Method for controlling Vienna rectifier under fault power grid based on frequency multiplication SVPWM (Space Vector Pulse Width Modulation) modulation

Abstract

The invention discloses a frequency multiplication SVPWM (Space Vector Pulse Width Modulation) modulation-based Vienna rectifier control method under a fault power grid, belongs to the technical field of power electronics, and mainly solves the problem that the stability of a power supply system is seriously influenced by shutdown check when a phase loss fault occurs in the power grid. According to the method, the Vienna rectifier can be helped to be controlled under the three-phase imbalance fault of the power grid, it can be ensured that the system can still operate normally when the power grid has an open-phase fault, the neutral-point potential balance can be ensured through frequency doubling SVPWM modulation, and the harmonic content is reduced. The control method greatly improves the stability and reliability of the power supply system.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a Vienna rectifier control method under a faulty power grid based on frequency-doubled SVPWM modulation. Background Art

[0002] With the intensification of environmental pollution and the growing energy crisis, gasoline-powered vehicles are losing favor with the general public due to rising oil prices and the high levels of exhaust emissions. Therefore, the development of green and clean energy has become a strategic core of the modern automotive industry. Charging piles, as the indispensable charging and energy supply infrastructure for new energy vehicles, play a significant role in accelerating the electrification of the transportation sector. Rectifiers, as core components in charging piles, have a direct impact on their development.

[0003] With the continuous development of power electronics technology in my country, Vienna rectifiers have been widely used in power systems due to their advantages of high efficiency, low harmonic pollution, high reliability and high power density. At the same time, with the large-scale grid connection of new energy and the surge in nonlinear loads, the probability of voltage imbalance and phase loss in the power grid has gradually increased. When a three-phase unbalanced fault occurs in the power grid, the method of separating the positive and negative sequences and controlling the positive and negative sequences of the power grid can be used to ensure the stable operation of the Vienna rectifier. However, when a phase loss fault occurs in the power grid, today's conventional control methods are ineffective. This also means that once a phase loss fault occurs in the power grid, the power can only be shut down for maintenance, which seriously affects the stability of the power supply system. Therefore, research on control methods to ensure the stable operation of the Vienna rectifier when a phase loss fault occurs in the power grid is imminent. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the present invention proposes a Vienna rectifier control method under faulty power grid based on frequency-doubled SVPWM modulation, which has a reasonable design, solves the shortcomings of the prior art, and has good effects.

[0005] A control method for a Vienna rectifier under fault power grid based on frequency multiplication SVPWM modulation, the Vienna rectifier includes a three-phase AC E a 、E b 、E c , input side inductor L a , L b , L c , equivalent impedance R a 、R b 、R c , three-phase rectifier bridge D ap 、D bp 、D cp 、D an 、D bn 、Dcn , 6 power switch tubes S a1 、S a2 、S b1 、S b2 、S c1 、S c2 , DC side capacitors C1, C2, DC side load R L When a single-phase failure occurs in the power grid, a frequency-doubled SVPWM modulation method is adopted, which includes the following steps:

[0006] S1: Vienna rectifier exhibits seven different operating modes under phase loss condition. Let these seven operating modes be Vi, i = 1, 2, ..., 7;

[0007] S2: The seven working modes are based on the AC side input voltage U ac The magnitude of the modulus is divided into zero vector, medium vector and large vector;

[0008] S3: Divide the space vector map into sectors I to IV according to the different modulus values ​​of each vector;

[0009] S4: Calculate the action time of the synthetic vector;

[0010] S5: Analyze the influence of each vector on the midpoint voltage and select the vector based on the grid-side current direction and the midpoint potential offset direction;

[0011] S6: Obtain the action sequence and action time of the reference voltage vector output vectors in different sectors.

