Single-arm modulation method for small-capacitor voltage source back-to-back converter

Abstract

The present invention provides a single bridge arm modulation method of a small-capacitor voltage source type back-to-back converter, including: S1, determining the current moment of the rectifier stage modulation bridge arm and the compensation phase according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module; S2, determining the first duty cycle of the rectifier stage modulation bridge arm at the current moment based on the volt-second balance principle of the inductor. The present invention modulates only one of the three bridge arms of the rectifier stage module at the same time, reduces the switching loss while ensuring the input side power quality, improves the power transmission efficiency of the small-capacitor voltage source type back-to-back converter, cancels the control of the DC side voltage, maintains the DC side voltage in a quasi-six-pulse state, greatly reduces the requirements for the DC energy storage capacitor, greatly reduces the DC energy storage capacitor on the basis of ensuring the output side power quality, ensures good input and output waveform quality, and reduces costs.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a single bridge arm modulation method of a small-capacitor voltage source type back-to-back converter. Background Art

[0002] The voltage source back-to-back converter achieves wide range regulation of voltage frequency and amplitude, and can convert the power grid frequency voltage into the voltage required by electrical equipment. It also has excellent characteristics such as bidirectional energy flow, sinusoidal input and output currents, controllable input power factor, and decoupling of front- and rear-stage controls. It is widely used in the field of AC-AC power conversion today.

[0003] However, there is a DC energy storage capacitor in the voltage source back-to-back converter, which accounts for a large volume and seriously affects the power density of the voltage source back-to-back converter. At the same time, a larger DC energy storage capacitor will increase the potential operating risk of the voltage source back-to-back converter and affect its working life, which is not conducive to the long-term reliable operation of the voltage source back-to-back converter. In addition, there are many power switches in the voltage source back-to-back converter, and the conventional modulation method will produce large switching losses, which seriously restricts the further improvement of its power conversion efficiency.

[0004] Currently, there is an indirect matrix converter solution that can significantly reduce or even eliminate DC energy storage capacitors, but this solution still has some shortcomings: first, there are bidirectional switches in its topology, which requires a commutation solution design; second, the front and rear stages need to be coordinated and modulated, and the modulation strategy is highly complex; third, there is no DC side path, and the load side commutation loop is large. Summary of the invention

[0005] The present invention provides a single-bridge-arm modulation method for a small-capacitor voltage source back-to-back converter, the purpose of which is to solve the problem that the DC energy storage capacitor in a traditional voltage source back-to-back converter is large in size and affects the power density and reliability of the converter.

[0006] In order to achieve the above object, an embodiment of the present invention provides a single bridge arm modulation method of a small capacitor voltage source type back-to-back converter, comprising:

[0007] S1, determining the rectifier stage modulation bridge arm and compensation phase at the current moment according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module;

[0008] S2, determining the first duty cycle of the rectifier stage modulation bridge arm at the current moment based on the volt-second balance principle of the inductor;

[0009] S3, determining the output power of the small-capacitor voltage source type back-to-back converter according to the three-phase output voltage and the three-phase output current of the inverter-stage module, and determining the reference current of the compensation phase of the rectifier-stage module at the current moment according to the output power of the small-capacitor voltage source type back-to-back converter;

[0010] S4, determining the real-time error value of the compensation phase current according to the reference current of the compensation phase of the rectifier stage module at the current moment, determining the second duty cycle of the rectifier stage modulation bridge arm at the current moment according to the real-time error value of the compensation phase current and the first duty cycle of the rectifier stage modulation bridge arm at the current moment, the rectifier stage modulation bridge arm at the current moment performs switching according to the second duty cycle of the rectifier stage modulation bridge arm at the current moment, and the remaining rectifier stage bridge arms perform low-frequency switching according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module;

[0011] S5, determining the zero-sequence component of the modulation signal of the inverter module according to the three-phase output voltage of the inverter module, and determining the zero-sequence superposition modulation signal of the inverter module according to the zero-sequence component of the modulation signal of the inverter module and the three-phase output voltage of the inverter module;

[0012] S6, determining the duty cycle of each bridge arm of the inverter module according to the bipolar carrier modulation principle and geometric theory, and switching each bridge arm of the inverter module according to the duty cycle of each bridge arm of the inverter module.

