CN112366723A - Electric energy quality comprehensive treatment device and method thereof - Google Patents

Electric energy quality comprehensive treatment device and method thereof Download PDF

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Publication number
CN112366723A
CN112366723A CN202011248628.5A CN202011248628A CN112366723A CN 112366723 A CN112366723 A CN 112366723A CN 202011248628 A CN202011248628 A CN 202011248628A CN 112366723 A CN112366723 A CN 112366723A
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phase
voltage
current
sequence
controller
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CN112366723B (en
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李新元
马骏
刘向立
林焱
高鹏
于浩然
吕海超
申振东
程兴邦
刘超
窦亚力
王佰超
宋红龙
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Xuji Group Co Ltd
XJ Electric Co Ltd
Electric Power Research Institute of State Grid Fujian Electric Power Co Ltd
State Grid Fujian Electric Power Co Ltd
Xuji Power Co Ltd
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Xuji Group Co Ltd
XJ Electric Co Ltd
Electric Power Research Institute of State Grid Fujian Electric Power Co Ltd
State Grid Fujian Electric Power Co Ltd
Xuji Power Co Ltd
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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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
    • 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
    • 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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

A comprehensive treatment device and method of electric energy quality, the apparatus includes converter module and control module; the converter module comprises an NPC three-level inverter circuit and a filter; the direct-current bus voltage outputs three-phase voltage and current of a power grid through the NPC three-level inverter circuit and the filter; the control module comprises a PLL phase-locked loop, a DFT detection unit, a voltage outer loop controller, a current inner loop controller and a feedforward voltage controller. The invention improves the control module, so that the electric energy quality comprehensive treatment device has a phase sequence self-adaptive function, simplifies the operation and reduces the cost. The phase sequence is quickly and accurately detected through the program, the phase sequence self-adaptive control is realized through the program modification control strategy, and the additional hardware cost is not required to be increased; by using a uniform current detection method, the functions of reactive power compensation, three-phase imbalance compensation, harmonic compensation and inter-harmonic compensation can be realized under different phase sequences.

Description

Electric energy quality comprehensive treatment device and method thereof
Technical Field
The invention relates to the technical field of power systems, in particular to a comprehensive treatment device and method for power quality.
Background
The problems of low power quality, high line loss, incapability of managing loads and the like caused by unbalanced three phases, low power factor, high reactive power, excessive harmonic and inter-harmonic content and the like exist in the conventional power distribution station. The problems of power quality in distribution in a distribution area cause unstable voltage, and in severe cases, power equipment facilities such as transformers and the like can be damaged, so that effective output of distribution transformers is limited, the power conversion efficiency is reduced, the power supply quality of a power grid is influenced, normal power consumption in production and life can be influenced, voltage breakdown can even occur in severe cases, large-area power failure is caused, and inestimable severe consequences are generated. With the construction of smart power grids, power distribution automation has been developed greatly, and the construction of smart distribution areas for improving the quality of electric energy is also an inevitable trend. The power electronic type power quality control device adopts a high-power turn-off type power electronic technology, and is power quality control equipment for main current in the industry at present. As a network-connected device, it is necessary to detect the phase sequence correctly and perform phase locking. At present, the electric energy quality treatment device in the industry only has a phase sequence judgment function, and can normally work only when the voltage of a power grid is in a positive sequence, otherwise, the device reports a phase sequence error and gives an alarm. Therefore, field installation and debugging personnel must firstly detect the phase of the power grid voltage, and manually adjust the wiring when the phase sequence is incorrect. Because the electric energy quality treatment device of platform district is the suspension installation on the post usually, consequently not only increase manpower and materials cost, troublesome moreover operation.
The electric energy quality comprehensive treatment device without the phase sequence self-adaption function is applied to the power distribution station, and is both cost and power consumption, so that the electric energy quality comprehensive treatment device in the station has the phase sequence self-adaption function and gradually becomes the rigid requirement of a user. Aiming at the problem, the influence of the phase sequence on the control of the electric energy quality comprehensive treatment device is researched, the control strategy of the electric energy quality comprehensive treatment device is modified through software, the electric energy quality comprehensive treatment device has the phase sequence self-adaption function, and the method has extremely important practical significance.
