Zero-sequence circulating current suppression modulation method based on improved double modulation waves

Abstract

The invention discloses a zero-sequence circulating current suppression modulation method based on improved double modulation waves. The method comprises the following steps: step 1, defining a zero-sequence circulating current; 2, a common mode voltage expression is deduced; 3, a common-mode voltage difference expression is deduced; step 4, deducing a zero-sequence circulating current expression; step 5, establishing a parallel rectifier zero-sequence circulation equivalent circuit; step 6, proposing a zero-sequence circulating current suppression modulation strategy; 7, deducing a common-mode voltage difference time domain expression of a zero-sequence circulating current suppression modulation strategy; step 8, deducing a zero-sequence circulating current time domain expression; step 9, deriving a zero-sequence circulating current peak-to-peak value expression; the method is suitable for a switch-type power amplifier rectifier-stage parallel rectifier system, and achieves the effect of suppressing the zero-sequence circulating current of a multi-parallel rectifier system by increasing the frequency of the zero-sequence circulating current and reducing the excitation of the common-mode voltage difference to the zero-sequence circulating current. The zero-sequence circulating current suppression modulation strategy MDRPWM based on the improved double modulation waves can suppress the zero-sequence circulating current in a full modulation degree range, and the suppression effect is better.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a zero-sequence circulating current suppression modulation method based on an improved dual modulation wave. Background Art

[0002] A single three-phase rectifier is limited by the capacity of the power switch tube, and its output power is difficult to meet the requirements of a high-power switching power amplifier. The AC / DC stage of a high-power wide-band switching power amplifier uses a parallel topology of two three-phase rectifiers. The advantage of this technology is that it can double the system capacity without increasing the current stress of the power switch tube. However, due to the use of a topological structure that shares the AC and DC bus, there is a zero-sequence circulating current flow path inside the parallel three-phase rectifier, which introduces a zero-sequence circulating current problem. Traditional modulation strategies cannot suppress zero-sequence circulating current under full modulation, resulting in severe distortion of the AC input current, increased voltage and current stress of the power switch tube, and attenuated stability of the parallel rectifier system.

