KR20130117547A - High voltage direct current transmission system, and controlling apparatus and overload controlling method of the same - Google Patents

Abstract

PURPOSE: A high-voltage DC power transmission system, a control device thereof, and an overload control method prevent accidents and improve the operation efficiency and reliability of a system by performing reliable overload control. CONSTITUTION: A transformer (10) converts input AC power into AC power for transmission. A power converter (20) converts the AC power for transmission into DC power or converts the DC power into the AC power for transmission. A DC cable (30) transmits the DC power. A control device (40) controls the transformer and the power converter. The control device includes an overload control unit which controls a current limit value for DC of the DC power and performs overload control for a line. [Reference numerals] (10,BB) Transformer; (20,AA) Power converter; (40) Control device; (53) Temperature sensor; (54) Humidity sensor; (60,CC) Cooling device; (80) Input device

Description

HIGH VOLTAGE DIRECT CURRENT TRANSMISSION SYSTEM, AND CONTROLLING APPARATUS AND OVERLOAD CONTROLLING METHOD OF THE SAME}

The present invention relates to an overload control method of a high voltage direct current transmission system that allows an overload capacity to prevent unnecessary accidents that may occur in the high pressure direct current transmission system.

There are two methods of linking the power system: a method of directly connecting an existing AC power system and a method of linking a system by converting AC power into DC power through a power converter. Recently, the interest in the method of linking the AC power system by connecting the power system by converting the AC power into DC power rather than the method of directly connecting the AC power system. In Korea, a high voltage direct current (HVDC) system using a power converter is installed between Jeju and Haenam to link the power system between Jeju and Haenam.

The high voltage direct current transmission (HVDC) method is one of electric transmission methods, and it is a supply method that converts high voltage AC power generated at a power plant into DC power and transmits it, and then converts it back into AC power in a desired power receiving area. . There are many advantages of DC power transmission.

First of all, the DC voltage is only about 70% of the maximum value of the AC voltage.The high-voltage DC transmission system can easily insulate the device and lower the voltage, thereby reducing the number of insulators installed in each device and the height of the steel tower. Can be. The system has the greatest advantage that the power transmission efficiency can be increased since the direct current method has less transmission loss than the AC method when sending the same power. The system can carry more than twice the current of direct current compared to alternating current.

The high voltage DC transmission system can reduce wire usage and reduce the area of the transmission line, which is effective and can improve the stability of the system by connecting between two AC systems of different voltage or frequency. The system has no limitation on the transmission distance, and the DC transmission method is low in construction cost for land power transmission of more than 450 km or power transmission over the sea bottom of more than 40 km. Recently, the supply of high-voltage DC transmission system is rapidly expanding in China and India because the distance between power plants and electric users is more than 1000 km.

Embodiments of the present invention have an object to provide a control device and an overload control method for stabilization of a high voltage direct current transmission system (HVDC).

Embodiments of the present invention have another object to provide a high-voltage direct current transmission system, a control device and an overload control method for allowing an overload capacity to be controlled so that there is no risk of unnecessary failure caused by thermal stress in the system equipment.

A high voltage direct current transmission system according to an embodiment includes a transformer connected to an AC bus and converting input AC power into AC power for transmission, and a switching element, and connected to the transformer, wherein the AC power for power transmission is DC power. Or a power converter for converting the DC power to the AC power for the transmission, and a DC cable for transmitting the DC power, receiving a power command value, and controlling the transformer and the power converter. It further comprises a control device. Here, the control device, the overload control for the line by adjusting the current limit value for the direct current of the direct current power based on one or more overload conditions of the temperature of the transformer, the temperature of the power converter, ambient temperature, and humidity. It is configured to include an overload control unit to perform the.

In the high-voltage DC power transmission system, the line detects the temperature of the power converter, transmits a condition signal corresponding to the overload condition to the overload control unit, further cooling device for cooling the switching element of the power converter. It is configured to include.

