WO2020177238A1 - 全功率因数范围三电平变流器中点平衡控制方法及系统 - Google Patents

全功率因数范围三电平变流器中点平衡控制方法及系统 Download PDF

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WO2020177238A1
WO2020177238A1 PCT/CN2019/091773 CN2019091773W WO2020177238A1 WO 2020177238 A1 WO2020177238 A1 WO 2020177238A1 CN 2019091773 W CN2019091773 W CN 2019091773W WO 2020177238 A1 WO2020177238 A1 WO 2020177238A1
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vector
level converter
phase
power factor
full power
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PCT/CN2019/091773
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English (en)
French (fr)
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张承慧
秦昌伟
李晓艳
邢相洋
胡顺全
姜英
陈阿莲
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山东大学
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Priority to US17/260,461 priority Critical patent/US11296593B2/en
Publication of WO2020177238A1 publication Critical patent/WO2020177238A1/zh

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
    • H02M1/4208—Arrangements for improving power factor of AC input
    • H02M1/425—Arrangements for improving power factor of AC input using a single converter stage both for correction of AC input power factor and generation of a high frequency AC output voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
    • H02M7/53876—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/123—Suppression of common mode voltage or current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the present disclosure relates to the technical field of common mode voltage suppression for three-level converter systems, and in particular to a method and system for controlling the neutral point balance of a three-level converter with a full power factor range.
  • the Neutral-Point-Clamped (NPC) three-level converter has been widely used. Compared with the traditional three-phase two-level converter topology, the NPC three-level converter has the advantages of low power device voltage stress and good output waveform quality.
  • the common-mode voltage is generated by the switching action of the power devices in the converter, which increases the electromagnetic interference of the system, and brings serious harm to the safe, reliable and stable operation of the power electronic system.
  • common-mode voltage generates common-mode leakage current, which seriously threatens personal safety.
  • the common mode current generated by the common mode voltage continuously flows through the motor insulation, causing serious damage to the motor; bearing current is generated, which damages the motor's bearings.
  • the present disclosure proposes a midpoint balance control method and system for a three-level converter with full power factor range, which realizes the common mode voltage suppression of an NPC three-level converter system under full power factor, and at the same time realizes midpoint potential low-frequency oscillation When the abnormal situation causes the midpoint potential to shift, the midpoint potential can be restored.
  • the present disclosure adopts the following technical solutions:
  • Adopt large vector, medium vector and zero vector modulation methods to synthesize the reference voltage vector and determine the duty ratios of the large vector, medium vector and zero vector respectively;
  • the duty cycle of each basic vector is updated to obtain the switching sequence for controlling the three-phase bridge arm power switch tube.
  • the determining the duty ratios of the large vector, the medium vector and the zero vector respectively is specifically as follows:
  • the volt-second balance equation is constructed, and the duty ratios of the large, medium, and zero vectors are obtained by solving the volt-second balance equation .
  • the large vector, the medium vector, the zero vector, and the small vector are respectively selected basic vectors, wherein there are six large, medium, and small vectors, and one zero vector.
  • the PI regulator is used to obtain the selected duty cycle of the small vector.
  • the midpoint potential of the three-level converter is not greater than the set threshold, select the small vector according to the sector where the reference voltage vector is located and the three-phase output current, and then perform the duty cycle of each basic vector Update and redesign the switch sequence.
  • the switching sequence is designed as OOO-POO-PON-PNN-PON-POO-OOO, the volt-second balance equation is corrected, the duty cycle of each basic vector is updated, and the small vector is considered
  • the constraint condition that the empty ratio needs to satisfy is further obtained the value of the small vector duty ratio.
  • the switching sequence is designed as OOO-OON-PON-PNN-PON-OON-OOO, the volt-second balance equation is corrected, the duty cycle of each basic vector is updated, and the small vector is considered
  • the constraint condition that the empty ratio needs to satisfy is further obtained the value of the small vector duty ratio.
