Chained Multilevel Converter Based on SVM Control in Line Voltage Coordinate System

Abstract

The present invention discloses a chain multi-level converter based on line voltage coordinate system SVM control. The chain multi-level converter is a three-phase converter, each phase is composed of n sub-modules connected in series, the structure of the sub-module is a voltage type H-bridge inverter, and each sub-module includes 4 IGBTs, 4 diodes, and 1 DC voltage source. The chain multi-level converter also includes a reference signal module and a control module. The reference signal module generates a normalized phase voltage reference signal. The control module generates 12*n PWM pulse signals according to the reference signal to control the operation state of the converter. The modulation method running in the control module is based on the line voltage coordinate system SVM method. The above scheme of the present invention avoids the complex Clarke transformation and reference vector positioning process. No trigonometric function and irrational number operation are required during the operation of the converter, which reduces the control difficulty and helps the promotion and application of the chain multi-level converter to high-level occasions.

Description

Technical Field

[0001] The invention belongs to the technical field of modulation of chained multi-level converters, and relates to a chained multi-level converter based on line voltage coordinate system SVM control. Background Art

[0002] New energy sources, represented by wind energy and solar energy, account for an increasing proportion of total social energy consumption and have the potential to become the main energy source. However, wind energy and solar energy are greatly affected by environmental factors and are highly unstable, requiring highly controllable power electronic devices to convert and distribute the electricity they generate. In high-voltage and high-power applications, a single power electronic device cannot meet the application needs. The chain multi-level converter connects multiple power electronic devices in a specific topology to reduce the voltage and current that a single device bears, thereby achieving high-voltage and high-power energy conversion. This is the current mainstream solution.

[0003] The modulation method is the working basis of the chain multilevel converter. In order to achieve the best performance of the converter, it is necessary to design the best modulation strategy according to the converter topology. Common multilevel converter modulation strategies include carrier phase shift modulation, carrier stacking modulation, space vector modulation (SVM), etc. Among them, space vector modulation is derived from the flux linkage theory of three-phase motor symmetrical operation. By locating the three space vectors closest to the reference vector and using the volt-second balance principle to act on the three space vectors in time, the reference vector is synthesized to finally generate a three-phase symmetrical sinusoidal voltage output. Compared with other multilevel converter modulation strategies, space vector modulation has the advantages of high DC voltage utilization, low converter output harmonic content, and easy digital control.

[0004] When the output voltage of the converter exceeds seven levels, the number of space vectors in the traditional SVM method is huge, and it is difficult to locate the three space vectors closest to the reference vector. In addition, the calculation process of the traditional SVM method includes a large number of trigonometric functions and irrational number operations, and the amount of calculation and complexity are huge, which greatly increases the difficulty of the implementation process of the SVM method and makes it difficult to apply it to multi-level converters with more than 7 levels.

[0005] Based on the above problems of the chain multilevel converter, it is necessary to study a chain multilevel converter based on line voltage coordinate system SVM control. Summary of the invention

[0006] The purpose of the present invention is to provide a chain multi-level converter based on line voltage coordinate system SVM control. The control module of the converter runs the SVM method based on the line voltage coordinate system. By transforming the reference phase voltage and the switch state of the chain multi-level converter to the line voltage coordinate system, the Clarke transformation is avoided, and the calculation amount and complexity in the space vector modulation implementation process are reduced, thereby solving the problem in the prior art that space vector modulation is difficult to apply to high-level converter occasions.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] Step 1: Sample the phase voltage reference signal and calculate α * β * Reference vector of line voltage coordinate system

[0009]

[0010] in, is the reference vector at α * β * The coordinate components in the line voltage coordinate system represent the reference line voltage between phase A and phase B and the reference line voltage between phase B and phase C respectively.

[0011] The switching state S(a,b,c) of the converter is related to α * β * The space vector V(α * ,β * ) is:

[0012]

[0013] Among them, a, b, c are the levels of the three-phase voltage output by the converter, and a, b, c ∈ (0, ±1, ±2, L, ±n), α * , β * is the space vector V(α * ,β * ) represent the line voltage level between phase A and phase B, and the line voltage level between phase B and phase C respectively.

