CN101090202A - Flexible AC Transmission System Based on Flywheel Energy Storage - Google Patents

Abstract

This invention relates to a flexible AC transmission system based on flywheel energy-storage including a double-feed flywheel energy-stored motor, an AC excitation supply, a monitor, a serial transformer and an inverse parallel two-way thyristor, in which, the supply includes a parallel side converter, a serial side converter and a capacitor, the AC end of the parallel side converter is connected with the rotor winding of the flywheel energy-stored motor, the two DC ends of which and those of the serial side converter are connected with two ends of the capacitor, the AC end of the serial converter is connected with the first winding of the serial transformer, the second winding of which is parallel to the inverse parallel two-way thyristor and one end of which is connected with the stator winding of the motor and the monitor device realizes by-pass protection by controlling the connection state of the thyristor.

Description

Flexible AC Transmission System Based on Flywheel Energy Storage

technical field

The invention belongs to flywheel energy storage technology and flexible AC power transmission technology, and specifically relates to a flexible AC power transmission system based on flywheel energy storage, including a double-fed flywheel energy storage motor, an AC excitation power supply and a monitoring device.

Background technique

In the current power system, since there are no devices with large capacity and fast access to electric energy, the production and consumption of electric energy must be basically kept in a state of electromechanical power balance at all times. Once the system is disturbed and causes dynamic power imbalance, it may pose a threat to the stability of the system, and serious electromechanical power imbalance will lead to system collapse.

In order to solve this problem, the current common method is to use relay protection and safety and stability control devices to perform operations such as machine cut-off, load shedding, or system de-loading when the system fails, so as to alleviate the power imbalance problem caused by the fault in the system as much as possible. . This kind of control device is often processed according to the accident handling table obtained through a large number of off-line calculations in advance, so it is impossible to fully meet the actual situation of the system when the fault occurs, and of course it may not be able to fully compensate the unbalanced power caused by the fault. We refer to this stabilization control measure as "passive stabilization".

It is precisely because the fundamental problem of dynamic power balance has not been well resolved, so although the operation technology of the power system has made great progress in recent years, the occurrence of large power grid collapse accidents cannot be avoided, especially in 2003 After August, several major power outages occurred continuously around the world, which not only caused huge economic losses, but also brought harm to people's lives and social stability. The safety of the power grid is related to national security.

The existing power grid structure is becoming more and more complex, and the uncoordinated operation and dispatching at the same time will cause unreasonable distribution of power flow in the power grid, making the power transmission network often appear circulation power oscillation, power circumvention, and power backflow during power transmission. The problem causes a large amount of power loss in the large interconnected power grid or is forced to reduce the transmission capacity of the power grid, and even causes a catastrophe in the power system, which greatly affects the operation and scheduling of the entire system, and cannot meet the requirements of ultra-large-scale power transmission and distribution and power grid security. Require.

In order to fundamentally improve the reliability and stability of power system operation from the perspective of power balance, Huazhong University of Science and Technology has proposed an energy-storage phase-modulating motor (the publication number is CN1595772A, and the publication date is March 16, 2005). The device is based on the existing synchronous condenser in the power system, and by improving the structure of the motor, the moment of inertia of the rotor is increased to store electric energy. Storage and release constitute a flexible power control device with functions of energy storage, power generation and phase modulation. The energy storage phase-modulating motor solves the problem of power balance, but it does not involve regulating the power flow of the transmission line to achieve the optimal distribution of the system power flow, suppressing the power oscillation caused by the line-to-ground short circuit, supporting the system node voltage, and ensuring that the transmission capacity of the transmission line is close to issues such as thermal stability limits.

Contents of the invention

The purpose of the present invention is to provide a flexible AC power transmission system based on flywheel energy storage, which has the functions of energy storage, power generation, synchronous phase modulation, stable node voltage, changing line impedance to suppress oscillation and regulating line flow, and can be mainly used in power systems Power flow control and dynamic stability control can effectively and quickly regulate the rapidly changing operating conditions and operating parameters of the power system to ensure safe, economical, efficient, and high-quality operation of the power system under various operating conditions.

