A space vector research strategy of three-phase four-bridge matrix converter based on quasi-z-source

Abstract

The application discloses a novel topology of three-phase four-bridge matrix converter based on quasi-Z source and a novel space vector modulation strategy based on the same. The application comprises the following steps: analyzing the novel topology of three-phase four-bridge matrix converter based on quasi-Z source and deducing the vector modulation of input current and output voltage; according to the vector modulation algorithm of the topology, listing all single-output-phase through zero vectors; determining the insertion mode of the suitable through state to improve the performance of the system; adjusting the through duty ratio to control the rise and fall of the input voltage of the three-phase four-bridge matrix converter. The application is based on the traditional space vector modulation strategy, adopts the novel insertion mode of through state to replace part of the zero vectors, divides the through zero vectors into 16 equal parts and inserts the through zero vectors into the space vector modulation strategy to reduce the fluctuation of the capacitor voltage and inductance current of the quasi-Z source circuit in the steady state, improve the anti-interference ability and the voltage transmission efficiency of the system. When the output load of the circuit is unbalanced, the positive sequence, negative sequence and zero sequence current components are separated according to the theory of symmetrical component method, and the symmetrical three-phase output voltage is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronic converter control strategy, in particular to a three-phase four-bridge matrix converter topology based on quasi-Z source and the space vector modulation strategy based on the topology. BACKGROUND

[0002] With the progress of science and technology and the improvement of social economy, the requirements for power quality and reliability are getting higher and higher in today's era. The existing power grid cannot meet these requirements due to its own defects. In the process of power conversion of power system, the converter can convert DC into AC and is applied in the fields of renewable energy power generation grid-connected converter, low-speed transmission, power factor correction and high-power conversion, etc. The technology of matrix converter provides a solution to the reactive and harmonic problems of power grid pollution and has broad application prospects. However, it has the disadvantages of low voltage utilization rate and complex control modulation, so the research and development of low-cost, high-transmission efficiency and high-reliability control strategy has become one of the research focuses of the converter.

[0003] In the AC variable frequency speed regulation system, the quasi-Z source three-phase four-bridge matrix converter is an AC direct variable frequency device with the advantages of small loss, high reliability and wide application range, which not only solves the problem that the voltage transmission ratio is not more than 0.866, but also realizes the purpose of carrying three-phase unbalanced load. The quasi-Z source circuit has two working states of direct through and non-direct through, and in the working process of the circuit, the direct through duty cycle can be adjusted to achieve the purpose of step-up and step-down. The space vector modulation of the three-phase four-bridge matrix converter mainly includes input end modulation and output end modulation. The input end modulation is the phase current space vector modulation. The output end modulation is the line voltage space vector modulation. In the space vector modulation method, how to generate the direct through state required for step-up and the insertion method of the direct through state are crucial. According to the different methods of injecting direct through zero vector, the modulation can be divided into six kinds: simple step-up, maximum step-up, 3rd harmonic injection step-up, maximum constant step-up, sinusoidal carrier pulse modulation and direct through state segmented space vector modulation. Among them, the direct through segmented space vector modulation has excellent comprehensive performance. Therefore, the direct through segmented space vector modulation method is commonly used at present.

[0004] In order to improve the simulation efficiency and overcome the disadvantage that the traditional control algorithm is realized by using modules to build, the space vector control strategy of the quasi-Z source three-phase four-bridge matrix converter is researched, and the S function modeling method is used to fully utilize Matlab / Simulink. The main circuit is built by using modules, and the core algorithm is programmed by using C language, which greatly improves the simulation speed and the reliability of system operation. SUMMARY

[0005] In view of the problems existing in the three-phase four-bridge matrix converter, the application discloses a three-phase four-bridge matrix converter topology based on a quasi-Z source and a space vector modulation strategy based on the same, which not only improves voltage transfer ratio and anti-interference capability, but also overcomes the defect that the traditional three-phase three-bridge matrix converter cannot realize three-phase unbalanced load.

[0006] The application solves the above technical problems by the following scheme:

[0007] The quasi-Z source three-phase four-bridge matrix converter topology is analyzed, and the vector modulation of input current and output voltage is derived;

[0008] According to the vector modulation algorithm of the topology, all single-output-phase direct-through zero vectors are listed;

[0009] The insertion mode of the suitable direct-through state is determined to improve the performance of the system;

[0010] The direct-through duty cycle is adjusted to control the rise and fall of the input voltage of the three-phase four-bridge matrix converter.