The high voltage direct current transmission system is configured to further include a protection device connected to the component of the line to protect the line, and generates a trip signal and transmits a trip signal to the control device when an error occurs in the protection function of the line. . The overload controller performs the overload control when the trip signal is received.

The control apparatus of the high-voltage DC power transmission system according to an embodiment of the present invention, in the high-voltage DC power transmission system for forming one or more lines, and converts high-voltage AC power into DC power for transmission, the current limit value for the DC current of the DC power And a line power controller configured to receive a power command value for power conversion, convert the AC power into the DC power, and an overload controller to adjust the current limit based on an overload condition to perform overload control. The overload condition is characterized in that at least one of the temperature of the transformer forming the line, the temperature of the power converter, the ambient temperature, and the humidity.

An overload control method of a high voltage direct current transmission system according to an embodiment of the present invention is a high voltage direct current transmission system that forms one or more lines, converts high voltage AC power into DC power, and transmits power. A normal power transmission step for transmitting power, a condition determining step for receiving an overload condition, an abnormality determining step for determining an abnormality in the protection function of the line, and an overload control when the overload condition or an abnormality occurs. And an overload release step of converting and transmitting power based on the new power command value when the overload control is released.

Embodiments of the present invention to prevent the accident by improving the stable overload control in the high-voltage DC power transmission system and improve the operating efficiency and stability of the system.

Embodiments of the present invention can perform the overload control by analyzing the factors affecting the overload in detail, and can be applied in consideration of the system equipment allowance to lower the probability of malfunction and to control the system more stably.

Embodiments of the present invention can closely control the protection function of the high-voltage DC power transmission system operating in the event of an accident.

Embodiments of the present invention can prevent the transient state by placing a slope at the return after the overload control.

1 is a schematic view showing the configuration of a general high voltage direct current transmission system;
2 is a block diagram schematically showing the configuration of a high-voltage DC power transmission system according to an embodiment of the present invention;
3 is a schematic view showing a control device of a high-voltage direct current power transmission system according to an embodiment of the present invention;
4 is a graph for explaining an operation of setting a current limit when performing overload control according to embodiments of the present disclosure; And
5 to 6b are flowcharts schematically illustrating an overload control method of a high voltage direct current transmission system according to embodiments of the present invention.

1 and 2, a high voltage DC power transmission system according to an embodiment includes a transformer 10 connected to an AC bus and converting input AC power into AC power for transmission, and a switching element. And a power converter 20 connected to the transformer 10 and converting the AC power to DC power, or converting the DC power to AC power, and a DC cable to transmit the DC power. 30 to form a line. The high voltage direct current transmission system may further include a filter for removing harmonics and compensating for reactive power.

The transformer 10 receives AC power from an AC bus, for example, a 154 kV bus bar, and transforms it into AC power for transmission. The transformer 10 generally uses a three-phase Y-Y-Δ (y-y-delta) method. Each of the secondary bridges of the wy-bridge and the delta-bridge may be provided with a current sensor to detect an overcurrent and protect a bridge.

The power converter 20 is composed of a plurality of switching elements. Here, the switching elements may be transistors such as an insulated gate bipolar transistor (IGBT) or a MOSFET (MOSFET) as a power semiconductor, but a thyristor capable of controlling current is mainly used. Power converter 20 is provided on the power transmission side rectifier (Rectifier, 21, 22) for converting the AC power transformed by the transformer 10 into direct current power, and the direct current provided on the power receiving side through DC cable Inverters 23 and 24 for converting power into AC power are included. The rectifier and the inverter each include a thyristor valve composed of a plurality of thyristors.