The invention proposes a flexible AC power transmission system based on flywheel energy storage, which includes a double-fed flywheel energy storage motor, an AC excitation power supply and a monitoring device. The AC excitation power supply includes a parallel-side converter, a series-side converter and a capacitor, and a Both the converter and the series side converter are three-phase voltage source pulse width modulation converters, the AC terminal of the parallel side converter is connected to the rotor winding of the doubly-fed flywheel energy storage motor, and the two DC terminals of the parallel side converter are connected to the series The two DC terminals of the side converter are respectively connected to both ends of the capacitor, and the monitoring device is used to monitor the parallel side converter and the series side converter, and monitor the voltage and power flow of the transmission line. It is characterized in that: the system also includes a series transformer and Anti-parallel bidirectional thyristor, the primary winding of the series transformer is connected to the AC end of the series side converter, both ends of the secondary winding of the series transformer are connected to both ends of the anti-parallel bidirectional thyristor, one end of the secondary winding of the series transformer is connected to the doubly-fed type The stator winding of the flywheel energy storage motor is connected, and the monitoring device is used to monitor the anti-parallel bidirectional thyristor, and realize bypass protection by controlling the connection state of the anti-parallel bidirectional thyristor.

The parallel-side converter is composed of fully-controlled power switching elements and inductors. The fully-controlled power switching elements form the first three-phase full-bridge structure. The midpoint of the three-phase bridge arm and the rotor winding of the doubly-fed flywheel energy storage motor pass through the three-phase Inductor connected.

The series-side converter is composed of a fully-controlled power switching element and an inductance-capacitor low-pass filter. The fully-controlled power switching element forms a second three-phase full-bridge structure. The midpoint of the three-phase bridge arm and the primary winding of the series transformer pass through three The phase inductance and capacitance low-pass filter is connected.

As an optimization of the present invention, the primary side windings of the series transformers are connected in a delta.

In addition to retaining the functions of the existing energy storage phase modulation motor, the present invention will have more powerful functions, and can realize series compensation, parallel compensation, phase shift control, impedance simulation and real-time control of transmission line flow and many other different functions separately or simultaneously. function, so as to improve the line transmission capacity, stability and damping system oscillation, implement effective and rapid regulation of the rapidly changing operating conditions and operating parameters of the power system, and ensure the safety, economy, efficiency and quality of the power system under various working conditions run. Specifically, the present invention can produce obvious effects in the following aspects:

(1) The converter on the parallel side can realize the decoupling control of the active and reactive power at the stator port and the stable control of the speed. The converter on the series side works in the static synchronous series compensator mode, which can realize the stability of the DC bus voltage and the variable line Impedance control. That is to say, the system has the functions of energy storage, power generation and line flow regulation.

(2) The converter on the parallel side can realize the decoupling control of the active power of the stator port and the stable node voltage and the stable control of the speed. variable impedance control. That is to say, the system has the functions of energy storage, power generation, node voltage stabilization and line power flow regulation.

(3) The converter on the parallel side works in the synchronous phase modulation mode, which has the function of supplying and absorbing reactive power to the system or stabilizing the node voltage and the stable control of the speed. The converter on the series side works in the static synchronous series compensator mode, which can realize DC bus voltage stabilization and line variable impedance control. That is to say, the system has the functions of synchronous phase modulation and line power flow regulation.

Description of drawings

Fig. 1 is a schematic structural diagram of the system of the present invention;

Fig. 2 is the circuit topological structure figure of parallel side converter among the present invention;

Fig. 3 is a circuit topology diagram of the series-side converter in the present invention.

Detailed ways

A flexible AC power transmission system based on flywheel energy storage proposed by the present invention has a structure as shown in Figure 1, including a doubly-fed flywheel energy storage motor 1, an AC excitation power supply, a monitoring device 7, a series transformer 3 and an anti-parallel bidirectional thyristor 6.

