WO2016155035A1 - 一种三电平逆变器中点电位平衡控制方法 - Google Patents

一种三电平逆变器中点电位平衡控制方法 Download PDF

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WO2016155035A1
WO2016155035A1 PCT/CN2015/076522 CN2015076522W WO2016155035A1 WO 2016155035 A1 WO2016155035 A1 WO 2016155035A1 CN 2015076522 W CN2015076522 W CN 2015076522W WO 2016155035 A1 WO2016155035 A1 WO 2016155035A1
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vector
voltage
module
midpoint potential
inverter
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PCT/CN2015/076522
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邹军
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成都麦隆电气有限公司
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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
    • 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

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  • the invention relates to the technical field of electric energy management, in particular to a method for controlling a point potential balance in a three-level inverter.
  • Inverters are widely used in industrial production, such as frequency conversion equipment and electric drive equipment. In order to provide sufficient power, most of them are two-level three-phase inverters. In some precision controllers, two levels cannot meet the requirements. Multiple levels of output harmonics must be used to reduce jitter in the control object.
  • Common multi-level topology diode clamps and flying capacitors, as well as MMC multi-module cascades, flying across capacitors because of the large number of capacitors The balance problem is not easy to solve, so the application is less, and the MMC multi-module cascading cost is higher, which is more suitable for high-voltage occasions. Therefore, the diode clamp topology is generally adopted, and the present invention also optimizes and improves the control method of the topology.
  • the three-level control method is mainly SPWM carrier method and SVPWM space vector method.
  • the space vector is controlled by vector synthesis control, and the control precision is high. Therefore, the space vector method output harmonic is lower than the carrier method, and the utilization of the DC side is higher.
  • the vector method is more suitable for occasions where the requirements are high. Since the upper and lower capacitors of the three-level inverter utilize the asymmetry and the difference in device loss, they gradually accumulate as voltage deviations, causing the upper and lower capacitor voltages to be unbalanced. Because the vector decomposition is based on the ideal symmetric model, once the balance is lost, the vectors participating in the decomposition no longer meet the requirements. The theory causes the control to deteriorate, the output harmonics increase, and the system shutdown protection in severe cases. Therefore, the core of the three-level control is the balance control of the midpoint potential.
  • the basic idea of the resistor equalization method is to discharge the upper and lower ends of the capacitor through the parallel resistor.
  • the unloading speed is proportional to the capacitor voltage. If the upper terminal voltage>the lower terminal voltage, then the upper end capacitor unloading speed>the lower end capacitor unloading speed, so that the two capacitors The voltage is in the direction of balance. The smaller the resistance is, the faster the balance is, but the additional resistance loss is added to reduce the efficiency of the device. Generally, the resistance is selected above 10K, which inhibits the midpoint imbalance. effect.
  • the basic idea of redistributing small and medium vector action time method is that according to the influence of medium and small vector on the midpoint balance, a fine adjustment amount is superimposed on the medium and small vectors by the upper and lower capacitance difference PI, so that the midpoint voltage tends to be balanced.
  • the direction is performed, the size of the fine adjustment amount is related to the difference degree of the upper and lower end loss, and the fine adjustment amount cannot be too large, otherwise the output vector sum will be affected, and the output will be deteriorated.
  • the object of the present invention is to overcome the above-mentioned deficiencies in the prior art, and to provide a three-level inverter midpoint potential balance control method, which aims to solve the difference in utilization and device loss between the upper and lower capacitors of the three-level inverter. It will gradually accumulate as a voltage deviation, resulting in an imbalance of the upper and lower capacitor voltages.