[0011] The technical effect of the application is that: based on the traditional space vector modulation strategy, the insertion mode of the direct-through state instead of part of the zero vectors, i.e. the strategy of equally dividing 16 parts of the direct-through zero vector and inserting it into the traditional space vector modulation, can reduce the voltage and current fluctuation of the quasi-Z source circuit, solve the problems of low voltage transfer ratio and utilization rate, and at the same time, the three-phase four-bridge matrix converter with unbalanced three-phase load is analyzed by the symmetric component method theory, the positive sequence, negative sequence and zero sequence current components are separated, and the symmetrical three-phase output voltage is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The application is a main circuit structure of the quasi-Z source three-phase four-bridge matrix converter.

[0013] Figure 2 The application is a voltage and current vector synthesis diagram.

[0014] Figure 3 The application is an insertion mode of the direct-through vector and a switch sequence diagram.

[0015] Figure 4 The application is a simulation system block diagram of the quasi-Z source three-phase four-bridge matrix converter.

[0016] Figure 5 The application is a work flowchart. DETAILED DESCRIPTION

[0017] The application will be further described in detail below with reference to the drawings.

[0018] The main circuit topology structure of the quasi-Z source three-phase four-bridge matrix converter is as follows Figure 1As shown, it mainly consists of a three-phase AC voltage source, a quasi-Z-source network, a three-phase four-bridge matrix converter, and resistive-inductive loads. Analysis of the main circuit structure reveals that the on / off state of the bidirectional switches allows any phase of the three-phase AC input to be directly connected to any phase of the four-phase AC output, achieving the desired output voltage and current. Therefore, the control of the quasi-Z-source three-phase four-bridge matrix converter is essentially the control of the on / off state of the included bidirectional switches.

[0019] The space vector modulation strategy of a three-phase four-bridge matrix converter consists of two parts: input-side modulation and output-side modulation. Input-side modulation is phase current space vector modulation, and output-side modulation is line voltage space vector modulation, i.e., three-dimensional space vector modulation. The algorithm implementation steps are as follows:

[0020] Step 1: Use equation (1) to transform the three-phase reference input phase current from coordinate system abc to the stationary coordinate system αβ.

[0021]

[0022] Where iA, iB, and iC represent the input current, and iα and iβ represent the two-phase currents after the coordinate system transformation.

[0023] Step 2: In the αβ coordinate system, the input phase current vector sector can be divided according to the traditional input-side current modulation. Since any current vector is synthesized from two basic vectors, the synthesis is as follows: Figure 2 As shown in (a).

[0024] Step 3: Use equation (2) to transform the three-phase reference output line voltage from coordinate system abc to the stationary coordinate system αβγ.

[0025]

[0026] Where uan, ubn, and ucn represent the desired output voltage, and uα, uβ, and uγ represent the three-phase voltages after coordinate system transformation.

[0027] Step 4: Decompose the three-dimensional basic voltage vector on the output side into 24 polyhedra. Based on the input voltage, determine the number of positive uan, ubn, and ucn, and determine the tetrahedron number containing the desired output voltage, as shown in Table 1.

[0028] Table 1 Tetrahedron Numbering

[0029]

[0030] Step 5: In the αβγ coordinate system, the desired output line voltage vector sector can be divided according to traditional output-side voltage modulation, and any voltage vector is synthesized from three basic vectors. The synthesis is as follows: Figure 2 As shown in (b).

[0031] Based on the above steps, the input phase current space vector modulation and the output phase voltage space vector modulation are combined to determine that the active vectors are composed of 6 non-zero vectors and 3 zero vectors. Due to the introduction of the quasi-Z source circuit, the through zero vector control is considered, that is, the through zero vector (i.e. the state of the single output phase through zero vector of the a, b, and c phases) is reasonably inserted in the traditional double space vector modulation strategy, as shown in Table 2.

[0032] Table 2 Through zero vector

[0033]

[0034] Assuming that the input reference phase current vector is located in sector |, the output reference line voltage vector is located in sector |, the tetrahedron number is 10, 6 effective vectors (i.e. BBBA, ABBA, AABA, AACA, ACCA, and CCC A) are formed after vector synthesis, 3 zero vectors (i.e. BBB B, AAA A, and CCC C) and the corresponding through zero vectors (BBBSt, StBBA, AStBA, AAStA, AAStA, AStCA, StCCA, and CCCSt) are formed. The space vector modulation algorithm steps of the quasi-Z source three-phase four-bridge matrix converter are as follows:

[0035] Step 1: Calculate the duty cycles of the working vectors, zero vectors, and through zero vectors in the switching period Ts using (3).