The AC excitation power supply includes a parallel-side converter 2, a series-side converter 4, and a capacitor 5. Both the parallel-side converter 2 and the series-side converter 4 are three-phase voltage source type pulse width modulation converters (PWM), and the parallel-side converter The AC terminal of 2 is connected to the rotor winding of the doubly-fed flywheel energy storage motor 1, the two DC terminals of the parallel-side converter 2 and the two DC terminals of the series-side converter 4 are respectively connected to both ends of the capacitor 5, and the series-side converter 4 The AC end of the AC terminal is connected to the primary winding of the series transformer 3.

Both ends of the secondary winding of the series transformer 3 are connected to both ends of the anti-parallel bidirectional thyristor 6 , and one end a of the secondary winding of the series transformer 3 is connected to the stator winding of the double-fed flywheel energy storage motor 1 . The primary side windings of the series transformer 3 are connected in a triangular form, and the effect is optimal.

The monitoring device 7 is used to monitor the parallel-side converter 2 , the series-side converter 4 , and the anti-parallel bidirectional thyristor 6 , and monitor the transmission line voltage, power flow and other electric quantities. The monitoring device 7 realizes bypass protection by controlling the connection state of the anti-parallel bidirectional thyristor 6 . The anti-parallel bidirectional thyristor 6 is turned off when the system works normally, and turned on when a fault occurs.

In power system applications, the stator winding of the doubly-fed flywheel energy storage motor 1 is connected to one end of the grid transmission line access point, and one end b of the secondary winding of the series transformer 3 is connected to the other end of the grid transmission line access point, Therefore, the system is connected in series to the power transmission line of the power grid.

X1 represents the transmission impedance before the power grid transmission line and the access point of the present invention, and X2 represents the transmission impedance after the power grid transmission line and the access point of the present invention.

The doubly-fed flywheel energy storage motor 1 is an electromechanical energy conversion component. Its structure is similar to that of a wound asynchronous motor. Both the stator and the rotor of the rotating motor are equipped with symmetrical three-phase windings. The stator is similar to the stator of an ordinary AC motor. The stator winding consists of Fixed-frequency symmetrical three-phase mains excitation. The motor stator and rotor have the same number of poles. The rotor windings are excited by a symmetrical three-phase power supply with adjustable frequency. The speed of the motor is determined by the slip frequency between the stator and rotor. The stator and rotor magnetic fields of the motor rotate synchronously, so it has characteristics similar to synchronous motors. Installing a flywheel on the rotor shaft increases the moment of inertia of the rotor to store more energy, so the double-fed flywheel energy storage motor 1 can be regarded as a generator without a prime mover and without a mechanical load electric motor. Flywheel energy storage technology uses a high-speed rotating flywheel to store the excess energy of the system in the form of kinetic energy. When the system energy is urgently lacking or needed, the flywheel decelerates and releases the stored kinetic energy. Therefore, the operating modes of the doubly-fed flywheel energy storage motor 1 during normal operation can be divided into the following three types: ①The flywheel keeps rotating at a high speed after starting at the set speed, and the system provides the minimum loss to maintain the energy storage state; ②According to the detection According to the unbalanced power requirements of the system, it is frequently accelerating and decelerating between the upper and lower limits of the rotational speed, absorbing and releasing energy; ③ while maintaining the high-speed rotation of the flywheel, perform synchronous phase modulation.

