CN112564087A - Flexible switch grid-connected and off-grid coordination control method based on static coordinate system - Google Patents

Flexible switch grid-connected and off-grid coordination control method based on static coordinate system Download PDF

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CN112564087A
CN112564087A CN202011246385.1A CN202011246385A CN112564087A CN 112564087 A CN112564087 A CN 112564087A CN 202011246385 A CN202011246385 A CN 202011246385A CN 112564087 A CN112564087 A CN 112564087A
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grid
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power
coordinate system
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CN112564087B (en
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范朕宁
苏强
张慧颖
朱汉卿
刘扬
张丽娜
赵长伟
张新民
徐科
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State Grid Corp of China SGCC
State Grid Tianjin Electric Power Co Ltd
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State Grid Tianjin Electric 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
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

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Abstract

The invention belongs to the technical field of power electronic control of a power distribution network, relates to a control technology of a flexible switch, and particularly relates to a flexible switch grid-connection and grid-disconnection coordination control method based on a static coordinate system. The traditional method for processing the control operation fault of the power distribution network generally needs to install a mechanical breaker in the power distribution network for power supply and power failure, a flexible switch is generally only used for power control during normal operation of the power distribution network, once the power distribution network fails, the flexible switch and the breaker cooperatively remove a fault feeder, and the flexible switch and the breaker are put into operation after the fault is cleared. This approach may increase the power-off time and may also cause voltage fluctuations, thereby increasing economic losses. The patent provides a flexible switch on/off-grid coordination control method based on a static coordinate system, and the control method establishes a basic control model based on the static coordinate system, can coordinate control operation mode switching and strategies when switching equipment normally operates and a line fails, and ensures the overall stability of a power distribution network system.

Description

Flexible switch grid-connected and off-grid coordination control method based on static coordinate system
Technical Field
The invention belongs to the technical field of power electronic control of a power distribution network, relates to a control technology of a flexible switch, and particularly relates to a flexible switch grid-connection and grid-disconnection coordination control method based on a static coordinate system.
Background
With the integrated access of a large-scale renewable energy distributed power generation system, a plurality of types of distributed energy storage units, an electric automobile and a controllable load, higher requirements are put forward on the power supply reliability, the electric energy quality and the flexible control capability of a power distribution network, and a traditional power distribution network is also changed from a passive mode to an active mode to form an intelligent power distribution network. Along with the high-speed development of semiconductor and power electronic technology, intelligent power electronic equipment is widely connected into an intelligent power distribution network, a flexible multi-state switch is used as key electrical equipment for improving the flexibility and reliability of the power distribution network, and the flexible multi-state switch has the advantages of being high in adjusting capacity, high in response speed, capable of achieving current suppression, fault isolation and the like.
The existing control method of the flexible switch is mainly executed under a two-phase synchronous rotating coordinate system, has the problems of large coordinate transformation operation, decoupling, feedforward control, phase-locked loop and the like, and does not consider the problem of the fixed direct-current voltage controlling the fault situation of a power grid at a rectifying side and how to coordinate converters at the rectifying side and an inverting side. At the present stage, a simpler, more convenient and more efficient control method is needed, the stable operation capacity of a power grid and the processing capacity under faults are considered, and the economic cost of operation is reduced.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a flexible switch control method based on a static coordinate system and a flexible switch grid-connection and off-grid coordination control method of a grid-connection/off-grid coordination control operation strategy under the condition of feeder line faults at two sides of a flexible switch.
The technical scheme adopted by the invention is as follows:
a flexible switch grid-connected and grid-disconnected coordination control method based on a static coordinate system comprises a flexible switch adopting a back-to-back structure, wherein a converter on one side of the flexible switch is a rectifier side converter, and a converter on the other side of the flexible switch is an inverter side converter, and the method is characterized in that: the method comprises the following steps:
step 1: building a model under a static coordinate system;
step 2: a flexible switch normal operation mode control method;
and step 3: a fault handling mode control method;
3.1: an inversion side fault;
3.2: a commutation side fault.