The high voltage direct current transmission system further includes a control device 40 that receives a power command value and controls the transformer and the power converter. Referring to FIG. 3, the control device 40 of the high-voltage DC power transmission system according to an embodiment may include one or more lines and convert the high-voltage AC power into DC power to transmit power. A line power control unit 42 which receives a current limit value of DC power of the DC power and a power command value for power conversion, converts the AC power into the DC power, and an overload control unit that performs an overload control by adjusting; 41). The line power control unit 42 receives the current limit value from the overload control unit 41 and drives the power converter 20 based on the power command value and the current limit value.

Here, the overload condition may be one or more of the temperature of the transformer forming the line, the temperature of the power converter, the ambient temperature, and the humidity, as shown in FIG. 3. Referring to FIG. 2, the high voltage direct current transmission system may include a temperature sensor 51 for detecting a temperature of the transformer 10, and a temperature sensor 52 for detecting a temperature of the power converter 20. In addition, the high-voltage DC power transmission system may further include a temperature sensor 53 for detecting the ambient temperature around the system equipment, and a humidity sensor 54 for detecting the humidity.

Referring to FIG. 2, in the high-voltage DC power transmission system, the line detects a temperature of the power converter 20, transmits a condition signal corresponding to the overload condition to the overload controller 41, and transmits the power. It further comprises a cooling system (Cooling system) 60 for cooling the switching element of the transducer 20. The cooling device 60 is driven according to the temperature of the power converter.

The temperature of the transformer is an allowable degree of the thermal temperature of the transformer. If the detected temperature is equal to or more than the preset allowable temperature, the temperature sensor 51 generates condition signal 1 to the control device. The condition signal 1 may be a logarithm of a Boolean of 0 and 1 type.

The thermal temperature of the thyristor valve constituting the power converter is an allowable cooling device. That is, if the temperature of the power converter is equal to or greater than the preset allowable temperature, the temperature sensor 52 generates the condition signal 2 to the control device. The condition signal 2 may be a logarithm of a Boolean of 0 and 1 form.

The temperature sensor 53 compares the atmospheric temperature of the ambient air of the system equipment with a preset allowable temperature, and generates a condition signal 3 to the control device when the detected temperature is equal to or higher than the allowable temperature. The condition signal 3 may be a logarithm of a Boolean of 0 and 1 type.

Humidity is associated with insulation around high voltage direct current transmission system installations. In other words, if the humidity is high, the insulation ability is lowered. The humidity sensor generates the condition signal 4 to the control device when the detected humidity becomes equal to or higher than the preset reference humidity. The condition signal 4 may be a logarithm of a Boolean of 0 and 1 type.

The control unit operates the system normally if all four conditions, such as transformer allowance, power converter allowance (cooling allowance), ambient temperature allowance and humidity allowance, are acceptable (if 1). At this time, the current limit has 1.0pu and does not limit the power slope. On the other hand, if any one of the four conditions is not acceptable (if 0), the overload controller raises the current limit to perform overload control.

Overload control is a control method to prevent the operation of the system due to the stress of the system during the operation of the high-voltage DC transmission system, failure, shutdown (shutdown). Overload control takes care of each pole, limiting the lower overload capacity of the rectifier and inverter side equipment.

Referring to FIG. 2, the high-voltage direct current power transmission system is connected to a component of the line to protect the line, and when an abnormality occurs in the protection function of the line, a protection device for generating a trip signal and transmitting it to the control device. It further comprises 70. Here, the overload control unit 41 performs the overload control when the trip signal is received. The trip signal of the protection device is a signal obtained by collecting protection function signals associated with each line. The trip signal of the protection device is a signal generated when an abnormality occurs in the protection function of each line, and may be, for example, 0 or 1 type of fire.

In FIG. 2, the protection device 70 is provided to the DC cable 30 to provide DC protection. However, the protection device 70 may be installed in the AC portion to perform AC protection. AC protection is AC bus overvoltage protection (154kV Busbar Protection), Transformer Transformer (Protection Transformer Protection), Filter Protection (High Pass & Double Tuned Filter Protection), etc., for example. If an abnormality occurs while performing the AC protection function, the protection device 70 may generate the trip signal and transmit the generated trip signal to the control device 40.