The AC excitation power supply adopts a dual-PWM voltage source converter structure with four-quadrant slip power, one end of which is connected to the primary three-phase winding of the series transformer 3, and the other end is connected to the rotor three of the double-fed flywheel energy storage motor 1. Phase windings are connected. Corresponding to the operating mode of the double-fed flywheel energy storage motor 1, the parallel side converter 2 also has three operating states: ① The parallel side converter 2 works in the speed mode to ensure that after the double-fed flywheel energy storage motor 1 is started, the flywheel high speed Rotate to maintain the energy storage state; ② through the monitoring device to sense the unbalanced power command of the power system, the parallel side converter 2 works in the power mode, providing and absorbing power, and the flywheel accelerates and decelerates frequently. However, since the doubly-fed flywheel energy storage motor 1 can be regarded as a doubly-fed motor without mechanical load and as a doubly-fed generator without a prime mover. Therefore, when the parallel-side converter 2 works in the power mode, the double-fed flywheel energy storage motor 1 cannot stabilize the motor speed, so when the speed is close to the upper and lower limits of the speed, the parallel-side converter 2 must switch from the power operation mode to the speed operation mode , to stabilize the rotational speed; ③ During synchronous phase modulation, the parallel side converter 2 works in the speed mode, and only accepts the reactive power command of the stator port of the system or the stable node voltage command. Parallel side converter 2 adopts the stator field-oriented vector control technology, and the functions that can be realized include: decoupling control of active power and reactive power at the stator port or decoupling control of active power and node voltage at the stator port; start-up process and power operation Speed stability control during mode and speed operation mode switching; speed stability control during synchronous phase modulation and other functions. The series-side converter 4 adopts grid current (secondary side winding current of the series transformer 3) oriented vector control, which can realize the stable control of the DC bus voltage of the intermediate link and adjust the equivalent impedance on the transmission line of the grid, so as to change the voltage on the transmission line. Active power and reactive power, so as to achieve the purpose of regulating line flow.

As shown in Figure 2, the parallel-side converter 2 is composed of fully-controlled power switching elements and inductors, and the fully-controlled power switching elements form the first three-phase full-bridge structure 8. The rotor windings of the motor 1 are connected through a three-phase inductance 9.

The detected quantities required for the control of the parallel-side converter 2 include stator voltage, stator current, rotor current, DC bus voltage and rotor position angle. The control process is as follows: detect the stator voltage, obtain the space position angle of the stator voltage synthesis vector through hardware or software phase phase, ignore the influence of the stator resistance, obtain the stator flux linkage amplitude and the stator flux angle, and compare with the detected rotor position angle It is used for the control system to perform control under the synchronously rotating dq coordinate system. The speed command is given by the upper and lower limits of the speed set by the system, the stator active power command and the stator reactive power command are given according to the system unbalanced power detected by the monitoring system, and the voltage amplitude command of the stator port node is based on the different functions of the system. Ask for it. The actual stator active power and reactive power are calculated from the detected stator voltage and stator current, and the actual speed is calculated and processed by the rotor position angle as the feedback quantity of the control system. According to different working modes, the dual-loop control dual-channel strategy under the synchronous rotating coordinate system is that the q-axis command of the rotor current is obtained by the upper and lower limit values of the rotational speed command and the feedback value of the rotational speed through the PI regulator or by the stator active power command and the stator active power The feedback amount of power is obtained by the PI regulator, and the d-axis command of the rotor current is obtained by the stator reactive power command and the feedback quantity of the stator reactive power through the PI regulator or by the stator voltage amplitude command and the detection value of the stator voltage amplitude It is obtained through the PI regulator, and then adjusted with the feedback value obtained by the coordinate transformation of the detected rotor current, and considering the influence of the cross-coupling voltage generated by the dq axis current of the motor in the actual system, a certain decoupling control is adopted , and finally get the command voltage of the rotor dq axis, and get the three-phase reference voltage of the rotor through coordinate transformation as the control command of the converter 2 on the parallel side, so as to control the rotor excitation current, which can realize energy storage, power generation, stable node voltage, and synchronization separately or simultaneously Adjustment and other functions.

As shown in FIG. 3 , the series-side converter 4 is composed of a fully-controlled power switching element and an inductance-capacitor (LC) low-pass filter. The fully-controlled power switching element forms a second three-phase full-bridge structure 11, and the three-phase bridge arm The midpoint is connected with the primary winding of the series transformer 3 through a three-phase LC low-pass filter 10 .