[0013] The above scheme of the present invention has the following beneficial effects:

[0014] The single-bridge-arm modulation method of the small-capacitor voltage source back-to-back converter described in the above-mentioned embodiment of the present invention only modulates one of the three bridge arms of the rectifier stage module at the same time, thereby reducing switching losses while ensuring the input side power quality, improving the power transmission efficiency of the small-capacitor voltage source back-to-back converter, canceling the control of the DC side voltage, maintaining the DC side voltage in a quasi-six-pulse state, greatly reducing the requirements for the DC energy storage capacitor, and greatly reducing the DC energy storage capacitor on the basis of ensuring the output side power quality, ensuring good input and output waveform quality, reducing costs, and effectively improving the power density and reliability of the small-capacitor voltage source back-to-back converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flow chart of the present invention;

[0016] Figure 2 It is a structural block diagram of the present invention;

[0017] Figure 3 It is a specific circuit diagram of a small-capacitor voltage source back-to-back converter;

[0018] Figure 4It is a modulation schematic diagram of the inverter-level module of the present invention;

[0019] Figure 5 (a) is a schematic diagram of the three-phase input current waveform of the present invention;

[0020] Figure 5 (b) is a schematic diagram of the three-phase output current waveform of the present invention;

[0021] Figure 5 (c) is a schematic diagram of the output two-phase line voltage waveform of the present invention;

[0022] Figure 5 (d) is a schematic diagram of the output two-phase line voltage waveform of the present invention;

[0023] Figure 6 It is a schematic diagram of the PI regulator structure of the present invention.

[0024] [Description of Reference Numerals]

[0025] 1-three-phase input power module; 2-first input power; 3-second input power; 4-third input power; 5-rectifier module; 6-input filter inductor unit; 7-first rectifier bridge arm; 8-second rectifier bridge arm; 9-third rectifier bridge arm; 10-DC energy storage module; 11-inverter module; 12-first inverter bridge arm; 13-second inverter bridge arm; 14-third inverter bridge arm; 15-three-phase resistive-inductive load module; 16-first input filter inductor; 17-second input filter inductor; 18-third input filter inductor; 19-first power switch tube; 20-second power switch tube; 21-third power switch tube; 22-fourth power switch tube; 23-fifth power switch tube; 24-sixth power switch tube; 25-DC energy storage capacitor; 26-seventh power switch tube; 27 - the eighth power switch tube; 28 - the ninth power switch tube; 29 - the tenth power switch tube; 30 - the eleventh power switch tube; 31 - the twelfth power switch tube; 32 - the first inductor; 33 - the first resistor; 34 - the second inductor; 35 - the second resistor; 36 - the third inductor; 37 - the third resistor. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0027] Aiming at the problem that the DC energy storage capacitor in the existing voltage source type back-to-back converter has a large volume and affects the power density and reliability of the converter, the present invention provides a single bridge arm modulation method of a small-capacitor voltage source type back-to-back converter.

[0028] like Figures 1 to 6As shown, an embodiment of the present invention provides a single-bridge arm modulation method for a small-capacitor voltage source back-to-back converter, comprising: S1, determining the rectifier stage modulation bridge arm and the compensation phase at the current moment according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module; S2, determining the first duty cycle of the rectifier stage modulation bridge arm at the current moment based on the volt-second balance principle of the inductor; S3, determining the output power of the small-capacitor voltage source back-to-back converter according to the three-phase output voltage and the three-phase output current of the inverter stage module, and determining the reference current of the compensation phase of the rectifier stage module at the current moment according to the output power of the small-capacitor voltage source back-to-back converter; S4, determining the real-time error value of the compensation phase current according to the reference current of the compensation phase of the rectifier stage module at the current moment, and determining the real-time error value of the compensation phase current according to the real-time error value of the compensation phase current. and the first duty cycle of the rectifier stage modulation bridge arm at the current moment determine the second duty cycle of the rectifier stage modulation bridge arm at the current moment, the rectifier stage modulation bridge arm at the current moment is switched according to the second duty cycle, and the remaining rectifier stage bridge arms are switched at a low frequency according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module; S5, determine the zero-sequence component of the inverter stage module modulation signal according to the three-phase output voltage of the inverter stage module, and determine the zero-sequence superposition modulation signal of the inverter stage module according to the zero-sequence component of the inverter stage module modulation signal and the three-phase output voltage of the inverter stage module; S6, determine the effective duty cycle of each bridge arm of the inverter stage module according to the bipolar carrier modulation principle and geometric theory, and each bridge arm of the inverter stage module is switched according to the effective duty cycle of each bridge arm of the inverter stage module.

