Self-adaptive transient stability control method and system based on trigger angle compensation and medium

Abstract

The invention discloses a self-adaptive transient stability control method and system based on trigger angle compensation and a medium. Relates to the technical field of power system control. The method comprises the following steps: firstly, analyzing the extinction angle offset of the high-voltage direct current system caused by each influence factor, and adding trigger lead angle control and current error control in the control of an inverter of the high-voltage direct current system according to the extinction angle offset of the high-voltage direct current system caused by each influence factor; negative effects caused by alternating-current voltage imbalance, alternating-current voltage reduction and phase angle jump during fault elimination are actively compensated by triggering lead angle control, so that sufficient commutation margin of a high-voltage direct-current system is maintained, and the risk of commutation failure during fault recovery is reduced; the transient stability of the high-voltage direct-current system under the alternating-current faults of the transmitting end and the receiving end is ensured; moreover, the trigger angle is not excessively advanced, and the reactive power consumption during the fault recovery period is minimized.

Description

Technical Field

[0001] The present invention relates to the technical field of power system control, and in particular to an adaptive transient stability control method, system and medium based on trigger angle compensation. Background Art

[0002] High voltage direct current (HVDC) systems based on line commutation have been widely used around the world. However, HVDC systems are prone to commutation failure and DC lockout under AC faults, which further endangers the safety of the power grid. Therefore, it is of great significance to study the transient stability mechanism and protection control method of HVDC systems.

[0003] According to existing research, commutation failure is the main safety and stability hazard of HVDC system under AC accidents. Continuous commutation failure (SCF) following the initial commutation failure (FCF) is particularly likely to cause DC blocking. In particular, AC faults in the sending and receiving grids will cause commutation failures in the HVDC system during fault recovery.

[0004] Therefore, in order to improve the transient stability of HVDC systems when AC faults occur in the transmission and receiving grids, a large number of studies have been conducted on its mechanism and protection methods. These methods can be divided into two categories: 1) installing additional equipment in the HVDC system; 2) improving the system control strategy.

[0005] Regarding the method of installing additional equipment in the HVDC system, the most famous method is to provide additional AC voltage by inserting a controllable capacitor. This method can eliminate both the initial commutation failure FCF and the commutation failure during fault recovery. In addition, there are studies that propose fault current limiters (SCFLs), reactive power compensation devices, dynamic series voltage compensators, and electrochemical energy storage to suppress commutation failures during fault recovery. Although these methods can effectively eliminate commutation failures during fault recovery, their economic costs and practical feasibility still need further study.

[0006] For the methods of improving control strategies, limiting DC current and advancing the firing angle are two main methods. The DC current control method dynamically adjusts the DC current reference to reduce the fault current and the commutation overlap angle, thereby reducing the risk of commutation failure and DC lockout in the HVDC system under transient accidents. In addition, the low voltage current limiting (VDCOL) method has been widely adopted. A study discussed two types of oscillation mechanisms caused by edge current control after AC disturbances, and proposed a coordinated edge current control method to enhance the fault recovery performance of the HVDC system. Since this method focuses on suppressing oscillations, it is not possible to simultaneously suppress commutation failures during fault recovery caused by faults at both ends. For the DC current control method, the communication delay between the rectifier and the inverter will affect the control performance after the fault, and even cause commutation failures during fault recovery. By advancing the firing angle, that is, maintaining sufficient commutation margin, commutation failures during fault recovery can also be mitigated. Control methods based on advanced firing angles, such as the adaptive extinction angle (EA) control method, the commutation failure prevention (CFPREV) method, and the adaptive CFPREV method, have been proposed. However, since the controller cannot be activated when there is a fault at the sending end, all of the above methods cannot be used to suppress the commutation failure during the fault recovery period caused by the sending end fault, that is, the safety and stability of the receiving end power grid cannot be guaranteed under the sending end fault.

[0007] In the study of commutation failure during fault recovery caused by AC fault in the sending grid, the improper interaction between constant current control (CC) and constant extinction angle control (CEA) at the inverter is considered to be the main cause. Therefore, a hybrid control method based on minimum firing angle control and limited current change rate control is proposed. However, since this control method can only be used for transient processes caused by AC faults at the sending end, the transient stability problem of the HVDC system under AC faults at the receiving end grid cannot be solved. Summary of the invention

[0008] The technical problem to be solved by the present invention is that the conventional transient stability control method of a high-voltage direct current system can only be used for transient processes caused by AC faults at the sending end, and it is difficult to achieve transient stability of the high-voltage direct current system under AC faults at the sending end and AC faults at the receiving end. The present invention aims to provide an adaptive transient stability control method, system and medium based on trigger angle compensation. First, the extinction angle offset of the high-voltage direct current system caused by various influencing factors is analyzed, and trigger lead angle control and current error control are added to the control of the inverter of the high-voltage direct current system according to the extinction angle offset of the high-voltage direct current system caused by various influencing factors. The negative effects caused by AC voltage imbalance, AC voltage reduction and phase angle jump when the fault is eliminated are actively compensated by trigger lead angle control, which not only maintains sufficient commutation margin of the high-voltage direct current system, thereby reducing the risk of commutation failure during fault recovery, and ensuring the transient stability of the high-voltage direct current system under AC faults at the sending and receiving ends; and the trigger angle will not be excessively advanced, minimizing the reactive power consumption during fault recovery.

[0009] The present invention is achieved through the following technical solutions:

[0010] This solution provides an adaptive transient stability control method based on trigger angle compensation, including:

[0011] Analyze the extinction angle offset of the high voltage DC system caused by various influencing factors; the influencing factors include AC voltage imbalance, voltage reduction, and phase angle jump of DC current and commutation voltage;

[0012] The trigger advance angle control and current error control are added to the control of the high voltage DC system inverter, wherein the trigger advance angle control is based on the extinction angle offset of each influencing factor.