Further, the step 1 includes a step 1.1 of a mathematical model under an alpha-beta static coordinate system of a typical structure of the flexible switch;
step 1.2: according to an instantaneous reactive power theory, an active power formula and a reactive power formula under an alpha-beta static coordinate system are given; step 1.3: and replacing the actual power by the power reference value to obtain an alpha component and a beta component of the current reference value of the flexible switch under an alpha-beta static coordinate system.
Further, in the step 1.1, mathematical models in an alpha-beta static coordinate system according to a typical structure of the flexible switch are shown as a formula (1) and a formula (2);
Figure BDA0002770164390000021
Figure BDA0002770164390000022
wherein Lk and Rk are respectively a filter inductor and an equivalent series resistance; i α k and i β k are α component and β component of the inductor current; e.g. of the typeαkAnd eβkAlpha component and beta component of the network voltage; sαkAnd sβkIs the alpha and beta components of the switching function; u. ofdcIs a direct current voltage; subscript k is 1, 2;
in the step 1.2, according to the instantaneous reactive power theory, an active power formula and a reactive power formula under an alpha-beta static coordinate system are given, and the formulas are shown as a formula (3) and a formula (4).
Figure BDA0002770164390000023
Figure BDA0002770164390000024
Calculating active and reactive currents by using the formula (3) and the formula (4), wherein the formula is (5);
Figure BDA0002770164390000031
in the step 1.3, the power reference value is used for replacing the actual power, so that an alpha component and a beta component of a current reference value of the flexible switch under an alpha-beta static coordinate system are obtained, and the formulas are shown as a formula (6) and a formula (7);
Figure BDA0002770164390000032
wherein P iskrefAnd QkrefActive and reactive power reference values; equations (6) and (7) are basic equations for controlling the static coordinate system of the flexible switch, and the control methods of the flexible switch in the normal state and the fault state are based on the basic equations.
Further, step 2 includes a control method of the 2.1 rectification-side converter and a control method of the 2.2 inversion-side converter.
Further, in the step 2.1, the method includes the following steps:
2.11. subtracting the collected direct current voltage from a direct current voltage reference value to obtain a voltage error signal;
2.12. the voltage error signal enters a PI regulator, a direct current is obtained through operation, and the direct current is multiplied by a voltage reference value to obtain an active power reference value;
2.13. reference value P of active powerrefAnd a reactive power reference value QrefSending the alpha component and the beta component of the power grid voltage into formulas (6) and (7) to calculate the alpha component and the beta component of the current inner loop reference value;
2.14. the reference value of the current inner ring is differenced with the corresponding component of the power grid current in a static coordinate system, the obtained error signal is an alternating current component, a proportional resonant PR controller is adopted to obtain a modulation signal to realize zero steady-state error tracking, and finally a drive pulse is obtained through a sinusoidal pulse width modulation strategy;
in the step 2.2, the method comprises the following steps: the PQ control for controlling active power and reactive power comprises the following steps:
2.21. obtaining reference values P of active power and reactive power of the system from an upper-layer dispatching systemrefAnd Qref；
2.22. The value of the grid current is obtained from the current measuring device and the alpha and beta components of the grid current in the stationary coordinate system are calculated.
2.23. Substituting the active power reference value and the reactive power reference value into the formulas (6) and (7) to calculate the component of the current reference value, and making a difference with the corresponding component of the power grid current to obtain an error signal which is an alternating current component;
2.24. and obtaining a modulation signal by adopting a proportional resonant PR controller to realize zero steady-state error tracking, and finally obtaining a driving pulse by a sinusoidal pulse width modulation strategy.
Further, the step 3 can be divided into a 3.1 inverter side fault and a 3.2 rectifier side fault according to the fault types.
