CN107482941A - A five-level DC conversion circuit and a generator excitation system including the circuit - Google Patents

Abstract

The invention discloses a five-level DC conversion circuit and a generator excitation system including the circuit. In the five-level chopping circuit of the present invention, one end of the first switch tube is connected to the positive output terminal of the excitation, and the other end is connected to the positive terminal of the DC power supply; one end of the second switch tube is connected to the negative end of the excitation output, and the other end is connected in series with the sixth dipole The tube is connected to the midpoint of the capacitor series circuit; one end of the third switching tube is connected to the negative terminal of the excitation output, and the other end is connected to the negative terminal of the DC power supply; One end of the four diodes is connected to the positive end of the power supply, and the other end is connected to the negative end of the excitation output. One end of the fifth diode is connected to the negative end of the power supply, and the other end is connected to the positive end of the excitation output. Based on the characteristic of unidirectional output of excitation current, the invention realizes five-level direct current chopper output of excitation voltage and bidirectional flow of excitation power, can reduce switch tube loss and improve efficiency of full-control excitation system.

Description

A five-level DC conversion circuit and a generator excitation system including the circuit

technical field

The invention belongs to the technical field of electrical engineering, in particular to a five-level direct-current conversion circuit applied to a generator excitation system and a generator excitation system including the circuit.

Background technique

With the large-scale commissioning of UHV DC and flexible DC and the rapid development of new energy power generation with high penetration rate, power electronic power system is in the field of ultra-low frequency power oscillation, sub-synchronous oscillation, millisecond-level reactive power voltage support and other electromagnetic/electromechanical hybrid systems. Increased operational risk in the field. The excitation system is an important part of the synchronous generator, which has an important impact on the safe and stable operation of the power system. Making full use of the regulation ability of the excitation system is one of the most economical and effective means to improve the stability of the power system.

The conventional excitation system based on the rectification of the semi-controlled device thyristor (SCR) is limited by its slow control speed and can only control the device to be turned on but not to be turned off, so it has been difficult to adapt to the operation requirements of the power electronic grid. Fully-controlled devices such as IGBTs can be turned on and off at the same time, so their control response speed and control flexibility have obvious advantages. At present, scholars at home and abroad have proposed to apply the rectifier circuit and chopper circuit composed of IGBT and other fully-controlled devices to the generator excitation system to realize the fully-controlled excitation system. While providing the DC excitation current of the synchronous generator, its AC side can be Controlling the reactive current component can quickly control the injection or absorption of reactive power to the synchronous generator. The millisecond-level direct support capability of the reactive power on the AC side can significantly improve the reactive power and voltage control performance and response speed of the unit, and provide means for the suppression technology of broadband low-frequency power oscillation and subsynchronous oscillation.

At present, the topological structure of the fully controlled excitation system can be divided into voltage source type and current source type. Due to the cost, volume and weight of large inductors for energy storage, and the complexity of control, there are few studies on current source fully controlled excitation systems. In the voltage source type full-control excitation circuit, in order to realize the requirements of the excitation system, such as zero-start current rise and energy exchange feedback, the topological structure of the combination of three-phase full-control rectification and DC-DC chopper circuit is the main one; among them, DC-DC chopper The wave circuit is mainly based on the H bridge or H bridge parallel structure, which can output the three-level voltage of the front-end DC voltage E, 0 and DC voltage -E, and the change amplitude of the voltage at both ends corresponding to the action of a single switch tube is the DC voltage E; The switching tube in the switch is not an ideal device in practice. There are overlaps of current and voltage waveforms in the turn-on and cut-off processes in use, resulting in switching losses of power devices. The efficiency of the overall system is reduced; at the same time, a higher voltage change rate will also bring more serious electromagnetic interference problems; on the DC output side, a large output voltage level change also affects the quality of the output voltage, which increases the voltage ripple. The higher common-mode voltages are more detrimental to motor shaft currents and insulation.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art and provide a five-level DC conversion circuit applied to the excitation system of a generator. According to the characteristics of the unidirectional flow of the excitation current, a bidirectional excitation voltage is designed. The five-level DC conversion circuit with two-way flow of output and excitation power can reduce the voltage change rate during the switching operation, reduce the switching loss of the switching tube, improve the system efficiency, and improve the output voltage quality.