  • the present invention provides the following technical solutions:
  • a three-level inverter midpoint potential balance control method comprising the following steps: Step 1: determining a sector in which a voltage is located according to an inverter voltage command, and calculating a command voltage through a current regulator;
  • Step 2 According to the current positive and negative direction of the three-phase output currents Ia, Ib, Ic, the position of the sector, and the magnitude of the upper capacitor DC voltage Udc1 and the lower capacitor DC voltage Udc2, and refer to the following vector selection table to select a suitable midpoint potential.
  • Step 3 Calculate the distribution time of the three vectors according to the command voltage and the selected vector, calculate the on-off time of each IGBT according to the vector distribution time, and calculate the driving signal.
  • the midpoint balance control inverter device provided by the three-level inverter midpoint potential balance control method includes an auxiliary power module, an acquisition module, an inverter control, a drive module, a power module, and a negative
  • the inverter controller is connected to the acquisition module, the drive module and the auxiliary power module, and the drive module is connected to the drive power module.
  • Auxiliary module Provide stable and reliable power supply for the acquisition module, inverter controller and drive circuit;
  • Acquisition module realizes the conversion of electricity and signals, and the system performs closed-loop control according to the collected feedback amount;
  • the invention is based on a diode clamp topology, and uses the current positive and negative direction of the three-phase output currents Ia, Ib, Ic, the sector position, and the upper capacitor DC voltage Udc1 and the lower capacitor DC voltage Udc2 to select a stable midpoint potential.
  • the vector is used to achieve a balance of the upper and lower capacitor voltages.
  • Figure 1 is a diode clamp topology diagram
  • FIG. 2 is a schematic diagram of a midpoint balance control inverter device
  • Figure 3 is a control block diagram of the inverter controller
  • Figure 4 is a three-level vector composite diagram
  • FIG. 5 is an equivalent circuit diagram of the PPP zero vector
  • Figure 6 is an equivalent circuit diagram of a POO small vector
  • Figure 7 is an equivalent circuit diagram of the ONN small vector
  • Figure 8 is an equivalent circuit diagram of a PPO small vector
  • Figure 9 is an equivalent circuit diagram of the OON small vector
  • Figure 10 is an equivalent circuit diagram of a vector in a PON
  • Figure 11 is an equivalent circuit diagram of a PNN large vector
  • Figure 12 is an equivalent circuit diagram of the PPN large vector.
  • the positive vector P is defined as: When the IGBT state of the A-phase insulated gate bipolar transistor is G1 on, G3 off, G2 on, and G4 off, the A phase outputs a positive voltage, and the A phase current rises.
  • the zero vector O is defined as: A-phase insulated gate bipolar transistor IGBT state is G1 open, G3 turned on, G2 turned on, G4 turned off, phase A current continues to flow through D1 and D2; negative vector N: When G1 is disconnected, G3 is turned on, G2 is turned off, and G4 is turned on, the A phase outputs a negative voltage, and the A phase current decreases.
  • UA is the voltage on RA
  • UB is the voltage on RB
  • UC is the voltage on RC
  • PPP zero vector equivalent circuit is shown in Figure 5.
  • PPP, OOO, and NNN are all zero level, the output voltage is 0, and the three-phase current has no effect on the midpoint potential.
  • control midpoint level can be properly controlled by the current flow to the midpoint potential. Only the small vector and the medium vector affect the midpoint potential, so the capacitance difference and current can be based on the upper and lower ends. Flow direction to select the appropriate small and medium vector to synthesize, in order to reduce the output pulsation when selecting, only one switch changes optimally during vector switching.
  • a sector 1 small sector can be composed of 4 vectors.
  • Zero vector + PPO or OON + POO or ONN to combine select the vector that is favorable for potential balance according to the action relationship of the following table

Abstract

一种三电平逆变器中点电位平衡控制方法，该方法包括如下步骤：步骤一：根据电流调节器计算得到指令电压，由电压指令判断所在扇区；步骤二：根据三相输出电流Ia、Ib、Ic的电流正负方向、扇区位置以及上端电容直流电压Udc1和下端电容直流电压Udc2的大小并参见矢量选择表来选择适合稳定中点电位的矢量；步骤三：根据指令电压和所选择的矢量，计算三个矢量的分配时间，根据矢量分配时间计算各个IGBT的通断时间，计算得到驱动信号。该方法基于二极管钳位式拓扑结构，利用三相输出电流正负方向、扇区位置以及上端电容直流电压和下端电容直流电压的大小来选择适合稳定中点电位的矢量来实现上下电容电压的平衡。

