Hybrid controllable series compensation device

Abstract

The utility model discloses a hybrid controllable series compensation device, which relates to the field of flexible alternating current power transmission of a power system and comprises fixed series capacitors C, CC and CTCSC, a reactor LTCSC and two anti-parallel thyristor valves. The fixed series capacitor C is a fixed series compensation device for a phase a and a phase b of the power transmission line; the reactor LTCSC and the two thyristor valves are connected in series to form a thyristor control reactor branch; the thyristor control reactor branch is connected with a fixed series capacitor CTCSC in parallel to form a single-phase controllable series compensation system; the fixed series capacitor CC and the single-phase controllable series compensation system are connected in series to serve as a compensation device of a c-phase power transmission line. According to the utility model, a control strategy of an active damping controller based on a synchronous voltage reversal control method is adopted to control the device, so that suppression of subsynchronous resonance is realized, and safe and stable operation of a power transmission line is ensured.

Description

Technical Field

[0001] The utility model relates to the field of flexible AC power transmission in power systems, in particular to a hybrid controllable series compensation device. Background Art

[0002] my country's energy distribution and demand are extremely unbalanced. "National networking, north-south mutual supply, west-to-east power transmission" has become the basic orientation of resource allocation. Large-capacity and long-distance power transmission is an inevitable trend in the development of the power system. Ultra-high / ultra-high voltage transmission can effectively save line corridors and improve economic benefits, but with the increase in the transmission capacity of long-distance ultra-high voltage AC lines, its transient stability will be limited. Under the premise of stable system operation, it is necessary to improve the economic benefits, protect the environment, improve the transmission capacity of the line, and save the transmission line corridor. Series compensation technology is an economical and effective method to improve the transient stability of the system, and is increasingly used in ultra-high / ultra-high voltage long-distance and large-capacity power transmission projects.

[0003] Series compensation technology is to connect capacitor banks in series in the AC line to reduce the reactance of the AC line and shorten the phase difference between the two ends of the capacitor bank, which can enhance the stability and reliability of the line during operation and achieve the goal of high efficiency, large capacity and long-distance transmission of the power system. Series compensation usually includes fixed series compensation (FSC) and controllable series compensation (TCSC).

[0004] FSC can effectively improve the transient stability of the system and increase the system's transmission capacity, but FSC cannot be flexibly adjusted to adapt to various operating conditions, cannot effectively suppress system oscillations, and is not ideal in terms of flexible control of system trends.

[0005] TCSC is an improvement on FSC. It uses flexible AC transmission technology to integrate various new power electronic compensation devices. It realizes smooth adjustment and dynamic response control of series compensation capacitors through triggering control of semiconductor thyristor valves, further improving the power transmission capacity of the power grid and the operating stability of the power system, and suppressing low-frequency oscillations and subsynchronous resonance of the power system.

[0006] The structure of TCSC is relatively simple. By continuously adjusting the impedance, the transmission capacity of the system can be increased, the stability of the system can be increased, and the purpose of controlling the power flow can be achieved. Therefore, many actual projects have applied the TCSC compensation method. However, compared with FSC, TCSC requires higher costs. According to the actual operation needs, the combination of FSC and TCSC is generally adopted. For example, the Yimin-Fengtun line adopts 30% FSC and 15% TCSC.

[0007] It is difficult to transform the FSC line to the FSC+TCSC mode, as the three-phase operation is required, and the fixed capacitor needs to be adjusted to ensure that the total compensation degree of the line remains unchanged. Therefore, in order to flexibly adjust the series compensation device and improve the economy of the system, the utility model proposes a hybrid controllable series compensation device. Utility Model Content

[0008] The purpose of the utility model is to provide a hybrid controllable series compensation device to solve the problems raised in the above background technology.

[0009] In order to solve the above technical problems, the utility model provides the following technical solutions: a hybrid controllable series compensation device, comprising fixed series capacitors C, C C , C TCSC , Reactor L TCSC and two parallel thyristor valves;

[0010] The fixed series capacitor C is used as a fixed series compensation device for the two phases a and b of the transmission line;

[0011] Two parallel thyristor valves are connected in anti-parallel;

[0012] The reactor L TCSC It is connected in series with two reverse parallel thyristor valves to form a thyristor controlled reactor branch;

[0013] The thyristor controlled reactor branch is connected to a fixed series capacitor C TCSC Connect in parallel to form a single-phase controllable series compensation system;

[0014] The fixed series capacitor C C It is connected in series with the single-phase controllable series compensation system as a compensation device for the C-phase transmission line.

[0015] Preferably, the capacitance values ​​of the fixed series capacitors C are equal.