[0013] Working principle of this scheme: Traditional transient stability control methods of high-voltage DC systems can only target transient processes caused by AC faults at the sending end. At the same time, it is difficult to achieve transient stability problems of high-voltage DC systems under AC faults at the sending end and AC faults at the receiving end. This scheme provides an adaptive transient stability control method, system and medium based on trigger angle compensation. First, the arc extinction angle offset of the high-voltage DC system caused by various influencing factors is analyzed. According to the arc extinction angle offset of the high-voltage DC system caused by various influencing factors, trigger advance angle control and current error control are added to the control of the inverter of the high-voltage DC system. The negative effects caused by AC voltage imbalance, AC voltage reduction and phase angle jump when the fault is eliminated are actively compensated by trigger advance angle control. Not only does it maintain sufficient commutation margin of the high-voltage DC system, thereby reducing the risk of commutation failure during fault recovery, and ensuring the transient stability of the high-voltage DC system under AC faults at the sending and receiving ends; but the trigger angle will not be excessively advanced, minimizing the reactive power consumption during fault recovery.

[0014] A further optimization scheme is that the analysis method of the arc extinction angle offset of the high voltage DC system caused by AC voltage imbalance includes:

[0015] The arc extinction angle deviation of the high-voltage DC system caused by AC voltage imbalance is calculated according to the following formula

[0016]

[0017] Wherein, ΔV represents the amplitude reduction of the phase voltage.

[0018] A further optimization scheme is that the analysis method of the arc extinction angle offset of the high voltage DC system caused by voltage reduction and DC current includes:

[0019] The arc extinction angle deviation of the high voltage DC system caused by voltage reduction and DC current is calculated according to the following formula

[0020]

[0021] Among them, I di Indicates the DC current on the inverter side; U LL Indicates the effective value of the commutation voltage; α inv represents the inverter side trigger angle; μ represents the commutation overlap angle; X c Represents the commutation reactance.

[0022] A further optimization scheme is that the analysis method of the arc extinction angle offset of the high voltage DC system caused by the phase angle jump of the commutation voltage includes:

[0023] The arc extinction angle offset of the high-voltage DC system caused by the phase angle jump of the commutation voltage is calculated according to the following formula:

[0024]

[0025] Among them, V tq Represents the q-axis component of the phase-locked loop PLL input voltage.

[0026] A further optimization scheme is that the parameter setting method of the trigger lead angle control and the current error control includes:

[0027] The PI controller parameter setting method for triggering the lead angle control is the same as the PI controller parameter setting method for the constant extinction angle control;

[0028] Configure the trigger lead angle β of the final output inv is the trigger lead angle β of the trigger lead angle control output AB , the trigger lead angle β of the constant current control output CC And the trigger advance angle β of the constant arc extinction angle control outputCEA The maximum value in ;

[0029] The parameter settings of current error control are the same as those of constant arc extinction angle control. The maximum limit value of the lead angle of current error control is Maximum limit of the lead angle with constant extinction angle control different.

[0030] A further optimization scheme is that the maximum limit value of the lead angle of the current error control is Determined according to the following formula:

[0031]

[0032] Among them, V ac Indicates bus voltage; X c Represents the commutation reactance; I di Indicates the DC current on the inverter side; γ m Represents the rectification angle.

[0033] A further optimization scheme is to trigger the lead angle β of the lead angle control AB It is expressed as:

[0034] β AB =K p3 e AB +K i3 ∫e AB dt

[0035] Among them, K p3 Represents the proportional parameter of the PI controller; e AB Indicates the commutation voltage; K i3 Represents the integral parameter of the PI controller.

[0036] A further optimization scheme is that the commutation voltage e AB It is expressed as:

[0037]

[0038] Among them, γ c represents the critical arc extinction angle; μ0 represents the commutation overlap angle during normal operation; β ref Indicates the reference value of the inverter's leading trigger angle; β inv Indicates the lead angle of the inverter; △γ CEC Indicates the output angle compensation of the current deviation control link.

[0039] The present solution also provides an adaptive transient stability control system based on trigger angle compensation, which is used to implement the above-mentioned adaptive transient stability control method based on trigger angle compensation; the system comprises:

[0040] An analysis module, used to analyze the extinction angle offset of the high voltage DC system caused by various influencing factors; the influencing factors include AC voltage imbalance, voltage reduction, and phase angle jump of DC current and commutation voltage;

[0041] The auxiliary control module is used to add trigger lead angle control and current error control in the control of the high-voltage DC system inverter, wherein the trigger lead angle control is based on the arc extinction angle offset of each influencing factor.

[0042] The present solution also provides a computer-readable medium on which a computer program is stored. The computer program is executed by a processor to implement the above-mentioned adaptive transient stability control method based on trigger angle compensation.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] This scheme provides an adaptive transient stability control method, system and medium based on trigger angle compensation. First, the extinction angle offset of the high-voltage DC system caused by various influencing factors is analyzed. According to the extinction angle offset of the high-voltage DC system caused by various influencing factors, trigger advance angle control and current error control are added to the control of the inverter of the high-voltage DC system. The negative effects caused by AC voltage imbalance, AC voltage reduction and phase angle jump when the fault is eliminated are actively compensated by trigger advance angle control. Not only does it maintain sufficient commutation margin of the high-voltage DC system, thereby reducing the risk of commutation failure during fault recovery and ensuring the transient stability of the high-voltage DC system under AC faults at the sending and receiving ends; but the trigger angle will not be excessively advanced, minimizing the reactive power consumption during fault recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0046] Figure 1 It is a schematic diagram of a typical control structure of a high voltage DC system;

[0047] Figure 2 It is a schematic diagram of transient response characteristics of the HVDC system under AC fault in the receiving-end power grid;

[0048] Figure 3 It is a schematic diagram of transient response characteristics of the HVDC system under AC fault in the sending-end power grid;

[0049] Figure 4It is a schematic diagram of the VI trajectory of the high voltage DC system;

[0050] Figure 5 This is the simulation result diagram of the HVDC system after a non-serious AC fault at the sending end;

[0051] Figure 6 This is the simulation result diagram of the high voltage DC system under the single-phase grounding fault of the sending end system;

