CN109066684B - Three-phase active power filter based on LCL filtering and control method thereof - Google Patents
Three-phase active power filter based on LCL filtering and control method thereof Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02E40/20—Active power filtering [APF]
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Abstract
The invention belongs to the technical field of three-phase active power filters, and particularly relates to a three-phase active power filter based on LCL filtering and a control method thereof. The LCL filtering-based three-phase active power filter comprises a three-phase inverter, an output filter and a control system; the three-phase inverter is a voltage type inverter, and the energy storage element is a direct current capacitor; the output filter is a three-order filter and comprises an inverter side filter inductor, a filter capacitor and a power grid side filter inductor; the control system is used for power grid current detection and current double closed-loop control of inverter side current feedback. According to the invention, the harmonic component of the current of the power grid is directly controlled in a power grid current closed-loop control mode, so that detection delay and assignment phase offset existing in the traditional load current detection method are avoided; and introducing virtual damping to suppress resonance spikes of the LCL filter through current feedback of the inverter side.
Description
Technical Field
The invention belongs to the technical field of three-phase active power filters, and particularly relates to a three-phase active power filter based on LCL filtering and a control method thereof.
Background
With the wide application of power electronic converter devices, electric energy is more fully utilized, but a large number of nonlinear load devices are widely used in a power grid, so that the problem of harmonic pollution in the power grid is more and more severe, and harmonic treatment is more and more emphasized by people. Compared with a traditional passive Power filter consisting of an inductor, a capacitor and a resistor, the Active Power Filter (APF) has the characteristics of good filtering characteristic, high controllability, high response speed, flexible application and the like. With the reduction of the cost of semiconductor devices, the APF gradually becomes a research hotspot and development direction of harmonic suppression of power supply systems at home and abroad.
The current control methods commonly used in the APF mainly include hysteresis current control, repetitive control and PI control. The hysteresis current control has the advantages of simple realization and good robustness, but can not realize no-static-error control, and the switching frequency is uncertain, thereby bringing difficulty to the design of an output filter; the repetitive control can realize zero steady-state error tracking on complex periodic signals, but the dynamic performance is poor, the disturbance cannot be responded in real time, and the delay of one reference period is usually generated. PI control is the most classical and widely used control method. The APF control method is simple in structure and easy to design, static error-free tracking can be achieved, but due to the fact that the APF command signal contains a plurality of frequency sine signals, the PI control method is not ideal in control effect on periodic command signals with high frequency, and zero steady-state error tracking is difficult to achieve. In addition, the generalized integral control, the sliding mode control and the composite control of various control methods are receiving more and more attention from scholars.
With the continuous development of semiconductor technology, the capacity of the semiconductor is continuously improved, the price is gradually reduced, so that the APF is gradually developed towards the direction of large capacity and high power density, and the selection of an output filter is particularly important in order to suppress the current harmonic of the APF switching frequency. The traditional L-shaped filter has poor effect of filtering the switch ripple, and can meet corresponding requirements only by needing a larger inductance value under the high-power application occasion, so that the change rate of the output compensating current is reduced, the dynamic performance of the system is reduced, and the whole system is large in size, high in cost and large in power loss. In recent years, the LCL filter has become a research hotspot of people, and has a prominent advantage over the former that ideal high-frequency harmonic attenuation and switch ripple suppression can be realized with a smaller total inductance, and in a high-power application occasion, the cost advantage is obvious, and the dynamic performance of the system is improved, but damping control needs to be added to suppress a resonance peak. At present, two methods of passive damping and active damping are available, the passive damping is simple and reliable, but the loss is serious in high-voltage and high-power occasions. The active damping avoids the resonance problem through a control algorithm, and mainly comprises an active damping method of a forward path additional digital filter, an active damping method based on model order reduction and an active damping method based on state variable feedback.
Disclosure of Invention
Technical problem to be solved
Aiming at the existing technical problems, the invention provides a three-phase active power filter based on LCL filtering and a control method thereof, which avoid the problems of detection delay and amplitude phase offset in the traditional load current detection method.
