A control method for reducing commutation failure caused by AC system faults on the rectifier side

Abstract

The present invention discloses a control method for reducing commutation failure caused by AC system fault on the rectifier side, specifically: a high voltage DC transmission system control and protection device collects DC transmission power P in real time d (t), reactive power Q provided by the AC filter f (t), reactive power Q consumed by the converter dc (t), the control output signal k of the HVDC reactive power control module RPC; calculating the reactive exchange amount of the rectifier side AC system at the current time t; starting the control module using the reactive exchange amount information of the rectifier side AC system; calculating the reference value I of the rectifier side DC current command value d_ref (t); The calculated DC current command value reference value I d_ref (t) is input into the constant current control link on the rectifier side to control the DC current of the high-voltage DC transmission. The present invention can effectively reduce commutation failures caused by faults in the AC system on the rectifier side, ensuring the safe and stable operation of the large power grid.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-voltage direct current (HVDC) transmission, and in particular relates to a control method for reducing commutation failure caused by faults in an AC system on a rectifier side. Background Art

[0002] High-voltage direct current (HVDC) transmission technology, due to its advantages such as large transmission capacity, long transmission distances, low line losses, and the absence of synchronization issues, has been widely used for long-distance power transmission in my country. It has effectively addressed the country's uneven energy distribution and promoted the implementation of my country's West-to-East Power Transmission strategy. In recent years, my country's HVDC technology has developed rapidly, but the converters at both ends of the HVDC system utilize thyristors without self-shutoff capability, making the inverters prone to commutation failure during commutation. According to existing statistics, commutation failure is one of the most common faults in DC transmission. Commutation failures can cause a surge in DC current, a sudden drop in DC voltage, and even cause the DC system to shut down, severely impacting the safe and stable operation of the system.

[0003] Current research has found that fault information in the rectifier-side AC system can be transmitted through the DC system to the inverter side, affecting the response of the receiving AC system and even causing commutation failure at the receiving end. However, conventional commutation failure suppression measures rely on the AC bus voltage amplitude at the receiving end as a criterion. However, during the rectifier-side AC system failure and recovery process, the AC bus voltage amplitude at the receiving end does not change significantly. In other words, conventional commutation failure suppression measures fail when the rectifier-side AC system fails. Currently, there are no measures to suppress commutation failure caused by rectifier-side AC system faults, which seriously threatens the safe and stable operation of the DC system. Therefore, it is urgent to propose measures to suppress commutation failure caused by rectifier-side AC system faults. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention provides a control method for reducing commutation failure caused by faults in the rectifier-side AC system.

[0005] A control method for reducing commutation failure caused by a rectifier-side AC system fault according to the present invention comprises the following steps:

[0006] Step A: Data collection:

[0007] The HVDC system control and protection device collects the DC transmission power P of the rectifier station in real time at a sampling frequency of 10kHz. d (t), reactive power Q provided by the AC filter f (t), reactive power Q consumed by the rectifier side converter dc (t), the control output signal k of the HVDC reactive power control module RPC, where t is the sampling time.

[0008] Step B: Obtain the reactive exchange amount of the AC system on the rectifier side:

[0009] The control and protection device calculates the reactive exchange amount ΔQ of the rectifier side AC system at the current time t ac (t), ΔQ ac (t)=|Q f (t)-Q dc (t)|.

[0010] Step C: Fault detection:

[0011] Step C1: Compare the reactive exchange amount ΔQ of the rectifier side AC system at the current time t and the previous 39 sampling times ac (t), ΔQ ac (t-1), ΔQ ac (t-2), ..., ΔQ ac (t-37), ΔQ ac (t-38), ΔQ ac (t-39) Construct the reactive exchange quantity sequence ΔQ(t) of the rectifier side AC system at the current time t, and calculate the average value Q of ΔQ(t) mean .

[0012] Step C2: Determine Q mean Greater than the threshold ΔQ set Is it true? If so, go to step C3; if not, return to step C1.

[0013] Step C3: Determine whether the output signal of the reactive power control module RPC at the current time t is 0. If so, proceed to step D; if not, return to step C1.

