CN108152619B - Power grid fault simulation device and control method thereof - Google Patents
Power grid fault simulation device and control method thereof Download PDFInfo
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- CN108152619B CN108152619B CN201711356839.9A CN201711356839A CN108152619B CN 108152619 B CN108152619 B CN 108152619B CN 201711356839 A CN201711356839 A CN 201711356839A CN 108152619 B CN108152619 B CN 108152619B
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Abstract
The invention provides a power grid fault simulation device and a control method thereof. The power grid fault simulation device adopts a four-bridge arm voltage source type main circuit topology; respectively acquiring positive sequence, negative sequence and zero sequence voltage instructions based on a symmetrical component method; the voltage + current double closed-loop control and the command voltage feedforward control are adopted to realize the accurate and rapid control of the output voltage and the frequency; by setting the voltage drop depth and the frequency value, the simulation of common grid faults such as three-phase symmetry, two-phase asymmetry, single-phase asymmetry and frequency abnormality is realized, and the requirements of fault ride-through and grid adaptability test of photovoltaic power stations and wind power plants can be met. The invention has clear functions of all parts, is simple and effective and is beneficial to engineering application.
Description
Technical Field
The invention belongs to the field of electrical engineering, and particularly relates to a power grid fault simulation device and a control method thereof.
Background
With the continuous improvement of the permeability of photovoltaic power generation and wind power generation in an electric power system, the influence of the permeability on a power grid is not negligible, particularly, when the photovoltaic power generation and the wind power generation in China both adopt a large-scale centralized power grid connection mode, when the grid is in fault and the voltage of a grid connection point drops, if a photovoltaic power station and a wind power generator set still adopt a passive protection splitting mode, the active power output is greatly reduced, the recovery difficulty of the whole system is increased, the fault is possibly aggravated, the voltage and the frequency of the power grid collapse are caused, the safe and stable operation of the power grid is seriously influenced, and the large-scale utilization of new energy is greatly limited. Therefore, photovoltaic power stations and wind turbines which are operated on a large-scale grid-connected basis must be required to have the capability of fault ride-through and abnormal response to the grid frequency.
At present, the domestic power grid fault ride-through simulation device mainly adopts an impedance voltage division type and a power electronic type, wherein the impedance voltage division type and the power electronic type are adopted, and the impedance voltage division type and the power electronic type are large in size, cannot realize continuous and smooth adjustment of a voltage drop amplitude value and are difficult to simulate high voltage ride-through and frequency abnormity of a power grid due to the adoption of a reactor; the latter, while compensating for the inherent drawbacks of impedance voltage divider devices, relies primarily on importation and is expensive.
Disclosure of Invention
The invention provides a novel power grid fault simulation device and a control method thereof, which can be used for simulating common power grid faults such as three-phase symmetry, two-phase asymmetry, single-phase asymmetry and frequency abnormality, are simple and effective and are beneficial to engineering application.
The technical scheme of the invention is as follows:
the power grid fault simulation device adopts a four-bridge arm voltage source type main circuit topology and is provided with a positive and negative sequence separation network and a slope control and amplitude limiter; a voltage and current double closed-loop control structure is adopted under a double-rotation coordinate system, wherein an inner loop is an inductive current loop, and an outer loop is an alternating current voltage loop; the positive and negative sequence separation network is used for separating positive sequence, negative sequence and zero sequence components of three-phase four-wire current and three-phase voltage, so that positive and negative sequence voltage and current participate in double closed-loop control; the slope control and amplitude limiter is used for flexibly setting a given rate of voltage or frequency and preventing misoperation in an amplitude limiting mode; the set voltage command and frequency command are used as corresponding control command values after passing through a slope control and amplitude limiter so as to realize the simulation of the power grid fault; the control output of the positive sequence, the negative sequence and the zero sequence components is modulated by PWM to drive the power device to act, and the output of the port voltage according to the requirement is realized.
Further, the control instruction value corresponding to the zero sequence component is output through the PR controller.
Further, under a double-rotation coordinate system, command voltage feedforward control is respectively introduced into d, q and 0 axes.
The control method based on the power grid fault simulation device comprises the following steps:
step 1) respectively collecting three-phase voltage and three-phase four-wire current, and performing positive and negative sequence separation through a positive and negative sequence separation network;
step 2) setting a proper voltage instruction and a proper frequency instruction according to the required power grid output voltage and frequency requirements, and taking the proper voltage instruction and the proper frequency instruction as a control instruction value after slope control and an amplitude limiter; the voltage instruction is obtained by respectively obtaining a positive sequence voltage instruction, a negative sequence voltage instruction and a zero sequence voltage instruction based on a symmetrical component method and carrying out dq0 rotation transformation under a double-rotation coordinate system;
and step 3: respectively carrying out double closed-loop control on positive and negative sequence voltages and currents of d and q axes under a double-rotation coordinate system, introducing a PR (pulse-width modulation) controller into the axis 0, and simultaneously introducing command voltage feedforward control into the axes d, q and 0;
and 4, step 4: under a double-rotation coordinate system, the control output of the dq0 shaft is subjected to PWM modulation, a power device is driven to act, and finally port voltage output according to requirements is achieved.
