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CN109474012B - Frequency coupling suppression method of three-phase grid-connected converter under weak grid condition - Google Patents

Frequency coupling suppression method of three-phase grid-connected converter under weak grid condition Download PDF

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CN109474012B
CN109474012B CN201811437103.9A CN201811437103A CN109474012B CN 109474012 B CN109474012 B CN 109474012B CN 201811437103 A CN201811437103 A CN 201811437103A CN 109474012 B CN109474012 B CN 109474012B
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voltage
current
loop
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张学广
易传卓
张思缘
夏丹妮
陈文佳
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Harbin Institute of Technology Shenzhen
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    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract

A frequency coupling suppression method of a three-phase grid-connected converter under the condition of weak power grid relates to the field of stability analysis of a power system grid-connected converter. The invention aims to solve the problem that the system stability is influenced by the impedance of a power grid, a phase-locked loop and the bandwidth of a voltage loop under the condition of a weak power grid. The frequency coupling suppression method of the three-phase grid-connected converter under the condition of weak power grid considers that the frequency coupling phenomenon is introduced by the coordinate transformation needed by the controller under a synchronous rotating coordinate system in the three-phase grid-connected converter, so that the problem of system stability caused by asymmetry of a phase-locked loop and a voltage loop in d and q axes under the condition of weak power grid is solved by using a compensation method, and the THD of grid side current is reduced when the grid voltage is disturbed.