[0003] The key to suppressing high-frequency zero-sequence circulating current is to reduce the common-mode voltage Common-ModeVoltage, CMV, of each parallel converter. The existing APOD-PWM modulation strategy has a lower common-mode voltage than the PD-PWM modulation strategy, and thus has a lower zero-sequence circulating current. The high-frequency zero-sequence circulating current can be further reduced by changing the reference signal of the parallel converter. The most commonly used method is the space vector modulation strategy Space Vector Pulse Width Modulation, SVPWM. Compared with the traditional sinusoidal PWM modulation strategy Sinusoidal Pulse Width Modulation, SPWM, the SVPWM modulation strategy has a higher DC voltage utilization rate and a lower common-mode voltage. Based on this, a modulation strategy based on double modulation waves Double Reference Pulse Width Modulation, DRPWM achieves the effect of suppressing zero-sequence circulating current by changing the common-mode voltage characteristics of the parallel converter. However, the modulation strategy has limited effect on suppressing zero-sequence circulating current when the low-profile system is used. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a zero-sequence circulating current suppression modulation method based on an improved dual modulation wave. The suppression principle of the method is to increase the frequency of the zero-sequence circulating current, thereby reducing the excitation of the zero-sequence circulating current by the common-mode voltage difference. Compared with the existing zero-sequence circulating current suppression strategies DRPWM, SVPWM, and SPWM, the proposed zero-sequence circulating current suppression modulation strategy MDRPWM based on an improved dual modulation wave can suppress the zero-sequence circulating current within the full modulation range, and the suppression effect is better.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A zero-sequence circulating current suppression modulation method based on an improved dual modulation wave comprises the following steps: Step 1. Define the zero-sequence circulating current of the parallel rectifier system of the switching power amplifier rectifier stage; Step 2, derive the common-mode voltage expression of the parallel rectifier system of the switching power amplifier rectification stage; Step 3, derive the common-mode voltage difference expression of the parallel rectifier system of the switching power amplifier rectification stage; Step 4, derive the zero-sequence circulating current expression of the parallel rectifier system of the switching power amplifier rectification stage; Step 5, establish the zero-sequence circulating current equivalent circuit of parallel rectifiers; Step 6: Propose a zero-sequence circulating current suppression modulation strategy based on improved dual modulation wave; Step 7, derive the time domain expression of the common mode voltage difference based on the zero-sequence circulating current suppression modulation strategy of the improved dual modulation wave; Step 8, derive the zero-sequence circulating current time domain expression based on the zero-sequence circulating current suppression modulation strategy of the improved dual modulation wave; Step 9, derive the zero-sequence circulating current peak-to-peak value expression of the zero-sequence circulating current suppression modulation strategy based on the improved dual modulation wave; The specific steps of Step 1 above are: Definition of zero-sequence circulating current of three-phase parallel T-type rectifier system i cir is the sum of the input currents of each phase, that is: ; (1) In the formula, i cir is the zero-sequence circulating current; i xi For rectifier i No. x Phase current; The specific steps of Step 2 above are: Defining Rectifier i Common mode voltage u cmi is the sum of the input voltages of each phase, that is: ; (2) In the formula, u cmi 、u xi Rectifier i The common mode voltage and x Phase voltage; The specific steps of Step 3 above are: Defining the common-mode voltage difference of parallel rectifiers u dcm The expression is: ; (3) In the formula, L i Rectifier i Input inductance; The specific steps of Step 4 above are: Calculation of zero-sequence circulating current in parallel systems i cir The expression is: ; (4) The specific steps of Step 5 above are: According to formula (4), the zero-sequence circulating current equivalent circuit of the parallel rectifier is obtained. i cir Input filter inductor with parallel rectifier L i Inversely proportional to the input filter inductance, increasing the input filter inductance can effectively reduce the circulating current; in addition, the zero-sequence circulating current i cir The common-mode voltage difference between each rectifier u dcm About Time t is related to the integral of, therefore, by reducing the instantaneous value of the common-mode voltage difference | u dcm | and the action time of the common mode voltage difference t udcm To suppress zero-sequence circulating current.

[0006] The specific steps of Step 6 above include: Two bias voltages are injected into each phase of the traditional sinusoidal modulation wave at the same time u offset_top and u offset_bottom , so that each phase generates two modulation waves, and the expression is: ; (5) In the formula, u refA_top , u refB_top , u refC_top Represent the up-modulation wave signals of phases A, B, and C respectively; u refA_bottom , u refB_bottom , u refC_bottom Respectively represent the down-modulation wave signals of phases A, B, and C;M Indicates the modulation system; Bias voltage injection voltage expression u offset_top and u offset_bottom The expression is: ; (6) In the formula, u max Indicates the maximum value of the three-phase sinusoidal modulation wave at the current moment; u min Indicates the minimum value of the three-phase sinusoidal modulation wave at the current moment; u x Indicates the current time x The instantaneous value of the phase modulated wave, x =A, B, C; The specific steps of Step 7 above are: Analysis of the common-mode voltage difference generated by parallel rectifiers under MDRPWM modulation strategy u dcm for: ; (7) In the formula, U dc Indicates DC voltage, t 1- t 6 represents each moment of the switching sequence; The specific steps of Step 8 above are: Substituting (7) into (4), assuming that the input inductance L 1= L 2= L , under the MDRPWM modulation strategy, the zero-sequence circulating current generated by the parallel rectifier is i cir for: ; (8) The specific steps of Step 9 above are: Step 9.1, calculate the modulation degree 0.5< M <1 under different modulation strategies, that is: ; (9) In the formula, T s represents the sampling time; u max, u mid、 u min represents the maximum value, middle value and minimum value of the three-phase modulation wave at the current moment; i p2p_SPWM, i p2p_SVPWM, ip2p_DRPWM, i p2p_MDRPWM represents the peak-to-peak value of zero-sequence circulating current under SPWM, SVPWM, DRPWM and MDRPWM modulation strategies respectively; Step9.2, calculate the modulation degree 0< M <0.5 under different modulation strategies, that is: ; (10) In the formula, T s represents the sampling time; u max, u mid、 u min represents the maximum value, middle value and minimum value of the three-phase modulation wave at the current moment; i p2p_SPWM, i p2p_SVPWM, i p2p_DRPWM, i p2p_MDRPWM represents the peak-to-peak value of zero-sequence circulating current under SPWM, SVPWM, DRPWM and MDRPWM modulation strategies respectively; Step 9.3, determine the peak-to-peak value of the zero-sequence circulating current at different modulation indices under different modulation strategies.

