CN113013882B - Medium-voltage parallel active power filter and control method - Google Patents
Medium-voltage parallel active power filter and control method Download PDFInfo
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Abstract
A medium voltage parallel active power filter and a control method are provided. A medium voltage three-phase parallel active power filter, the active power filter comprising: three single-phase H-bridges; three single-phase transformers, the low-voltage sides of which are connected to a corresponding one of the single-phase H-bridges respectively by means of filter components, and the high-voltage sides of which are connected to the power grid. The high-voltage sides of three single-phase transformers in the active power filter are connected in an angle mode, and the low-voltage sides of the three single-phase transformers are connected in a star mode.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a medium-voltage parallel active power filter and a control method.
Background
With the rapid development of high-voltage power networks and power electronic technologies, the harmonic pollution generated by the power networks is increasingly serious due to the increase of a large number of power electronic devices, and the demand for high-voltage high-capacity active power filters is becoming urgent. At present, two main schemes exist for realizing the medium-high voltage high-capacity active power filter, one is to adopt a cascading multi-level technology, and the other is to adopt a step-up transformer.
Although the active power filter has been developed for many years, the application in the low-voltage power distribution system is still perfect, but the application in the field of medium-high voltage and large capacity is still immature, how to solve the harmonic pollution existing in the medium-high voltage and large capacity alternating current power distribution system by using the active power filter has important significance for the development of the power electronic technology.
In the implementation scheme of the medium-high voltage high-capacity active power filter, the cascade multi-level technology is too complex to control, poor in stability and reliability, slower in dynamic response, more cascade units particularly along with the increase of voltage level, and higher in cost.
The main difference between micro-grids and traditional grids is that they can operate in island mode, digest distributed energy in situ, balance in situ, and exchange energy with large grids. Thus, the control and related protection techniques inside the micro-grid are correspondingly different compared to the large grid: the large power grid is mainly unidirectional tide and simple in interaction, and is connected to users from a power plant through a power transmission line; the micro-grid is an internal circulation, is bidirectional operation, can exchange energy between a user and the micro-grid, and is active interaction.
If the micro-grid is well controlled, when the large grid fails, the large grid can be supported to improve the power supply reliability. The micro-grid can also provide frequency modulation and voltage regulation services for the large power grid to improve the power quality. Therefore, the control performance of the micro-grid is critical, and compared with a large power grid, the renewable energy source in the micro-grid has high permeability, and the energy storage and other devices enable the micro-grid to have obvious power electronization characteristics, small inertia and high harmonic content. Therefore, harmonic suppression of the micro grid is indispensable.
Disclosure of Invention
The scheme of adopting the step-up transformer is a powerful supplement to the realization scheme of cascading the multi-level technology of the medium-high voltage high-capacity active power filter, the capacity of the step-up transformer can be large or small, the control is relatively simple, the reliability is higher, the problem that a medium-high voltage system has no central line is solved by reasonable design of the side-angle connection of the transformer network, and the topological structure of the single-phase H bridge is also convenient for independent control.
The invention aims to at least partially overcome the defects in the existing power filter and provide a medium-voltage (below 35kV, for example, 10 kV) parallel active power filter and a control method. The main circuit topology structure of three single-phase H-bridges is adopted, and the three single-phase H-bridges are output to a power grid through three single-phase step-up transformers (working in the linear section of a B-H curve), so that the application problem of an active power filter in a medium-voltage system is solved. The high-voltage side (network side) of the three single-phase step-up transformers adopts an angle connection mode, so that the problem that a medium-voltage system has no neutral line is solved. The single-phase-locked loop based on virtual average reactive phase discrimination solves the phase locking problem of single-phase variables. Based on the concept of the instantaneous reactive power theory, coordinate transformation and filtering control are carried out on load current, and the problem of harmonic detection of a single-phase circuit is solved. The output of the direct current voltage control loop is multiplied by cos omega t and converted into an alternating current system to be used as a given input of a current loop, so that the control problem of direct current voltage is solved. A single-phase SVPWM control technology is adopted in the parallel active power filter.
According to an aspect of the present invention, a medium voltage three-phase parallel active power filter includes: three single-phase H-bridges; three single-phase transformers, the low-voltage sides of the three single-phase transformers are respectively connected to a corresponding one of the single-phase H bridges through a filter assembly, and the high-voltage sides of the three single-phase transformers are connected to a power grid; the high-voltage sides of three single-phase transformers in the active power filter are connected in an angle mode, and the low-voltage sides of the three single-phase transformers are connected in a star mode.
The medium-voltage three-phase parallel active power filter further comprises a controller, wherein the controller independently controls each H bridge in the three single-phase H bridges by adopting a voltage and current double-closed loop feedback control strategy so as to perform harmonic compensation. The controller is configured to: and superposing the voltage outer loop regulating quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop given value, calculating the difference value between the current loop given value and the current measured value of the alternating current side of each H bridge, and carrying out sorting regulation on the result of calculating the difference value to obtain the input of the space vector pulse width modulation control of each H bridge, wherein the controller calculates the difference value between the voltage reference value of the direct current side of each H bridge and the voltage measured value of the direct current side of each H bridge, carries out sorting regulation on the result of calculating the difference value, and multiplies the result of sorting regulation by the cosine value of the power grid voltage phase to obtain the voltage outer loop regulating quantity.
