CN103715704B

CN103715704B - A kind of micro-electrical network common bus Voltage unbalance inhibition method

Info

Publication number: CN103715704B
Application number: CN201310722247.XA
Authority: CN
Inventors: 李永丽; 张玮亚; 孙广宇; 靳伟; 李小叶
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2013-12-18
Filing date: 2013-12-18
Publication date: 2016-05-04
Anticipated expiration: 2033-12-18
Also published as: CN103715704A

Abstract

The invention belongs to the technical field of distributed power supply control in a microgrid system, and relates to a method for suppressing the voltage imbalance of a common busbar in a microgrid system. The distributed power supply can automatically respond to the change of the bus voltage unbalance at the PCC node of the microgrid, and adaptively adjust the negative sequence voltage compensation controller (UVC), so that each distributed power supply can output negative sequence reactive power according to its rated negative sequence reactive power capacity. Maintain the voltage balance of the bus at the PCC node. The invention can make the parallel distributed power supply in the micro-grid have the function of suppressing the voltage unbalance of the micro-grid.

Description

A method for suppressing voltage unbalance of common bus in microgrid

技术领域 technical field

本发明属于微电网系统中分布式电源控制技术领域，涉及一种基于多分布式电源并联的公共母线电压不平衡抑制方法。 The invention belongs to the technical field of distributed power supply control in a microgrid system, and relates to a common bus voltage imbalance suppression method based on the parallel connection of multiple distributed power supplies.

背景技术 Background technique

新能源发电系统的广泛使用，使得基于多种分布式电源，负载以及储能装置的微电网系统成为智能电网的基本单元。微电网系统一般为低压系统，在低压系统中单相负荷是广泛存在的，导致了三相逆变器三相输出电压的不对称，从而造成较大的能量损失，影响微电网系统的稳定性。因此，必须采取措施加以抑制，保证分布式电源在不平衡负载下保持输出电压的相对平衡。 The widespread use of new energy power generation systems has made the microgrid system based on a variety of distributed power sources, loads and energy storage devices the basic unit of the smart grid. The microgrid system is generally a low-voltage system, and single-phase loads are widely present in the low-voltage system, which leads to the asymmetry of the three-phase output voltage of the three-phase inverter, which causes a large energy loss and affects the stability of the microgrid system. . Therefore, measures must be taken to suppress it to ensure that the distributed power supply maintains a relatively balanced output voltage under unbalanced loads.

IEEE和IEC均对电压不平衡度的定义、最大允许值等作出了明确的规定^[1]。我国国家技术监督局颁布的国家标准GB/T15543-2008《电能质量三相电压不平衡》中规定，电力系统公共连接点（PointofCommonCoupling，PCC）正常电压不平衡度允许值为2%，短时不得超过4%^[2]。因此，微电网电压不平衡补偿极其重要。 Both IEEE and IEC have made clear regulations on the definition and maximum allowable value of voltage unbalance ^[1] . The national standard GB/T15543-2008 "Power Quality Three-phase Voltage Unbalance" promulgated by China's State Bureau of Technical Supervision stipulates that the allowable value of the normal voltage unbalance of the power system public connection point (Point of Common Coupling, PCC) is 2%. More than 4% ^[2] . Therefore, microgrid voltage unbalance compensation is extremely important.

现有的低压微电网不平衡电压补偿主要有两种方式，一种是通过串联电能质量调节器，向线路注入负序电压实现；另外一种是采用并联电能质量调节器，通过向线路注入负序电流实现。前者由于成本高和影响线路参数而应用较少，后者当线路出现严重不平衡时其输入到系统的负序电流将快速增加，严重时会超过电能质量调节器的输出极限，造成事故。不仅如此，这两种常见的不平衡补偿装置只在电压不平衡出现时投入，而在系统正常运行时是不起作用的，设备利用率低，经济效益较差。 There are two main ways to compensate the unbalanced voltage of the existing low-voltage microgrid. One is to inject negative sequence voltage into the line through series power quality regulators; the other is to use parallel power quality regulators to inject negative sequence voltage into the line. Sequence current is realized. The former is seldom used due to its high cost and influence on line parameters. The latter, when the line is seriously unbalanced, the negative sequence current input to the system will increase rapidly, and in severe cases it will exceed the output limit of the power quality conditioner, causing accidents. Not only that, these two common unbalance compensation devices are only used when the voltage unbalance occurs, but do not work when the system is running normally, the equipment utilization rate is low, and the economic benefit is poor.

微电网中大量的分布式电源通过三相并网逆变器接入系统，其逆变器的结构和电能质量调节装置类似，因此利用微电网中的分布式电源实现电压不平衡抑制是一种经济有效的电压质量改善方案。 A large number of distributed power sources in the microgrid are connected to the system through a three-phase grid-connected inverter. The structure of the inverter is similar to that of a power quality adjustment device. Therefore, it is a kind of A cost-effective voltage quality improvement solution.

