Active power and reactive power coordination control method for high-voltage direct-current power transmission system

Abstract

The invention discloses an active and reactive coordination control method in a high-voltage direct-current power transmission system. The method comprises the following steps: acquiring a system state; active power adjustment and reactive power demand calculation; determining the step number of reactive compensation; calculating a coordinated active power adjustment instruction; and determining an active and reactive coordination time sequence. The method can accurately predict the change of reactive power under the condition that the active power of the high-voltage direct-current power transmission system is changed, coordinates the control of the active power and the control of the reactive power through the cooperation of the action of the reactive power compensation device and the adjustment of the active power, achieves the target of maintaining the stability of the reactive voltage of the system, and improves the reliability of the system. The stability of the power system is improved. The target of flexible adjustment of the high-voltage direct-current transmission active power can be achieved, and the power transmission capacity of the high-voltage direct-current transmission system is improved. The method has reactive power active compensation capability, reactive compensation equipment performs active switching action, and the problem of voltage fluctuation of an alternating current system during active adjustment is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of high-voltage direct current transmission, and relates to an active and reactive coordinated control method for a high-voltage direct current transmission system. Background Art

[0002] With the increase in power demand in the power grid and the uneven distribution of load and power generation resources in my country, HVDC transmission technology has been widely used in large-scale power transmission and interconnection between different types of power grids due to its large transmission capacity, relatively mature technology and low cost. Due to the power fluctuation problem of the power grid caused by the large-scale grid connection of new energy sources and the "AC to DC" phenomenon of lines caused by the increase in load demand, the HVDC transmission system faces the need to adjust the active power. When the HVDC transmission system is in operation, the converter valve will absorb a large amount of reactive power, which will cause reactive power and voltage fluctuations when the transmitted active power changes. In order to maintain the stability of reactive power and voltage, the HVDC transmission system requires a corresponding active and reactive coordination strategy.

[0003] At present, the main reactive power compensation strategy of the HVDC transmission system is to set reactive power groups and AC voltage dead zones. When the AC voltage exceeds the limit, the reactive power compensation equipment is switched on and off in reactive groups until the voltage is readjusted to the dead zone. The current reactive power support strategy lacks initiative and cannot accurately and efficiently predict the change in reactive power. When the voltage exceeds the limit, reactive power compensation is passively performed, which will cause voltage fluctuations. In addition, the current reactive power support strategy lacks strategies for active power adjustment or coordination strategies with active power. The current reactive power compensation strategy will have problems such as insufficient reactive power compensation equipment and more severe voltage fluctuations when active power is adjusted. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a method for coordinated control of active and reactive power in a high-voltage direct current transmission system, which actively and reasonably utilizes reactive compensation devices such as AC filters and reactive compensation capacitors configured in the AC system, so that the system can achieve flexible adjustment of the transmitted active power while maintaining reactive voltage stability.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for coordinated control of active and reactive power in a high voltage direct current transmission system comprises the following steps:

[0007] Step 1, system status acquisition;

[0008] Step 2: Calculate active power adjustment according to the active power instruction issued by the dispatching system, and calculate reactive power demand according to the active power adjustment;

[0009] Step 3, calculating the number of reactive power compensation steps according to the capacity of the reactive power compensation device configured in the system and the reactive power demand;

[0010] Step 4, calculating the active power adjustment instruction according to the determined reactive power compensation amount;

[0011] Step 5: Determine the active and reactive power coordination timing.

[0012] Furthermore, it also includes: active power adjustment and reactive power control are coordinated through the coordination sequence determined in step 5, and the system state is updated before each step of active power and reactive power coordinated adjustment.

[0013] Furthermore, in the control of the high-voltage direct current transmission system, the control reference value of the direct current active power is also converted into a direct current reference value of the control system, and input into the converter station controlled by the fixed direct current for control.