In order to achieve the above object, the technical solution adopted by the present invention is: a five-level DC conversion circuit, which includes a DC power supply circuit, a first capacitor C1, a second capacitor C2 and a five-level DC chopper circuit;

The five-level DC chopper circuit includes a first switching tube V1, a second switching tube V2, a third switching tube V3, a first diode VD1, a second diode VD2, a third diode VD3, a Four diodes VD4, fifth diode VD5 and sixth diode VD6,

The first capacitor C1 and the second capacitor C2 are connected in series and parallel to both ends of the DC power supply circuit. The two ends of the DC power supply circuit are positive voltage terminal P and negative voltage terminal N respectively. The connection point between the two capacitors is Intermediate voltage terminal O;

One end of the first switching tube V1 is connected to the positive voltage terminal P, and the other end is connected to the positive output terminal of the excitation; one end of the second switching tube V2 is connected to the negative voltage terminal N, and the other end is connected to the negative output terminal of the excitation; the third The switch tube V3 is connected in series with the sixth diode VD6, one end of the series branch is connected to the intermediate voltage terminal O, and the other end is connected to the excitation output negative terminal;

The first diode VD1, the second diode VD2, and the third diode VD3 are respectively connected in antiparallel to both ends of the first switching tube V1, the second switching tube V2, and the third switching tube V3;

One terminal of the fourth diode VD4 is connected to the positive voltage terminal P, and the other terminal is connected to the negative terminal of the excitation output; one terminal of the fifth diode VD5 is connected to the negative voltage terminal N, and the other terminal is connected to the positive terminal of the excitation output.

As a supplement to the above technical solution, the first switching tube V1 , the second switching tube V2 and the third switching tube V3 all use IGBT fully-controlled devices.

As a supplement to the above technical solution, the collector of the first switching tube V1 is connected to the positive voltage terminal P, and the emitter is connected to the positive excitation output terminal;

The emitter of the second switching tube V2 is connected to the negative voltage terminal N, and the collector is connected to the excitation output negative terminal;

The emitter of the third switching tube V3 is connected to the anode of the sixth diode VD6, the cathode of the sixth diode VD6 is connected to the intermediate voltage terminal O, and the collector of the third switching tube V3 is connected to the excitation output negative terminal;

The cathode of the fourth diode VD4 is connected to the positive voltage terminal P, and the anode is connected to the excitation output negative terminal;

The anode of the fifth diode VD5 is connected to the negative voltage terminal N, and the cathode is connected to the positive output terminal of the excitation.

Another object of the present invention is to provide a generator excitation system including the above-mentioned five-level DC conversion circuit, the control terminals of the first switching tube V1, the second switching tube V2 and the third switching tube V3 are controlled by the generator excitation system Field regulator control.

As a supplement to the excitation system of the above-mentioned generator, when the excitation system is running, when the first switching tube V1 and the second switching tube V2 are turned on, the circuit output voltage +E;

When the first switching tube V1 and the third switching tube V3 are turned on, the circuit output voltage +E/2;

When the first switch tube V1 is turned on, the current continues to flow through the fourth diode VD4, and the circuit output voltage is 0;

When the second switch tube V2 is turned on, the current continues to flow through the fifth diode VD5, and the circuit also outputs a voltage of 0;

When the third switch tube V3 is turned on, the current continues to flow through the fifth diode VD5 and the sixth diode VD6, and the circuit output voltage is -E/2;

When the current continues to flow through the fourth diode VD4 and the fifth diode V5, the circuit outputs a voltage of -E.

As a supplement to the above generator excitation system, the control method of the excitation system is as follows:

The combination of +E/2 and 0 level is used to realize normal excitation, and the output is adjusted between 0 and rated excitation voltage;

The combination of +E/2 and +E levels is used to realize short-term strong excitation, and the adjustment between the output rated voltage and the maximum excitation voltage is realized;

Use 0 and -E/2 level combination mode for inverter control to realize slow de-excitation;

The combination of -E/2 and -E levels is used for inverter control to realize rapid demagnetization and demagnetization.

The five-level DC conversion circuit of the present invention can output five-level DC excitation voltages of E, E/2, 0, -E/2, and -E according to different conduction control signals. Compared with a typical H-bridge Three-level chopping, adding E/2 and -E/2 two-way level output, the turn-on and turn-off voltage during operation can reduce E/2, thereby reducing the switching loss of the switch tube, improving system efficiency, and reducing electromagnetic interference and DC output voltage ripple; at the same time, when a smaller DC excitation voltage output is required, E/2, 0 is compared with E, 0 at the same switching frequency, and the turn-on duty cycle is doubled, which is more conducive to realizing the DC output voltage More precise control.

Description of drawings

Fig. 1 is a five-level DC conversion circuit diagram of the present invention;

Fig. 2 is a schematic diagram of the chopping waveform of the output voltage of the five-level DC conversion circuit of the present invention;

Fig. 3 is a schematic diagram of the present invention applied to a self-shunt excitation system.

detailed description

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

As shown in Figure 1, the present invention provides a five-level DC conversion circuit applied to the generator excitation system, which is composed of a DC power supply circuit, a first capacitor C1, a second capacitor C2 and a five-level DC chopper circuit .