[0052] Figure 7 It is a schematic diagram of the simulation results of the high voltage DC system under the grounding fault of phase B and C of the receiving system;

[0053] Figure 8 It is a schematic diagram of three-phase voltage under a typical single-phase fault;

[0054] Fig. 9 This is a schematic diagram of the principle diagram of a 6-pulse inverter;

[0055] Fig.10 Schematic diagram of the effect of voltage reduction on commutation;

[0056] Fig.11 It is a schematic diagram of actual commutation voltage and reference commutation voltage;

[0057] Fig.12 It is a schematic diagram of the principle of adaptive transient stability control based on trigger angle compensation;

[0058] Fig.13 It is a schematic diagram of the test system structure;

[0059] Fig.14 It is a schematic diagram of simulation results under TPG fault at the sending end;

[0060] Fig.15 It is a schematic diagram of simulation results under TPG fault at the sending end;

[0061] Fig.16 It is a schematic diagram of the simulation results of the inverter bus voltage under the control of method 1;

[0062] Fig.17 This is a schematic diagram of the simulation results under the SLG fault at the receiving end;

[0063] Fig.18 It is a schematic diagram of simulation results under TPG fault at the receiving end; DETAILED DESCRIPTION

[0064] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0065] Typical control structures of HVDC systems are as follows: Figure 1 As shown, the rectifier side has constant current control (CC), constant firing angle control (CIA) and low voltage current limiting control (VDCOL); the inverter side is equipped with constant current control (CC), constant extinction angle control (CEA), current error control (CEC) and VDCOL control.

[0066] Firstly, the transient response characteristics of the HVDC system under AC fault in the receiving grid are studied: the GIGRE benchmark system of a typical HVDC system is modeled and simulated in PSCAD software. Figure 2 The simulation results of a three-phase fault with a duration of 100 ms occurring at the inverter bus are shown, the fault impedance is 20Ω, and the fault occurrence time is t=4.0s. Figure 2 The dynamic process shown is divided into three stages.

[0067] Phase 1: Constant extinction angle control of the inverter under the condition of initial commutation failure. The inverter encountered the initial commutation failure. The measured extinction angle EA and commutation angle γ m The minimum measurement unit (MGM) is responsible for the fact that the constant arc extinction angle control output trigger lead angle β during the initial commutation failure. CEA When the low voltage current limiting control (VDCOL) causes the inverter side DC current I di Reduce and be less than the DC current setting value I dI When the constant current control output trigger lead angle β CC It also increases from its lower limit.

[0068] In addition, due to I di dR (rectifier side DC current setting value), current error control is activated; if Figure 2 As shown in Figure 2, when the inverter resumes normal commutation at t = 4.022s, according to formula (1), the inverter side shutdown angle measurement value γ m Increases rapidly. When the rectification angle γ m >γ ref When (γ ref is the reference value of the inverter side turn-off angle), the trigger lead angle β of the constant arc extinction angle control output CEA Start to decrease.

[0069] γ m =β inv -μ (1)

[0070] Among them, γ m Indicates the measured value of the inverter side turn-off angle; μ indicates the commutation overlap angle; β inv Indicates the leading conduction angle of the inverter side;​

[0071] However, the trigger lead angle β of the constant arc extinction angle control output CEA Still greater than the trigger lead angle β of the constant current control output CC , so the inverter is still in constant arc extinction angle control mode during this period.

[0072] Phase 2: The inverter is under constant current control, when the rectifier angle γ m >γ ref When CEA It decreases rapidly and becomes less than β at t = 4.043s CC Therefore, the inverter control is switched from constant extinction angle control to constant current control on the inverter side. As a result, due to the combined effect of constant current control of the rectifier and the inverter, I di is controlled within the range of formula (2):

[0073] I dI di dR =I dI +I M (2)

[0074] After the fault is cleared (t = 4.10s), the DC voltage gradually recovers and the DC current reference value I dR and the inverter side DC current reference value I dI The inverter side DC current I di Rapid decline, β CC It rises rapidly and grows faster. According to formula (1), since β CC Larger and I di Relatively small, the rectification angle γ m However, the rectifier angle γ m It decreases significantly at t=4.103s, which greatly increases the risk of commutation failure in stage 3; the inventors of the present application found that the reason is that the commutation voltage has a phase angle jump of 57.72° after the fault is cleared.

[0075] Phase 3: Constant extinction angle control of the inverter under commutation failure conditions during fault recovery. In phase 2, as γ m and I di The inverter switches back to constant arc extinction angle control; in stage 3, the inverter side DC current I di is completely controlled by the rectifier, so it quickly approaches I dR , causing the turn-off angle deviation Δγ to drop rapidly to 0.

[0076] In this process, the proportional part of the PI controller of the constant arc extinction angle control plays a leading role, so β​​CEA It can be expressed as: CEA =K P2 e CEA =K P2 (γ set +△γ-γ m ) (3)

[0077] Among them, K P2 represents the proportional parameter of the PI controller in the cut-off angle control; γ set Indicates the initial setting value of the inverter turn-off angle;

[0078] The change rate of constant extinction angle control CEA can be obtained by the following formula:

[0079] dβ CEA / dt=K P2 {d(γ set -γ m ) / dt+d(△γ) / dt} (4)

[0080] Where: d(γ set -γ m ) / dt>0,d(△γ) / dt|<0 (5)

[0081] Here, t represents time.

[0082] Formula (5) reveals that the continuous decrease of Δγ may lead to β CEA At the same time, due to I di As the overlap angle OA increases, the overlap angle OA also increases. Therefore, according to formula (1), the rectification angle γ m Further reduction increases the risk of commutation failure during fault recovery. Based on the above analysis, it can be seen that the main reason for commutation failure during fault recovery is the ambiguity of the DC current control reference value in stage 2, which leads to the arc extinction angle being reduced to the critical arc extinction angle by the end of stage 2, and the weakness of constant arc extinction angle control in stage 3. In addition, it is worth noting that the phase angle jump after fault removal has a considerable impact on the commutation process.