[0016] Preferably, the single-phase controllable series compensation system dynamically adjusts its equivalent impedance by adjusting the trigger angle, and its equivalent impedance satisfies the following conditions at the power frequency: Z a =Z b =Z c At non-industrial frequency, the three-phase impedances are not equal, resulting in unbalanced stator three-phase current. The amplitude of the positive component of the armature winding magnetomotive force is smaller than the amplitude of the positive armature magnetomotive force generated by the three-phase balanced current, thereby weakening the electromechanical coupling of the generator and suppressing subsynchronous oscillations to a certain extent.

[0017] Preferably, the hybrid controllable series compensation device adopts a hierarchical control method, in which the upper-level control is mainly used for power system control and provides control commands according to system requirements; the middle-level control is impedance control, and the system variable commands of the upper-level control are converted into impedance commands according to the circuit relationship; the task of the bottom-level control is to realize the triggering of the thyristor and obtain the command value of the trigger angle according to the relationship between impedance and the trigger angle.

[0018] Preferably, the hybrid controllable series compensation device is controlled by an active damping controller based on a synchronous voltage reversal control method. The synchronous voltage reversal control method avoids the highly nonlinear relationship between fundamental impedance and trigger angle, and only determines the triggering moment of the thyristor by controlling the voltage zero crossing point, so the control is more accurate, the suppression effect on subsynchronous oscillation is good, and the stable operation of the power transmission system is ensured.

[0019] Compared with the prior art, the beneficial effects of the utility model are:

[0020] The utility model adopts fixed series compensation devices for phases a and b to compensate reactive power of the transmission line, and phase c adopts single-phase TCSC and fixed series capacitor in series as compensation devices. The three phases together form a hybrid controllable series compensation device, and the control strategy of active damping controller based on synchronous voltage reversal control method is used to control the device to achieve subsynchronous resonance suppression, so as to ensure that the transmission line can operate safely and stably. Compared with three-phase TCSC, this method reduces the number of thyristors by 2 / 3, and the control and protection only need to be designed as a single phase, which reduces the cost and control difficulty; compared with fixed series compensation, it can more effectively improve the system transmission capacity, suppress system oscillation and improve the system transient stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a structural diagram of the hybrid controllable series compensation device of the utility model;

[0022] Figure 2 This is the principle diagram of the active damping controller of the utility model;

[0023] Figure 3 This is the control block diagram of the active damping controller of the utility model;

[0024] Figure 4 This is a control block diagram of the synchronous voltage reversal control method of the utility model. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0026] Referring to 1-4, this embodiment provides a hybrid controllable series compensation device, including fixed series capacitors C, C C , C TCSC , Reactor L TCSC and two anti-parallel thyristor valves.

[0027] In this embodiment, if Figure 1 As shown in the figure, the fixed series capacitor C is used as a fixed series compensation device FSC for the two phases of the transmission line a and b. By compensating the corresponding capacitive reactance in the line, the electrical distance between the generator sets is shortened to achieve the purpose of improving the stability of the system operation, increasing the system power transmission capacity and saving the line corridor.

[0028] Reactor L TCSC And two reverse parallel thyristor valves in series, and with capacitor C TCSC In order to reduce the economic cost and improve the economic efficiency of the device, a fixed series capacitor C is set C It is connected in series with the single-phase TCSC as the line phase C compensation device. The TCSC realizes smooth regulation and dynamic response control of the series compensation capacitor through the triggering control of the semiconductor thyristor valve, further improving the power transmission capacity of the power grid and the stability of the power system operation, and suppressing the low-frequency oscillation and subsynchronous resonance of the power system.

[0029] In this embodiment, phases a and b use FSC, and phase c uses a single-phase TCSC and capacitor C C The three-phase equivalent impedance should satisfy the following conditions at power frequency: Z a =Z b =Z c At non-industrial frequency, the three-phase impedances are not equal, resulting in unbalanced stator three-phase currents. The positive component amplitude of the armature winding magnetomotive force is smaller than the positive armature magnetomotive force amplitude generated by the three-phase balanced current, thereby weakening the electromechanical coupling of the generator and suppressing subsynchronous oscillations.

[0030] The steady-state fundamental wave equivalent impedance of TCSC has a nonlinear relationship with the trigger angle. Assuming the current source is a sinusoidal current wave, the line current i L is a synchronous signal, and its equivalent impedance expression is:

[0031]

[0032] in,

[0033] ω0=2πf0;

[0034]

[0035]

[0036] Where:

[0037] α is the thyristor trigger angle;

[0038] C TCSC is the capacitance value of the TCSC system; L TCSC is the inductance value of the inductor;

[0039] f0 is the frequency;

[0040] To trigger the front angle;

[0041] ω is the angular frequency component of the power frequency;

[0042] ω r is the natural oscillation frequency component;

[0043] k is a constant, generally between 2.2-2.7.

