KR101637928B1 - Apparatus for controlling real time stability of voltage and power in hvdc system - Google Patents

Abstract

A real time voltage and power stabilization device of an HVDC system is disclosed. The real-time voltage and power stabilization device of the HVDC system of the present invention calculates and outputs a DC current variation, a DC power variation, and a voltage stability index based on active power, reactive power, DC current and AC system information in an HVDC system, Analyzer; And a stabilization controller for checking the stability of the voltage and the power based on the output of the real-time stability analyzer and changing the sign of the command value of the current.

Description

Technical Field [0001] The present invention relates to a real-time voltage and power stabilization device for an HVDC system,

The present invention relates to a real-time voltage and power stabilization apparatus for an HVDC system, and more particularly, to a power-voltage characteristic curve and a current-power characteristic curve obtained by active power transmission and reactive power supply with an AC system associated with an HVDC system Time voltage and power stabilization device of the HVDC system that automatically returns to the voltage stabilized state by changing the current command of the controller at the time of transition from the voltage stabilized state to the voltage instable state exceeding the maximum power transmission point will be.

The power system is a system from power generation to consumption by connecting power plants, substations and loads to power transmission lines in response to electricity demand.

Since the power system must balance the supply and demand with the homogeneity of the generation and consumption of electric power, the monitoring of the electric power demand must be continuously carried out.

Although the initial small-scale system was easy to monitor, as the demand for electricity increased due to the advancement of the industry and information, and the power generation using renewable energy increased, the power facilities became larger and more complicated. It has reached its limit to operate. Therefore, a comprehensive automation of the facility is being rapidly promoted by efficiently collecting, processing, analyzing and controlling information by a computer and applying communication functions to efficiently perform power system operation tasks.

High Voltage Direct Current (HVDC) refers to a system that converts AC power generated by a power plant into DC and supplies power by re-converting power from a water supply point to AC.

This transmission scheme enables economical power transmission over AC transmission in long-distance power transmission, enables transmission of large-capacity power over long distances, and has the advantage of being able to connect with other systems having different frequencies. In addition, since it is possible to instantly control power transmission, it is possible to improve transient stability by suppressing low-frequency vibration of AC system when AC is used as auxiliary controller, to isolate system disturbance, and to control isolated small-scale system frequency Do.

In the current type HVDC system, unstable voltage or power supply is generated because the HVDC converter does not supply sufficient reactive power consumed. Therefore, reactive power is supplied through a switching type capacitor or a filter, and a control strategy is required at this time. Especially, the effect of voltage and power instability can be significant in the case of a weak system in which the short circuit capacity of the AC system is smaller than the rated capacity of the HVDC system. Voltage stability factor (VSF) is used as an indicator of such voltage instability.

In order to solve this voltage instability, a voltage dependent current limit (VDCOL) in the HVDC system itself has a short circuit ratio (SCR), which is the ratio of the short-circuit capacity of the AC system to the HVDC transmission capacity Ratio changes in the system are too fast or too slow to operate reliably and the real-time stability analysis can not be done. Therefore, the stability analysis should be performed at the design stage, the analysis result should be implemented in the controller, and there is no adaptation ability due to the variation of the system condition.

The determination of the stability margin, which is dependent on a particular system condition, provides information on the DC power that can be transmitted at the appropriate AC voltage level. So, during operation, the power is automatically adjusted to a pre-determined value stored in the converter power controller. Although this method provides stability for predictable system conditions, it does not provide stability for undesirable conditions such as extended power system or poorly coordinated operation or maintenance.

BACKGROUND OF THE INVENTION [0002] The background art of the present invention is disclosed in Korean Patent Laid-Open Publication No. 2014-0041146 (published on April 04, 044, entitled HVDC Voltage Stability Control Apparatus and Method).