Further, in the 3.1 inverter-side fault, the inverter-side converter switches the PQ control strategy to constant-voltage constant-frequency control so as to maintain the stability of the voltage and the frequency of the ac bus and provide reliable power supply for the load on the ac bus, and the control method includes the following steps:
3.11. when the power grid is normal, the control switch S is connected to 1, and the inverter side converter works in a PQ control mode;
3.12. after the power grid on the inversion side breaks down, triggering a switch S to be connected into 2 after island detection, and switching the PQ control to constant-voltage constant-frequency control under a static coordinate system;
3.13. in the constant voltage and constant frequency control, a voltage outer ring reference value is subtracted from the voltage of an actual load terminal to obtain a voltage alternating current error signal, then a current inner ring reference value is obtained through a PR controller, then current inner ring control is carried out, and finally a driving signal is generated;
in the 3.2 rectification side fault, the control strategies of the rectification side converter and the inversion side converter need to be adjusted: the inverter side converter is switched to direct current bus voltage control from PQ control so as to maintain the stability of the direct current bus voltage; the rectification side converter switches from direct current bus voltage control to constant voltage and constant frequency control so as to maintain the stability of alternating current bus voltage and frequency at a fault side, and the control method comprises the following steps:
3.21. under the normal condition of a power grid, a control switch S of a rectification and inversion side converter is connected into 1;
3.22. after the grid at the rectification side fails, triggering a control switch S to be connected into the control switch 2 after island detection;
3.23. PQ control of the inverter converter is switched to a direct current voltage and reactive power control mode, an inner loop current reference value is calculated according to a direct current error and a reactive power reference value after PI operation, and a driving pulse is obtained after the inner loop current reference value passes through a PR controller;
3.24. the rectification side converter is switched to a constant voltage and constant frequency control mode from direct current bus voltage control, a voltage alternating current error signal is obtained by subtracting the voltage of an actual load end from the voltage of a voltage outer ring, then a current inner ring reference value is obtained through a PR controller, then current inner ring control is carried out, and finally a driving pulse is generated.
The invention has the advantages and positive effects that:
in the invention, the mentioned flexible switch control method under normal and fault conditions can overcome the defects of the conventional power distribution network control operation method and the general flexible switch control scheme, and has the following advantages:
(1) the response speed is high: the normal operation mode and the fault handling mode of the flexible switch are performed by the power device switch without worrying about the switch contact dielectric strength problem existing in the mechanical switch.
(2) And (3) reducing economic loss: the normal operation mode and the fault processing mode of the flexible switch can be switched seamlessly, the fault recovery time can be shortened, and the related economic loss is reduced. And fully considers the problem of the coordinated operation of the converter at the rectifying side and the converter at the inverting side.
(3) Avoid equipment damage and voltage fluctuations of adjacent feeders: the flexible switch can maintain the voltage and the current of the fault feeder line within a normal range in a fault processing mode, and avoids equipment damage and voltage fluctuation of adjacent feeder lines caused by repeated fault input/removal in a traditional method.
(4) Simple structure easily realizes: compared with the traditional flexible switch control strategy, the flexible switch control strategy and the method provided by the invention have the advantages of simple control structure, easiness in implementation, less coordinate transformation operation, no need of synchronous phase-locked loops, no need of decoupling and power grid voltage feedforward control.
Drawings
Fig. 1 is a schematic diagram showing a typical structure of a flexible switch used in the present invention;
FIG. 2 is a control block diagram of a rectifier side converter under normal grid conditions;
FIG. 3 is a control block diagram of the inverter-side converter under normal grid conditions;
FIG. 4 is a schematic diagram of a control strategy of the flexible switch in case of an inverter-side grid fault;
FIG. 5 is a control block diagram of a rectifier side converter under a rectifier side grid fault;
FIG. 6 is a control block diagram of an inverter-side converter under a grid fault on a rectification side;
FIG. 7 is a flexible switch control method verification model in an embodiment of the invention;
FIG. 8 shows the reactive power and reactive power of the inverter-side converter in a normal operating state;
FIG. 9 is the AC bus voltage during normal operation;
FIG. 10 is the DC bus voltage during normal operation;
FIG. 11 shows the DC bus voltage at inverter side fault;
FIG. 12 shows the inverter-side converter active power at inverter-side fault;
FIG. 13 is the inverter side AC bus voltage at inverter side fault;
FIG. 14 is the DC bus voltage at rectifier side fault;
FIG. 15 shows the inverter side converter active power at rectifier side fault;
FIG. 16 illustrates the rectifier side converter active power at rectifier side fault;
fig. 17 shows the rectifying-side ac bus voltage at the time of the rectifying-side fault.