  • the switch sequence is designed as OPO-OOO-PON-PNN-PON-OOO-OPO, the volt-second balance equation is corrected, and the basic vector is updated Duty cycle, considering the constraint conditions that the small vector duty cycle needs to meet, and further obtain the value of the small vector duty cycle.
  • the small vector duty cycle is determined by a method similar to that of the first sector, combined with the symmetry of the space vector diagram for analysis and determination.
  • the present disclosure adopts the following solutions:
  • a full power factor range three-level converter midpoint balance control system including a controller and an algorithm program, the controller realizes the above-mentioned full power factor range three-level converter midpoint when the controller executes the algorithm program Balance control method.
  • the amplitude of the common-mode voltage of the NPC three-level converter is equal to one-sixth of the DC side voltage. Compared with the traditional space vector modulation method, the amplitude of the common-mode voltage is reduced by one-half. The electromagnetic interference of the system effectively reduces the adverse effect of the common mode voltage on the motor windings.
  • the method of the present invention also considers the sign and magnitude relationship of the sector and the three-phase current, selects the basic voltage vector and designs the switching sequence of each sector, which can achieve the full power factor range and eliminate the low-frequency oscillation of the midpoint potential .
  • Figure 1 shows the topology of the NPC three-level converter system in the first embodiment
  • Fig. 2 is a spatial vector diagram of the midpoint balance control method of the full power factor range three-level converter in the first embodiment
  • Fig. 3 is a control block diagram of the midpoint balance control method of a three-level converter with full power factor range in the first embodiment
  • a midpoint balance control method for a full power factor range three-level converter is disclosed, as shown in Fig. 3, including the following steps:
  • This method is mainly aimed at the NPC three-level converter system, as shown in Figure 1, including A-phase, B-phase and C-phase bridge arms.
  • Each phase bridge arm includes four power switch tubes and two clamp diodes.
  • the DC side includes two filter capacitors connected in series, the middle of the two filter capacitors forms a neutral point, and the middle of the two clamping diodes of each phase bridge arm is connected to the neutral point.
  • the power switch tube is an insulated gate bipolar transistor (IGBT); of course, the power switch tube can also be implemented by other forms of transistors.
  • IGBT insulated gate bipolar transistor
  • each phase bridge arm of the NPC three-level converter system has three working states P, O and N.
  • the neutral point of the two filter capacitors on the DC side is taken as the reference point, and the bridge arm output voltage in the P state is the output One-half of the DC voltage value, the bridge arm output voltage is zero in the O state, and the bridge arm output voltage is the negative half of the output DC voltage value in the N state.
  • the power switch tube is turned on and off by the control system.
  • the method of the present invention designs a new space vector modulation method to control the on and off of the power switch tube in the NPC three-level converter system.
  • Table 1 lists the basic voltage vector selected by the method of the present invention and the corresponding common mode voltage amplitude.
  • the common mode voltage is defined as the average value of the three-phase output voltage of the NPC three-level converter.
  • Table 1 The basic voltage vector selected by the method of the present invention and the corresponding common-mode voltage amplitude
  • d L , d M and d Z are the duty ratios of the large vector, the medium vector and the zero vector respectively, and V ref is the amplitude of the reference voltage vector.
  • m is the modulation degree, defined as V ref is the amplitude of the reference voltage vector, and V dc is the DC input voltage.
  • a small vector is selected according to the sector where the reference voltage vector is located and the three-phase output current, and then the duty cycle of each basic vector is updated, and the switching sequence is redesigned.
  • the duty ratios of the large vector, medium vector, small vector, and zero vector are updated to d' L , d' M , d' S and d' Z respectively .
  • i a , i b and i c respectively represent the output currents of phase A, phase B and phase C of the NPC three-level converter system.