In order to maintain the AC voltage and power stability, the current type HVDC system needs to keep the short circuit ratio (SCR, short circuit ratio) of the AC system to the minimum value above the actual converter power. That is, a minimum shorting ratio of 3 or more is required for proper operation.

However, in the case of a weak system in which the short-circuit ratio varies frequently or the capacity of the system is smaller than the capacity of the HVDC system, voltage instability often occurs, which may cause problems in operation of the HVDC system. Therefore, to solve this problem, the tuning of the controller for the system change must be performed for all the conditions, but this is physically difficult.

The present invention has been made to overcome the above problems, and it is an object of the present invention to provide a power-voltage characteristic curve and a current-power characteristic curve obtained by active power transmission and reactive power supply with an AC system associated with an HVDC system , A real-time voltage and power stabilization device of the HVDC system is provided which automatically returns to the voltage stabilized state by changing the current command of the controller at the time of transition from the voltage stable state to the voltage instable state exceeding the maximum power transmission point .

A real-time stability analyzer of a HVDC system according to the present invention includes: a real-time stability analyzer for calculating and outputting a DC current variation, a DC power variation, and a voltage stability index based on active power, reactive power, DC current, and AC grid information in an HVDC system; And a stabilization controller which changes the sign of the current command value of the converter controller of the HVDC system by confirming whether the voltage and the power are stable or not based on the output of the real-time stability analyzer, and the AC system information includes an AC voltage And a short-circuit ratio.

In the present invention, the real-time stability analyzer includes: a DC current variation calculation unit for calculating and outputting a variation in DC current of the HVDC system; A DC power variation amount calculation unit for calculating and outputting a DC power variation amount of the HVDC system; And a VSF operation unit for calculating and outputting a voltage stability index based on DC current, active power, reactive power and AC system information of the HVDC system.

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In the present invention, the stabilization controller includes: a multiplier for multiplying the output of the real-time stability analyzer, that is, the DC current variation, the DC power variation, and the voltage stability index, A mode selection unit for determining a mode of the voltage stability index and outputting an activation signal; And a level generator for generating a pulse according to the code determined by the multiplier and the activation signal of the mode selection unit to change the sign of the current command value of the converter controller of the HVDC system.

In the present invention, the mode selection unit switches the constant current control mode when the HVDC system is in the constant current control mode, and outputs an activation signal when the voltage stability index is out of the reference limit value.

The real-time voltage and power stabilization device of the HVDC system according to the present invention is based on the power-voltage characteristic curve and the current-power characteristic curve obtained by the active power transmission with the AC system associated with the HVDC system and the reactive power supply and demand, By changing the current command of the controller at the time when it transitions from the voltage stable state to the voltage instability state exceeding the transmission point, it can be automatically returned to the voltage stable state and the self adaptation ability So that the reliability of the operation can be increased and an economical system can be realized.

FIG. 1 is a diagram showing a configuration and a simplified diagram of a current type HVDC system according to an embodiment of the present invention.
2 is a graph showing voltage-power characteristics in a current type HVDC system according to an embodiment of the present invention.
FIG. 3 is a graph illustrating a voltage-dependent current command limiting function of a current type HVDC system according to an exemplary embodiment of the present invention.
4 is a block diagram illustrating a converter controller of a current type HVDC system according to an embodiment of the present invention.
FIG. 5 is a graph illustrating a relation between a maximum power transmission and a voltage stability index in a current type HVDC system according to an embodiment of the present invention.
6 is a diagram illustrating a real-time voltage and power stabilization apparatus for an HVDC system according to an embodiment of the present invention.
7 is a block diagram illustrating a stability analyzer and a stabilization controller of a real-time voltage and power stabilization apparatus of an HVDC system according to an embodiment of the present invention.
8 is a block diagram illustrating a mode selection unit of a stabilization controller in a real-time voltage and power stabilization apparatus of an HVDC system according to an embodiment of the present invention.