Detailed Description
The present invention is further illustrated by the following examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.
The invention discloses a flexible switch grid-connected and grid-disconnected coordination control method based on a static coordinate system, which comprises a flexible switch adopting a back-to-back structure, wherein a converter on one side of the flexible switch is a rectifier side converter, and a converter on the other side of the flexible switch is an inverter side converter, and the invention is characterized by comprising the following steps:
step 1: building a model under a static coordinate system;
in the step 1, a mathematical model under an alpha-beta static coordinate system of a typical structure of the flexible switch is included in the step 1.1;
step 1.2: according to an instantaneous reactive power theory, an active power formula and a reactive power formula under an alpha-beta static coordinate system are given; step 1.3: and replacing the actual power by the power reference value to obtain an alpha component and a beta component of the current reference value of the flexible switch under an alpha-beta static coordinate system.
In the step 1.1, mathematical models in an alpha-beta static coordinate system according to a typical structure of the flexible switch are shown as a formula (1) and a formula (2);
Figure BDA0002770164390000071
Figure BDA0002770164390000072
wherein Lk and Rk are respectively a filter inductor and an equivalent series resistance; i α k and i β k are α component and β component of the inductor current; e.g. of the typeαkAnd eβkAlpha component and beta component of the network voltage; sαkAnd sβkIs the alpha and beta components of the switching function; u. ofdcIs a direct current voltage; subscript k is 1, 2;
in the step 1.2, according to the instantaneous reactive power theory, an active power formula and a reactive power formula under an alpha-beta static coordinate system are given, and the formulas are shown as a formula (3) and a formula (4).
Figure BDA0002770164390000073
Figure BDA0002770164390000074
Calculating active and reactive currents by using the formula (3) and the formula (4), wherein the formula is (5);
Figure BDA0002770164390000075
in the step 1.3, the power reference value is used for replacing the actual power, so that an alpha component and a beta component of a current reference value of the flexible switch under an alpha-beta static coordinate system are obtained, and the formulas are shown as a formula (6) and a formula (7);
Figure BDA0002770164390000076
wherein P iskrefAnd QkrefActive and reactive power reference values; equations (6) and (7) are basic equations for controlling the static coordinate system of the flexible switch, and the control methods of the flexible switch in the normal state and the fault state are based on the basic equations.
Step 2: a flexible switch normal operation mode control method; the step 2 includes a control method of the 2.1 rectification side converter and a control method of the 2.2 inversion side converter.
In the step 2.1, the method comprises the following steps:
2.11. subtracting the collected direct current voltage from a direct current voltage reference value to obtain a voltage error signal;
2.12. the voltage error signal enters a PI regulator, a direct current is obtained through operation, and the direct current is multiplied by a voltage reference value to obtain an active power reference value;
2.13. reference value P of active powerrefAnd a reactive power reference value QrefSending the alpha component and the beta component of the power grid voltage into formulas (6) and (7) to calculate the alpha component and the beta component of the current inner loop reference value;
2.14. the reference value of the current inner ring is differenced with the corresponding component of the power grid current in a static coordinate system, the obtained error signal is an alternating current component, a proportional resonant PR controller is adopted to obtain a modulation signal to realize zero steady-state error tracking, and finally a drive pulse is obtained through a sinusoidal pulse width modulation strategy;
in the step 2.2, the method comprises the following steps: the PQ control for controlling active power and reactive power comprises the following steps:
2.21. obtaining reference values P of active power and reactive power of the system from an upper-layer dispatching systemrefAnd Qref；
2.22. The value of the grid current is obtained from the current measuring device and the alpha and beta components of the grid current in the stationary coordinate system are calculated.