Disclosure of Invention
The invention aims to provide a device and a method for comprehensively treating power quality aiming at the defects of the prior art, and the device and the method are realized by adopting the following technical scheme:
the invention provides a power quality comprehensive treatment device, which comprises a converter module and a control module, wherein the converter module is connected with the control module;
the converter module comprises an NPC three-level inverter circuit and a filter; the direct-current bus voltage outputs three-phase voltage and current of a power grid through the NPC three-level inverter circuit and the filter;
the control module comprises a PLL (phase locked loop), a DFT (discrete Fourier transform) detection unit, a voltage outer loop controller, a current inner loop controller and a feedforward voltage controller;
the PLL is used for judging the phase sequence of the three-phase voltage of the power grid and locking the phase of the three-phase voltage;
the DFT detection unit detects three-phase load current and extracts fundamental active current, fundamental reactive current and harmonic and inter-harmonic current which are respectively used for reactive compensation, harmonic and inter-harmonic compensation under different phase sequences;
the voltage outer ring controller is used for stabilizing and equalizing the voltage of the direct current bus;
and signals output after the signals respectively pass through the PLL, the DFT detection unit and the voltage outer loop controller are superposed with the three-phase current of the power grid to form a current instruction signal which is input into the voltage inner loop controller, and the current instruction signal is output after the output is superposed with the three-phase voltage of the power grid and is processed by the feedforward voltage controller.
Further, the PLL phase-locked loop is used for performing phase sequence determination on the three-phase voltage of the power grid and performing phase locking on the three-phase voltage of the power grid, and includes:
sampling the three-phase voltage of the power grid, judging a positive sequence and a negative sequence according to preset conditions, and if the positive sequence is positive, locking the phase according to the following settings: the first phase has a phase theta and the second phase has a phase theta
Figure BDA0002770856660000021
The third phase is
Figure BDA0002770856660000022
If the negative sequence is adopted, the phase locking is carried out according to the following setting: the first phase has a phase theta and the second phase has a phase theta
Figure BDA0002770856660000023
The third phase is
Figure BDA0002770856660000024
Further, the DFT detection unit is used for the current signal i as followsn(k) And (3) processing:
Figure BDA0002770856660000031
Figure BDA0002770856660000032
wherein N is the number of sampling points in each fundamental wave period; k is 0,1,2 … (N-1); t is the fundamental wave signal period; τ is T/N; i (k tau) is the sampling value of the kth sampling point, theta is the phase, and n is the harmonic frequency;
when the phase sequence is positive:
the first phase is: θ is 0; the second phase is:
Figure BDA0002770856660000033
the third phase is:
Figure BDA0002770856660000034
when the phase sequence is negative:
the first phase is: θ is 0; the second phase is:
Figure BDA0002770856660000035
the third phase is:
Figure BDA0002770856660000036
further, the voltage outer ring controller comprises a voltage stabilizing ring and a voltage equalizing ring, which are respectively realized by PI regulators.
Further, the voltage stabilizing ring acquires positive and negative bus voltages Udc1 and Udc2 on the direct current side through the DSP, the sum of the positive and negative bus voltages is differed with a given bus voltage, an error signal is sent to the PI controller, and the obtained active components Iapref, Ibpref and Icprof are superposed on the current command signal through DQ inverse transformation.
Further, the DQ inverse transformation includes:
judging the phase sequence, and performing positive sequence DQ inverse transformation when the phase sequence is a positive sequence; and when the sequence is negative, carrying out inverse transformation of the negative sequence DQ.
Further, the feedforward voltage controller performs feedforward voltage control according to different phase sequences:
when the phase sequence is positive, the voltage feed forward is:
Figure BDA0002770856660000037
when the phase sequence is negative, the voltage feed forward is:
Figure BDA0002770856660000041
in the formula (I), the compound is shown in the specification,
Figure BDA0002770856660000042
is the instantaneous value of the three-phase voltage of the power grid,
Figure BDA0002770856660000043
the effective value of the three-phase voltage of the power grid is obtained.