[0012] Furthermore, in S1, it is assumed that phase B is missing and the AC side input voltage is U ac , load R L The voltage is U dc , C1 and C2 have the same capacitance value, and the voltage on both sides is the same, that is, U C1 =U C2 =U dc / 2; Taking the midpoint o as the reference point, each phase bridge arm has three output levels: +U dc / 2, 0, -U dc / 2; Now assume that all switches are ideal switches, with the switch function S x Indicates the on and off of the switch tube, x = a, c, where S a Indicates S a1 and S a2 The opening and closing of S c Indicates S c1 and S c2 The opening and closing of

[0013]

[0014] Assume that the current i ac By the input side inductor L a Flow equivalent impedance R a is in the negative direction, where S a =P represents S a1 and S a2 Turn off and current i ac In the negative direction, S a =O represents S a1 and S a2 The direction of the turn-on current is ignored, S a =N represents S a1 and S a2 Turn off and current i ac is the positive direction; S c =P represents S c1 and S c2 Turn off and current i ac is the positive direction, S c =O represents S c1 and S c2 The direction of the turn-on current is ignored, S c =N represents S c1 and S c2 Turn off and current i ac is the negative direction;

[0015] Let u ao is the voltage across C1, u co is the voltage across C2, u ac is the load R L The voltage at both ends, the seven working modes are as follows: a =P, S c =N、u ao =U dc / 2、u co =-U dc / 2、u ac =U dc When S a =P, S c =O、u ao =U dc / 2、u co =0,u ac =U dc / 2, the working mode is V2; when S a =O, S c =N、u ao =0,u co =-U dc / 2、u ac =U dc / 2, the working mode is V3; when S a =O, Sc =O、u ao =0,u co =0,u ac = 0, the working mode is V4; when S a =N、S c =P、u ao =-U dc / 2、u co =U dc / 2、u ac =-U dc When S a =N、S c =O、u ao =-U dc / 2、u co =0,u ac =-U dc / 2, the working mode is V6; when S a =O, S c =P、u ao =0,u co =U dc / 2、u ac =-U dc / 2, the working mode is V7.

[0016] Furthermore, in S2, V4 is a zero vector, V2, V3, V6, and V7 are medium vectors, and V1 and V5 are large vectors.

[0017] Furthermore, in S3, let the reference vector U ref The vector circle is formed by moving counterclockwise from sector I to sector IV at an angular velocity ω, and then returning from sector IV to sector I, and finally forming a vector circle whose radius is equal to the reference voltage vector U. ref The amplitude U, where U ref The size is:

[0018] U ref =Ucos(ωt);

[0019] According to the reference voltage U ref The amplitude of the sector is used to determine the sector, and the sector judgment rule is as follows: dc / 2 ref dc When 0 is satisfied, it is divided into sector I. ref dc / 2, it is divided into sector II, when -U dc / 2 ref <0, divided into sector III, when -U dc ref <-U dc ​​​​​​ / 2, it is divided into sector IV.

[0020] Furthermore, in S4, according to the volt-second balance principle, U ref Considered as a value in one switching cycle, the following formula is obtained:

[0021]

[0022] Among them, T s is the total action time of a switching cycle, T a With T b They are the resultant vector V a and V b The action time of , simplified to:

[0023]

[0024] Furthermore, in S5, after analysis, only the neutral vector will affect the midpoint potential of the system, and is related to the grid-side current direction. The vector is selected based on the grid-side current direction and the midpoint potential offset direction. Based on the above analysis, the following formula is introduced:

[0025] H=sign(U C1 -U C2 )sign(i ac );

[0026] Among them, H represents the basis for vector selection;

[0027] In S6, the order in which the reference voltage vector outputs the vectors in different sectors is as follows:

[0028] For sector I, when H=1, the vector action order is V1-V2-V1-V2-V1, and when H=-1, the vector action order is V1-V3-V1-V3-V1;

[0029] For sector II, when H=1, the vector action order is V4-V2-V4-V2-V4, and when H=-1, the vector action order is V4-V3-V4-V3-V4;

[0030] For sector III, when H=1, the vector action order is V4-V6-V4-V6-V4; when H=-1, the vector action order is V4-V7-V4-V7-V4;

[0031] For sector IV, when H=1, the vector action order is V5-V6-V5-V6-V5, and when H=-1, the vector action order is V5-V7-V5-V7-V5;

[0032] The action time of the five output vectors in each sector is Ta / 4、T b / 2、T a / 2、T b / 2、T a / 4.