In the voltage and current double closed loop feedback control strategy, the controller controls the current inner loop to control the main circuit to track the current given value, and controls the direct current voltage outer loop to control the direct current side voltage stability of each H bridge.
In a voltage and current dual closed loop feedback control strategy, the dc voltage outer loop is outside the current inner loop.
In a voltage and current double closed loop feedback control strategy, the controller selects the low-voltage side of the single-phase transformer to perform voltage acquisition so as to perform alternating current voltage feedforward control.
In a voltage and current dual closed loop feedback control strategy, the controller obtains a line voltage phase based on a single phase locked loop of virtual average reactive phase discrimination.
In a voltage and current dual closed loop feedback control strategy, the controller converts the grid load current of an active power filter connected in an angle at the high voltage side of a single phase transformer into an in-angle phase current.
In a voltage and current double closed loop feedback control strategy, the controller takes the in-angle phase current of an active power filter connected in an angle mode at the high voltage side of a single-phase transformer as a control object, and subtracts fundamental reactive current and fundamental active current from grid load current to extract harmonic current signals.
The finishing adjustment includes proportional integral adjustment and clipping adjustment.
According to another aspect of the present invention, a method for controlling filtering of medium-voltage three-phase parallel active power includes:
the voltage and current double closed loop feedback control strategy is adopted, the high voltage sides of three single-phase transformers of the active power filter are connected in an angle mode, the low voltage sides of the three single-phase transformers are connected in a star mode, and the control method comprises the following steps: and superposing the voltage outer loop regulation quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop set value, and differencing the current loop set value with a current measurement value of an alternating current side of each H bridge in three single-phase H bridges of the active power filter, and performing trimming adjustment on the result of the difference so as to obtain the input of space vector pulse width modulation control of each H bridge, wherein the voltage outer loop regulation quantity is obtained by differencing a voltage reference value of a direct current side of each H bridge and a voltage measurement value of a direct current side of each H bridge, performing trimming adjustment on the result of the difference, and multiplying the result of the trimming adjustment by a cosine value of a power grid voltage phase.
In the control method, in a voltage and current double closed loop feedback control strategy, a current inner loop is used for controlling a main circuit to track a current given value, and a direct current voltage outer loop is used for controlling the voltage stability of the direct current side of each H bridge.
In the control method, in a voltage and current double-closed-loop feedback control strategy, the direct-current voltage outer loop is outside the current inner loop.
In the control method, in a voltage and current double closed loop feedback control strategy, the low-voltage side of a single-phase transformer is selected for voltage acquisition so as to perform alternating voltage feedforward control.
In the control method, in a voltage and current double closed loop feedback control strategy, a line voltage phase is acquired based on a single-phase-locked loop of virtual average reactive phase discrimination.
In the control method, in a voltage and current double closed loop feedback control strategy, the grid load current of an active power filter connected with a high-voltage side of a single-phase transformer in an angle mode is converted into an in-angle phase current.
In the control method, in a voltage and current double closed loop feedback control strategy, the in-angle phase current of an active power filter connected in an angle mode is used as a control object on the high-voltage side of a single-phase transformer, and fundamental wave reactive current and fundamental wave active current are subtracted from grid load current to extract harmonic current signals.
In the control method, the finishing adjustment includes proportional integral adjustment and clipping adjustment.
According to another aspect of the present invention, a medium voltage three-phase parallel active power filter for a micro-grid, the active power filter comprising: three single-phase H-bridges; and the low-voltage sides of the three single-phase transformers are respectively connected to a corresponding one of the single-phase H bridges through a filter component, and the high-voltage sides of the three single-phase transformers are connected to buses of a micro-grid, wherein the high-voltage sides of the three single-phase transformers in the active power filter are connected in an angle mode, and the low-voltage sides of the three single-phase transformers are connected in a star mode.
According to another aspect of the present invention, a method for controlling active power filtering of a medium-voltage three-phase parallel type for a micro-grid, the control method employing a voltage and current dual closed loop feedback control strategy, the high voltage sides of three single-phase transformers of the active power filter connected to a busbar of the micro-grid employing an angular connection, and the low voltage sides of the three single-phase transformers employing a star connection, wherein the control method further comprises: and superposing the voltage outer loop regulation quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop set value, and differencing the current loop set value with a current measurement value of an alternating current side of each H bridge in three single-phase H bridges of the active power filter, and performing trimming adjustment on the result of the difference so as to obtain the input of space vector pulse width modulation control of each H bridge, wherein the voltage outer loop regulation quantity is obtained by differencing a voltage reference value of a direct current side of each H bridge and a voltage measurement value of a direct current side of each H bridge, performing trimming adjustment on the result of the difference, and multiplying the result of the trimming adjustment by a cosine value of a power grid voltage phase.
According to another aspect of the present invention, a computer readable storage medium storing a computer program which, when executed by a processor, implements the medium voltage three-phase parallel active power filter control method described above.