[0014] Furthermore, in the constant DC current controller structure, according to the difference between the DC current reference value and the actual value, after adjustment by the PI controller, a control instruction of the trigger angle is output, and the active power is adjusted by controlling the valve.

[0015] Furthermore, the system state in step 1 includes: the AC voltage U collected from the common coupling point of the converter PCC , active power data P and reactive power data Q, DC voltage U collected from the DC grid point dc and DC current data I dc , the trigger angle α and commutation angle μ of the converter valve, the power factor of the system .

[0016] Furthermore, the step 2 specifically includes the following sub-steps:

[0017] Step 2-1, calculate the active power adjustment according to the active power instruction issued by the dispatching system:

[0018] ΔP=P sref -P

[0019] Among them, P sref is the reference value of active power, ΔP is the active power adjustment;

[0020] Step 2-2, calculate reactive power demand based on active power adjustment:

[0021] ΔQ=ΔQ l +ΔQ conv

[0022]

[0023]

[0024] Among them, ΔQ l is the change in reactive power loss of the line during active power adjustment, ΔQ conv is the change in reactive power consumption of the DC converter valve during active power adjustment, ΔQ is the reactive power demand of the entire system during active power adjustment, and U PCC , P LCC , Q LCC They are the AC voltage, reactive power and active power collected from the common coupling point, U dc0 is the ideal DC voltage value of the system, U dc is the current DC voltage value, X ac is the reactance value of the AC line.

[0025] Furthermore, the number of steps of reactive power compensation in step 3 is calculated by the following formula:

[0026] k=int(ΔQ / Q c )

[0027] Among them, Q c It is the reactive capacity of a single reactive compensation device.

[0028] Furthermore, in step 4, the active power adjustment instruction is calculated by the following formula:

[0029] AΔP 2 +BΔP+C=0

[0030] In the above formula, A, B, and C are obtained and calculated by the high-voltage direct current transmission system state measurement device, as shown in the following formula:

[0031]

[0032] In the formula, Q ck Represents the reactive power provided by the kth group of reactive power compensation equipment.

[0033] Furthermore, the active and reactive coordination timing in step 5 refers to the timing of active power adjustment and coordinated switching of reactive compensation devices, including: the switching of reactive compensation devices slightly precedes the adjustment of active power; the switching of reactive compensation devices is simultaneous with the adjustment of active power; the switching of reactive power slightly lags behind the adjustment of active power.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] 1. The present invention can accurately predict the change of reactive power when the active power of the high-voltage direct current transmission system changes, and coordinate the control of active power and reactive power through the action of the reactive compensation device and the coordination of active power adjustment, so as to achieve the goal of maintaining the reactive voltage stability of the system and improve the stability of the power system. The present invention can achieve the goal of flexible adjustment of active power of high-voltage direct current transmission and improve the transmission capacity of the high-voltage direct current transmission system.

[0036] 2. The method of the present invention has the ability to actively compensate for reactive power, and the reactive power compensation equipment is actively switched on and off, thereby improving the voltage fluctuation problem of the AC system during active power adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic flow chart of the active and reactive power coordinated control method for a high voltage direct current power transmission system provided by the present invention;

[0038] Figure 2 It is a schematic diagram of the structure of a typical high-voltage direct current transmission system;

[0039] Figure 3 Active power curves under the coordinated control strategy of the present invention, the traditional compensation strategy, and the non-compensation strategy;

[0040] Figure 4 Reactive power curves under the coordinated control strategy of the present invention, the traditional compensation strategy, and the non-compensation strategy;

[0041] Figure 5 The common coupling bus AC voltage curves under the coordinated control strategy of the present invention, the traditional compensation strategy, and the non-compensation strategy. DETAILED DESCRIPTION

[0042] The technical solution provided by the present invention will be described in detail below in conjunction with specific embodiments. It should be understood that the following specific implementation methods are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0043] The high-voltage direct current transmission system used in the present invention comprises at least a rectifier station and an inverter station, wherein the rectifier station usually adopts a fixed direct current control method, and the inverter station usually adopts a fixed arc extinction angle control method. The AC part of the system comprises at least reactive compensation equipment such as an AC filter and reactive compensation capacitors.