[0029] Among them, S1 specifically includes: determining the modulation phase sequence of the rectifier stage according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module: the corresponding phase of the maximum input phase voltage instantaneous value is the first modulation phase, the corresponding phase of the second input phase voltage instantaneous value is the second modulation phase, and the corresponding phase of the minimum input phase voltage instantaneous value is the third modulation phase; determining that the rectifier stage bridge arm corresponding to the second modulation phase is the rectifier stage modulation bridge arm at the current moment, and the compensation phase is the second modulation phase.

[0030] The single bridge arm modulation method of the small capacitor voltage source back-to-back converter described in the above embodiment of the present invention, Figure 3The invention is a small-capacitor voltage source type back-to-back converter, which includes: a three-phase input power module 1, wherein the three-phase input power module 1 includes a first input power 2, a second input power 3 and a third input power 4, wherein a first end of the second input power 3 is electrically connected to a first end of the first input power 2, and a first end of the third input power 4 is electrically connected to a first end of the second input power 3; a rectifier module 5, wherein a first end of the rectifier module 5 is electrically connected to a first end of the three-phase input power module 1, a second end of the rectifier module 5 is electrically connected to a second end of the three-phase input power module 1, and a third end of the rectifier module 5 is electrically connected to a third end of the three-phase input power module 1, wherein the rectifier module 5 includes an input A filter inductor unit 6, a first rectifier bridge arm 7, a second rectifier bridge arm 8 and a third rectifier bridge arm 9; a DC energy storage module 10, wherein a first end of the DC energy storage module 10 is electrically connected to a fourth end of the rectifier module 5, and a second end of the DC energy storage module 10 is electrically connected to a fifth end of the rectifier module 5; an inverter module 11, wherein a first end of the inverter module 11 is electrically connected to a first end of the DC energy storage module 10, and a second end of the inverter module 11 is electrically connected to a second end of the DC energy storage module 10, and the inverter module 11 includes a first inverter bridge arm 12, a second inverter bridge arm 13 and a third inverter bridge arm 14; a three-phase resistance-inductance load module 15, wherein a first end of the three-phase resistance-inductance load module 15 is electrically connected to the inverter module 11 The third end of the three-phase resistance-inductance load module 15 is electrically connected to the fourth end of the inverter module 11, and the third end of the three-phase resistance-inductance load module 15 is electrically connected to the fifth end of the inverter module 11;

[0031] The input filter inductor unit 6 includes: a first input filter inductor 16, a first end of the first input filter inductor 16 is electrically connected to the second end of the first input power supply 2; a second input filter inductor 17, a first end of the second input filter inductor 17 is electrically connected to the second end of the second input power supply 3; a third input filter inductor 18, a first end of the third input filter inductor 18 is electrically connected to the second end of the third input power supply 4;

[0032] The first rectifier bridge arm 7 includes: a first power switch tube 19, the emitter of the first power switch tube 19 is electrically connected to the second end of the first input filter inductor 16; a second power switch tube 20, the collector of the second power switch tube 20 is electrically connected to the emitter of the first power switch tube 19;

[0033] The second rectifier bridge arm 8 includes: a third power switch tube 21, the collector of the third power switch tube 21 is electrically connected to the collector of the first power switch tube 19, and the emitter of the third power switch tube 21 is electrically connected to the second end of the second input filter inductor 17; a fourth power switch tube 22, the collector of the fourth power switch tube 22 is electrically connected to the emitter of the third power switch tube 21, and the emitter of the fourth power switch tube 22 is electrically connected to the emitter of the second power switch tube 20;

[0034] The third rectifier bridge arm 9 includes: a fifth power switch tube 23, the collector of the fifth power switch tube 23 is electrically connected to the collector of the third power switch tube 21, and the emitter of the fifth power switch tube 23 is electrically connected to the second end of the third input filter inductor 18; a sixth power switch tube 24, the collector of the sixth power switch tube 24 is electrically connected to the emitter of the fifth power switch tube 23, and the emitter of the sixth power switch tube 24 is electrically connected to the emitter of the fourth power switch tube 22;

[0035] The DC energy storage module 10 includes: a DC energy storage capacitor 25, a first end of the DC energy storage capacitor 25 is electrically connected to the collector of the fifth power switch tube 23, and a second end of the DC energy storage capacitor 25 is electrically connected to the emitter of the sixth power switch tube 24;