[0014] Step 2: Extract reference vector The corresponding feature vector

[0015] in, INT is a rounding function, which discards the decimal part of a real number and retains only the integer part. The characteristic vector is located in the central rectangle of the line voltage coordinate system. The central rectangle contains 9 source vectors, namely V0(0,0), V1(1,0), V2(1,1), V3(0,1), V4(-1,1), V5(-1,0), V6(-1,-1), V7(0,-1), and V8(1,-1). The 9 source vectors constitute 8 source sectors. V0(0,0), V1(1,0), and V3(0,1) constitute source sector 1, and V1(1,0), V2(1,1), and V3(0,1) constitute source sector 2. Sector 2, V0(0,0), V4(-1,1), V5(-1,0) constitute source sector 3, V0(0,0), V3(0,1), V4(-1,1) constitute source sector 4, V5(-1,0), V6(-1,-1), V7(0,-1) constitute source sector 5, V0(0,0), V5(-1,0), V7(0,-1) constitute source sector 6, V0(0,0), V7(0,-1), V8(1,-1) constitute source sector 7, V0(0,0), V1(1,0), V8(1,-1) constitute source sector 8, and the 8 source sectors together form the central rectangle;

[0016] Step 3: Determine the feature vector The quadrant to which the source sector belongs within the central rectangle, and the specific location of the source sector:

[0017] Step 3.1: If At this time, the eigenvector is located in quadrant I of the central rectangle. Located in source sector 1, otherwise located in source sector 2;

[0018] Step 3.2: If At this time, the eigenvector is located in quadrant II of the central rectangle. If Located in source sector 3, otherwise located in source sector 4;

[0019] Step 3.3: If At this time, the eigenvector is located in quadrant III of the central rectangle. If is located in source sector 5, otherwise it is located in source sector 6;

[0020] Step 3.4: If At this time, the eigenvector is located in quadrant IV of the central rectangle. If Located in source sector 7, otherwise located in source sector 8;

[0021] Step 4: Based on the reference vector The corresponding feature vector The source sector where the synthetic reference vector is located The three space vectors

[0022] Step 4.1: If the eigenvector is located in source sector 1, then The coordinate components of are:

[0023] Step 4.2: If the eigenvector is located in source sector 2, then The coordinate components of are:

[0024] Step 4.3: If the eigenvector is located in source sector 3, then The coordinate components of are:

[0025] Step 4.4: If the eigenvector is located in source sector 4, then The coordinate components of are:

[0026] Step 4.5: If the eigenvector is located in source sector 5, then The coordinate components of are:

[0027] Step 4.6: If the eigenvector is located in source sector 6, then The coordinate components of are:

[0028] Step 4.7: If the eigenvector is located in source sector 7, then The coordinate components of are:

[0029] Step 4.8: If the eigenvector is located in source sector 8, then The coordinate components of are:

[0030] Step 5: Calculate the space vector The corresponding switch state S a (a a ,b a ,c a ), S b (ab ,b b ,c b ), S c (a c ,b c ,c c ):

[0031] Step 5.1: If the eigenvector is in quadrant I of the central rectangle, then Corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) are:

[0032] Step 5.2: If the eigenvector is in quadrant II of the central rectangle, then Corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) are:

[0033] Step 5.3: If the eigenvector is in quadrant III of the central rectangle, then Corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) are:

[0034] Step 5.4: If the eigenvector is in quadrant IV of the central rectangle, then Corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) are:

[0035] Step 6: Calculate the switch state S according to the volt-second balance principle a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) Their respective action times t1, t2, t3:

[0036]

[0037] Step 7: According to the five-segment algorithm, within one sampling period, the switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) time-sharing action, synthesizing the reference vector, generating a PWM signal, and the synthesized switching path is S a (a a ,b a ,c a ) → S b (a b ,b b ,c b ) → S c (a c ,bc ,c c ) → S b (a b ,b b ,c b ) → S a (a a ,b a ,c a ), the switching time is: t1 / 2→t2 / 2→t3→t2 / 2→t1 / 2;

[0038] Continue sampling the reference voltage and repeat steps 1 to 7 to complete the normal operation of the chain multi-level converter.

[0039] It can be seen from the above steps that the scheme of the present invention transforms the reference phase voltage and the switch state of the chain multilevel converter into the line voltage coordinate system. By judging the source sector where the characteristic vector corresponding to the reference vector is located, three space vectors of the synthetic reference vector can be obtained, and the coordinate components of the space vector are all integers, which simplifies the positioning of the reference vector and the calculation of the action time of the space vector. At the same time, since the Clarke transformation step of the traditional SVM method is not required, irrational number operations are avoided in the calculation process, reducing the complexity of the SVM method implementation; BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the prior art and the drawings required for use in the embodiments. The following drawings are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0041] Figure 1 :Structure diagram of chained multilevel converter based on SVM control of line voltage coordinate system;

[0042] Figure 2 :Flowchart of implementation steps;

[0043] Figure 3 : Schematic diagram of the central rectangle and source sector distribution of the line voltage coordinate system;

[0044] Figure 4 : Space vector switching timing diagram of synthetic reference vector;