2.23. Substituting the active power reference value and the reactive power reference value into the formulas (6) and (7) to calculate the component of the current reference value, and making a difference with the corresponding component of the power grid current to obtain an error signal which is an alternating current component;
2.24. and obtaining a modulation signal by adopting a proportional resonant PR controller to realize zero steady-state error tracking, and finally obtaining a driving pulse by a sinusoidal pulse width modulation strategy.
And step 3: a fault handling mode control method; and 3.1 inverter side faults and 3.2 rectifier side faults can be divided in the step 3 according to the fault types.
In the 3.1 inverter side fault, the inverter side converter switches the PQ control strategy to constant voltage and constant frequency control so as to maintain the stability of the voltage and the frequency of the alternating current bus and provide reliable power supply for the load on the alternating current bus, and the control method comprises the following steps:
3.11. when the power grid is normal, the control switch S is connected to 1, and the inverter side converter works in a PQ control mode;
3.12. after the power grid on the inversion side breaks down, triggering a switch S to be connected into 2 after island detection, and switching the PQ control to constant-voltage constant-frequency control under a static coordinate system;
3.13. in the constant voltage and constant frequency control, a voltage outer ring reference value is subtracted from the voltage of an actual load terminal to obtain a voltage alternating current error signal, then a current inner ring reference value is obtained through a PR controller, then current inner ring control is carried out, and finally a driving signal is generated;
in the 3.2 rectification side fault, the control strategies of the rectification side converter and the inversion side converter need to be adjusted: the inverter side converter is switched to direct current bus voltage control from PQ control so as to maintain the stability of the direct current bus voltage; the rectification side converter switches from direct current bus voltage control to constant voltage and constant frequency control so as to maintain the stability of alternating current bus voltage and frequency at a fault side, and the control method comprises the following steps:
3.21. under the normal condition of a power grid, a control switch S of a rectification and inversion side converter is connected into 1;
3.22. after the grid at the rectification side fails, triggering a control switch S to be connected into the control switch 2 after island detection;
3.23. PQ control of the inverter converter is switched to a direct current voltage and reactive power control mode, an inner loop current reference value is calculated according to a direct current error and a reactive power reference value after PI operation, and a driving pulse is obtained after the inner loop current reference value passes through a PR controller;
3.24. the rectification side converter is switched to a constant voltage and constant frequency control mode from direct current bus voltage control, a voltage alternating current error signal is obtained by subtracting the voltage of an actual load end from the voltage of a voltage outer ring, then a current inner ring reference value is obtained through a PR controller, then current inner ring control is carried out, and finally a driving pulse is generated.
The using process of the invention is as follows:
the simulation verification model of the flexible switch grid-connected and off-grid coordination control method based on the static coordinate system is shown in FIG. 7. Modeling was performed using MATLAB/SIMULINK. Alternating current buses on two sides are connected together through a flexible switch with the capacity of 10MVA, the voltage of a direct current bus is 20kV, alternating current filter inductors on two sides in a converter are 5mH, the capacitance of the direct current bus is 10mF, alternating current feeders on two sides are connected with a local load of 5MVA, and a short-circuit fault module is arranged inside the alternating current feeder. And (4) performing simulation verification on the normal operation, namely the fault, of the system.
