An autonomous synchronous medium voltage interconnection system and a control method thereof

Abstract

The application discloses an autonomous synchronous medium-voltage interconnection system and a control method thereof, and the system comprises a total control device, a phase-shifting voltage regulating transformer T1, a series transformer T2, a parallel transformer T3, a solid-state switch, a series power module, a parallel power module, a first circuit breaker QF1, a second circuit breaker QF2, a first voltage transformer, a second voltage transformer, a third voltage transformer and a shell; the method comprises an initial state, system access, voltage amplitude and phase coarse adjustment, voltage amplitude and phase fine adjustment, line operation in a closed-loop state and power flow adjustment. The application realizes flexible and safe interconnection and power supply without power interruption of distribution networks, realizes bidirectional power flow control and power support through changing line voltage amplitude, phase and impedance and other modes, fully excavates the potential of existing lines, enhances the interconnection, intercommunication, bearing and photovoltaic consumption capacity of the distribution network, and has important significance for improving the power supply reliability of the distribution network.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power distribution system, in particular to an autonomous synchronous medium voltage interconnection system and a control method thereof. BACKGROUND

[0002] Based on the development goal of the new power system of State Grid, the power grid has gradually changed from the original source and load architecture to a complex system combined with distributed power supply, energy storage system and new type of control device. New energy will be connected to the power grid in a centralized or distributed manner. It is not uncommon for part of the distribution network line to send the main network in reverse. Long-term reverse sending of a large number of distributed photovoltaic will affect the correct rate of the function of feeder automation and the quality of line voltage, resulting in low overall operation efficiency of the system. At the same time, due to the unreasonable structure of the power grid and the increasingly prominent problem of development lag, the load of the receiving end power grid is in high position for a long time during the peak load period. Unbalanced load distribution leads to frequent overload of distribution network lines and equipment. The existing technology generally adopts closed-loop design and open-loop operation. Power electronic technology is the main choice to realize long-time loop closing operation. However, the flexible interconnection device based on power electronic technology has large occupation area, high engineering cost, difficult operation and maintenance, large loss and poor reliability, and is difficult to be widely applied in the distribution network. The phase difference between each gear of the phase-shift voltage regulator scheme is at least 2°, and the precision cannot meet the requirement of accurate control of power flow. Therefore, it is necessary to propose an autonomous synchronous medium voltage interconnection system to reduce the occupation area, engineering cost and loss of the device, and improve the reliability of the system. SUMMARY

[0003] The purpose of the present application is to provide an autonomous synchronous medium voltage interconnection system and a control method thereof.

[0004] Technical scheme: The autonomous synchronous medium voltage interconnection system provided by the present application comprises a total control device, a phase-shift voltage regulator transformer T1, a series transformer T2, a parallel transformer T3, a solid-state switch, a series power module, a parallel power module, a first circuit breaker QF1, a second circuit breaker QF2, a first voltage transformer, a second voltage transformer, a third voltage transformer and a shell. The first voltage transformer collects the voltage at the input end of the series transformer T2. The second voltage transformer and the third voltage transformer collect the phase and amplitude of the voltage on both sides of the second circuit breaker QF2, respectively, and transmit them to the total control device. The total control device controls the closing of the first circuit breaker QF1, and performs loop closing according to the phase difference and amplitude difference of the voltage on both sides of the second circuit breaker QF2. After loop closing, the total control device obtains the output power of line A and line B at the outlet of the substation through wireless communication, and adjusts the gear of the phase-shift voltage regulator transformer T1 and the voltage coupled to the primary line, so that the output power of line A and line B at the outlet of the substation is consistent.

[0005] Further, the phase-shifting and voltage-regulating transformer T1 comprises a phase-shifting and voltage-regulating transformer body, a voltage-regulating switch, a phase-regulating switch, a voltage-regulating controller and a phase-regulating controller.

[0006] Further, the total control device controls the phase-shifting and voltage-regulating transformer T1 to be adjusted in real time under load to a suitable gear, realizes preliminary adjustment, controls the series power module to generate a voltage on the secondary side of the series transformer T2, and couples to the primary side of the series transformer T2 for fine adjustment, until the voltages on both sides of the second circuit breaker QF2 are consistent, and then the loop is closed.

