application of model prediction in the rectifier can accurately adjust the output voltage and current, reduce fluctuations and ensure stable operation of the system when the load changes or the input fluctuates. Model prediction can also handle constraints such as voltage and current to ensure that the equipment operates within a safe range, while coordinating multivariable control and optimizing the overall performance of the rectifier. In addition, model prediction can dynamically adapt to load changes and external disturbances, improve the adaptability and anti-interference ability of the system, thereby significantly improving the efficiency and reliability of the rectifier.

Claims

1. A three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode, characterized in that: The inner loop active rectifier uses a fast optimal three-vector model predictive controller; The inner loop passive rectifier adopts a third-order extended state observer-model predictive controller; The voltage outer loop adopts variable exponential reaching law sliding mode control.

2. The three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode according to claim 1 is characterized in that: The fast optimal three-vector model predictive controller includes the following calculation steps: Step (1): Calculate the corresponding optimal voltage vector through the reference current, as shown in the following formula: Where: u d (k) is the optimal voltage vector of the d-axis in the dq coordinate system at time k; u q (k) is the optimal voltage vector of the q axis at time k; i d1 (k) and i d1 (k+1) are the calculated values ​​of the active rectifier d-axis current at time k and k+1 respectively; i q1 (k) and i q1 (k+1) are the calculated values ​​of the active rectifier q-axis current at time k and k+1 respectively; T S is the sampling period; u gd (k) and u gq (k) are the grid voltages of the d-axis and q-axis respectively; ω is the grid angular frequency; L1 represents the filter inductance at the front end of the active rectifier; Step (2): Transform the optimal voltage vector to the αβ coordinate system. The transformation formula is: Where: θ is the phase information of the grid voltage; u α (k) and u β (k) is the value of the voltage vector calculated in step (1) transformed into the αβ coordinate system; u d (k) and u q (k) is the optimal vector in the dq coordinate system calculated in step (1); Step (3): Use u α (k) and u β (k) Determine the sector position of the optimal voltage vector: Assume that the angle between the optimal voltage vector and the α axis is η: Step (4): Calculate the three voltage vectors V at the sector where the optimal voltage vector is located i , V j and V0 action time; Where: S xi ,S xj ,S x0 is the voltage vector V i , V j The current change rate when V0 acts, x = d, q; t i , t j and t0 are the action times of the three voltage vectors respectively; i dr and i qr are the d-axis and q-axis current reference values ​​respectively; T s is the sampling period; Step (5): Perform switching control through SVPWM modulation.

3. The three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode according to claim 1, characterized in that: The weight function of the third-order extended state observer-model predictive controller is: Where: F is the weight function; is the predicted inductor current reference value of the passive rectifier at the k+1th moment; i D (k+1) is the predicted value of the inductor current of the passive rectifier at the k+1th moment; ζ is the weight coefficient of the duty cycle; d(k+1) is the duty cycle at the k+1th moment; d prev (k+1) is the duty cycle reference value at the k+1th moment.

4. The three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode according to claim 1, characterized in that: In the third-order extended state observer-model predictive controller: The predicted value of the inductor current of the passive rectifier at the k+1th moment i D (k+1) is calculated by the following formula: i D (k+1)=T S / L 22 ×(0.5U D (k)-R 22 i D (k)-0.5(1-d)u dc (k))+i D (k); Where: L 22 is the boost inductance value of the passive rectifier; R 22 is the equivalent resistance of the boost inductor; U D (k) is the grid voltage after the uncontrolled rectifier bridge, which is obtained from the third-order extended state observer get;i D (k) is the inductor current of the passive rectifier; d is the duty cycle of the passive rectifier; u dc (k) DC side voltage sampling value.

5. The three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode according to claim 4 is characterized in that: The equation of the third-order extended state observer is: Where: are the observed value of the passive rectifier inductor current, the observed value of the input voltage and the bounded disturbance respectively; l1, l2, l3 are the third-order extended observer gains; L 22 is the boost inductance value of the passive rectifier; R 22 The equivalent resistance of the passive rectifier boost inductor; u dc represents the DC side voltage; d represents the duty cycle; i D Inductor current.

6. The three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode according to claim 5, characterized in that: The third-order extended observer gain is: Where: ω is the observer cutoff angular frequency.

7. The three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode according to claim 1, characterized in that: In the voltage outer loop variable exponential reaching law sliding mode control: The sliding mode controller is designed as: i=u dc / R L +C(-k0S-((2 |S| / (2 |S| +1)-0.5)ε0+λρ)sign(S)-e) / λ Where: i represents the output signal of the sliding mode controller; u dc is the DC side voltage sampling value; R L is the load resistance value; C is the DC side capacitance value; k0 is the exponential gain, ε0 is the switching gain; λ is the control gain; 0<ρ<1 is the error boundary; e is the difference between the DC side voltage and the reference voltage; sign(S) is a sign function, S represents the sliding surface, when S≥0, sign(S)=1, when S≤0, sign(S)=0; the output of the sliding mode controller is multiplied by the control coefficients k1 and k2 respectively as the reference value of the current inner loop.

8. The three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode according to claim 7, characterized in that: The variable exponential reaching law is: in: represents the derivative of S; k0 and ε0 represent control gains, k0>0, ε0>0; e is the difference between the DC bus voltage and the reference voltage; S is the sliding surface.

9. The three-phase hybrid rectifier model predictive current control method based on variable exponential sliding mode according to claim 8, characterized in that: In the voltage outer loop variable exponential reaching law sliding mode control: When the difference between the load voltage and the reference voltage increases, the function of parameter k0 is to make the DC load voltage quickly approach the reference value; When it reaches the reference value, k0S is approximately 0. Play a leading role; Since 2 in the second part of the variable exponential reaching law |S| / (2 |S| +1)-0.5 is variable. When the error between the DC load voltage and the reference voltage is zero, the variable exponential approach law The part will also be equal to zero; therefore, the variable exponential reaching law can reduce the jitter existing in the output signal of the voltage outer loop sliding mode controller, especially when the gain ε0 is large.

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