Low common-mode voltage modulation method for Vienna rectifier based on double-modulation wave optimization

Abstract

The application discloses a low common-mode voltage modulation method for a Vienna rectifier based on double-modulation-wave optimization, and belongs to the technical field of Vienna rectifier modulation. The application aims at the problem that common-mode voltage, midpoint voltage fluctuation and grid-side current harmonics are coupled with each other and affect the performance of the Vienna rectifier. The application comprises the following steps: calculating a voltage optimization zero sequence component u com_NP according to the three-phase grid voltage and the three-phase grid current of the Vienna rectifier, and making the midpoint current of the Vienna rectifier be zero; calculating three-phase reference voltage duty cycles according to the voltage optimization zero sequence component u com_NP ; and obtaining three-phase optimization double-modulation-waves according to the three-phase reference voltage duty cycles, wherein the three-phase optimization double-modulation-waves are combined with carriers to obtain driving signals for the Vienna rectifier. The application is used for common-mode voltage modulation of the Vienna rectifier.

Description

Technical Field

[0001] This invention relates to a low common-mode voltage modulation method for Vienna rectifiers based on dual modulation wave optimization, and belongs to the field of Vienna rectifier modulation technology. Background Technology

[0002] Vienna rectifiers are three-level converters connected to the power grid, providing stable DC-side voltage and sinusoidal input current. Compared to NPC three-level converters, Vienna rectifiers offer advantages such as higher efficiency, higher power density, and higher reliability, making them widely used in electric vehicle charging stations, wind power generation, and aerospace systems. Similar to two-level converters, three-level converters also exhibit common-mode voltage.

[0003] The presence of common-mode voltage has many negative impacts. For example, in wind power applications, it can lead to significant voltage stress on the motor windings, generate substantial common-mode noise from common-mode leakage current, and potentially create system safety hazards. Furthermore, due to midpoint current fluctuations, the Vienna rectifier experiences midpoint voltage imbalance, increasing voltage stress on switching devices and input current harmonics. These issues—common-mode voltage, midpoint voltage fluctuations, and input current harmonics—couple together, degrading the performance of the Vienna rectifier. Therefore, it is necessary to reduce common-mode voltage, midpoint voltage fluctuations, and input current harmonics to improve the performance of the Vienna rectifier.

[0004] To reduce the impact of common-mode voltage, traditional methods mainly include zero common-mode voltage modulation (ZCM) and common-mode voltage reduction modulation (CMPD). ZCM selects voltage vectors with zero common-mode voltage to synthesize a reference voltage vector, which can completely eliminate the influence of common-mode voltage. CMPD selects voltage vectors with zero common-mode voltage amplitude to synthesize a reference voltage vector, which can reduce the impact of common-mode voltage.

[0005] However, under high-modulation conditions, the zero common-mode voltage modulation method is prone to overmodulation and cannot suppress midpoint voltage fluctuations. Modulation methods that reduce common-mode voltage suppress midpoint voltage fluctuations by introducing an additional non-nearest voltage vector, but suffer from poor input current harmonic performance. Therefore, further research is needed on how to reduce common-mode voltage, midpoint voltage fluctuations, and input current harmonics. Summary of the Invention

[0006] To address the problem of mutual coupling between common-mode voltage, midpoint voltage fluctuations, and grid-side current harmonics affecting the performance of Vienna rectifiers, this invention provides a low common-mode voltage modulation method for Vienna rectifiers based on dual-modulation wave optimization.

[0007] The present invention provides a method for low common-mode voltage modulation of Vienna rectifiers based on dual-modulation wave optimization, comprising:

[0008] Based on the three-phase grid voltage and three-phase grid current of the Vienna rectifier, calculate the voltage optimization zero-sequence component u when the neutral point current of the Vienna rectifier is zero. com NP ;

[0009] Based on voltage optimization of zero-sequence component u com_NP The duty cycle of the three-phase reference voltage was calculated.

[0010] The three-phase optimized dual-modulation wave is calculated based on the duty cycle of the three-phase reference voltage. The three-phase optimized dual-modulation wave is then combined with the carrier wave to obtain the drive signal for the Vienna rectifier.