[0014] Step D: Calculation of DC current command value:

[0015] Obtain the reference value Q of reactive power consumption of the rectifier side converter at the current time t d_ref (t):Q d_ref (t) = Q f (t)-ΔQ set ;

[0016] Then calculate the DC current command value I d_ref (t): Among them U d0r It is the ideal no-load DC voltage of the rectifier station.

[0017] Step E: The DC current command value I calculated in step D is d_ref (t) is input to the constant current control link on the rectifier side to control the DC current of the high-voltage DC transmission, and the DC current command value I d_ref (t) The duration of the input is a milliseconds.

[0018] Furthermore, in step C2, ΔQset The value is 50Mvar.

[0019] Furthermore, in step E, a takes a value of 12.

[0020] The beneficial technical effects of the present invention are:

[0021] 1. The present invention considers utilizing the reactive power consumption characteristics of the converter itself to reduce commutation failure. Compared with other methods, the present invention is more operable.

[0022] 2. The present invention sets a reactive power regulation module on the rectifier side, which can more quickly suppress the impact of the rectifier side AC system fault on the DC system. Compared with other methods, the action is faster.

[0023] 3. This invention does not require changes to the hardware structure of the DC power transmission system. Instead, it implements control functions by performing simple operations such as multiplication, division, addition, subtraction, and comparison based on the system's existing measured information. This requires minimal hardware and software, offers rapid response, and is suitable for practical engineering applications. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific implementation methods and simulation experiments.

[0025] A control method for reducing commutation failure caused by a rectifier-side AC system fault according to the present invention comprises the following steps:

[0026] Step A: Data collection:

[0027] The control and protection device of the HVDC transmission system collects the DC transmission power P of the rectifier station in real time at a sampling frequency of 10kHz. d (t), reactive power Q provided by the AC filter f (t), reactive power Q consumed by the rectifier side converter dc (t), the control output signal k of the HVDC reactive power control module RPC, where t is the sampling time.

[0028] Step B: Obtain the reactive exchange amount of the AC system on the rectifier side:

[0029] The control and protection device calculates the reactive exchange amount ΔQ of the rectifier side AC system at the current time t ac (t), ΔQ ac (t)=|Q f (t)-Q dc (t)|.

[0030] Step C: Fault detection:

[0031] Step C1: Compare the reactive exchange amount ΔQ of the rectifier side AC system at the current time t and the previous 39 sampling times ac (t), ΔQac (t-1), ΔQ ac (t-2), ..., ΔQ ac (t-37), ΔQ ac (t-38), ΔQ ac (t-39) Construct the reactive exchange quantity sequence ΔQ(t) of the rectifier side AC system at the current time t, and calculate the average value Q of ΔQ(t) mean .

[0032] Step C2: Determine Q mean Greater than the threshold ΔQ set (ΔQ set If yes, go to step C3; if not, return to step C1.

[0033] Step C3: Determine whether the output signal of the reactive power control module RPC at the current time t is 0. If so, proceed to step D; if not, return to step C1.

[0034] Step D: Calculation of DC current command value:

[0035] Obtain the reference value Q of reactive power consumption of the rectifier side converter at the current time t d_ref (t):Q d_ref (t) = Q f (t)-ΔQ set ;

[0036] Then calculate the DC current command value I d_ref (t): Among them U d0r It is the ideal no-load DC voltage of the rectifier station.

[0037] Step E: The DC current command value I calculated in step D is d_ref (t) is input to the constant current control link on the rectifier side to control the DC current of the high-voltage DC transmission, and the DC current command value I d_ref (t) The duration of the input is a milliseconds (a is 12).

[0038] The principle and basis of the present invention for reducing commutation failure caused by rectifier-side AC system faults are as follows:

[0039] The factors influencing commutation failure caused by AC system faults on the rectifier side of a DC transmission system indicate that reactive imbalance in the rectifier-side AC system affects the probability of commutation failure, and excessive reactive compensation exacerbates the risk of commutation failure. Switching AC filters during this process cannot continuously and rapidly adjust reactive power, while adding static VAR compensators (SVCs) has drawbacks such as poor practicality and high investment. Therefore, improving the reactive power consumption of the rectifier-side converter is considered to further suppress commutation failure. Therefore, the present invention constructs a reactive power regulation module based on the reactive power consumption characteristics of the rectifier, which can reduce the risk of commutation failure during rectifier-side faults and recovery.

