CN106026122A - Integrated asynchronous excitation phase modifier and reactive compensation and active balance method thereof - Google Patents

Abstract

The invention discloses an asynchronous excitation integrated condenser and a method for reactive power compensation and active power balance thereof, comprising a three-phase AC excitation winding, a voltage source inverter, a supercapacitor and a voltage source rectifier. The supercapacitor is used to provide energy to the voltage source inverter and maintain the voltage level of the voltage source inverter. The voltage source rectifier is used to absorb active power from the grid side, convert the AC power on the grid side into DC power, provide active power to the supercapacitor and voltage source inverter, and send reactive power to the grid. The voltage source inverter is used to invert the direct current delivered by the voltage source rectifier into the three-phase AC excitation current required by the three-phase rotor excitation winding. After adopting the above structure and method, by controlling the rotor speed, the condenser can absorb the excess energy in the power grid when a part of the line has a short-circuit fault, and its inertia is strong, which is conducive to the safety and stability of the power grid; in addition, the reactive power compensation capability and transient performance better.

Description

A kind of asynchronous excitation integrated condenser and its method of reactive power compensation and active power balance

technical field

The invention relates to a condenser in a high-voltage power transmission system, in particular to an asynchronous excitation integrated condenser.

Background technique

With the development of our country's economy, the demand for electric power is increasing day by day, and the unbalanced distribution of resources in our country makes long-distance power transmission a necessity. However, there are various disadvantages in the traditional long-distance high-voltage AC transmission system, which almost do not exist in the high-voltage direct current transmission system, so high-voltage direct current transmission has become a trend. Although the transmission line of the HVDC transmission system itself does not consume reactive power, the converter station of the HVDC transmission still consumes a large amount of reactive power due to the extensive use of power electronic equipment. In addition, a large amount of investment in high-voltage direct current transmission also reduces the inherent inertia of the power grid and reduces the ability to resist disturbances. Therefore, even in the HVDC transmission system, there is a problem of reactive power compensation.

In my country's current power system, static var compensation devices (mainly SVC) have been gradually used to replace traditional condensers. This is because although traditional condensers have large capacity and reliable performance, their dynamic adjustment capabilities are poor, while SVCs are Able to respond quickly. Compared with SVC, STATCOM has a larger capacity, and more importantly, because it uses a fully-controlled device IGBT, it has stronger dynamic adjustment capability and shorter response time. Although there are many studies on static var compensation devices at present, there is almost no precedent for combining the condenser and the more advanced STATCOM into use.

Contents of the invention

The technical problem to be solved by the present invention is to provide an asynchronous excitation integrated condenser with stronger reactive power compensation, active power balance and dynamic adjustment capabilities in view of the above-mentioned deficiencies in the prior art.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

An asynchronous excitation integrated condenser includes a three-phase AC excitation winding, a voltage source inverter, a supercapacitor and a voltage source rectifier.

The three-phase AC excitation winding includes a three-phase rotor excitation winding and a stator winding, and the excitation mode of the three-phase AC excitation winding is asynchronous excitation.

The stator winding is connected to the grid-side busbar, the three-phase rotor excitation winding is connected in series with one end of the voltage source inverter, and the other end of the voltage source inverter is connected in parallel with the supercapacitor.

One end of the voltage source rectifier is connected to the grid-side busbar, and the other end of the voltage source rectifier is also connected in parallel with the supercapacitor.

The supercapacitor is used to provide energy to the voltage source inverter and maintain the voltage level of the voltage source inverter.

The voltage source rectifier is used to absorb active power from the grid side, convert the AC power on the grid side into DC power, provide active power to the supercapacitor and voltage source inverter, and send reactive power to the grid.

The voltage source inverter is used to invert the direct current delivered by the voltage source rectifier into the three-phase AC excitation current required by the three-phase rotor excitation winding.

