A virtual flux model predictive power control strategy based on OSS

Abstract

A virtual flux model prediction direct power control strategy based on OSS, specifically: Step 1, collect the switching state of the power device and the DC side voltage U dc , and obtain the rectifier output phase voltage in the αβ coordinate system. Step 2, calculate the virtual flux Ψ in the αβ coordinate system α ,Ψ β Step 3: Collect the grid-side current i in the αβ coordinate system α 、i β , combined with α ,Ψ β Calculate the instantaneous active power p and reactive power q, and get the change rate of p and q. Step 4: Determine the OSS switching sequence of each sector. Step 5: Use the instantaneous change rate of power to predict the instantaneous power of each OSS switching sequence. And minimize the cost function to get the optimal switching sequence. Step 6: Use the optimal switching sequence and the optimal voltage vector action time T op Calculate the output duty cycle d op The invention solves the problem of large error in model prediction of grid-side current and unstable switching frequency, and eliminates the need for an AC voltage sensor, thus reducing costs.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics and relates to a virtual flux linkage model prediction direct power control strategy based on OSS. Background Art

[0002] As people pay more and more attention to the ecological environment, higher requirements are placed on the utilization of clean energy. Three-phase voltage source rectifier (VSR) plays a vital role in energy, industry and other fields due to its advantages of high power factor, controllable DC side voltage and four-quadrant operation. For example, converter stations, static VAR generators and mining inverters in high-voltage DC transmission systems.

[0003] However, the widespread application of VSR has made people increasingly pursue more reliable, fast and efficient performance. After decades of research, a wide variety of power converter control methods have been developed, which can be roughly divided into linear control represented by voltage-oriented vector control (VOC) and virtual flux-oriented control (VFOC) and nonlinear control represented by model predictive control (MPC) and direct power control (DPC). VOC transforms the current in the three-phase static abc coordinate system of the AC side into d-axis and q-axis currents through synchronous rotating coordinate transformation based on the AC side voltage phase information, and then obtains the reference values ​​of the d-axis current and q-axis current through the DC voltage outer loop and power loop, and sends them to the PI controller for adjustment, thereby achieving better steady-state control. However, in practical applications, the complexity of PI controller parameter adjustment and its slow dynamic response have limited its development prospects. Based on VOC and with some improvements, VFOC was developed. Its basic principle is to virtually equate the VSR AC side voltage and filter elements to an AC motor. After passing through the integration link, the AC side voltage can be regarded as the virtual flux vector of the motor, and the phase information of the AC voltage can be obtained based on the virtual flux vector. Since the integration link has a low-pass filtering characteristic, VFOC not only has the advantage of eliminating the voltage sensor, but also has a good suppression effect on AC voltage interference signals.

[0004] The traditional model-predictive direct power control strategy with optimal switching sequence based on voltage sensor has poor anti-interference performance against AC side voltage distortion, high grid-side current harmonic content, large rectifier size, high manufacturing cost and other defects, which affect the reliability and stability of the system. Summary of the invention

[0005] The purpose of the present invention is to provide a virtual flux model prediction power control strategy based on OSS, which solves the problems of large current prediction error and unstable switching frequency in the model predictive control in the prior art. The virtual flux orientation is used to improve the robustness of the three-phase voltage type rectifier to the AC side disturbance voltage, and the AC voltage sensor is eliminated to reduce the cost.

[0006] The technical solution adopted by the present invention is a power control strategy based on the virtual flux model prediction of OSS, which is implemented in the following steps:

[0007] Step 1: Collect the switch status S of the power switch device a , S b , S c and DC side voltage U dc And the rectifier output phase voltage in the two-phase stationary coordinate system is expressed through coordinate transformation.

[0008] Step 2: Collect the three-phase AC current i on the grid side a 、i b 、i c , and transform it into i in the two-phase stationary coordinate system through coordinate transformation α 、i β The filter inductor L, filter resistor R and AC voltage vector E on the AC side of the voltage-type rectifier are equivalent to a virtual motor, and the virtual flux Ψ in the αβ coordinate system is calculated. α ,Ψ β .

[0009] Step 3: Combine α ,Ψ β The instantaneous active power p and reactive power q are calculated, and the rates of change of p and q are obtained.