The detected quantities required for the control of the series-side converter 4 include the DC bus voltage, the inductor current and capacitor voltage of the LC low-pass filter 10 , and the secondary winding current of the series-connected transformer 3 . The control process is as follows: detect the grid current flowing through the secondary winding of the series transformer 3, and after considering the connection form of the primary and secondary windings of the series transformer 3 and the nature of the impedance to be simulated, obtain the LC low-pass through hardware or software. The capacitor voltage of the filter 10, that is, the space position angle of the voltage synthesis vector of the primary winding of the series transformer 3, is used for the control system to perform control in the synchronously rotating dq coordinate system. The dual-channel strategy under the synchronous rotating coordinate system adopts the multi-loop control based on the inductor current and the capacitor voltage of the LC low-pass filter 10 . The DC bus voltage command and the detected DC bus voltage feedback amount are obtained through the PI regulator to obtain the capacitor voltage d-axis command of the LC low-pass filter 10, and the capacitor voltage q-axis command of the LC low-pass filter 10 is compensated by the required linear impedance Or voltage compensation reference quantity decision. The dq-axis command of the capacitance voltage of the LC low-pass filter 10 and the detected capacitance voltage of the LC low-pass filter 10 undergo coordinate transformation to obtain the dq-axis voltage feedback amount through the PI regulator to obtain the inductor current of the LC low-pass filter 10 The dq-axis command is then PI adjusted with the dq-axis current feedback obtained after coordinate transformation of the detected inductance current of the LC low-pass filter 10, and the cross-coupling voltage generated by the dq-axis current of the converter in the actual system is considered. Affected by certain decoupling control, the dq-axis command voltage at the midpoint of the three-phase full-bridge structure bridge arm in the series-side converter 4 is finally obtained, and the three-phase reference voltage at the midpoint of the three-phase full-bridge structure bridge arm is obtained through coordinate transformation as The control command of the converter 4 on the series side realizes the stable control of the DC bus voltage of the intermediate link and adjusts the equivalent impedance on the transmission line of the power grid, so as to change the active power and reactive power on the transmission line, so as to achieve the purpose of regulating the power flow of the line.

Claims (4)

1. A flexible AC power transmission system based on flywheel energy storage, including a doubly-fed flywheel energy storage motor (1), an AC excitation power supply and a monitoring device (7), and the AC excitation power supply includes a parallel side converter (2), a series side The converter (4) and the capacitor (5), the parallel side converter (2) and the series side converter (4) are all three-phase voltage source pulse width modulation converters, and the AC terminal of the parallel side converter (2) is connected to The rotor winding of the doubly-fed flywheel energy storage motor (1) is connected, the two DC terminals of the parallel side converter (2) and the two DC terminals of the series side converter (4) are respectively connected to both ends of the capacitor (5), and the monitoring device (7) It is used to monitor the parallel-side converter (2) and the series-side converter (4), and it is characterized in that: the system also includes a series transformer (3) and an anti-parallel bidirectional thyristor (6), and the series transformer (3) The primary side winding is connected to the AC end of the series side converter (4), the two ends of the secondary side winding of the series transformer (3) are connected to the two ends of the anti-parallel bidirectional thyristor (6), and the secondary side winding of the series transformer (3) is connected to the bidirectional thyristor (6). Stator windings of the feed-fed flywheel energy storage motor (1) are connected, and the monitoring device (7) realizes bypass protection by controlling the connection state of the anti-parallel bidirectional thyristor (6). 2. The flexible AC power transmission system based on flywheel energy storage according to claim 1, characterized in that: the primary windings of the series transformer (3) are connected in a triangle. 3. The flexible AC transmission system based on flywheel energy storage according to claim 1 or 2, characterized in that: the parallel-side converter (2) is composed of a fully-controlled power switching element and an inductor, and the fully-controlled power switching element is composed of In the first three-phase full-bridge structure (8), the midpoint of the three-phase bridge arm is connected to the rotor winding of the doubly-fed flywheel energy storage motor (1) through a three-phase inductance (9). 4. The flexible AC transmission system based on flywheel energy storage according to claim 1 or 2, characterized in that: the series-side converter (4) is composed of a fully-controlled power switching element and an inductance-capacitance low-pass filter, and the fully-controlled Type power switching elements form a second three-phase full-bridge structure (11), and the midpoint of the three-phase bridge arms is connected to the primary winding of the series transformer (3) through a three-phase inductance-capacitance low-pass filter (10).

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