According to another aspect of the invention, a computer device includes: a processor; and the memory is used for storing a computer program, and when the computer program is executed by the processor, the medium-voltage three-phase parallel active power filtering control method is realized.
Drawings
Fig. 1 is a schematic illustration of an Active Power Filter (APF) structure in accordance with an embodiment of the present invention;
Fig. 2 is a diagram of a single phase locked loop control based on virtual average reactive phase discrimination in accordance with an embodiment of the present invention;
FIG. 3 is a diagram of APF intra-angular phase current calculation based on the harmonic detection principle of a single phase power system according to an embodiment of the invention;
FIG. 4 is a diagram of DC voltage and harmonic current tracking control according to an embodiment of the invention;
FIG. 5A is a diagram of Total Harmonic Distortion (THD) of line voltage U ab before compensation according to an embodiment of the invention;
FIG. 5B is a diagram of THD of current I Sa before compensation according to an embodiment of the invention;
FIG. 6 is a waveform diagram of I La and I Sa according to an embodiment of the present invention;
FIG. 7 is a diagram of harmonic current I a_h and compensation current I as according to an embodiment of the invention;
FIG. 8 is a diagram of load current I La and compensated I Sa according to an embodiment of the invention;
FIG. 9A is a diagram of THD of compensated line voltage U ab according to an embodiment of the invention;
fig. 9B is a diagram of THD of compensated current I Sa according to an embodiment of the present invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, specific embodiments thereof will be described in detail below with reference to the drawings.
The definition of technical terms used in the present invention is as follows:
APF: active Power Filter, an active power filter, also known as an active filter;
SVPWM: space Vector Pulse Width Modulation, space vector pulse width modulation;
FFT: fast Fourier Transform, fast fourier transform, decomposing the periodic signal into a series of sinusoidal signals of different frequencies;
THD: total Harmonic Distortion, total harmonic distortion.
Fig. 1 is a schematic illustration of an APF topology and signal measurement points according to an embodiment of the present invention.
Main circuit topology
The embodiment of the invention is a parallel APF topology structure based on magnetic flux compensation, and as shown in fig. 1, a control system (not shown) of an active power filter adopts a single-phase independent control structure to compensate the harmonic current of the system. The control system of the active power filter may be any type of controller. In the active power filter, the low-voltage sides of the three single-phase transformers are each connected to a corresponding one of the three single-phase H-bridges by a filter component and the high-voltage sides W1 (grid side) of the transformers are each connected to the grid. The high-voltage sides of three single-phase transformers in the active power filter are connected in an angle mode, and the low-voltage sides of the three single-phase transformers are connected in a star mode. The signal measurement points in the topology structure are marked by arrows in the figure, and the following is specifically described by taking phase A as an example:
(1) The measuring point of the harmonic current i as selects a line between the APF parallel network point and the load to collect a current signal;
(2) The compensation current i ao selects a current signal at the outlet of the H bridge for acquisition;
(3) Collecting a three-phase H bridge direct current side capacitor voltage U adc as a direct current voltage control signal;
(4) The method comprises the steps that an alternating-current voltage feedforward control selects a port voltage U ao of a low-voltage side W2 (an inversion side of an H bridge) of a single-phase transformer to collect;
(4) The phase-locked control is involved in measuring the power grid line voltage signal U ab;
(5) And collecting a transformer grid side current signal I La and carrying out comparison analysis on the harmonic current.
In fig. 1, PI Section is a cable parameter setting module from a 10kV power grid to an active power filter and a harmonic load grid-connection point, U adc,Ubdc and U cdc are respectively direct-current side voltages of A, B, C three single-phase H-bridges, I La、ILb、ILc are respectively three-phase currents of the harmonic load, I Sa、ISb、ISc are respectively three-phase currents at an APF grid-connection point, I ao、ibo、ico are respectively output currents of A, B, C three-phase H-bridges, U ao、ubo、uco are respectively port voltages of a low-voltage side (an inversion side of the H-bridge) of a A, B, C three-phase transformer, I as、ibs、ics are respectively harmonic compensation currents of an active power filter A, B, C three-phase injection power grid, U ab,Ubc、Uca are respectively line voltages of power grids AB, BC and CA, L a1、Lb1、Lc1 are respectively filter inductances of A, B, C three single-phase H-bridges, C a、Cb、Cc is a filter capacitance of A, B, C, R a、Rb、Rc is a series resistance of the filter capacitance of A, B, C, and L a2、La2、La2 is an equivalent inductance of the three-phase transformer of the A, B, C.
Fig. 2 is a diagram of a single phase locked loop control based on virtual average reactive phase discrimination in accordance with an embodiment of the present invention.
In the phase-locked control system shown in fig. 2, a phase-locked loop is directly constructed by using a single-phase-locked loop scheme based on a single-phase variable by referring to the basic idea of multiplication phase-discrimination phase locking, that is, a closed-loop system can be constructed by taking the average value of the product of two orthogonal variables as a given variable and making the given variable zero.