1. The embodiment normally operates the performance simulation result;
fig. 8, 9 and 10 are simulation diagrams of the flexible switch in normal operation. The initial active power reference value and the initial reactive power reference value of the simulated inverter side converter are-10 MW and 0MVar respectively, the output power of the inverter shown in figure 10 can quickly track the reference values, the direct-current bus voltage in figure 10 is stabilized at 20kV by the rectifier side converter, the output current of the inverter and the voltage of a power grid have the same frequency and are in opposite phase at the moment, and the inverter works in an inversion state. The power reference values were suddenly changed to-5 MW and 5MVar at 0.2s for the simulation, the power fast tracking in fig. 8 was stable, and the dc bus voltage of fig. 10 was briefly regulated to 20 kV. When the simulation is carried out for 0.4s, the active power reference value becomes zero, the reactive power reaches 10MVar, and at the moment, the flexible multi-state switch works in a STATCOM state to provide reactive power for a system, so that the reactive compensation function is realized. The power reference values are abruptly changed to 5MW and 5MVar at 0.6s for the simulation, and the inverter output power in fig. 8 tracks quickly. When the simulation is carried out for 0.8s, the reactive power is zero, the active power is increased to 10MW, the output current of the inverter and the voltage of the power grid are in the same frequency and phase, and the energy is transmitted from the inverter to the rectifying side. The ac bus voltage shown in fig. 9 is not substantially affected by the active and reactive power changes, and the curve is smooth and frequency stable. According to the simulation result, the flexible multi-state switch can ensure the stable operation of the system in the states of flexible power flow regulation, reactive compensation and the like.
2. The inverter side fault simulation result of the embodiment;
under the initial condition, the power grids on two sides of the simulation system are normal, the initial active power reference value and the initial reactive power reference value are-8 MW and 0MVar respectively, and at the moment, the direct-current bus voltage shown in the graph 11 is controlled by a rectification side converter and is stabilized at 20 kV; the output power of the inverter side shown in fig. 12 can be quickly tracked to-8 MW and is stable; the current waveform shown in fig. 13 is smooth and normal. When the simulation system is in 0.3s, a three-phase short circuit fault occurs in an inversion side power grid, then an inversion side converter is switched to a constant voltage and constant frequency control strategy from PQ, the voltage and frequency of an alternating current bus are maintained to be stable, uninterrupted power supply is carried out on a 5MW alternating current load, and the voltage of the direct current bus is quickly recovered to 20kV and kept stable after being slightly increased; the active power is changed rapidly and kept stable due to the need of supplying power to the load; the alternating current bus current changes, but can still be quickly stabilized, the smoothness is kept, and the amplitude and the frequency are normal.
3. Simulation result of rectifying side fault
Under the initial condition of the simulation system, the power grids on two sides are normal, the voltage of the direct current bus is stabilized at 20kV by the rectifier side converter, the inverter side converter is controlled by PQ, the initial active power reference value and the initial reactive power reference value are respectively 5MW and 0MVar, the voltage of the direct current bus is stabilized correctly according to the initial state shown in the graphs 14, 15 and 16, and the output power of the inverter side converter can quickly track the reference value. When the simulation system is in 0.3s, a three-phase short-circuit fault occurs in a power grid at a rectification side, then a converter at the rectification side is switched to a constant-voltage constant-frequency control strategy from direct-current bus voltage control, the voltage and the frequency of an alternating-current bus are kept stable, a converter at the inversion side is switched to direct-current bus constant-voltage control from PQ control, the voltage of the direct-current bus is kept stable, at the moment, according to the scheme shown in figures 14, 15 and 16, the voltage of the direct-current bus is quickly recovered to 20kV after a little reduction, the power at the rectification side is quickly reduced due to the fault, but the voltage is quickly recovered after the control method is switched, uninterrupted power supply is provided for an alternating-current load of 4MW, the power is then stable, the original inversion side is changed into. The rectified side ac bus voltage shown in fig. 17 also recovers to normal quickly after a fault, the amplitude and frequency are correct, and the curve is smooth.
In the invention, the mentioned flexible switch control method under normal and fault conditions can overcome the defects of the conventional power distribution network control operation method and the general flexible switch control scheme, and has the following advantages:
(1) the response speed is high: the normal operation mode and the fault handling mode of the flexible switch are performed by the power device switch without worrying about the switch contact dielectric strength problem existing in the mechanical switch.