[0036] The first inverter bridge arm 12 includes: a seventh power switch tube 26, the collector of the seventh power switch tube 26 is electrically connected to the first end of the DC energy storage capacitor 25; an eighth power switch tube 27, the collector of the eighth power switch tube 27 is electrically connected to the emitter of the seventh power switch tube 26, and the emitter of the eighth power switch tube 27 is electrically connected to the second end of the DC energy storage capacitor 25;

[0037] The second inverter bridge arm 13 includes: a ninth power switch tube 28, the collector of the ninth power switch tube 28 is electrically connected to the collector of the seventh power switch tube 26; a tenth power switch tube 29, the collector of the tenth power switch tube 29 is electrically connected to the emitter of the ninth power switch tube 28, and the emitter of the tenth power switch tube 29 is electrically connected to the emitter of the eighth power switch tube 27;

[0038] The third inverter bridge arm 14 includes: an eleventh power switch tube 30, the collector of the eleventh power switch tube 30 is electrically connected to the collector of the ninth power switch tube 28; a twelfth power switch tube 31, the collector of the twelfth power switch tube 31 is electrically connected to the emitter of the eleventh power switch tube 30, and the emitter of the twelfth power switch tube 31 is electrically connected to the emitter of the tenth power switch tube 29;

[0039] The three-phase resistance-inductance load module 15 includes: a first inductor 32, wherein a first end of the first inductor 32 is electrically connected to the emitter of the seventh power switch tube 26; a first resistor 33, wherein a first end of the first resistor 33 is electrically connected to a second end of the first inductor 32; a second inductor 34, wherein a first end of the second inductor 34 is electrically connected to the emitter of the ninth power switch tube 28; a second resistor 35, wherein a first end of the second resistor 35 is electrically connected to a second end of the second inductor 34, and a second end of the second resistor 35 is electrically connected to a first end of the first resistor 33; a third inductor 36, wherein a first end of the third inductor 36 is electrically connected to the emitter of the eleventh power switch tube 30; and a third resistor 37, wherein a first end of the third resistor 37 is electrically connected to a second end of the third inductor 36, and a second end of the third resistor 37 is electrically connected to a second end of the second resistor 35.

[0040] The capacitance value of the DC energy storage capacitor 25 is 2 μF, and the upper switch S in the first rectifier bridge arm 7 is a+ is the first power switch tube 19, the lower switch S in the first rectifier bridge arm 7 a- is the second power switch tube 20; the upper switch S in the second rectifier bridge arm 8 b+ The third power switch tube 21, the lower switch S in the second rectifier bridge arm 8 b- is the fourth power switch tube 22; the upper switch S in the third rectifier bridge arm 9 c+ is the fifth power switch tube 23, the lower switch S in the third rectifier bridge arm 9 c- is the sixth power switch tube 24; the upper switch S in the first inverter bridge arm 12 r+ The seventh power switch tube 26 is the lower switch S in the first inverter bridge arm 12. r- is the eighth power switch tube 27; the upper switch S in the second inverter bridge arm 13 s+ The ninth power switch tube 28 is the lower switch S in the second inverter bridge arm 13. s- is the tenth power switch tube 29; the upper switch S in the third inverter bridge arm 14 t+is the eleventh power switch tube 30, the lower switch S in the third inverter bridge arm 14 t- The twelfth power switch tube 31 ; the inverter module 11 is connected to the three-phase resistive-inductive load module 15 to achieve voltage and current control of the inductance and resistance in the three-phase resistive-inductive load module 15 .

[0041] Built a reference in Matlab / Simulink environment Figure 3 The topology of the small capacitor voltage source back-to-back converter is shown in Table 1.

[0042] Table 1 Parameters of small capacitor voltage source back-to-back converter

[0043]

[0044] According to the first input power u a , the second input power u b and the third input power u c The instantaneous value relationship of determines the modulation phase sequence of the rectifier stage module 5, assuming that the instantaneous value relationship of the current three-phase input phase voltage is: a >u b >u c , then phase a is the first modulation phase, phase b is the second modulation phase, phase c is the third modulation phase, the rectifier stage modulation bridge arm at the current moment is the rectifier stage bridge arm corresponding to phase b, and the compensation phase is phase b. The simulation results are as follows: Figure 5 As shown, the single-arm modulation method of the small-capacitor voltage source back-to-back converter cancels the control of the DC side voltage, that is, maintains the DC side voltage in a quasi-six-pulse state, greatly reducing the requirements for the DC energy storage capacitor 25, while ensuring good input and output waveform quality. Figure 5 The simulation results fully verify the correctness of the single-bridge arm modulation method of the small-capacitor voltage source back-to-back converter.

