CN104076204A - Phase extraction method applied to active power filter - Google Patents
Phase extraction method applied to active power filter Download PDFInfo
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- CN104076204A CN104076204A CN201410357826.3A CN201410357826A CN104076204A CN 104076204 A CN104076204 A CN 104076204A CN 201410357826 A CN201410357826 A CN 201410357826A CN 104076204 A CN104076204 A CN 104076204A
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Abstract
The invention discloses a phase extraction method applied to an active power filter. The method comprises the steps of converting three-phase voltage Ua, Ub and Uc into a static alpha-beta coordinate system, then converting from the static alpha-beta coordinate system into a dq coordinate system synchronously rotating with the three-phase voltage to obtain direct-current components Ud and Uq of alternating voltage, comparing the Ud which is zero with a reference value to obtain an error signal, outputting the error signal omega after controlled by a nonlinear PI (Proportional Integral) regulator, and then adding with a theoretical angular frequency 2pif to obtain an actual angular frequency. When the three-phase voltage is unbalanced or has a jump, the method can extract a phase quickly and accurately and well meet the requirements of the active power filter on high harmonic detection precision and timeliness.
Description
Technical Field
The invention relates to a novel phase extraction technology applied to an active power filter, and belongs to the technical field of power electronics.
Background
The active filter is used as a novel harmonic and reactive compensation device, can effectively inhibit harmonic pollution, balances load current, has excellent dynamic and static performances and self-adaptive capacity to power grid load parameter change, and has strong development potential in harmonic compensation. The premise that the active power filter can work normally is that the phase information of a system can be accurately acquired in real time, the phase extraction mainly adopts a phase-locked loop technology, but when sudden change or unbalanced three-phase voltage occurs in system voltage, the conventional phase-locked loop is easy to have the defect of poor phase extraction precision and low tracking speed, and therefore a novel phase-locked loop technology is provided for improvement based on the current situation.
The phase-locked loop (PLL) mainly provides a fast, stable and high-precision synchronous signal for an Active Power Filter (APF), so that the APF can fast, stably and real-timely eliminate harmonic current of a system. Therefore, the accuracy of the phase-locked loop directly influences the accuracy of the control system, and is an important link of the APF control system. In the mode selection of the phase-locked loop, the traditional modes comprise an analog phase-locked loop adopting hardware, an open-loop phase-locked loop calculating an alpha beta coordinate and a phase-locked loop adopting Fourier decomposition, but the phase-locked loops have the characteristics of low phase-locking speed and low precision when the voltage is suddenly changed or a three-phase system is unbalanced, and have poor dynamic and static characteristics and large errors. Even if the dq phase-locked loop is adopted to suppress the negative sequence voltage under the condition of voltage unbalance, the PI parameter of the dq phase-locked loop is generally designed by taking a 100Hz component as an attenuation coefficient, so the characteristic of slow response speed exists.
Disclosure of Invention
The invention mainly aims to solve the phase extraction defect of APF when the system has voltage mutation or three-phase voltage unbalance, and provides a novel phase extraction technology based on a variable-gain PI controller, so that the practicability of an active power filter is stronger, and the adopted technical scheme is as follows:
the phase extraction method comprises the following steps:
(1) the method comprises the following steps of collecting three-phase voltage of a power grid in real time, and normalizing collected actual voltage signals into:
in the formula,an ideal phase;
(2) clark transformation is carried out on the collected three-phase voltage of the power grid, namely, a three-phase voltage vector is projected to a rectangular coordinate system alpha beta from abc coordinates:
in the formula,，transforming matrices for stationary coordinates ；
(3) After converting the three-phase power grid voltage signal from an abc coordinate system to an alpha beta coordinate system, carrying out Park transformation, and realizing the steps of converting a rectangular coordinate system，Projecting to a dq coordinate system of a synchronous rotating coordinate system, and converting the data by the following method:in the formula,，is a synchronous rotation coordinate transformation matrixAnd the calculated D-axis component is:since the D-axis component is very small, the above equation can be linearized as:
；
(4) for the calculated small componentCarry out PI control, this time adopted a neotype PI control model, this kind of neotype PI controller's mathematical model is:whereinFor the minor component calculated aboveThe output y being the angular frequency of the extracted voltage；
The PI control model has two proportional control coefficients, which are respectively，Wherein the proportional gain parameterThe mathematical model of (a) is:
wherein,，，is a positive real constant and is a real constant,as a non-linear function, when the error isWhen the temperature of the water is higher than the set temperature,maximum value of(ii) a When in useWhen the temperature of the water is higher than the set temperature,take the minimum value；Is composed ofIs adjusted in the variation interval ofCan be adjusted in sizeThe rate of change;
integral gain parameterThe mathematical model of (a) is:
wherein,，is a positive real constant and is a real constant,in the form of a non-linear function,has a value range ofWhen is coming into contact withWhen the temperature of the water is higher than the set temperature,take the maximum value as(ii) a Adjustment ofCan be adjusted in sizeThe rate of change.