参考文献 references

PillayP,ManyageM.Definitionsofvoltageunbalance[J].IEEEPowerEngineeringReview,2001,21(5):50-51. PillayP, ManyageM.Definitionsofvoltageunbalance[J].IEEEPowerEngineeringReview,2001,21(5):50-51.

中国国家标准GB/T15543-2008：电能质量三相电压不平衡[S].北京：中国标准出版社，2008. Chinese National Standard GB/T15543-2008: Power Quality Three-phase Voltage Unbalance [S]. Beijing: China Standard Press, 2008.

林新春,段善旭,康勇,陈坚.基于下垂特性控制的无互联线并联UPS建模与稳定性分析[J].中国电机工程学报,2004,24(2),34-39. Lin Xinchun, Duan Shanxu, Kang Yong, Chen Jian. Modeling and Stability Analysis of Uninterconnected Parallel UPS Based on Droop Characteristic Control[J]. Chinese Journal of Electrical Engineering, 2004, 24(2), 34-39.

鲍薇,胡学浩,李光辉,鲍威宇.独立型微电网中基于虚拟阻抗的改进下垂控制[J].电力系统保护与控制,2013,41(16),7-13. Bao Wei, Hu Xuehao, Li Guanghui, Bao Weiyu.Improved Droop Control Based on Virtual Impedance in Independent Microgrid[J].Power System Protection and Control,2013,41(16),7-13.

WangX,BlaabjergF,ChenZ.SynthesisofVariableHarmonicImpedanceinInverter-InterfacedDistributedGenerationUnitforHarmonicDampingThroughoutaDistributionNetwork[J].IndustryApplications,IEEETransactionson,2012,48(4),1407-1417. WangX, BlaabjergF, ChenZ.SynthesisofVariableHarmonicImpedanceinInverter-InterfacedDistributedGenerationUnitforHarmonicDampingThroughoutaDistributionNetwork[J].IndustryApplications,IEEETransactionson,2012,48(4),1407-1417.

发明内容 Contents of the invention

本发明的目的是克服现有技术的上述不足，提供一种利用微电网中的分布式电源实现电压不平衡抑制，是一种经济有效的电压质量改善方案。本发明的技术方案如下： The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a cost-effective voltage quality improvement solution that utilizes distributed power sources in a microgrid to suppress voltage imbalance. Technical scheme of the present invention is as follows:

一种微电网公共母线电压不平衡抑制方法，其特征是，该方法对微电网系统PCC节点处母线负序电压进行直接补偿，微电网中的各个分布式电源能够自动响应微电网PCC节点处母线电压不平衡度的变化，自适应调整负序电压补偿控制器（UVC），使得各个分布式电源按照其额定负序无功容量输出负序无功，维持PCC节点处母线的电压平衡度，包括以下步骤： A microgrid common bus voltage unbalance suppression method, characterized in that the method directly compensates the negative sequence voltage of the bus at the PCC node of the microgrid system, and each distributed power source in the microgrid can automatically respond to the bus at the PCC node of the microgrid Changes in voltage unbalance, adaptively adjust the negative sequence voltage compensation controller (UVC), so that each distributed power supply outputs negative sequence reactive power according to its rated negative sequence reactive power capacity, and maintains the voltage balance of the bus at the PCC node, including The following steps:

1)步骤1，实时检测微电网PCC节点处母线的正序电压和负序电压计算微电网PCC节点处母线的实时电压不平衡度系数 1) Step 1, real-time detection of the positive sequence voltage of the busbar at the PCC node of the microgrid and negative sequence voltage Calculate the real-time voltage unbalance coefficient of the busbar at the PCC node of the microgrid

2)步骤2，实时检测微电网中第i个分布式电源DG_i的负序输出无功 2) Step 2, real-time detection of the negative-sequence output reactive power of the i-th distributed power supply DG _i in the microgrid

3)步骤3，当VUB_pcc大于某个预设的百分比时，投入负序电压补偿控制器（UVC）：设为微电网公共连接点（PCC）的额定电压不平衡度系数；n_i为DG_i的负序无功分配系数；k_e为电压不平衡度误差比例系数；k_P，k_I为PI控制的比例系数和积分系数，则DG_i的UVC的负序电压补偿系数： 3) Step 3, when VUB _pcc is greater than a certain preset percentage, turn on the negative sequence voltage compensation controller (UVC): set is the rated voltage unbalance coefficient of microgrid common connection point (PCC); n _i is the negative sequence reactive power distribution coefficient of DG _i ; k _e is the voltage unbalance error proportional coefficient; k _P , k _I are the PI control Proportional coefficient and integral coefficient, then the negative sequence voltage compensation coefficient of UVC of DG _i :