[0045] Figure 5 : Waveform diagram of the simulation output of the 2-stage chain multilevel converter, Figure 5 (a) Single-phase voltage waveform, Figure 5 (b) is the line voltage waveform. DETAILED DESCRIPTION

[0046] In order to clearly illustrate the purpose, technical solutions and advantages of the present invention, one embodiment of the present invention will be fully described below in conjunction with the accompanying drawings:

[0047] In a specific embodiment, taking a three-phase n-stage chain multilevel converter as an example, any phase of the converter is composed of n voltage-type H-bridge submodules in series, which can output 2n+1 levels. The phase voltage reference signal u of the three phases A, B, and C of the chain multilevel converter is ra 、u rb 、u rc for:

[0048]

[0049] Where n is the number of single-phase submodules, m is the modulation coefficient of SVM, 0<m≤1, and ω represents the angular frequency of the reference phase voltage.

[0050] Taking a two-stage chain multilevel converter as an example, assuming that the modulation coefficient is 0.85, n = 2, the phase voltage reference signal angular frequency ω is 100π, and the sampling period is T s =0.2ms, sample the phase voltage reference signal at t=0.66ms, and obtain the reference phase voltage u of phases A, B, and C respectively ra =1.92,u rb =-0.6, u rc =-1.31. According to formula (1), the reference vector V of the reference phase voltage in the line voltage coordinate system is obtained r (2.53,0.7).

[0051] According to formula (3), the reference vector V is extracted r The eigenvector V corresponding to (2.53,0.7) e (0.53,0.7), according to step 3.1, judge and Characteristic vector V e (0.53,0.7) is in quadrant I of the central rectangle. Since 0.7>-0.53+1, it does not satisfy Characteristic vector V e (0.53,0.7) is located in source sector 2.

[0052] because According to step 4.2, determine the reference vector V involved in the synthesis r The three space vectors of (2.53,0.7)

[0053]

[0054] That is, participating in the synthesis of V rThe space vectors of (2.53,0.7) are V a (3,1), V b (3,0), V c (2,1).

[0055] According to step 5.1, calculate the space vector V a (3,1), V b (3,0), V c (2,1) respectively correspond to the switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ):

[0056]

[0057] That is, V a (3,1), V b (3,0), V c The corresponding switch states of (2,1) are S a (2,-1,-2), S b (2,-1,-1), S c (2,0,-1).

[0058] Calculate S according to formula (4): a (2,-1,-2), S b (2,-1,-1), S c The action time of (2,0,-1) is:

[0059]

[0060] Calculation shows that t1=0.046ms, t2=0.06ms, and t3=0.094ms.

[0061] According to step 7, the synthetic switching path and switching time of the switch state are determined, such as Figure 4 As shown, a PWM signal is generated.

[0062] Finally, it should be noted that the above embodiments are only part of the embodiments of the present invention, rather than all of the embodiments, and are used to illustrate the technical solutions of the present invention. The present invention has been described in detail with reference to the aforementioned embodiments, and those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chain multilevel converter based on line voltage coordinate system SVM control, characterized in that: The chain-type multilevel converter is a three-phase converter, any phase of which is composed of n submodules connected in series, the structure of the submodule is a voltage-type H-bridge inverter, each submodule includes 4 IGBTs, 4 diodes, and 1 DC voltage source, wherein the diode is connected in anti-parallel with the IGBT, and the chain-type multilevel converter also includes a reference signal module and a control module; The reference signal module generates a normalized phase voltage reference signal u ra 、u rb 、u rc , are the reference phase voltages of the converter phase A, phase B, and phase C respectively; The control module generates 12×n PWM pulse signals according to the phase voltage reference signal to control the operation state of the converter. The modulation method running in the control module is a SVM control method based on the line voltage coordinate system, including the following steps: Step 1: Sample the phase voltage reference signal and calculate the corresponding reference vector in the line voltage coordinate system in, are the coordinate components of the reference vector in the line voltage coordinate system, representing the reference line voltage between phase A and phase B, and the reference line voltage between phase B and phase C respectively; The switching state S(a, b, c) of the converter is related to the space vector V(α * ,β * ) is: Among them, a, b, c are the levels of the three-phase voltage output by the converter, and a, b, c ∈ (0, ±1, ±2, L, ±n), α * , β * is the space vector V(α * ,β * ), which represent the line voltage level between phase A and phase B, and the line voltage level between phase B and phase C respectively; Step 2: Extract reference vector The corresponding feature vector in the central rectangle is the feature vector The coordinate components of ; Step 3: Determine the feature vector The quadrant to which the source sector belongs in the central rectangle, and the specific source sector location: Step 3.1: If At this time, the eigenvector is located in quadrant I of the central rectangle. Located in source sector 1, otherwise located in source sector 2; Step 3.2: If At this time, the eigenvector is located in quadrant II of the central rectangle. If Located in source sector 3, otherwise located in source sector 4; Step 3.3: If At this time, the eigenvector is located in quadrant III of the central rectangle. If is located in source sector 5, otherwise it is located in source sector 6; Step 3.4: If At this time, the eigenvector is located in quadrant IV of the central rectangle. If Located in source sector 7, otherwise located in source sector 8; Step 4: Based on the reference vector The corresponding feature vector The source sector where the synthetic reference vector The three space vectors Step 5: Calculate the space vector The corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ); Step 5.1: If the eigenvector is in quadrant I of the central rectangle, then Corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) are: Step 5.2: If the eigenvector is in quadrant II of the central rectangle, then Corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) are: Step 5.3: If the eigenvector is in quadrant III of the central rectangle, then Corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) are: Step 5.4: If the eigenvector is in quadrant IV of the central rectangle, then Corresponding switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) are: Step 6: Calculate the switch state S according to the volt-second balance principle a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) Their respective action times t1, t2, t3; Step 7: Through the five-stage algorithm, the switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) time-sharing action, synthesizing the reference vector, generating a PWM pulse signal, and the synthesized switching path is S a (a a ,b a ,c a ) → S b (a b ,b b ,c b ) → S c (a c ,b c ,c c ) → S b (a b ,b b ,c b ) → S a (a a ,b a ,c a ), the switching time is: t1 / 2→t2 / 2→t3→t2 / 2→t1 / 2; Continue sampling the phase voltage reference signal and repeat steps 1 to 7 to complete the normal operation of the chain-type multilevel converter.