  • the midpoint potential fluctuation produced by the medium vector PON is equal to the midpoint potential fluctuation produced by the small vector POO, namely
  • the midpoint potential fluctuation produced by the medium vector PON is equal to the midpoint potential fluctuation produced by the small vector OON, namely
  • the midpoint potential fluctuation produced by the medium vector PON is equal to the midpoint potential fluctuation produced by the small vector OPO, namely
  • a midpoint balance control system for a full power factor range three-level converter which is characterized in that it includes a controller and an algorithm program, and when the controller executes the algorithm program The midpoint balance control method of the full power factor range three-level converter described in the first embodiment is realized.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Inverter Devices (AREA)
  • Dc-Dc Converters (AREA)

Abstract

本公开公开了一种全功率因数范围三电平变流器中点平衡控制方法及系统，包括：采用大矢量、中矢量和零矢量调制方法，合成参考电压矢量，分别确定大矢量、中矢量和零矢量的占空比；通过信号采集得到直流侧两电容器组之间的电压差，确定为三电平变流器中点电位；根据三电平变流器中点电位与设定阈值的大小关系，进行小矢量的选择及其占空比计算；对各个基本矢量的占空比进行更新，得到控制三相桥臂功率开关管的开关序列。本公开方法等到的NPC三电平变流器共模电压的幅值等于直流侧电压的六分之一，与传统空间矢量调制方法相比，共模电压的幅值降低了二分之一，降低了系统的电磁干扰，有效降低了共模电压对电机绕组的不利影响。

Description

全功率因数范围三电平变流器中点平衡控制方法及系统 技术领域
本公开涉及三电平变流器系统的共模电压抑制技术领域，尤其涉及一种全功率因数范围三电平变流器中点平衡控制方法及系统。
背景技术
本部分的陈述仅仅是提供了与本公开相关的背景技术信息，不必然构成在先技术。
近年来，随着大功率交流电力传动技术的快速发展，中点箝位型(Neutral-Point-Clamped,NPC)三电平变流器得到了广泛应用。与传统三相两电平变流器拓扑相比，NPC三电平变流器具有功率器件电压应力低、输出波形质量好等优势。
共模电压由变流器中的功率器件的开关动作产生，增加了系统的电磁干扰，对电力电子系统的安全、可靠、稳定运行带来了严重的危害。在光伏发电系统中，共模电压产生共模漏电流，严重威胁人身安全。在电力传动系统中，共模电压产生的共模电流持续地流过电机绝缘，对电机造成严重的损害；产生轴承电流，损害电机的轴承。这些问题使得共模电压的抑制成为了一个必须考虑的问题。