[0083] Secondly, the transient response characteristics of the HVDC system under AC fault in the sending-end power grid: The transient response characteristics of the HVDC system under AC fault in the sending-end power grid can also be divided into three stages. Figure 3 The simulation results for a 100ms three-phase fault at the rectifier bus are shown, with a fault impedance of 0.1Ω and a fault occurrence time of t=4.0s.

[0084] Phase 1: Inverter under constant arc-off angle control, rectifier fault causes I di Less than I dI In addition, due to the delay of the MGM unit, the commutation angle γm The actual arc extinction angle is delayed by one cycle. Therefore, after the fault occurs, the rectifier angle γ m Still equal to one cycle of γ set Therefore, β CC and β CEA Both increase in stage 1. inv large, the overlap angle OA is small, and the rectification angle γ m Increase. When γ m >γ ref When CEA It starts to decrease at t=4.027s and finally reaches the minimum at t=4.034s.

[0085] Phase 2: Inverter constant current control, when β CC Greater than β CEA At t = 4.10s, the inverter switches from constant arc extinction angle control to constant current control. After the fault is eliminated, the rectifier control switches back to constant current control. di is also controlled to (2). Figure 3 In, when I di At t = 4.107s, it is greater than I di When CC Further reduction leads to the rectification angle γ m decreases, and the overlap angle OA increases. m Reduced to less than γ ref When CEA from Figure 3 The minimum value at t=4.201s rises.

[0086] Phase 3: The inverter fails to commutate during fault recovery under constant arc extinction angle control. CEA >β CC , and at t = 4.260 seconds, the inverter control switches back to constant arc extinction angle control. It should be noted that at this time the rectifier angle γ m Much smaller than γ ref , close to the critical arc extinction angle. At this stage, I di is controlled only by the rectifier, so I di Increase to I dR , causing Δγ to drop rapidly to 0. As a result, γ ref and the PI controller input deviation signal e in the cut-off angle control CEA As Δγ decreases, β CEA This increases the risk of commutation failure during fault recovery, especially when γ m has returned to less than γ set hour.

[0087] The similarity between the sending-end AC fault and the receiving-end AC fault in phase 2 and phase 3 proves that the transient response mechanism of the HVDC system is the same in both cases. This is further verified by analyzing the VI trajectory of the HVDC system in each case.

[0088] The nature of the commutation failure during the fault recovery period caused by the AC fault in the sending and receiving systems is the same, that is, the transient stability mechanism of the high-voltage DC system under the AC fault at the sending and receiving ends is the same. The VI trajectory of the high-voltage DC system after the fault is as follows: Figure 4 As shown, according to the above analysis and simulation results, it can be found that Figure 4 The operating points in (a) and (b) experience different trajectories in phase 1 (i.e., trajectory RA-B). However, the operating points experience very similar trajectories in phases 2 and 3 (i.e., trajectory BCDE). This is because the HVDC system cannot detect the fault location. However, any AC fault will cause the low-voltage current limiting control to start, thereby causing the DC voltage and DC current to drop. Therefore, the operating trajectory of the HVDC system from the fault steady state to normal operation is the same in both fault scenarios. In other words, no matter where the fault occurs, the system operates under the same conditions in phases 2 and 3; precisely for the following two reasons: a) In phase 2, both sides of the converter are under constant current control, and the system cannot establish a stable operating point. The arc extinction angle is reduced to the critical arc extinction angle at the end of phase 2. b) In phase 3, the inverter is under constant arc extinction angle control, but it cannot accurately control the arc extinction angle due to the exit of current error control and the measurement error of the arc extinction angle. Therefore, the HVDC system cannot operate at a stable operating point.

[0089] It should be noted that in the case of non-serious AC faults at the sending end, the inverter may be under constant arc extinction angle control before commutation failure occurs, such as Figure 5 However, point B is still the cause of commutation failure during fault recovery.

[0090] From the above analysis, it can be seen that if the system trajectory is kept at a stable operating point by reasonably compensating the arc extinction angle during the fault recovery process, the commutation failure during the fault recovery period can be effectively suppressed, that is, the transient stability of the HVDC system under AC faults at the transmitting and receiving ends can be guaranteed.

[0091] Finally, the transient response characteristics of the HVDC system under asymmetric faults

[0092] In order to demonstrate the previous findings that the mechanism of transient stability of HVDC system under two-end fault is the same due to 1) long constant current control time at both sending and receiving converter stations and 2) weakness of constant extinction angle control, asymmetric fault conditions are considered in this section.

[0093] Asymmetric fault of the sending end system: Figure 6 The simulation results for a 100 ms single-phase-to-ground fault occurring at t = 4.0 s with a fault resistance of 0.1 Ω are shown. Figure 6 As shown in Figure 1, the dynamics of inverter control under a single-phase ground fault at the sending end can still be divided into three stages, which is essentially the same as the case under a symmetrical fault. The only difference is the duration of each stage. In stage 1, the fault causes I di Less than the inverter side DC current reference value I dI In addition, due to the delay of the minimum turn-off angle measurement (MGM) unit, γ m The actual arc extinction angle is delayed by one cycle. Therefore, in phase 1, β CC and β CEA Increase. Due to β inv The larger the overlap angle OA, the smaller the rectification angle γ m Increase. When the rectifier angle γ m >γ ref When CEA It starts to decrease at t=4.034 seconds and finally reaches its minimum limit at t=4.067 seconds. The inverter control switches from constant extinction angle control CEA to constant current control CC at t=4.041 seconds. In stage 2, when the fault is cleared at t=4.10 seconds, the rectifier control switches back to constant current control. Therefore, the DC current is controlled by both ends of the converter. When I di Greater than I dI When CC Further reduce, so that the rectification angle γ m Decrease and increase the overlap angle OA. Once γ m Drop to less than γ ref , β CEA From the minimum limit of t = 4.121 seconds, as Figure 6 When βCEA>βCC and t=4.142 seconds, the inverter control switches back to constant arc extinction angle control. At this time, the rectifier angle γ m Much smaller than γ ref , close to the critical value. Although the inverter is under constant arc extinction angle control, it cannot accurately control the arc extinction angle. Therefore, the inverter experiences commutation failure during fault recovery.