The control device normally operates the high-voltage DC power transmission system when there is no abnormality of the protection function, that is, when a trip signal of 0 is received from the protection device. However, even if all four conditions are acceptable, if the protection device transmits a trip signal of 1, the overload controller 41 raises the power limit and performs overload control.

Referring to FIG. 2, in the high voltage direct current transmission system, the line further includes an input device 80 that receives a change command for the current limit value. In addition, the input device 80 may receive a power command value. Here, the input device is a Human Man Interface (HMI) which may include an output function.

The administrator or the user may input a change command, for example, a slope with respect to the current limit value, to the current limit setting unit 41a through the input device 80. When the overload controller corresponds to the overload condition or receives the trip signal, the overload controller raises the current limit value from the first current limit value to a second current limit value larger than a predetermined level and maintains the predetermined time period. Here, the predetermined time is determined in consideration of the time that can be tolerated according to the system equipment. The power command value, which is an input of the line control unit, is maintained at the power at the time of performing the overload control. The overcurrent controller 41 transmits to the line power controller 42 whether the overcurrent limit and the power slope stop.

The overload controller changes the current limit value by a predetermined slope from the second current limit value to the first current limit value when the overload control is released. However, even if the overload control is released after a certain time, if the trip signal from the protection device is not reset to zero and the temperature or humidity allowance is not acceptable, the control device will not wait until a new power command value for the line is input. Do not start the slope.

Referring to FIG. 4, the overload controller changes the current limit value Idc from the first current limit value A to the second current limit value B when performing the overload control. For example, A is 1.0pu, B is 1.2pu or 1.3pu. After the predetermined time T has elapsed, the overload controller changes the current limit value to the current limit value A in normal operation. At this time, the overcurrent controller changes the current limit value according to the slope a received through the input device 80. In this case, the change command is a tilt (a) setting command. Although the present invention has been described only for changing the current limit, the same applies to changing the voltage limit or the power limit.

Referring to FIG. 5, in the overload control method of the high-voltage DC power transmission system according to an embodiment, the power command value is formed in the high-voltage DC power transmission system in which one or more lines are formed and the high-voltage AC power is converted into DC power for transmission. A normal power transmission step (S10) of converting power on the basis of power transmission, a condition determination step (S20) of receiving an overload condition, an abnormality determination step (S30) of determining an abnormal occurrence in the protection function of the line, and the overload If the condition corresponds to or abnormality occurs, the overload control step (S40) for performing the overload control, and if the overload control is released, the overload release step (S50) for converting and transmitting power based on the new power command value. It is configured to include. A description of the following configuration is made with reference to FIGS. 1 to 4.

Here, the overload condition is at least one of the temperature of the transformer forming the line, the temperature of the power converter, the ambient temperature, and the humidity.

Referring to FIG. 6A, the temperature of the transformer is an allowable degree of the thermal temperature of the transformer. If the detected temperature is greater than or equal to a preset allowable temperature, the high pressure DC power transmission system performs overload control (S21). The thermal temperature of the thyristor valve constituting the power converter is an allowable cooling device. That is, if the temperature of the power converter is higher than the preset allowable temperature, the system performs the overload control (S22). The system compares the atmospheric temperature of the ambient air of the system equipment with a preset allowable temperature, and if the detected temperature is higher than the allowable temperature, performs overload control (S23). Humidity is associated with insulation around high voltage direct current transmission system installations. In other words, if the humidity is high, the insulation ability is lowered. The system also performs overload control when the detected humidity is equal to or higher than a preset reference humidity. That is, the system operates normally if all four conditions, such as the transformer allowance, the power converter allowance (the cooling device allowance), the air temperature allowance, and the humidity allowance, are acceptable (if 1). At this time, the current limit has 1.0pu and does not limit the power slope. On the other hand, if any of the four conditions is not acceptable (if zero), the system raises the current limit to perform overload control.