The second aspect of the invention provides a power quality comprehensive treatment method, which adopts the power quality comprehensive treatment device to carry out comprehensive treatment and comprises the following steps:
the PLL judges the phase sequence of the three-phase voltage of the power grid and locks the phase of the three-phase voltage;
the DFT detection unit detects the three-phase load current, extracts fundamental active current, fundamental reactive current, harmonic and inter-harmonic current, and respectively performs reactive compensation, harmonic and inter-harmonic compensation under different phase sequences;
the voltage outer ring controller is used for stabilizing and equalizing the voltage of the direct current bus;
after each signal passes through the PLL, the DFT detection unit and the voltage outer loop controller respectively, the output signal is superposed with the three-phase current of the power grid to form a current command signal input voltage inner loop controller;
the output processed by the voltage inner-loop controller is superposed with the three-phase voltage of the power grid and then is processed by the feedforward voltage controller and then is output.
In summary, the invention provides a device and a method for comprehensive treatment of electric energy quality, wherein the device comprises a converter module and a control module; the converter module comprises an NPC three-level inverter circuit and a filter; the direct-current bus voltage outputs three-phase voltage and current of a power grid through the NPC three-level inverter circuit and the filter; the control module comprises a PLL phase-locked loop, a DFT detection unit, a voltage outer loop controller, a current inner loop controller and a feedforward voltage controller. The invention improves the control module, so that the electric energy quality comprehensive treatment device has a phase sequence self-adaptive function, simplifies the operation and reduces the cost.
The beneficial technical effects of the invention are as follows:
(1) the phase sequence can be quickly and accurately detected through a program, the phase sequence self-adaptive control is realized through a program modification control strategy, and extra hardware cost is not required to be increased;
(2) by using a uniform current detection method, the functions of reactive power compensation, three-phase unbalance compensation, harmonic compensation and inter-harmonic compensation can be realized under different phase sequences;
(3) by adopting a three-level topology and an LCLLC filter, the whole machine has small loss and good compensation effect;
(4) the device can perform web access or APP operation through a mobile phone, an iPad, a notebook computer and the like, so that the functions of remote measurement, remote control, remote signaling, remote regulation and fixed value calling are realized.
Drawings
FIG. 1 is a schematic view of a system configuration of an electric energy quality comprehensive treatment apparatus according to an embodiment of the present invention;
FIG. 2(a) is an NPC three-level inverter circuit; FIG. 2(b) is a schematic diagram of a filter circuit;
FIG. 3 is a block diagram of a control strategy architecture;
FIG. 4 is a phase lock control block diagram;
FIG. 5 is a phase lock control flow chart;
FIG. 6 is a block diagram of a DC side voltage stabilization ring implementation strategy;
FIG. 7 is a flow chart of DC voltage regulation loop control;
fig. 8 is a schematic flow chart of the power quality comprehensive treatment method according to the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
The electric energy quality comprehensive treatment device system with the phase sequence self-adaption function is shown in a figure 1, a main circuit topology is shown in a figure 2, specific control strategies are shown in figures 3-7, and the realization of the phase sequence self-adaption function is described from the composition, the function and the control strategies by combining figures 1-7, and the specific implementation mode is as follows:
as shown in figure 1, the device is an electric energy quality comprehensive treatment device with a phase sequence self-adaption function and comprises a converter module, an input circuit breaker, a lightning protection device, a wifi module, an external cooling fan, a temperature and humidity sensor and the like.