Assuming that the fundamental component of the input voltage e i is Vcos θ, if the phase estimation value isDefining another accurate phase lock by using the principle of multiplication phase discriminatorVariables orthogonal thereto, i.e. virtual currentsAnd defining the product of the two as virtual reactive power p, filtering out 2 times of necessary harmonic waves, namely the average value of the reactive power p, and recording asConsistent with the phase locking principle of the multiplication phase discriminator, the phase locking method is realized through closed-loop controlWhen, i.e., the virtual current i s is orthogonal to the fundamental component of the input voltage, phase locking is achieved, the specific analysis is as follows.
Virtual reactive Power in FIG. 2The expression of (2) is:
The reactive power alternating current in the formula (1) is filtered by adopting a Low Pass Filter (LPF), and the average value of the reactive power can be obtained Consider at steady state: Angular velocity of Wherein the superscript indicates the corresponding estimate. Obviously for sufficiently small phase deviationsThen there are:
As can be seen from equation (2), if the average reactive power is controlled Zero, then in a steady state condition,Will be equal to the input voltage phase θ, so in a voltage and current dual closed loop feedback control strategy, the line voltage phase can be locked, i.e., taken, based on a single Phase Locked Loop (PLL) with virtual average reactive phase discrimination.
Fig. 3 is a diagram of APF intra-angular phase current calculation based on the principle of single phase power system harmonic detection, according to an embodiment of the present invention.
The ideal compensation effect is to make the power factor of the grid side be 1, i.e. the grid side current is in phase with the grid voltage and does not contain harmonic current. Thus, the APF needs to inject a harmonic current into the grid that is opposite to the load current harmonic component when reactive compensation and unbalance control are not considered. Angular phase current in net side angular connected APFFor the control object, the following relationship is satisfied between the line current and the intra-angular phase current which are injected into the power grid:
zero sequence current in (4) It can be seen that the reference value of the compensation current in the APF angle cannot be obtained by directly decomposing the three-phase load current on the network side.
In general, the three phase current of the load is known, reference (4), and there is an infinite set of solutions for converting the load current into an angular phase current since the zero sequence current is unknown. However, the analysis in physical terms shows that the zero sequence current in the equivalent angle of the load current does not affect the reactive power and the unbalance degree of the three-phase system, so that the value of the zero sequence current does not affect the extraction of the reference value of the compensation current. For unified processing with the reference value of the base frequency current, it is assumed thatThe equivalent conversion of load current into angular phase current of an angular connection has the following relationship:
the transformation of the formula (5) is based on the special connection mode of the transformer network side angle type connection and combines the premise of harmonic extraction and compensation control, and the compensation current injected by the APF is also necessarily compensation for the line current due to the connection mode of the network side angle type connection, so that the conversion of the line current into the in-angle phase current is a premise. Therefore, only the equivalent in-angle phase current to the load current is needed And processing, extracting harmonic current signals, and converting the power grid load current of the active power filter connected with the high-voltage side of the single-phase transformer in an angle mode into an angle phase current, so that a compensation current reference value can be calculated.
The harmonic detection method of the single-phase power system will be described below. The traditional current detection method is suitable for a three-phase power system and cannot be applied to a single-phase environment. Let the grid voltage of single-phase circuit be:
es(t)＝Um cos ωt (6)
the voltage sine signal with the same frequency and the same phase and the amplitude of 1 is:
us(t)＝cos ωt (7)
the periodic non-sinusoidal grid current signal containing harmonics is:
Fourier transforming equation (8) gives:
Order the Then equation (9) can be rewritten as:
It is apparent that I q (t) in the formula (10) represents an instantaneous fundamental reactive current, I p (t) represents an instantaneous fundamental active current, and I h (t) represents a harmonic current. If the instantaneous fundamental wave reactive current I q (t) and the instantaneous fundamental wave active current I p (t) can be separated from the current of the power system, the harmonic current I h (t) needing compensation can be eliminated. As shown in the following equation (11), u s (t) is multiplied by the single-phase grid current i s (t):
As can be seen from equation (11), the DC component has an amplitude of I p/2, which is exactly half the instantaneous active current amplitude. After the alternating current component is filtered by using the LPF, the amplitude I p/2 is the direct current component, the direct current component is expanded by 2 times, and the instantaneous fundamental wave active current amplitude can be obtained, so that the fundamental wave active current expression I p(t)＝Ip cos omega t can be obtained.
Multiplying the voltage signal with u s (t) phase lag of 90 DEG with the single-phase grid current i s (t) to obtain
The DC component in equation (12) has an amplitude I q/2, which is exactly half the instantaneous reactive current amplitude. After the alternating current component is filtered by the LPF, the direct current component with the amplitude of I q/2 can be obtained. The direct current component is expanded by 2 times, so that the instantaneous reactive current amplitude can be obtained, and the fundamental reactive current expression I q(t)＝Iq sin omega t can be obtained.
After subtracting the obtained fundamental reactive current and fundamental active current components from the grid load current, a harmonic current component I h (t) in the single-phase grid can be obtained, namely, the intra-angle phase current of the active power filter which is connected in an angle mode at the high-voltage side of the single-phase transformer is taken as a control object, and the fundamental reactive current and the fundamental active current are subtracted from the grid load current to extract a harmonic current signal.