[0040] When a fault in the rectifier-side AC system is detected and the reactive exchange of the rectifier-side AC system exceeds the rated value, and the reactive power regulation module RPC on the rectifier side is locked, the reactive power regulation module is started. This module calculates the DC current reference value based on the reactive exchange reference value set by the system and inputs it into the constant current control module on the rectifier side, so that the fault in the rectifier-side AC system is recovered smoothly and the risk of commutation failure is reduced.

[0041] Simulation experiment:

[0042] To verify the adaptability of the reactive power regulation module under different fault conditions, the fault inductance of the rectifier-side AC system is set to 0-0.8H. The rectifier-side AC system is in the original RPC control mode and the reactive power regulation module control mode, respectively. The number of commutation failures on the inverter side under these two modes is shown in Table 1.

[0043] Table 1 Impact of RPC and this control strategy on commutation failure when the rectifier side AC system fails

[0044]

[0045] Note: The numbers in the table represent the number of commutation failures that occurred when the numbers met the standard. “2” represents two commutation failures, “1” represents a single commutation failure, and “0” represents no commutation failure.

[0046] Table 1 shows that, under the existing RPC control function, because RPC cannot further reduce the reactive power exchange in the AC system, excess reactive power increases the risk of commutation failure. Even with a minor ground fault (0.5 to 0.7 hours) in the rectifier-side AC system, the system is still susceptible to commutation failure. However, with the addition of a reactive power regulation module to the rectifier-side AC system, the probability of commutation failure decreases. Commutation failure on the inverter side only occurs when a serious fault occurs in the rectifier-side AC system. Therefore, commutation failure suppression measures based on converter reactive power consumption effectively reduce reactive power exchange in the rectifier-side AC system and further mitigate the risk of commutation failure in the system.

Claims

1. A control method for reducing commutation failure caused by rectifier-side AC system faults, characterized in that: The following steps are involved: Step A: Data collection: The control and protection device of the HVDC transmission system collects the DC transmission power P of the rectifier station in real time at a sampling frequency of 10kHz. d (t), reactive power Q provided by the rectifier side AC filter f (t), reactive power Q consumed by the rectifier side converter dc (t), the control output signal k of the HVDC reactive power control module RPC, where t is the sampling time; Step B: Obtain the reactive exchange amount of the AC system on the rectifier side: The control and protection device calculates the reactive exchange amount ΔQ of the rectifier side AC system at the current time t ac (t), ΔQ ac (t)=|Q f (t)-Q dc (t)|; Step C: Fault detection: Step C1: Compare the reactive exchange amount ΔQ of the rectifier side AC system at the current time t and the previous 39 sampling times ac (t), ΔQ ac (t-1), ΔQ ac (t-2), ..., ΔQ ac (t-37), ΔQ ac (t-38), ΔQ ac (t-39) Construct the reactive exchange quantity sequence ΔQ(t) of the rectifier side AC system at the current time t, and calculate the average value Q of ΔQ(t) mean ; Step C2: Determine Q mean Greater than the threshold ΔQ set Is it true? If so, go to step C3; If not, return to step C1; Step C3: Determine whether the output signal of the reactive power control module RPC at the current time t is 0. If so, proceed to step D; if not, return to step C1; Step D: Calculation of DC current command value: Obtain the reference value Q of reactive power consumption of the rectifier side converter at the current time t d_ref (t):Q d_ref (t) = Q f (t)-ΔQ set ; Then calculate the DC current command value I d_ref (t): Among them U d0r is the ideal no-load DC voltage of the rectifier station; Step E: The DC current command value I calculated in step D is d_ref (t) is input to the constant current control link on the rectifier side to control the DC current of the high-voltage DC transmission, and the DC current command value I d_ref (t) The duration of the input is a milliseconds.

2. A control method for reducing commutation failure caused by rectifier-side AC system faults according to claim 1, characterized in that: ΔQ in step C2 set The value is 50Mvar.

3. A control method for reducing commutation failure caused by rectifier-side AC system faults according to claim 1, characterized in that: In step E, the value of a is 12.

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