[0007] The present invention provides a zero-sequence circulating current suppression modulation method based on an improved dual modulation wave. The present invention is applicable to a parallel rectifier system of a rectifier stage of a switching power amplifier. By increasing the frequency of the zero-sequence circulating current and reducing the excitation of the zero-sequence circulating current by the common-mode voltage difference, the zero-sequence circulating current of the multi-parallel rectifier system can be suppressed. Compared with the existing zero-sequence circulating current suppression strategies DRPWM, SVPWM, and SPWM, the proposed zero-sequence circulating current suppression modulation strategy MDRPWM based on an improved dual modulation wave can suppress zero-sequence circulating current within the full modulation range, and the suppression effect is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 It is a topological schematic diagram of a three-phase parallel T-type rectifier of the present invention; Figure 2 It is the schematic diagram of the zero-sequence circulating current equivalent circuit; Figure 3 It is a schematic diagram of modulation wave based on the zero-sequence circulating current suppression modulation strategy of improved dual modulation wave; Figure 4 It is a schematic diagram of each bridge arm voltage, common mode voltage difference and zero-sequence circulating current under the zero-sequence circulating current suppression modulation strategy based on the improved dual modulation wave; Figure 5 Schematic diagram of zero-sequence circulating current peak-to-peak value at different modulation indices under different modulation strategies; Figure 6 The modulation degree in the embodiment M =0.9, zero-sequence circulating current waveform of parallel rectifier under SPWM, SVPWM, DRPWM, and MDRPWM modulation strategies; Figure 7 The modulation degree in the embodiment M =0.45, the zero-sequence circulating current waveform of the parallel three-phase T-type rectifier under SPWM, SVPWM, DRPWM, and MDRPWM modulation strategies. DETAILED DESCRIPTION

[0009] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0010] Three-phase parallel T-type rectifier topology Figure 1 As shown; the zero-sequence circulating current equivalent circuit is as follows Figure 2 As shown; the modulation wave based on the zero-sequence circulating current suppression modulation strategy of the improved dual modulation wave is as follows Figure 3 As shown; the bridge arm voltage, common mode voltage difference and zero-sequence circulating current under the zero-sequence circulating current suppression modulation strategy based on the improved dual modulation wave are shown as follows Figure 4 As shown in the figure; the peak value of zero-sequence circulating current at different modulation degrees under different modulation strategies is as follows Figure 5 shown.

[0011] Step 1 includes: Step 1.1: Define Figure 1 The zero-sequence circulating current of the three-phase parallel T-type rectifier system shown in i cir is the sum of the input currents of each phase, that is: ; (1) (1) In the formula, i cir is the zero-sequence circulating current; i xi For rectifier i No. x Phase current.

[0012] Step 1.2: Define the Rectifier i Common mode voltage u cmi is the sum of the input voltages of each phase, that is: ; (2) (2) In the formula, u cmi 、u xi Rectifier i The common mode voltage and x Phase voltage.