[0010] Step 4: Divide the αβ coordinate system into 6 sectors, each sector is described by a voltage vector sequence consisting of 8 corresponding known voltage vectors. The corresponding relationship between the switch state of the voltage source rectifier VSR and the output voltage is obtained. At the same time, the optimal switching sequence OSS of the voltage vector of each sector is determined.

[0011] Step 5: Use the instantaneous rate of change of power to predict the instantaneous power corresponding to the ith voltage vector in the voltage vector sequence. And use the cost function on power to obtain an optimal voltage vector sequence corresponding to a set of instantaneous powers that minimizes the cost function value.

[0012] Step 6: Use the optimal switching sequence OSS and the optimal voltage vector action time T op Calculate the optimal output duty cycle d op, compare the duty cycle with the triangular carrier, obtain the switching state under the voltage optimal switching sequence and act on the power switching device.

[0013] The present invention is also characterized in that

[0014] Step 1 is as follows:

[0015] Collect the switching state S of the power switching device a , S b , S c and DC side voltage U dc , and the rectifier a, b, c phase output voltage u is obtained ra 、u rb 、u rc ,get:

[0016]

[0017] Where: U dc is the DC voltage, u ra 、u rb 、u rc is the rectifier a, b, c phase output voltage.

[0018] And the rectifier output phase voltage in the two-phase stationary coordinate system is expressed by coordinate transformation, which are:

[0019]

[0020] Where: u rα 、u rβ It is the component of the output phase voltage of the voltage source rectifier VSR in the αβ coordinate system.

[0021] Step 2 is as follows:

[0022] Collect the three-phase AC current i on the grid side a 、i b 、i c , and transform it into i in the two-phase stationary coordinate system through coordinate transformation α 、i β According to Kirchhoff's voltage law and combined with the virtual flux VF directional principle diagram, the loop voltage equation of the VSR AC side in the αβ coordinate system can be obtained as follows:

[0023]

[0024] According to the definition of virtual magnetic flux, we can get the virtual magnetic flux Ψ α ,Ψ β The relationship between the AC side current and the VSR output phase voltage is:

[0025]

[0026] Where: L is the AC side filter inductor, R is the AC side filter resistor, i in the two-phase stationary coordinate system α 、i β .

[0027] Step 3 is as follows:

[0028] In the αβ coordinate system, since the complex power vector can be represented by the AC voltage vector and the AC current conjugate vector, the instantaneous active power p and reactive power q can be represented by virtual flux and current respectively:

[0029]

[0030] Where: c is the magnitude of the virtual flux vector.

[0031] Then the change rates dp / dt and dq / dt of instantaneous active power p and instantaneous reactive power q are respectively:

[0032]

[0033] Step 4 is as follows:

[0034] The αβ coordinate system is divided into 6 sectors, each sector is described by a voltage vector sequence consisting of 8 corresponding known voltage vectors. The 8 voltage vectors output by the VSR are defined as u r，x =u rα，x +ju rβ，x (x=0,1,…,7). And the corresponding relationship between the switch state of the voltage source rectifier VSR and the output voltage is obtained. The 8 different switch states S x Corresponding to 8 different space voltage vectors u r，x , except for two zero vectors, the remaining six non-zero vectors are evenly distributed in the αβ coordinate system. For any given spatial voltage vector, it can be represented by the synthesis of the remaining voltage vectors near the sector where it is located.

[0035] Depend on Figure 3 The optimal switching sequence OSS of the voltage vector can be determined. The voltage vector sequence assigned to each sector is defined as u sj = {u 1 ,u 2 ,u 3 ,u 4 ,u 4 ,u 3 ,u 2 ,u 1}(j=1, 2, ..., 6, indicating the sector number). The first four voltage vectors are arranged symmetrically with the last four. sis the voltage vector output by VSR. s When it falls in sector 1, u s Available s1 = {u r0 ,u r1 ,u r2 ,u r7 ,u r7 ,u r2 ,u r1 ,u r0 The voltage vector switching sequence OSS corresponding to different sectors is shown in Table 1.