Further, the voltage command in step 2) has the following d-axis and q-axis positive sequence and negative sequence component magnitudes and 0-axis zero sequence component in a dual-rotation coordinate system:
1) single phase asymmetric fall
4) Two-phase asymmetric fall
5) Three-phase symmetrical falling
v0＝0 (13)
And (3) setting the d-axis positive sequence and negative sequence, the q-axis positive sequence and negative sequence and the 0-axis voltage command value according to the formulas (5) to (12) according to different fault types of the power grid, namely corresponding to the required power grid output voltage.
The invention has the following beneficial effects:
the controlled output of zero-sequence voltage is realized by adopting a four-bridge arm voltage source type main circuit topology; based on a symmetric component method, accurate and rapid control of output voltage and frequency is realized by adopting positive and negative sequence separation, double closed loops and a command voltage feedforward strategy; the output voltage and the frequency can be flexibly set, so that the fault ride-through capability (covering low voltage ride-through and high voltage ride-through) test of a photovoltaic power station and a wind power plant can be met, and the simulation of frequency abnormal events can be met; the power density is high, the transportation is convenient, and the field test of the inverter and the converter in a photovoltaic power station and a wind power plant can be realized.
Drawings
Fig. 1 shows a four-leg three-phase four-wire system main circuit topology.
Fig. 2 is a positive and negative sequence separation network.
Fig. 3 is a block diagram of the overall control of the system of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Referring to fig. 1, a four leg three phase four wire system main circuit topology.
According to the positive and negative sequence separation network shown in fig. 2, the separation of the positive sequence, the negative sequence and the zero sequence components can be realized, which is specifically as follows:
according to the symmetric component method, for a three-phase system, each phase voltage is composed of positive sequence, negative sequence and zero sequence components, and the formula (1) shows that:
for a three-phase symmetric system, the output phase voltages contain only positive sequence components, so V-＝0，V 00; for three-phase asymmetric system, the output phase voltage contains positive sequence, negative sequence and zero sequence components at the same time, so V-≠0，V0≠0。
Setting the rated peak value of the voltage phase under the normal state of the power grid as VTDropping phase voltagePeak value of nxVT(n is more than or equal to 0 and less than or equal to 1), the following three power grid voltage expressions can be respectively obtained by a symmetrical component method according to different dropping modes:
1) single phase asymmetric fall
The positive sequence, negative sequence and zero sequence component amplitudes are as follows:
therefore, the voltage values of the three-phase voltage when the single-phase asymmetric drop occurs are as follows:
2) two-phase asymmetric fall
The positive sequence, negative sequence and zero sequence component amplitudes are as follows:
therefore, the three-phase voltage value when the two phases fall asymmetrically is obtained as follows:
3) three-phase symmetrical falling
The grid voltage contains only positive sequence components, whose values are:
because a four-arm converter is adopted, the three-phase four-wire system can carry out dq0 rotation transformation on the formulas (2) to (4) under a double-rotation coordinate system, and the positive sequence and negative sequence component sizes of the d axis and the q axis and the zero sequence component of the 0 axis under the double-rotation coordinate system are obtained as follows:
1) single phase asymmetric fall
6) Two-phase asymmetric fall
7) Three-phase symmetrical falling
v0＝0 (13)
And (3) setting d-axis positive sequence and negative sequence, q-axis positive sequence and negative sequence and 0-axis voltage command values according to formulas (5) to (12) respectively under the double-rotation coordinate system according to different fault types of the power grid, and synthesizing an expected voltage amplitude at the output port of the four-bridge-arm converter by adopting reasonable control.
Based on the above topology, the overall control structure adopted by the present invention is shown in fig. 3:
the whole system is controlled by adopting a voltage and current double closed loop under a double-rotation coordinate system, wherein an inner loop is an inductance current loop, so that on one hand, the resonance of the LC filter can be damped, and on the other hand, the response speed of a voltage loop can be effectively improved; the outer ring is an alternating current voltage ring and is used for controlling output voltage; meanwhile, in order to improve the response speed of the output voltage, voltage command feedforward control is added.
a. Regarding the voltage command, setting voltage positive sequence, negative sequence and zero sequence command values according to equations (5) to (13) respectively according to the type of the power grid fault to be simulated;
b. regarding the frequency instruction, according to the power grid frequency abnormal event needing to be simulated, the frequency value can be directly set as required, the value can obtain the angle required by dq0 rotation transformation through integration, and finally the change of the output frequency of the four-leg converter is realized through voltage + current double closed-loop control and PWM modulation.
