A carrier discontinuous modulation method for three-phase Vienna rectifier

Abstract

The invention discloses a carrier discontinuous modulation method for a three-phase Vienna rectifier. According to the three-phase normalization formula of the SPWM modulation strategy of the three-phase Vienna rectifier, the normalized sinusoidal waves of the A-phase voltage, the B-phase voltage and the C-phase voltage are obtained as u respectively. ma ,u mb ,u mc ; Define the maximum value of the three-phase normalized sine wave at a certain moment as u max , the middle value is u mid , the minimum value is u min ; When the load is balanced, the injected zero-sequence voltage is u z1 , the modulation method is u mid ≥0 when u z1 =max(‑u mid ,‑1‑u min ), in u mid <0 time u z1 =min(‑u mid ,1‑u max ); when the load is unbalanced, the injected zero-sequence voltage is u z2 , the modulation method is u mid ≥0 when u z2 =max(‑u mid ,‑2U dc2 / U dc ‑u min ), in u mid <0 time u z2 =min(‑u mid ,2U dc1 / U dc ‑u max );and by converting the zero sequence voltage u z1 / u z2 Injecting three-phase normalized sine waves, we get the three-phase modulated waves of the three-phase Vienna rectifier.

Description

Technical Field

[0001] The invention relates to the field of power electronics, and in particular to a carrier discontinuous modulation method for a three-phase Vienna rectifier. Background Art

[0002] The three-phase Vienna rectifier is suitable for high-frequency three-phase power factor correction applications, such as electric vehicle charging and aerospace power supply, due to its advantages of high efficiency, high power density and unity power factor. Aviation applications require the converter to have the characteristics of miniaturization and higher power density. High power density means that the switching frequency of the device's switch tube needs to be increased. However, at a higher switching frequency of the switch tube, on the one hand, the buffering, circuit and parasitic parameters of the switching device will affect the switching transient process, resulting in a deterioration in the quality of the input current waveform; on the other hand, it will increase the switching loss of the converter, reduce the overall efficiency of the system, and shorten the calculation cycle, which will bring a greater calculation burden to the controller.

[0003] The literature "Hang Lijun, Li Bin, Zhang Ming, et al. Equation of SVM and Carrier-Based PWM in Three-Phase / Wire / Level Vienna Rectifier and Capability of Unbalanced-Load Control. IEEE Transactions on Industrial Electronics, 2014, 61(1): 20-28" derived the equivalent relationship between SVM and carrier PWM modulation. Compared with space vector modulation, carrier modulation generally only requires comparison and simple calculation, and is more suitable for high-frequency applications. The literature "Z. Zhang, O. C. Thomsen, and MAE Andersen, Discontinuous PWM modulation strategy with circuit-level decoupling concept of three-level neutral-point-clamped (NPC) inverter, IEEE Trans. Ind. Electron., vol. 60, no. 5, pp. 1897–1906, May 2013." proposes a carrier discontinuous modulation method for the traditional three-level converter, but this method cannot meet the important condition that the reference voltage and current are in phase near the current zero crossing. When this method is applied to the Vienna rectifier, it cannot achieve unit power operation and will introduce additional low-frequency harmonics to the input current. Therefore, this method is not suitable for the Vienna rectifier. The document "Lee J, Lee K. Carrier-based discontinuous PWM method for Vienna rectifiers [J], IEEE Transactions on Power Electronics, 2015, 30 (6): 2896-2900." proposes a carrier discontinuous modulation method for Vienna rectifiers. This method can make the Vienna rectifier operate with unity power factor and clamp the reference voltage to zero at the current zero crossing, solving the problem of voltage and current being out of phase. However, this method adds additional intermediate variables and judgment conditions, making its calculation complicated.In response to the unbalanced midpoint voltage, the document "X. Wu, G. Tan, G. Yao, C. Sun and G. Liu, A Hybrid PWM Strategy for Three-Level Inverter With Unbalanced DC Links, in IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 6, no. 1, pp. 1-15, March 2018." proposed a hybrid modulation method of SVPWM and CBPWM, which can enable the T-type inverter to still operate in the state of unbalanced midpoint voltage. However, when this method is applied to the Vienna rectifier, the reference voltage and current cannot be in phase at the current zero crossing, resulting in poor current THD performance. In response to the load imbalance situation, the document "Y. Ming et al., "A Hybrid Carrier-Based DPWM with Controllable NP Voltage for Three-Phase Vi enna Rectifiers," in IEEE Transactions on Transportation Electrification, doi: 10.1109 / TTE.2021.3129778." proposed a carrier intermittent modulation method. By introducing different adjustment coefficients to change the effect of the zero-sequence component, the current zero-crossing distortion problem is reduced. However, this method requires complex sector judgment and determines multiple coefficients according to different sectors and the positive and negative reference voltages. It also adds the comparison of intermediate variables, and the judgment steps are cumbersome and the implementation is complex.