[0013] Step 1.3: Define the common-mode voltage difference of parallel rectifiers u dcm The expression is: ; (3) (3) In the formula, L i Rectifier i The input inductance.

[0014] Step 1.4: Calculate the zero-sequence circulating current of the parallel system i cir The expression is: ; (4) Step 1.5: According to equation (4), the zero-sequence circulating current equivalent circuit of the parallel rectifier is obtained, as Figure 2 As shown; from formula (4) and Figure 2 It can be obtained that the zero-sequence circulating current of the parallel rectifier is i cir Input filter inductor with parallel rectifier L i Inversely proportional to the input filter inductance, increasing the input filter inductance can effectively reduce the circulating current; in addition, the zero-sequence circulating current i cir The common-mode voltage difference between each rectifier u dcm About Time t The integral of is related, therefore, considering the instantaneous value of the common-mode voltage difference by reducing | u dcm | and the action time of the common mode voltage difference t udcm To suppress zero-sequence circulating current.

[0015] Step 2 includes: Step 2.1: Simultaneously inject two bias voltages into each phase of the traditional sinusoidal modulation wave u offset_top and u offset_bottom , so that each phase generates two modulation waves respectively, and the modulation wave signal is improved as follows Figure 3 As shown, its expression is: ; (5) (5) In the formula, u refA_top , u refB_top , u refC_top Represent the up-modulation wave signals of phases A, B, and C respectively; u refA_bottom , u refB_bottom , urefC_bottom Respectively represent the down-modulation wave signals of phases A, B, and C; M Indicates the modulation system.

[0016] Bias voltage injection voltage expression u offset_top and u offset_bottom The expression is: ; (6) (6) In the formula, u max Indicates the maximum value of the three-phase sinusoidal modulation wave at the current moment; u min Indicates the minimum value of the three-phase sinusoidal modulation wave at the current moment; u x Indicates the current time x The instantaneous value of the phase modulated wave, x =A, B, C.

[0017] Step 2.2: Analyze the common-mode voltage difference generated by parallel rectifiers under MDRPWM modulation strategy u dcm for: ; (7) (7) In the formula, U dc Indicates DC voltage, t 1- t 6 represents the various moments of the switching sequence.

[0018] Step 2.3: Substitute (7) into (4), assuming that the input inductance is L 1= L 2= L , under the MDRPWM modulation strategy, the zero-sequence circulating current generated by the parallel rectifier is i cir for: ; (8) From equations (7) and (8), the common-mode voltage difference of the MDRPWM modulation strategy is ± U dc / 3 has a short duration ( t 1- t 2 moment); In addition, the frequency of the common-mode voltage difference is doubled to twice the original frequency, so the common-mode voltage difference u dcm About Time t The integral of is very small, and the peak value of the zero-sequence circulating current is effectively suppressed.

[0019] Step 2.4: Calculate the modulation degree 0.5< M<1 under different modulation strategies, that is: ; (9) (9) In the formula, T s represents the sampling time; u max, u mid、 u min represents the maximum value, middle value and minimum value of the three-phase modulation wave at the current moment; i p2p_SPWM, i p2p_SVPWM, i p2p_DRPWM, i p2p_MDRPWM represents the peak-to-peak value of zero-sequence circulating current under SPWM, SVPWM, DRPWM and MDRPWM modulation strategies respectively.

[0020] Step 2.5: Calculate the modulation index 0< M <0.5 under different modulation strategies, that is: ; (10) In formula (10), T s represents the sampling time; u max, u mid、 u min represents the maximum value, middle value and minimum value of the three-phase modulation wave at the current moment; i p2p_SPWM, i p2p_SVPWM, i p2p_DRPWM, i p2p_MDRPWM represents the peak-to-peak value of zero-sequence circulating current under SPWM, SVPWM, DRPWM and MDRPWM modulation strategies respectively.

[0021] Step 2.6: Make the peak-to-peak value of zero-sequence circulating current under different modulation strategies and different modulation indices, such as Figure 5 shown by Figure 5 It can be concluded that within the full modulation range, the MDRPWM modulation strategy has a good suppression effect on the zero-sequence circulating current.