[0045] Wherein, S2 specifically includes: determining the first duty cycle of the rectifier stage modulation bridge arm based on the volt-second balance principle of the inductor, as shown below:

[0046]

[0047] Where d1 represents the first duty cycle of the rectifier stage modulation bridge arm, u max Indicates the maximum input phase voltage of the rectifier module at the current moment, u mid Indicates the second input phase voltage of the rectifier module at the current moment, u min Indicates the minimum input phase voltage of the rectifier stage module at the current moment.

[0048] Wherein, the S3 specifically includes: assuming that the three-phase output voltage of the inverter module and the three-phase output current of the inverter module are as follows:

[0049]

[0050] Among them, u r Indicates the first output phase voltage of the inverter module, u s Indicates the second output phase voltage of the inverter module, u t Indicates the third output phase voltage of the inverter module, U om Represents the output phase voltage amplitude of the inverter module, ω o represents the output angular frequency, t1 represents the running time, φ u Indicates the initial phase of the output phase voltage of the inverter module, i r Represents the first output phase current of the inverter module, i s Indicates the second output phase current of the inverter module, i t Indicates the third output phase current of the inverter module, I om Indicates the output phase current amplitude of the inverter module, φ i Indicates the initial phase of the output phase current of the inverter module;

[0051] The output power of the small capacitor voltage source back-to-back converter is determined according to the three-phase output voltage and the three-phase output current of the inverter module, as shown below:

[0052] P=1.5U om I om cos(φ u -φ i ) (3)

[0053] Where P represents the output power of the small capacitor voltage source back-to-back converter;

[0054] The reference current of the compensation phase of the rectifier stage module is determined according to the output power of the small capacitor voltage source back-to-back converter, as shown below:

[0055]

[0056] in, Indicates the reference current of the compensation phase of the rectifier module. y is determined according to the compensation phase. y=a,b,c, U im Represents the input phase voltage amplitude of the rectifier module, ω i represents the input angular frequency, Indicates the input power factor angle.

[0057] Wherein, the S4 specifically includes: determining the real-time error value of the compensation phase current according to the reference current of the compensation phase of the rectifier stage module, as shown below:

[0058]

[0059] Among them, i y It represents the real-time current of the compensation phase of the rectifier stage module, which is obtained through real-time current sampling. y is determined according to the compensation phase, y=a,b,c.

[0060] Wherein, the S4 further includes: determining the second duty cycle of the rectifier stage modulation bridge arm according to the real-time error value of the compensation phase current and the first duty cycle of the rectifier stage modulation bridge arm, as shown below:

[0061]

[0062] Where d2 represents the second duty cycle of the rectifier stage modulation bridge arm, U dc represents the DC side voltage of the small capacitor voltage source back-to-back converter, Δi(k p +k i / e) represents the output of the PI regulator, that is, the voltage reference value on the corresponding input filter inductor is compensated, (k p +k i / e) represents the transfer function of the PI regulator, k p Indicates the proportional coefficient of the PI regulator, k i represents the integral coefficient of the PI regulator, and e represents the complex variable used for Laplace transform.

[0063] Among them, S4 also includes: dividing a switching cycle into two durations according to the second duty cycle, taking the product of the second duty cycle and the switching cycle as the first duration, and the remaining part as the second duration, during the first duration, the upper switch of the rectifier stage modulation bridge arm is turned on, and the lower switch is turned off; during the second duration, the upper switch of the rectifier stage modulation bridge arm is turned off, and the lower switch is turned on; the remaining rectifier stage bridge arms perform low-frequency switching according to the instantaneous value relationship of the symmetrical three-phase input phase voltage, at any time, the upper switch of the rectifier stage bridge arm corresponding to the maximum input phase voltage instantaneous value is turned on, and the lower switch is turned off, and the lower switch of the rectifier stage bridge arm corresponding to the minimum input phase voltage instantaneous value is turned on, and the upper switch is turned off.