[0036] Table 1

[0037]

[0038] According to the voltage vector switching sequence u in Table 1 sj It can accurately determine the corresponding relationship between the VSR output voltage vector and the sector in which it is located. sj The eight output voltage vectors in the equation are composed of four zero vectors and two pairs of identical non-zero vectors. The complex voltage vectors in the two αβ coordinate systems are composed of the voltage vectors u in Table 1. r，x express.

[0039] Step 5 is as follows:

[0040] Step 5.1, using the instantaneous rate of change of power, predict the instantaneous power corresponding to the i-th voltage vector in the voltage vector sequence. It can be concluded that under the action of a given VSR voltage vector, the change trajectory of active power p and reactive power q within the relevant action time is:

[0041] p i =p i-1 +f pi t ij

[0042] q i =q i-1 +f qi t ij

[0043] Where: {p i-1 ,q i-1} represents the initial value of active power and reactive power when the ith voltage vector starts to act in the voltage switching sequence. ij represents the voltage vector action time, and t 1j =t 4j =t 5j =t 8j , t 2j =t 7j , t 3j =t6j For the convenience of calculation, let t s0j =t 1j =t 4j =t 5j =t 8j , t s1j =t 2j =t 7j , t s2j =t 3j =t 6j , t s0j Represents the zero voltage vector action time; t s1j Represents the first effective voltage vector action time; t s2j Represents the second effective vector action time. i ,q i} represents the power value at the end of the voltage vector action time.

[0044] Step 5.2, and use the cost function for power to obtain the optimal voltage vector sequence corresponding to a set of instantaneous powers that can minimize the cost function value. In model predictive control, the cost function is often used to describe the desired system operating state, and the cost function is minimized to determine the optimal operation mode. The cost function for power in the control method proposed in this paper is expressed as:

[0045]

[0046] Where: p ref ,q ref are given active power and given reactive power respectively, p ref Given by the power voltage outer loop, since the VSR operates at unity power factor, q ref Set to 0.

[0047] Using the conditions that minimize the cost function, we can find t that minimizes the cost function. s0j ,t s1j ,t s2j , as shown below:

[0048]

[0049]

[0050] t s0j =(T s / 2-t s1i -t s2i ) / 2

[0051] Where: e pk =p ref -p k , e qk =qref -q k .

[0052] By traversing and solving the voltage vector sequences corresponding to 6 different sectors, the voltage switching sequence that minimizes the cost function can be obtained, which is defined as the optimal voltage vector sequence.

[0053] Step 6 is as follows:

[0054] The voltage vector sequence corresponding to the set of instantaneous powers that can minimize the cost function value is considered to be the optimal switching sequence (OSS), defined as u sj =u sop The sector j corresponding to the group of OSS is considered to be the optimal sector. sop The corresponding zero vector and two non-zero vector action times are t s0j ,t s1j ,t s2j , the optimal voltage vector action time is expressed as T op ={t s0op , t s1op , t s2op By calculating the time that the voltage vector in the optimal switching sequence OSS generates a high level, it accounts for the sampling period T s The ratio of can be used to obtain the optimal duty cycle d op , and its calculation formula is:

[0055]

[0056] Where: u sop (0),u sop (1) u sop (2) are the optimal voltage vector switching sequence u sop The zero voltage vector, the first effective vector and the second effective vector in S x represents the voltage vector u r,x The corresponding switching status of the three phases abc.

[0057] The beneficial effects of the present invention are:

[0058] The control strategy of the present invention is applied to the current three-phase two-level voltage type rectifier, the grid-side current harmonic content is smaller, the output DC voltage is more stable, the switching frequency is adjustable, the anti-interference ability to the AC side disturbance voltage is stronger, the AC voltage sensor is omitted, and the cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is the main circuit topology of three-phase voltage type rectifier VSR.

[0060] Figure 2 It is the schematic diagram of virtual flux orientation of three-phase voltage type rectifier VSR.

[0061] Figure 3 Output voltage vector and partition for three-phase voltage source rectifier VSR.

[0062] Figure 4 is a sampling period T s The p and q change trajectories are described by the symmetric 8-vectors.

[0063] Figure 5 It is a cross-compensation virtual flux observer.

[0064] Figure 6 This is the schematic diagram of the proposed control method.