The five-level DC chopper circuit consists of a first switching tube V1, a second switching tube V2, a third switching tube V3, a first diode VD1, a second diode VD2, a third diode VD3, a Composed of four diodes VD4, fifth diode VD5, and sixth diode VD6.

The first capacitor C1 and the second capacitor C2 are connected in parallel to the two ends of the DC power supply circuit after being connected in series, the two ends of the DC power supply circuit are positive voltage terminal P and negative voltage terminal N respectively, and the connection point between the two capacitors is Intermediate voltage terminal O.

One end of the first switching tube V1 is connected to the positive voltage terminal P, and the other end is connected to the positive excitation output terminal. One end of the second switching tube V2 is connected to the negative voltage terminal N, and the other end is connected to the excitation output negative terminal. The third switching tube V3 is connected in series with the sixth diode VD6, one end of the series branch is connected to the intermediate voltage terminal O, and the other end is connected to the excitation output negative terminal.

The first diode VD1 , the second diode VD2 and the third diode VD3 are connected in antiparallel to the two ends of the first switching tube V1 , the second switching tube V2 and the third switching tube V3 respectively.

One terminal of the fourth diode VD4 is connected to the positive voltage terminal P, and the other terminal is connected to the negative terminal of the excitation output. One terminal of the fifth diode VD5 is connected to the negative voltage terminal N, and the other terminal is connected to the positive terminal of the excitation output.

The first switching tube V1 , the second switching tube V2 and the third switching tube V3 are all IGBT fully-controlled devices.

The collector of the first switching tube V1 is connected to the positive voltage terminal P, and the emitter is connected to the positive excitation output terminal. The emitter of the second switching tube V2 is connected to the negative voltage terminal N, and the collector is connected to the negative terminal of the excitation output. The emitter of the third switching tube V3 is connected to the anode of the sixth diode VD6, the cathode of the sixth diode VD6 is connected to the intermediate voltage terminal O, and the collector of the third switching tube V3 is connected to the excitation output negative terminal. The cathode of the fourth diode VD4 is connected to the positive voltage terminal P, and the anode is connected to the negative terminal of the excitation output. The anode of the fifth diode VD5 is connected to the negative voltage terminal N, and the cathode is connected to the positive output terminal of the excitation.

The control terminals of the first switching tube V1, the second switching tube V2 and the third switching tube V3 are controlled by the excitation regulator of the generator excitation system.

As shown in Figure 1, when the excitation system is running, the DC excitation current flows in one direction as shown in the figure: when the first switching tube V1 and the second switching tube V2 are turned on, the circuit output voltage +E; when the first switching tube V1 When the third switch tube V3 is turned on, the circuit output voltage +E/2; when the first switch tube V1 is turned on, the current continues to flow through the fourth diode VD4, and the circuit output voltage is 0; when the second switch tube V2 is turned on , the current continues to flow through the fifth diode VD5, and the circuit also outputs a voltage of 0; when the third switch tube V3 is turned on, the current continues to flow through the fifth diode VD5 and the sixth diode VD6, and the circuit output voltage is -E /2; when the current continues to flow through the fourth diode VD4 and the fifth diode V5, the circuit outputs a voltage of -E.

Applying the above chopper output combination, the excitation system control can be designed as follows: use the combination of +E/2 and 0 levels to realize normal excitation, and adjust the output between 0 and rated excitation voltage; use +E/2 and +E levels The combination method realizes short-time strong excitation, and the adjustment between the output rating and the maximum excitation voltage; the combination of 0 and -E/2 levels is used for inverter control to realize slow de-excitation; the -E/2 and -E levels are used Inverter control is carried out in a combination mode to realize rapid demagnetization and demagnetization. The waveform diagram is shown in Figure 2 in sequence.

Combined with the self-shunt excitation system, the application of the five-level DC conversion circuit to the generator excitation system is described in detail. As shown in Figure 3, the DC power supply circuit uses a three-level full-control rectifier circuit as an example. The AC side of the rectifier circuit is connected to the low-voltage side of the excitation transformer, the high-voltage side of the AC side of the excitation transformer is connected to the generator terminal, and the DC side of the rectifier circuit is connected to the five A level DC conversion circuit, the excitation voltage output end of the five-level DC conversion circuit is connected to the excitation winding of the generator. When the unit is in normal operation, the excitation system obtains energy from the machine end through the excitation transformer, completes the AC-DC rectification through the three-level full-control rectification circuit to provide DC power, and then outputs stable DC excitation through the DC-DC chopping of the five-level DC conversion circuit voltage, and then provide the excitation current required for the normal operation of the unit; when the excitation of the unit is reversed, the energy flows in the opposite direction, and the energy of the excitation winding passes through the five-level DC conversion circuit, the three-level full-control rectification circuit and the excitation transformer, and is reversed to the machine end. Send, and then realize the shutdown and de-excitation with the rapid reduction of the excitation current.

