KR100334924B1 - High Voltage Direct Current System - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct current transmission system, comprising: a plurality of insulated gate bipolar transistors and a plurality of gates having an arc extinguishing power for transmitting power at a predetermined distance to a high voltage direct current state instead of an alternating current. An insulated gate bipolar transistor inverter 10 and an insulated gate bipolar transistor converter 12 in which a semiconductor device 18 such as a turn off thyrister is formed in series and in parallel, an inverter transformer 14 for step-down, and The converter transformer 16 for boosting, and this device, represented by the semiconductor device 18, has its own on-off capability, and the semiconductor device 18 has its own diode. Because of this, even if the insulated gate bipolar transistor inverter 10 is not switched, the insulated gate bipolar transistor converter 12 It includes a capacitor 20 for applying a rectified voltage of the input voltage of the current without a reactive power compensation device using a semiconductor device having a self-extinguishing capability, such as an insulated gate bipolar transistor or a gate turn-off thyristor It solves the problem of failure and harmonics in the flow.

Description

DC Transmission System {High Voltage Direct Current System}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct current transmission system. More particularly, the present invention relates to a direct current transmission system having a self-extinguishing capability, such as an insulated gate bipolar transistor or a gate turn-off thyristor, in order to transmit a high voltage direct current instead of an alternating current when power is transmitted at a predetermined distance. The present invention relates to a direct current transmission system that solves problems of current failure and harmonics without a reactive power compensation device using a semiconductor device.

AC voltage and AC current output from the generator are low voltage and large current. These types of voltages and currents transmit power over long distances in the form of low currents while maintaining a high voltage using high or ultra high voltage transformers due to conductor losses caused by large currents during power transfer.

However, this transmission of AC power is limited to long distance transmission due to capacitive loads between the transmission line and the ground and inductances present in the transmission line. Therefore, the DC transmission system has been developed in order to remove the limitation of such transmission, and this DC transmission has an advantage that the insulation breakdown is reduced compared to the AC transmission, and the capacitive load does not occur between the transmission line and the ground. In addition to the expensive power converter for converting AC into direct current, there is a disadvantage in that reactive power is generated due to phase control because the ultracapacitive semiconductor devices developed to date are thyristors.

Referring to the configuration diagram of a conventional DC power transmission system using a thyristor, a converter unit 1 for converting AC power into DC power, an inverter unit 2 for converting DC power into AC power, and AC power having a predetermined size A converter transformer 3 for boosting the voltage, an inverter transformer 4 for stepping down AC power of a predetermined size, a plurality of filters 5a-5d for simultaneously compensating harmonics and reactive power, and the converter unit ( 1) and a controller 6 for controlling the inverter unit 2 is included.

In addition, since the converter unit 1 and the inverter unit 2 including the plurality of thyristors SCR control the phase of the AC voltage, the current flows from the controlled phase, thereby causing a power factor and harmonic problem between the AC voltage and the AC current. Will occur.

Therefore, in order to increase the voltage of the converter unit 1 having a plurality of thyristors SCR, the converter transformer 3 is made into a high-voltage direct current. In order to make the high-pressure direct current to the alternating current by using the inverter unit (2) and to lower the AC voltage suitable for the system, it is to be connected to the system via a step-down transformer, that is, an inverter transformer (4). Since the power converter using the thyristor performs phase control, it causes harmonics and reactive power problems, and thus has a plurality of filters 5a-5d to compensate for harmonics and reactive power.

As described above, the disadvantage of the conventional DC power transmission system using a thyristor is that first, the thyristor DC power transmission system generates reactive power of about 60% of the load as the load increases. This can cause voltage stability problems in which the voltage collapses under conditions. Therefore, a synchronous shunt or static var compensator (SVC) for compensating reactive power must be installed at the transmission and reception terminals of the DC power transmission system.

Second, since the thyristor converter and inverter are phase control systems, a filter for current harmonic rejection should be installed on the AC side, and a filter for voltage harmonic control on the DC side.

Third, the DC power transmission system has a narrow control range of the phase controller because the generation of reactive power varies depending on the thyristor phase point.

Fourth, since the thyristor of the DC transmission system has no self-extinguishing capability, the voltage of the transmission stage must always exist, and if the receiving terminal voltage becomes smaller than a certain voltage, it causes a current failure.

The present invention has been made to solve the above problems, to provide a direct current transmission system that does not require a reactive power compensation device, the direct current transmission system is an Insulated Gate Bipolar Transistor (IGBT) or gate A converter and an inverter of a direct current transmission system were constructed by using a device having a self-extinguishing capability such as a turn off thyrister (GTO). The present invention basically adopts a PWM control method to control unit power factor. In addition, since reactive power and active power can be controlled intentionally, it can be used as a reactive power compensation device according to the system situation, and there is no current failure like thyristors, and the purpose is to solve the harmonic problem. .