The rotor in the integrated condenser is connected with the condenser controller, and the condenser controller can adjust the rotating speed of the rotor, so as to balance the active power of the power grid.

When the speed of the rotor in the integrated condenser increases, the active power will flow from the integrated condenser to the voltage source rectifier, that is, output active power to the power grid; when the rotational speed of the rotor in the integrated condenser decreases, the active power will flow from the voltage source rectifier It flows to the integrated condenser, that is, to absorb the excess active power of the grid.

Both the stator winding and the voltage source rectifier can transmit reactive power to the grid, wherein the reactive power transmitted by the stator winding to the grid is Q1, and the reactive power transmitted by the voltage source rectifier to the grid is Q2.

The present invention also provides a method for reactive power compensation and active power balance using an asynchronous excitation integrated controller, which has stronger reactive power compensation and active power balance. ability and dynamic adjustment ability.

A method for reactive power compensation and active power balance using an asynchronous excitation integrated condenser, comprising the following steps:

The first step is grid disturbance signal detection: when a fault occurs somewhere in the grid, the controller of the condenser will receive the fault information and detect the grid disturbance signal, which includes the grid voltage drop and the rotor speed in the integrated condenser Changes occur; at this time, the integrated condenser will turn from steady-state operation to transient operation.

The second step is to balance the active power of the grid: after the controller of the condenser detects the disturbance signal of the grid, it will instruct the rotor in the integrated condenser to reduce the speed, absorb the excess active power of the grid, and balance the active power of the grid.

The third step is grid reactive power compensation: the voltage source inverter will increase the excitation current of the three-phase rotor excitation winding in the integrated condenser according to the demand, so as to keep the reactive power Q1 delivered by the stator winding to the grid normal; at the same time, the voltage source The type rectifier transmits reactive power Q2 to the grid to maintain the voltage level of the grid.

The fourth step, fault removal signal reception: within the set time, if the controller of the condenser does not receive the fault removal signal, it will continue to the second step to the third step until it receives the fault removal signal.

The fifth step is to turn to steady-state operation: when the condenser controller receives the fault removal signal and the grid voltage recovers, the condenser controller will instruct the voltage source inverter in the integrated condenser to gradually reduce the excitation current until When all indicators return to the state before the failure, it will turn to steady-state operation.

In the third step, while supplying energy to the voltage source inverter, the voltage source rectifier maintains a constant grid voltage in the form of additional reactive power Q2.

After the present invention adopts the above structure and method, it has the following beneficial effects:

1. The above-mentioned voltage source rectifier can not only provide stable power supply for the three-phase rotor excitation winding, but also can transmit reactive power to the grid, which improves the reactive power compensation capability of the integrated condenser; and the voltage source rectifier can increase the power system Damping, suppressing the shock in the power system.

2. The above-mentioned voltage source inverter can directly supply power to the three-phase rotor excitation winding, and can change the magnitude of the three-phase AC excitation current according to the demand, so that the regulator has better flexibility.

3. Through the adjustment of the rotor speed, the effect of using the condenser to balance the active power can be achieved, so that the condenser has better performance than the traditional conventional condenser.

Description of drawings

Fig. 1 shows a schematic structural diagram of an asynchronous excitation integrated condenser of the present invention.

Fig. 2 shows the control block diagram of the reactive power compensation and active power balance method of the asynchronous excitation integrated condenser of the present invention.

Including:

1. Three-phase AC excitation winding; 11. Three-phase rotor excitation winding; 12. Stator winding;

2. Grid-side bus; 3. Voltage source inverter; 4. Supercapacitor; 5. Voltage source rectifier.

In addition, the characters involved in Figure 2 are defined as follows:

P: Indicates the transmitted active power in grid fault state.

f: Indicates the frequency in grid fault state.

Q: Indicates the delivered reactive power in the grid fault state.

U’: Indicates the voltage under the grid fault state.