[0004] Therefore, it is necessary to study a Vienna rectifier carrier discontinuous modulation method that is simple to calculate and easy to implement under load balance and load unbalance conditions, so as to reduce the calculation burden of the controller and improve the quality of the input current waveform. Summary of the invention

[0005] The purpose of the present invention is to propose a carrier discontinuous modulation method for a three-phase Vienna rectifier, so as to reduce the current zero-crossing distortion of the Vienna rectifier under load balance and load imbalance, improve the input current quality, simplify the calculation method, and reduce the calculation burden of the digital controller.

[0006] The three-phase Vienna rectifier carrier discontinuous modulation method of the present invention is as follows: according to the three-phase normalization formula of the three-phase Vienna rectifier SPWM modulation strategy, the normalized sine waves of phase A, phase B and phase C are obtained as u respectively. ma ,u mb ,umc ; Define the maximum value of the normalized sine wave of phase A, phase B, and phase C at a certain moment as u max , the middle value is u mid , the minimum value is u min ; When the load is balanced, the injected zero-sequence voltage is u z1 The modulation method of the present invention is u mid ≥0 when u z1 =max(-u mid ,-1-u min ), in u mid <0 time u z1 =min(-u mid ,1-u max ); When the load is unbalanced, the injected zero-sequence voltage is u z2 The modulation method of the present invention is u mid ≥0 when u z2 =max(-u mid ,-2U dc2 / U dc -u min ), in u mid <0 time u z2 =min(-u mid ,2U dc1 / U dc -u max );and by converting the zero sequence voltage u z1 / u z2 Injecting three-phase normalized sine waves, we get the three-phase modulation waves of the Vienna rectifier.

[0007] The three-phase Vienna rectifier carrier discontinuous modulation method of the present invention is specifically as follows:

[0008] 1. Get the three-phase normalized sine wave and calculate the maximum, middle and minimum values ​​of the three-phase normalized sine wave

[0009] According to the three-phase normalization formula of the three-phase Vienna rectifier SPWM modulation strategy, the normalized sine wave u of phase A voltage is obtained. ma , B phase voltage normalized sine wave u mb , C phase voltage normalized sine wave u mc The specific method of the present invention for obtaining a three-phase normalized sine wave is as follows:

[0010]

[0011] In formula (I), f g is the grid frequency, m is the modulation ratio, m∈(0,1), the modulation ratio m can be calculated by the formula Find, where U m Indicates the amplitude of the AC reference phase voltage, Udc Indicates the DC bus voltage.

[0012] The normalized sine wave u of the voltage of phase A, phase B, and phase C at a certain moment is obtained ma ,u mb ,u mc The maximum, middle and minimum values ​​of max ,u mid ,u min .

[0013] 2. Determine the zero-sequence voltage u when the load is balanced z1

[0014] Define the zero-sequence voltage when the load is balanced as u z1 , the present invention is for u z1 The determination method is as follows:

[0015]

[0016] In the above formula, u z1 Indicates the zero-sequence voltage injected when the load is balanced; u max ,u mid ,u min Respectively represent the normalized sine wave u of phase A, phase B, and phase C at a certain moment ma ,u mb ,u mc The maximum, middle and minimum values ​​of mid ,1-u max ) means to obtain -u mid with 1-u max Minimum value: When -u mid ≤1-u max When, min(-u mid ,1-u max )=-u mid , when 1-u max <-u mid When, min(-u mid ,1-u max )=1-u max ; max(-u mid ,-1-u min ) means to obtain -u mid with -1-u min Maximum value: When -u mid ≥-1-u min When max(-u mid ,-1-u min )=-u mid , when -1-u min >-u mid When max(-umid ,-1-u min )=-1-u min .