(2) And (3) reducing economic loss: the normal operation mode and the fault processing mode of the flexible switch can be switched seamlessly, the fault recovery time can be shortened, and the related economic loss is reduced. And fully considers the problem of the coordinated operation of the converter at the rectifying side and the converter at the inverting side.
(3) Avoid equipment damage and voltage fluctuations of adjacent feeders: the flexible switch can maintain the voltage and the current of the fault feeder line within a normal range in a fault processing mode, and avoids equipment damage and voltage fluctuation of adjacent feeder lines caused by repeated fault input/removal in a traditional method.
(4) Simple structure easily realizes: compared with the traditional flexible switch control strategy, the flexible switch control strategy and the method provided by the invention have the advantages of simple control structure, easiness in implementation, less coordinate transformation operation, no need of synchronous phase-locked loops, no need of decoupling and power grid voltage feedforward control.

Claims (7)

1. A flexible switch grid-connected and grid-disconnected coordination control method based on a static coordinate system comprises a flexible switch adopting a back-to-back structure, wherein a converter on one side of the flexible switch is a rectifier side converter, and a converter on the other side of the flexible switch is an inverter side converter, and the method is characterized in that: the method comprises the following steps:
step 1: building a model under a static coordinate system;
step 2: a flexible switch normal operation mode control method;
and step 3: a fault handling mode control method;
3.1: an inversion side fault;
3.2: a commutation side fault.
2. The flexible switch grid-connected and grid-disconnected coordination control method based on the static coordinate system is characterized by comprising the following steps of: in the step 1, a mathematical model under an alpha-beta static coordinate system of a typical structure of the flexible switch is included in the step 1.1; step 1.2: according to an instantaneous reactive power theory, an active power formula and a reactive power formula under an alpha-beta static coordinate system are given; step 1.3: and replacing the actual power by the power reference value to obtain an alpha component and a beta component of the current reference value of the flexible switch under an alpha-beta static coordinate system.
3. The flexible switch grid-connected and grid-disconnected coordination control method based on the static coordinate system is characterized by comprising the following steps of: in the step 1.1, mathematical models in an alpha-beta static coordinate system according to a typical structure of the flexible switch are shown as a formula (1) and a formula (2);
Figure FDA0002770164380000011
Figure FDA0002770164380000012
wherein Lk and Rk are respectively a filter inductor and an equivalent series resistance; i α k and i β k are α component and β component of the inductor current; e.g. of the typeαkAnd eβkAlpha component and beta component of the network voltage; sαkAnd sβkIs the alpha and beta components of the switching function; u. ofdcIs a direct current voltage; subscript k is 1, 2;
in the step 1.2, according to the instantaneous reactive power theory, an active power formula and a reactive power formula under an alpha-beta static coordinate system are given, and the formulas are shown as a formula (3) and a formula (4).
Figure FDA0002770164380000021
Figure FDA0002770164380000022
Calculating active and reactive currents by using the formula (3) and the formula (4), wherein the formula is (5);
Figure FDA0002770164380000023
in the step 1.3, the power reference value is used for replacing the actual power, so that an alpha component and a beta component of a current reference value of the flexible switch under an alpha-beta static coordinate system are obtained, and the formulas are shown as a formula (6) and a formula (7);
Figure FDA0002770164380000024
wherein P iskrefAnd QkrefActive and reactive power reference values; equations (6) and (7) are basic equations for controlling the static coordinate system of the flexible switch, and the control methods of the flexible switch in the normal state and the fault state are based on the basic equations.
4. The flexible switch grid-connected and grid-disconnected coordination control method based on the static coordinate system is characterized by comprising the following steps of: the step 2 includes a control method of the 2.1 rectification side converter and a control method of the 2.2 inversion side converter.