P1: Indicates the transmitted active power after the condenser absorbs the excess active power of the grid.

f1: Indicates the grid frequency after the condenser absorbs the excess active power of the grid.

U: Indicates the grid voltage after the condenser generates reactive power to the grid.

Δp: Indicates the difference between P1 after the condenser absorbs excess active power from the grid and the original power P.

Δf: Indicates the difference between the grid frequency f1 and the original frequency f after the condenser absorbs the excess active power of the grid.

ΔU: Indicates the difference between the grid voltage U and the original voltage U' after the regulator sends additional reactive power to the grid.

PI: Indicates PI algorithm, that is, proportional and integral algorithm, which is a commonly used control strategy in automatic control.

ω0: Indicates the rotor speed under power frequency, usually 3000r/min.

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific preferred embodiments.

As shown in FIG. 1 , an integrated condenser with asynchronous excitation includes a three-phase AC excitation winding 1 , a voltage source inverter 3 , a supercapacitor 4 and a voltage source rectifier 5 .

The three-phase AC excitation winding includes a three-phase rotor excitation winding 11 and a stator winding 12, and the excitation mode of the three-phase AC excitation winding is asynchronous excitation.

The stator winding is connected to the grid-side bus 2, the three-phase rotor excitation winding is connected in series with one end of the voltage source inverter, and the other end of the voltage source inverter is connected in parallel with the supercapacitor.

One end of the voltage source rectifier is connected to the grid-side busbar, and the other end of the voltage source rectifier is also connected in parallel with the supercapacitor.

The supercapacitor is used to provide energy to the voltage source inverter and maintain the voltage level of the voltage source inverter. The supercapacitor is an energy element with a simple structure.

The voltage source rectifier is used to absorb active power from the grid side, convert the AC power on the grid side into DC power, provide active power to the supercapacitor and voltage source inverter, and send reactive power to the grid.

In this application, the voltage source rectifier is also the STATCOM in Figure 2 .

STATCOM, also known as static synchronous compensator, is not only an important reactive power compensation device, but also a rectifier itself. In this patent, STATCOM is used as a voltage source rectifier, connected with a supercapacitor, etc. Rectification is its main function, and it also has the function of compensating reactive power.

The magnitude of the DC current generated by the voltage source rectifier has a strict correspondence with the on-off period of the switching device (that is, the duty cycle of the PWM wave). The cycle will naturally affect the size of its reissued reactive power Q2.

The voltage source inverter, also known as the rotor excitation current controller, is used to invert the direct current delivered by the voltage source rectifier into the three-phase AC excitation current required by the three-phase rotor excitation winding.

The rotor in the integrated condenser is connected with the condenser controller, and the condenser controller can adjust the rotating speed of the rotor, so as to balance the active power of the power grid.

When the speed of the rotor in the integrated condenser increases, the active power will flow from the integrated condenser to the voltage source rectifier, that is, output active power to the power grid; when the rotational speed of the rotor in the integrated condenser decreases, the active power will flow from the voltage source rectifier It flows to the integrated condenser, that is, to absorb the excess active power of the grid.

Both the stator winding and the voltage source rectifier can transmit reactive power to the grid, wherein the reactive power transmitted by the stator winding to the grid is Q1, and the reactive power transmitted by the voltage source rectifier to the grid is Q2.

As shown in Figure 2, a method for reactive power compensation and active power balance using an asynchronous excitation integrated condenser includes the following steps.

The first step is grid disturbance signal detection: when a fault occurs somewhere in the grid, the condenser controller will receive the fault information and detect the grid disturbance signal.

The condenser controller includes a man-machine interface, an input signal processing unit and an output unit, etc.

The input signal processing unit is built in the power plant where the integrated condenser is located. Its status is similar to that of ordinary power plants, which must accept the instructions and related parameters of the grid dispatching center and need to upload relevant data.