Hereinafter, an integrated frequency control apparatus and method of an HVDC system according to an embodiment of the present invention will be described with reference to the accompanying drawings. In this process, the thicknesses of the lines and the sizes of the components shown in the drawings may be exaggerated for clarity and convenience of explanation.

In addition, the terms described below are defined in consideration of the functions of the present invention, which may vary depending on the intention or custom of the user, the operator. Therefore, definitions of these terms should be made based on the contents throughout this specification.

2 is a graph illustrating voltage-power characteristics in a current type HVDC system according to an exemplary embodiment of the present invention. FIG. 2 is a graph illustrating voltage- FIG. 3 is a graph illustrating a voltage-dependent current command limiting function of an HVDC system according to an embodiment of the present invention. FIG. 4 is a block diagram illustrating a converter controller of an HVDC system according to an embodiment of the present invention. Is a graph illustrating the relation between the maximum power transmission and the voltage stability index in the HVDC system according to an embodiment of the present invention.

As shown in FIG. 1, in the current type HVDC system, a DC current flows due to a DC voltage difference between the rectifier 10 and the converter 20, and DC power is transmitted by the DC current and the DC voltage thus flowing. In this power transmission process, the rectifier 10 consumes 50 to 60% of the reactive power. Therefore, in order to supply such reactive power, the HVDC system usually uses an open-close type filter 30 or a parallel capacitor.

FIG. 2 is a graph showing voltage-power characteristics of the rectifier 10 at a constant point angle of the current type HVDC system. FIG. 2 (a) is a graph showing a maximum power curve (MPC) of the HVDC system. ) Is a graph showing the power-voltage curve of the AC / DC system.

As shown in FIG. 2, in the HVDC system, the maximum power curve shows that as the DC current increases, the DC power increases and the AC power decreases as the DC power increases and the reactive power consumption increases. The maximum available power (MAP) is the point at which the DC power can be maximally transmitted when the HVDC system increases the DC current. If the DC power increases, . In the power-voltage curve shown in (b), the upper branch of the MAP point is divided into the stable region, and the lower branch is classified into the unstable region.

 FIG. 3 shows a Voltage Dependent Current Order Limit (VDCOL) function used in a current type HVDC system. As shown here, when the DC voltage is greatly reduced, the control operation increases the current to maintain the command power value. This increase in current increases the consumption of the reactive power to further reduce the voltage, Will again increase the current. Repeating this vicious cycle can cause voltage collapse.

The function of limiting the DC current in proportion to the DC voltage drop is the voltage dependent current command limit (VDCOL) function in order to suppress the voltage decrease due to the increase of the reactive power when the DC voltage drops. However, the VDCOL function of the HVDC system connected to the AC system having a large change of the short circuit ratio (SCR) is operated too fast or too slow, so that it can not operate reliably. In addition, if the HVDC system has already exceeded the maximum transmission power point, exceeds the stability boundary, or is operating in the lower branch of the power-voltage curve as shown in FIG. 2, the voltage-dependent current command restricting function may not be recognized.

4 is a converter controller 40 of a current-type HVDC system having a voltage-dependent current command limit (VDCOL) function. The converter controller 40 selects a minimum fulcrum angle through a fulcrum selection unit 44, (41), the voltage controller (42), and the small angle controller (43). Here, the reference value of the current controller 41 is generated through a voltage dependent current command limit (VDCOL) function.

FIG. 5 is a graph showing a relationship between a maximum power curve and a voltage stability factor (VSF). It can be seen that the pattern of the voltage stability index curve varies according to the control mode. Therefore, in the three modes of constant current control (b), constant power control (a), and constant voltage control (c), the voltage stability index (VSF) . Here, the point at which the voltage stability index (VSF) becomes zero is a point at which the slope of the change in DC power with respect to the DC current becomes zero. Thus, it can be seen that the condition that both the voltage stability index (VSF) and the rate of change of the DC power with respect to the DC current have a positive value is a condition where the power and the voltage are stable.