Description

一种三电平逆变器中点电位平衡控制方法 技术领域
本发明涉及电能治理技术领域，具体及一种三电平逆变器中点电位平衡控制方法。
背景技术
工业生产中广泛使用逆变器，如变频设备、电力拖动设备，为了提供足够功率，多为两电平三相逆变器，而在在一些精密控制器中，两电平不能满足要求，必须采用多电平降低输出谐波，以减少控制对象的抖动，常见多电平拓扑二极管钳位式和飞跨电容式以及MMC多模块级联，飞跨电容式因为电容数目多，相互之间平衡问题不易解决，所以应用较少，而MMC多模块级联成本较高，更适合高压场合，故一般采用二极管钳位式拓扑结构，本发明也针对该拓扑的控制方法进行优化改进。
三电平控制方法主要为SPWM载波法和SVPWM空间矢量法，空间矢量通过矢量合成控制输出，控制精度高，因此空间矢量法输出谐波比载波法要低，并且直流侧的利用率更高，空间矢量法更适合在要求高的场合。由于三电平逆变器上下电容利用不对称和器件损耗差异会逐渐累积为电压偏差，导致上下电容电压不平衡，因为矢量分解是基于理想对称模型，一旦失去平衡各参与分解的矢量不再符合理论，导致控制变差，输出谐波增加，严重时系统停机保护，因此三电平控制中最为核心的是中点电位的平衡控制。
为了解决上下电容平衡问题，目前常见为电阻均压法和重新分配中小矢量作用时间法或两者兼用。
电阻均压法基本思想为通过并联电阻对上下端电容泄荷，卸荷速度和电容电压成正比，如果上端电压>下端电压，那么上端电容卸荷速度>下端电容卸荷速度，使两个电容电压沿着平衡的方向进行，阻值越小平衡作用速度越快，但是会额外增加电阻损耗，降低设备效率，通常阻值都选定在10K级以上，对中点不平衡起到一定的抑制作用。
重新分配中小矢量作用时间法基本思想是根据中、小矢量对中点平衡的影响趋势不同，通过上下端电容压差PI得到一个微调量叠加在中、小矢量上，使中点电压趋向平衡的方向进行，微调量的大小和上下端损耗差异程度有关，微调量不能过大，否则会影响输出矢量和，导致输出变差。
发明内容
本发明的目的在于克服现有技术中所存在的上述不足，提供一种三电平逆变器中点电位平衡控制方法,旨在解决三电平逆变器上下电容利用不对称和器件损耗差异会逐渐累积为电压偏差从而导致上下电容电压不平衡的问题。
为了实现上述发明目的，本发明提供了以下技术方案：
一种三电平逆变器中点电位平衡控制方法，其特征在于，包括如下步骤：步骤一：根据逆变电压指令判断电压所在扇区，以及经电流调节器计算得到指令电压；
步骤二：根据三相输出电流Ia、Ib、Ic的电流正负方向、扇区位置以及上端电容直流电压Udc1和下端电容直流电压Udc2的大小并参见如下矢量选择表来选择适合稳定中点电位的矢量；
Figure PCTCN2015076522-appb-000001
Figure PCTCN2015076522-appb-000002
Figure PCTCN2015076522-appb-000003
Figure PCTCN2015076522-appb-000004
Figure PCTCN2015076522-appb-000005
Figure PCTCN2015076522-appb-000006
步骤三：根据指令电压和所选择的矢量，计算三个矢量的分配时间，根据矢量分配时间计算各个IGBT的通断时间，计算得到驱动信号。
在本发明中，依据三电平逆变器中点电位平衡控制方法提供的中点平衡控制逆变装置，包括辅电模块、采集模块，逆变控制，驱动模块、功率模块和负 载；逆变控制器分别与采集模块、驱动模块和辅电模块连接通信，驱动模块连接驱动功率模块。
辅电模块：为采集模块、逆变控制器、驱动电路提供稳定可靠的电源；
采集模块：实现电和信号的转换，系统根据采集的反馈量进行闭环控制；
驱动模块和功率模块：实现信号和功率的转换。
与现有技术相比，本发明的有益效果：
本发明基于二极管钳位式拓扑结构，利用三相输出电流Ia、Ib、Ic的电流正负方向、扇区位置以及上端电容直流电压Udc1和下端电容直流电压Udc2的大小来选择适合稳定中点电位的矢量来实现上下电容电压的平衡。
附图说明
图1为二极管钳位式拓扑结构图；
图2为中点平衡控制逆变装置原理图；
图3为逆变控制器控制框图；
图4为三电平矢量合成图；
图5为PPP零矢量的等效电路图；
图6为POO小矢量的等效电路图；
图7为ONN小矢量的等效电路图；
图8为PPO小矢量的等效电路图；
图9为OON小矢量的等效电路图；
图10为PON中矢量的等效电路图；
图11为PNN大矢量的等效电路图；
图12PPN大矢量的等效电路图。
具体实施方式
下面结合试验例及具体/实施方式对本发明作进一步的详细描述。但不应将此理解为本发明上述主题的范围仅限于以下的实施例，凡基于本发明内容所实现的技术均属于本发明的范围。