Due to the fact that，Will follow the parametersIs varied, so that the extraction angular frequency is controlled at the PI controllerWhen can be according toThe change of the voltage is used for quick response, thereby satisfying the dynamic response characteristic.
The basic principle of the invention is to apply three-phase voltageConversion to restCoordinate system, then from restThe coordinate system being converted to rotation in synchronism with three-phase voltageCoordinate system to obtain DC component of AC voltageComponent of direct currentIs zero, willAnd comparing with the reference value to obtain an error signal,the error signal is output after being controlled by a nonlinear PI regulatorAnd then the theoretical angular frequencyAnd adding to obtain the actual angular frequency. After the following integration link, the voltage phase of the power grid can be output。
The core algorithm of the invention is the construction of a nonlinear PI control model, the tracking and locking of the phase are realized by controlling the D-axis component to be fast response to zero, the gain parameter in the nonlinear PI controller needs to be fast response along with the change of the control error, therefore, the anti-interference capability of the nonlinear PI controller is better than that of the conventional linear PI controller, and the nonlinear PI controller obtains the frequency through the nonlinear PI controllerThen, by aligning the micro componentsThe phase angle theta is obtained by integration, the function of phase locking is realized, the phase can be extracted quickly and accurately when three-phase voltage is unbalanced or sudden change occurs, and the requirements of an active power filter on high precision and real-time performance of harmonic detection can be well met.
Drawings
FIG. 1 is a phase tracking contrast diagram under an asymmetric sine wave;
fig. 2 is a phase tracking plot under a frequency abrupt sine wave.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The phase extraction method comprises the following steps:
(1) the method comprises the following steps of collecting three-phase voltage of a power grid in real time, and normalizing collected actual voltage signals into:
in the formula,an ideal phase;
(2) clark transformation is carried out on the collected three-phase voltage of the power grid, namely, a three-phase voltage vector is projected to a rectangular coordinate system alpha beta from abc coordinates:
in the formula,，transforming matrices for stationary coordinates ；
(3) After converting the three-phase power grid voltage signal from an abc coordinate system to an alpha beta coordinate system, carrying out Park transformation, and realizing the steps of converting a rectangular coordinate system，Projecting to a dq coordinate system of a synchronous rotating coordinate system, and converting the data by the following method:in the formula,，is a synchronous rotation coordinate transformation matrixAnd the calculated D-axis component is:since the D-axis component is very small, the above equation can be linearized as:
；
(4) and (3) sending the calculated d-axis component to a nonlinear PI controller, wherein the mathematical model of the nonlinear PI controller is as follows:
whereinFor the D-axis component calculated above, the output y is the angular frequency of the extracted phase；
Established proportional gain parameterThe mathematical model of (a) is:
wherein,，，is a positive real constant and is a real constant,as a non-linear function, when the error isWhen the temperature of the water is higher than the set temperature,maximum value of(ii) a When in useWhen the temperature of the water is higher than the set temperature,take the minimum value；Is composed ofIs adjusted in the variation interval ofCan be adjusted in sizeThe rate of change;
established integral gain parameterThe mathematical model of (a) is:
wherein,，is a positive real constant and is a real constant,in the form of a non-linear function,has a value range ofWhen is coming into contact withWhen the temperature of the water is higher than the set temperature,take the maximum value as(ii) a Adjustment ofCan be adjusted in sizeThe rate of change.
In order to verify the feasibility of the phase extraction method, a simulation system based on matlab is set up, wherein the voltage peak-to-peak value: 380V, frequency: 50Hz, the proportional gain parameter and the integral gain parameter of the nonlinear PI controller are respectively,,,,。
In fig. 1, a diagram is a symmetrical three-phase voltage waveform, and b diagram and d diagram are a standard a-phase voltage waveform, a PLL tracking voltage waveform and a phase tracking waveform respectively under the conventional PI control. At time 0.03s, the sinusoidal tracking and phase tracking errors are 0.038 and 0.0412, respectively. And the c diagram and the e diagram are respectively a standard A-phase voltage waveform, a PLL tracking voltage waveform and a phase tracking waveform under the adoption of a novel phase extraction method, and from the simulation result, under the control mode, a good sine tracking effect and a good phase tracking effect can be achieved within a short time in the first period. At time 2.386ms, the sinusoidal tracking and phase tracking errors are 0.0001 and 0.0001, respectively. But after entering steady state, the average tracking error is slightly higher than the effect of conventional PI control. Therefore, under the condition of asymmetric three-phase sinusoidal signals, the novel phase extraction method has higher phase tracking speed and higher phase tracking precision.