[0011] According to the dual-modulation wave optimized Vienna rectifier low common-mode voltage modulation method of the present invention, the voltage optimization zero-sequence component u com_NP The calculation method is as follows:

[0012]

[0013] In the formula u ra Let u be the per-unit value of phase a voltage. rc Per-unit value of phase c voltage:

[0014]

[0015] e ga Let e ​​be the voltage of phase a of the power grid. gc The voltage of phase c of the power grid; u DC The rectifier outputs DC voltage;

[0016] i a For phase a grid current, i b Let i be the phase b grid current. c This represents the current in phase c of the power grid.

[0017] According to the dual-modulation wave optimized Vienna rectifier low common-mode voltage modulation method of the present invention, the voltage optimization zero-sequence component u com_NP The process of obtaining it includes:

[0018] Based on the spatial voltage vector distribution diagram of the Vienna rectifier, small vectors U6, U1, U2, and U3 with low common-mode voltage amplitudes are selected to synthesize the reference voltage vector. Here, small vector U6 corresponds to vector POO, small vector U1 corresponds to vector OON, medium vector U2 corresponds to vector PON, and large vector U3 corresponds to vector PNN. The duty cycles d1, d2, d3, and d6 of small vector U1, medium vector U2, large vector U3, and small vector U6 are obtained.

[0019]

[0020] In the formula d a Let d be the duty cycle of the phase a reference voltage. b Let b be the duty cycle of the reference voltage, and d be the duty cycle of the reference voltage. c The duty cycle of the c-phase reference voltage;

[0021] To satisfy the volt-second balance principle, the duty cycle of the three-phase reference voltage must meet the following requirements within one switching cycle:

[0022]

[0023] In the formula u rb Per-unit value of phase b voltage: e gb Let u be the voltage of phase b of the power grid. com These are the superimposed zero-order components;

[0024] The average midpoint current i during one switching cycle of the Vienna rectifier np for:

[0025] i np =d6(-i a )+d2(i b )+d1(-i c (4)

[0026] Combining equations (3) and (2), we get:

[0027] i np =(u ra i c -u rc i a -2u rc i b )+u com (-i a +i b +i c (5)

[0028] When the average midpoint current i np If the value is 0, the zero-order component u is obtained. com The optimal value u com_NP .

[0029] According to the Vienna rectifier low common-mode voltage modulation method based on dual modulation wave optimization of the present invention, the zero-sequence component u is optimized based on voltage. com_NP The calculated duty cycle of the three-phase reference voltage is:

[0030]

[0031] According to the Vienna rectifier low common-mode voltage modulation method based on dual-modulation wave optimization of the present invention, the method for calculating the three-phase optimized dual-modulation wave based on the duty cycle of the three-phase reference voltage is as follows:

[0032]

[0033] In the formula u a1 For phase a, the optimized modulation wave is u. a2 For phase a, the optimized modulation wave two, u a1 and u a2 Composition of phase a optimized dual-modulation wave; u b1 For phase b, optimize the modulation wave one, u b2 For phase b, the optimized modulation wave two, u b1 and u b2 Composition of b-phase optimized dual-modulation wave; u c1 For the optimized modulation wave of phase c, u c2 For the optimized modulation wave of phase c, u c1 and u c2 A c-phase optimized dual-modulation wave is formed.

[0034] The beneficial effects of this invention are as follows: The method of this invention drives the Vienna rectifier through optimized dual-modulation waves, eliminating the need for voltage vector duty cycle and angle calculations, thus reducing the computational burden on the controller. This invention combines zero-sequence components and dual-modulation waves to optimize the switching sequence and duty cycle of the voltage vector, simultaneously reducing common-mode voltage, high-order harmonics of the input current, and midpoint voltage fluctuations, thereby improving the performance of the Vienna rectifier. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the circuit structure of the Vienna rectifier described in this invention; in the diagram, M is the midpoint of the three-phase power grid voltage, and L... s For inductance, R a R b and R c D is the three-phase resistance on the grid side. ap D an D bp D bn D cp D cn The six diodes forming the rectifier bridge; S a1 S a2 S b1 S b2 S c1 S c2 For three-phase switching transistors, D a1 D a2 D b1 D b2 D c1D c2 For the diode associated with the switching transistor, i p For the DC bus current, C p For the upper DC bus capacitor, i cp i is the current of the DC bus capacitor. np Let i be the midpoint current. cn C is the current of the lower DC bus capacitor. n For the lower DC bus capacitor, i n Where P is the DC bus current, O is the DC bus top, O is the DC bus capacitance midpoint, and N is the DC bus low end.