[0094] From the above analysis, it can be seen that the control dynamics of the inverter station under an asymmetric fault in the sending-end system are the same as those under a symmetric fault in the sending-end system.

[0095] Asymmetric fault of the receiving system: Figure 7The simulation results of a 100 ms BC phase ground fault occurring at t = 4.0 seconds with a fault resistance of 20Ω are shown. The inverter control dynamics after the B and C phase ground faults in the receiving system can also be divided into three stages. In stage 3, the fault is cleared at t = 4.10 seconds, and I di Less than I dI , β CC This results in a short control switch in phase 3, with the inverter switching to constant current control between 4.128 seconds and 4.142 seconds. When the inverter control switches back to constant extinction angle control again at t = 4.142 seconds, the commutation angle γ m Much smaller than γ ref , close to the critical arc extinction angle. Although the inverter is under constant arc extinction angle control, it cannot accurately control the arc extinction angle. Therefore, the inverter experiences a commutation failure during fault recovery. It should be noted that even if the impact of constant current control during this period is ignored, the inability of constant arc extinction angle control to accurately control the arc extinction angle can still be regarded as the cause of the commutation failure during fault recovery due to the withdrawal of current error control and the measurement error of the arc extinction angle. This means that point B in Section 2.3 is still the cause of the commutation failure during fault recovery from an asymmetric fault in the receiving system.

[0096] From the above analysis, it can be seen that the inverter control dynamics under an asymmetric fault at the receiving end are similar to those under a symmetric fault at the receiving end.

[0097] After the above analysis, the traditional HVDC system transient stability control method can only be used for the transient process caused by the AC fault at the sending end. At the same time, it is difficult to achieve the transient stability problem of the HVDC system under the AC fault at the sending end and the AC fault at the receiving end. In view of this, this solution provides the following embodiments to solve the above technical problems:

[0098] Example 1

[0099] This embodiment provides an adaptive transient stability control method based on trigger angle compensation, including:

[0100] Step 1: Analyze the arc extinction angle offset of the high voltage DC system caused by various influencing factors; the influencing factors include AC voltage imbalance, voltage reduction, and phase angle jump of DC current and commutation voltage;

[0101] (1) The analysis methods of the arc extinction angle offset of the high voltage DC system caused by AC voltage unbalance include:

[0102] according to Figure 8 The three-phase voltages under a typical single-phase fault are shown, where Ea is the phase A voltage during the fault, ΔV is the amplitude reduction of the phase A voltage, and Aμ is the voltage-time area reduction under normal operation. is the arc extinction angle offset;

[0103] When the phase voltage amplitude decreases, the intersection point will move forward; assuming that the inverter side trigger angle α inv If the overlap angle OA remains unchanged, the arc extinction angle EA will decrease from γ to γ', thereby increasing the risk of commutation failure and being detrimental to the stable operation of the HVDC system. Figure 8 , the intersection point of phase A and phase B voltage can be expressed as:

[0104]

[0105] Among them, E m Indicates the normal amplitude of the inverter commutation bus voltage; E b Indicates the B phase voltage; E a represents the A-phase voltage; t represents time; ω represents the electrical angular velocity; ΔV represents the amplitude reduction of the phase voltage.

[0106] like Figure 8 As shown, since the intersection point between phase A and phase B is 0° or 180° in normal operation, the arc extinction angle offset of the high-voltage DC system caused by AC voltage unbalance is calculated according to the following formula:

[0107]

[0108] Wherein, ΔV represents the amplitude reduction of the phase voltage.

[0109] The above derivation assumes that α inv and Aμ remain unchanged, so Only the phase shift effect caused by phase voltage imbalance is reflected.

[0110] (2) The analysis methods for the extinction angle offset of the high voltage DC system caused by voltage reduction and DC current include:

[0111] 6-pulse inverter schematic diagram Fig. 9 As shown, considering the commutation from V1 to V3, according to the voltage-time area and Fig.10 The effect of voltage reduction on commutation. Assuming that during the commutation process, I di Since the inverter bus voltage can be restored within 1-2 cycles after the fault is eliminated, only the commutation voltage e is considered. ab The commutation process can be described as:

[0112]

[0113] in, Indicates the inverter side commutation voltage e ab Initial phase angle;

[0114] If the firing angle and DC current remain unchanged, the dependence of the arc extinction angle on the voltage drop can be expressed as Fig.10 As shown. When it is known that I di , U LL and α inv When the arc extinction angle offset is The following formula is used for calculation:

[0115]

[0116] Among them, I di Indicates the DC current on the inverter side; U LL Indicates the effective value of the commutation voltage; α inv represents the inverter side trigger angle; μ represents the commutation overlap angle; X c Indicates the commutation reactance; in order to avoid under-compensation, the minimum amplitude of the three-phase commutation voltage is used to calculate

[0117] (3) The analysis method of the arc extinction angle offset of the high voltage DC system caused by the phase angle jump of the commutation voltage includes:

[0118] When the fault is cleared, the commutation voltage will experience a phase angle jump, which prevents the PLL from providing the correct firing angle reference immediately. Fig.11 The effect of phase angle jump on the arc extinction angle is shown; the phase angle of the commutation voltage increases sharply, while the inverter firing angle remains unchanged. As a result, the inverter advance angle β inv and the arc extinction angle EA is reduced, thereby increasing the risk of commutation failure. Therefore, the phase angle of the commutation voltage is sharply reduced, such as Fig.11 As shown by the blue dotted line in the figure. Since the inverter trigger angle remains unchanged, β inv The arc extinction angle EA will increase, which is usually beneficial to the commutation process. The effect of phase jump on the commutation process can be described as:

[0119]

[0120] When the phase shift When the phase shift is When , the actual advance angle β is greater than β', and the arc extinction angle EA increases, which is beneficial to the commutation process.

