New energy reactive power control method for suppressing transient overvoltage of DC sending-end power grid

Abstract

The invention discloses a new energy reactive power control method for transient overvoltage suppression of a direct-current sending-end power grid, and the method comprises the steps: estimating the change trend of the voltage of a power grid through the current and historical signals of the voltage of the power grid, calculating the additional value of a reactive power instruction to generate a reactive power advanced control effect, and combining a reactive power optimization value subjected to delay compensation. And the instruction value can ensure that the new energy effectively outputs reactive power to participate in transient overvoltage suppression of the direct current converter station. According to the method, the new energy reactive power instruction value can be improved and optimized only on the basis of the existing electrical quantity observation signal without modifying the topological structure of a direct current converter station and a new energy power generation system and without additionally arranging various reactive compensation devices or various voltages or voltage sensors; no additional influence is generated on links such as new energy power instruction tracking control and direct current converter station power control, and the method has good engineering practicability and scene 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 of a DC sending-end power grid. Background Art

[0002] New energy resources are usually located in remote areas such as deserts, mountains, and offshore, far away from power load centers. The resulting reverse distribution characteristics of source and load make long-distance DC transmission an important way to transmit new energy power. However, for conventional DC transmission systems that have been built in large numbers before, namely, grid voltage-commutated DC transmission systems (LCC-HVDC), the semi-controlled characteristics of their thyristors lead to inevitable DC commutation failures in LCC-HVDC, which in turn causes transient overvoltages in the AC sending-end grid. This transient overvoltage phenomenon increases the risk of overvoltage disconnection of new energy power sources and may further cause chain failures. Therefore, suppressing transient overvoltages in the LCC-HVDC sending-end grid has become one of the key requirements for ensuring stable operation of new energy DC transmission systems.

[0003] At present, the measures to suppress transient overvoltage in the LCC-HVDC sending-end power grid are mainly divided into two categories. One is to add reactive compensation equipment in 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 of 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 Regulators" in Issue 2 of 2024, which clearly stated the effectiveness of additional grid-type energy storage and additional phase regulators in suppressing transient overvoltages. Another method of transient overvoltage suppression is to adjust the DC control strategy of LCC-HVDC. For example, the IEEE Transactions on Power Systems journal, Vol. 36, No. 5, 2021, proposed a HVDC constant reactive power control strategy, which can control the DC voltage and current of the DC transmission system during the fault to increase the reactive power consumption of the rectifier during the fault, thereby reducing the transient overvoltage of the sending-end power grid. However, it should be made clear that the method of suppressing transient overvoltages through additional reactive power regulation equipment in the sending-end power grid will introduce additional construction and maintenance costs, and the reactive power equipment has a low utilization rate for a long time, and the overall economic efficiency is poor. Adjusting the LCC-HVDC DC control will affect the dynamic performance of the DC control system while reducing transient overvoltages, such as fault ride-through capability and DC current recovery capability. 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 a DC sending-end power grid. The current and historical signals of the power grid voltage are used to estimate the trend of the grid voltage change, thereby producing the effect of reactive advance control. At the same time, the power command signal is delayed and compensated to offset the reactive lag generated by the power command calculation and transmission processes, thereby ensuring that the advanced reactive power can be applied to 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, thereby flexibly exerting the power regulation capability of new energy power sources. 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; according to the voltage of the new energy source terminal at each sampling moment, the equivalent grid voltage amplitude V at different moments is calculated 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 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 differential 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 difference component of the equivalent grid voltage amplitude at the current moment is V t 3 , the voltage amplitude three-order difference components 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 command compensation component ΔQ of the new energy unit at the current time t t * , the reactive power command 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 command;

[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 command Q of the new energy unit t * , the power command is sent to the new energy converter, and the new energy converter completes the power command 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 times in step S2 is obtained by the following formula (2):

[0015]

[0016] Furthermore, the second-order difference component of the voltage amplitude at different times 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 is the reactive power compensation coefficient, which can be designed to be 1.5 according to the grid connection guidelines, or 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 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 command optimization value at the initial moment and the first moment of the algorithm, Q1 and Q0 are the reactive power command 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 t * The reactive power command optimizes the value Q p_t * and reactive power command compensation component ΔQ t * Add them together and 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 with the existing transient overvoltage suppression method of the DC sending-end power grid. The existing transient overvoltage suppression method of the sending-end power grid either requires the introduction of additional reactive equipment to increase construction and operation costs, or requires sacrificing DC dynamic control performance, while the overvoltage suppression method developed in the present invention does not need to rely on additional equipment, will not have a negative impact on 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 need to adjust the original system structure, control method and parameters of the converter of the new energy conversion control system, nor does it need to obtain 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 the present invention has no special requirements on the type, control mode, and signal acquisition method of the new energy generator set, including voltage signal acquisition, power tracking control mode, reactive power command issuance method, etc. There are no specific restrictions. This algorithm is applicable to a wide range of power sources or energy storage based on power electronic devices such as photovoltaic, wind power, and energy storage with different control modes, and has adaptability to engineering scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the operation 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 reactive power control method of new energy of the present invention;