发明人发现，现有的共模电压抑制方法主要针对单位功率因数或功率因数较高的运行工况，在全功率因数范围内对于NPC三电平变流器系统共模电压抑制方法的研究并不多见。
发明内容
本公开提出了全功率因数范围三电平变流器中点平衡控制方法及系统，实现了全功率因数下NPC三电平变流器系统的共模电压抑制，同时实现了中点电位低频振荡的消除，当异常情况导致中点电位发生偏移时，能够实现中点电位的恢复。
根据一些实施例，本公开采用如下技术方案：
全功率因数范围三电平变流器中点平衡控制方法，其特征在于，包括：
采用大矢量、中矢量和零矢量调制方法，合成参考电压矢量，分别确定大矢量、中矢量和零矢量的占空比；
通过信号采集得到直流侧两电容器组之间的电压差，确定为三电平变流器中点电位；
根据三电平变流器中点电位与设定阈值的大小关系，进行小矢量的选择及其占空比计算；
对各个基本矢量的占空比进行更新，得到控制三相桥臂功率开关管的开关序列。
进一步地，所述分别确定大矢量、中矢量和零矢量的占空比，具体为：
根据大矢量、中矢量、零矢量以及它们各自对应的占空比与参考电压矢量的关系，构建 伏秒平衡方程，通过求解伏秒平衡方程，得到大矢量、中矢量和零矢量的占空比。
进一步地，所述大矢量、中矢量、零矢量和小矢量分别为选取的基本矢量，其中，大矢量、中矢量和小矢量分别为6个，零矢量为1个。
进一步地，当三电平变流器中点电位大于设定阈值时，采用PI调节器得到选择的小矢量的占空比。
进一步地，当三电平变流器中点电位不大于设定阈值时，根据参考电压矢量所在的扇区和三相输出电流的情况，选择小矢量，然后对各个基本矢量的占空比进行更新，并重新设计开关序列。
进一步地，参考电压矢量在第1扇区时：如果B相电流大于0、且A相电流大于0，或者，B相电流小于0、且A相电流小于0，选取大矢量PNN、中矢量PON、小矢量POO和零矢量OOO合成参考电压矢量，开关序列设计为OOO-POO-PON-PNN-PON-POO-OOO，修正伏秒平衡方程，更新各个基本矢量的占空比，考虑小矢量占空比需要满足的约束条件，进一步得到小矢量占空比的值。
进一步地，参考电压矢量在第1扇区时：如果B相电流大于0、且C相电流大于0，或者，B相电流小于0、且C相电流小于0，选取大矢量PNN、中矢量PON、小矢量OON和零矢量OOO合成参考电压矢量，开关序列设计为OOO-OON-PON-PNN-PON-OON-OOO，修正伏秒平衡方程，更新各个基本矢量的占空比，考虑小矢量占空比需要满足的约束条件，进一步得到小矢量占空比的值。
进一步地，参考电压矢量在第1扇区时：如果B相电流大于0、且A相和C相电流均小于0，或者，B相电流小于0、且A相和C相电流均大于0，选取大矢量PNN、中矢量PON、小矢量OPO和零矢量OOO合成参考电压矢量，开关序列设计为OPO-OOO-PON-PNN-PON-OOO-OPO，修正伏秒平衡方程，更新各个基本矢量的占空比，考虑小矢量占空比需要满足的约束条件，进一步得到小矢量占空比的值。
进一步地，对于参考电压矢量在其它扇区的情形，小矢量占空比的确定采用与第1扇区类似的方法，结合空间矢量图的对称性进行分析确定。
根据另外一些实施例，本公开采用如下方案：
一种全功率因数范围三电平变流器中点平衡控制系统，包括控制器及算法程序，所述控制器执行所述算法程序时实现上述的全功率因数范围三电平变流器中点平衡控制方法。
与现有技术相比，本公开的有益效果是：
(1)NPC三电平变流器共模电压的幅值等于直流侧电压的六分之一，与传统空间矢量调 制方法相比，共模电压的幅值降低了二分之一，降低了系统的电磁干扰，有效降低了共模电压对电机绕组的不利影响。
(2)本发明方法同时考虑扇区和三相电流的符号及大小关系，选择基本电压矢量并设计各扇区的开关序列，能够实现在全功率因数范围内，消除了中点电位的低频振荡。
(3)当异常情况导致中点电位发生偏移时，能够实现中点电位恢复。
(4)由于直流侧电容的电压振荡减小，直流侧可以采用容量较小的电容器，进而减小了整个变流器系统的体积。
附图说明
构成本申请的一部分的说明书附图用来提供对本申请的进一步理解，本申请的示意性实施例及其说明用于解释本申请，并不构成对本申请的不当限定。