The main circuit of the converter module is shown in a schematic block diagram in fig. 2(a), the main circuit adopts an NPC three-level inverter circuit, a neutral point of the circuit is extracted from a midpoint of a direct-current bus capacitor, Q1-Q3 are three-phase IGBT devices, Udc is direct-current bus voltage, E1 is a positive bus capacitor, E2 is a negative bus capacitor, Udc1 is positive bus voltage, Udc2 is negative bus voltage, Uina-Uinc is inverter side three-phase voltage, Usa-Usc are grid three-phase voltage, and RELAY 1-RELAY 3 are three-phase main RELAYs. As shown in fig. 2(b), the filter circuit adopts an LCLLC filter, L1-L3 are inverter-side high-frequency filter inductors, L4-L6 are network-side inductors, C1-C3 are ac filter capacitors, R1-R3 are capacitor branch damping resistors, Lf 1-Lf 3 are series resonant branch resonant inductors, and Cf 1-Cf 3 are series resonant branch resonant capacitors. Compared with the LCL filter, the LCLLC filter increases the resonant inductance and the resonant capacitance. The series resonant branch generates resonance at the switching frequency to provide a filtering path with zero impedance, thereby achieving the best filtering effect at the designated frequency. Meanwhile, the circuit of the capacitor connected in parallel with the series resonance branch circuit ensures that the filter can have a high harmonic attenuation rate of-60 dB/dec in a high frequency band, thereby ensuring the filtering performance of the filter in the high frequency band.
The control strategy is shown in fig. 3, Udc1 is a positive bus voltage, Udc2 is a negative bus voltage, Udcref is a given value of the bus voltage, Ila, Ilb and Ilc are three-phase load currents, Usa, Usb and Usc are three-phase grid voltages, and Ica, Icb and Icc are three-phase currents output by the device; it can be seen that the PLL phase-locked loop is used to detect the grid voltage synchronization signal for phase locking; because the electric energy quality comprehensive treatment device needs to have the functions of unbalance compensation, reactive compensation and harmonic and inter-harmonic compensation, fundamental active current, fundamental reactive current and inter-harmonic current are extracted through a DFT-based detection algorithm, the fundamental active current is extracted to be used for calculating the current value to be transferred of each phase reaching a balance state, the fundamental reactive current is extracted to be used for reactive compensation, and the harmonic and inter-harmonic current is extracted to be used for harmonic and inter-harmonic compensation; the voltage outer ring comprises a voltage stabilizing ring and a voltage equalizing ring, the voltage stabilizing ring is used for ensuring the voltage at the direct current side to be stable, the voltage equalizing ring is used for realizing the voltage equalizing of the positive bus and the negative bus and maintaining the stability of the midpoint voltage at the direct current side, and a PI regulator is adopted because the direct current quantity is controlled; the current inner loop controller is used for tracking the change of the instruction current and controlling the alternating current, so that a PR + PI combined composite controller is adopted to ensure the compensation effect and the influence speed of the system; feed forward voltage control is used to reduce the effects of grid voltage fluctuations.
Therefore, the invention provides a comprehensive treatment device for power quality in a first aspect, which comprises a converter module and a control module; the converter module comprises an NPC three-level inverter circuit and a filter; the direct-current bus voltage outputs three-phase voltage and current of a power grid through the NPC three-level inverter circuit and the filter; the control module comprises a PLL (phase locked loop), a DFT (discrete Fourier transform) detection unit, a voltage outer loop controller, a current inner loop controller and a feedforward voltage controller; the PLL is used for judging the phase sequence of the three-phase voltage of the power grid and locking the phase of the three-phase voltage; the DFT detection unit detects the three-phase load current and extracts fundamental active current, fundamental reactive current and harmonic and inter-harmonic current which are respectively used for reactive compensation, harmonic and inter-harmonic compensation under different phase sequences; the voltage outer ring controller is used for stabilizing and equalizing the voltage of the direct current bus; and signals output after the signals respectively pass through the PLL, the DFT detection unit and the voltage outer loop controller are superposed with the three-phase current of the power grid to form a current instruction signal which is input into the voltage inner loop controller, and the current instruction signal is output after the output is superposed with the three-phase voltage of the power grid and is processed by the feedforward voltage controller.
The device functions are as follows: the device has the phase sequence self-adaptation function, can realize under different phase sequences idle work, unbalanced three-phase, harmonic and inter-harmonic compensation function.