[0033] Figure 4 It is the transient voltage waveform of 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 be combined with the accompanying drawings to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments 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 the 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-end grid is 5000MW, of which 2500MW is new energy power. The DC rated voltage is ±800kV, the AC rated voltage is 525kV, and the DC transmission adopts the LCC-HVDC structure. Figure 1 In the figure, ① is a synchronous power supply with a rated voltage of 530kV; ② is a new energy power supply, which is obtained by aggregating the power of multiple wind turbines using a wind farm as an example in this example; ③ is a passive AC filter, which is used to meet the reactive power consumption of the sending-end converter during normal operation, with a capacity of 1500MVar, U ac ④ is the sending-end converter AC bus; ⑤ 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 power grid.

[0035] Figure 2 The logical relationship between the algorithm of the present invention and the original control system of new energy is demonstrated. The algorithm proposed in the present invention uses the voltage detection signal of the new energy unit to obtain the grid voltage, corrects the original reactive power instruction of the new energy unit according to the grid voltage, and calculates the optimized reactive power instruction. The specific reactive power instruction tracking process is completed by the inverter control of the unit.

[0036] Figure 3 The specific implementation methods of the algorithm of the present invention are given, wherein 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 new energy accounts for 50% of the sending end power grid and the short-circuit ratio of the power grid 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, in which 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, in which the transient overvoltage amplitude is 1.268pu, which shows that the algorithm proposed in the present invention is effective and feasible when applied 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; according to the voltage of the new energy source terminal at each sampling moment, the equivalent grid voltage amplitude V at different moments is calculated 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 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 differential 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 difference component of the equivalent grid voltage amplitude at the current moment is V t 3 , the voltage amplitude three-order difference components 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 command compensation component ΔQ of the new energy unit at the current time t t * , the reactive power command 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 command;

[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 command Q of the new energy unit t * , the power command is sent to the new energy converter, and the new energy converter completes the power command 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 times in step S2 is obtained by the following formula (2):

[0049]

[0050] Furthermore, the second-order difference component of the voltage amplitude at different times 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 is the reactive power compensation coefficient, which can be designed to be 1.5 according to the grid connection guidelines, or 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 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 command optimization value at the initial moment and the first moment of the algorithm, Q1 and Q0 are the reactive power command 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 t * The reactive power command optimizes the value Q p_t * and reactive power command compensation component ΔQ t * Add them together and 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 creative work. Therefore, the present invention is not limited to the above embodiments. The technical personnel in this field adopt the algorithm ideas that are suppressed by the ideas of the present invention. Only the irrelevant core improvements and modifications made to the present invention should be within the protection scope of the present invention, including but not limited to the following situations, such as the signal detection in S1 adopts other methods other than the voltage amplitude or phase-locked loop detection described in this example, the signal filtering link in S1 is replaced by other methods from the average value filtering, and different signal delay compensation algorithms are adopted in S6, etc.

Claims

1. A new energy reactive power control method for transient overvoltage suppression of a DC power grid at the 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; according to the voltage of the new energy source terminal at each sampling moment, the equivalent grid voltage amplitude V at different moments is calculated 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 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 differential 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 difference component of the equivalent grid voltage amplitude at the current moment is V t 3 , the voltage amplitude three-order difference components 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 command compensation component ΔQ of the new energy unit at the current time t t * , the reactive power command 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 command; 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 command Q of the new energy unit t * , the power command is sent to the new energy converter, and the new energy converter completes the power command tracking.

2. The new energy reactive power control method for transient overvoltage suppression of a DC power grid at the sending end according to claim 1 is 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 new energy reactive power control method for transient overvoltage suppression of a DC sending-end power grid according to claim 1 is 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 new energy reactive power control method for transient overvoltage suppression of a DC power grid at the sending end according to claim 1 is characterized by: The second-order difference of the voltage amplitude at different times in step S3 is obtained by the following formula (3):

5. The new energy reactive power control method for transient overvoltage suppression of a DC sending-end power grid according to claim 1 is 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 new energy reactive power control method for transient overvoltage suppression of a DC sending-end power grid according to claim 1 is characterized by: The reactive power compensation amount at different times in step S5 is obtained by the following formula (5), where k v is the reactive power compensation coefficient, which can be designed to be 1.5 according to the grid connection guidelines, or can be increased according to the actual reactive power output capacity of the new energy unit; 7. The new energy reactive power control method for transient overvoltage suppression of a DC power grid at the sending end according to claim 1 is characterized by: 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 command optimization value at the initial moment and the first moment of the algorithm, Q1 and Q0 are the reactive power command values ​​at the initial moment and the first moment of the algorithm; 8. The new energy reactive power control method for transient overvoltage suppression of a DC sending-end power grid according to claim 1 is characterized by: The reactive power command Q of the new energy generator set at different times t in step S7 t * The reactive power command optimizes the value Q p_t * and reactive power command compensation component ΔQ t * Add them together and the specific process is completed by the following formula (7); Q t * =Q p_t * +ΔQ t * 。 (7)。

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