${VCR VCR}_{i i} = = (({k k}_{P P} + + \frac{{k k}_{I I}}{s the s})) Δ Δ {VCR VCR}_{i i},,$

其中， $Δ {VCR}_{i} = k_{e} ({VUB}_{pcc} - {VUB}_{pcc}^{*}) - n_{i} Q_{i}^{-};$ in, $Δ {VCR}_{i} = k_{e} ({VUB}_{pcc} - {VUB}_{pcc}^{*}) - {no}_{i} Q_{i}^{-};$

4)步骤4，将VCR_i与DG_i输出的负序电压相乘得到DG_i的负序电压补偿的参考值； 4) Step 4, multiplying the negative-sequence voltage output by VCR _i and DG _i to obtain the reference value of the negative-sequence voltage compensation of DG _i ;

5)步骤5，得到DG_i的负序电压补偿的参考值后，配合其正序有功/频率和无功/电压下垂控制，虚拟阻抗控制，合成DG_i控制系统的参考电压，经过电压电流双环控制后进行脉冲宽度调制。 5) Step 5, after obtaining the reference value of the negative sequence voltage compensation of DG _i , cooperate with its positive sequence active power/frequency and reactive power/voltage droop control, virtual impedance control, synthesize the reference voltage of the DG _i control system, and pass through the voltage and current double loop Pulse width modulation is performed after control.

本发明通过改变微电网中接入的分布式电源的控制系统，使得微电网中并联的分布式电源具有抑制微电网电压不平衡的功能，各个分布式电源通过各自传输线并联，在进行PCC节点处母线电压不平衡抑制控制时各分布式电源之间无需信号传输线。同时实现了两个独立控制目标：（1）确保了微电网PCC节点处母线的电压质量；（2）并联的分布式电源按照自身的额定负序补偿能力分配输出的负序无功。该方法不仅适用于并网运行方式下的微电网系统，也适用于独立运行的微电网系统，增强了分布式电源对微电网电压质量的控制能力，提高了微电网的电压质量，实现了微电网的经济和稳定运行。 In the present invention, by changing the control system of the distributed power source connected in the micro-grid, the distributed power source in parallel in the micro-grid has the function of suppressing the voltage imbalance of the micro-grid. There is no need for signal transmission lines between distributed power sources during bus voltage unbalance suppression control. At the same time, two independent control objectives are achieved: (1) to ensure the voltage quality of the busbar at the PCC node of the microgrid; (2) the parallel distributed power generation distributes the output negative sequence reactive power according to its own rated negative sequence compensation capacity. This method is not only applicable to the microgrid system under the grid-connected operation mode, but also to the microgrid system operating independently. Economical and stable operation of the grid.

附图说明 Description of drawings

图1为含有多个分布式电源的微电网系统示意图； Figure 1 is a schematic diagram of a microgrid system containing multiple distributed power sources;

图2为一个分布式电源的一次电路结构和控制系统结构； Figure 2 is a primary circuit structure and control system structure of a distributed power supply;

图3为PSCAD仿真模型示意图； Fig. 3 is the schematic diagram of PSCAD simulation model;

图4为PCC节点处母线电压不平衡度变化曲线； Figure 4 is the change curve of the bus voltage unbalance degree at the PCC node;

图5为两台分布式电源输出负序无功曲线； Figure 5 is the output negative sequence reactive power curve of two distributed power supplies;

图6为负序电压补偿控制器投入前PCC电压曲线； Figure 6 is the PCC voltage curve before the negative sequence voltage compensation controller is put into operation;

图7为负序电压补偿控制器投入后PCC电压曲线。 Figure 7 is the PCC voltage curve after the negative sequence voltage compensation controller is put into operation.

具体实施方式 detailed description

下面结合附图和实施例对本发明进行说明。 The present invention will be described below in conjunction with the accompanying drawings and embodiments.