[0065] Explanation of symbols and reference numerals in the accompanying drawings: L, R—filter inductance and resistance of the three-phase rectifier; C—capacitor on the DC side; e k (k=a,b,c)—three-phase stationary coordinate system grid voltage; e k (k=α, β)—two-phase stationary coordinate system grid voltage; i k (k=a,b,c)—grid-side current of three-phase stationary coordinate system; n—neutral point; i r —rectifier current; u dc —DC side voltage; i dc —DC side current; i L —DC side load current; i α 、i β —Grid-side current of two-phase stationary coordinate system; u r，k (k=a,b,c)—rectifier output phase voltage in three-phase stationary coordinate system; u r，k (k=α, β)—rectifier output phase voltage in two-phase stationary coordinate system; S k (k=a,b,c)—the switching state of the power switch device; e s —rectifier AC voltage; s —Virtual magnetic link; i s —AC side current; u rs —Rectifier output phase voltage; u r，x (x=0,1,2,3,4,5,6,7)—rectifier output basic voltage vector; S x (x=0,1,2,3,4,5,6,7)—8 switching states of the power switch device; u s —VSR output voltage vector; f pi (i=0,1,2,3,4,5,6,7)—active power change rate; f qi (i=0,1,2,3,4,5,6,7)—reactive power change rate; t s0j (j=1, 2, ..., 6, indicating the sector number)—zero voltage vector action time; ts1j (j=1, 2, ..., 6, indicating the sector number) - the first effective voltage vector action time; t s2j (j=1, 2, ..., 6, indicating the sector number) - the second effective voltage vector action time; p i (i=0,1,2,3,4,5,6,7)—active power value at the end of voltage vector action time; q i (i=0,1,2,3,4,5,6,7)—reactive power value at the end of voltage vector action time; ω c —cutoff frequency of the first-order low-pass filter; — estimated virtual flux vector; ψ — actual virtual flux vector; G i —cost function; U dc_ref —DC reference voltage; P ref —Active reference power; Q ref —Reactive reference power; S op —Optimal switching state; d op —Optimal duty cycle; T op —Optimal action time. DETAILED DESCRIPTION

[0066] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0067] The present invention provides a direct power control strategy based on eliminating the zero voltage vector switch table, which is specifically implemented according to the following steps:

[0068] Step 1: Collect the switch status S of the power switch device a , S b , S c and DC side voltage U dc , and the rectifier output phase voltage in the two-phase stationary coordinate system is expressed through coordinate transformation. Specifically:

[0069] Collect the switching state S of the power switching device a , S b , S c and DC side voltage U dc , and the rectifier a, b, c phase output voltage u is obtained ra 、u rb 、u rc ,get:

[0070]

[0071] Where: U dc is the DC voltage, u ra 、u rb 、u rc is the rectifier a, b, c phase output voltage.

[0072] And the rectifier output phase voltage in the two-phase stationary coordinate system is expressed by coordinate transformation, which are:

[0073]

[0074] Where: u rα 、u rβ It is the component of the output phase voltage of the voltage source rectifier VSR in the αβ coordinate system.

[0075] Step 2: Collect the three-phase AC current i on the grid side a 、i b 、i c , and transform it into i in the two-phase stationary coordinate system through coordinate transformation α 、i β The filter inductor L, filter resistor R and AC voltage vector E on the AC side of the voltage-type rectifier are equivalent to a virtual motor, and the virtual flux Ψ in the αβ coordinate system is calculated. α ,Ψ β Specifically:

[0076] Collect the three-phase AC current i on the grid side a 、i b 、i c , and transform it into i in the two-phase stationary coordinate system through coordinate transformation α 、i β According to Kirchhoff's voltage law and combined with the virtual flux VF directional principle diagram, the loop voltage equation of the VSR AC side in the αβ coordinate system can be obtained as follows:

[0077]

[0078] According to the definition of virtual magnetic flux, we can get the virtual magnetic flux Ψ α ,Ψ β The relationship between the AC side current and the VSR output phase voltage is:

[0079]

[0080] Where: L is the AC side filter inductor, R is the AC side filter resistor, i in the two-phase stationary coordinate system α 、i β .