FIG. 6 is a diagram illustrating a real-time voltage and power stabilization apparatus for an HVDC system according to an embodiment of the present invention. FIG. 7 is a block diagram of a stability analyzer and stabilization apparatus for a real-time voltage and power stabilization apparatus of an HVDC system according to an exemplary embodiment of the present invention. FIG. 8 is a block diagram illustrating a mode selection unit of a stabilization controller in a real-time voltage and power stabilization apparatus of an HVDC system according to an embodiment of the present invention. Referring to FIG.

6 and 7, the real-time voltage and power stabilization apparatus of the HVDC system includes a real-time stability analyzer 100 and a stabilizing controller 200.

The real-time stability analyzer 100 includes a DC current variation calculation unit 130 for calculating and outputting a DC current variation amount of the HVDC system, a DC power variation calculation unit 120 for calculating and outputting a DC power variation amount of the HVDC system, And a VSF operation unit 110 for calculating and outputting a voltage stability index (VSF) based on the current, active power (P _d ), reactive power (Q _d ), and AC system information.

Therefore, the real-time stability analyzer 100 calculates the effective power P _d , the reactive power Q _d , the DC current I _d , the AC voltage U, and the short-circuit ratio ESCR in the HVDC system, (DI _d / dt), the DC power variation (dP _d / dt), and the voltage stability index (VSF), based on

The stabilization controller 200 includes a multiplier 210 for multiplying the output of the real-time stability analyzer 100 by a sign of a DC current change amount, a DC power change amount, and a voltage stability index to determine a sign, a mode of a voltage stability index (VFS) A mode selector 250 for outputting an activation signal Active and a pulse generated in accordance with a code determined by the multiplier 210 and an activation signal of the mode selector 250, And a level generator 220 for changing the sign of the current command signal of the motor 40.

Therefore, the stabilization controller 200 changes the current command value code of the converter controller 40 by checking whether the voltage and the power are stable or not based on the output of the real-time stability analyzer 100.

Specifically, the sign of the DC current change amount dI _d / dt, the DC power change amount dP _d / dt, and the voltage stability index (VSF), which are the output values of the real-time stability analyzer 100, Likewise, it indicates whether the operating point of the HVDC system is in the lower or upper branch of the power-voltage curve. The sign can be obtained through the DC current variation (dI _d / dt), the DC power variation (dP _d / dt), and the voltage stability index (VSF), which are differential values with respect to time. Since the time derivative is determined continuously, the stability analysis analyzes the real-time stability in synchronism with time.

The stability criterion is determined by the stabilization controller 200 through the multiplier 210, the DC current variation dI _d / dt, the dc power variation dP _d / dt, and the voltage stability index VSF ) Signals. The multiplication of these signals is accomplished by generating a pulse through the level generator 220 and changing the sign of the current command signal in the converter controller 40.

When the power-voltage stability is in the stable region, the control signal is generated so that the power error increases the DC current through the sign of the current control loop. In order to activate the control signal, the stabilization controller 200 determines the mode of the voltage stability index VFS inputted through the mode selector 250 and outputs the activation signal Active.

Therefore, when increasing the DC current in the HVDC system, the power will decrease even if the DC current is increased even further after passing the maximum available point (MAP) point. Then, the real-time stability analyzer 100 senses this point of time through the sign of the DC current change amount dI _d / dt, the DC power change amount dP _d / dt, and the voltage stability index (VSF) ) Changes the sign of the current loop, thereby reducing the DC current.

In this way, the operating point of FIG. 2 moves back to the top of the power-voltage curve, and by repeating this process, the operating point is cycled near the maximum power transmission point. If the voltage is stabilized through this process, the rectification failure can also be prevented.

In the voltage stability index (VSF) calculator 110 of the real-time stability analyzer 100, the voltage stability index is calculated by Equation (1).