[0007] The autonomous synchronization type medium voltage interconnection control method comprises the following steps:

[0008] S1: In the initial state, the A station and the B station are operated in parallel, the disconnecting switch QS1 and the disconnecting switch QS2 are closed, the first circuit breaker QF1 and the second circuit breaker QF2 are opened, and the system is in a hot standby state;

[0009] S2: The total control device first controls the solid-state switch to be closed, so that the secondary side of the series transformer is short-circuited, at this time, the series transformer functions as a current-limiting reactor, then the first circuit breaker QF1 is closed, and after the first circuit breaker QF1 is closed, the solid-state switch is opened, and a voltage generated by the series power module is applied to the series transformer;

[0010] S3: The total control device controls the phase-shifting and voltage-regulating transformer T1 to adjust the phase and voltage gear according to the phase difference and voltage difference on both sides of the second circuit breaker QF2 collected by the second voltage transformer and the third voltage transformer;

[0011] S4: The total control device controls the series power module to output a specified voltage to the secondary side of the series transformer T2 in real time according to the phase difference and voltage difference on both sides of the second circuit breaker QF2 collected by the second voltage transformer and the third voltage transformer, and then the voltage is coupled into the primary circuit;

[0012] S5: The total control device closes the second circuit breaker QF2 when the loop closing condition is met, so that the line is in a loop operating state;

[0013] S6: The total control device acquires the currents of the line A and the line B at the outlet of the substation through wireless communication, controls the voltage-regulating and phase-regulating gears of the phase-shifting and voltage-regulating transformer T1 for coarse adjustment, and then controls the series power module for fine adjustment, so as to ensure that the output powers of the line A and the line B at the outlet of the substation are basically consistent.

[0014] Further, the step S3 comprises controlling the phase-shifting and voltage-regulating transformer T1 until the voltage difference ≤130V, and the phase difference ≤2°, wherein , , and The voltage and phase collected by the third voltage transformer, and The voltage and phase collected by the second voltage transformer.

[0015] Further, the step S4 includes controlling the series power module in real time to make the angle difference and the pressure difference on both sides of the second circuit breaker QF2 and dynamically zero, that is, , , wherein and The voltage and phase collected by the second voltage transformer, and The voltage and phase collected by the first voltage transformer.

[0016] Further, the step S5 of the loop closing condition is that the angle difference and the pressure difference on both sides of the second circuit breaker QF2 are dynamically zero.

[0017] Further, the step S6 of the adjustment logic includes:

[0018] After the system loop is closed, the currents on the line A and the line B are self-balanced, the active power flowing through the medium voltage interconnection system is , and the reactive power is By monitoring the output power of the line A and the line B at the substation outlet, the size of the power flow that needs to be adjusted is calculated, that is, and ;

[0019] The active power and the reactive power flowing through the phase-shifting voltage regulator are preliminarily calculated:

[0020] ,

[0021] ,

[0022] wherein, is the voltage at the beginning of the line; is the voltage at the end of the line; δ is the phase difference between the beginning and the end of the line; is the additional electromotive force generated by the phase-shifting voltage regulator after voltage regulation; is the additional phase angle generated by the phase-shifting voltage regulator after phase regulation; is the line impedance; is the impedance of the phase-shifting voltage regulator.

[0023] Further, the active power flowing through the phase-shifting voltage regulator is ; and the reactive power When the phase-shifting voltage regulator is adjusted in place, the output voltage of the series power module is controlled to the secondary side of the series transformer, which is coupled to the primary circuit for fine adjustment until , .

[0024] Further, the active power and the reactive power flowing through the phase-shifting voltage regulator are calculated by transverse voltage regulation and longitudinal voltage regulation principles.

[0025] Advantages: Compared with the prior art, the present application has the following significant advantages:

[0026] (1) The phase-shifting voltage regulator and the series transformer adopt a common oil tank design, effectively reducing the size, weight and overall cost of the medium-voltage interconnection device;

[0027] (2) The phase-shifting voltage regulator and the power electronic module are mixedly regulated, i.e., the phase-shifting voltage regulator is coarsely regulated, and the power electronic module is finely regulated, while the power at the outlet of the substation is collected in real time, and the automatic and accurate control of the power flow is realized through a power flow control algorithm;

[0028] (3) The excitation inrush current and short-circuit current anti-through protection function is added, the series transformer adopts a high leakage reactance design, and the secondary side uses solid-state switches for short-circuit protection, when the phase-shifting voltage regulator is loaded at no load or a short-circuit fault occurs in the 10kV line, the secondary side of the series transformer is quickly short-circuited, at this time, the series transformer is equivalent to a current limiting reactor, effectively avoiding the excitation inrush current and short-circuit current through the phase-shifting voltage regulator when the phase-shifting voltage regulator is loaded at no load;

[0029] (4) By integrating the phase-shifting voltage regulator and the power electronic module, compared with the pure power electronic power flow control device, the capacity of the power electronic module can be effectively reduced under the premise of ensuring the power flow control, thereby reducing the cost and maintenance difficulty. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a system structure diagram of the present application. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be further described below with reference to the drawings.