The comprehensive electric energy quality treating device is connected to the power grid in six wiring modes, and three phases are defined as the first phase-1 according to the sequence of the connected devicesstphase, second phase-2ndphase and third phase-3rdphase。
Figure BDA0002770856660000071
No matter which type of connection is adopted by the device, the control strategy is executed only by dividing the positive sequence and the negative sequence, and the phase-locking, the current detection, the direct-current bus voltage stabilizing ring and the voltage feedforward of the electric energy quality comprehensive treatment device can be influenced by the difference of the phase sequence.
Further, the PLL phase-locked loop is used for performing phase sequence determination on the three-phase voltage of the power grid and performing phase locking on the three-phase voltage of the power grid, and includes: sampling the three-phase voltage of the power grid, judging a positive sequence and a negative sequence according to preset conditions, and if the positive sequence is positive, locking the phase according to the following settings: the first phase has a phase theta and the second phase has a phase theta
Figure BDA0002770856660000081
The third phase is
Figure BDA0002770856660000082
If the negative sequence is adopted, the phase locking is carried out according to the following setting: the first phase has a phase theta and the second phase has a phase theta
Figure BDA0002770856660000083
The third phase is
Figure BDA0002770856660000084
Specifically, the judgment of the phase sequence adopts positive sequence DQ conversion and negative sequence DQ conversion for judgment; the device adopts a Fourier transform method to carry out phase locking, fundamental wave information (including phase and amplitude) in an input signal can be extracted through an FFT algorithm, and the method can eliminate the influence of harmonic waves in an external synchronous signal. Since the phase calculated by the FFT is the phase difference of the input signal and the internal reference signal, it can be used for phase discrimination of the phase locked loop. As shown in fig. 4, the phase-locked control block diagram obtains Δ θ as a phase-locked loop error adjustment signal by performing fourier transform and arc tangent operation (as shown in the following formula) on an input signal u (t), and outputs the Δ θ as an error signal Δ f of the locked frequency, Δ f and a frequency reference value f as an input of the proportional-integral controller0F is obtained by addition, and a phase signal theta is generated through the action of an integral controller.
Let u (t) be the input signal, transform the relation as follows:
Figure BDA0002770856660000085
whatever the wiring, the device is a lock 1stphase, fig. 5 shows a specific positive-sequence and negative-sequence phase-locking control flow chart.
Furthermore, the device adopts a DFT-based current detection method, can simultaneously realize detection of unbalance, reactive power, harmonic waves and inter-harmonic waves, and a current signal in(k) The discretized fourier expression of (a) is as follows:
Figure BDA0002770856660000086
Figure BDA0002770856660000087
wherein N is the number of sampling points in each fundamental wave period; k is 0,1,2 … (N-1); t is the fundamental wave signal period; τ is T/N; i (k tau) is the sampling value of the kth sampling point, theta is the phase, and n is the harmonic frequency;
when the phase sequence is positive:
first phase 1stThe phase is: θ is 0; second phase 2ndThe phase is:
Figure BDA0002770856660000091
third phase 3rdThe phase is:
Figure BDA0002770856660000092
when the phase sequence is negative:
first phase 1stThe phase is: θ is 0; second phase 2ndThe phase is:
Figure BDA0002770856660000093
third phase 3rdThe phase is:
Figure BDA0002770856660000094
further, the voltage outer ring controller comprises a voltage stabilizing ring and a voltage equalizing ring, which are respectively realized by PI regulators. The voltage stabilizing ring acquires positive and negative bus voltages Udc1 and Udc2 on the direct current side through the DSP, makes a difference between the sum of the positive and negative bus voltages and a given bus voltage, sends an error signal to the PI controller, and superimposes the obtained active components Iapref, Ibpref and Icprof on a current command signal through DQ inverse transformation. Taking the positive sequence U-V-W as an example, the control strategy block diagram is shown in FIG. 6. Fig. 7 shows a control flow of the phase sequence adaptive voltage stabilization loop.
Further, the DQ inverse transformation includes: judging the phase sequence, and performing positive sequence DQ inverse transformation when the phase sequence is a positive sequence; and when the sequence is negative, carrying out inverse transformation of the negative sequence DQ.
Specifically, positive sequence DQ conversion:
Figure BDA0002770856660000095
negative sequence DQ conversion:
Figure BDA0002770856660000101
wherein, Ud、UqRespectively d-axis and q-axis voltages.