本发明一实施例多分布式电源并联系统包括若干个并联的分布式电源通过PCC连接在同一微电网母线上，母线电压为400V，如图1所示。分布式电源包括直流微源，三相全桥逆变器，LC滤波电路以及控制系统。如图2所示，每台分布式电源的控制策略包括正序有功/频率和无功/电压下垂控制，虚拟阻抗控制以及电压不平衡抑制控制。正序有功/频率和无功/电压下垂控制确保各个分布式电源的输出电压水平和功率水平；虚拟阻抗控制通过在分布式电源控制系统中附加阻抗保证正序有功/频率和无功/电压下垂控制的控制效果；电压不平衡抑制控制实时检测PCC处的电压不平衡度VUB_pcc，当VUB_pcc≥2%时启动，各个分布式电源通过快速调节维持PCC处的电压不平衡度维持在设定水平。 An embodiment of the present invention, a multi-distributed power parallel system includes several parallel distributed power connected to the same microgrid bus through PCC, and the bus voltage is 400V, as shown in FIG. 1 . Distributed power supply includes DC micro-source, three-phase full-bridge inverter, LC filter circuit and control system. As shown in Figure 2, the control strategy of each DG includes positive sequence active power/frequency and reactive power/voltage droop control, virtual impedance control and voltage unbalance suppression control. Positive sequence active power/frequency and reactive power/voltage droop control ensures the output voltage level and power level of each distributed power supply; virtual impedance control ensures positive sequence active power/frequency and reactive power/voltage droop by adding impedance in the distributed power supply control system The control effect of the control; the voltage unbalance suppression control detects the voltage unbalance VUB _pcc at the PCC in real time, and starts when VUB _pcc ≥ 2%, and each distributed power supply maintains the voltage unbalance at the PCC at the set value through rapid adjustment Level.

1.微电网中的多分布式电源并联的电压不平衡抑制方法，包括以下步骤： 1. A voltage imbalance suppression method for parallel connection of multiple distributed power sources in a microgrid, comprising the following steps:

（1）如图2所示，各个分布式电源实时检测微电网PCC节点处母线的正序电压和负序电压形成微电网PCC节点处母线的实时电压不平衡度常数 (1) As shown in Figure 2, each distributed power source detects the positive sequence voltage of the bus at the PCC node of the microgrid in real time and negative sequence voltage Form the real-time voltage unbalance degree constant of the busbar at the PCC node of the microgrid

1)分布式电源的控制系统采集出口电压v_Cabc＝[v_Cav_Cbv_Cc]^T和出口电流i_Cabc＝[i_Cai_Cbi_Cc]^T。根据对称分量法，在三相电路中，任意不对称的三相电压或电流均可通过对称分量法分解成三组三相对称的分量，即正序，负序和零序分量。在三相三线电路中，由于没有零序通路，因此不存在零序电流，且零序电压对微电网系统的影响也可忽略。由瞬时对称分量法可知，瞬时电压正序分量和负序分量可以分别表示为， 1) The control system of the distributed power source collects the outlet voltage v _Cabc =[v _Ca v _Cb v _Cc ] ^T and the outlet current i _Cabc =[i _Ca i _Cb i _Cc ] ^T . According to the symmetrical component method, in a three-phase circuit, any asymmetrical three-phase voltage or current can be decomposed into three groups of three-phase symmetrical components by the symmetrical component method, namely positive sequence, negative sequence and zero sequence components. In the three-phase three-wire circuit, since there is no zero-sequence path, there is no zero-sequence current, and the influence of zero-sequence voltage on the microgrid system can also be ignored. According to the instantaneous symmetrical component method, the positive sequence component of the instantaneous voltage and negative sequence components can be expressed as, respectively,

$\{\begin{matrix} {v v}_{Cabc Cabc}^{+ +} = = {[[{v v}_{Ca Ca}^{+ +} {v v}_{Cb Cb}^{+ +} {v v}_{Cc Cc}^{+ +}]]}^{T T} = = {T T}_{+ +} {[[{v v}_{Ca Ca} {v v}_{Cb Cb} {v v}_{Cc Cc}]]}^{T T} \\ {v v}_{Cabc Cabc}^{- -} = = {[[{v v}_{Ca Ca}^{- -} {v v}_{Cb Cb}^{- -} {v v}_{Cc Cc}^{- -}]]}^{T T} = = {T T}_{- -} {[[{v v}_{Ca Ca} {v v}_{Cb Cb} {v v}_{Cc Cc}]]}^{T T} \end{matrix},,$

瞬时电流正序分量和负序分量可以分别表示为， Positive sequence component of instantaneous current and negative sequence components can be expressed as, respectively,

$\{\begin{matrix} {i i}_{Cabc Cabc}^{+ +} = = {[[{i i}_{Ca Ca}^{+ +} {i i}_{Cb Cb}^{+ +} {i i}_{Cc Cc}^{+ +}]]}^{T T} = = {T T}_{+ +} {[[{i i}_{Ca Ca} {i i}_{Cb Cb} {i i}_{Cc Cc}]]}^{T T} \\ {i i}_{Cabc Cabc}^{- -} = = {[[{i i}_{Ca Ca}^{- -} {i i}_{Cb Cb}^{- -} {i i}_{Cc Cc}^{- -}]]}^{T T} = = {T T}_{- -} {[[{i i}_{Ca Ca} {i i}_{Cb Cb} {i i}_{Cc Cc}]]}^{T T} \end{matrix} . .$