[0032] For example, Figure 1As shown, the autonomous synchronous medium voltage interconnection system provided by the application comprises a total control device, a phase-shifting voltage regulating transformer T1 (including a phase-shifting voltage regulating transformer body, a voltage regulating switch, a phase regulating switch, a voltage regulating controller and a phase regulating controller), a series transformer T2, a parallel transformer T3, a solid state switch, a series power module, a parallel power module, a first circuit breaker QF1, a second circuit breaker QF2, a first voltage transformer, a second voltage transformer, a third voltage transformer and a shell; the first voltage transformer collects the voltage at the incoming line end of the series transformer T2, the second voltage transformer and the third voltage transformer respectively collect the phase and amplitude of the voltage on both sides of the second circuit breaker QF2, and transmit to the total control device; the total control device controls the closing of the first circuit breaker QF1, and performs loop closing according to the phase difference and amplitude difference of the voltage on both sides of the second circuit breaker QF2; after loop closing, the total control device obtains the output power of line A and line B at the outlet of the substation through wireless communication, and then adjusts the gear of the phase-shifting voltage regulating transformer T1 and the voltage coupled to the primary circuit of the series transformer, so that the output power of line A and line B at the outlet of the substation is consistent. The total control device controls the phase-shifting voltage regulating transformer T1 to be adjusted to a suitable gear in real time under load, so as to realize preliminary adjustment, and then controls the series power module to generate a voltage at the secondary side of the series transformer T2 and couple to the primary side of the series transformer T2 for fine adjustment, until the voltage on both sides of the second circuit breaker QF2 is consistent, and then loop closing is performed.

[0033] The autonomous synchronous medium voltage interconnection control method provided by the application comprises the following steps:

[0034] S1: initial state: A station and B station operate in separate columns, disconnectors QS1 and QS2 are closed, the first circuit breaker QF1 and the second circuit breaker QF2 are opened, and the system is in a hot standby state;

[0035] S2: system access: the total control device first controls the solid state switch to be closed, so that the secondary side of the series transformer is short-circuited, at this time the series transformer plays the role of a current limiting reactor, then the first circuit breaker QF1 is controlled to be closed, and after the first circuit breaker QF1 is closed, the solid state switch is disconnected, and a voltage is generated by the series power module and applied to the series transformer;

[0036] S3: coarse adjustment of voltage amplitude and phase: the total control device controls the phase-shifting voltage regulating transformer T1 to adjust the gear of the phase and voltage according to the phase difference and voltage difference of the voltage on both sides of the second circuit breaker QF2 collected by the second voltage transformer and the third voltage transformer; the phase-shifting voltage regulating transformer T1 is controlled until the voltage difference ≤130V, the phase difference ≤2°, wherein , , and are the voltage and phase collected by the third voltage transformer, and The voltage and phase collected by the second voltage transformer;

[0037] S4: Fine adjustment of voltage amplitude and phase: The total control device controls the series power module to output specified voltage to the secondary side of the series transformer T2 according to the angle difference and pressure difference on both sides of the second circuit breaker QF2 collected by the second voltage transformer and the third voltage transformer, and then coupled into the primary circuit; the total control device controls the series power module to make the angle difference and pressure difference on both sides of the second circuit breaker QF2 and pressure difference dynamics zero, that is , , wherein and is the voltage and phase collected by the second voltage transformer, and is the voltage and phase collected by the first voltage transformer;

[0038] S5: Loop closing: the total control device closes the second circuit breaker QF2 to make the line in a loop closing operation state after judging that the loop closing condition (the angle difference and pressure difference on both sides of the second circuit breaker QF2 dynamics zero) is met;

[0039] S6: Power flow regulation: the total control device obtains the current of the line A and the line B at the outlet of the substation through wireless communication, controls the voltage regulation and phase regulation position of the phase shifting voltage regulator T1 for coarse adjustment, and then controls the series power module for fine adjustment, so as to ensure that the output power of the line A and the line B at the outlet of the substation is basically consistent.