[0017] 3. Get the three-phase modulation wave when the load is balanced

[0018] The three-phase modulation waves of the Vienna rectifier after the zero-sequence component is injected are defined as u ref_x , x=a, b, and c, the method to obtain the three-phase modulation wave when the load is balanced is as follows:

[0019] u ref_x =u mx +u z1 ,x=a,b and c (Ⅲ)

[0020] In formula (III), u ref_x , x=a, b, and c represent the three-phase modulation wave of Vienna rectifier, u mx , x=a, b, and c represent three-phase normalized sine waves, u z1 Represents the injected zero-sequence voltage when the load is balanced.

[0021] 5. Determine the zero-sequence voltage u when the load is unbalanced z2

[0022] Define the zero-sequence voltage when the load is balanced as u z2 , the present invention is for u z2 The determination method is as follows:

[0023]

[0024] u z2 It represents the zero-sequence voltage under load unbalanced condition or injection, u max ,u mid ,u min Respectively represent the normalized sine wave u of phase A, phase B, and phase C at a certain moment ma ,u mb ,u mc The maximum, middle and minimum values ​​of U dc1 , U dc2 They represent the upper capacitor voltage and the lower capacitor voltage of the DC busbar, respectively. dc Indicates the total voltage of the DC busbar, min(-u mid ,2U dc1 / U dc -u max ) means to obtain -u mid With 2U dc1 / U dc -u max Minimum value: When -u mid ≤2Udc1 / U dc -u max When, min(-u mid ,1-u max )=-u mid , when 2U dc1 / U dc -u max <-u mid When, min(-u mid ,1-u max )=2U dc1 / U dc -u max ; max(-u mid ,-2U dc2 / U dc -u min ) means to obtain -u mid With -2U dc2 / U dc -u min Maximum value: When -u mid ≥-2U dc2 / U dc -u min When max(-u mid ,-1-u min )=-u mid , when -2U dc2 / U dc -u min >-u mid When max(-u mid ,-1-u min )=-2U dc2 / U dc -u min .

[0025] 6. Get the three-phase modulation wave when the load is unbalanced

[0026] The three-phase modulation waves of the Vienna rectifier after the zero-sequence component is injected are defined as u ref_x , x=a, b, and c, the method to obtain the three-phase modulation wave when the load is unbalanced is as follows:

[0027]

[0028] In formula (V), u ref_x , x=a, b, and c represent the three-phase modulation wave of Vienna rectifier, u mx ,x=a,b,andc represents a three-phase normalized sine wave, u z2 Indicates the zero-sequence voltage under load unbalance conditions or injection, U dc1 , U dc2respectively represent the upper-side capacitor voltage and the lower-side capacitor voltage of the DC bus, and U dc represents the total voltage of the DC bus.

[0029] The present invention discloses a carrier-interrupted modulation method for a three-phase Vienna rectifier, and its beneficial effects are as follows:

[0030] The present invention can improve the input current quality and current waveform quality of a three-phase Vienna rectifier under both balanced and unbalanced load conditions. Moreover, the judgment condition is simple, and the time required for the modulation wave calculation process is short, which can reduce the operation burden of the digital controller. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the main circuit topology diagram of a carrier-interrupted modulation method for a three-phase Vienna rectifier;

[0032] Figure 2 is the implementation flowchart of a carrier-interrupted modulation method for a three-phase Vienna rectifier in the present invention;

[0033] Figure 3 is the waveform diagram of the three-phase normalized sine wave signal and the sector relationship diagram within one cycle of the present invention;

[0034] Figure 4 is the clamping mode diagram of the method of the present invention under balanced load;

[0035] Figure 5a 、 Figure 5b is the clamping mode diagram of the method of the present invention under unbalanced load, Figure 5a is the clamping mode diagram when the load resistance R1 < R2, Figure 5b is the clamping mode diagram when R1 > R2;

[0036] Figure 6a 、 Figure 6b is the circuit simulation waveform diagram of the modulation method of the present invention under balanced load conditions;

[0037] Figure 7a 、 Figure 7b is the circuit simulation waveform diagram of the modulation method of the present invention under unbalanced load conditions. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0039] Please refer to Figure 1 to FIG. 7, which shows a carrier-interrupted modulation method for a three-phase Vienna rectifier in the present invention.