The above embodiments are only to illustrate the technical ideas of the present invention, and can not limit the protection scope of the present invention with this. All technical ideas proposed in accordance with the present invention, any changes made on the basis of technical solutions, all fall within the protection scope of the present invention. Inside.

Claims (6)

1. A kind of 1. five level DC translation circuits, it is characterised in that it include dc source provide circuit, the first capacitor C1, Second capacitor C2 and five level DC chopper circuits；

   The five level DCs chopper circuit includes first switch pipe V1, second switch pipe V2, the 3rd switching tube V3, the one or two pole Pipe VD1, the second diode VD2, the 3rd diode VD3, the 4th diode VD4, the 5th diode VD5 and the 6th diode VD6,

   Dc source is parallel to after the first described capacitor C1 and the second capacitor C2 series connection, and circuit both ends, dc source are provided The both ends for providing circuit are respectively positive voltage terminal P and negative voltage side N, and the tie point between two capacitors is medium voltage end O；

   One end connection positive voltage terminal P of the first switch pipe V1, other end connection excitation output plus terminal；The second switch pipe V2 one end connection negative voltage side N, other end connection excitation output negative terminal；The 3rd switching tube V3 and the 6th diode VD6 Series connection, one end connection medium voltage end O of the series arm, other end connection excitation output negative terminal；

   The first diode VD1, the second diode VD2, the 3rd diode VD3 difference reverse parallel connections and first switch pipe V1, Second switch pipe V2, the 3rd switching tube V3 both ends；

   One end of the 4th diode VD4 is connected to positive voltage terminal P, and the other end exports negative terminal in excitation in succession；Five or two pole Pipe VD5 one end is connected to negative voltage side N, and the other end is in succession in excitation output plus terminal.
2. 2. five level DCs translation circuit as claimed in claim 1, it is characterised in that first switch pipe V1, second switch pipe V2 and the 3rd switching tube V3 uses IGBT full-controlled devices.
3. 3. five level DCs translation circuit as claimed in claim 1 or 2, it is characterised in that

   The colelctor electrode connection positive voltage terminal P of the first switch pipe V1, emitter stage connection excitation output plus terminal；

   The emitter stage connection negative voltage side N of the second switch pipe V2, colelctor electrode connection excitation output negative terminal；

   The emitter stage of the 3rd switching tube V3 is connected with the 6th diode VD6 anodes, in the 6th diode VD6 negative electrode connection Between voltage end O, the 3rd switching tube V3 colelctor electrode connection excitation output negative terminal；

   The negative electrode of the 4th diode VD4 is connected to positive voltage terminal P, and anode exports negative terminal in excitation in succession；

   5th diode VD5 anode is connected to negative voltage side N, and negative electrode is in succession in excitation output plus terminal.
4. 4. include the generator excited system of any one of the claim 1-3 five level DCs translation circuit, it is characterised in that Described first switch pipe V1, second switch pipe V2 and the 3rd switching tube V3 control terminal are by generator excited system adjustment of field excitation Device controls.
5. 5. generator excited system as claimed in claim 4, it is characterised in that

   When excitation system is run, when first switch pipe V1 and second switch pipe V2 is opened, circuit output voltage+E；

   When first switch pipe V1 and the 3rd switching tube V3 are opened, circuit output voltage+E/2；

   When first switch pipe V1 is opened, electric current passes through the 4th diode VD4 afterflows, circuit output voltage 0；

   When second switch pipe V2 is opened, electric current passes through the 5th diode VD5 afterflows, the same output voltage 0 of circuit；

   When the 3rd switching tube V3 is opened, electric current passes through the 5th diode VD5 and the 6th diode VD6 afterflows, circuit output electricity Pressure-E/2；

   When electric current passes through the 4th diode VD4 and the 5th diode V5 afterflows, circuit output voltage-E.
6. 6. generator excited system as claimed in claim 5, it is characterised in that：The control method of the excitation system is as follows：

   Normal excitation, the regulation that output 0 is arrived between rated excitation voltage are realized using+E/2 and 0 level combinations mode；

   Realized using+E/2 and+E level combinations modes and encouraged by force in short-term, the specified regulation arrived between maximum excitation voltage of output；

   Inversion control is carried out using 0 and-E/2 level combinations mode, realizes slow demagnetization；

   Inversion control is carried out using-E/2 and-E level combinations mode, realization quickly subtracts by force demagnetization.