首先，作矢量定义：以A相为例
根据图1硬件电路，以A相为例，共有4种状态，描述如下：
Figure PCTCN2015076522-appb-000007
同理B、C两相与A相一样,Uc1＝Uc2＝Udc，下表中UA为RA上的电压，UB为RB上的电压,UC为RC上的电压,不同的矢量，三相输出电压如下：
ABC矢量组合 对输出电压的作用 矢量定义
PPP NNN OOO UA＝0UB＝0UC＝0 零矢量
PPO OON UA＝UB＝1/3Udc UC＝-2/3Udc 小矢量
POO ONN UA＝2/3Udc UB＝UC＝-1/3Udc 小矢量
PON UA＝Udc UB＝0UC＝-Udc 中矢量
PPN UA＝UB＝2/3Udc UC＝-4/3Udc 大矢量
PNN UA＝4/3Udc UB＝UC＝-2/3Udc 大矢量
据以上所述，正矢量P的定义为：A相绝缘栅双极型晶体管IGBT状态为G1导通、G3断开、G2导通、G4断开时，A相输出正电压，A相电流上升；零矢量O的定义为：A相绝缘栅双极型晶体管IGBT状态为G1断开、G3导通、G2导通、G4断开时，A相电流通过D1和D2续流；负矢量N:G1断开、G3导通、G2断开、G4导通时，A相输出负电压，A相电流下降；同理B、C两相与A相一样，Uc1＝Uc2＝Udc
三相输出电压：UA为RA上的电压，UB为RB上的电压,UC为RC上的电压，零矢量：当UA＝0、UB＝0、UC＝0时A相B相C相的矢量组合为：PPP NNN OOO；小矢量:UA＝UB＝1/3Udc UC＝-2/3Udc时A相B相C相的矢量组合为:PPO OON或者UA＝2/3Udc UB＝UC＝-1/3Udc时A相B相C相的矢量组合为POO ONN；中矢量：UA＝Udc UB＝0UC＝-Udc时A相B相C相的矢量组合为PON；大矢量：UA＝UB＝2/3Udc UC＝-4/3Udc时A相B相C相的矢量组合为PPN或者UA＝4/3Udc UB＝UC＝-2/3Udc时A相B相C相的矢量组合为PNN。
三电平矢量合成图见图4，下面就第一大扇区的所有矢量对中点点位影响进行分析：
a)PPP零矢量等效电路见图5，PPP、OOO、NNN均为零电平，输出电压为0，三相电流对中点电位无影响
b)POO小矢量等效电路见图6，中点电位受到
Figure PCTCN2015076522-appb-000008
的影响，由于 Ia+Ib+Ic＝0，即受到
Figure PCTCN2015076522-appb-000009
影响，当Ia>0时，Udc1放电，电压下降；当Ia<0时，Udc1充电，电压上升。
c)ONN小矢量等效电路见图7，中点电位受到
Figure PCTCN2015076522-appb-000010
的影响，当Ia>0时，Udc2放电，电压下降；当Ia<0时，Udc2充电，电压上升
d)PPO小矢量等效电路见图8，中点电位受到
Figure PCTCN2015076522-appb-000011
的影响，当Ic>0时，Udc2放电，电压下降；当Ic<0时，Udc2充电，电压上升
e)OON小矢量等效电路见图9，中点电位受到
Figure PCTCN2015076522-appb-000012
的影响，由于Ia+Ib+Ic＝0，即受到
Figure PCTCN2015076522-appb-000013
影响，当Ic>0时，Udc2充电，电压上升；当Ic<0时，Udc2放电，电压下降
f)PON中矢量等效电路见图10，中点电位受到
Figure PCTCN2015076522-appb-000014
的影响，当Ib>0时，中线输出电流，Udc1上升，Udc2下降；当Ib<0时中线输入电流，Udc1下降，Udc2上升。
g)PNN大矢量等效电路见图11，中点没有任何连接，不受影响
h)PPN大矢量等效电路见图12，中点没有任何连接，不受影响
经过汇总后得出下表：
表1 电位与矢量、电流作用关系
Figure PCTCN2015076522-appb-000015
Figure PCTCN2015076522-appb-000016
从上面的分析可以得出，控制中点电平可以通过电流流向对中点电位进行恰当的控制，其中只有小矢量和中矢量对中点电位造成影响，因此可以根据上下端电容压差和电流流向来选择合适的中小矢量来合成，选择时为了减小输出脉动，矢量切换时只有一个开关变化为最佳。
例如扇区一1小扇区，可以由4种矢量组合
零矢量+PPO或OON+POO或ONN来组合，根据如下表的作用关系，选择有利于电位平衡的矢量
Figure PCTCN2015076522-appb-000017