[0040] As Figure 1 shown, the main circuit topology diagram of the present invention includes the voltage source e of phase Aa , voltage source e of phase B b 、C phase voltage source e c , the first to third inductors L a , L b , L c , the first to sixth diodes D a+ , D a- , D b+ , D b- , D c+ , D c- , the first to sixth switch tubes Q1, Q2, Q3, Q4, Q5, Q6, the first capacitor C1, the second capacitor C2, the first resistor R1, the second resistor R2, the voltage source e of the A phase a , voltage source e of phase B b 、C phase voltage source e c One end of the first inductor L a The voltage source e is connected in series with phase A. a With the first diode D a+ The second inductor L b The voltage source e is connected in series with the B phase b With the third diode D b+ The third inductor L c The voltage source e is connected in series with the phase C c With the fifth diode D c+ The anode of the second diode D a- , the fourth diode D b- , the sixth diode D c- The cathodes of the diodes are connected together, denoted as point N, and the anodes are connected to the first diode D a+ The anode of the third diode D b+ The anode of the fifth diode D c+ The anode of the second switch tube Q2, the fourth switch tube Q4, and the sixth switch tube Q6 are connected together, which is marked as point O. The first switch tube Q1 and the second switch tube Q2 are connected in series to the first diode D a+ The third switch tube Q3 and the fourth switch tube Q4 are connected in series to the third diode D b+ The fifth switch tube Q5 and the sixth switch tube Q6 are connected in series to the fifth diode D c+ Between the anode and point O, the first diode D a+ The anode of the third diode D b+ , the fifth diode D c+ The cathodes of the first and second capacitors C1 and R1 are connected together, which is marked as point P. The first capacitor C1 and the first resistor R1 are connected in parallel between point P and point O. The second capacitor C2 and the second resistor R2 are connected in parallel between point N and point O.

[0041] The three-phase Vienna rectifier carrier discontinuous modulation method of the present invention is as follows: according to the three-phase normalization formula of the three-phase Vienna rectifier SPWM modulation strategy, the normalized sine waves of phase A, phase B and phase C are obtained as u respectively. ma ,u mb ,u mc ; Define the maximum value of the normalized sine wave of phase A, phase B, and phase C at a certain moment as u max , the middle value is u mid , the minimum value is u min ; When the load is balanced, the injected zero-sequence voltage is u z1 The modulation method of the present invention is u mid ≥0 when u z1 =max(-u mid ,-1-u min ), in u mid <0 time u z1 =min(-u mid ,1-u max ); When the load is unbalanced, the injected zero-sequence voltage is u z2 The modulation method of the present invention is u mid ≥0 when u z2 =max(-u mid ,-2U dc2 / U dc -u min ), in u mid <0 time u z2 =min(-u mid ,2U dc1 / U dc -u max );and by converting the zero sequence voltage u z1 / u z2 Injecting three-phase normalized sine waves, we get the three-phase modulation waves of the Vienna rectifier.

[0042] like Figure 2 As shown, the specific process of the three-phase Vienna rectifier carrier discontinuous modulation method of the present invention is as follows:

[0043] 1. Get the three-phase normalized sine wave and calculate the maximum, middle and minimum values ​​of the three-phase normalized sine wave

[0044] According to the three-phase normalization formula of the three-phase Vienna rectifier SPWM modulation strategy, the normalized sine waves of phase A, phase B, and phase C are u ma ,u mb ,u mc The specific method of the present invention for obtaining a three-phase normalized sine wave is as follows:

[0045]

[0046] In formula (I), f g is the grid frequency, m is the modulation ratio, m∈(0,1), the modulation ratio m can be calculated by the formula Find, where U m Indicates the amplitude of the AC reference phase voltage, U dc Indicates the DC bus voltage.

[0047] Combination Figure 3 The three-phase normalized sine wave signal waveform diagram and sector relationship diagram within one cycle can show that the normalized sine waves of phase A, phase B, and phase C are u ma ,u mb ,u mc The maximum value, the middle value and the minimum value of u max ,u mid ,u min For example, 2πf g When it is between 0 and π / 3, it corresponds to sector I. The normalized sine waves u of phase A, phase B, and phase C described in sector I are ma ,u mb ,u mc in, u ma is the maximum value, u mb is the middle value, u mc is the minimum value.