(II) technical scheme
In order to achieve the purpose, the invention adopts the main technical scheme that:
a three-phase active power filter based on LCL filtering comprises a three-phase inverter, an output filter and a control system;
the three-phase inverter is a voltage type inverter, and the energy storage element is a direct current capacitor;
the output filter is a three-order filter and comprises an inverter side filter inductor, a filter capacitor and a power grid side filter inductor;
the control system is used for power grid current detection and current double closed-loop control of inverter side current feedback.
Preferably, the inverter of the three-phase active power filter is a three-phase voltage type inverter.
Preferably, the output filter of the three-phase active power filter is an LCL type filter.
Preferably, the power grid side current detection closed-loop control mode directly controls the power grid current harmonic component.
Preferably, inverter side inductive current feedback is introduced into the power grid current closed-loop control, and the inverter side inductive current is sampled and added into the current instruction after a proportion link.
Preferably, the grid-side current control comprises a harmonic current control loop and a fundamental current control loop;
the harmonic current control loop controls the harmonic component of the power grid current by adopting a multi-resonance controller, so that the controlled current can track the harmonic instruction current without difference;
the fundamental current control loop controls the fundamental component of the power grid current by adopting a proportional resonant controller, so that the controlled current can track the fundamental instruction current without difference.
A control method of controlling the LCL filtering based three-phase active power filter as described above, comprising the steps of:
the method comprises the following steps: detecting the current of the power grid as the closed-loop control of the current of the power gridThe control object of the medium harmonic control loop is used for controlling the harmonic current component injected into the power grid to be zero; harmonic current command
Step two: detecting the phases of the direct current bus voltage and the power grid A-phase voltage, subtracting the detected actual value from the direct current bus capacitor voltage reference value to obtain an error value of the direct current bus voltage, obtaining a fundamental current amplitude value through a PI (proportional-integral) controller, and multiplying the fundamental current amplitude value by the detected phase information to obtain fundamental instruction current;
step three: the fundamental wave command current is used as a command signal of a fundamental wave control loop;
step four: further obtaining the command current of the compensation current through the harmonic current command and the fundamental current command;
step five: and carrying out closed-loop control on the inverter side inductive current of the active power filter by combining the current instruction, wherein the current loop controller obtains a modulation wave by adopting a proportional control mode.
(III) advantageous effects
The invention has the beneficial effects that: the LCL filtering-based three-phase active power filter and the control method thereof have the following advantages that:
the three-phase active power filter control system based on LCL filtering controls the inverter to output a complementary harmonic current by collecting the current of a power grid, the voltage of a direct current capacitor and the side inductive current of the inverter, thereby realizing the filtering function.
According to the LCL filtering-based three-phase active power filter control method, the harmonic component of the power grid current is directly controlled by detecting the power grid current, so that detection delay and amplitude phase offset existing in the traditional load current detection method are avoided; the compensation effect and the real-time performance are superior to those of the traditional load side current detection control.
Furthermore, the frequency division independent control of harmonic current and fundamental current is realized by adopting a multi-resonance controller and a proportional resonance controller, and meanwhile, the harmonic compensation and the direct-current bus voltage control are mutually independently controlled.
The three-phase active power filter control method based on LCL filtering provided by the invention adopts power grid current closed-loop control, simultaneously adds active damping control of inverter side inductive current feedback, introduces virtual damping, inhibits resonance peak of the LCL filter, and enables compensation current to accurately track instruction current.
Drawings
FIG. 1 is a block diagram of the overall control of a three-phase active power filter system based on LCL filtering;
FIG. 2 is a control block diagram of a single-phase LCL type active power filter;
FIG. 3 is a block diagram of a grid current closed-loop control strategy system.
Detailed Description
For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.
The invention discloses a three-phase active power filter based on LCL filtering, which comprises a three-phase inverter T1An output filter and a control system. Three-phase inverter T1Is a voltage-type inverter, and the energy storage element is a DC capacitor Cdc(ii) a The output filter is an LCL third-order filter and comprises an inverter-side filter inductor L1Filter capacitor C, electric network side filter inductor L2(ii) a The control system is used for power grid current detection and current double closed-loop control of inverter side current feedback.