In addition, another object of the present invention is similar to an ideal generator system with a very fast speed, and has characteristics similar to the excitation system of the generator system, that is, a reactive power controller for controlling the voltage or reactive power of the system and turbine system control of the generator. In other words, it has an active power controller that controls the frequency or active power of the system, which is similar to that of the active power controller and the reactive power controller is controlled independently, and finally converted to three-phase power to the system To inject.

1 is a configuration diagram of a DC power transmission system using a thyristor conventionally;

2 is a configuration diagram of a DC power transmission system using a semiconductor device according to the present invention;

3 is a control block diagram of a direct current power transmission system having an arc extinguishing ability of the present invention;

4 is a converter control block diagram of a direct current power transmission system having an arc extinguishing ability of the present invention;

5 shows a detailed module of the active power controller of FIG. 3;

6 illustrates a detailed module of the reactive power controller of FIG. 3;

7 is a configuration diagram of a phase converter.

♣ Explanation of symbols for the main parts of the drawing ♣

10: Isolated Gate Bipolar Transistor (IGBT) Converter

12: Insulated Gate Bipolar Transistor (IGBT) Inverter

14: inverter transformer 16: converter transformer

18: semiconductor device 20: capacitor

22: controller 30, 65: automatic frequency controller

35, 60: automatic active power controller 36, 69: automatic reactive power controller

37, 67: AC-automatic voltage controller 38: DC-automatic voltage controller

51, 57, 58: 3 / 2-phase converter 52, 53, 61, 63, 66, 68, 70: PI controller

62: converter DC voltage controller 72: stop / rotation coordinate system

In order to achieve the above object, the present invention provides a semiconductor device such as a plurality of insulated gate bipolar transistors having an arc extinguishing power and a plurality of gate turn off thyristers. The gate bipolar transistor inverter and the insulated gate bipolar transistor converter, the inverter transformer for step-down and the transformer transformer for step-up, and this semiconductor device have on-off capability of their own, Since the semiconductor device has a diode in itself, the semiconductor device includes a capacitor for applying a voltage rectified from the input voltage of the isolated gate bipolar transistor converter even without switching the inverter.

In addition, the present invention is an automatic frequency controller (Automatic Frequency Controller) to follow the frequency of the system when looking at the upper controller related to the active power, an Automatic Power Regulator (Automatic Power Regulator) for controlling the active power of the system, DC Direct Current Automatic Voltage Regulator that controls the voltage at the output stage, Automatic Reactive Regulator that controls the reactive power of the system Alternating Current Automatic Voltage Regulator for controlling the voltage, and a mode selector for logic selection whether to select DC-Automatic Voltage Control Mode or Automatic Frequency Control Mode / Auto Active Power Control Mode. to be.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram of a DC power transmission system using a semiconductor device according to the present invention.

The present invention utilizes semiconductor devices such as a plurality of insulated gate bipolar transistors and a plurality of gate turn off thyristers having an arc extinguishing capability, such as The insulated gate bipolar transistor inverter 10 and the insulated gate bipolar transistor converter 12 which are formed in parallel are comprised, and it has the inverter transformer 14 for step-down, and the converter transformer 16 for step-up.

This device, represented by semiconductor device 18, has its own on-off capability, and since the semiconductor device 18 has its own diode, it does not switch an isolated gate bipolar transistor, even if it does not switch the DC power transmission system. A voltage obtained by rectifying the input voltage of the insulated gate bipolar transistor converter 12 is applied to both ends of the capacitor 20 attached to the output terminal of the insulated gate bipolar transistor converter 12. At this time, when the insulated gate bipolar transistor is switched, when the inductance in the converter transformer 16 is short-circuited alternately in three phases, a voltage applied to the inductance is sent to the condenser 20 to direct a voltage higher than the voltage rectified by the diode. The voltage can be boosted. Since the DC output voltage of the insulated gate bipolar transistor converter 12 is proportional to the effective current, the condition for switching the insulated gate bipolar transistor is a vector-phase three-phase line current in front of the insulated gate bipolar transistor converter 12. By dividing into active current and reactive current, the active current is controlled to be a function of DC output voltage, and the reactive current is controlled to maintain the power factor 1 or follow the AC voltage of the system.

3 is a control block diagram of a DC power transmission system having an arc extinguishing capability using an insulated gate bipolar transistor, wherein an automatic frequency controller 30 which tracks the frequency of a system in view of an upper controller related to active power; It consists of an automatic active power controller (35) for controlling the active power of the system, and a direct current automatic voltage regulator (38) for controlling the voltage of the DC output terminal. On the other hand, the upper controller related to the reactive power, the automatic reactive regulator 36 for controlling the reactive power of the grid, and the alternating current automatic voltage regulator for controlling the voltage of the grid There is 37. The controller related to the active power is converted to the D-axis current command value, and the output of the controller related to the reactive power is converted to the Q-axis current command value. The commanded D-axis command value and Q-axis command value are converted into three-phase command values using a 2/3 phase conversion formula, and the three-phase command values are sent to the pulse width modulation inverter / converter.