[0036]

[0037] where θ1, θ2, and θ3 respectively represent the angles between the vectors , , and the target expected output voltage vector Vd, Uim represents the amplitude of the input voltage, |Vd| represents the amplitude of the expected output voltage vector, represents the angle of the sector bisector where the current vector is located, and the value range is

[0038] Step 2: Calculate the working vector, zero vector, and through zero vector action time in the switching period Ts using (4).

[0039]

[0040] where T1, T2, T3, T4, T5, T6, Tst, and T0 respectively represent the switching times corresponding to the 8 switching states.

[0041] Step 3: The modulation principle of quasi-Z-source three-phase four-leg matrix converter is that the action time Tst of the direct zero vector in a switching cycle Ts is equally divided into 16 parts and inserted into the space vector modulation strategy. First, the action time Tst of the direct zero vector in a switching cycle Ts is equally divided into 16 parts. Then, the appropriate direct zero vector is selected and inserted into the effective vector of the half-cycle space vector modulation. Finally, the action time is adjusted to complete the entire modulation process. The insertion mode of the 16-equalized segmented direct vector and the switching sequence diagram are shown in Figure 3 .

[0042] Step 4: When the quasi-Z-source three-phase four-leg matrix converter is connected with unbalanced load, the zero sequence current will cause voltage drift at the neutral point, resulting in the output three-phase voltage no longer being symmetrical. At this time, according to the theory of symmetrical component method, the positive sequence, negative sequence and zero sequence current components generated by the three-phase four-leg matrix converter output with unbalanced load are separated, and the expected output three-phase voltage of the three-phase four-leg matrix converter can be obtained.

[0043] For the proposed quasi-Z-source three-phase four-leg matrix converter topology, a simulation model is built in the Matlab / Simulink environment. The main circuit includes an AC power source, a quasi-Z-source circuit packaging module, a three-phase four-leg matrix converter module and a load part; the control part includes a three-phase modulation wave module, a coordinate transformation module, a voltage and current vector angle calculation module, an S-function control algorithm part and a PWM output module. The specific simulation system block diagram is shown in Figure 4 .

[0044] Through the above steps, the control workflow diagram of the space vector modulation of the quasi-Z-source three-phase four-leg matrix converter is shown in Figure 5 .

Claims

1. A space vector modulation strategy based on a quasi-Z source three-phase four-bridge matrix converter topology, comprising the following steps: Analyze the topology of the quasi-Z source three-phase four-bridge matrix converter and derive the vector modulation of the input current and output voltage; Based on the vector modulation algorithm of this topology, list all single-output phase cut-through zero vectors; Determine the appropriate insertion method for the through state to improve system performance; Adjusting the direct duty cycle controls the rise and fall of the input voltage of the three-phase four-bridge matrix converter; Steps of the space vector modulation algorithm for a quasi-Z source three-phase four-bridge matrix converter: Step 1: Calculate the switching period T s The duty cycle of the working vector, zero vector, and through-zero vector within the system; Step 2: Calculate the switching period T s The working vector, zero vector, and the duration of action of the through-zero vector within the vector; Step 3: The modulation principle of the quasi-Z source three-phase four-bridge matrix converter is: to convert the direct zero vector within one switching period T s The duration of action within T st The space vector modulation strategy is divided into 16 equal parts; firstly, the switching period T is... s The time of action of the direct zero vector T st Divide the vector into 16 equal parts; then, select appropriate through-zero vectors in sequence and insert them into the effective vectors of half-cycle space vector modulation; finally, adjust the action time to complete the entire modulation process. Step 4: When the quasi-Z source three-phase four-bridge matrix converter is driven by an unbalanced load, the zero-sequence current will cause voltage drift at the neutral point, resulting in the output three-phase voltage being no longer symmetrical. At this time, according to the theory of symmetrical components, the positive-sequence, negative-sequence and zero-sequence current components generated when the output of the three-phase four-bridge matrix converter is driven by an unbalanced load are separated to obtain the expected output three-phase voltage of the three-phase four-bridge matrix converter.

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