[0044] In the parameter design of the hybrid controllable series compensation device, the fixed series capacitor C value mainly determines the line compensation degree and is given according to the requirements related to the actual system transmission capacity and stability. C The parameters of CSC are matched to meet the three-phase impedance of power frequency. Due to the low cost of fixed capacitors, C should be used to meet the requirements of subsynchronous oscillation suppression of the system. C The compensation ratio occupied is as large as possible. The parameters that need to be determined by TCSC are mainly C TCSC , L TCSC and firing angle α, C TCSC The setting of C is determined by the line compensation ratio occupied by TCSC. The cost of TCSC device is high. Under the premise of achieving the same oscillation suppression performance, C TCSC The compensation ratio should be as small as possible.

[0045] The hybrid controllable series compensation device adopts a hierarchical control method. The upper-level control adopts a hierarchical control method. The upper-level control is mainly used for power system control and provides control commands according to system requirements; the middle-level control is impedance control, and the system variable commands of the upper-level control are converted into impedance commands according to the circuit relationship; the task of the bottom-level control is to realize the triggering of the thyristor, and obtain the command value of the trigger angle according to the relationship between impedance and trigger angle.

[0046] This embodiment uses an active damping controller based on a synchronous voltage reversal control method to control the TCSC thyristor trigger angle, so as to continuously and smoothly adjust the thyristor trigger angle, thereby achieving the purpose of improving the stability of system operation, increasing the system power transmission capacity, and suppressing subsynchronous resonance problems. The device adopts a synchronous voltage reversal control method and designs an active damping controller to change the TCSC thyristor trigger angle to suppress the subsynchronous resonance problem of the system. The synchronous voltage reversal control method avoids the highly nonlinear relationship between the fundamental impedance and the trigger angle, and only determines the triggering moment of the thyristor by controlling the voltage zero point. Therefore, the control is more accurate, the suppression effect on subsynchronous oscillation is good, and the stable operation of the transmission system is ensured.

[0047] like Figure 2 As shown in the figure, the design principle of the active damping controller is to establish a coordinate system based on the speed deviation Δω. e When in the 3rd and 4th quadrants, ΔT eD If an additional electromagnetic torque ΔT in the 1st or 2nd quadrant is provided, sup , and the electromagnetic torque ΔT e Perform vector superposition to obtain the total electromagnetic torque ΔT t , at this time the system has a positive damping torque ΔT tD , in order to suppress the subsynchronous resonance problem of the system and ensure the stability of the transmission line.

[0048] like Figure 3 As shown in the figure, the speed deviation Δω is output as an additional signal kB after bandpass filtering, proportional amplification, phase compensation and amplitude limiting. S , then kB S Added to the controller of synchronous voltage reversal method to further realize thyristor trigger angle control.

[0049] The present application adopts an active damping controller based on a synchronous voltage reversal control method to suppress the subsynchronous resonance of the system to ensure stable operation of the system. Figure 4 The control strategy block diagram of the active damping controller based on the synchronous voltage reversal control method is shown in Figure 2. L The signal synchronization quantity is obtained by PLL phase locking to obtain the phase angle θ, and the capacitor voltage u is obtained through the voltage transformer and current transformer C and line current i L , the phasor is estimated to be Divide the two and take the imaginary part to get the equivalent reactance X TCSC , according to the definition, we can find k B . k Bref is the impedance factor reference value, and the difference between the measured value and the reference value is the obtained error. The input of the capacitor voltage zero-crossing controller is the impedance error, and the output is After passing through the comparator, the time reference pulse required by the synchronous voltage reversal control module is generated to change the thyristor trigger angle, suppress the subsynchronous resonance problem of the system, and ensure the stable operation of the transmission line.

[0050] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A hybrid controllable series compensation device, characterized in that: Including fixed series capacitors C, C C , C TCSC , Reactor L TCSC and two parallel thyristor valves; The fixed series capacitor C is used as a fixed series compensation device for the two phases a and b of the transmission line; Two parallel thyristor valves are connected in anti-parallel; The reactor L TCSC It is connected in series with two reverse parallel thyristor valves to form a thyristor controlled reactor branch; The thyristor controlled reactor branch is connected to a fixed series capacitor C TCSC Connect in parallel to form a single-phase controllable series compensation system; The fixed series capacitor C C It is connected in series with the single-phase controllable series compensation system as a compensation device for the C-phase transmission line.

2. A hybrid controllable series compensation device according to claim 1, characterized in that: The capacitance values ​​of the fixed series capacitors C are equal.

3. A hybrid controllable series compensation device according to claim 2, characterized in that: The single-phase controllable series compensation system dynamically adjusts its equivalent impedance by adjusting the trigger angle, and its equivalent impedance satisfies the following at the power frequency: Z a =Z b =Z c .

4. A hybrid controllable series compensation device according to claim 1 or 2, characterized in that: The a and b phases adopt fixed series compensation, and the c phase adopts a single-phase controllable series compensation system.

5. A hybrid controllable series compensation device according to claim 4, characterized in that: The compensation device is controlled by an active damping controller.

Images