其中 $T_{+} = \frac{1}{3} [\begin{matrix} 1 & a & a^{2} \\ a^{2} & 1 & a \\ a & a^{2} & 1 \end{matrix}],$ $T_{-} = \frac{1}{3} [\begin{matrix} 1 & a^{2} & a \\ a & 1 & a^{2} \\ a^{2} & a & 1 \end{matrix}],$ 且 $a = e^{j \frac{2}{3} π} .$ in $T_{+} = \frac{1}{3} [\begin{matrix} 1 & a & a^{2} \\ a^{2} & 1 & a \\ a & a^{2} & 1 \end{matrix}],$ $T_{-} = \frac{1}{3} [\begin{matrix} 1 & a^{2} & a \\ a & 1 & a^{2} \\ a^{2} & a & 1 \end{matrix}],$ and $a = e^{j \frac{2}{3} π} .$

2)通过abc→αβ变换将该输出电压和输出电流转化为v_Cαβ以及i_Cαβ： 2) Transform the output voltage and output current into v _Cαβ and i _Cαβ through abc→αβ transformation:

$\{\begin{matrix} v_{Cαβ} = {[v_{Cα} v_{Cβ}]}^{T} = T_{abc &RightArrow; αβ} {[v_{Ca} v_{Cb} v_{Cc}]}^{T} \\ i_{Cαβ} = {[i_{Cα} i_{Cβ}]}^{T} = T_{abc &RightArrow; αβ} {[i_{Ca} i_{Cb} i_{Cc}]}^{T} \end{matrix},$ 其中 $T_{abc &RightArrow; αβ} = \frac{2}{3} [\begin{matrix} 1 & - 1 / 2 & - 1 / 2 \\ 0 & \sqrt{3} / 2 & \sqrt{3} / 2 \end{matrix}] .$ $\{\begin{matrix} v_{Cαβ} = {[v_{Cα} v_{Cβ}]}^{T} = T_{abc &Right Arrow; αβ} {[v_{Ca} v_{Cb} v_{Cc}]}^{T} \\ i_{Cαβ} = {[i_{Cα} i_{Cβ}]}^{T} = T_{abc &Right Arrow; αβ} {[i_{Ca} i_{Cb} i_{Cc}]}^{T} \end{matrix},$ in $T_{abc &Right Arrow; αβ} = \frac{2}{3} [\begin{matrix} 1 & - 1 / 2 & - 1 / 2 \\ 0 & \sqrt{3} / 2 & \sqrt{3} / 2 \end{matrix}] .$

3)利用v_Cαβ以及i_Cαβ分别计算出基波正序输出电压基波负序输出电压基波正序输出电流基波负序输出电流其中， 3) Use v _Cαβ and i _Cαβ to calculate the fundamental positive sequence output voltage respectively Fundamental negative sequence output voltage Fundamental positive sequence output current Fundamental negative sequence output current in,

$\{\begin{matrix} {v v}_{Cαβ Cαβ}^{+ +} = = {[[{v v}_{Cα Cα}^{+ +} {v v}_{Cβ Cβ}^{+ +}]]}^{T T} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {v v}_{Cabc Cabc}^{+ +} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {T T}_{+ +} {v v}_{Cabc Cabc} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {T T}_{+ +} {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ}^{T T} {v v}_{Cαβ Cαβ} \\ {v v}_{Cαβ Cαβ}^{- -} = = {[[{v v}_{Cα Cα}^{- -} {v v}_{Cβ Cβ}^{- -}]]}^{T T} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {v v}_{Cabc Cabc}^{- -} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {T T}_{- -} {v v}_{Cabc Cabc} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {T T}_{- -} {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ}^{T T} {v v}_{Cαβ Cαβ} \end{matrix},,$

$\{\begin{matrix} {i i}_{Cαβ Cαβ}^{+ +} = = {[[{i i}_{Cα Cα}^{+ +} {i i}_{Cβ Cβ}^{+ +}]]}^{T T} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {i i}_{Cabc Cabc}^{+ +} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {T T}_{+ +} {i i}_{Cabc Cabc} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {T T}_{+ +} {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ}^{T T} {i i}_{Cαβ Cαβ} \\ {i i}_{Cαβ Cαβ}^{- -} = = {[[{i i}_{Cα Cα}^{- -} {i i}_{Cβ Cβ}^{- -}]]}^{T T} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {i i}_{Cabc Cabc}^{- -} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {T T}_{- -} {i i}_{Cabc Cabc} = = {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ} {T T}_{- -} {T T}_{abc abc &RightArrow; &Right Arrow; αβ αβ}^{T T} {i i}_{Cαβ Cαβ} \end{matrix} . .$

