A new energy reactive power control method for transient overvoltage suppression in DC power grid

Abstract

The present invention discloses a new energy reactive power control method for transient overvoltage suppression of a DC sending-end power grid. The method uses current and historical signals of the power grid voltage to estimate the trend of the power grid voltage change, calculates the reactive power instruction additional value to produce the effect of reactive advance control, and combines the reactive power optimization value after delay compensation. The two are superimposed to produce the final instruction value of the new energy power supply. The instruction value can ensure that the new energy effectively outputs reactive power to participate in the transient overvoltage suppression of the DC converter station. The present invention does not require topological structure modification of the DC converter station and the new energy power generation system, nor does it require the addition of various types of reactive compensation equipment or various types of voltage or voltage sensors. It only needs to be based on the existing electrical quantity observation signal to improve and optimize the new energy reactive power instruction value, and will not have additional impacts on the new energy power instruction tracking control, DC converter station power control and other links. It has good engineering practicality and scenario adaptability.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy operation control, and in particular relates to a renewable energy reactive power control method for suppressing transient overvoltage in a DC sending-end power grid. Background Art

[0002] Renewable energy resources are often located in remote areas such as deserts, high mountains, and offshore, far from power load centers. The resulting reverse source-load distribution makes long-distance direct current (DC) transmission an important method for transmitting renewable energy power. However, for conventional DC transmission systems that have been built in large quantities, namely, grid voltage-commutated DC transmission systems (LCC-HVDC), the semi-controlled nature of their thyristors leads to inevitable DC commutation failures in LCC-HVDC, which in turn causes transient overvoltages in the AC sending-end grid. This transient overvoltage increases the risk of overvoltage disconnection of renewable energy power sources and may further trigger cascading failures. Therefore, suppressing transient overvoltages in the LCC-HVDC sending-end grid has become a key requirement for ensuring the stable operation of renewable energy DC transmission systems.

[0003] Currently, the measures to suppress transient overvoltages in the LCC-HVDC sending-end power grid are mainly divided into two categories. One is to add reactive compensation equipment to the sending-end power grid. For example, the IEEE Transactions on Power Systems journal published the paper "A Flexible Control Strategy to Prevent Sending-end Power System From Transient Instability Under Hvdc Repetitive Commutation Failures" in Volume 35, Issue 6 in 2020, which proposed a design and control method for energy storage links for transient overvoltages, and suppressed transient overvoltages through active voltage control of the energy storage link; Zhejiang Electric Power Journal published the paper "Comparative Study on Transient Overvoltage Suppression Capability of Grid-Type Energy Storage and Phase-Regulating Phases" in Issue 2 in 2024, which clearly stated the effectiveness of additional grid-type energy storage and additional phase-regulating phases in suppressing transient overvoltages. Another method for suppressing transient overvoltages is to adjust the DC control strategy of LCC-HVDC. For example, the IEEE Transactions on Power Systems journal, Vol. 36, No. 5, 2021, entitled "Reactive Power Control Strategy for Inhibiting Transient Overvoltage Causedby Commutation Failure," proposed an HVDC constant reactive power control strategy that controls the DC voltage and current of the DC transmission system during a fault, thereby increasing the reactive power consumption of the rectifier during the fault and reducing transient overvoltages in the sending-end grid. However, it should be made clear that suppressing transient overvoltages through additional reactive power regulation equipment in the sending-end grid will introduce additional construction and maintenance costs, and the reactive power equipment will have low long-term utilization, resulting in poor overall economic efficiency. Adjusting the LCC-HVDC DC control will affect the dynamic performance of the DC control system, such as fault ride-through capability and DC current recovery capability, while reducing transient overvoltages. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art. The present invention proposes a new energy reactive power control method for transient overvoltage suppression of the DC sending-end power grid. The method estimates the grid voltage change trend through the current and historical grid voltage signals, produces the effect of reactive power advance control, and at the same time, performs delay compensation on the power command signal to offset the reactive power lag generated by the power command calculation, transmission and other processes, ensuring that the advanced reactive power can be used for overvoltage suppression. While achieving transient overvoltage suppression, the algorithm does not require the introduction of additional equipment and will not have additional impact on the DC control system, which is a flexible use of the power regulation capability of the new energy power supply. The specific implementation steps are as follows:

[0005] Step S1: Use the voltage detection link or phase-locked loop output of the new energy power supply to obtain the real-time effective value U of the voltage at the terminal of the new energy power supply, perform fixed-step sampling on U according to the sampling period of ΔT, and obtain the real-time effective value of the voltage at the terminal of the new energy power supply at the current time t as U t ; The real-time effective values ​​of the voltage at the new energy power source terminal at the previous sampling time are recorded as U t-1 , U t-2 ,…,U t-n , and so on; the equivalent grid voltage amplitude V at different times is calculated based on the terminal voltage of the new energy power source at each sampling moment t , V t-1 ,…,V t-n ;

[0006] Step S2: Using the equivalent grid voltage amplitude V at different times t , V t-1 ,…,V t-n , calculate the first-order difference component V of the grid voltage amplitude at different times 1 , the first-order difference component of the equivalent grid voltage amplitude at the current moment is V t 1 , the first-order difference of the voltage amplitude at the previous moment is recorded as V t-1 1 , V t-2 1 ,…,V t-n 1 , and so on;

[0007] Step S3: Using the first-order difference of the voltage amplitude at different times, calculate the second-order difference of the grid voltage amplitude at different times V 2 , the second-order difference component of the equivalent grid voltage amplitude at the current moment is V t 2 , the second-order difference of the voltage amplitude at the previous moment is recorded as V t-1 2 , V t-2 2 ,…,V t-n 2 , and so on;

[0008] Step S4: Using the second-order difference of the voltage amplitude at different times, calculate the third-order difference of the grid voltage amplitude at different times V 3 , the third-order differential component of the equivalent grid voltage amplitude at the current moment is V t 3 , the third-order difference components of the voltage amplitude at the previous moment are recorded as V t-1 3 , V t-2 3,…,V t-n 3 , and so on;

[0009] Step S5: Using the first-order, second-order and third-order differential components of the voltage amplitude at the current time t, that is, V t 1 , V t 2 , V t 3 , calculate the reactive power instruction compensation component ΔQ of the new energy unit at the current time t t * , the reactive power instruction compensation components at the previous moment are recorded as ΔQ t-1 * , ΔQ t-2 * ,…,ΔQ t-n * , and so on;

[0010] Step S6: Using the basic reactive power command value (Q t ,Q t-1, …,Q t-n ), calculate the optimal value Q of reactive power command at different times p_t * , realize the delay compensation of reactive power instruction;

[0011] Step S7: Optimize the reactive power command value Q p_t * and reactive power command compensation component ΔQ t * Add together to get the reactive power instruction Q of the new energy unit t * ,The power instruction is sent to the new energy converter, and the new energy converter completes the power instruction tracking.

[0012] Furthermore, the equivalent grid voltage amplitude at different times in step S1 is obtained by the following formula (1), which plays a smoothing filtering role;

[0013]

[0014] Furthermore, the first-order difference component of the voltage amplitude at different moments in step S2 is obtained by the following formula (2):

[0015]

[0016] Furthermore, the second-order difference component of the voltage amplitude at different moments in step S3 is obtained by the following formula (3):

[0017]

[0018] Furthermore, the third-order difference component of the voltage amplitude at different times in step S4 is obtained by the following formula (4):

[0019]

[0020] Furthermore, the reactive power compensation amount at different times in step S5 is obtained by the following formula (5), where k v The reactive power compensation coefficient can be designed to be 1.5 according to the grid connection guidelines, or it can be increased according to the actual reactive power output capacity of the new energy unit;

[0021]

[0022] Furthermore, the reactive power command optimization value Q at different times t in step S6 is p_t * , is the basic reactive power command value Q at different times t It is calculated by the lead delay compensation, the specific formula is (6), where Q p_1 * and Q p_0 * is the basic reactive power instruction optimization value at the initial moment and the first moment of the algorithm, Q1 and Q0 are the reactive power instruction values ​​at the initial moment and the first moment of the algorithm;

[0023]

[0024] Furthermore, the reactive power command Q of the new energy generator set at different times t in step S7 is t * The optimized value Q is obtained by the reactive power instruction p_t * and reactive power command compensation component ΔQ t * The specific process is completed by the following formula (7);

[0025] Q t * =Q p_t * +ΔQ t * (7)

[0026] Compared with the prior art, the present invention adopts the above technical solution and has the following beneficial effects:

[0027] (1) The transient overvoltage suppression method proposed in the present invention has the advantages of high economy and low control cost compared to existing methods for suppressing transient overvoltages in DC power transmission lines. Existing methods for suppressing transient overvoltages in DC power transmission lines either require the introduction of additional reactive equipment, which increases construction and operating costs, or sacrifices DC dynamic control performance. However, the overvoltage suppression method developed in the present invention does not require additional equipment, does not negatively impact the DC control system, and has the advantage of low control cost.