[0121] The q-axis component of the PLL input voltage can be expressed as:

[0122]

[0123] Therefore, the arc extinction angle phase shift It can be calculated according to the following formula:

[0124]

[0125] Among them, V tq Represents the q-axis component of the phase-locked loop PLL input voltage.

[0126] Step 2, such as Fig.12 As shown, trigger advance angle control and current error control are added to the control of the high-voltage DC system inverter. The trigger advance angle control is based on the arc extinction angle offset of each influencing factor, and the trigger angle will not be excessively advanced, thereby minimizing the reactive power consumption during the fault recovery period. In addition, in order to reduce the problem that the rectifier station and the inverter station are under constant current control for a long time and the trigger angle is insufficient during the fault recovery period, this solution also adds additional current error control.

[0127] Under normal operation, the arc extinction angle phase offset and Δγ CEC It means that the output of the current deviation control link is 0. In order to provide a "dead zone" for the proposed method and maintain a certain commutation margin, the critical turn-off angle γc in the proposed control is set to 12°, which is between the critical value and the set value of the arc extinction angle.

[0128] The parameter setting methods for triggering lead angle control and current error control include:

[0129] Because β inv There is a direct algebraic relationship between and γm; therefore, the PI controller parameter setting method for triggering the lead angle control is the same as the PI controller parameter setting method for the constant arc extinction angle control;

[0130] Configure the trigger lead angle β of the final output inv is the trigger lead angle β of the trigger lead angle control output AB , the trigger lead angle β of the constant current control output CC And the trigger advance angle β of the constant arc extinction angle control output CEA The maximum value among the trigger lead angle β AB It is expressed as:

[0131] β AB =K p3 e AB +K i3 ∫e AB dt (13)

[0132] Among them, e AB Represents the PI controller input in the proposed control; K p3 and K i3 They represent the proportional and integral parameters of the PI controller in the proposed control respectively;

[0133] Commutation voltage e AB It is expressed as:

[0134]

[0135] Among them, γ c represents the critical arc extinction angle; μ0 is the commutation overlap angle during normal operation; β ref Indicates the leading trigger angle of the inverter; β inv Indicates the lead angle of the inverter; △γ CEC Represents the output variable of the power deviation link;

[0136] The parameter settings of current error control are the same as those of constant arc extinction angle control. The maximum limit value of the lead angle of current error control is Maximum limit of the lead angle with constant extinction angle control In order to avoid insufficient compensation of βref in the case of AC fault at the sending end, and considering that single-phase grounding fault accounts for most AC faults, the maximum limit value of the lead angle of current error control is calculated in the case of single-phase zero impedance fault on the rectifier AC bus. for:

[0137]

[0138] Among them, V ac Indicates bus voltage; X c Represents the commutation reactance; I di Indicates the DC current on the inverter side.

[0139] In order to avoid AC fault at the sending end, ref Insufficient compensation, and considering that single-phase grounding faults account for the majority of AC faults, the maximum limit value is calculated in the case of a single-phase zero-impedance fault on the rectifier AC bus.

[0140] This scheme does not require mathematical iteration or solving complex nonlinear equations. The calculations involved are (7), (9) and (12), which are algebraic equations with minimal computational burden. No additional control startup module is required, and it is automatically activated and deactivated during faults. It can be seen from (13) that when e AB >0, β AB starts to rise. When β AB Greater than β CC and β CEA When e AB <0, β AB starts to decrease. When β AB Less than β CC or β CEAThe input variables of this scheme are all from the inverter station; it does not rely on the communication between converter stations, thus avoiding the negative impact of communication delay.

[0141] Example 2

[0142] This embodiment provides an adaptive transient stability control system based on trigger angle compensation, which is used to implement the adaptive transient stability control method based on trigger angle compensation described in Embodiment 1; the system includes:

[0143] An analysis module, used to analyze the extinction angle offset of the high voltage DC system caused by various influencing factors; the influencing factors include AC voltage imbalance, voltage reduction, and phase angle jump of DC current and commutation voltage;

[0144] The auxiliary control module is used to add trigger lead angle control and current error control in the control of the high-voltage DC system inverter, wherein the trigger lead angle control is based on the arc extinction angle offset of each influencing factor.

[0145] Example 3

[0146] This embodiment provides a computer-readable medium on which a computer program is stored. The computer program is executed by a processor to implement the adaptive transient stability control method based on trigger angle compensation as described in Embodiment 1.

[0147] Example 4

[0148] This embodiment is based on Fig.13 The test system shown verifies the method of this application. The minimum turn-off time of the thyristor in the test system model is set to 400μs (7.2°), the DC power is 1000MW, and the DC voltage is 500kV. The method of this application is marked as method 4; it is compared with three other control methods under different fault conditions: method 1: traditional GIGRE control method; method 2: CFPREV control method; method 3: traditional control method;

[0149] AC fault at the sending end: 1) Three-phase grounding (TPG) fault: A three-phase grounding fault occurs at the rectifier station bus (such as Fig.13 ) and on the transmission line 100 km from the rectifier station bus (as shown in F1 in Fig.13 The fault occurs in 4.0 seconds, lasts for 90 milliseconds, and has a fault resistance of 0.1Ω. m ), DC current (I di ), DC voltage (V di ), inverter station bus voltage (V ac ) and the reactive power (Q i) The simulation results are as follows Fig.14 As shown in Figure 2, Method 3 is mainly aimed at faults on the inverter side and will not be activated under AC faults in the sending system, so its simulation results are not given.