图1为实施例一中NPC三电平变流器系统的拓扑结构；
图2为实施例一中全功率因数范围三电平变流器中点平衡控制方法的空间矢量图；
图3为实施例一中全功率因数范围三电平变流器中点平衡控制方法的控制框图；
图4为实施例一中功率因数PF＝1时，提出方法与传统空间电压矢量调制仿真波形，从上到下依次是：三相电流、线电压、共模电压、直流侧上下电容电压；
图5为实施例一中功率因数PF＝0时，提出方法与传统空间电压矢量调制仿真波形，从上到下依次是：三相电流、线电压、共模电压、直流侧上下电容电压；
具体实施方式
应该指出，以下详细说明都是示例性的，旨在对本申请提供进一步的说明。除非另有指明，本公开使用的所有技术和科学术语具有与本申请所属技术领域的普通技术人员通常理解的相同含义。
需要注意的是，这里所使用的术语仅是为了描述具体实施方式，而非意图限制根据本申请的示例性实施方式。如在这里所使用的，除非上下文另外明确指出，否则单数形式也意图包括复数形式，此外，还应当理解的是，当在本说明书中使用术语“包含”和/或“包括”时，其指明存在特征、步骤、操作、器件、组件和/或它们的组合。
实施例一
在一个或多个实施方式中公开了一种全功率因数范围三电平变流器中点平衡控制方法，如图3所示，包括以下步骤：
(1)采用大矢量、中矢量和零矢量调制方法，合成参考电压矢量，分别确定大矢量、中矢量和零矢量的占空比；
(2)通过信号采集得到直流侧两电容器组之间的电压差，确定为三电平变流器中点电位；
(3)根据三电平变流器中点电位与设定阈值的大小关系，进行小矢量的选择及其占空比计算；
(4)对各个基本矢量的占空比进行更新，得到控制三相桥臂功率开关管的开关序列。
该方法主要针对NPC三电平变流器系统，如图1所示，包括A相、B相和C相桥臂，每相桥臂包括四个功率开关管和两个箝位二极管。直流侧包括两个串联连接的滤波电容，两个滤波电容的中间形成一个中性点，每相桥臂的两个箝位二极管的中间与中性点相连接。
应理解，功率开关管为绝缘栅双极型晶体管(IGBT)；当然，功率开关管也可采用其他形式晶体管来实现。
具体地，NPC三电平变流器系统的每相桥臂有三种工作状态P、O和N，以直流侧两个滤波电容的中性点为参考点，P状态时桥臂输出电压为输出直流电压值的二分之一，O状态时桥臂输出电压为零，N状态时桥臂输出电压为输出直流电压值的负二分之一。
其中，功率开关管的开通与关断由控制系统完成。
本发明方法设计新型空间矢量调制方法控制NPC三电平变流器系统中的功率开关管的通断，采用的基本矢量共19个，根据幅值的不同，分为大矢量、中矢量、小矢量和零矢量，空间矢量图如图2所示，
表1列出了本发明方法选用的基本电压矢量及对应的共模电压幅值。
共模电压定义为NPC三电平变流器三相输出电压的平均值。
Figure PCTCN2019091773-appb-000001
表1 本发明方法选用的基本电压矢量及对应的共模电压幅值
Figure PCTCN2019091773-appb-000002
首先，采用大矢量、中矢量和零矢量调制方法，合成参考电压矢量，得到伏秒平衡方程
Figure PCTCN2019091773-appb-000003
其中，d L、d M和d Z分别为大矢量、中矢量和零矢量的占空比，V ref为参考电压矢量的幅值。
求解伏秒平衡方程，得到大矢量、中矢量和零矢量的占空比分别为
Figure PCTCN2019091773-appb-000004
其中，m为调制度，定义为
Figure PCTCN2019091773-appb-000005
V ref为参考电压矢量的幅值，V dc为直流输入电压。
NPC三电平变流器中点电位等于两个电容电压的差值，即Δv＝v P-v N，设置中点电位的阈值Δv th，当Δv>Δv th时，采用PI调节器得到选择的小矢量的占空比，具体地，将直流侧两个电容的电压偏差值送入一个PI调节器，PI调节器的输出取绝对值运算，得到选择的小矢量的占空比。当Δv≤Δv th时，采用如下步骤精确计算选择的小矢量的占空比。