The control method mainly comprises the following steps:
step 1: respectively collecting three-phase voltage and three-phase four-wire current, and performing positive-negative sequence separation based on the positive-negative sequence separation network shown in the figure 2;
step 2: according to the required power grid output voltage and frequency requirements, appropriate voltage instruction and frequency instruction values are set according to the formulas (5) to (13), the voltage instruction and the frequency instruction values are used as voltage closed-loop control instruction values after passing through a slope control and a limiter, the slope control can flexibly set voltage or frequency given rate, and the limiter can prevent misoperation.
And step 3: and performing double closed-loop control on positive and negative sequence voltages and currents of d and q axes respectively under a double-rotation coordinate system, introducing a PR (pulse-width modulation) controller into the axis 0, and introducing command voltage feedforward control into the axes d, q and 0 respectively, so as to realize accurate and rapid control on output voltage.
And 4, step 4: under a double-rotation coordinate system, the output of the dq0 shaft closed-loop regulator is subjected to PWM modulation, a power device is driven to act, and finally port voltage is output as required.
In summary, the invention adopts a four-leg voltage source type main circuit topology, and realizes three-phase four-wire system output; respectively acquiring positive sequence, negative sequence and zero sequence voltage instructions based on a symmetrical component method; the voltage + current double closed-loop control and the command voltage feedforward control are adopted to realize the accurate and rapid control of the output voltage and the frequency; by setting the voltage drop depth and the frequency value, the simulation of common power grid faults such as three-phase symmetry, two-phase asymmetry, single-phase asymmetry and frequency abnormality is realized, the requirements of fault ride-through and power grid adaptability test of photovoltaic power stations and wind power plants can be met, the method is simple and effective, and engineering application is facilitated.
The above embodiments are merely examples of the present invention, and do not limit the scope of the claims of the present application. Various changes or modifications may be made by those skilled in the art without departing from the spirit and scope of the invention, and all equivalents should fall within the scope of the invention.
Claims (3)
1. A grid fault simulation device is characterized in that: a four-bridge arm voltage source type main circuit topology is adopted, and a positive-negative sequence separation network, a slope control and an amplitude limiter are configured; a voltage and current double closed-loop control structure is adopted under a double-rotation coordinate system, wherein an inner loop is an inductive current loop, and an outer loop is an alternating current voltage loop; respectively carrying out double closed-loop control on positive and negative sequence voltages and currents of d and q axes under a double-rotation coordinate system, introducing a PR (pulse-width modulation) controller into the 0 axis, and simultaneously respectively introducing command voltage feedforward control into the d, q and 0 axes; the positive and negative sequence separation network is used for separating positive sequence, negative sequence and zero sequence components of three-phase four-wire current and three-phase voltage, so that positive and negative sequence voltage and current participate in double closed-loop control; the slope control and amplitude limiter is used for flexibly setting a given rate of voltage or frequency and preventing misoperation in an amplitude limiting mode; the set voltage command and frequency command are used as corresponding control command values after passing through a slope control and amplitude limiter so as to realize the simulation of the power grid fault; the voltage instruction is obtained by respectively obtaining a positive sequence voltage instruction, a negative sequence voltage instruction and a zero sequence voltage instruction based on a symmetrical component method and carrying out dq0 rotation transformation under a double-rotation coordinate system; the control output of the positive sequence, the negative sequence and the zero sequence components is modulated by PWM to drive the power device to act, and the output of the port voltage according to the requirement is realized.
2. The grid fault simulation apparatus of claim 1, wherein: and outputting a control instruction value corresponding to the zero sequence component through the PR controller.
3. The control method of the grid fault simulation device according to claim 1, comprising the steps of:
step 1) respectively collecting three-phase voltage and three-phase four-wire current, and performing positive and negative sequence separation through a positive and negative sequence separation network;
step 2) setting a proper voltage instruction and a proper frequency instruction according to the required power grid output voltage and frequency requirements, and taking the proper voltage instruction and the proper frequency instruction as a control instruction value after slope control and an amplitude limiter; the voltage instruction is obtained by respectively obtaining a positive sequence voltage instruction, a negative sequence voltage instruction and a zero sequence voltage instruction based on a symmetrical component method and carrying out dq0 rotation transformation under a double-rotation coordinate system;
and step 3: respectively carrying out double closed-loop control on positive and negative sequence voltages and currents of d and q axes under a double-rotation coordinate system, introducing a PR (pulse-width modulation) controller into the axis 0, and simultaneously introducing command voltage feedforward control into the axes d, q and 0;
and 4, step 4: under a double-rotation coordinate system, the control output of the dq0 shaft is subjected to PWM modulation, a power device is driven to act, and finally port voltage output according to requirements is achieved.
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