2. A chained multi-level converter based on line voltage coordinate system SVM control as claimed in claim 1, characterized in that: In the step 2, the reference vector The corresponding feature vector in the central rectangle Extraction is performed by formula (3): in, INT is a rounding function that discards the decimal part of a real number and only retains the integer part; The characteristic vector is located in the central rectangle of the line voltage coordinate system. The central rectangle contains 9 source vectors, namely V0(0,0), V1(1,0), V2(1,1), V3(0,1), V4(-1,1), V5(-1,0), V6(-1,-1), V7(0,-1), and V8(1,-1). The 9 source vectors constitute 8 source sectors. V0(0,0), V1(1,0), and V3(0,1) constitute source sector 1, V1(1,0), V2(1,1), and V3(0,1) constitute source sector 2, and V0(0,0), V4( V0(0,0), V3(0,1), V4(-1,1) constitute source sector 4, V5(-1,0), V6(-1,-1), V7(0,-1) constitute source sector 5, V0(0,0), V5(-1,0), V7(0,-1) constitute source sector 6, V0(0,0), V7(0,-1), V8(1,-1) constitute source sector 7, V0(0,0), V1(1,0), V8(1,-1) constitute source sector 8. The 8 source sectors together form the central rectangle.

3. The chained multi-level converter based on line voltage coordinate system SVM control according to claim 1, characterized in that: In step 4, the reference vector involved in the synthesis The coordinate components of the three space vectors need to be calculated according to the eigenvector The location of the source sector is determined, and step four is specifically as follows: Step 4.1: If the eigenvector is located in source sector 1, then The coordinate components of are: Step 4.2: If the eigenvector is located in source sector 2, then The coordinate components of are: Step 4.3: If the eigenvector is located in source sector 3, then The coordinate components of are: Step 4.4: If the eigenvector is located in source sector 4, then The coordinate components of are: Step 4.5: If the eigenvector is located in source sector 5, then The coordinate components of are: Step 4.6: If the eigenvector is located in source sector 6, then The coordinate components of are: Step 4.7: If the eigenvector is located in source sector 7, then The coordinate components of are: Step 4.8: If the eigenvector is located in source sector 8, then The coordinate components of are: in, INT is a rounding function that discards the decimal part of a real number and only retains the integer part.

4. The chained multi-level converter based on line voltage coordinate system SVM control as claimed in claim 1, characterized in that: In step 6, the switch state S a (a a ,b a ,c a ), S b (a b ,b b ,c b ), S c (a c ,b c ,c c ) Their respective action times t1, t2, t3 need to be calculated based on the characteristic vector And three space vectors The coordinate components are calculated: Among them, T s is the sampling period of the SVM control method based on the line voltage coordinate system, INT is a rounding function that discards the decimal part of a real number and only retains the integer part. For the reference vector Coordinate components.

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