[0036] Figure 2 This is a low common-mode voltage vector distribution diagram;

[0037] Figure 3 It is based on Figure 2 The resulting low common-mode voltage vector combination diagram; S in the diagram a S b S c T is the pulse signal of the three-phase switching transistor in one switching cycle. s The switching period is represented by the x-axis; the x-axis represents time.

[0038] Figure 4 This is a schematic diagram illustrating the process of obtaining a three-phase optimized dual-modulation wave based on the duty cycle of the three-phase reference voltage; in the diagram, U0 is...

[0039] Figure 5 This is a control block diagram of the method of the present invention; in the diagram, x represents a, b, or c;

[0040] Figure 6 The experimental waveforms for the traditional space vector modulation method are shown.

[0041] Figure 7 Yes Figure 6 A schematic diagram of performing a Fast Fourier Transform;

[0042] Figure 8 The experimental waveforms for the traditional low common-mode voltage modulation method are shown.

[0043] Figure 9 Yes Figure 8 A schematic diagram of performing a Fast Fourier Transform;

[0044] Figure 10 The experimental waveforms of the method of this invention are shown in the comparison diagram.

[0045] Figure 11 Yes Figure 10 A schematic diagram of performing a Fast Fourier Transform. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0049] Specific Implementation Method 1: Combination Figures 1 to 5 As shown, this invention provides a method for low common-mode voltage modulation of a Vienna rectifier based on dual-modulation wave optimization, comprising:

[0050] Based on the three-phase grid voltage and three-phase grid current of the Vienna rectifier, calculate the voltage optimization zero-sequence component u when the neutral point current of the Vienna rectifier is zero. com_NP ;

[0051] Based on voltage optimization of zero-sequence component u com_NP The duty cycle of the three-phase reference voltage was calculated.

[0052] The three-phase optimized dual-modulation wave is calculated based on the duty cycle of the three-phase reference voltage. The three-phase optimized dual-modulation wave is then combined with the carrier wave to obtain the driving signal for the Vienna rectifier, thereby driving the Vienna rectifier.

[0053] This implementation is based on a dual-modulation wave driven Vienna rectifier. The dual-modulation wave is calculated directly using the optimal zero-sequence component, reducing the controller's computation time. By optimizing the switching sequence and duty cycle of the low common-mode voltage vector combination, the common-mode voltage, midpoint voltage fluctuations, and grid-side current harmonics of the Vienna rectifier are simultaneously reduced.

[0054] Furthermore, voltage optimization of zero-sequence component u com_NP The calculation method is as follows:

[0055]

[0056] In the formula u ra Let u be the per-unit value of phase a voltage. rc Per-unit value of phase c voltage:

[0057]

[0058] e gaLet e ​​be the voltage of phase a of the power grid. gc The voltage of phase c of the power grid; u DC The rectifier outputs DC voltage;

[0059] i a For phase a grid current, i b Let i be the phase b grid current. c This represents the current in phase c of the power grid.

[0060] Voltage optimization zero-sequence component u com_NP The process of obtaining the midpoint current involves: selecting a voltage vector with a low common-mode voltage amplitude; combining the influence of the voltage vector on the midpoint current; and obtaining the midpoint current within one switching cycle. When the midpoint current is zero, the optimal zero-sequence component u is obtained. com_NP .

[0061] Combination Figures 2 to 4 As shown, according to the spatial voltage vector distribution diagram of the Vienna rectifier, when the reference voltage vector is located in sub-region 5 of sector I of the spatial voltage vector distribution diagram of the Vienna rectifier, small vectors U6, U1, U2 and U3 with low common-mode voltage amplitude are selected to synthesize the reference voltage vector. Among them, small vector U6 corresponds to vector POO, small vector U1 corresponds to vector OON, medium vector U2 corresponds to vector PON and large vector U3 corresponds to vector PNN. Figure 2 The voltage vector OOO is a zero vector with low common-mode amplitude; voltage vectors PON, OPN, NPO, NOP, ONP, and PNO are medium vectors with low common-mode amplitude; voltage vectors PNN, PPN, NPN, NPP, NNP, and PNP are large vectors with low common-mode amplitude; voltage vectors POO, OON, OPO, NOO, NNO, and ONO are small vectors with low common-mode amplitude; voltage vectors ONN, PPO, NON, OPP, OOP, and POP are small vectors with high common-mode amplitude; combined with... Figure 3 The duty cycle d1 of small vector U1, the duty cycle d2 of medium vector U2, the duty cycle d3 of large vector U3, and the duty cycle d6 of small vector U6 can be obtained:

[0062]

[0063] In the formula d a Let d be the duty cycle of the phase a reference voltage. b Let b be the duty cycle of the reference voltage, and d be the duty cycle of the reference voltage. c The duty cycle of the c-phase reference voltage;

[0064] In order to satisfy the volt-second balance principle, the duty cycle of the three-phase reference voltage must meet the following requirements within one switching cycle:

[0065]

[0066] In the formula u rb Per-unit value of phase b voltage: e gb Let u be the voltage of phase b of the power grid. com These are the superimposed zero-order components;

[0067] When the Vienna rectifier outputs different voltage vectors, the switching transistors are in a conducting state, and phase currents flow into / out of the midpoint, thus affecting the magnitude of the midpoint voltage. For example, when the Vienna rectifier outputs voltage vector POO, the currents in the grid-side b-phase and c-phase flow out of the midpoint, thereby reducing the midpoint voltage. Voltage vectors PON and OON can control the currents in the grid-side b-phase and c-phase flow into or out of the midpoint. Therefore, the average midpoint current i during one switching cycle of the Vienna rectifier... np for:

[0068] i np =d6(-i a )+d2(i b )+d1(-i c (4)

[0069] Combining equations (3) and (2), we get:

[0070] i np =(u ra i c -u rc i a -2u rc i b )+u com (-i a +i b +i c (5)

[0071] To reduce midpoint voltage fluctuations, the average midpoint current needs to be zero over a switching cycle. When the average midpoint current i np If the value is 0, the zero-order component u is obtained. com The optimal value u com_NP As shown in equation (1).

[0072] Furthermore, the zero-sequence component u is optimized based on voltage. com_NP The calculated duty cycle of the three-phase reference voltage is:

[0073]

[0074] Figure 5In the dual-modulation wave calculation module, the switch is turned on when the carrier rise phase equals modulation wave one. When the carrier rise phase equals modulation wave two, the switch is turned off. When the carrier fall phase equals modulation wave 1, the switch is turned off; when the carrier fall phase equals modulation wave 2, the switch is turned on. For example, the initial state of the b-phase switch is 1. In [0, T... s During the / 2] time period, the carrier is in the rising phase, and the carrier is equal to the b-phase optimized modulation wave u. b2 At that time, the b-phase switch is turned off. When the carrier wave continues to increase, it equals the optimal modulation wave of the b-phase – u. b1 At that time, phase b switch is turned on. In [T] s / 2,T s During the time period, in the carrier descent phase, when the carrier is equal to the b-phase optimized modulation wave - u b1 At that time, the b-phase switch is turned off. When the carrier wave continues to decrease to equal the optimal modulation wave of the b-phase, u... b2 When the phase b switch is turned on, a phase b switch pulse is generated.

[0075] Combination Figure 4 The method for calculating the optimized three-phase dual-modulation wave based on the duty cycle of the three-phase reference voltage is as follows:

[0076]

[0077] In the formula u a1 For phase a, the optimized modulation wave is u. a2 For phase a, the optimized modulation wave two, u a1 and u a2 Composition of phase a optimized dual-modulation wave; u b1 For phase b, optimize the modulation wave one, u b2 For phase b, the optimized modulation wave two, u b1 and u b2 Composition of b-phase optimized dual-modulation wave; u c1 For the optimized modulation wave of phase c, u c2 For the optimized modulation wave of phase c, u c1 and u c2 A c-phase optimized dual-modulation wave is formed.

[0078] Figure 5 Medium carrier drive module: Under the premise of known three-phase optimized dual modulation wave, the carrier is combined to complete the drive of Vienna rectifier.

[0079] Figures 6 to 11 Experimental waveforms and Fast Fourier Transform (FFT) analyses were performed using the traditional space vector modulation method, the traditional low common-mode voltage modulation method, and the method of this invention, respectively. This includes the rectifier output DC voltage u. DC DC bus capacitor voltage uPO DC bus capacitor voltage u ON Phase b grid current i b and common-mode voltage u OM .