[0033] Beneficial technical effects brought about by the present invention:

[0034] This invention provides a Vienna rectifier modulation method for faulty power grids based on double-frequency SVPWM (Space Vector Pulse Width Modulation). This method not only helps Vienna rectifiers control under three-phase imbalance faults but also ensures normal operation during phase loss faults. Double-frequency SVPWM modulation also ensures midpoint potential balance and reduces harmonic content. This control method significantly improves the stability and reliability of the power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the main circuit topology diagram of the Vienna rectifier.

[0036] Figure 2 This is the main circuit topology diagram of the Vienna rectifier with phase B missing.

[0037] Figure 3 This is the working mode diagram of the phase-missing Vienna rectifier.

[0038] Among them, (a) is the working modal diagram of V1 (P, N); (b) is the working modal diagram of V2 (P, O); (c) is the working modal diagram of V3 (O, N); (d) is the working modal diagram of V4 (O, O); (e) is the working modal diagram of V5 (N, P); (f) is the working modal diagram of V6 (N, O); (g) is the working modal diagram of V7 (O, P).

[0039] Figure 4 It is the spatial vector diagram of SVPWM modulation.

[0040] Figure 5 This is the equivalent circuit diagram when V4 is acting.

[0041] Figure 6 This is the equivalent circuit diagram when V2 acts.

[0042] Figure 7 This is the equivalent circuit diagram when V3 is acting.

[0043] Figure 8 This is the equivalent circuit diagram when V1 acts.

[0044] Figure 9This is the switching action timing diagram when the reference voltage vector is located in sector I.

[0045] Among them, (a) is the switching action timing diagram when H=1; (b) is the switching action timing diagram when H=-1.

[0046] Figure 10 This is the control block diagram of Vienna rectifier under unbalanced grid.

[0047] Figure 11 This is the control block diagram of the Vienna rectifier under grid phase loss.

[0048] Figure 12 The waveform diagram of the three-phase input current and DC output voltage of the three-phase unbalanced system.

[0049] Figure 13 This is the THD value change diagram of the three-phase input current.

[0050] Figure 14 The input current i is obtained by using different modulation strategies under the condition of grid phase failure. a And the output voltage U dc Waveform diagram;

[0051] Where, (a) is the input current i when using SPWM a And the output voltage U dc (b) is the waveform of the input current i when using double frequency SVPWM a And the output voltage U dc waveform.

[0052] Figure 15 is the input current i under different modulation strategies a THD analysis chart.

[0053] Figure 16 The waveform of the voltage on the upper and lower bus capacitors of the Vienna rectifier using the double-frequency SVPWM modulation strategy.

[0054] Figure 17 This is the switching waveform diagram of the phase loss fault. DETAILED DESCRIPTION

[0055] The specific implementation of the present invention will be further described below with reference to specific embodiments:

[0056] A control method for Vienna rectifier under faulty power grid based on frequency multiplication SVPWM modulation, the main circuit of Vienna rectifier is as follows Figure 1 As shown, including three-phase AC E a 、E b 、E c , input side inductor L a , L b , Lc , equivalent impedance R a 、R b 、R c , three-phase rectifier bridge D ap 、D bp 、D cp 、D an 、D bn 、D cn , 6 power switch tubes S a1 、S a2 、S b1 、S b2 、S c1 、S c2 , DC side capacitors C1, C2, DC side load R L ; Among them, the controllable switch tube S a1 The drain of diode D ap The positive electrode and diode D an The negative electrode and the equivalent impedance R a Connected, controllable switch tube S a1 The source and the controllable switch tube S a2 The source of the controllable switch S b1 The drain of diode D bp The positive electrode and diode D bn The negative electrode and the equivalent impedance R b Connected, controllable switch tube S c1 The source and the controllable switch tube S c2 The source of the controllable switch S c1 The drain of diode D cp The positive electrode and diode D cn The negative electrode and the equivalent impedance R c Connected, controllable switch tube S c1 The source and the controllable switch tube S c2 The source of the controllable switch S a2 The drain of the controllable switch tube S b2 The drain and controllable switch tube S c2 The drain is connected to the negative electrode of the DC side capacitor C1 and the positive electrode of the DC side capacitor C2, and the positive electrode of the DC side capacitor C1 is connected to the diode D ap The cathode of diode D bp The cathode of diode D cp The negative electrode of the DC side capacitor C2 is connected to the negative electrode of the diode D an The positive electrode of diode D bn The positive electrode and diode D cn The positive pole is connected.