[0064] The single-bridge-arm modulation method of the small-capacitor voltage source back-to-back converter described in the above embodiment of the present invention selects a bandwidth of 3000 Hz and a damping ratio of 0.707, and calculates the k of the PI regulator. p With k iParameters. The voltage reference value on the input filter inductor corresponding to the compensation is obtained by the output of the PI regulator, and then compared with the DC side voltage to obtain a modified duty cycle. The modified duty cycle is added to the first duty cycle to obtain the second duty cycle of the rectifier stage modulation bridge arm. The rectifier stage modulation bridge arm performs switch switching based on the second duty cycle. According to the second duty cycle, a switching cycle is divided into two durations. The product of the second duty cycle and the switching cycle is the first duration, and the remaining part is the second duration. During the first duration, the upper switch of the rectifier stage modulation bridge arm is turned on and the lower switch is turned off. During the second duration, the upper switch of the rectifier stage modulation bridge arm is turned off and the lower switch is turned on. The three-phase input current is sinusoidally controlled by switching the rectifier stage modulation bridge arm. The remaining rectifier stage bridge arms perform low-frequency switch switching according to the instantaneous value relationship of the symmetrical three-phase input phase voltage. At any time, the upper switch of the rectifier stage bridge arm corresponding to the instantaneous value of the maximum input phase voltage is turned on and the lower switch is turned off. The lower switch of the rectifier stage bridge arm corresponding to the instantaneous value of the minimum input phase voltage is turned on and the upper switch is turned off.

[0065] Wherein, the S5 specifically includes: determining the zero-sequence component of the modulation signal of the inverter-stage module according to the three-phase output voltage of the inverter-stage module, as shown below:

[0066] u no =-[max(u r ,u s ,u t )+min(u r ,u s ,u t )] / 2 (7)

[0067] Among them, u no Represents the zero-sequence component of the modulation signal of the inverter-stage module;

[0068] The zero-sequence superposition modulation signal of the inverter module is determined according to the zero-sequence component of the inverter module modulation signal and the three-phase output voltage of the inverter module, as shown below:

[0069]

[0070] in, Indicates the zero-sequence superposition modulation signal of the inverter module, u i represents the three-phase output voltage of the inverter module, r represents the first output phase of the inverter module, s represents the second output phase of the inverter module, and t represents the third output phase of the inverter module.

[0071] Wherein, the S6 specifically includes: determining the action duty ratio of each bridge arm of the inverter stage module according to the bipolar carrier modulation principle and geometric theory, as shown below:

[0072]

[0073] Among them, d i Represents the duty cycle of each bridge arm of the inverter module, i = r, s, t;

[0074] Wherein, the S6 also includes: dividing a switching cycle into two durations according to the action duty cycle, the product of the action duty cycle and the switching cycle is the third duration, and the remaining part is the fourth duration; at the beginning of a switching cycle, the upper switch of each bridge arm of the inverter stage module is turned on, and the lower switch is turned off; after maintaining 1 / 2 of the third duration, the switch state of each bridge arm of the inverter stage module is switched to the upper switch off, and the lower switch on; after maintaining the fourth duration, the switch state of each bridge arm of the inverter stage module is switched to the upper switch on, and the lower switch off; and the third duration is maintained for 1 / 2 until the end of the current switching cycle.

[0075] The single bridge arm modulation method of the small capacitor voltage source back-to-back converter described in the above embodiment of the present invention, the method for obtaining the duty cycle of each bridge arm in the inverter stage module 11 and the switching mode of each bridge arm of the inverter stage are as follows: Figure 4 As shown, the switching mode of each bridge arm of the inverter module is consistent. Taking the r bridge arm corresponding to the first output phase of the inverter module as an example, a switching cycle is divided into two durations according to the duty cycle. The product of the duty cycle and the switching cycle is the third duration, and the remaining part is the fourth duration. At the beginning of a switching cycle, the upper switch of the r bridge arm is turned on and the lower switch is turned off. After maintaining 1 / 2 of the third duration, the switch state of the r bridge arm is switched to the upper switch off and the lower switch on. After maintaining the fourth duration, the switch state of the r bridge arm is switched to the upper switch on and the lower switch off, and continues to maintain 1 / 2 of the third duration until the end of the switching cycle. Through the switching of each bridge arm of the inverter module, the amplitude, frequency and phase of the three-phase output voltage are controlled, ensuring that the small-capacitor voltage source back-to-back converter has the ability to output the three-phase voltage required by the electrical equipment.