[0080] Depend on Figures 6 to 11 It can be seen that the common-mode voltage amplitudes of the low common-mode voltage modulation method and the method of this invention are 12V and 28V respectively, which are significantly lower than the common-mode voltage amplitude of 70V of the traditional space vector modulation method, thus reducing the common-mode voltage. When using the traditional low common-mode voltage modulation method, the grid current switching harmonic is 0.27A, while the switching harmonic of the method of this invention is only 0.07A, which is 26% of that of the traditional low common-mode voltage modulation method. The modulation method of this invention results in essentially equal upper and lower DC bus voltages, and the midpoint voltage fluctuation is essentially zero. Therefore, the method of this invention simultaneously reduces the common-mode voltage of the Vienna rectifier, grid-side current harmonics, and midpoint voltage fluctuation.

[0081] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for low common-mode voltage modulation of Vienna rectifiers based on dual-modulation wave optimization, characterized in that... include, Based on the three-phase grid voltage and three-phase grid current of the Vienna rectifier, calculate the voltage optimization zero-sequence component u when the neutral point current of the Vienna rectifier is zero. com_NP ; Based on voltage optimization of zero-sequence component u com_NP The duty cycle of the three-phase reference voltage was calculated. The three-phase optimized dual modulation wave is calculated based on the duty cycle of the three-phase reference voltage. The three-phase optimized dual modulation wave is then combined with the carrier wave to obtain the drive signal for the Vienna rectifier. Voltage optimization zero-sequence component u com_NP The process of obtaining it includes: Based on the spatial voltage vector distribution diagram of the Vienna rectifier, small vectors U6, U1, U2, and U3 with low common-mode voltage amplitudes are selected to synthesize the reference voltage vector. Here, small vector U6 corresponds to vector POO, small vector U1 to vector OON, medium vector U2 to vector PON, and large vector U3 to vector PNN. The duty cycles d1, d2, d3, and d6 of small vector U1, medium vector U2, large vector U3, and small vector U6 are obtained. （2）， In the formula d a Let d be the duty cycle of the phase a reference voltage. b Let b be the duty cycle of the reference voltage, and d be the duty cycle of the reference voltage. c The duty cycle of the c-phase reference voltage; To satisfy the volt-second balance principle, the duty cycle of the three-phase reference voltage must satisfy the following within one switching cycle: （3）， In the formula Let u be the per-unit value of phase a voltage. rc U is the per-unit value of the c-phase voltage. rb Per-unit value of phase b voltage: ; This is the voltage of phase b of the power grid. The rectifier outputs DC voltage, u com These are the superimposed zero-order components; Average midpoint current over one switching cycle of the Vienna rectifier for: （4）， Combining equations (3) and (2), we get: （5）， When the average midpoint current If the value is 0, the zero-order component u is obtained. com The optimal value u com_NP In the formula, i a For phase a grid current, i b Let i be the phase b grid current. c This represents the current in phase c of the power grid.

2. The Vienna rectifier low common-mode voltage modulation method based on dual-modulation wave optimization according to claim 1, characterized in that, Voltage optimization zero-sequence component u com_NP The calculation method is as follows: （1）， ， ； In the formula Let a be the voltage of the grid phase a. This is the voltage of phase c of the power grid.

3. The Vienna rectifier low common-mode voltage modulation method based on dual-modulation wave optimization according to claim 2, characterized in that, Based on voltage optimization of zero-sequence component u com_NP The calculated duty cycle of the three-phase reference voltage is: （6）。 4. The Vienna rectifier low common-mode voltage modulation method based on dual-modulation wave optimization according to claim 3, characterized in that, The method for calculating the optimized three-phase dual-modulation wave based on the duty cycle of the three-phase reference voltage is as follows: （7）， In the formula To optimize the modulation wave for phase a, To optimize the modulation wave of phase a, and Composition of phase a optimized dual-modulation wave; To optimize the modulation wave for phase b, To optimize the modulation wave for phase b, and Forming a phase b optimized dual-modulation wave; To optimize the modulation wave for phase c, To optimize the modulation wave for phase c, and A c-phase optimized dual-modulation wave is formed.

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