[0057] Since the present invention studies a three-phase three-wire Vienna rectifier, it cannot form a circuit when two phases are missing in the power grid, so only the case of single-phase missing is discussed. When a single-phase missing fault occurs in the power grid, the circuit of the failed phase no longer functions. At this time, the three-phase Vienna rectifier can be regarded as a single-phase PWM rectifier. Assuming that phase B is missing, its main circuit is as follows Figure 2 As shown. Among them, the controllable switch tube S a1 The drain of diode D ap The positive electrode and diode D an The negative electrode and the equivalent impedance R a Connected, controllable switch tube S a1 The source and the controllable switch tube S a2 The source of the controllable switch S c1 The drain of diode D cp The positive electrode and diode D cn The negative electrode and the equivalent impedance R c Connected, controllable switch tube S c1 The source and the controllable switch tube S c2 The source of the controllable switch S a2 The drain and controllable switch tube S c2 The drain is connected to the negative electrode of the DC side capacitor C1 and the positive electrode of the DC side capacitor C2, and the positive electrode of the DC side capacitor C1 is connected to the diode D ap The cathode of diode D cp The negative electrode of the DC side capacitor C2 is connected to the negative electrode of the diode D an The positive electrode and diode D cn The positive pole is connected.

[0058] When a single-phase failure occurs in the power grid, a frequency-doubled SVPWM modulation method is adopted, including the following steps:

[0059] S1: Vienna rectifier exhibits seven different operating modes under phase loss condition. Let these seven operating modes be Vi, i = 1, 2, ..., 7;

[0060] In S1, assuming that phase B is missing, the AC side input voltage is U ac , load R L The voltage is U dc , C1 and C2 have the same capacitance value, and the voltage on both sides is the same, that is, U C1 =U C2 =U dc / 2; Taking the midpoint o as the reference point, each phase bridge arm has three output levels: +U dc / 2, 0, -U dc / 2; Now assume that all switches are ideal switches, with the switch function S xIndicates the on and off of the switch tube, x = a, c, where S a Indicates S a1 and S a2 The opening and closing of S c Indicates S c1 and S c2 The opening and closing of

[0061]

[0062] Assume that the current i ac By the input side inductor L a Flow equivalent impedance R a is in the negative direction, where S a =P represents S a1 and S a2 Turn off and current i ac In the negative direction, S a =O represents S a1 and S a2 The direction of the turn-on current is ignored, S a =N represents S a1 and S a2 Turn off and current i ac is the positive direction; S c =P represents S c1 and S c2 Turn off and current i ac is the positive direction, S c =O represents S c1 and S c2 The direction of the turn-on current is ignored, S c =N represents S c1 and S c2 Turn off and current i ac is the negative direction;

[0063] Through the above analysis, it can be regarded as a single-phase PWM rectifier in the phase loss state, so it has seven working modes, such as Figure 3 As shown in (a) to (g), let u ao is the voltage across C1, u co is the voltage across C2, u ac is the load R L The voltage at both ends and the working mode are as follows:

[0064] When S a =P, S c =N、u ao =U dc / 2、u co =-U dc / 2、u ac =U dc When Sa =P, S c =O、u ao =U dc / 2、u co =0,u ac =U dc / 2, the working mode is V2; when S a =O, S c =N、u ao =0,u co =-U dc / 2、u ac =U dc / 2, the working mode is V3; when S a =O, S c =O、u ao =0,u co =0,u ac = 0, the working mode is V4; when S a =N、S c =P、u ao =-U dc / 2、u co =U dc / 2、u ac =-U dc When S a =N、S c =O、u ao =-U dc / 2、u co =0,u ac =-U dc / 2, the working mode is V6; when S a =O, S c =P、u ao =0,u co =U dc / 2、u ac =-U dc / 2, the working mode is V7;

[0065] As shown in Table 1:

[0066] Table 1 Working status table under phase loss state

[0067] Working mode <![CDATA[S a ]]> <![CDATA[S c ]]> <![CDATA[u ao ]]> <![CDATA[u co ]]> <![CDATA[u ac ]]> V1 P N <![CDATA[+U dc / 2]]> <![CDATA[-U dc / 2]]> <![CDATA[U dc ]]> V2 P O <![CDATA[+U dc / 2]]> 0 <![CDATA[+U dc / 2]]> V3 O N 0 <![CDATA[-U dc / 2]]> <![CDATA[+U dc / 2]]> V4 O O 0 0 0 V5 N P <![CDATA[-U dc / 2]]> <![CDATA[+U dc / 2]]> <![CDATA[-U dc ]]> V6 N O <![CDATA[-U dc / 2]]> 0 <![CDATA[-U dc / 2]]> V7 O P 0 <![CDATA[+U dc / 2]]> <![CDATA[-U dc / 2]]>

[0068] S2: The seven working modes are based on the AC side input voltage U ac The modulus values ​​are divided into zero vector, medium vector and large vector, V4 is the zero vector, V2, V3, V6, V7 are medium vectors, V1, V5 are large vectors;

[0069] S3: Divide the space vector map into sectors I to IV according to the different modulus values ​​of each vector;

[0070] According to different vectors, the space vector diagram of SVPWM modulation can be obtained as follows Figure 4 As shown. Assume that the reference vector U ref The vector circle is formed by moving counterclockwise from sector I to sector IV at an angular velocity ω, and then returning from sector IV to sector I, and finally forming a vector circle whose radius is equal to the reference voltage vector U. ref The amplitude U, where U ref The size is:

[0071] U ref =Ucos(ωt);

[0072] According to the reference voltage U ref The amplitude of is used to determine the sector. The specific sector judgment rules are as follows:

[0073] When U is satisfied dc / 2 ref dc When 0 is satisfied, it is divided into sector I. ref dc / 2, it is divided into sector II, when -U dc / 2 ref <0, divided into sector III, when -U dc ref <-U dc / 2, it is divided into sector IV;

[0074] As shown in Table 2:

[0075] Table 2 Sector judgment rules

[0076] sector Judgment Rules Ⅰ <![CDATA[U dc / 2<U ref <U dc ]]> Ⅱ <![CDATA[0<U ref <U dc / 2]]> Ⅲ <![CDATA[-U dc / 2<U ref <0]]> Ⅳ <![CDATA[-U dc ref <-U dc / 2]]> ​

[0077] S4: Calculate the action time of the synthetic vector;

[0078] According to the volt-second balance principle, U ref Considered as a value in one switching cycle, the following formula is obtained:

[0079]

[0080] Among them, T s is the total action time of a switching cycle, T a With T b They are the resultant vector V a and V b The action time, V a and V b The amplitude difference U dc / 2, simplifying to:​​​​​​

[0081]

[0082] S5: Analyze the influence of each vector on the midpoint voltage and select the vector based on the grid-side current direction and the midpoint potential offset direction;

[0083] After calculating the time, the action vectors within a switching cycle need to be distributed. However, conventional vector distribution methods can cause midpoint voltage imbalance. To properly distribute the action vectors within the switching cycle and maintain a balanced midpoint voltage, the following analyzes the impact of each vector on the midpoint voltage.