Ih(t)＝is(t)-Iq(t)-Ip(t) (13)
Fig. 4 is a diagram of dc voltage and harmonic current tracking control according to an embodiment of the invention.
The dc voltage and harmonic current tracking control strategy will be described below. For single-phase parallel APF, voltage-current double closed loop feedback control is the most widely used control strategy. The voltage loop control objective is to maintain the stability of the direct-current side voltage, the stability of the direct-current voltage is the premise of the stable operation of the single-phase H bridge, the current loop control objective is to compensate the harmonic current, but the current loop control objective is different from the common control of converting the control quantity into the dq coordinate system for direct-current control, wherein the current loop control input quantity is an alternating-current component, the direct-current voltage loop control output quantity is a direct-current component, and the direct-current voltage loop PI output is multiplied by cos omega At for superposing the direct-current voltage control output quantity in the alternating-current voltage loop. The current inner loop and the voltage outer loop are the basis for the normal operation of the APF. The PI controller (for example, may be included in the controller of the active power filter) has the advantages of simple structure, convenient implementation, good performance and the like as a classical control technology, so that both the current loop and the voltage loop designed by the invention adopt PI controllers. Alternatively, the controller may also employ a repetitive controller, a PR controller, a P controller, or a PID controller. Taking phase a as an example, the control strategy is shown in fig. 4.
The embodiment of the invention adopts a voltage and current double closed loop feedback control strategy to independently control each H bridge in the three single-phase H bridges to carry out harmonic compensation, and a direct current voltage outer ring is arranged outside a current inner ring. In fig. 4, U adc_ref is a given reference value of a phase a dc side voltage, U adc is a voltage measurement value of an a phase dc side voltage measurement feedback signal, ω A t is a phase obtained by an a phase locked loop, K ah is a transformer transformation ratio, i ah is a harmonic component obtained by an a phase harmonic separation link, i ao is a measured value of an a phase H bridge output current feedback signal, voltage feedforward control U ao is an a phase transformer inversion side voltage signal, and U ar is a modulation signal generated by control as an input quantity of SVPWM.
The product of the voltage outer loop adjustment quantity and the harmonic current i ah extracted from the power grid and the transformer transformation ratio K ah is overlapped to be used as a current loop set value, the current loop set value is differentiated from a current measured value i ao on the alternating current side of each H bridge, and the result of the differentiation is subjected to finishing adjustment (for example, proportional integral PI adjustment and amplitude limiting adjustment) to obtain the input of the space vector pulse width modulation control of each H bridge. Preferably, the voltage reference value U adc_ref on the dc side of each H-bridge and the voltage measurement value U adc on the dc side of each H-bridge are differentiated, and a trimming adjustment is performed on the result of the differentiation (for example, the trimming adjustment may include performing PI adjustment and clipping adjustment), and the result of the trimming adjustment is multiplied by the cosine value cos ω A t of the grid voltage phase, to obtain the voltage outer loop adjustment amount. In this case, the a-phase is taken as an example, ω A t is an AB two-phase line voltage phase, and since the transformer network side adopts a delta connection mode, it is determined that the compensation current injected into the network side must compensate the line current harmonic wave, so both the harmonic wave extraction and the direct current voltage control should adopt corresponding line voltage phases.
Fig. 5A is a diagram of THD of line voltage U ab before compensation according to an embodiment of the present invention. Fig. 5B is a diagram of THD of current I Sa before compensation according to an embodiment of the present invention. Fig. 6 is a waveform diagram of I La and I Sa according to an embodiment of the present invention. Fig. 7 is a diagram of harmonic current I a_h and compensation current I as according to an embodiment of the invention. Fig. 8 is a diagram of load current I La and compensated I Sa according to an embodiment of the invention. Fig. 9A is a diagram of THD of compensated line voltage U ab according to an embodiment of the present invention. Fig. 9B is a diagram of THD of compensated current I Sa according to an embodiment of the present invention.
In the topology shown in fig. 1, the capacity of the harmonic load can be set to 380kVA. Taking phase a as an example, a THD diagram of the line voltage U ab and the current I Sa at the grid-connected point when the active power filter is not put into the power filter is shown in fig. 5, and fig. 6 is a comparison diagram of the load current I La and the current I Sa at the APF grid-connected point. As can be seen from fig. 5 and fig. 6, when the active power filter is not put into grid connection, the load current I La is basically coincident with the waveform of the current I Sa at the APF grid connection point, I Sa is severely affected by I La, the total harmonic distortion rate is up to 25%, and the total harmonic distortion rate of the line voltage U ab is about 5.05%.