4)PCC节点处母线的正序电压 $V_{pcc}^{+} = \sqrt{{(v_{Cα}^{+})}^{2} + {(v_{Cβ}^{+})}^{2}}$ ，负序电压 $V_{pcc}^{-} = \sqrt{{(v_{Cα}^{-})}^{2} + {(v_{Cβ}^{-})}^{2}}$ 。则微电网PCC节点处母线的实时电压不平衡度系数 4) Positive sequence voltage of busbar at PCC node $V_{pcc}^{+} = \sqrt{{(v_{Cα}^{+})}^{2} + {(v_{Cβ}^{+})}^{2}}$ , negative sequence voltage $V_{pcc}^{-} = \sqrt{{(v_{Cα}^{-})}^{2} + {(v_{Cβ}^{-})}^{2}}$ . Then the real-time voltage unbalance coefficient of the bus at the PCC node of the microgrid

（2）实时检测微电网中第i个分布式电源DG_i的负序输出无功 (2) Real-time detection of the negative-sequence output reactive power of the i-th distributed power supply DG _i in the microgrid

${Q Q}_{i i}^{- -} = = {v v}_{Cα Cα}^{- -} {i i}_{Cβ Cβ}^{- -} - - {v v}_{Cβ Cβ}^{- -} {i i}_{Cα Cα}^{- -} . .$

（3）当VUB_pcc≥2%时，投入UVC。设为微电网PCC节点处母线的额定电压不平衡度系数；n_i为DG_i的负序无功分配系数；k_e为电压不平衡度误差比例系数；k_P，k_I为PI控制的比例系数和积分系数。则DG_i的UVC的负序电压补偿系数： (3) When VUB _pcc ≥ 2%, turn on UVC. Assume is the rated voltage unbalance coefficient of the bus bar at the microgrid PCC node; n _i is the negative sequence reactive power distribution coefficient of DG _i ; k _e is the proportional coefficient of voltage unbalanced degree error; k _P , k _I are the proportional coefficients of PI control and integral coefficients. Then the negative sequence voltage compensation coefficient of UVC of DG _i :

${VCR}_{i} = (k_{P} + \frac{k_{I}}{s}) Δ {VCR}_{i},$ 其中 $Δ {VCR}_{i} = k_{e} ({VUB}_{pcc} - {VUB}_{pcc}^{*}) - n_{i} Q_{i}^{-} .$ ${VCR}_{i} = (k_{P} + \frac{k_{I}}{the s}) Δ {VCR}_{i},$ in $Δ {VCR}_{i} = k_{e} ({VUB}_{pcc} - {VUB}_{pcc}^{*}) - {no}_{i} Q_{i}^{-} .$

在系统进入稳态时，由于各个DG的VUB_pcc和对应同一个PCC节点，而k_e为固定常数，因此（下标i，j分别代表微电网中不同的两个分布式电源DG_i和DG_j），按照DG_i的额定负序无功容量设置n_i，则任意两个不同的分布式电源将按照各自额定负序无功容量成比例输出负序无功。 When the system enters a steady state, Due to the VUB _pcc of each DG and correspond to the same PCC node, and k _e is a fixed constant, so (The subscripts i and j respectively represent two different distributed power sources DG _i and DG _j in the microgrid), and if n _{i is set according to the rated negative-sequence reactive capacity of DG i} _, then any two different distributed power The negative sequence reactive power is output in proportion to the respective rated negative sequence reactive power capacity.

（4）将步骤（3）中计算出的VCR_i与DG_i输出的负序电压相乘得到负序电压补偿的参考值（将VCR_i与DG_i输出的负序电压相乘保证DG_i的负序电压补偿的参考值和微电网系统PCC节点处母线的实际负序电压的相位一致）： (4) Multiply the VCR _i calculated in step (3) with the negative sequence voltage output by DG _i to obtain the reference value for negative sequence voltage compensation ₍ multiply VCR _i and the negative sequence voltage output by DG _i to ensure the The reference value of negative-sequence voltage compensation is consistent with the phase of the actual negative-sequence voltage of the bus at the PCC node of the microgrid system):

${v v}_{Cαβ Cαβ}^{- - * *} = = {VCR VCR}_{i i} \cdot &Center Dot; {v v}_{Cαβ Cαβ}^{- -} . .$

（5）得到负序电压补偿的参考值后，配合正序有功/频率和无功/电压下垂控制[3]，虚拟阻抗控制[4]，合成逆变器的参考电压，经过内环电压电流双环控制^[5]后进行脉冲宽度调制。 (5) After obtaining the reference value of negative sequence voltage compensation, cooperate with positive sequence active power/frequency and reactive power/voltage droop control [3], virtual impedance control [4], synthesize the reference voltage of the inverter, and pass through the inner loop voltage current Pulse width modulation is performed after double-loop control ^[5] .