[0028] (2) The control method proposed in the present invention only optimizes the power command. It does not require adjustment of the original system structure, control mode and parameters of the converter of the new energy conversion control system, nor does it require acquisition of the parameters of the new energy unit. It can be directly applied to the existing operating units without changing the original power tracking control logic of the new energy, and has good engineering practicality.

[0029] (3) The control method proposed in this invention has no special requirements for the type, control mode, or signal acquisition method of the renewable energy generator set, including no specific restrictions on voltage signal acquisition, power tracking control mode, or reactive power command issuance method. This algorithm is applicable to a wide range of power electronic device-based power or energy storage devices, such as photovoltaic, wind power, and energy storage, with different control modes, and is adaptable to engineering scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the operating topology diagram of the new energy power source through LCC-HVDC direct current transmission;

[0031] Figure 2 The logical relationship between the algorithm of the present invention and the original control system of new energy;

[0032] Figure 3 The reactive power instruction generation algorithm flow of the new energy reactive power control method of the present invention;

[0033] Figure 4 This is the transient voltage waveform at the new energy machine end when the new energy power generation capacity is 2500MW, including the comparison with and without adding the algorithm of the present invention. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in this field without creative work are within the scope of protection of the present invention. A new energy reactive power control method for transient overvoltage suppression of a DC power grid at the sending end, such as Figure 1The total power capacity of the sending grid is 5000MW, of which 2500MW is from renewable energy sources. The DC rated voltage is ±800kV, the AC rated voltage is 525kV, and the DC transmission adopts an LCC-HVDC structure. Figure 1 In the figure, ① is a synchronous power source with a rated voltage of 530kV; ② is a new energy power source. In this example, a wind power station is used as an example, which is obtained by aggregating the power of multiple wind turbines; ③ is a passive AC filter used to meet the reactive power consumption of the sending-end converter during normal operation, with a capacity of 1500MVar, U ac is the AC busbar of the sending-end converter; ④ is the LCC-HVDC sending-end converter, which together with ⑤ the DC transmission line and ⑥ the receiving-end converter constitute the LCC-HVDC transmission system; ⑦ is the receiving-end AC grid.

[0035] Figure 2 The proposed algorithm demonstrates the logical relationship between the proposed algorithm and the original renewable energy control system. The proposed algorithm uses the voltage detection signal from the renewable energy generator to obtain the grid voltage. Based on the grid voltage, it modifies the generator's original reactive power command to calculate an optimized reactive power command. The specific reactive power command tracking process is accomplished by the generator's built-in converter control.

[0036] Figure 3 The specific implementation methods of the algorithm of the present invention are given, among which ① is the smoothing filtering process of the voltage detection signal, ② is the calculation process of the first-order difference component of the voltage amplitude, ③ is the calculation process of the second-order difference component of the voltage amplitude, ④ is the calculation process of the third-order difference component of the voltage amplitude, ⑤ is the calculation process of the reactive power instruction compensation component, ⑥ is the calculation of the reactive power instruction optimization value, and ⑦ is the calculation of the reactive power instruction of the new energy unit.

[0037] Figure 4 This is the transient voltage waveform at the new energy machine end when the new energy power generation capacity is 2500MW, that is, the proportion of new energy in the sending end power grid is 50% and the power grid short circuit ratio is 2.5. Figure 4 In the figure, the solid line is the transient voltage curve of the new energy machine end without adding the transient overvoltage suppression algorithm, where the transient overvoltage amplitude is 1.309pu; the dotted line is the transient voltage curve of the new energy machine end with adding the algorithm of the present invention, where the transient overvoltage amplitude is 1.268pu, which shows that the algorithm proposed in the present invention is effective and feasible in applying to transient overvoltage suppression.

[0038] The specific implementation includes the following steps:

[0039] Step S1: Use the voltage detection link or phase-locked loop output of the new energy power supply to obtain the real-time effective value U of the voltage at the terminal of the new energy power supply, perform fixed-step sampling on U according to the sampling period of ΔT, and obtain the real-time effective value of the voltage at the terminal of the new energy power supply at the current time t as Ut ; The real-time effective values ​​of the voltage at the new energy power source terminal at the previous sampling time are recorded as U t-1 , U t-2 ,…,U t-n , and so on; the equivalent grid voltage amplitude V at different times is calculated based on the terminal voltage of the new energy power source at each sampling moment t , V t-1 ,…,V t-n ;