[0048] 2. Determine the zero-sequence voltage u when the load is balanced z1

[0049] like Figure 1 In the three-phase Vienna rectifier topology shown in FIG, when the first load resistor R1 is equal to the second load resistor R2, that is, R1 = R2, the load is balanced. The zero-sequence voltage when the load is balanced is defined as u z1 , the present invention is for u z1 The determination method is as follows:

[0050]

[0051] In the above formula, u z1 Indicates the zero-sequence voltage injected when the load is balanced; u max ,u mid ,u min At a certain moment, the normalized sine wave u of phase A, phase B, and phase C ma ,u mb ,u mc The maximum, middle and minimum values ​​of mid ,1-u max ) means to obtain -u mid with 1-umax Minimum value: When -u mid ≤1-u max When, min(-u mid ,1-u max )=-u mid , when 1-u max <-u mid When, min(-u mid ,1-u max )=1-u max ; max(-u mid ,-1-u min ) means to obtain -u mid with -1-u min Maximum value: When -u mid ≥-1-u min When max(-u mid ,-1-u min )=-u mid , when -1-u min >-u mid When max(-u mid ,-1-u min )=-1-u min .

[0052] 3. Get the three-phase modulation wave when the load is balanced

[0053] The three-phase modulation waves of the Vienna rectifier after the zero-sequence component is injected are defined as u ref_x , x=a, b, and c, the method to obtain the three-phase modulation wave when the load is balanced is as follows:

[0054] u ref_x =u mx +u z1 ,x=a,b and c (Ⅲ)

[0055] In formula (III), u ref_x , x=a, b, and c represent the three-phase modulation wave of Vienna rectifier when the load is balanced, u mx , x=a, b, and c represent three-phase normalized sine waves, u z1 Represents the injected zero-sequence voltage when the load is balanced.

[0056] When the load is balanced, the three-phase Vienna rectifier carrier is intermittently modulated in the clamping area of ​​the first sector as shown in FIG. Figure 4 shown.

[0057] 5. Determine the zero-sequence voltage u when the load is unbalanced z2

[0058] like Figure 1The topology of the three-phase Vienna rectifier is shown. When the load resistance R1≠R2, the load is balanced. The zero-sequence voltage when the load is unbalanced is defined as u z2 , the present invention is for u z2 The determination method is as follows:

[0059]

[0060] u z2 It represents the zero-sequence voltage under load unbalanced condition or injection, u max ,u mid ,u min At a certain moment, the normalized sine wave u of phase A, phase B, and phase C ma ,u mb ,u mc The maximum, middle and minimum values ​​of U dc1 , U dc2 Respectively Figure 1 The upper capacitor voltage and the lower capacitor voltage of the DC bus, U dc express Figure 1 Total bus voltage on the DC side, min(-u mid ,2U dc1 / U dc -u max ) means to obtain -u mid With 2U dc1 / U dc -u max Minimum value: When -u mid ≤2U dc1 / U dc -u max When, min(-u mid ,1-u max )=-u mid , when 2U dc1 / U dc -u max <-u mid When, min(-u mid ,1-u max )=2U dc1 / U dc -u max ; max(-u mid ,-2U dc2 / U dc -u min ) means to obtain -u mid With -2U dc2 / U dc -u min Maximum value: When -u mid ≥-2U dc2 / U dc -umin When max(-u mid ,-1-u min )=-u mid , when -2U dc2 / U dc -u min >-u mid When max(-u mid ,-1-u min )=-2U dc2 / U dc -u min .

[0061] 6. Get the three-phase modulation wave when the load is unbalanced

[0062] The three-phase modulation waves of the Vienna rectifier after injecting the zero-sequence component are defined as u ref_x , x=a, b, and c, the method to obtain the three-phase modulation wave when the load is unbalanced is as follows:

[0063]

[0064] In formula (V), u ref_x , x=a, b, and c represent the three-phase modulation wave of Vienna rectifier, u mx ,x=a,b,andc represents a three-phase normalized sine wave, u z2 Indicates the zero-sequence voltage under load unbalance conditions or injection, U dc1 , U dc2 Respectively Figure 1 The upper capacitor voltage and the lower capacitor voltage of the DC bus, U dc express Figure 1 Total bus voltage on the DC side.