[0084] The equivalent circuit diagram when zero vector V4 acts is as follows Figure 5 As shown, the bridge arm is connected to the midpoint O, the grid side charges the inductor, and capacitors C1 and C2 provide energy to the load side. C1 with U C2 At the same time, it decreases, so the zero vector has no effect on the midpoint voltage.

[0085] Taking V2 and V3 as examples, the influence of the midpoint voltage on the midpoint voltage is analyzed. The equivalent circuit diagram is as follows: Figure 6 and Figure 7 As shown, Figure 2 in i ac The direction is negative. When V2 acts and i ac <0, capacitor C1 is in charging state, U C1 Increase. When V2 acts and i ac >0, capacitor C1 is in discharge state, U C1 When V3 acts and i ac <0, capacitor C2 is in charging state, U C2 Increase. When V3 acts and i ac >0, capacitor C2 is in discharge state, U C2 Therefore, the neutral vector will cause the midpoint voltage to shift.

[0086] Taking V1 as an example, the influence of large vector on midpoint voltage is analyzed. The equivalent circuit diagram is as follows: Figure 8 As shown, at this time, capacitors C1 and C2 charge and discharge at the same time, U C1 with U C2 The changes are made at the same time, so the large vector will not affect the midpoint voltage.

[0087] After analysis, only the neutral vector will affect the midpoint potential of the system, and it is related to the grid-side current direction. The vector is selected according to the grid-side current direction and the midpoint potential offset direction. Based on the above analysis, the following formula is introduced:

[0088] H=sign(UC1 -U C2 )sign(i ac );

[0089] Among them, H represents the basis for vector selection;

[0090] S6: Obtain the action sequence and action time of the reference voltage vector output vectors in different sectors.

[0091] Depend on Figure 4 It can be seen that the reference vector in sector I is composed of the large vector V1 and the medium vectors V2 and V3. Based on the continuity consideration when switching the switch state, the initial vector is selected as the large vector V1. When H = 1 and i ac >0, U C1 >U C2 When H=1 and i ac <0, U C1 C2 From the above analysis, we can get the middle vector V2 at this time. ac >0, C1 is in discharge state, U C1 Decrease, when i ac <0, capacitor C1 is in charging state, U C1 Increase to maintain the midpoint voltage balance. ac >0, U C1 C2 When H=-1 and i ac <0, U C1 >U C2 From the above analysis, we can get the middle vector V3 at this time. ac >0, C2 is in discharge state, U C2 Decrease, when i ac <0, capacitor C2 is in charging state, U C2 Therefore, when H=1, the vector action sequence is V1-V2-V1-V2-V1, and when H=-1, the vector action sequence is V1-V3-V1-V3-V1. Figure 9 is the switching action timing when the reference voltage vector is located in sector I.

[0092] Based on this logic, the order in which the reference voltage vector outputs the vector in different sectors is as follows:

[0093] For sector I, when H=1, the vector action order is V1-V2-V1-V2-V1, and when H=-1, the vector action order is V1-V3-V1-V3-V1;

[0094] ​​For sector II, when H=1, the vector action order is V4-V2-V4-V2-V4, and when H=-1, the vector action order is V4-V3-V4-V3-V4;

[0095] For sector III, when H=1, the vector action order is V4-V6-V4-V6-V4; when H=-1, the vector action order is V4-V7-V4-V7-V4;

[0096] For sector IV, when H=1, the vector action order is V5-V6-V5-V6-V5, and when H=-1, the vector action order is V5-V7-V5-V7-V5;

[0097] As shown in Table 3, it can be seen that this modulation can achieve a frequency doubling effect and reduce the harmonic content while ensuring the balance of the midpoint potential.

[0098] Table 3 Vector action sequence table

[0099]

[0100] The action time of the five output vectors in each sector is T a / 4、T b / 2、T a / 2、T b / 2、T a / 4.