[0040] The regulation logic includes:

[0041] The current on the line A and the line B will self-balance after the system loop closing, the active power flowing through the medium voltage interconnection system is , the reactive power is , by monitoring the output power of the line A and the line B at the outlet of the substation, the size of the power flow that needs to be adjusted is calculated, that is and ;

[0042] Through the principle of horizontal voltage regulation and vertical voltage regulation, the active power and the reactive power flowing through the phase shifting voltage regulator are preliminarily calculated:

[0043] ,

[0044]

[0045] wherein, is the voltage at the beginning of the line; is the voltage at the end of the line; δ is the phase difference between the beginning and the end of the line; The additional electromotive force generated by the phase-shifting voltage regulator after voltage regulation The additional phase angle generated by the phase-shifting voltage regulator after phase adjustment The line impedance The impedance of the phase-shifting voltage regulator

[0046] The active power flowing through the phase-shifting voltage regulator = The reactive power flowing through the phase-shifting voltage regulator After the phase-shifting voltage regulator is adjusted to the right position, the output voltage of the series power module is controlled to the secondary side of the series transformer, which is coupled to the primary circuit for fine adjustment until , .

[0047] The main functions of the system include basic functions and protection functions:

[0048] The basic functions include remote signaling and remote measurement functions: collecting three-phase voltage, current, phase, frequency, and parameters such as active power, reactive power, and power factor at the sending end and receiving end; phase adjustment and voltage regulation functions: the system can adjust the phase difference and voltage difference on both sides of the loop point; loop detection function: the system can automatically detect whether the loop conditions (i.e., voltage and phase within the allowed range) are met before the loop is connected; loop transfer function: the total control device coordinates the FTU, phase-shifting switch, and voltage regulation switch to realize manual or automatic loop transfer; wave recording function: fault recording, energy storage circuit recording, and switching action recording functions; automation function: 4G / 5G private network communication function, supporting remote data acquisition, processing, and remote control operation functions of the dispatching master station.

[0049] The protection functions include short-circuit fault and ground fault detection and processing functions; phase-shifting voltage regulator body protection functions: gas, oil level, pressure, and temperature protection functions, which alarm or trip the incoming and outgoing line breakers when abnormalities are detected; overcurrent protection function: three-stage protection, which can set the protection action time limit and current value;

[0050] Zero sequence current protection function: two-stage protection, which can set the protection action time limit and current value; fault event uploading function: fault events include fault remote signaling information and analog quantities such as voltage and current at the time of fault occurrence; excitation inrush current and short-circuit current anti-penetration protection function: when the phase-shifting voltage regulator is empty, the secondary side of the series transformer is quickly short-circuited, at which time the series transformer is equivalent to a current-limiting reactor, which can effectively avoid the excitation inrush current when the phase-shifting voltage regulator is empty; when a short-circuit fault occurs in the 10kV line, the secondary side of the series transformer is quickly short-circuited, at which time the series transformer is equivalent to a current-limiting reactor, and the breakers on both sides of the medium-voltage interconnection device are tripped, which can avoid fault penetration.