1)正序有功/频率和无功/电压下垂控制的正序有功和正序无功的求解方法为： 1) The solution method of positive sequence active power and positive sequence reactive power of positive sequence active power/frequency and reactive power/voltage droop control is:

$\{\begin{matrix} {P P}_{i i}^{+ +} = = {v v}_{Cα Cα}^{+ +} {i i}_{Cα Cα}^{+ +} + + {v v}_{Cβ Cβ}^{+ +} {i i}_{Cβ Cβ}^{+ +} \\ {Q Q}_{i i}^{+ +} = = {v v}_{Cα Cα}^{+ +} {i i}_{Cβ Cβ}^{+ +} - - {v v}_{Cβ Cβ}^{+ +} {i i}_{Cα Cα}^{+ +} \end{matrix} . .$

得到了正序有功和正序无功后，有功/频率和无功/电压下垂控制的控制方法为： After obtaining positive sequence active power and positive sequence reactive power, the control method of active power/frequency and reactive power/voltage droop control is:

$\{\begin{matrix} {ω ω}_{i i}^{* *} = = {ω ω}_{00} - - {m m}_{pi p} {P P}_{i i}^{+ +} \\ {E E.}_{i i}^{* *} = = {E E.}_{00} - - {n no}_{qi qi} {Q Q}_{i i}^{+ +} \end{matrix},,$

其中，为DGi输出正序电压的参考值和幅度参考值；ω₀和E₀为DG_i的额定频率和额定电压幅值；m_pi和n_qi分别为有功和无功下垂系数。得到了DG_i输出正序电压的参考值和幅度参考值后，通过abc→αβ变换得到DG_i输出正序电压的参考值 in, Output positive sequence voltage reference value and amplitude reference value for DGi; ω ₀ and E ₀ are rated frequency and rated voltage amplitude of DG _i ; m _pi and n _qi are active and reactive droop coefficients respectively. Get the reference value of DG _i output positive sequence voltage and magnitude reference After that, the reference value of the output positive sequence voltage of DG _i is obtained by abc→αβ transformation

2)虚拟阻抗控制通过在分布式电源控制系统中附加阻抗保证正序电压、频率下垂控制的控制效果，其控制方法为： 2) Virtual impedance control ensures the control effect of positive sequence voltage and frequency droop control by adding impedance in the distributed power supply control system. The control method is:

$\{\begin{matrix} {v v}_{Cfα Cfα} = = {i i}_{Cα Cα} {R R}_{vi vi} - - {i i}_{Cβ Cβ} {ω ω}_{i i}^{* *} {L L}_{fi the fi} \\ {v v}_{Cfβ Cfβ} = = {i i}_{Cβ Cβ} {R R}_{vi vi} + + {i i}_{Cα Cα} {ω ω}_{i i}^{* *} {L L}_{fi the fi} \end{matrix},,$

其中，v_Cfαβ=[v_Cfαv_Cfβ]^T为虚拟阻抗控制的输出参考值，R_vi和L_fi为在控制环节中虚拟出的等效输出电阻值和输出电感值。 Among them, v _Cfαβ =[v _Cfα v _Cfβ ] ^T is the output reference value of virtual impedance control, R _vi and L _fi are the virtual equivalent output resistance and output inductance in the control link.

3)综合每台分布式电源的正序有功/频率和无功/电压下垂控制，虚拟阻抗控制以及电压不平衡抑制控制，得到电压外环的输入参考值 3) Integrate the positive sequence active power/frequency and reactive power/voltage droop control, virtual impedance control and voltage unbalance suppression control of each distributed power supply to obtain the input reference value of the voltage outer loop

${U u}_{αβ αβ}^{* *} = = {v v}_{Cαβ Cαβ}^{+ + * *} - - {v v}_{Cfαβ Cfαβ} - - {v v}_{Cαβ Cαβ}^{- - * *} . .$

4)电压电流双环控制采用了比例谐振控制器（PR），和v_Cαβ通过PR控制器，得到静止坐标下的电流参考值减去i_Lαβ，经过PR控制器，得到静止坐标系下的PWM控制输入信号U_PWMαβ；U_PWMαβ经过αβ→abc变换得到三相坐标系下的PWM控制输入信号U_PWMabc，输入值PWM生成单元进行脉冲宽度调制。PR控制的传递函数为： 4) Voltage and current double loop control adopts proportional resonance controller (PR), and v _Cαβ pass through the PR controller to get the current reference value in the static coordinates Subtracting i _Lαβ , through the PR controller, the PWM control input signal U _PWMαβ in the static coordinate system is obtained; U _PWMαβ undergoes αβ→abc transformation to obtain the PWM control input signal U _PWMabc in the three-phase coordinate system, and the input value PWM generation unit performs Pulse Width Modulation. The transfer function of PR control is:

$G G ((s the s)) = = {k k}_{PRp PRp} + + \frac{{22 k k}_{PRr PRr} {ω ω}_{c c} s the s}{{s the s}^{22} + + {22 ω ω}_{c c} s the s + + {(({ω ω}_{i i}^{* *}))}^{22} s the s},,$

其中，k_PRp和k_PRr分别是PR控制的比例系数和谐振增益，ω_c为截止频率。 Among them, k _PRp and k _PRr are the proportional coefficient and resonance gain of PR control respectively, ω _c is the cut-off frequency.

2.为了验证本发明所提方法的正确性，参照图3，在PSCAD仿真平台上搭建了含有两个分布式电源的微电网系统，系统电压为400V，负载为一个接在PCC母线上A相和B相之间的10Ω电阻，不平衡度为2.5%。两个分布式电源的系统参数是相同的，控制参数和负载情况如表1所示。在t=0.5秒时，加入负序电压补偿控制器。载波频率设为12.8kHz。由图可见，加入负序电压补偿控制器之后，电压不平衡度降低至1.6%，两个分布式电源输出的负序无功之比和负序无功分配系数之比相反，证明了本发明所提方法的有效性。表1控制系统参数： 2. In order to verify the correctness of the proposed method of the present invention, with reference to Fig. 3, a microgrid system containing two distributed power sources has been built on the PSCAD simulation platform, the system voltage is 400V, and the load is a phase A connected to the PCC bus 10Ω resistor between phase B and phase B, the unbalance is 2.5%. The system parameters of the two distributed power sources are the same, and the control parameters and load conditions are shown in Table 1. When t=0.5 seconds, add negative sequence voltage compensation controller. The carrier frequency is set to 12.8kHz. It can be seen from the figure that after adding the negative-sequence voltage compensation controller, the voltage unbalance is reduced to 1.6%, and the ratio of negative-sequence reactive power output by the two distributed power sources is Contrary to the ratio of the negative sequence reactive power distribution coefficient, it proves the effectiveness of the method proposed in the present invention. Table 1 Control system parameters:

Claims

1. A microgrid public busbar voltage unbalance suppression method is characterized in that the method directly compensates the negative sequence voltage of the busbar at the microgrid system common connection point (PCC), and each distributed power supply in the microgrid can respond automatically Adaptively adjust the negative-sequence voltage compensation controller (UVC) for changes in the bus voltage unbalance at the point of common connection (PCC) of the microgrid, so that each distributed power source outputs negative-sequence reactive power according to its rated negative-sequence reactive power capacity, maintaining The voltage balance of the bus at the point of common connection (PCC), including the following steps:

1) Step 1, real-time detection of the positive sequence voltage of the bus at the point of common connection (PCC) of the microgrid and negative sequence voltage Calculate the real-time voltage unbalance coefficient of the bus at the point of common connection (PCC) of the microgrid

2) Step 2, real-time detection of the negative-sequence output reactive power of the i-th distributed power supply DG _i in the microgrid

3) Step 3, when VUB _pcc is greater than a certain preset percentage, turn on the negative sequence voltage compensation controller (UVC): set is the rated voltage unbalance coefficient of the bus at the PCC of the microgrid; n _i is the negative sequence reactive power distribution coefficient of DG _i ; k _e is the voltage unbalance error proportional coefficient; k _P , k _I is PI The proportional coefficient and integral coefficient of the control, then the negative sequence voltage compensation coefficient of the negative sequence voltage compensation controller (UVC) of DG _i :

{VCR VCR}_{i i} = = (({k k}_{P P} + + \frac{{k k}_{I I}}{s the s})) {ΔVCR Δ VCR}_{i i},,

in,

{Δ VCR}_{i} = k_{e} ({VUB}_{p c c} - {VUB}_{p c c}^{*}) - {no}_{i} Q_{i}^{-};

4) Step 4, multiplying the negative-sequence voltage output by VCR _i and DG _i to obtain the reference value of the negative-sequence voltage compensation of DG _i ;

5) Step 5, after obtaining the reference value of the negative sequence voltage compensation of DG _i , cooperate with its positive sequence active power/frequency and reactive power/voltage droop control, virtual impedance control, synthesize the reference voltage of the DG _i control system, and pass through the voltage and current double loop Pulse width modulation is performed after control.

2. The microgrid common bus voltage unbalance suppression method according to claim 1, characterized in that, when VUB _pcc ≥ 2%, a negative sequence voltage compensation controller (UVC) is put into operation.