Description

Frequency coupling suppression method of three-phase grid-connected converter under weak grid condition
Technical Field
The invention belongs to the field of stability analysis of a grid-connected converter of a power system, and particularly relates to analysis of influence of a frequency coupling phenomenon on stability under a weak point grid condition.
Background
With the large number of applications of power electronic devices in power systems, the trend of electronization changes many characteristics of the conventional power systems, but a new stability problem inevitably occurs.
Currently, there are two main types of methods for analyzing the stability of a power system: the method can accurately analyze the resonance characteristics of the system through characteristic values, but needs to acquire detailed information of the system and is difficult to model a converter system containing multi-time scale control; the other is a frequency domain impedance analysis method, which converts the dynamic characteristics of the converter port into an impedance form through a frequency domain transfer function and further analyzes the system stability through a circuit theory.
Today, the most common method of analyzing the stability problem of the grid-connected converter is the impedance-based stability analysis method, which was first proposed by Middlebrook with the aim of designing the filter parameters of the DC/DC converter. The method has the advantages that the small signal stability of the system can be conveniently determined only by acquiring the output or input impedance of the converter or the power grid and applying the Nyquist stability criterion.
Under the condition of weak power grid, the system stability is influenced by the power grid impedance, the phase-locked loop and the voltage loop bandwidth, and the stability is also influenced by the frequency coupling phenomenon which is influenced by the factors. However, the existing stability improvement methods for these factors do not consider the influence of the frequency coupling phenomenon caused by these factors on the stability.
Disclosure of Invention
The invention aims to solve the problems that the system stability is influenced by the impedance of a power grid, the bandwidth of a phase-locked loop and the voltage loop under the condition of a weak power grid and the stability is influenced by the frequency coupling phenomenon which is influenced by the factors.
The frequency coupling suppression method of the three-phase grid-connected converter under the condition of weak power grid comprises the following steps:
the method comprises the following steps: respectively to three-phase voltage Ua、Ub、UcAnd three-phase current Ia、Ib、IcClark conversion and Park conversion are sequentially carried out to obtain d-axis and q-axis voltage components U under a synchronous rotating coordinate systemd、UqAnd d, q-axis current components Id、Iq，
Step two: are respectively paired with Ud、UqAnd Id、IqHigh-pass filtering is carried out to respectively extract Ud、Uq、IdAnd IqThe disturbance component of (a) is,
step three: according to the main circuit element parameters and the voltage ring PI parameters G of the three-phase grid-connected converterc_vdcObtaining the coefficientsk1According to Ud、Uq、IdAnd IqObtaining a vector of the disturbance component
Figure BDA0001884040190000021
Will be provided with
Figure BDA0001884040190000022
Real part and k of1The product of (a) and (b) is compensated into the d-axis given signal of the current loop
Figure BDA0001884040190000023
Imaginary part of and k1The product of (a) is compensated into the q-axis given signal of the current loop,
step four: obtaining a coefficient k from a phase-locked loop parameter2Will U isdAnd UqRespectively with a stable value I of the grid-connected point current0Multiply and then multiply Ud·I0And Uq·I0Are respectively connected with k2The multiplied product is compensated to the Park transformed grid-connected point current,
step five: will UdAnd UqRespectively with a stable value E of the grid voltage0Multiply and then multiply Ud·E0And Uq·E0Are respectively connected with k2And compensating the multiplied product into the grid voltage subjected to Park conversion to finish frequency coupling suppression.
The frequency coupling suppression method of the three-phase grid-connected converter under the condition of weak power grid considers that the coordinate transformation needed by the controller under a synchronous rotating coordinate system can introduce the frequency coupling phenomenon in the three-phase grid-connected converter, so that the system stability problem caused by asymmetry of phase-locked loops and voltage loops at d and q axes under the condition of weak power grid is solved by using a compensation method, and the THD (total harmonic distortion) of grid side current when the grid voltage has disturbance is reduced. The invention is completely realized in the controller, and other parameters of the main circuit do not need to be additionally measured, hardware does not need to be additionally added, and the cost is not increased.