[0044] like Figure 1As shown in the figure, the current operating state of the system, including the values ​​of DC voltage, DC current, active power, reactive power, AC voltage, and the target value of the system active power adjustment, is used as the input of the coordinated control, and coordinated reactive power control is performed according to the configuration and grouping of the reactive compensation device of the system. The coordinated reactive power control includes calculating the reactive power demand of the AC line and the converter valve according to the active power adjustment target, and calculating the reactive power compensated by the reactive compensation devices such as the single switching AC filter and reactive compensation capacitor.

[0045] The coordinated active power adjustment control is coordinated with the reactive power control, and the switching of reactive compensation equipment such as AC filters and reactive compensation capacitors is coordinated to achieve the change of active power reference value, and finally achieve the goal of active power adjustment. Active power adjustment and reactive power control are coordinated and distributed, and the system status is updated before each step of active power and reactive power adjustment to ensure the accuracy of control. In the control of the high-voltage direct current transmission system, it is also necessary to convert the control reference value of the DC active power into the DC current reference value of the control system, and input it into the converter station controlled by the fixed DC current for control.

[0046] In the commonly used constant DC current controller structure, according to the difference between the DC current reference value and the actual value, the PI controller is adjusted to output the control instruction of the trigger angle, and the active power is adjusted by controlling the valve.

[0047] The structure of the constant DC current controller for active and reactive coordinated control is as follows: Figure 2 As shown. The reference value of DC current is different from the fixed value under conventional constant power operation. It is calculated through coordinated control of active power and reactive power, coordinated reactive control and coordinated active power adjustment. At the same time, in the AC system, devices such as AC filters and reactive power compensation capacitors are switched in coordination to achieve coordinated control of active and reactive power.

[0048] Specifically, the active and reactive coordinated control method of the high voltage direct current transmission system provided by the present invention comprises the following steps:

[0049] Step 1: Obtaining the system status. The system status includes: the AC voltage U collected from the common coupling point of the converter PCC , active power data P and reactive power data Q, DC voltage U collected from the DC grid point dc and DC current data I dc , the collected data of the trigger angle α and commutation angle μ of the converter valve, and the power factor of the system (Specific sampling points and sampling variable names are as follows Figure 2 shown).

[0050] Step 2, active power adjustment and reactive power demand calculation, includes the following sub-steps:

[0051] Step 2-1, calculate the active power adjustment according to the active power instruction issued by the dispatching system:

[0052] ΔP=P sref -P

[0053] Among them, P sref is the reference value of active power, and ΔP is the active power adjustment amount.

[0054] Step 2-2, calculate reactive power demand based on active power adjustment:

[0055] ΔQ=ΔQ l +ΔQ conv

[0056]

[0057]

[0058] Among them, ΔQ l is the change in reactive power loss of the line during active power adjustment, ΔQ conv The sum of the two constitutes the reactive power demand of the entire system during active power adjustment. PCC , P LCC , Q LCC They are the AC voltage, reactive power and active power collected from the common coupling point, U dc0 is the ideal DC voltage value of the system, U dc is the current DC voltage value, X ac is the reactance value of the AC line, and ΔQ is the reactive power demand.

[0059] Step 3: Determine the number of steps of reactive compensation. The number of steps of reactive compensation is calculated based on the capacity of the reactive compensation device configured in the system and the reactive power demand. First, based on the currently measured voltage at the common coupling point and the impedance of the reactive compensation device, the reactive power Q of the reactive compensation device switched on and off is calculated. c , which is calculated by the following formula:

[0060]

[0061] Then, take the integer part of the quotient of the reactive power demand and the reactive capacity of a single reactive compensation device, the formula is as follows:

[0062] k=int(ΔQ / Q c )

[0063] Among them, Q c It is the reactive capacity of a single reactive compensation device.