The fault information received by the above-mentioned condenser controller includes: the transmission active power P in the grid fault state transmitted from the grid dispatching center, the frequency f in the grid fault state, the reactive power Q in the grid fault state and the transmission reactive power Q in the grid fault state. The voltage U' and other information.

The power grid disturbance signal detected by the controller of the condenser includes the drop of the grid voltage and the change of the rotor speed in the integrated condenser; at this time, the integrated condenser will turn from steady-state operation to transient operation.

The second step is to balance the active power of the power grid, which is the active power control in the control link in Figure 2: after the controller of the condenser detects the disturbance signal of the power grid, it will instruct the rotor in the integrated condenser to reduce the speed, absorb the excess active power of the power grid, and carry out power grid Active power balance.

As shown in Figure 2, the rotor speed ω1 is adjusted so that when ω1>ω0, the active power is delivered to the grid; when ω1<ω0, the surplus active power of the grid is absorbed, so as to realize the control of active power balance.

The third step is the reactive power compensation of the power grid, that is, the reactive power compensation and voltage stability control in the control link in Figure 2: the voltage source inverter will increase the excitation current of the three-phase rotor excitation winding in the integrated condenser according to the demand, Keep the reactive power Q1 delivered by the stator winding to the grid normally; at the same time, the voltage source rectifier delivers reactive power Q2 to the grid to maintain the grid voltage level.

In the third step above, while the voltage source rectifier provides energy to the voltage source inverter, it maintains a constant grid voltage in the form of additional reactive power Q2.

That is to say, after a fault occurs, on the one hand, it is necessary to increase the excitation current of the rotor, and on the other hand, it is necessary to increase reactive power. The calculated PWM waveform is transmitted to meet the requirements of forced excitation of the rotor and compensation of reactive power.

The power plant uses data calculations to adjust the parameters of the local regulator (PWM duty cycle of STATCOM, rotor speed, etc.), and uses PI algorithm to perform active power control, reactive power compensation and voltage stability control respectively, so that the active power transmitted by the grid can be reduced. As small as p1, the grid frequency becomes f1, and the grid voltage becomes U.

And through Δp, Δf, ΔU to correct the parameters of the condenser, maintain the indicators of the power grid, so that the power grid will not be unstable in the transient process until the fault is removed.

The fourth step, fault removal signal reception: within the set time, if the controller of the condenser does not receive the fault removal signal, it will continue to the second step to the third step until it receives the fault removal signal.

The fifth step is to turn to steady-state operation: when the condenser controller receives the fault removal signal and the grid voltage recovers, the condenser controller will instruct the voltage source inverter in the integrated condenser to gradually reduce the excitation current until When all indicators return to the state before the failure, it will turn to steady-state operation.

Since most of the faults in the power grid are short-circuit faults, the "fault" mentioned in this patent also basically refers to short-circuit faults. When a short-circuit fault occurs in the power system, it can be seen from the "equal area law" that in order to reduce the acceleration area, the strategy often used is to increase the output electromagnetic power of the generator, that is, to increase the excitation current (that is, to force excitation), so in The excitation current in the transient operation stage will be greater than the excitation current in normal operation. Therefore, when turning to normal operation, it is necessary to reduce the large current that was originally forcibly excited to a normal value.

To sum up, in the present invention, by controlling the rotor speed, the condenser absorbs the excess energy in the power grid when a part of the line has a short-circuit fault, and its inertia is strong, which is conducive to the safety and stability of the power grid; in the present invention, the asynchronous excitation control system is used to improve The reactive power compensation ability of the integrated condenser is improved, and its transient performance is better; the voltage source rectifier is used in the present invention, which can increase the damping of the power system and suppress the oscillation in the power system.

Compared with the prior art, the present invention can utilize the respective advantages of the novel condenser and the voltage source rectifier, not only overcoming the respective deficiencies in the process of reactive power compensation, but also under the premise of not increasing the size of the existing components, The inertia and system damping of the condenser are greatly increased, which is conducive to the stable and safe operation of the power grid.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be carried out to the technical solutions of the present invention. These equivalent transformations All belong to the protection scope of the present invention.