Drawings
FIG. 1 is a schematic view ofThe structure of the three-phase grid-connected converter controller after frequency coupling suppression is added, and u in the figuredcRepresenting the voltage loop output voltage, EdAs d-axis component, E, of the grid voltageqThe q-axis component of the grid voltage, Acc for the current regulator and PWM for the pulse width modulation.
Detailed Description
The first embodiment is as follows: specifically describing the present embodiment with reference to fig. 1, the method for suppressing frequency coupling of a three-phase grid-connected converter in the present embodiment under weak grid conditions includes the following steps:
the method comprises the following steps: three-phase voltage U of grid-connected point by using voltage sensora、Ub、UcSampling, and utilizing current sensor to make grid-connected point three-phase current Ia、Ib、IcSampling is performed.
Step two: respectively carrying out Clark conversion (changing variables in an abc coordinate system with three phases being static and different from each other by 120 degrees into an alpha beta coordinate system with two phases being static and different from each other by 90 degrees) and Park conversion (converting into a synchronous rotating coordinate system) on three-phase voltage and three-phase current in sequence to obtain d-axis and q-axis voltage components U under the synchronous rotating coordinate systemd、UqAnd d, q-axis current components Id、Iq。
Step three: are respectively paired with Ud、UqAnd Id、IqHigh-pass filtering is carried out to eliminate fundamental wave components of all parameters, and then U is extracted respectivelyd、Uq、IdAnd IqThe disturbance component of (1).
Step four: according to the main circuit element parameters and the voltage ring PI parameters G of the three-phase grid-connected converterc_vdcObtaining the coefficient k1According to Ud、Uq、IdAnd IqObtaining a vector of the disturbance component
Figure BDA0001884040190000031
Will be provided with
Figure BDA0001884040190000032
Real part and k of1The product of the first and second currents is compensated to a d-axis given signal of the current loop to obtain a d-axis given signal I of the compensated current loopdref1：
Figure BDA0001884040190000033
Will be provided with
Figure BDA0001884040190000034
Imaginary part of and k1The product of the first and second currents is compensated to a q-axis given signal of the current loop to obtain a q-axis given signal I of the compensated current loopqref1：
Figure BDA0001884040190000035
In the above formula, IqrefA q-axis current reference value when no decoupling control is performed,
Figure BDA0001884040190000036
Is a transfer function of the outer ring of the DC voltage,
Figure BDA0001884040190000037
DC side impedance, U, in complex vector formdc,0The dc side voltage is in complex vector form.
Step five: obtaining a coefficient k from a phase-locked loop parameter2Will U isdAnd UqRespectively with a stable value I of the grid-connected point current0Multiply and then multiply Ud·I0And Uq·I0Are respectively connected with k2The multiplied product is compensated to the grid-connected point current after Park conversion, and the compensated grid-connected point current
Figure BDA0001884040190000038
(including d-axis current
Figure BDA0001884040190000039
And q-axis current
Figure BDA00018840401900000310
) Comprises the following steps:
Figure BDA00018840401900000311
in the above formula, IdqGrid connection point current G in complex vector form under synchronous rotating coordinate systemPLLFor the phase-locked loop transfer function, UdqThe grid-connected point voltage is in a complex vector form under a synchronous rotating coordinate system.
Step six: will UdAnd UqRespectively with a stable value E of the grid voltage0Multiply and then multiply Ud·E0And Uq·E0Are respectively connected with k2The multiplied product is compensated to the Park converted network voltage, the compensated network voltage
Figure BDA00018840401900000312
(including d-axis current
Figure BDA00018840401900000313
And q-axis current
Figure BDA00018840401900000314
) Comprises the following steps:
Figure BDA00018840401900000315
in the above formula, EdqGrid voltage G in complex vector form under synchronous rotating coordinate systemPLLFor the phase-locked loop transfer function, UdqThe grid-connected point voltage is in a complex vector form under a synchronous rotating coordinate system.
By respectively compensating the d-axis given signal and the q-axis given signal of the current loop, the grid-connected point current and the power grid voltage, the suppression of the frequency coupling phenomenon can be achieved, and the purpose of improving the stability of the converter under the condition of weak power grid is achieved.