In fig. 2, a is a symmetrical three-phase voltage waveform when the frequency is suddenly changed, and b and d are a standard a-phase voltage waveform, a PLL tracking voltage waveform and a phase tracking waveform respectively under the conventional PI control. At time 0.08s (frequency ramp time 0.06s, after two cycles), the sinusoidal tracking and phase tracking errors are 0.0532 and 0.0779, respectively. And the c diagram and the e diagram are respectively a standard A-phase voltage waveform, a PLL tracking voltage waveform and a phase tracking waveform under the adoption of a novel phase extraction method, and from the simulation result, under the control mode, a good sine tracking effect and a good phase tracking effect can be achieved in the first period. At time 0.0612s (instant after the mutation), the sinusoidal tracking and phase tracking errors were 0.0012 and 0.0104, respectively. It can be seen that the novel phase extraction method has better dynamic characteristics and tracking accuracy than the conventional phase extraction method.
Claims (1)
1. The phase extraction method applied to the active power filter is characterized by comprising the following steps of:
(1) the method comprises the following steps of collecting three-phase voltage of a power grid in real time, and normalizing collected actual voltage signals into:
in the formula,an ideal phase;
(2) clark transformation is carried out on the collected three-phase voltage of the power grid, namely, a three-phase voltage vector is projected to a rectangular coordinate system alpha beta from abc coordinates:
the conversion method isIn the formula,，transforming matrices for stationary coordinates ；
(3) Converting the voltage vectorCarrying out Park conversion;
the realization steps are that a rectangular coordinate system is adopted，Projecting to a dq coordinate system of a synchronous rotating coordinate system, and converting the data by the following method:in the formula,，is a synchronous rotation coordinate transformation matrixBy the formulaAfter the calculation, the calculation is carried out,due to the fact thatThe component is very small, canThe linearity is:
；
(4) for the calculated small componentCarry out PI control, this time adopted a neotype PI control model, this kind of neotype PI controller's mathematical model is:whereinFor the minor component calculated aboveThe output y being the angular frequency of the extracted voltage；
(5) The PI control model has two proportional control coefficients, which are respectively，Wherein the proportional gain parameterThe mathematical model of (a) is:
integral gain parameterThe mathematical model of (a) is:
due to the fact that，Will follow the parametersIs varied, so that the extraction angular frequency is controlled at the PI controllerWhen can be according toThe change of the response time is changed to quickly respond, so that the dynamic response characteristic is met;
(6) obtaining angular frequencyThen, through the pairAnd (4) integrating to obtain a phase angle theta, so that a phase extraction function is realized.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107831366A (en) * | 2017-11-02 | 2018-03-23 | 中车永济电机有限公司 | The method for obtaining power network single-phase voltage phase |
| CN112595893A (en) * | 2020-11-16 | 2021-04-02 | 闽南理工学院 | Power grid phase synchronization signal detection method based on adaptive filter |
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| US5343404A (en) * | 1992-11-12 | 1994-08-30 | Maritec Corp. | Precision digital multimeter and waveform synthesizer for multi-signals with distorted waveforms embedded in noise |
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| CN101777912A (en) * | 2010-01-15 | 2010-07-14 | 浙江大学 | Method for realizing software phase-locked loop with unfixed sampling frequency |
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| XIAOCHU QIU等: "Research of Variable Gain Nonlinear PI Controller based Three-Phase Phase-Locked-Loop System", 《2010 INTERNATIONAL CONFERENCE ON ELECTRICAL AND CONTROL ENGINEERING》, 31 December 2010 (2010-12-31) * |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107831366A (en) * | 2017-11-02 | 2018-03-23 | 中车永济电机有限公司 | The method for obtaining power network single-phase voltage phase |
| CN107831366B (en) * | 2017-11-02 | 2020-06-09 | 中车永济电机有限公司 | Method for obtaining single-phase voltage phase of power grid |
| CN112595893A (en) * | 2020-11-16 | 2021-04-02 | 闽南理工学院 | Power grid phase synchronization signal detection method based on adaptive filter |
| CN112595893B (en) * | 2020-11-16 | 2023-09-08 | 闽南理工学院 | Power grid phase synchronization signal detection method based on adaptive filter |
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