[0101] The control block diagram of Vienna rectifier under unbalanced grid is as follows Figure 10 As shown in Figure 2. This control strategy can effectively control the Vienna rectifier under unbalanced power grid conditions. However, when a phase failure occurs in the power grid, this control strategy will fail. Therefore, the control block diagram of the Vienna rectifier under phase failure in the power grid is redesigned, as shown in Figure 2. Figure 11 When the system is actually running, it continuously collects and analyzes the positive and negative sequence components of the power grid to determine whether the power grid is missing a phase; if the power grid is missing a phase, use Figure 11 If the power grid is normal or an unbalanced fault occurs, the phase loss control strategy is adopted. Figure 10 Unbalance control.

[0102] Figure 12 The waveforms of the system's three-phase input current and DC output voltage when the input is three-phase unbalanced. Figure 13 is the THD value of the three-phase input current, and you can see that i a 、i b and i c The THDs of the three power modules are 2.65%, 3.80% and 3.22% respectively, all below 5%, meeting the grid requirements.

[0103] Figure 14(a) shows the SPWM input current i under the grid phase failure a And the output voltage U dc The waveform, Figure 14 (b) shows the input current i of the grid under a phase failure using double-frequency SVPWM. a And the output voltage U dc waveform. Figure 15 is the input current i under different modulation strategies a THD analysis diagram, using SPWM input current i a The THD is 11.33%, using the double frequency SVPWM input current i a The THD is 3.83%. It can be seen that the harmonics of the double-frequency SVPWM proposed by the present invention are significantly suppressed.

[0104] Figure 16 Figure 3 shows the voltage waveforms of the upper and lower bus capacitors of a Vienna rectifier using the double-frequency SVPWM modulation strategy. As can be seen, when the double-frequency SVPWM modulation strategy is adopted, the voltages of the upper and lower bus capacitors are both maintained at 180V, achieving midpoint potential balance.

[0105] Figure 17 This is the switching waveform for a phase loss fault. At a certain moment, disconnecting the air switch simulates a phase loss of phase B. As can be seen from the figure, when a phase loss fault occurs, the system switches to the phase loss control algorithm, and the output voltage hardly fluctuates, and the system can be effectively controlled.

[0106] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A Vienna rectifier control method under faulty power grid based on frequency-doubled SVPWM modulation, characterized in that: Vienna rectifier includes three-phase AC E a 、E b 、E c , input side inductor L a , L b , L c , equivalent impedance R a 、R b 、R c , three-phase rectifier bridge D ap 、D bp 、D cp 、D an 、D bn 、D cn , 6 power switch tubes S a1 、S a2 、S b1 、S b2 、S c1 、S c2 , DC side capacitors C1, C2, DC side load R L When a single-phase failure occurs in the power grid, a frequency-doubled SVPWM modulation method is adopted, which includes the following steps: S1: Vienna rectifier exhibits seven different operating modes under phase loss condition. Let the seven operating modes be Vi, i = 1, 2, ..., 7; S2: The seven working modes are based on the AC side input voltage U ac The magnitude of the modulus is divided into zero vector, medium vector and large vector; S3: Divide the space vector map into sectors I to IV according to the different modulus values ​​of each vector; S4: Calculate the action time of the synthetic vector; S5: Analyze the influence of each vector on the midpoint voltage and select the vector based on the grid-side current direction and the midpoint potential offset direction; S6: Obtain the action sequence and action time of the reference voltage vector output vectors in different sectors.