In FIG. 3, when the converter or the inverter receiving the power is applied at the same time or the converter selects the DC-automatic voltage control mode, the inverter selects the automatic frequency control mode or the automatic active power control mode. The problem of selecting an AC-automatic voltage control mode or an automatic reactive power control mode can be arbitrarily selected without any major problem.

In addition, the mode selector 39, which is a logic selection of FIG. 3, is a selector for selecting whether to select a DC-automatic voltage control mode or an automatic frequency control mode / auto active power control mode. If the inverter is in the automatic frequency control mode / auto active power control mode and you want to change the control mode according to the fault or other external factors, the converter is in the auto frequency control mode / auto active power control mode, and the inverter is DC-automatic. The mode can be changed in the voltage control mode. The internal logic of the mode selector 39 selects the minimum value / maximum value between the output value of the DC-automatic voltage control mode and the output value of the automatic frequency control mode / auto active power control mode. Maximum and minimum values depend on the environment and design criteria.

FIG. 4 is a converter control block diagram of a DC power transmission system having an arc extinguishing ability. When a command value of the active current Iqref and the reactive current Idref is applied from the two-axis / 3-phase converter 41 of FIG. 3, the line currents Ia, Ib, Ic) 50 feeds back the actual active current Iq and the reactive current Id, which have passed through the 3 / 2-phase converter 51, so that the command value and the error value are passed through the PI controller 52, and the actual phase voltage Va, Vb, Vc) 54 is added to the 3/2 phase conversion value, and this value is made through the 3/2 phase converter 58 to generate the command values A, B, C of the pulse width modulator 59. .

FIG. 5 shows a detailed module of the active power controller of FIG. 3. The inputs of the active power controller include two Pref reference values expressed as active power command values and two f-ref command values expressed as frequency command values. In a three-phase system, frequency or phase is related to active power, so the variation of frequency can be thought of as the variation of active power.

Therefore, the active power controller includes an active power controller 60 having a PI controller 61 and a frequency controller 65 having a PI controller 66. The DC voltage of the converter having the PI controller is the active power. Since the converter DC voltage controller 62 having the PI controller 63 and the output of the converter DC voltage controller and the output values from the active power controller and the frequency controller, the minimum selector 64 can be selected according to the system conditions. There is).

FIG. 6 shows a detailed module of the reactive power controller of FIG. 3. Inputs of the reactive power controller include a Qref reference value expressed as a reactive power command value and two Vac ref command values expressed as a system frequency command value. Usually, in a three-phase system, the three-phase AC voltage of the system is related to the reactive power, so the variation of the three-phase AC voltage of the system can be thought of as a change in the reactive power. Accordingly, the reactive power controller includes an reactive power controller 69 having a PI controller 70 and an AC voltage controller 67 having a PI controller 68 for controlling a three-phase AC grid voltage.

7 is a configuration diagram of a phase converter, and shows logic for changing three phases to two phases. The three phases are converted into a stationary two phases having a 90 degree phase difference, and then converted into a rotating two phases according to the angular velocity. That is, the input three phases are converted into two phases through the stop / rotation coordinate system 74 through the 3 / 2-phase converter 72 and output.

As described above, the present invention configures a converter and an inverter of a DC power transmission system using a semiconductor element having self-extinguishing capability such as an insulated gate bipolar transistor or a gate turn-off thyristor without requiring a reactive power compensation device, and PWM control. It is possible to control unit power factor by adopting the method, and it can be used as reactive power compensation device according to the system situation because reactive power and active power can be controlled in aesthetic manner, and there is no current failure like thyristors. This has the effect of solving the harmonic problem.

Claims (3)

An insulated gate bipolar transistor inverter 10 in which a semiconductor device 18 such as a plurality of insulated gate bipolar transistors having an arc extinguishing power and a plurality of gate turn off thyristers is formed in parallel and in parallel; An insulated gate bipolar transistor converter 12, An inverter transformer 14 for step-down and a converter transformer 16 for step-up, This device, represented by the semiconductor device 18, has its own on-off capability, and since the semiconductor device 18 has its own diode, it switches the insulated gate bipolar transistor inverter 10. In the well-known DC power transmission system comprising a capacitor 20 for applying a voltage rectified to the input voltage of the insulated gate bipolar transistor converter 12, Automatic frequency controller 30 to follow the frequency of the system when looking at the upper controller related to the active power for controlling the frequency or active power of the system of the DC power transmission system; An active power controller 60 having a PI controller 61, a frequency controller 65 having a PI controller 66, and a converter DC voltage controller having a PI controller 63 as controlling the active power of the system. An automatic active power controller 35 comprising a 62, a minimum selector 64 for selecting the output of the converter DC voltage controller and the value output from the active power controller and the frequency controller according to the system conditions; A DC-automatic voltage controller 38 for controlling the voltage at the DC output stage; Looking at the upper controller related to the reactive power, the automatic reactive power controller 36 for controlling the reactive power of the system, AC-automatic voltage controller 37 for controlling the voltage of the system, And a mode selector (39) for logically selecting whether to select a DC-automatic voltage control mode or an automatic frequency control mode / automatic active power control mode. delete delete