[0076] The single-bridge-arm modulation method of the small-capacitor voltage source back-to-back converter described in the above-mentioned embodiment of the present invention only modulates one of the three bridge arms of the rectifier stage module 5 at the same time, thereby reducing switching losses while ensuring the power quality on the input side, improving the power transmission efficiency of the small-capacitor voltage source back-to-back converter, canceling the control of the DC side voltage, maintaining the DC side voltage in a quasi-six-pulse state, greatly reducing the requirements for the DC energy storage capacitor 25, and greatly reducing the DC energy storage capacitor 25 on the basis of ensuring the power quality on the output side, ensuring good input and output waveform quality, reducing costs, and effectively improving the power density and reliability of the small-capacitor voltage source back-to-back converter, while improving the power conversion efficiency of the small-capacitor voltage source back-to-back converter and greatly reducing the DC energy storage capacitor 25.

[0077] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A single-bridge-arm modulation method for a small-capacitor voltage source back-to-back converter, characterized in that: include: S1, determining the rectifier stage modulation bridge arm and compensation phase at the current moment according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module, including: Determine the modulation phase sequence of the rectifier stage according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module: the corresponding phase of the maximum input phase voltage instantaneous value is the first modulation phase, the corresponding phase of the second input phase voltage instantaneous value is the second modulation phase, and the corresponding phase of the minimum input phase voltage instantaneous value is the third modulation phase; determine that the rectifier stage bridge arm corresponding to the second modulation phase is the rectifier stage modulation bridge arm at the current moment, and the compensation phase is the second modulation phase; S2, determining the first duty cycle of the rectifier stage modulation bridge arm at the current moment based on the volt-second balance principle of the inductor; S3, determining the output power of the small-capacitor voltage source type back-to-back converter according to the three-phase output voltage and the three-phase output current of the inverter-stage module, and determining the reference current of the compensation phase of the rectifier-stage module at the current moment according to the output power of the small-capacitor voltage source type back-to-back converter; S4, determining the real-time error value of the compensation phase current according to the reference current of the compensation phase of the rectifier stage module at the current moment, determining the second duty cycle of the rectifier stage modulation bridge arm at the current moment according to the real-time error value of the compensation phase current and the first duty cycle of the rectifier stage modulation bridge arm at the current moment, the rectifier stage modulation bridge arm at the current moment performs switching according to the second duty cycle, and the remaining rectifier stage bridge arms perform low-frequency switching according to the instantaneous value relationship of the symmetrical three-phase input phase voltage of the rectifier stage module; S5, determining the zero-sequence component of the modulation signal of the inverter-stage module according to the three-phase output voltage of the inverter-stage module, and determining the zero-sequence superposition modulation signal of the inverter-stage module according to the zero-sequence component of the modulation signal of the inverter-stage module and the three-phase output voltage of the inverter-stage module; S6, determining the duty cycle of each bridge arm of the inverter module according to the bipolar carrier modulation principle and geometric theory, and switching each bridge arm of the inverter module according to the duty cycle of each bridge arm of the inverter module.

2. The single bridge arm modulation method of the small capacitor voltage source back-to-back converter according to claim 1, characterized in that: The S2 specifically includes: The first duty cycle of the rectifier stage modulation bridge arm is determined based on the volt-second balance principle of the inductor, as shown below: Where d1 represents the first duty cycle of the rectifier stage modulation bridge arm, u max Indicates the maximum input phase voltage of the rectifier module at the current moment, u mid Indicates the second input phase voltage of the rectifier module at the current moment, u min Indicates the minimum input phase voltage of the rectifier stage module at the current moment.

3. The single bridge arm modulation method of the small capacitor voltage source back-to-back converter according to claim 2, characterized in that: The S3 specifically includes: Assume that the three-phase output voltage of the inverter module and the three-phase output current of the inverter module are as follows: Among them, u r Indicates the first output phase voltage of the inverter module, u s Indicates the second output phase voltage of the inverter module, u t Indicates the third output phase voltage of the inverter module, U om Represents the output phase voltage amplitude of the inverter module, ω o represents the output angular frequency, t1 represents the running time, φ u Indicates the initial phase of the output phase voltage of the inverter module, i r Represents the first output phase current of the inverter module, i s Indicates the second output phase current of the inverter module, i t Indicates the third output phase current of the inverter module, I om Indicates the output phase current amplitude of the inverter module, φ i Indicates the initial phase of the output phase current of the inverter module; The output power of the small capacitor voltage source back-to-back converter is determined according to the three-phase output voltage and the three-phase output current of the inverter module, as shown below: P=1.5U om I om cos(φ u -f i (3) Where P represents the output power of the small capacitor voltage source back-to-back converter; The reference current of the compensation phase of the rectifier stage module is determined according to the output power of the small capacitor voltage source back-to-back converter, as shown below: in, Indicates the reference current of the compensation phase of the rectifier module. y is determined according to the compensation phase. y=a,b,c,U im Represents the input phase voltage amplitude of the rectifier module, ω i represents the input angular frequency, Indicates the input power factor angle.