[0022] Example: A simulation model of a parallel three-phase T-type rectifier was built on the Matlab / Simulink platform, and the SPWM, SVPWM, DRPWM, and MDRPWM modulation strategies were used to control the simulation model.

[0023] Figure 6 For adjustment system M=0.9, the zero-sequence circulating current waveform of the parallel rectifier under SPWM, SVPWM, DRPWM, and MDRPWM modulation strategies. In the figure, i a. i b. i c represent the three-phase input current respectively; i cir represents the zero-sequence circulating current, I RMS_cir and I peak_cir represents the effective value and peak value of the zero-sequence circulating current respectively.

[0024] contrast Figure 6 (a)-(d) show that the relationship between the effective value of zero-sequence circulating current and the peak value of zero-sequence circulating current under each modulation strategy is: (11) (12) From equations (11) and (12), it can be obtained that the MDRPWM modulation strategy has a modulation index of M =0.9, the suppression effect on zero-sequence circulating current is best.

[0025] Figure 7 For adjustment system M =0.45, the zero-sequence circulating current waveform of the parallel three-phase T-type rectifier under SPWM, SVPWM, DRPWM, and MDRPWM modulation strategies.

[0026] contrast Figure 7 (a)-(d) show that the relationship between the effective value of zero-sequence circulating current and the peak value of zero-sequence circulating current under each modulation strategy is: (13) (14) From equations (13) and (14), it can be obtained that the MDRPWM modulation strategy has a modulation index of M =0.45, the suppression effect on zero-sequence circulating current is still optimal.

Claims

1. A zero-sequence circulating current suppression modulation method based on improved dual modulation wave, characterized in that: The following steps are involved: Step 1. Define the zero-sequence circulating current of the parallel rectifier system of the switching power amplifier rectifier stage; Step 2, derive the common-mode voltage expression of the parallel rectifier system of the switching power amplifier rectification stage; Step 3, derive the common-mode voltage difference expression of the parallel rectifier system of the switching power amplifier rectification stage; Step 4, derive the zero-sequence circulating current expression of the parallel rectifier system of the switching power amplifier rectification stage; Step 5, establish the zero-sequence circulating current equivalent circuit of parallel rectifiers; Step 6: Propose a zero-sequence circulating current suppression modulation strategy based on improved dual modulation wave; Step 7, derive the time domain expression of the common mode voltage difference based on the zero-sequence circulating current suppression modulation strategy of the improved dual modulation wave; Step 8, derive the zero-sequence circulating current time domain expression based on the zero-sequence circulating current suppression modulation strategy of the improved dual modulation wave; Step 9. Derive the expression of the zero-sequence circulating current peak-to-peak value based on the zero-sequence circulating current suppression modulation strategy of the improved dual modulation wave.

2. According to the zero-sequence circulating current suppression modulation method based on improved dual modulation wave as described in claim 1, it is characterized in that: The specific steps of Step 1 are: Definition of zero-sequence circulating current of three-phase parallel T-type rectifier system i cir is the sum of the input currents of each phase, that is: ；（1） In the formula, i cir is the zero-sequence circulating current; i xi For rectifier i No. x Phase current.

3. According to the zero-sequence circulating current suppression modulation method based on improved dual modulation wave as described in claim 2, it is characterized in that: The specific steps of Step 2 are: Defining Rectifier i Common mode voltage u cmi is the sum of the input voltages of each phase, that is: ；（2） In the formula, u cmi 、u xi Rectifier i The common mode voltage and x Phase voltage.

4. According to the zero-sequence circulating current suppression modulation method based on improved dual modulation wave as described in claim 3, it is characterized in that: The specific steps of Step 3 are: Defining the common-mode voltage difference of parallel rectifiers u dcm The expression is: ；（3） In the formula, L i Rectifier i The input inductance.