Claims (2)

  1. 一种三电平逆变器中点电位平衡控制方法，其特征在于，包括如下步骤：
    步骤一：根据逆变电压指令判断电压所在扇区，以及经电流调节器计算得到指令电压；
    步骤二：根据三相输出电流Ia、Ib、Ic的电流正负方向、扇区位置以及上端电容直流电压Udc1和下端电容直流电压Udc2的大小并参见如下矢量选择表来选择适合稳定中点电位的矢量；
    Figure PCTCN2015076522-appb-100001
    Figure PCTCN2015076522-appb-100002
    Figure PCTCN2015076522-appb-100003
    Figure PCTCN2015076522-appb-100004
    Figure PCTCN2015076522-appb-100005
    Figure PCTCN2015076522-appb-100006
    步骤三：根据指令电压和所选择的矢量，计算三个矢量的分配时间，根据矢量分配时间计算各个IGBT的通断时间，计算得到驱动信号。
  2. 一种中点平衡控制逆变装置，其特征在于，包括辅电模块、采集模块，逆变控制，驱动模块、功率模块和负载；逆变控制器分别与采集模块、驱动模块和辅电模块连接通信，驱动模块连接驱动功率模块；
    辅电模块：为采集模块、逆变控制器、驱动电路提供稳定可靠的电源；
    采集模块：实现电和信号的转换，系统根据采集的反馈量进行闭环控制；
    驱动模块和功率模块：实现信号和功率的转换。
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