为抑制中点电位的低频振荡，根据参考电压矢量所在的扇区和三相输出电流的情况，选择小矢量，然后对各个基本矢量的占空比进行更新，并重新设计开关序列。设选择小矢量后，大矢量、中矢量、小矢量和零矢量的占空比分别更新为d' L、d' M、d' S和d' Z。i a、i b和i c分别表示NPC三电平变流器系统A相、B相和C相的输出电流。以参考电压矢量在第1扇区时为例，分析该发明方法的实施步骤，分为以下6种情况。
(1)当B相电流大于0，且A相电流大于0时，选取大矢量PNN、中矢量PON、小矢量POO和零矢量OOO合成参考电压矢量，开关序列设计为OOO-POO-PON-PNN-PON-POO-OOO，根据修正的伏秒平衡方程，更新各个基本矢量的占空比
Figure PCTCN2019091773-appb-000006
为消除中点电位的低频振荡，令中矢量PON产生的中点电位波动量等于小矢量POO产生的中点电位波动量，即
d Mi b＝yi a                                          (5)
得到
Figure PCTCN2019091773-appb-000007
考虑小矢量占空比需要满足的约束条件，进一步得到小矢量占空比的值为
Figure PCTCN2019091773-appb-000008
(2)当B相电流大于0，且C相电流大于0时，选取大矢量PNN、中矢量PON、小矢量OON和零矢量OOO合成参考电压矢量，开关序列设计为OOO-OON-PON-PNN-PON-OON-OOO，根据修正的伏秒平衡方程，更新各个基本矢量的占空比
Figure PCTCN2019091773-appb-000009
为消除中点电位的低频振荡，令中矢量PON产生的中点电位波动量等于小矢量OON产生的中点电位波动量，即
(d M-y)i b＝yi c                                 (9)
得到
Figure PCTCN2019091773-appb-000010
考虑小矢量占空比需要满足的约束条件，进一步得到小矢量占空比的值为
Figure PCTCN2019091773-appb-000011
(3)当B相电流大于0，且A相和C相电流均小于0时，选取大矢量PNN、中矢量PON、小矢量OPO和零矢量OOO合成参考电压矢量，开关序列设计为OPO-OOO-PON-PNN-PON-OOO-OPO，根据修正的伏秒平衡方程，更新各个基本矢量的占空比
Figure PCTCN2019091773-appb-000012
为消除中点电位的低频振荡，令中矢量PON产生的中点电位波动量等于小矢量OPO产生的中点电位波动量，即
(d M-y)i b＝yi b          (13)
得到
Figure PCTCN2019091773-appb-000013
考虑小矢量占空比需要满足的约束条件，进一步得到小矢量占空比的值为
Figure PCTCN2019091773-appb-000014
(4)当B相电流小于0，且A相电流小于0时，基本电压矢量的选取、占空比更新和开关序列设计与情况(1)相同。
(5)当B相电流小于0，且C相电流小于0时，基本电压矢量的选取、占空比更新和开关序列设计与情况(2)相同。
(6)当B相电流小于0，且A相和C相电流均大于0时，基本电压矢量的选取、占空比更新和开关序列设计与情况(3)相同。
对于参考电压矢量在其它扇区的情形，可以采用与第1扇区类似的方法，结合空间矢量图的对称性进行分析。
图4和图5分别为功率因数PF＝1和PF＝0时，提出方法与传统空间电压矢量调制仿真波形，从上到下依次是：三相电流、线电压、共模电压、直流侧上下电容电压；当时间t<0.5s 时，采用提出的方法。t>0.5s时，采用传统的空间矢量调制。可以看出采用两种方法三相电流的正弦度相近，线电压都含有5个电平。但是采用提出方法的共模电压只有传统方法的1/2，共模电压的幅值有效减低。同时，提出方法与传统方法相比直流侧中点电位波动量得到有效抑制。特别是在PF＝0时，采用传统方法的中点电位波动量达到10V以上，而采用提出方法的直流侧中点电位的波动量得到有效降低。