Claims (6)

1. An asynchronous excitation integrated condenser, characterized in that: it comprises a three-phase AC excitation winding, a voltage source inverter, a supercapacitor and a voltage source rectifier; The three-phase AC excitation winding includes three-phase rotor excitation winding and stator winding, and the excitation mode of the three-phase AC excitation winding is asynchronous excitation; The stator winding is connected to the grid-side busbar, the three-phase rotor excitation winding is connected in series with one end of the voltage source inverter, and the other end of the voltage source inverter is connected in parallel with the supercapacitor; One end of the voltage source rectifier is connected to the grid-side busbar, and the other end of the voltage source rectifier is also connected in parallel with the supercapacitor; Supercapacitors are used to provide energy to the voltage source inverter and maintain the voltage level of the voltage source inverter; The voltage source rectifier is used to absorb active power from the grid side, convert the AC power on the grid side into DC power, provide active power to the supercapacitor and voltage source inverter, and send reactive power to the grid; The voltage source inverter is used to invert the direct current delivered by the voltage source rectifier into the three-phase AC excitation current required by the three-phase rotor excitation winding. 2. The asynchronous excitation integrated condenser according to claim 1, characterized in that: the rotor in the integrated condenser is connected to the controller of the condenser, and the controller of the condenser can adjust the rotating speed of the rotor, thereby improving the active power of the power grid Power is balanced. 3. The asynchronous excitation integrated condenser according to claim 2, characterized in that: when the rotating speed of the rotor in the integrated condenser increases, the active power will flow from the integrated condenser to the voltage source rectifier, that is, output active power to the grid; When the speed of the rotor in the integrated condenser decreases, the active power will flow from the voltage source rectifier to the integrated condenser, that is, to absorb the excess active power of the grid. 4. The asynchronous excitation integrated condenser according to claim 1, characterized in that: both the stator winding and the voltage source rectifier can transmit reactive power to the grid, wherein the reactive power transmitted by the stator winding to the grid is Q1 , the reactive power delivered by the voltage source rectifier to the grid is Q2. 5. A method for reactive power compensation and active power balance using the asynchronous excitation integrated condenser according to any one of claims 1-4, characterized in that: comprising the following steps: The first step is grid disturbance signal detection: when a fault occurs somewhere in the grid, the controller of the condenser will receive the fault information and detect the grid disturbance signal, which includes the grid voltage drop and the rotor speed in the integrated condenser Changes occur; at this time, the integrated condenser will turn from steady-state operation to transient operation; The second step is to balance the active power of the grid: after the controller of the condenser detects the disturbance signal of the grid, it will instruct the rotor in the integrated condenser to reduce the speed, absorb the excess active power of the grid, and balance the active power of the grid; The third step is grid reactive power compensation: the voltage source inverter will increase the excitation current of the three-phase rotor excitation winding in the integrated condenser according to the demand, so as to keep the reactive power Q1 delivered by the stator winding to the grid normal; at the same time, the voltage source The type rectifier transmits reactive power Q2 to the grid to maintain the grid voltage level; The fourth step, fault removal signal reception: within the set time, if the controller of the condenser does not receive the fault removal signal, it will continue to the second step to the third step until it receives the fault removal signal; The fifth step is to turn to steady-state operation: when the condenser controller receives the fault removal signal and the grid voltage recovers, the condenser controller will instruct the voltage source inverter in the integrated condenser to gradually reduce the excitation current until When all indicators return to the state before the failure, it will turn to steady-state operation. 6. The method for reactive power compensation and active power balance using an asynchronous excitation integrated condenser as claimed in claim 5, characterized in that: in the third step, the voltage source rectifier provides energy to the voltage source inverter At the same time, the grid voltage is kept constant in the form of additional reactive power Q2.