Furthermore, in order to reduce the impact of the power grid voltage fluctuation on the direct current bus of the power quality comprehensive treatment device and improve the dynamic performance of the device, feedforward voltage control needs to be added in the device control strategy. The feedforward voltage controller performs feedforward voltage control according to different phase sequences:
when the phase sequence is positive, the voltage feed forward is:
Figure BDA0002770856660000102
when the phase sequence is negative, the voltage feed forward is:
Figure BDA0002770856660000103
in the formula (I), the compound is shown in the specification,
Figure BDA0002770856660000104
is the instantaneous value of the three-phase voltage of the power grid,
Figure BDA0002770856660000105
the effective value of the three-phase voltage of the power grid is obtained.
The second aspect of the present invention provides a power quality comprehensive treatment method, which uses the power quality comprehensive treatment device as described above to perform comprehensive treatment, as shown in fig. 8, and includes the following steps:
and S100, the phase sequence of the three-phase voltage of the power grid is judged by the PLL and phase locking is carried out on the three-phase voltage.
Step S200, a DFT detection unit detects the three-phase load current, extracts fundamental active current, fundamental reactive current, harmonic and inter-harmonic current, and respectively performs reactive compensation, harmonic and inter-harmonic compensation under different phase sequences.
And step S300, the voltage outer loop controller carries out voltage stabilization and voltage equalization on the direct current bus voltage.
And S400, superposing signals output after the signals pass through the PLL, the DFT detection unit and the voltage outer loop controller respectively and the three-phase current of the power grid to form a current command signal input voltage inner loop controller.
And S500, superposing the output processed by the voltage inner-loop controller and the three-phase voltage of the power grid, and then processing the superposed output by the feedforward voltage controller and outputting the processed output.
In summary, the invention provides a device and a method for comprehensive treatment of electric energy quality, wherein the device comprises a converter module and a control module; the converter module comprises an NPC three-level inverter circuit and a filter; the direct-current bus voltage outputs three-phase voltage and current of a power grid through the NPC three-level inverter circuit and the filter; the control module comprises a PLL phase-locked loop, a DFT detection unit, a voltage outer loop controller, a current inner loop controller and a feedforward voltage controller. The invention improves the control module, so that the electric energy quality comprehensive treatment device has a phase sequence self-adaptive function, simplifies the operation and reduces the cost. The phase sequence is quickly and accurately detected through the program, the phase sequence self-adaptive control is realized through the program modification control strategy, and the additional hardware cost is not required to be increased; by using a uniform current detection method, the functions of reactive power compensation, three-phase unbalance compensation, harmonic compensation and inter-harmonic compensation can be realized under different phase sequences; by adopting a three-level topology and an LCLLC filter, the whole machine has small loss and good compensation effect; the device can perform web access or APP operation through a mobile phone, an iPad, a notebook computer and the like, so that the functions of remote measurement, remote control, remote signaling, remote regulation and fixed value calling are realized.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.

Claims (8)

1. The comprehensive treatment device for the power quality is characterized by comprising a converter module and a control module;
the converter module comprises an NPC three-level inverter circuit and a filter; the direct-current bus voltage outputs three-phase voltage and current of a power grid through the NPC three-level inverter circuit and the filter;
the control module comprises a PLL (phase locked loop), a DFT (discrete Fourier transform) detection unit, a voltage outer loop controller, a current inner loop controller and a feedforward voltage controller;
the PLL is used for judging the phase sequence of the three-phase voltage of the power grid and locking the phase of the three-phase voltage;
the DFT detection unit detects three-phase load current and extracts fundamental active current, fundamental reactive current and harmonic and inter-harmonic current which are respectively used for reactive compensation, harmonic and inter-harmonic compensation under different phase sequences;
the voltage outer ring controller is used for stabilizing and equalizing the voltage of the direct current bus;
and signals output after the signals respectively pass through the PLL, the DFT detection unit and the voltage outer loop controller are superposed with the three-phase current of the power grid to form a current instruction signal which is input into the voltage inner loop controller, and the current instruction signal is output after the output is superposed with the three-phase voltage of the power grid and is processed by the feedforward voltage controller.