4. The single bridge arm modulation method of the small capacitor voltage source back-to-back converter according to claim 3, characterized in that: The S4 specifically includes: The real-time error value of the compensation phase current is determined according to the reference current of the compensation phase of the rectifier stage module, as shown below: Among them, i y It represents the real-time current of the compensation phase of the rectifier stage module, which is obtained through real-time current sampling. y is determined according to the compensation phase, y = a, b, c.

5. The single bridge arm modulation method of the small capacitor voltage source back-to-back converter according to claim 4, characterized in that: The S4 further comprises: The second duty cycle of the rectifier stage modulation bridge arm is determined according to the real-time error value of the compensation phase current and the first duty cycle of the rectifier stage modulation bridge arm, as shown below: Where d2 represents the second duty cycle of the rectifier stage modulation bridge arm, U dc represents the DC side voltage of the small capacitor voltage source back-to-back converter, Δi(k p +k i / e) represents the output of the PI regulator, that is, the voltage reference value on the corresponding input filter inductor is compensated, (k p +k i / e) represents the transfer function of the PI regulator, k p Indicates the proportional coefficient of the PI regulator, k i represents the integral coefficient of the PI regulator, and e represents the complex variable used for Laplace transform.

6. The single bridge arm modulation method of a small capacitor voltage source back-to-back converter according to claim 5, characterized in that: The S4 further comprises: A switching cycle is divided into two durations according to a second duty cycle, the product of the second duty cycle and the switching cycle is taken as the first duration, and the remaining part is taken as the second duration. During the first duration, the upper switch of the rectifier stage modulation bridge arm is turned on, and the lower switch is turned off; during the second duration, the upper switch of the rectifier stage modulation bridge arm is turned off, and the lower switch is turned on; the remaining rectifier stage bridge arms perform low-frequency switching according to the instantaneous value relationship of the symmetrical three-phase input phase voltage, and at any time, the upper switch of the rectifier stage bridge arm corresponding to the instantaneous value of the maximum input phase voltage is turned on, and the lower switch is turned off, and the lower switch of the rectifier stage bridge arm corresponding to the instantaneous value of the minimum input phase voltage is turned on, and the upper switch is turned off.

7. The single bridge arm modulation method of a small capacitor voltage source back-to-back converter according to claim 6, characterized in that: The S5 specifically includes: The zero-sequence component of the modulation signal of the inverter module is determined according to the three-phase output voltage of the inverter module, as shown below: u no =-[max(u r ,u s ,u t )+min(u r ,u s ,u t )] / 2(7) Among them, u no Represents the zero-sequence component of the modulation signal of the inverter-stage module; The zero-sequence superposition modulation signal of the inverter module is determined according to the zero-sequence component of the inverter module modulation signal and the three-phase output voltage of the inverter module, as shown below: in, Indicates the zero-sequence superposition modulation signal of the inverter module, u i represents the three-phase output voltage of the inverter module, r represents the first output phase of the inverter module, s represents the second output phase of the inverter module, and t represents the third output phase of the inverter module.

8. The single bridge arm modulation method of a small capacitor voltage source back-to-back converter according to claim 7, characterized in that: The S6 specifically includes: According to the bipolar carrier modulation principle and geometric theory, the duty cycle of each bridge arm of the inverter module is determined as follows: Among them, d i Represents the duty cycle of each bridge arm of the inverter module, i=r,s,t.

9. The single bridge arm modulation method of a small capacitor voltage source back-to-back converter according to claim 8, characterized in that: The S6 further includes: A switching cycle is divided into two durations according to the effective duty cycle, the product of the effective duty cycle and the switching cycle is the third duration, and the remaining part is the fourth duration. At the beginning of a switching cycle, the upper switch of each bridge arm of the inverter-stage module is turned on and the lower switch is turned off. After maintaining 1 / 2 of the third duration, the switch state of each bridge arm of the inverter-stage module is switched to the upper switch off and the lower switch on. After maintaining the fourth duration, the switch state of each bridge arm of the inverter-stage module is switched to the upper switch on and the lower switch off. It continues to maintain 1 / 2 of the third duration until the end of the current switching cycle.

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