After the active power filter is put into operation, fig. 7 to 9 show the same. Fig. 7 is a diagram showing a comparison of the harmonic current I a_h (blue curve in the figure) and the APF compensation current I as (green curve in the figure) obtained in the harmonic separation step, and it can be seen that the current compensated by the active power filter control strategy according to the present invention can better track the harmonic current; FIG. 8 is a diagram of a load current I La and a compensated I Sa, it can be seen that the compensated I Sa is substantially sinusoidal, and an active power filter according to an embodiment of the invention can have excellent compensation effects; fig. 9A and 9B show the THD of the compensated line voltage U ab and the current I Sa, wherein the THD of U ab is about 3.3%, the THD of I Sa is about 4.36%, and as can be seen from a comparison analysis with fig. 5, the active power filter according to the embodiment of the present invention has an effective compensation effect on the harmonic wave after being put into grid connection, and can reduce the total harmonic distortion of the voltage and the current at the grid connection point, and significantly improve the power quality. The B phase and the C phase are similar to the a phase, and a detailed description thereof will be omitted herein.
The method provided by the invention can provide the following advantages: the main circuit topology structure of three single-phase H bridges is adopted, and the three single-phase H bridges are output to a power grid through three single-phase step-up transformers (working in the linear section of a B-H curve), so that the application problem of an active power filter in a medium-voltage system is solved; the high-voltage side (network side) of the three single-phase step-up transformers adopts an angle connection mode, so that the problem that a medium-voltage system has no neutral line is solved; the phase-locked loop based on virtual average reactive phase discrimination solves the phase-locked problem of single-phase variables; based on the concept of the instantaneous reactive power theory, coordinate transformation and filtering control are carried out on load current, so that the problem of harmonic detection of a single-phase circuit is solved; the output quantity of the direct current voltage control loop is multiplied by cos omega t and converted into an alternating current system to be used as the given value input of a current loop, so that the control problem of direct current voltage is solved; a single-phase SVPWM control technology is adopted in the parallel active power filter.
There is also provided, in accordance with an exemplary embodiment of the present invention, a medium voltage three-phase parallel active power filter for a micro-grid, the active power filter including: three single-phase H-bridges; three single-phase transformers, the low-voltage sides of which are respectively connected to a corresponding one of the single-phase H-bridges through a filter assembly, and the high-voltage sides of which are all connected to the bus bars of the micro-grid. The high-voltage sides of three single-phase transformers in the active power filter are connected in an angle mode, and the low-voltage sides of the three single-phase transformers are connected in a star mode.
The active power filter further includes: and the controller is used for independently controlling each H bridge in the three single-phase H bridges by adopting a voltage and current double-closed loop feedback control strategy so as to carry out harmonic compensation. The controller is configured to: and superposing the voltage outer loop regulating quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop given value, calculating the difference value between the current loop given value and the current measured value of the alternating current side of each H bridge, and carrying out sorting regulation on the result of calculating the difference value to obtain the input of the space vector pulse width modulation control of each H bridge, wherein the controller calculates the difference value between the voltage reference value of the direct current side of each H bridge and the voltage measured value of the direct current side of each H bridge, carries out sorting regulation on the result of calculating the difference value, and multiplies the result of sorting regulation by the cosine value of the power grid voltage phase to obtain the voltage outer loop regulating quantity.
According to an exemplary embodiment of the present invention, there is further provided a medium-voltage three-phase parallel active power filtering control method for a micro-grid, where the control method uses a voltage and current dual closed loop feedback control strategy, a high-voltage side of three single-phase transformers of an active power filter connected to a micro-grid bus is connected in an angle type, and a low-voltage side of the three single-phase transformers is connected in a star type. The control method further includes: and superposing the voltage outer loop regulating quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop given value, calculating the difference value between the current loop given value and the current measured value of the alternating current side of each H bridge in the three single-phase H bridges of the active power filter, and finishing and regulating the difference value result to obtain the input of the space vector pulse width modulation control of each H bridge. And obtaining the voltage outer ring adjustment quantity by obtaining a difference value from the voltage reference value of the direct current side of each H bridge and the voltage measurement value of the direct current side of each H bridge, executing finishing adjustment on the result of the difference value, and multiplying the result after finishing adjustment by the cosine value of the voltage phase of the power grid.
There is also provided, in accordance with an exemplary embodiment of the present invention, a computer-readable storage medium storing a computer program. The computer readable storage medium stores instructions that, when executed by a processor, cause the processor to perform a medium voltage parallel active power filter control method according to the present invention. The computer readable recording medium is any data storage device that can store data which can be read out by a computer system. Examples of the computer-readable recording medium include: read-only memory, random access memory, compact disc read-only, magnetic tape, floppy disk, optical data storage device, and carrier waves (such as data transmission through the internet via wired or wireless transmission paths).
There is also provided, in accordance with an exemplary embodiment of the present invention, a computer device. The computer device includes a processor and a memory. The memory is used for storing a computer program. The computer program is executed by a processor to cause the processor to perform the medium voltage parallel active power filter control method according to the invention.
While particular embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the following claims and their equivalents, which are to be accorded the full scope of the invention as defined by the appended claims.