As shown in FIG. 6B, in the overload control step S40, the current limit value is raised from the first current limit value to a second current limit value larger than a predetermined level (S41) and maintained for a predetermined time (S42). Referring to FIG. 4, the system changes the current limit Idc from the first current limit A to the second current limit B when the overload control is performed, and maintains it for a predetermined time T. For example, A is 1.0pu, B is 1.2pu or 1.3pu.

The overload release step S50 may include receiving a slope for the current limit value to be applied when the overload control is released (not shown), and a current limit value from the second current limit value to the first current limit value. It is configured to include a process of changing (S52). After a certain time T has elapsed, the system changes the current limit to the current limit A in normal operation. At this time, the system changes the current limit value according to the slope a received through the input device 80. In this case, the change command is a tilt (a) setting command. However, even if the overload control is released after a certain time, if the trip signal from the protection device is not reset to zero and the temperature or humidity allowance is not acceptable, the system does not input the new power command value for the line. Do not start the slope (S53).

As described above, the high voltage direct current transmission system, the control device and the overload control method according to the embodiments of the present invention overcomes the disadvantages of the conventional overload control and improves the stability of the high pressure direct current transmission system. Embodiments of the present invention to prevent the accident by improving the stable overload control in the high-voltage DC power transmission system and improve the operating efficiency and stability of the system. Embodiments of the present invention can perform the overload control by analyzing the factors affecting the overload in detail, and can be applied in consideration of the system equipment allowance to lower the probability of malfunction and to control the system more stably.

10: transformer 20: power converter
30: DC cable 40: controller
51, 52, 53: temperature sensor 54: humidity sensor
60: cooling device 70: protection device
80: input device

Claims (9)

A transformer connected with the AC bus and converting the input AC power into the AC power for transmission;
A power converter comprising a switching element and connected to the transformer and converting the AC power to DC power or converting the DC power to AC power; And
A direct current cable for transmitting the direct current power;
And a control device for receiving a power command value and controlling the transformer and the power converter.
The control device includes:
An overload controller configured to perform an overload control on the line by adjusting a current limit value of the DC current of the DC power based on at least one of an overload condition of the temperature of the transformer, the temperature of the power converter, ambient temperature, and humidity; High voltage direct current transmission system comprising a. The method of claim 1, wherein the line is,
And a cooling device that detects a temperature of the power converter, transmits a condition signal corresponding to the overload condition to the overload controller, and cools the switching element of the power converter. 3. The method according to claim 1 or 2,
A protection device connected to a component of the line to protect the line, and generating a trip signal to the control device when an error occurs in the protection function of the line;
The overload control unit performs the overload control when the trip signal is received. The method of claim 3, wherein the control device,
And a line power control unit which receives the current limit value from the overload control unit and drives the power converter based on the power command value and the current limit value. The method of claim 4, wherein the line is,
And an input device configured to receive a change command for the current limit value. In the high-voltage DC power transmission system for forming one or more lines, and converts high-voltage AC power into DC power to transmit power,
A line power controller configured to receive a current limit value for the DC current of the DC power, a power command value for power conversion, and convert the AC power into the DC power; And
And an overload controller configured to perform an overload control by adjusting the current limit based on an overload condition.
The overload condition,
And at least one of a temperature of a transformer, a temperature of a power converter, an ambient temperature, and a humidity forming the line. The method of claim 6, wherein the overload control unit,
And controlling the overload control when the trip signal is received from a protection device that generates a trip signal when an error occurs in the protection function of the line. The method of claim 7, wherein the overload control unit,
When the overload condition or the trip signal is received, the current limiting value is increased from the first current limiting value to a second current limiting value greater than a predetermined level and maintained for a predetermined time. . The method of claim 8, wherein the overload control unit,
And when the overload control is released, the current limiting value is changed by a predetermined slope from the second current limiting value to the first current limiting value.

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