[0065] When the load is unbalanced, the clamping area of ​​the three-phase Vienna rectifier carrier intermittent modulation in the first sector is shown in FIG5 , where Figure 5a Indicates the clamping region when R1<R2, Figure 5b It shows the clamping region when R1>R2.

[0066] The present invention uses PLECS software to build a three-phase Vienna rectifier simulation model, and uses simulation to verify the effectiveness of the three-phase Vienna rectifier carrier discontinuous modulation method of the present invention. The simulation conditions of the example are: simulation step length 3us, AC voltage effective value 115V, fundamental frequency 400Hz, and switching frequency of the switch tube is 100kHz.

[0067] FIG6 is a simulation waveform diagram of the three-phase Vienna rectifier carrier discontinuous modulation method invented when the load is balanced, and u in the figure is mais the normalized sine wave of phase A in the three-phase normalized sine wave, u z1 is the injected zero-sequence voltage when the load is balanced, u ref_a is the three-phase modulation wave when the load is balanced, u a is the AC input voltage, i a is the input current on the AC side, u AO is the voltage of the bridge arm of phase A. AP indicates that the voltage of the bridge arm of phase A is clamped to P, AO indicates that the voltage of the bridge arm of phase A is clamped to 0, and AN indicates that the voltage of the bridge arm of phase A is clamped to N. Figure 6a and Figure 6b It can be seen that when load balancing is carried out, the invented carrier discontinuous modulation method is adopted. Under different modulation ratios, the modulation wave is clamped to 0 near the current zero crossing, which is similar to Figure 4 The clamping area in is consistent, and the current waveform quality is good, which verifies the effectiveness of the proposed carrier discontinuous modulation method in load balancing. Figure 1 When the load resistance is R1=9Ω, R2=6Ω(R1>R2) and R1=6Ω, R2=9Ω(R1<R2), Figure 7a and Figure 7b It can be seen that when the load is unbalanced, the invented carrier intermittent modulation method is used, and the modulation wave is clamped to 0 near the current zero crossing, which is similar to Figure 5a and Figure 5b The clamping area in the circuit is consistent, and the current waveform quality is good, which verifies the effectiveness of the proposed carrier discontinuous modulation method when the load is unbalanced. The simulation shows that the three-phase Vienna rectifier carrier discontinuous modulation method of the present invention is simple to calculate and easy to implement.

[0068] The working principle and working process of the present invention are as follows:

[0069] According to the three-phase normalization formula of the three-phase Vienna rectifier SPWM modulation strategy, the normalized sine waves of the A phase voltage, the B phase voltage, and the C phase voltage are obtained as u ma ,u mb ,u mc ; Define the maximum value of the three-phase normalized sine wave at a certain moment as u max , the middle value is u mid , the minimum value is u min ; When the load is balanced, the injected zero-sequence voltage is u z1 , in u mid ≥0 when u z1 =max(-u mid ,-1-u min ), in u mid <0 time u z1 =min(-u mid ,1-u max ); when the load is unbalanced, the injected zero-sequence voltage is u z2 , in umid ≥0 when u z2 =max(-u mid ,-2U dc2 / U dc -u min ), in u mid <0 time u z2 =min(-u mid ,2U dc1 / U dc -u max );and by converting the zero sequence voltage u z1 / u z2 A three-phase normalized sine wave is injected to obtain a three-phase modulation wave of a three-phase Vienna rectifier. A three-phase Vienna rectifier simulation model is built with the help of PLECS software, and the effectiveness of the three-phase Vienna rectifier carrier discontinuous modulation method of the present invention is verified by simulation.