The control method of the LCL type active power filter comprises the following steps: the harmonic component of the current of the power grid is directly controlled in a closed-loop control mode of current detection of the power grid, so that detection delay and assignment phase offset existing in the traditional load current detection method are avoided; introducing a resonance peak of a virtual damping suppression LCL filter through current feedback of an inverter side; the frequency division independent control of harmonic waves and fundamental waves is realized through the design of a controller, and meanwhile, the harmonic compensation and the independent control of direct-current bus voltage are realized.
Among them, the inverter T1 of the three-phase active power filter is a three-phase voltage type inverter. The output filtering of the active power filter adopts an LCL type filter.
The power grid current detection closed-loop control is adopted to directly control the power grid current harmonic component, so that detection delay and assignment phase offset existing in the traditional load current detection method are avoided; the compensation effect and the real-time performance are superior to the traditional load side current detection control
The inverter side inductive current feedback is introduced into the power grid current closed-loop control, and the inverter side inductive current is sampled and added into a current instruction after a proportion link, so that a capacitor is connected with a virtual resistor in parallel, the damping is increased, and the resonance peak of an LCL filter is suppressed;
the adopted power grid current control comprises a harmonic current control loop and a fundamental current control loop. The harmonic current control loop controls the harmonic component of the power grid current by adopting a multi-resonance controller, so that the controlled current can track the harmonic instruction current without difference; the fundamental current control loop controls the basic component of the power grid current by adopting a proportional resonant controller, so that the controlled current can track the fundamental instruction current without difference.
In this embodiment, there is also provided a control method for controlling the above-mentioned three-phase active power filter based on LCL filtering, including the steps of:
the method comprises the following steps: detecting the current of the power grid to be used as a control object of a harmonic control loop in the current closed-loop control of the power grid side, wherein the control target is to enable the harmonic current component injected into the power grid to be zero; harmonic current command
Step two: detecting the phases of the direct-current bus voltage and the power grid A-phase voltage, subtracting the detected actual value from the direct-current bus capacitor voltage reference value to obtain an error value of the direct-current bus voltage, obtaining a fundamental current amplitude value through an P I controller, and multiplying the fundamental current amplitude value by the detected phase information to obtain fundamental instruction current;
step three: the fundamental wave command current is used as a command signal of a fundamental wave control loop;
step four: further obtaining the command current of the compensation current through the harmonic current command and the fundamental current command;
step five: and carrying out closed-loop control on the inverter side inductive current of the active power filter by combining the current instruction, wherein the current loop controller obtains a modulation wave by adopting a proportional control mode.
The LCL filtering-based three-phase active power filter control method is suitable for three-phase systems and single-phase systems, and the overall control block diagram of the LCL filtering-based three-phase active power filter control method is shown in figure 1 and comprises an LCL type three-phase active power filter main circuit topology and a current control part. The current control part is realized in a digital processor with SP28335 as a core. The specific control method will now be described by taking a single phase as an example.
Control block diagram of single-phase active power filter based on LCL filtering is shown in figure 2 and is composed of single-phase inverter T1The LCL filter, the current and voltage sampling circuit and the control circuit. Single-phase inverter T1DC side parallel DC capacitor CdcThe AC side is an LCL filter including an inverter side inductor L1Filter capacitor C, network side inductor L2(ii) a The control system is respectively connected with the power grid and the direct current capacitor C through the power grid current sampling circuit, the power grid voltage sampling current, the phase-locked loop, the direct current capacitor voltage sampling circuit, the inverter side current sampling circuitdcAnd a single-phase inverter T1Is connected with the output end of the power supply.
The amplitude phase information of the power grid current, the power grid voltage phase and the direct current capacitor voltage are detected, the frequency division of the harmonic current and the fundamental current is independently controlled, and the active damping control of the current feedback of the inverter side is combined, so that the inverter outputs a complementary harmonic current, and the function of filtering the power grid harmonic is realized.
As shown in fig. 3, the error tracking of the harmonic current and the fundamental current is respectively realized by adopting multi-resonance control and proportional resonance control in the control algorithm; because the fundamental current controller only controls the fundamental frequency signal, the direct feedback of the inverter side inductive current realizes the stable control of the direct current capacitor voltage.