实施例二
在一个或多个实施方式中，公开了一种全功率因数范围三电平变流器中点平衡控制系统，其特征在于，包括控制器及算法程序，所述控制器执行所述算法程序时实现实施例一中所述的全功率因数范围三电平变流器中点平衡控制方法。
上述虽然结合附图对本公开的具体实施方式进行了描述，但并非对本公开保护范围的限制，所属领域技术人员应该明白，在本公开的技术方案的基础上，本领域技术人员不需要付出创造性劳动即可做出的各种修改或变形仍在本公开的保护范围以内。

Claims (10)

  1. 全功率因数范围三电平变流器中点平衡控制方法，其特征在于，包括：
    采用大矢量、中矢量和零矢量调制方法，合成参考电压矢量，分别确定大矢量、中矢量和零矢量的占空比；
    通过信号采集得到直流侧两电容器组之间的电压差，确定为三电平变流器中点电位；
    根据三电平变流器中点电位与设定阈值的大小关系，进行小矢量的选择及其占空比计算；
    对各个基本矢量的占空比进行更新，得到控制三相桥臂功率开关管的开关序列。
  2. 如权利要求1所述的全功率因数范围三电平变流器中点平衡控制方法，其特征在于，所述分别确定大矢量、中矢量和零矢量的占空比，具体为：
    根据大矢量、中矢量、零矢量以及它们各自对应的占空比与参考电压矢量的关系，构建伏秒平衡方程，通过求解伏秒平衡方程，得到大矢量、中矢量和零矢量的占空比。
  3. 如权利要求1所述的全功率因数范围三电平变流器中点平衡控制方法，其特征在于，所述大矢量、中矢量、零矢量和小矢量分别为选取的基本矢量，其中，大矢量、中矢量和小矢量分别为6个，零矢量为1个。
  4. 如权利要求1所述的全功率因数范围三电平变流器中点平衡控制方法，其特征在于，当三电平变流器中点电位大于设定阈值时，采用PI调节器得到选择的小矢量的占空比。
  5. 如权利要求1所述的全功率因数范围三电平变流器中点平衡控制方法，其特征在于，当三电平变流器中点电位不大于设定阈值时，根据参考电压矢量所在的扇区和三相输出电流的情况，选择小矢量，然后对各个基本矢量的占空比进行更新，并重新设计开关序列。
  6. 如权利要求5所述的全功率因数范围三电平变流器中点平衡控制方法，其特征在于，参考电压矢量在第1扇区时：如果B相电流大于0、且A相电流大于0，或者，B相电流小于0、且A相电流小于0，选取大矢量PNN、中矢量PON、小矢量POO和零矢量OOO合成参考电压矢量，开关序列设计为OOO-POO-PON-PNN-PON-POO-OOO。
  7. 如权利要求5所述的全功率因数范围三电平变流器中点平衡控制方法，其特征在于，参考电压矢量在第1扇区时：如果B相电流大于0、且C相电流大于0，或者，B相电流小于0、且C相电流小于0，选取大矢量PNN、中矢量PON、小矢量OON和零矢量OOO合成参考电压矢量，开关序列设计为OOO-OON-PON-PNN-PON-OON-OOO。
  8. 如权利要求5所述的全功率因数范围三电平变流器中点平衡控制方法，其特征在于，参考电压矢量在第1扇区时：如果B相电流大于0、且A相和C相电流均小于0，或者，B相电流小于0、且A相和C相电流均大于0，选取大矢量PNN、中矢量PON、小矢量OPO和零矢量OOO合成参考电压矢量，开关序列设计为OPO-OOO-PON-PNN-PON-OOO-OPO。
  9. 如权利要求6-8任一项所述的全功率因数范围三电平变流器中点平衡控制方法，其特征是在于，对于参考电压矢量在其它扇区的情形，小矢量占空比的确定采用与第1扇区类似的方法，结合空间矢量图的对称性进行分析确定。
  10. 一种全功率因数范围三电平变流器中点平衡控制系统，其特征在于，包括服务器，所述服务器包括存储器、处理器及存储在存储器上并可在处理器上运行的计算机程序，所述处理器执行所述程序时实现权利要求1-8任一项所述的全功率因数范围三电平变流器中点平衡控制方法。
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