5. The flexible switch grid-connected and grid-disconnected coordination control method based on the static coordinate system is characterized by comprising the following steps of:
in the step 2.1, the method comprises the following steps:
2.11. subtracting the collected direct current voltage from a direct current voltage reference value to obtain a voltage error signal;
2.12. the voltage error signal enters a PI regulator, a direct current is obtained through operation, and the direct current is multiplied by a voltage reference value to obtain an active power reference value;
2.13. reference value P of active powerrefAnd a reactive power reference value QrefSending the alpha component and the beta component of the power grid voltage into formulas (6) and (7) to calculate the alpha component and the beta component of the current inner loop reference value;
2.14. the reference value of the current inner ring is differenced with the corresponding component of the power grid current in a static coordinate system, the obtained error signal is an alternating current component, a proportional resonant PR controller is adopted to obtain a modulation signal to realize zero steady-state error tracking, and finally a drive pulse is obtained through a sinusoidal pulse width modulation strategy;
in the step 2.2, the method comprises the following steps: the PQ control for controlling active power and reactive power comprises the following steps:
2.21. obtaining reference values P of active power and reactive power of the system from an upper-layer dispatching systemrefAnd Qref；
2.22. The value of the grid current is obtained from the current measuring device and the alpha and beta components of the grid current in the stationary coordinate system are calculated.
2.23. Substituting the active power reference value and the reactive power reference value into the formulas (6) and (7) to calculate the component of the current reference value, and making a difference with the corresponding component of the power grid current to obtain an error signal which is an alternating current component;
2.24. and obtaining a modulation signal by adopting a proportional resonant PR controller to realize zero steady-state error tracking, and finally obtaining a driving pulse by a sinusoidal pulse width modulation strategy.
6. The flexible switch grid-connected and grid-disconnected coordination control method based on the static coordinate system is characterized by comprising the following steps of: and 3.1 inverter side faults and 3.2 rectifier side faults can be divided in the step 3 according to the fault types.
7. The flexible switch grid-connected and grid-disconnected coordination control method based on the static coordinate system is characterized in that: in the 3.1 inverter side fault, the inverter side converter switches the PQ control strategy to constant voltage and constant frequency control so as to maintain the stability of the voltage and the frequency of the alternating current bus and provide reliable power supply for the load on the alternating current bus, and the control method comprises the following steps:
3.11. when the power grid is normal, the control switch S is connected to 1, and the inverter side converter works in a PQ control mode;
3.12. after the power grid on the inversion side breaks down, triggering a switch S to be connected into 2 after island detection, and switching the PQ control to constant-voltage constant-frequency control under a static coordinate system;
3.13. in the constant voltage and constant frequency control, a voltage outer ring reference value is subtracted from the voltage of an actual load terminal to obtain a voltage alternating current error signal, then a current inner ring reference value is obtained through a PR controller, then current inner ring control is carried out, and finally a driving signal is generated;
in the 3.2 rectification side fault, the control strategies of the rectification side converter and the inversion side converter need to be adjusted: the inverter side converter is switched to direct current bus voltage control from PQ control so as to maintain the stability of the direct current bus voltage; the rectification side converter switches from direct current bus voltage control to constant voltage and constant frequency control so as to maintain the stability of alternating current bus voltage and frequency at a fault side, and the control method comprises the following steps:
3.21. under the normal condition of a power grid, a control switch S of a rectification and inversion side converter is connected into 1;
3.22. after the grid at the rectification side fails, triggering a control switch S to be connected into the control switch 2 after island detection;
3.23. PQ control of the inverter converter is switched to a direct current voltage and reactive power control mode, an inner loop current reference value is calculated according to a direct current error and a reactive power reference value after PI operation, and a driving pulse is obtained after the inner loop current reference value passes through a PR controller;
3.24. the rectification side converter is switched to a constant voltage and constant frequency control mode from direct current bus voltage control, a voltage alternating current error signal is obtained by subtracting the voltage of an actual load end from the voltage of a voltage outer ring, then a current inner ring reference value is obtained through a PR controller, then current inner ring control is carried out, and finally a driving pulse is generated.
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