The technical principles of the present invention have been described above in connection with specific embodiments, which are intended to explain the principles of the present invention and should not be construed as limiting the scope of the present invention in any way. Based on the explanations herein, those skilled in the art will be able to conceive of other embodiments of the present invention without inventive efforts, which shall fall within the scope of the present invention.
Claims (5)
1. A three-phase active power filter based on LCL filtering is characterized in that: the system comprises a three-phase inverter, an output filter and a control system;
the three-phase inverter is a voltage type inverter, and the energy storage element is a direct current capacitor;
the output filter is a three-order filter and comprises an inverter side filter inductor, a filter capacitor and a power grid side filter inductor; the output filter of the three-phase active power filter adopts an LCL type filter;
the control system is used for detecting the current of the power grid, carrying out current double closed-loop control fed back by the current at the side of the inverter and controlling the amplitude phase information of the current of the power grid, the voltage phase of the power grid and the voltage of the direct current capacitor;
the inverter side inductive current feedback is introduced into the power grid current closed-loop control, and the inverter side inductive current is sampled and added into a current instruction after a proportion link, so that the capacitor is connected with the virtual resistor in parallel.
2. The LCL filtering based three-phase active power filter according to claim 1, wherein the inverter of the three-phase active power filter is a three-phase voltage source inverter.
3. The LCL filtering based three-phase active power filter according to claim 1, wherein the grid side current detection closed-loop control mode directly controls the grid current harmonic component.
4. The LCL filtering based three-phase active power filter according to claim 1, wherein the grid side current control comprises a harmonic current control loop and a fundamental current control loop;
the harmonic current control loop controls the harmonic component of the power grid current by adopting a multi-resonance controller, so that the controlled current can track the harmonic instruction current without difference;
the fundamental current control loop controls the fundamental component of the power grid current by adopting a proportional resonant controller, so that the controlled current can track the fundamental instruction current without difference.
5. A control method for controlling the LCL filtering based three-phase active power filter according to any one of claims 1-4, wherein: the method comprises the following steps:
the method comprises the following steps: detecting the current of the power grid to be used as a control object of a harmonic control loop in the current closed-loop control of the power grid side, wherein the control target is to enable the harmonic current component injected into the power grid to be zero; harmonic current command
Step two: detecting the phases of the direct current bus voltage and the power grid A-phase voltage, subtracting the detected actual value from the direct current bus capacitor voltage reference value to obtain an error value of the direct current bus voltage, obtaining a fundamental current amplitude value through a PI (proportional-integral) controller, and multiplying the fundamental current amplitude value by the detected phase information to obtain fundamental instruction current;
step three: the fundamental wave command current is used as a command signal of a fundamental wave control loop;
step four: further obtaining the command current of the compensation current through the harmonic current command and the fundamental current command;
step five: and carrying out closed-loop control on the inverter side inductive current of the active power filter by combining the current instruction, wherein the current loop controller obtains a modulation wave by adopting a proportional control mode.
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| CN110572068B (en) * | 2019-08-26 | 2020-12-08 | 华中科技大学 | Current source access device with additional control signal |
| CN111917131A (en) * | 2020-08-04 | 2020-11-10 | 西安热工研究院有限公司 | Harmonic suppression method for photovoltaic LCL grid-connected inverter based on PI and MPR |
| CN113629984B (en) * | 2021-07-27 | 2023-02-28 | 浙江大学 | Three-phase LCL type SAPF parameter design method based on double-loop current control strategy |
| CN113890033A (en) * | 2021-10-26 | 2022-01-04 | 深圳市锐风电子科技有限公司 | Active damping circuit of active power filter and control method thereof |
| CN114024315B (en) * | 2021-11-12 | 2023-08-29 | 国网山东省电力公司德州供电公司 | Current transformer ripple current sharing control method and system based on virtual resistor |
| CN113839388B (en) * | 2021-11-29 | 2022-02-08 | 湖北工业大学 | Current double-loop control method of active power filter based on hybrid load |
| CN113839387A (en) * | 2021-11-29 | 2021-12-24 | 湖北工业大学 | LCL type active power filter system and method of passive interface |
| CN115453855A (en) * | 2022-09-05 | 2022-12-09 | 国网安徽省电力有限公司六安供电公司 | Design method of repetitive control compensator for LCL type APF |
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