[0081] Step 3, combine α ,Ψ β Calculate the instantaneous active power p and reactive power q, and get the rate of change of p and q. Specifically:

[0082] In the αβ coordinate system, since the complex power vector can be represented by the AC voltage vector and the AC current conjugate vector, the instantaneous active power p and reactive power q can be represented by virtual flux and current respectively:

[0083]

[0084] Where: c is the magnitude of the virtual flux vector.

[0085] Then the change rates dp / dt and dq / dt of instantaneous active power p and instantaneous reactive power q are respectively:

[0086]

[0087] Step 4, divide the αβ coordinate system into 6 sectors, each sector is described by a voltage vector sequence consisting of 8 corresponding known voltage vectors. And the corresponding relationship between the switch state of the voltage source rectifier VSR and the output voltage is obtained. Specifically:

[0088] The αβ coordinate system is divided into 6 sectors, each sector is described by a voltage vector sequence consisting of 8 corresponding known voltage vectors. The 8 voltage vectors output by the VSR are defined as u r，x =u rα，x +ju rβ，x (x=0,1,…,7). And the corresponding relationship between the switch state of the voltage source rectifier VSR and the output voltage is obtained. The 8 different switch states S x Corresponding to 8 different space voltage vectors u r，x , except for two zero vectors, the remaining six non-zero vectors are evenly distributed in the αβ coordinate system. For any given spatial voltage vector, it can be represented by the synthesis of the remaining voltage vectors near the sector where it is located. At the same time, the optimal switching sequence OSS of the voltage vector of each sector is determined.

[0089] Step 5: Use the instantaneous rate of change of power to predict the instantaneous power corresponding to the ith voltage vector in the voltage vector sequence. And use the cost function about power to obtain the optimal voltage vector sequence corresponding to a set of instantaneous powers that minimizes the cost function value. Specifically:

[0090] Step 5.1, using the instantaneous rate of change of power, predict the instantaneous power corresponding to the i-th voltage vector in the voltage vector sequence. It can be concluded that under the action of a given VSR voltage vector, the change trajectory of active power p and reactive power q within the relevant action time is:

[0091] p i =p i-1 +f pi t ij

[0092] q i =q i-1 +f qi t ij

[0093] Where: {p i-1 ,q i-1} represents the initial value of active power and reactive power when the ith voltage vector starts to act in the voltage switching sequence. ij represents the voltage vector action time, and t 1j =t 4j =t 5j =t 8j , t 2j =t 7j , t 3j =t 6j For the convenience of calculation, let t s0j =t 1j =t 4j =t 5j =t 8j , t s1j =t 2j =t 7j , t s2j =t 3j =t 6j , t s0j Represents the zero voltage vector action time; t s1j Represents the first effective voltage vector action time; t s2j Represents the second effective vector action time. i ,q i} represents the power value at the end of the voltage vector action time.

[0094] Step 5.2, and use the cost function for power to obtain the optimal voltage vector sequence corresponding to a set of instantaneous powers that can minimize the cost function value. In model predictive control, the cost function is often used to describe the desired system operating state, and the cost function is minimized to determine the optimal operation mode. The cost function for power in the control method proposed in this paper is expressed as:

[0095]

[0096] Where: p ref ,q ref are given active power and given reactive power respectively, p ref Given by the power voltage outer loop, since the VSR operates at unity power factor, q ref Set to 0.

[0097] Using the conditions that minimize the cost function,

[0098]

[0099] Get t that minimizes the cost function s0j ,t s1j ,t s2j , as shown below:

[0100]

[0101]

[0102] t s0j =(T s / 2-t s1i -t s2i ) / 2

[0103] Where: e pk =p ref -p k , e qk =q ref -q k .

[0104] By traversing and solving the voltage vector sequences corresponding to 6 different sectors, the voltage switching sequence that minimizes the cost function can be obtained, which is defined as the optimal voltage vector sequence.