2. The Vienna rectifier control method based on frequency-doubled SVPWM modulation under faulty power grid according to claim 1, characterized in that: In S1, it is assumed that phase B is missing and the AC input voltage is U ac , load R L The voltage is U dc , C1 and C2 have the same capacitance value, and the voltage on both sides is the same, that is, U C1 =U C2 =U dc / 2; Taking the midpoint o as the reference point, each phase bridge arm has three output levels: +U dc / 2, 0, -U dc / 2; Now assume that all switches are ideal switches, with the switch function S x Indicates the on and off of the switch tube, x = a, c, where S a Indicates S a1 and S a2 The opening and closing of S c Indicates S c1 and S c2 The opening and closing of Assume that the current i ac By the input side inductor L a Flow equivalent impedance R a is in the negative direction, where S a =P represents S a1 and S a2 Turn off and current i ac In the negative direction, S a =O represents S a1 and S a2 The direction of the turn-on current is ignored, S a =N represents S a1 and S a2 Turn off and current i ac is the positive direction; S c =P represents S c1 and S c2 Turn off and current i ac is the positive direction, S c =O represents S c1 and S c2 The direction of the turn-on current is ignored, S c =N represents S c1 and S c2 Turn off and current i ac is the negative direction; Let u ao is the voltage across C1, u co is the voltage across C2, u ac is the load R L The voltage at both ends, the seven working modes are as follows: a =P, S c =N、u ao =U dc / 2、u co =-U dc / 2、u ac =U dc When S a =P, S c =O、u ao =U dc / 2、u co =0,u ac =U dc / 2, the working mode is V2; when S a =O, S c =N、u ao =0,u co =-U dc / 2、u ac =U dc / 2, the working mode is V3; when S a =O, S c =O、u ao =0,u co =0,u ac = 0, the working mode is V4; when S a =N、S c =P、u ao =-U dc / 2、u co =U dc / 2、u ac =-U dc When S a =N、S c =O、u ao =-U dc / 2、u co =0,u ac =-U dc / 2, the working mode is V6; when S a =O, S c =P、u ao =0,u co =U dc / 2、u ac =-U dc / 2, the working mode is V7.

3. The Vienna rectifier control method based on frequency-doubled SVPWM modulation under faulty power grid according to claim 2, characterized in that: In S2, V4 is the zero vector, V2, V3, V6, and V7 are medium vectors, and V1 and V5 are large vectors.

4. The Vienna rectifier control method based on frequency-doubled SVPWM modulation under faulty power grid according to claim 3, characterized in that: In S3, let the reference vector U ref The vector circle is formed by moving counterclockwise from sector I to sector IV at an angular velocity ω, and then returning from sector IV to sector I, and finally forming a vector circle whose radius is equal to the reference voltage vector U. ref The amplitude U, where U ref The size is: U ref =Ucos(ωt); According to the reference voltage U ref The amplitude of the sector is used to determine the sector, and the sector judgment rule is as follows: satisfy U dc / 2 ref dc When 0 is satisfied, it is divided into sector I. ref dc / 2, it is divided into sector II, when -U dc / 2 ref <0, divided into sector III, when -U dc ref <-U dc / 2, it is divided into sector IV.​​​​​​ 5. The Vienna rectifier control method based on frequency-doubled SVPWM modulation under faulty power grid according to claim 4, characterized in that: In S4, according to the volt-second balance principle, U ref Considered as a value in one switching cycle, the following formula is obtained: Among them, T s is the total action time of a switching cycle, T a With T b They are the resultant vector V a and V b The action time of , simplified to:

6. The Vienna rectifier control method based on frequency-doubled SVPWM modulation under faulty power grid according to claim 5, characterized in that: In S5, after analysis, only the neutral vector will affect the midpoint potential of the system, and it is related to the grid-side current direction. The vector is selected based on the grid-side current direction and the midpoint potential offset direction. Based on the above analysis, the following formula is introduced: H=sign(U C1 -U C2 )sign(i ac ); Among them, H represents the basis for vector selection; In S6, the order in which the reference voltage vector outputs the vectors in different sectors is as follows: For sector I, when H=1, the vector action order is V1-V2-V1-V2-V1, and when H=-1, the vector action order is V1-V3-V1-V3-V1; For sector II, when H=1, the vector action order is V4-V2-V4-V2-V4, and when H=-1, the vector action order is V4-V3-V4-V3-V4; For sector III, when H=1, the vector action order is V4-V6-V4-V6-V4; when H=-1, the vector action order is V4-V7-V4-V7-V4; For sector IV, when H=1, the vector action order is V5-V6-V5-V6-V5, and when H=-1, the vector action order is V5-V7-V5-V7-V5; The action time of the five output vectors in each sector is T a / 4、T b / 2、T a / 2、T b / 2、T a / 4.

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