[0040] Step S2: Using the equivalent grid voltage amplitude V at different times t , V t-1 ,…,V t-n , calculate the first-order difference component V of the grid voltage amplitude at different times 1 , the first-order difference component of the equivalent grid voltage amplitude at the current moment is V t 1 , the first-order difference of the voltage amplitude at the previous moment is recorded as V t-1 1 , V t-2 1 ,…,V t-n 1 , and so on;

[0041] Step S3: Using the first-order difference of the voltage amplitude at different times, calculate the second-order difference of the grid voltage amplitude at different times V 2 , the second-order difference component of the equivalent grid voltage amplitude at the current moment is V t 2 , the second-order difference of the voltage amplitude at the previous moment is recorded as V t-1 2 , V t-2 2 ,…,V t-n 2 , and so on;

[0042] Step S4: Using the second-order difference of the voltage amplitude at different times, calculate the third-order difference of the grid voltage amplitude at different times V 3 , the third-order differential component of the equivalent grid voltage amplitude at the current moment is V t 3 , the third-order difference components of the voltage amplitude at the previous moment are recorded as V t-1 3 , V t-2 3 ,…,V t-n 3 , and so on;

[0043] Step S5: Using the first-order, second-order and third-order differential components of the voltage amplitude at the current time t, that is, V t1 , V t 2 , V t 3 , calculate the reactive power instruction compensation component ΔQ of the new energy unit at the current time t t * , the reactive power instruction compensation components at the previous moment are recorded as ΔQ t-1 * , ΔQ t-2 * ,…,ΔQ t-n * , and so on;

[0044] Step S6: Using the basic reactive power command value (Q t , Q t-1 ,…,Q t-n ), calculate the optimal value Q of reactive power command at different times p_t * , realize the delay compensation of reactive power instruction;

[0045] Step S7: Optimize the reactive power command value Q p_t * and reactive power command compensation component ΔQ t * Add together to get the reactive power instruction Q of the new energy unit t * ,The power instruction is sent to the new energy converter, and the new energy converter completes the power instruction tracking.

[0046] Furthermore, the equivalent grid voltage amplitude at different times in step S1 is obtained by the following formula (1), which plays a smoothing filtering role;

[0047]

[0048] Furthermore, the first-order difference component of the voltage amplitude at different moments in step S2 is obtained by the following formula (2):

[0049]

[0050] Furthermore, the second-order difference component of the voltage amplitude at different moments in step S3 is obtained by the following formula (3):

[0051]

[0052] Furthermore, the third-order difference component of the voltage amplitude at different times in step S4 is obtained by the following formula (4):

[0053]

[0054] Furthermore, the reactive power compensation amount at different times in step S5 is obtained by the following formula (5), where k v The reactive power compensation coefficient can be designed to be 1.5 according to the grid connection guidelines, or it can be increased according to the actual reactive power output capacity of the new energy unit;

[0055]

[0056] Furthermore, the reactive power command optimization value Q at different times t in step S6 is p_t * , is the basic reactive power command value Q at different times t It is calculated by the lead delay compensation, the specific formula is (6), where Q p_1 * and Q p_0 * is the basic reactive power instruction optimization value at the initial moment and the first moment of the algorithm, Q1 and Q0 are the reactive power instruction values ​​at the initial moment and the first moment of the algorithm;

[0057]

[0058] Furthermore, the reactive power command Q of the new energy generator set at different times t in step S7 is t * The optimized value Q is obtained by the reactive power instruction p_t * and reactive power command compensation component ΔQ t * The specific process is completed by the following formula (7);

[0059] Q t * =Q p_t * +ΔQ t * (7)

[0060] The above description of the embodiments is to facilitate the staff in the relevant technical field to quickly understand and apply the present invention. The staff who have mastered the basic knowledge of this technical field can obviously easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without having to go through creative work. Therefore, the present invention is not limited to the above embodiments. Those skilled in the art use algorithm ideas that are inconsistent with the ideas of the present invention. Only irrelevant core improvements and modifications made to the present invention should be within the scope of protection of the present invention, including but not limited to the following situations, such as the signal detection in S1 adopts other methods besides the voltage amplitude or phase-locked loop detection described in this example, the signal filtering link in S1 is replaced by other methods instead of average value filtering, and different signal delay compensation algorithms are used in S6, etc.