Claims

1. A carrier discontinuous modulation method for a three-phase Vienna rectifier, characterized in that: According to the three-phase normalization formula of the three-phase Vienna rectifier SPWM modulation strategy, the normalized sine waves of phase A, phase B, and phase C are obtained as u ma ,u mb ,u mc ; Define the maximum value of the normalized sine wave of phase A, phase B, and phase C at a certain moment as u max , the middle value is u mid , the minimum value is u min ; When the load is balanced, the injected zero-sequence voltage is u z1 The modulation method of the present invention is u mid ≥0 when u z1 =max(-u mid ,-1-u min ), in u mid <0 time u z1 =min(-u mid ,1-u max ); When the load is unbalanced, the injected zero-sequence voltage is u z2 The modulation method of the present invention is u mid ≥0 when u z2 =max(-u mid ,-2U dc2 / U dc -u min ), in u mid <0 time u z2 =min(-u mid ,2U dc1 / U dc -u max ), where U dc1 , U dc2 They represent the upper capacitor voltage and the lower capacitor voltage of the DC busbar, respectively. dc Indicates the total voltage of the DC busbar; and by converting the zero-sequence voltage u z1 / u z2 Injecting three-phase normalized sine waves, we get the three-phase modulation waves of the Vienna rectifier.

2. The carrier discontinuous modulation method of the three-phase Vienna rectifier according to claim 1, characterized in that: According to the three-phase normalization formula of the three-phase Vienna rectifier SPWM modulation strategy, the normalized sine wave u of phase A voltage is obtained. ma , B phase voltage normalized sine wave u mb , C phase voltage normalized sine wave u mc , and obtain the maximum value u of the normalized three-phase sine wave max , the middle value u mid , minimum value u min , the specific method is: The A phase voltage normalized sine wave u is obtained according to the three-phase normalization formula ma , B phase voltage normalized sine wave u mb , C phase voltage normalized sine wave u mc The normalized formula is: In the formula, f g is the grid frequency, m is the modulation ratio, m∈(0,1), and the modulation ratio m can be expressed by the formula Find, where U m Indicates the amplitude of the AC reference phase voltage, U dc Indicates the DC bus voltage, and the normalized sine wave u of phase A, phase B, and phase C voltage at a certain moment is obtained ma ,u mb ,u mc The maximum, middle and minimum values ​​of max 、u mid 、u min .

3. The carrier discontinuous modulation method of the three-phase Vienna rectifier according to claim 1, characterized in that: The zero sequence voltage u z1 The method of determining is as follows: In the above formula, u z1 Indicates the zero-sequence voltage injected when the load is balanced; u max ,u mid ,u min At a certain moment, the normalized sine wave u of phase A, phase B, and phase C ma ,u mb ,u mc The maximum, middle and minimum values ​​of min(-u mid ,1-u max ) display get-u mid Give 1-u max Minimum value: To-u mid ≤1-u max hour, min(-u mid ,1-u max )=-u mid , this 1-u max <-u mid hour, min(-u mid ,1-u max )=1-u max ;max(-u mid ,-1-u min ) display get-u mid Give-1-u min Maximum value: this-u mid ≥-1-u min time, max(-u mid ,-1-u min )=-u mid , this-1-u min >-u mid time, max(-u mid ,-1-u min )=-1-u min .

4. The carrier discontinuous modulation method of the three-phase Vienna rectifier according to claim 1, characterized in that: The three-phase modulation waves of the Vienna rectifier after the zero-sequence component is injected are defined as u ref_x , x=a, b, and c, and the calculation method is as follows: u ref_x =u mx +u z1 ,x=a,b and c (Ⅲ) In the above formula, u ref_x , x=a, b and c represent the three-phase modulation wave of Vienna rectifier, u mx represents a three-phase normalized sine wave, u z1 Represents the injected zero-sequence voltage when the load is balanced.

5. The carrier discontinuous modulation method of the three-phase Vienna rectifier according to claim 1, characterized in that: The zero-sequence voltage u injected when the load is unbalanced z2 The method of determining is as follows: 。 6. The carrier discontinuous modulation method of the three-phase Vienna rectifier according to claim 1, characterized in that: The three-phase modulation waves of the Vienna rectifier after the zero-sequence component is injected are defined as u ref_x , x=a, b, and c, and the calculation method is as follows: In the above formula, u ref_x , x=a, b, and c represent the three-phase modulation wave of Vienna rectifier, u mx ,x=a,b,and c represent three-phase normalized sine wave, u z2 Indicates the zero-sequence voltage under load unbalance conditions or injection, U dc1 , U dc2 They represent the upper capacitor voltage and the lower capacitor voltage of the DC busbar, respectively. dc Indicates the total DC bus voltage.

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