[0105] Step 6: Use the optimal switching sequence OSS and the optimal voltage vector action time T op Calculate the optimal output duty cycle d op , compare the duty cycle with the triangular carrier, obtain the switch state under the voltage optimal switching sequence and act on the power switch device. Specifically:

[0106] The voltage vector sequence corresponding to the set of instantaneous powers that can minimize the cost function value is considered to be the optimal switching sequence (OSS), defined as u sj =u sop The sector j corresponding to the group of OSS is considered to be the optimal sector. sop The corresponding zero vector and two non-zero vector action times are t s0j ,t s1j ,t s2j , the optimal voltage vector action time is expressed as T op ={t s0op , t s1op , t s2op By calculating the time that the voltage vector in the optimal switching sequence OSS generates a high level, it accounts for the sampling period T s The ratio of can be used to obtain the optimal duty cycle d op , and its calculation formula is:

[0107]

[0108] Where: u sop (0),u sop (1) u sop (2) are the optimal voltage vector switching sequence u sop The zero voltage vector, the first effective vector and the second effective vector in S x represents the voltage vector u r,x The corresponding switching status of the three phases abc.

Claims

1. A virtual flux model prediction power control strategy based on OSS, characterized in that: The specific steps are as follows: Step 1: Collect the switch status S of the power switch device a , S b , S c and DC side voltage U dc , and the rectifier output phase voltage in the two-phase stationary coordinate system is expressed by coordinate transformation; Step 2: Collect the three-phase AC current i on the grid side a 、i b 、i c , and transform it into i in the two-phase stationary coordinate system through coordinate transformation α 、i β , the filter inductor L, filter resistor R and AC voltage vector E on the AC side of the voltage-type rectifier are equivalent to a virtual motor, and the virtual flux Ψ in the αβ coordinate system is calculated α ,Ψ β ; Step 3: Combine α ,Ψ β Calculate the instantaneous active power p and reactive power q, and get the rate of change of p and q; Step 4: Divide the αβ coordinate system into 6 sectors, each sector is described by a voltage vector sequence consisting of 8 corresponding known voltage vectors, and obtain the corresponding relationship between the switch state of the voltage source rectifier VSR and the output voltage, and determine the optimal switching sequence OSS of the voltage vector of each sector; Step 5: using the instantaneous rate of change of power, predict the instantaneous power corresponding to the ith voltage vector in the voltage vector sequence, and using the cost function on power, obtain an optimal voltage vector sequence corresponding to a set of instantaneous powers that minimizes the cost function value; Step 6: Use the optimal switching sequence OSS and the optimal voltage vector action time T op Calculate the optimal output duty cycle d op , compare the duty cycle with the triangular carrier, obtain the switching state under the voltage optimal switching sequence and act on the power switching device.

2. The OSS-based virtual flux model prediction power control strategy according to claim 1, characterized in that: The step 1 is specifically as follows: Collect the switching state S of the power switching device a , S b , S c and DC side voltage U dc , and the rectifier a, b, c phase output voltage u is obtained ra 、u rb 、u rc ,get: Where: U dc is the DC voltage, u ra 、u rb 、u rc is the rectifier a, b, c phase output voltage; And the rectifier output phase voltage in the two-phase stationary coordinate system is expressed by coordinate transformation, which are: Where: u rα 、u rβ It is the component of the output phase voltage of the voltage source rectifier VSR in the αβ coordinate system.

3. The OSS-based virtual flux model prediction power control strategy according to claim 1, characterized in that: The step 2 is specifically as follows: Collect the three-phase AC current i on the grid side a 、i b 、i c , and transform it into i in the two-phase stationary coordinate system through coordinate transformation α 、i β According to Kirchhoff's voltage law and combined with the virtual flux VF directional principle diagram, the loop voltage equation of the VSR AC side in the αβ coordinate system can be obtained as follows: According to the definition of virtual magnetic flux, we can get the virtual magnetic flux Ψ α ,Ψ β The relationship between the AC side current and the VSR output phase voltage is: Where: L is the AC side filter inductor, R is the AC side filter resistor, i in the two-phase stationary coordinate system α 、i β .