[0064] Step 4, coordinated active power adjustment instruction calculation, specifically includes:

[0065] According to the determined reactive power compensation amount, the active power adjustment instruction is calculated according to the following relationship:

[0066] AΔP 2 +BΔP+C=0

[0067] In the above formula, by solving the quadratic equation, the adjustment amount of the active power command value Δ is obtained P , where each coefficient of the equation can be obtained and calculated through the high-voltage direct current transmission system state measurement device, as shown in the following formula:

[0068]

[0069] In the formula, Q ck Represents the reactive power provided by the kth group of reactive power compensation equipment.

[0070] Step 5: Determine the active and reactive power coordination timing.

[0071] The active and reactive power coordination timing determination refers to the timing of active power adjustment and coordinated switching of reactive compensation devices, which are as follows: the switching of reactive compensation devices is slightly ahead of the active power adjustment; the switching of reactive compensation devices is simultaneous with the active power adjustment; the switching of reactive power is slightly behind the active power adjustment.

[0072] Application examples:

[0073] See also Figure 3 It is a typical high-voltage direct current transmission system. The reactive power compensation equipment is connected to the system common connection point. The DC voltage is ±200kV, the AC bus voltage is 220kV, the resistance of the AC transmission line is 7.992Ω, the reactance is 10.202Ω, the capacitance of the reactive power compensation capacitor is 26uF, and it is switched in groups. The reactive power of the reactive power compensation equipment in a single action at the rated AC voltage is 50MVar. The active power of the system changes from 200MW to 420MW and then decreases to 150MW.

[0074] The traditional high-voltage direct current transmission reactive power compensation strategy, the non-compensation strategy and the new coordinated control strategy of the present invention are compared. In the traditional reactive power compensation strategy, during the active power adjustment process, after the AC voltage exceeds the threshold, the reactive power compensation device is activated until the AC voltage is detected to be adjusted to the set range, and the reactive power compensation device does not operate. Under the new coordinated control strategy of the present invention, the action of the reactive power compensation device is coordinated with the adjustment of the active power to maintain the stability of the system AC voltage.

[0075] Depend on Figure 3 and Figure 4It can be seen that under the traditional reactive power compensation strategy and the non-compensation strategy, the adjustment of active power is realized in one go, and in the novel coordinated control of the present invention, the adjustment of active power is realized in steps by coordinating the switching of reactive power compensation device, and in the process of active power changing from 200MW to 420MW, according to the principle capacity of 50MVar of capacitor switching each time, the adjustment of active power is changed from 200MW to 275.44MW, then adjusted to 348.28MW, and finally adjusted to 420MW. The whole process is realized in three steps, coordinating the input of three groups of reactive power compensation capacitors. The reactive power change amount of the traditional reactive power compensation strategy and the non-compensation strategy is provided by the near-zone AC system, and the switching of reactive power compensation equipment is also passive, resulting in the limitation of system reactive power, and in the novel coordinated control of the present invention, three groups of 50MVar capacitors are put into the system in three steps to coordinate the adjustment of active power.

[0076] Depend on Figure 5 It can be seen that for the common bus AC voltage, the traditional reactive compensation strategy has an AC voltage fluctuation of 8.86kV during the active power adjustment process, and the non-compensation strategy has an AC voltage fluctuation of 12.83kV during the active power adjustment process, and both cannot achieve the control target of stabilizing the common coupling bus AC voltage. The AC bus voltage fluctuation of the new coordinated control strategy of the present invention is only 0.37kV, which greatly reduces the reactive voltage fluctuation during active power adjustment. The coordinated control of active power adjustment and reactive power compensation is well achieved.

[0077] The above simulations verify that the coordinated control strategy of the present invention is superior to the traditional control strategy, can achieve flexible adjustment of active power, maintain AC system voltage stability, reduce AC voltage fluctuations, and effectively suppress reactive voltage problems.