2. The electric energy quality comprehensive treatment device according to claim 1, wherein the PLL phase-locked loop is configured to perform phase sequence determination and phase locking on the three-phase voltage of the power grid, and comprises:
sampling the three-phase voltage of the power grid, judging a positive sequence and a negative sequence according to preset conditions, and if the positive sequence is positive, locking the phase according to the following settings: the first phase has a phase theta and the second phase has a phase theta
Figure FDA0002770856650000011
The third phase is
Figure FDA0002770856650000012
If the negative sequence is adopted, the phase locking is carried out according to the following setting: the first phase has a phase theta and the second phase has a phase theta
Figure FDA0002770856650000013
The third phase is
Figure FDA0002770856650000014
3. The power quality comprehensive treatment device according to claim 2, wherein the DFT detection unit is used for the current signal i as followsn(k) And (3) processing:
Figure FDA0002770856650000015
Figure FDA0002770856650000021
wherein N is the number of sampling points in each fundamental wave period; k is 0,1,2 … (N-1); t is the fundamental wave signal period; τ is T/N; i (k tau) is the sampling value of the kth sampling point, theta is the phase, and n is the harmonic frequency;
when the phase sequence is positive:
the first phase is: θ is 0; the second phase is:
Figure FDA0002770856650000022
the third phase is:
Figure FDA0002770856650000023
when the phase sequence is negative:
the first phase is: θ is 0; the second phase is:
Figure FDA0002770856650000024
the third phase is:
Figure FDA0002770856650000025
4. the electric energy quality comprehensive treatment device according to any one of claims 1 to 3, wherein the voltage outer ring controller comprises a voltage stabilizing ring and a voltage equalizing ring, which are respectively realized by a PI regulator.
5. The electric energy quality comprehensive treatment device according to claim 4, wherein the voltage regulation loop collects positive and negative bus voltages Udc1 and Udc2 on the direct current side through a DSP, the sum of the positive and negative bus voltages is differentiated from a given bus voltage, an error signal is sent to a PI controller, and the obtained active components Iapref, Ibpref and Icprof are superposed on the current command signal through DQ inverse transformation.
6. The electric energy quality comprehensive treatment device according to claim 5, wherein the DQ inverse transformation comprises:
judging the phase sequence, and performing positive sequence DQ inverse transformation when the phase sequence is a positive sequence; and when the sequence is negative, carrying out inverse transformation of the negative sequence DQ.
7. The electric energy quality comprehensive treatment device according to claim 5 or 6, wherein the feedforward voltage controller performs feedforward voltage control according to different phase sequences:
when the phase sequence is positive, the voltage feed forward is:
Figure FDA0002770856650000031
when the phase sequence is negative, the voltage feed forward is:
Figure FDA0002770856650000032
in the formula (I), the compound is shown in the specification,
Figure FDA0002770856650000033
is the instantaneous value of the three-phase voltage of the power grid,
Figure FDA0002770856650000034
the effective value of the three-phase voltage of the power grid is obtained.
8. An electric energy quality comprehensive treatment method, which is characterized in that the electric energy quality comprehensive treatment device according to any one of claims 1 to 7 is adopted for comprehensive treatment, and comprises the following steps:
the PLL judges the phase sequence of the three-phase voltage of the power grid and locks the phase of the three-phase voltage;
the DFT detection unit detects the three-phase load current, extracts fundamental active current, fundamental reactive current, harmonic and inter-harmonic current, and respectively performs reactive compensation, harmonic and inter-harmonic compensation under different phase sequences;
the voltage outer ring controller is used for stabilizing and equalizing the voltage of the direct current bus;
after each signal passes through the PLL, the DFT detection unit and the voltage outer loop controller respectively, the output signal is superposed with the three-phase current of the power grid to form a current command signal input voltage inner loop controller;
the output processed by the voltage inner-loop controller is superposed with the three-phase voltage of the power grid and then is processed by the feedforward voltage controller and then is output.
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