Claims (20)
1. A medium voltage three-phase parallel active power filter for use in a medium voltage micro grid power system without a neutral line, the active power filter comprising:
Three single-phase H-bridges;
three single-phase transformers, the low-voltage sides of the three single-phase transformers are respectively connected to a corresponding one of the single-phase H bridges through a filter assembly, and the high-voltage sides of the three single-phase transformers are connected to a power grid;
A controller which independently controls each of the three single-phase H-bridges for harmonic compensation using a voltage and current dual closed loop feedback control strategy,
Wherein, the high-voltage sides of three single-phase transformers in the active power filter are connected by adopting an angle type, the low-voltage sides of the three single-phase transformers are connected by adopting a star type,
The method comprises the steps of obtaining a line voltage phase based on a virtual average reactive phase discrimination single-phase-locked loop, converting a grid load current of an active power filter connected at a high voltage side of the single-phase transformer in an angle mode into an intra-angle phase current, setting zero sequence current to be zero, wherein a current loop control input quantity of a voltage and current double-closed loop feedback control strategy is an alternating current time domain signal, and a voltage loop control output quantity multiplied by cos omega t is superposed in an alternating current control loop.
2. The medium voltage three phase parallel active power filter of claim 1,
Wherein the controller is configured to: and superposing the voltage outer loop regulating quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop given value, calculating the difference value between the current loop given value and the current measured value of the alternating current side of each H bridge, and carrying out sorting regulation on the result of calculating the difference value to obtain the input of the space vector pulse width modulation control of each H bridge, wherein the controller calculates the difference value between the voltage reference value of the direct current side of each H bridge and the voltage measured value of the direct current side of each H bridge, carries out sorting regulation on the result of calculating the difference value, and multiplies the result of sorting regulation by the cosine value of the power grid voltage phase to obtain the voltage outer loop regulating quantity.
3. The medium voltage three phase parallel active power filter of claim 2 wherein in a voltage and current dual closed loop feedback control strategy, the controller controls the current inner loop to control the main circuit to track a current setpoint and controls the dc voltage outer loop to control the dc side voltage stabilization of each H-bridge.
4. A medium voltage three phase parallel active power filter according to claim 3 wherein the dc voltage outer loop is outside the current inner loop in a voltage and current double closed loop feedback control strategy.
5. The medium voltage three phase parallel active power filter of claim 2 wherein the controller selects the single phase transformer low voltage side for voltage harvesting for ac voltage feedforward control in a voltage and current double closed loop feedback control strategy.
6. The medium-voltage three-phase parallel active power filter according to claim 2, wherein in the voltage and current double closed-loop feedback control strategy, the controller takes the in-angle phase current of the active power filter connected in an angle mode on the high-voltage side of the single-phase transformer as a control object, and subtracts the fundamental reactive current and the fundamental active current from the grid load current to extract the harmonic current signal.
7. The medium voltage three phase parallel active power filter of claim 2 wherein the trim adjustment includes a proportional integral adjustment and a clipping adjustment.
8. The utility model provides a three-phase parallelly connected type active power filter control method of middling pressure, its characterized in that, control method adopts voltage and electric current double closed loop feedback control strategy to little electric wire netting electric power system, and the high-voltage side of three single-phase transformers of active power filter adopts angle type connection, and the low-voltage side of three single-phase transformers adopts star type connection, and control method includes:
Superposing the voltage outer loop regulating quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop given value, calculating the difference value between the current loop given value and the current measured value of the alternating current side of each H bridge in the three single-phase H bridges of the active power filter, sorting and regulating the difference value result to obtain the input of the space vector pulse width modulation control of each H bridge,
Wherein the voltage outer loop adjustment amount is obtained by taking a difference between the voltage reference value of the direct current side of each H bridge and the voltage measurement value of the direct current side of each H bridge, executing finishing adjustment on the result of the difference, multiplying the result of the finishing adjustment by the cosine value of the voltage phase of the power grid,
The method comprises the steps of obtaining a line voltage phase based on a virtual average reactive phase discrimination single-phase-locked loop, converting a grid load current of an active power filter connected at a high voltage side of the single-phase transformer in an angle mode into an intra-angle phase current, setting zero sequence current to be zero, wherein a current loop control input quantity of a voltage and current double-closed loop feedback control strategy is an alternating current time domain signal, and a voltage loop control output quantity multiplied by cos omega t is superposed in an alternating current control loop.
9. The control method of claim 8, wherein in a voltage and current dual closed loop feedback control strategy, a current inner loop is used to control the main circuit to track a current set point, and a dc voltage outer loop is used to control the dc side voltage stabilization of each H-bridge.
10. The control method of claim 9, wherein the dc voltage outer loop is outside the current inner loop in a voltage and current dual closed loop feedback control strategy.
11. The control method of claim 8, wherein in the voltage and current dual closed loop feedback control strategy, the voltage acquisition is selected on the low voltage side of the single phase transformer for ac voltage feedforward control.
12. The control method of claim 8, wherein the line voltage phase is obtained based on a virtual average reactive phase discrimination single phase locked loop in a voltage and current dual closed loop feedback control strategy.
13. The control method of claim 8, wherein in a voltage and current dual closed loop feedback control strategy, the grid load current of an active power filter connected in an angle at the high voltage side of a single phase transformer is converted to an in-angle phase current.
14. The control method according to claim 8, wherein in the voltage and current double closed loop feedback control strategy, the harmonic current signal is extracted by subtracting the fundamental reactive current and the fundamental active current from the grid load current with the control object of the in-corner phase current of the active power filter connected in an angle at the high voltage side of the single-phase transformer.