Claims

1. A new energy reactive power control method for suppressing transient overvoltage in a DC power grid at a sending end, comprising the following steps: Step S1: Use the voltage detection link or phase-locked loop output of the new energy power supply to obtain the real-time effective value U of the voltage at the terminal of the new energy power supply, perform fixed-step sampling on U according to the sampling period of ΔT, and obtain the real-time effective value of the voltage at the terminal of the new energy power supply at the current time t as U t ; The real-time effective values ​​of the voltage at the new energy power source terminal at the previous sampling time are recorded as U t-1 , U t-2 ,…,U t-n , and so on; the equivalent grid voltage amplitude V at different times is calculated based on the terminal voltage of the new energy power source at each sampling moment t , V t-1 ,…,V t-n ; Step S2: Using the equivalent grid voltage amplitude V at different times t , V t-1 ,…,V t-n , calculate the first-order difference component V of the grid voltage amplitude at different times 1 , the first-order difference component of the equivalent grid voltage amplitude at the current moment is V t 1 , the first-order difference of the voltage amplitude at the previous moment is recorded as V t-1 1 , V t-2 1 ,…,V t-n 1 , and so on; Step S3: Using the first-order difference of the voltage amplitude at different times, calculate the second-order difference of the grid voltage amplitude at different times V 2 , the second-order difference component of the equivalent grid voltage amplitude at the current moment is V t 2 , the second-order difference of the voltage amplitude at the previous moment is recorded as V t-1 2 , V t-2 2 ,…,V t-n 2 , and so on; Step S4: Using the second-order difference of the voltage amplitude at different times, calculate the third-order difference of the grid voltage amplitude at different times V 3 , the third-order differential component of the equivalent grid voltage amplitude at the current moment is V t 3 , the third-order difference components of the voltage amplitude at the previous moment are recorded as V t-1 3 , V t-2 3 ,…,V t-n 3 , and so on; Step S5: Using the first-order, second-order and third-order differential components of the voltage amplitude at the current time t, that is, V t 1 , V t 2 , V t 3 , calculate the reactive power instruction compensation component ΔQ of the new energy unit at the current time t t * , the reactive power instruction compensation components at the previous moment are recorded as ΔQ t-1 * , ΔQ t-2 * ,…,ΔQ t-n * , and so on; Step S6: Using the basic reactive power command value (Q t , Q t-1 ,…,Q t-n ), calculate the optimal value Q of reactive power command at different times p_t * , realize the delay compensation of reactive power instruction; Step S7: Optimize the reactive power command value Q p_t * and reactive power command compensation component ΔQ t * Add together to get the reactive power instruction Q of the new energy unit t * ,The power instruction is sent to the new energy converter, and the new energy converter completes the power instruction tracking.

2. The method for controlling reactive power of a new energy source for suppressing transient overvoltage in a DC power grid at a sending end according to claim 1, characterized in that: The equivalent grid voltage amplitude at different times in step S1 is obtained by the following formula (1), which plays a smoothing filtering role; 3. The method for controlling reactive power of a new energy source for suppressing transient overvoltage in a DC power grid at a sending end according to claim 1, characterized in that: The first-order difference of the voltage amplitude at different times in step S2 is obtained by the following formula (2):

4. The method for controlling reactive power of a new energy source for suppressing transient overvoltage in a DC power grid at a sending end according to claim 1, characterized in that: The second-order difference component of the voltage amplitude at different times in step S3 is obtained by the following formula (3); 5. The method for controlling reactive power of a new energy source for suppressing transient overvoltage in a DC power grid at a sending end according to claim 1, characterized in that: The third-order difference of the voltage amplitude at different times in step S4 is obtained by the following formula (4):

6. The method for controlling reactive power of a new energy source for suppressing transient overvoltage in a DC power grid at a sending end according to claim 1, characterized in that: The reactive power compensation amount at different times in step S5 is obtained by the following formula (5), where k v The reactive power compensation coefficient can be designed to be 1.5 according to the grid connection guidelines, or it can be increased according to the actual reactive power output capacity of the new energy unit; 7. The method for controlling reactive power of a new energy source for suppressing transient overvoltage in a DC power grid at a sending end according to claim 1, characterized in that: The reactive power command optimization value Q at different times t in step S6 p_t * , is the basic reactive power command value Q at different times t It is calculated by the lead delay compensation, the specific formula is (6), where Q p_1 * and Q p_0 * is the basic reactive power instruction optimization value at the initial moment and the first moment of the algorithm, Q1 and Q0 are the reactive power instruction values ​​at the initial moment and the first moment of the algorithm; 8. The method for controlling reactive power of a new energy source for suppressing transient overvoltage in a DC power grid at a sending end according to claim 1, characterized in that: The reactive power command Q of the new energy generator at different times t in step S7 t * The optimized value Q is obtained by the reactive power instruction p_t * and reactive power command compensation component ΔQ t * The specific process is completed by the following formula (7); Q t * =Q p_t * +ΔQ t * 。 (7)

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