[0078] It should be noted that the above content merely illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. A method for coordinated control of active and reactive power in a high voltage direct current transmission system, characterized in that: The steps include: Step 1, system status acquisition; Step 2: Calculate active power adjustment according to the active power instruction issued by the dispatching system, and calculate reactive power demand according to the active power adjustment; Step 3, calculating the number of reactive power compensation steps according to the capacity of the reactive power compensation device configured in the system and the reactive power demand; Step 4, calculating the active power adjustment instruction according to the determined reactive power compensation amount; Step 5: Determine the active and reactive power coordination timing.

2. The active and reactive power coordinated control method in a high voltage direct current transmission system according to claim 1, characterized in that: Also includes: Active power adjustment and reactive power control are coordinated through the coordination sequence determined in step 5, and the system state is updated before each step of active power and reactive power coordination adjustment.

3. The active and reactive coordinated control method in a high voltage direct current power transmission system according to claim 1, characterized in that: In the control of the high-voltage direct current transmission system, the control reference value of the direct current active power is also converted into a direct current reference value of the control system and input into the converter station controlled by the fixed direct current for control.

4. The active and reactive power coordinated control method in a high voltage direct current power transmission system according to claim 1, characterized in that: In the constant DC current controller structure, according to the difference between the DC current reference value and the actual value, the PI controller is adjusted to output the control instruction of the trigger angle, and the active power is adjusted by controlling the valve.

5. The active and reactive coordinated control method in a high voltage direct current power transmission system according to claim 1, characterized in that: The system state in step 1 includes: the AC voltage U collected from the common coupling point of the converter PCC , active power data P and reactive power data Q, DC voltage U collected from the DC grid point dc and DC current data I dc , the trigger angle α and commutation angle μ of the converter valve, the power factor of the system 6. The active and reactive power coordinated control method in a high voltage direct current power transmission system according to claim 1, characterized in that: The step 2 specifically includes the following sub-steps: Step 2-1, calculate the active power adjustment according to the active power instruction issued by the dispatching system: ΔP=P sref -P Among them, P sref is the reference value of active power, ΔP is the active power adjustment; Step 2-2, calculate reactive power demand based on active power adjustment: ΔQ=ΔQ l +ΔQ conv Among them, ΔQ l is the change in reactive power loss of the line during active power adjustment, ΔQ conv is the change in reactive power consumption of the DC converter valve during active power adjustment, ΔQ is the reactive power demand of the entire system during active power adjustment, and U PCC , P LCC , Q LCC They are the AC voltage, reactive power and active power collected from the common coupling point, U dc0 is the ideal DC voltage value of the system, U dc is the current DC voltage value, X ac is the reactance value of the AC line.

7. The method for coordinated control of active and reactive power in a high voltage direct current power transmission system according to claim 1, characterized in that: The number of steps of reactive power compensation in step 3 is calculated by the following formula: k=int(ΔQ / Q c ) Among them, Q c It is the reactive capacity of a single reactive compensation device.

8. The active and reactive power coordinated control method in a high voltage direct current power transmission system according to claim 1, characterized in that: In step 4, the active power adjustment instruction is calculated by the following formula: ADP 2 +BΔP+C=0 In the above formula, A, B, and C are obtained and calculated by the high-voltage direct current transmission system state measurement device, as shown in the following formula: In the formula, Q ck Represents the reactive power provided by the kth group of reactive power compensation equipment.

9. The active and reactive power coordinated control method in a high voltage direct current power transmission system according to claim 1, characterized in that: The active and reactive coordination timing in step 5 refers to the timing of active power adjustment and coordinated switching of reactive compensation devices, including: the switching of reactive compensation devices is slightly ahead of the active power adjustment; the switching of reactive compensation devices is simultaneous with the active power adjustment; the switching of reactive power is slightly behind the active power adjustment.

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