Claims

1. A self-synchronized medium voltage interconnection control method, realized by a self-synchronized medium voltage interconnection system, characterized in that, The autonomous synchronous medium-voltage interconnection system comprises a total control device, a phase-shifting voltage regulating transformer T1, a series transformer T2, a parallel transformer T3, a solid-state switch, a series power module, a parallel power module, a first circuit breaker QF1, a second circuit breaker QF2, a first voltage transformer, a second voltage transformer, a third voltage transformer, and a housing; the first voltage transformer collects the voltage at the incoming line end of the series transformer T2, the second voltage transformer and the third voltage transformer collect the phase and amplitude of the voltage on both sides of the second circuit breaker QF2, and transmit the voltage to the total control device; the total control device controls the closing of the first circuit breaker QF1, and performs loop closing according to the phase difference and amplitude difference of the voltage on both sides of the second circuit breaker QF2; after loop closing, the total control device obtains the output power of line A and line B at the outlet of the substation through wireless communication, and adjusts the gear of the phase-shifting voltage regulating transformer T1 and the voltage coupled to the primary circuit of the series transformer, so that the output power of line A and line B at the outlet of the substation is consistent. The autonomous synchronous medium-voltage interconnection control method comprises the following steps: S1: In the initial state, substation A and substation B are operated in parallel, the disconnecting switch QS1 and the disconnecting switch QS2 are closed, the first circuit breaker QF1 and the second circuit breaker QF2 are opened, and the system is in a hot standby state; S2: The total control device first controls the closing of the solid-state switch, so that the secondary side of the series transformer is short-circuited, at this time the series transformer functions as a current-limiting reactor, then controls the closing of the first circuit breaker QF1, and after the closing of the first circuit breaker QF1, the solid-state switch is opened, and a voltage is generated by the series power module and applied to the series transformer; S3: The total control device controls the phase-shifting voltage regulating transformer T1 to adjust the phase and voltage gear according to the phase difference and voltage difference of the voltage on both sides of the second circuit breaker QF2 collected by the second voltage transformer and the third voltage transformer; S4: The total control device controls the series power module to output a specified voltage to the secondary side of the series transformer T2 and then coupled to the primary circuit in real time according to the phase difference and voltage difference of the voltage on both sides of the second circuit breaker QF2 collected by the second voltage transformer and the third voltage transformer; S5: The total control device closes the second circuit breaker QF2 when it is determined that the loop closing condition is met, so that the line is in a loop closing operation state; S6: The total control device obtains the current of line A and line B at the outlet of the substation through wireless communication, controls the voltage regulating and phase adjusting gears of the phase-shifting voltage regulating transformer T1 for coarse adjustment, and then controls the series power module for fine adjustment, so as to ensure that the output power of line A and line B at the outlet of the substation is basically consistent; The step S6 adjustment logic comprises: The current on line A and line B will self-balance after the system closes, and the active power flowing through the medium-voltage interconnection system is , the reactive power is , by monitoring the output power of line A and line B at the substation outlet, the size of the power flow that needs to be adjusted is calculated, that is and ; Preliminary calculation of active power flowing through phase-shifting voltage regulator and reactive power : ， ， wherein, V is the line end voltage; V is the line end voltage; δ is the phase difference between the line end and the line end itself; E is the additional electromotive force generated by the phase-shifting voltage regulator after voltage regulation; φ is the additional phase angle generated by the phase-shifting voltage regulator after phase shifting; Z is the line impedance; Z is the phase-shifting voltage regulator impedance.

2. The autonomous synchronous medium voltage interconnection control method according to claim 1, characterized in that, The phase-shifting voltage regulating transformer T1 comprises a phase-shifting voltage regulating transformer body, a voltage regulating switch, a phase adjusting switch, a voltage regulating controller, and a phase adjusting controller.

3. The autonomous synchronous medium voltage interconnection control method according to claim 1, characterized in that, The total control device controls the phase-shifting voltage regulating transformer T1 to be adjusted to a suitable gear in real time under load, realizes preliminary adjustment, controls the series power module to generate a voltage at the secondary side of the series transformer T2, and couples the voltage to the primary side of the series transformer T2 for fine adjustment, until the voltage on both sides of the second circuit breaker QF2 is consistent, and then loop closing is performed.

4. The autonomous synchronous medium voltage interconnection control method according to claim 1, characterized in that, Said step S3 comprises controlling the phase displacement voltage transformer T1 until the voltage difference ≤ 130 V, the angular difference ≤ 2°, wherein , , and are the voltage and phase acquired by the third voltage transformer, and are the voltage and phase acquired by the second voltage transformer.

5. The autonomous synchronous medium voltage interconnection control method according to claim 1, characterized in that, The step S4 comprises controlling in real time the series power module to make the angular difference and the pressure difference dynamic to be zero, i.e. , wherein and are the voltage and phase collected by the second voltage transformer, and are the voltage and phase collected by the first voltage transformer.

6. The autonomous synchronous medium voltage interconnection control method according to claim 1, characterized in that, The step S5 loop closing condition is that the phase difference and voltage difference of the voltage on both sides of the second circuit breaker QF2 are dynamically zero.

7. The autonomous synchronous medium voltage interconnection control method according to claim 1, characterized in that, active power flowing through the phase-shifting voltage regulator = ; Reactive power flowing through phase-shifting voltage regulator When the phase-shifting voltage regulator is adjusted to the right position, the series power module is controlled to output a specified voltage to the secondary side of the series transformer, which is coupled to the primary circuit for fine adjustment until , .

8. The autonomous synchronous medium voltage interconnection control method according to claim 1, characterized in that, The active power flowing through the phase shifting voltage regulator and the reactive power are calculated by transversal and longitudinal voltage regulation principles.

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