5. According to the zero-sequence circulating current suppression modulation method based on improved dual modulation wave as described in claim 4, it is characterized in that: The specific steps of Step 4 are: Calculation of zero-sequence circulating current in parallel systems i cir The expression is: ；（4）。 6. According to the zero-sequence circulating current suppression modulation method based on improved dual modulation wave as described in claim 5, it is characterized in that: The specific steps of Step 5 are: According to formula (4), the zero-sequence circulating current equivalent circuit of the parallel rectifier is obtained. i cir Input filter inductor with parallel rectifier L i Inversely proportional to the input filter inductance, increasing the input filter inductance can effectively reduce the circulating current; in addition, the zero-sequence circulating current i cir The common-mode voltage difference between each rectifier u dcm About Time t is related to the integral of, therefore, by reducing the instantaneous value of the common-mode voltage difference | u dcm | and the action time of the common mode voltage difference t udcm To suppress zero-sequence circulating current.

7. A zero-sequence circulating current suppression modulation method based on improved dual modulation wave according to claim 6, characterized in that: The specific steps of Step 6 include: Two bias voltages are injected into each phase of the traditional sinusoidal modulation wave at the same time u offset_top and u offset_bottom , so that each phase generates two modulation waves, and its expression is: ；（5） In the formula, u refA_top , u refB_top , u refC_top Respectively represent the up-modulation wave signals of phases A, B, and C; u refA_bottom , u refB_bottom , u refC_bottom Respectively represent the down-modulation wave signals of phases A, B, and C; M Indicates the modulation system; Bias voltage injection voltage expression u offset_top and u offset_bottom The expression is: ；（6） In the formula, u max Indicates the maximum value of the three-phase sinusoidal modulation wave at the current moment; u min Indicates the minimum value of the three-phase sinusoidal modulation wave at the current moment; u x Indicates the current time x The instantaneous value of the phase modulated wave, x =A, B, C.

8. A zero-sequence circulating current suppression modulation method based on improved dual modulation wave according to claim 7, characterized in that: The specific steps of Step 7 include: Analysis of the common-mode voltage difference generated by parallel rectifiers under MDRPWM modulation strategy u dcm for: ；（7） In the formula, U dc represents the DC voltage, t 1- t 6 represents the various moments of the switching sequence.

9. A zero-sequence circulating current suppression modulation method based on improved dual modulation wave according to claim 8, characterized in that: The specific steps of Step 8 include: Substituting (7) into (4), assuming that the input inductance L 1= L 2= L , under the MDRPWM modulation strategy, the zero-sequence circulating current generated by the parallel rectifier is i cir for: ；（8）。 10. The zero-sequence circulating current suppression modulation method based on improved dual modulation wave according to claim 9, characterized in that: The specific steps of Step 9 include: Step 9.1, calculate the modulation degree 0.5< M <1 under different modulation strategies, that is: ；（9） In the formula, T s represents the sampling time; u max, u mid、 u min represents the maximum value, middle value and minimum value of the three-phase modulation wave at the current moment; i p2p_SPWM, i p2p_SVPWM, i p2p_DRPWM, i p2p_MDRPWM represents the peak-to-peak value of zero-sequence circulating current under SPWM, SVPWM, DRPWM and MDRPWM modulation strategies respectively; Step9.2, calculate the modulation degree 0< M <0.5 under different modulation strategies, that is: ；（10） In the formula, T s represents the sampling time; u max, u mid、 u min represents the maximum value, middle value and minimum value of the three-phase modulation wave at the current moment; i p2p_SPWM, i p2p_SVPWM, i p2p_DRPWM, i p2p_MDRPWM represents the peak-to-peak value of zero-sequence circulating current under SPWM, SVPWM, DRPWM and MDRPWM modulation strategies respectively; Step 9.3, determine the peak-to-peak value of the zero-sequence circulating current at different modulation indices under different modulation strategies.

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