4. The OSS-based virtual flux model prediction power control strategy according to claim 1, characterized in that: The step 3 is specifically as follows: In the αβ coordinate system, since the complex power vector can be represented by the AC voltage vector and the AC current conjugate vector, the instantaneous active power p and reactive power q can be represented by virtual flux and current respectively: Where: c is the magnitude of the virtual flux vector; Then the change rates dp / dt and dq / dt of instantaneous active power p and instantaneous reactive power q are respectively:

5. The OSS-based virtual flux model prediction power control strategy according to claim 1, characterized in that: The step 4 is specifically as follows: The αβ coordinate system is divided into 6 sectors, each sector is described by a voltage vector sequence consisting of 8 corresponding known voltage vectors; the 8 voltage vectors output by the VSR are defined as u r,0 =u rα,0 +ju rβ,0 、u r,1 =u rα,1 +ju rβ,1 、u r,2 =u rα,2 +ju rβ,2 、u r,3 =u rα,3 +ju rβ,3 、u r,4 =u rα,4 +ju rβ,4 、u r,5 =u rα,5 +ju rβ,5 、u r,6 =u rα,6 +ju rβ,6 、u r,7 =u rα,7 +ju rβ,7 ; And the corresponding relationship between the switch state of the voltage source rectifier VSR and the output voltage is obtained, 8 different switch states S x Corresponding to 8 different space voltage vectors u r，x , except for two zero vectors, the remaining six non-zero vectors are evenly distributed in the αβ coordinate system. For any given spatial voltage vector, it can be represented by the synthesis of the remaining voltage vectors near the sector where it is located, and the optimal switching sequence OSS of the voltage vector of each sector can be determined at the same time.

6. The OSS-based virtual flux model prediction power control strategy according to claim 1, characterized in that: The step 5 is specifically as follows: Step 5.1, using the instantaneous rate of change of power, predict the instantaneous power corresponding to the i-th voltage vector in the voltage vector sequence, and it can be obtained that under the action of a given VSR voltage vector, the change trajectory of active power p and reactive power q within the relevant action time is: p i =p i-1 +f pi t ij q i =q i-1 +f qi t ij Where: {p i-1 ,q i-1 } represents the initial value of active power and reactive power when the i-th voltage vector starts to act in the voltage switching sequence, t ij represents the voltage vector action time, and t 1j =t 4j =t 5j =t 8j , t 2j =t 7j , t 3j =t 6j ; For the convenience of calculation, let t s0j =t 1j =t 4j =t 5j =t 8j , t s1j =t 2j =t 7j , t s2j =t 3j =t 6j , t s0j Represents the zero voltage vector action time, t s1j Represents the first effective voltage vector action time, t s2j represents the second effective vector action time; {p i ,q i } represents the power value at the end of the voltage vector action time; Step 5.2, using the cost function of power, obtain an optimal voltage vector sequence corresponding to a set of instantaneous powers that can minimize the cost function value. The cost function is often used in model predictive control to describe the desired system operating state, and the cost function is minimized to determine the optimal operation mode; the power cost function is expressed as: Where: p ref ,q ref are given active power and given reactive power respectively, p ref Given by the power voltage outer loop, since the VSR operates at unity power factor, q ref Set to 0; Using the conditions that minimize the cost function, we can find t that minimizes the cost function. s0j ,t s1j ,t s2j , as shown below: t s0j =(T s / 2-t s1i -t s2i ) / 2 Where: e pk =p ref -p k , e qk =q ref -q k ; By traversing and solving the voltage vector sequences corresponding to 6 different sectors, the voltage switching sequence that minimizes the cost function can be obtained, which is defined as the optimal voltage vector sequence.

7. The OSS-based virtual flux model prediction power control strategy according to claim 1, characterized in that: The step 6 is specifically as follows: The voltage vector sequence corresponding to the set of instantaneous powers that can minimize the cost function value is considered to be the optimal switching sequence (OSS), defined as u sj =u sop , the sector j corresponding to the group of OSS is considered to be the optimal sector; at the same time u sop The corresponding zero vector and two non-zero vector action times are t s0j ,t s1j ,t s2j , the optimal voltage vector action time is expressed as T op ={t s0op , t s1op , t s2op }; By calculating the time that the voltage vector in the optimal switching sequence OSS generates a high level, it accounts for the sampling period T s The ratio of can be used to obtain the optimal duty cycle d op , and its calculation formula is: Where: u sop (0),u sop (1) u sop (2) are the optimal voltage vector switching sequence u sop The zero voltage vector, the first effective vector and the second effective vector in S x represents the voltage vector u r,x The corresponding switching status of the three phases abc.

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