[0150] from Fig.14 It can be seen that method 4 (method of the present application) can effectively enhance the transient stability of the high voltage DC system during fault recovery. The minimum values ​​of the arc extinction angle EA during the recovery process are 10.32° and 9.3° respectively. Fig.14 (a)-(3) and Fig.14 The arc extinction angle offset result in method 4 is shown in (b)-(3). Fig.14 As shown in (1). It can be seen that and Promotes recovery ( Fig.14 (a)-(1)). Since the fault occurred at the rectifier station side, it is expected that is equal to 0, which is verified in the simulation results. It increases from 0° at 4.23 seconds to 10.1° at 4.26 seconds, while It increases from 0° at 4.10 seconds to 21.7° at 4.24 seconds. and The inverter switches from constant current control to the proposed control at 4.24 seconds ( Fig.14 (a)-(2)). Fig.14 (b)-(1) shows that The angle increases from 0° at 4.10 seconds to 19.8° at 4.22 seconds. The inverter switches from constant current control to the proposed control at 4.22 seconds ( Fig.14 (b)-(2)). Therefore, the duration of both converters under constant current control is significantly reduced. This ensures that the arc extinction angle offset EA is sufficient and continuously controllable during fault recovery, and the "over-advance" of the inverter firing angle is limited.

[0151] Although the system does not experience commutation failure (CF) using method 2, this is not due to the direct effect of its control strategy, because method 2 does not actually consider the transient recovery process of the HVDC system after the fault at the sending end. For method 2, the minimum values ​​of the arc extinction angle EA during the recovery process are 3.6° and 5.4°, respectively. Fig.14 As shown in (a)-(3) of 14 and (b)-(3) of 14, this indicates that there is a high stability risk. In addition, the fluctuation of the arc extinction angle EA will cause the reactive power absorbed by the inverter to fluctuate. Fig.14 As shown in (a)-(7), in method 2, the reactive power Q iThe minimum values ​​of are -257.73Mvar and -209.29Mvar respectively. In contrast, in method 4, the reactive power Q i The minimum values ​​of are -102.46Mvar and -102.72Mvar, respectively, which makes the AC voltage higher than 0.9pu during the recovery period, while in method 2, the minimum voltage of the inverter bus is 0.78pu and 0.82pu, respectively. Fig.14 (6) is shown. This situation is undesirable. Therefore, it can be seen that the proposed method can actively reduce the transient stability risk of the HVDC system during the recovery of the TPG fault at the sending end, while minimizing the reactive power consumption.

[0152] Single-phase to ground (SLG) fault: In this case, a single-phase to ground fault occurs at F1 and F2 at 4.0 seconds, the fault duration is 90 milliseconds, and the fault resistance is 0.1Ω.

[0153] The simulation results are as follows Fig.15 As shown in Figure 1, neither method 1 nor method 2 can alleviate the commutation failure during fault recovery, which is not conducive to the transient stability of the high-voltage DC system. On the contrary, method 4 (the method of the present application) can effectively enhance the transient stability of the high-voltage DC system during fault recovery. The minimum values ​​of EA during the recovery process are 9.3° and 9.4°, respectively. Fig.15 As shown in (a)-(3) of 15 and (b)-(3) of 15. Fig.15 As shown in (1), after the fault is cleared, and are all greater than zero, which obviously helps to suppress commutation failure during fault recovery. Since the fault occurs on the rectifier side, such as Fig.16 As shown, it has little effect on the AC voltage on the inverter side. Equal to 0 is expected, the simulation results (such as Fig.15 (1) also confirms this. Fig.16 As shown in (a), during the period from 4.141 seconds to 4.168 seconds, the inverter bus voltage drops slightly, while and They rise from 0° to 9.93° and 15.21° respectively. This proves that the adaptive transient stability control based on trigger angle compensation in this scheme can handle asymmetric faults at the sending end.

[0154] In method 4, the reactive power Q i The minimum values ​​are -164.00Mvar and -94.75Mvar respectively. Fig.15 (a)-(7) and Fig.15This shows that method 4 can effectively enhance the transient stability of the HVDC system during fault recovery and also minimize the reactive power consumption of the converter station.

[0155] In addition, due to the inverter commutation failure (CF) under method 1 and method 2, the DC voltage and DC current have significant jumps (such as Fig.15 (4) and (5)). Therefore, the recovery speed in Method 1 and Method 2 is slower than that in Method 4. In addition, in Method 1 and Method 2, there is still a significant jump in the reactive power and inverter bus voltage after the commutation failure, as shown in Fig.15 (6) and (7). This is undesirable because it may lead to commutation failure, but this situation is effectively avoided in method 4.

[0156] Receiving end AC fault: 1) Single-phase grounding (SLG) fault: In this case, the single-phase grounding fault occurs on the inverter bus (F3) and the transmission line (F4) 40 km away from the inverter bus. The fault occurs in 4.0 seconds and lasts for 100 milliseconds (the fault clearing time of the 230kV transmission line is less than 120 milliseconds). The fault resistance is 0.1Ω. The simulation results are shown in Fig.17 As shown. Fig.17 As shown in (3), method 4 (the proposed method) can maintain a larger EA angle during fault recovery and effectively enhance the transient stability of the HVDC system. Fig.17 (1) is similar to the asymmetric fault at the sending end. and All of these play a role in alleviating commutation failure during fault recovery. is not equal to 0, which verifies that the adaptive transient stability control method based on trigger angle compensation can actively suppress commutation failure during fault recovery under asymmetric fault at the receiving end, as described in Sections 3 and 4. At 4.0 seconds, and All increased, Returns to 0 at 4.15 seconds, Returns to 0 at 4.04 seconds. and The combined effect of makes the inverter adopt the proposed adaptive transient stability control method based on trigger angle compensation at 4.01 seconds, such as Fig.17As shown in (2). Therefore, the switching between constant current control and constant arc extinction angle control is avoided during fault recovery. This ensures that the arc extinction angle EA is sufficient and continuously controllable during fault recovery. The minimum value of EA in method 2 is 8.77°, indicating a high risk of commutation failure; method 3 fails to suppress commutation failure during fault recovery, as shown in Fig.17 As shown in (b)-(3), therefore, Method 2 and Method 3 are not as good as Method 4 in transient stability control of HVDC system.