15. The control method of claim 8, wherein the trim adjustment includes a proportional integral adjustment and a clipping adjustment.
16. A medium voltage three-phase parallel active power filter for a microgrid, characterized in that it is applied to a medium voltage microgrid power system without a neutral line, the active power filter comprising:
Three single-phase H-bridges;
Three single-phase transformers, the low-voltage sides of the three single-phase transformers are respectively connected to a corresponding one of the single-phase H bridges through a filtering component, and the high-voltage sides of the three single-phase transformers are connected to a bus of a micro-grid;
A controller which independently controls each of the three single-phase H-bridges for harmonic compensation using a voltage and current dual closed loop feedback control strategy,
Wherein, the high-voltage sides of three single-phase transformers in the active power filter are connected by adopting an angle type, the low-voltage sides of the three single-phase transformers are connected by adopting a star type,
The method comprises the steps of obtaining a line voltage phase based on a virtual average reactive phase discrimination single-phase-locked loop, converting a grid load current of an active power filter connected at a high voltage side of the single-phase transformer in an angle mode into an intra-angle phase current, setting zero sequence current to be zero, wherein a current loop control input quantity of a voltage and current double-closed loop feedback control strategy is an alternating current time domain signal, and a voltage loop control output quantity multiplied by cos omega t is superposed in an alternating current control loop.
17. The medium voltage three phase parallel active power filter of claim 16,
Wherein the controller is configured to: and superposing the voltage outer loop regulating quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop given value, calculating the difference value between the current loop given value and the current measured value of the alternating current side of each H bridge, and carrying out sorting regulation on the result of calculating the difference value to obtain the input of the space vector pulse width modulation control of each H bridge, wherein the controller calculates the difference value between the voltage reference value of the direct current side of each H bridge and the voltage measured value of the direct current side of each H bridge, carries out sorting regulation on the result of calculating the difference value, and multiplies the result of sorting regulation by the cosine value of the power grid voltage phase to obtain the voltage outer loop regulating quantity.
18. The utility model provides a medium voltage three-phase parallel active power filter control method for micro grid, characterized in that is applied to the medium voltage micro grid power system of no central line, the control method adopts voltage and electric current double closed loop feedback control strategy, the high voltage side of three single phase transformers of active power filter that are connected to micro grid busbar adopts angle type connection, the low voltage side of three single phase transformers adopts star type connection, wherein, the control method still includes:
Superposing the voltage outer loop regulating quantity and the product of the harmonic current extracted from the power grid and the transformer transformation ratio as a current loop given value, calculating the difference value between the current loop given value and the current measured value of the alternating current side of each H bridge in the three single-phase H bridges of the active power filter, sorting and regulating the difference value result to obtain the input of the space vector pulse width modulation control of each H bridge,
Wherein the voltage outer loop adjustment amount is obtained by taking a difference between the voltage reference value of the direct current side of each H bridge and the voltage measurement value of the direct current side of each H bridge, executing finishing adjustment on the result of the difference, multiplying the result of the finishing adjustment by the cosine value of the voltage phase of the power grid,
The method comprises the steps of obtaining a line voltage phase based on a virtual average reactive phase discrimination single-phase-locked loop, converting a grid load current of an active power filter connected at a high voltage side of the single-phase transformer in an angle mode into an intra-angle phase current, setting zero sequence current to be zero, wherein a current loop control input quantity of a voltage and current double-closed loop feedback control strategy is an alternating current time domain signal, and a voltage loop control output quantity multiplied by cos omega t is superposed in an alternating current control loop.
19. A computer-readable storage medium storing a computer program, characterized in that the computer program, when executed by a processor, implements the medium-voltage three-phase parallel type active power filter control method according to any one of claims 8 to 15.
20. A computer device, the computer device comprising:
A processor;
a memory storing a computer program which, when executed by a processor, implements the medium-voltage three-phase parallel active power filter control method according to any one of claims 8 to 15.
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| CN201911316278.9A CN113013882B (en) | 2019-12-19 | Medium-voltage parallel active power filter and control method |
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| CN206041494U (en) * | 2016-01-19 | 2017-03-22 | 北京禄智科技股份有限公司 | High frequency active power filter |
| CN108490295A (en) * | 2018-04-25 | 2018-09-04 | 合肥为民电源有限公司 | A kind of active island detection method and device based on virtually average idle phase demodulation |
| CN109742758A (en) * | 2019-01-04 | 2019-05-10 | 南京亚派科技股份有限公司 | A kind of APF compensation method based on Dyn11 transformer |
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN206041494U (en) * | 2016-01-19 | 2017-03-22 | 北京禄智科技股份有限公司 | High frequency active power filter |
| CN108490295A (en) * | 2018-04-25 | 2018-09-04 | 合肥为民电源有限公司 | A kind of active island detection method and device based on virtually average idle phase demodulation |
| CN109742758A (en) * | 2019-01-04 | 2019-05-10 | 南京亚派科技股份有限公司 | A kind of APF compensation method based on Dyn11 transformer |
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