Claims (2)

1.三相并网变换器在弱电网条件下的频率耦合抑制方法，其特征在于，包括以下步骤：1. The frequency coupling suppression method of three-phase grid-connected converter under weak grid condition, is characterized in that, comprises the following steps: 步骤一：分别对三相电压Ua、Ub、Uc和三相电流Ia、Ib、Ic依次进行Clark变换和Park变换，获得同步旋转坐标系下d、q轴电压分量Ud、Uq和d、q轴电流分量Id、Iq，Step 1: Perform Clark transformation and Park transformation on the three-phase voltages U a , U b , U c and three-phase currents I a , I b , and I c in turn to obtain the d and q-axis voltage components U d in the synchronous rotating coordinate system , U q and d, q-axis current components I d , I q , 步骤二：分别对Ud、Uq和Id、Iq进行高通滤波，分别提取Ud、Uq、Id和Iq的扰动分量，Step 2: Perform high-pass filtering on U d , U q and I d , I q respectively, and extract the disturbance components of U d , U q , I d and I q respectively, 步骤三：根据三相并网变换器的主电路元件参数和电压环PI参数Gc_vdc获得系数k1，根据Ud、Uq、Id和Iq的扰动分量获得矢量
Figure FDF0000015742160000011
将
Figure FDF0000015742160000012
的实部与k1的乘积补偿到电流环的d轴给定信号中，将
Figure FDF0000015742160000013
的虚部与k1的乘积补偿到电流环的q轴给定信号中，Step 3: Obtain the coefficient k 1 according to the main circuit element parameters of the three-phase grid-connected converter and the voltage loop PI parameter G c_vdc , and obtain the vector according to the disturbance components of U d , U q , I d and I q
Figure FDF0000015742160000011
Will
Figure FDF0000015742160000012
The product of the real part and k 1 is compensated into the d-axis given signal of the current loop, and the
Figure FDF0000015742160000013
The product of the imaginary part of and k 1 is compensated into the q-axis given signal of the current loop, 步骤四：根据锁相环参数获得系数k2，将Ud和Uq分别与并网点电流的稳定值I0相乘，再将Ud·I0和Uq·I0分别与k2相乘的乘积补偿到经过Park变换的并网点电流中，Step 4: Obtain the coefficient k 2 according to the phase-locked loop parameters, multiply U d and U q by the stable value I 0 of the grid-connected current, and then multiply U d · I 0 and U q · I 0 with k 2 respectively. The product of the multiplication is compensated to the current of the grid connection point after Park transformation, 步骤五：将Ud和Uq分别与电网电压的稳定值E0相乘，再将Ud·E0和Uq·E0分别与k2相乘的乘积补偿到经过Park变换的电网电压中，完成频率耦合抑制；Step 5: Multiply U d and U q by the stable value E 0 of the grid voltage respectively, and then compensate the product of U d · E 0 and U q · E 0 by k 2 to the grid voltage after Park transformation , complete the frequency coupling suppression; 步骤三中，In step three, 补偿后电流环的d轴给定信号Idref1为：The d-axis reference signal I dref1 of the current loop after compensation is:
Figure FDF0000015742160000014
Figure FDF0000015742160000014
 补偿后电流环的q轴给定信号Iqref1为：The q-axis reference signal I qref1 of the current loop after compensation is:
Figure FDF0000015742160000015
Figure FDF0000015742160000015
 上式中，Iqref为无解耦控制时的q轴电流参考值、
Figure FDF0000015742160000016
为直流电压外环的传递函数、
Figure FDF0000015742160000017
为复矢量形式的直流侧阻抗、Udc,0为复矢量形式的直流侧电压；In the above formula, I qref is the q-axis current reference value without decoupling control,
Figure FDF0000015742160000016
is the transfer function of the DC voltage outer loop,
Figure FDF0000015742160000017
is the DC side impedance in the form of a complex vector, and U dc,0 is the DC side voltage in the form of a complex vector; 步骤四中，补偿后的并网点电流
Figure FDF0000015742160000018
为：In step 4, the grid-connected point current after compensation
Figure FDF0000015742160000018
for:
Figure FDF0000015742160000019
Figure FDF0000015742160000019
 上式中，Idq为复矢量形式的同步旋转坐标系下的并网点电流、GPLL为锁相环传递函数、Udq为复矢量形式的同步旋转坐标系下的并网点电压；In the above formula, I dq is the grid-connected point current in the synchronous rotating coordinate system in the form of a complex vector, G PLL is the phase-locked loop transfer function, and U dq is the grid-connected point voltage in the synchronous rotating coordinate system in the form of a complex vector; 步骤五中，补偿后的电网电压
Figure FDF0000015742160000021
为：In step 5, the compensated grid voltage
Figure FDF0000015742160000021
for:
Figure FDF0000015742160000022
Figure FDF0000015742160000022
 上式中，Edq为复矢量形式的同步旋转坐标系下的电网电压、GPLL为锁相环传递函数、Udq为复矢量形式的同步旋转坐标系下的并网点电压。In the above formula, E dq is the grid voltage in the synchronous rotating coordinate system in the form of a complex vector, G PLL is the phase-locked loop transfer function, and U dq is the grid connection point voltage in the synchronous rotating coordinate system in the form of a complex vector. 2.根据权利要求1所述的三相并网变换器在弱电网条件下的频率耦合抑制方法，其特征在于，步骤一之前，利用电压传感器对并网点三相电压Ua、Ub、Uc进行采样，利用电流传感器对并网点三相电流Ia、Ib、Ic进行采样。2. The frequency coupling suppression method for a three-phase grid-connected converter under weak grid conditions according to claim 1, characterized in that, before step 1, the three-phase voltages U a , U b , U at the grid-connected point are measured by voltage sensors c to sample, and use the current sensor to sample the three-phase currents I a , I b , and I c of the grid-connected point.
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CN111525922B (en) * 2020-05-12 2022-04-08 中国石油大学(华东) A Low Bandwidth Symmetrical Phase Locking Method to Suppress Frequency Coupling Effects of Grid-connected Inverters
CN113328743B (en) * 2021-05-09 2024-02-20 深圳市禾望电气股份有限公司 Method and system for eliminating frequency coupling effect of phase-locked loop of grid-connected device
CN113162117B (en) * 2021-05-12 2022-05-31 合肥工业大学 Method for designing bandwidth of grid-connected inverter controller under weak grid
CN114400703B (en) * 2022-01-18 2024-07-26 燕山大学 Phase locking method for improving stability of grid-connected system under weak current grid condition

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