는 각각 정류기(10)의 유효전력(P_d) 및 무효전력(Q_d)의 교류전압(U) 의존값이며, 제어모드에 따라서 다음과 같이 정의된다. 이때

는 소호각이고,

는 위상변위이다. In the above, ESCR is the short-circuit ratio,

(U) of the reactive power (P _d ) and the reactive power (Q _d ) of the rectifier (10), respectively, and is defined as follows according to the control mode. At this time

Is a soho angle,

Is the phase shift.

That is, in the case of constant so-called angle control and constant power control,

로 정의되고,

Lt; / RTI >

In case of Constant Loop Angle Control and Constant Current Control,

로 정의되며,

Lt; / RTI >

In the case of constant DC voltage control and constant power control,

로 정의된다.

.

As shown in FIG. 8, the mode selection unit 250 can select two modes depending on the control mode information of the HVDC system. One mode is a constant power control and a constant DC control, and the other is a constant current control . In the case of constant power control and constant DC control, as shown in FIG. 5, the voltage stability index (VSF) is a positive value regardless of the values of the DC current change amount dI _d / dt and the DC power change amount dP _d / The stability reference evaluated by the slope of the DC power and the DC current is applied to the current control as it is.

On the other hand, in the case of constant current control, the voltage stability index (VSF) becomes closer to the infinite value as the DC power variation and the DC current variation become closer to the point where the sign changes. In this case, the mode selector 250 is switched to the constant current mode and activates the output signal of the stabilization controller 200 when the voltage stability index (VSF) deviates from a preset reference limit value.

As described above, according to the real-time voltage and power stabilization apparatus of the HVDC system according to the present invention, the power-voltage characteristic curve and the current-power characteristic obtained by the active power transmission and reactive power supply with the AC system connected with the HVDC system Based on the curve, it is possible to return to the voltage stabilized state automatically by changing the current command of the controller at the time of transition from the voltage stable state to the voltage instable state exceeding the maximum power transmission point, It has the self-adaptive ability according to the change, thereby increasing the reliability of operation and making it possible to implement an economical system.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. I will understand.

Accordingly, the technical scope of the present invention should be defined by the following claims.

10: rectifier 20: converter
30: filter 40: converter controller
41: current controller 42: power controller
43: Loop angle controller 44:
100: real-time stability analyzer 110: VSF operation unit
120: power variation calculation unit 130: current variation calculation unit
200: Stabilization controller 210: Multiplier
220: level generator 250: mode selector

Claims (5)

A real time stability analyzer for calculating and outputting DC current variation, DC power variation and voltage stability index based on active power, reactive power, DC current and AC system information in HVDC system; And
And a stabilization controller for checking the stability of the voltage and the power based on the output of the real time stability analyzer and changing the sign of the current command value of the converter controller of the HVDC system,
Wherein the AC system information includes an AC voltage and a short circuit ratio in the HVDC system.
The real-time stability analyzer according to claim 1,
A DC current change amount calculation unit for calculating and outputting the DC change amount of the HVDC system;
A DC power variation amount calculation unit for calculating and outputting the DC power variation amount of the HVDC system; And
And a VSF arithmetic unit for calculating and outputting the voltage stability index based on the DC current, the active power, the reactive power, and the AC system information of the HVDC system.
delete The apparatus of claim 1, wherein the stabilization controller comprises:
A multiplier for multiplying the output of the real-time stability analyzer by a sign of the DC current variation, the DC power variation, and the voltage stability index to determine a sign;
A mode selection unit for determining a mode of the voltage stability index and outputting an activation signal; And
And a level generator for generating a pulse according to the code determined by the multiplier and the activation signal of the mode selection unit to change sign of the current command value of the converter controller of the HVDC system.
The HVDC system according to claim 4, wherein the mode selector switches the constant current control mode when the HVDC system is in a constant current control mode and outputs the activation signal when the voltage stability index is out of a reference limit value. System real time stabilization device.

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