[0157] 2) Three-phase to ground (TPG) fault: In this case, the three-phase to ground fault occurs at F3 and F4, the fault occurrence time is 4.0 seconds, the duration is 100 milliseconds, and the fault resistance is 0.1Ω. The simulation results are shown in Fig.18 shown.

[0158] from Fig.18 It can be seen that method 4 (the proposed method) can effectively suppress the occurrence of commutation failure during fault recovery and maintain sufficient EA during fault recovery. Although methods 2 and 3 can also suppress the occurrence of commutation failure during fault recovery, such as Fig.18 As shown in (1), the duration of FCF is prolonged in method 3, and fluctuations in EA are observed in both methods 2 and 3. This causes a jump in the reactive power absorbed by the inverter, as shown in Fig.18 As shown in (5), for AC voltage ( Fig.18 (4)) has a negative impact. Therefore, the fluctuation of DC voltage and DC current during fault recovery is Fig.18 persists in (2) and (3).

[0159] although Fig.18 (3) shows that the fault recovery is slower due to the slow decline of EA caused by the presence of the PI controller, but the risk of commutation failure during fault recovery is significantly reduced. The faster recovery of the other methods is driven by the significant jump in reactive power consumption after the fault is cleared. Fig.18 (a)-(5) and Fig.18 It can be seen from (b)-(5) that the reactive power Q in method 2 during fault recovery is i The minimum values ​​are -249.09Mvar and -209.61Mvar, and the reactive power Q in method 4 i The minimum values ​​are -152.42Mvar and -86.88Mvar respectively. Fig.18As shown in (2) and (4), the DC current and inverter bus voltage in the proposed method recover more smoothly and quickly compared with the other three methods. Therefore, it can be seen that the proposed method can effectively reduce the risk of commutation failure during fault recovery during RE TPG fault, while minimizing the impact on inverter reactive power consumption and AC voltage.

[0160] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An adaptive transient stability control method based on trigger angle compensation, characterized in that: include: Analyze the extinction angle offset of the high voltage DC system caused by various influencing factors; the influencing factors include AC voltage imbalance, voltage reduction, and phase angle jump of DC current and commutation voltage; The trigger advance angle control and current error control are added to the control of the high voltage DC system inverter, wherein the trigger advance angle control is based on the extinction angle offset of each influencing factor.

2. The adaptive transient stability control method based on trigger angle compensation according to claim 1 is characterized in that: The analysis methods of the arc extinction angle offset of the high voltage DC system caused by AC voltage unbalance include: The arc extinction angle deviation of the high-voltage DC system caused by AC voltage imbalance is calculated according to the following formula Wherein, ΔV represents the amplitude reduction of the phase voltage.

3. The adaptive transient stability control method based on trigger angle compensation according to claim 1, characterized in that: The analysis methods of the extinction angle deviation of the high voltage DC system caused by voltage reduction and DC current include: The arc extinction angle deviation of the high voltage DC system caused by voltage reduction and DC current is calculated according to the following formula Among them, I di Indicates the DC current on the inverter side; U LL Indicates the effective value of the commutation voltage; α inv represents the inverter side trigger angle; μ represents the commutation overlap angle; X c Represents the commutation reactance.

4. The adaptive transient stability control method based on trigger angle compensation according to claim 1, characterized in that: The analysis method of the arc extinction angle offset of the high voltage DC system caused by the phase angle jump of the commutation voltage includes: The arc extinction angle offset of the high-voltage DC system caused by the phase angle jump of the commutation voltage is calculated according to the following formula: Among them, V tq Represents the q-axis component of the phase-locked loop PLL input voltage.

5. The adaptive transient stability control method based on trigger angle compensation according to claim 1, characterized in that: The parameter setting method for triggering lead angle control and current error control includes: The PI controller parameter setting method for triggering the lead angle control is the same as the PI controller parameter setting method for the constant extinction angle control; Configure the trigger lead angle β of the final output inv is the trigger lead angle β of the trigger lead angle control output AB , the trigger lead angle β of the constant current control output CC And the trigger advance angle β of the constant arc extinction angle control output CEA The maximum value in ; The parameter settings of current error control are the same as those of constant arc extinction angle control. The maximum limit value of the lead angle of current error control is Maximum limit of the lead angle with constant extinction angle control different.

6. The adaptive transient stability control method based on trigger angle compensation according to claim 5 is characterized in that: The maximum limit value of the lead angle of the current error control Determined according to the following formula: Among them, V ac Indicates bus voltage; X c Represents the commutation reactance; I di Indicates the DC current on the inverter side; γ m Represents the rectification angle.

7. The adaptive transient stability control method based on trigger angle compensation according to claim 5, characterized in that: Trigger lead angle β of trigger lead angle control output AB It is expressed as: β AB =K p3 e AB +K i3 ∫e AB dt Among them, K p3 Represents the proportional parameter of the PI controller; e AB Indicates the commutation voltage; K i3 Represents the integral parameter of the PI controller.

8. The adaptive transient stability control method based on trigger angle compensation according to claim 7 is characterized in that: Commutation voltage e AB It is expressed as: Among them, γ c represents the critical arc extinction angle; μ0 represents the commutation overlap angle during normal operation; β ref Indicates the reference value of the inverter's leading trigger angle; β inv Indicates the lead angle of the inverter; △γ CEC Indicates the output angle compensation of the current deviation control link.

9. An adaptive transient stability control system based on trigger angle compensation, characterized in that: Used to implement the adaptive transient stability control method based on trigger angle compensation according to any one of claims 1 to 8; the system comprises: An analysis module, used to analyze the extinction angle offset of the high voltage DC system caused by various influencing factors; the influencing factors include AC voltage imbalance, voltage reduction, and phase angle jump of DC current and commutation voltage; The auxiliary control module is used to add trigger lead angle control and current error control in the control of the high-voltage DC system inverter, wherein the trigger lead angle control is based on the arc extinction angle offset of each influencing factor.

10. A computer readable medium having a computer program stored thereon, characterized in that: The computer program is executed by a processor to implement the adaptive transient stability control method based on trigger angle compensation as described in any one of claims 1 to 8.

Images