Sliding-mode control and disturbance observer collaborative STATCOM construction method for suppressing LCC-HVDC commutation failure

Abstract

The invention discloses a sliding mode control and disturbance observer collaborative STATCOM construction method for suppressing LCC-HVDC commutation failure. The sliding mode control and disturbance observer collaborative STATCOM construction method comprises the steps that sliding mode control is adopted for current inner loop control of an STATCOM control circuit; the sliding mode control comprises a sliding mode surface, an index reaching law and a sliding mode control law; a sliding mode disturbance observer is introduced to estimate actual disturbance; actual disturbance estimated by the sliding mode disturbance observer is added to the sliding mode control law, and a corrected sliding mode control law is constructed. According to the novel STATCOM based on SMC-SMDO cooperative control, a multi-target sliding mode surface is designed, comprehensive optimization is realized in combination with an exponential reaching law, a sliding mode disturbance observer is introduced to weaken the influence of disturbance, and reactive power can be quickly injected to improve the commutation failure defense capability. Meanwhile, due to the introduction of the sliding mode disturbance observer, the disturbance of the system is estimated, the disturbance is accurately compensated, the precision of the STATCOM is greatly improved, the fault recovery time is effectively shortened, and the anti-interference performance is remarkably enhanced.

Description

Technical Field

[0001] This invention relates to a method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC transmission systems, belonging to the field of commutation failure suppression technology in high-voltage direct current transmission systems. Background Technology

[0002] Line commutated converter based high-voltage direct current (LCC-HVDC) transmission systems have become the core method for long-distance, large-scale power transmission due to their unique technological advantages. However, because this system relies on the AC system to provide the commutation voltage, the commutation process on the AC inverter side is susceptible to interference under grid disturbances, leading to commutation failure and posing a serious threat to the safe and stable operation of the power grid.

[0003] Static Synchronous Compensators (STATCOMs), as dynamic reactive power compensation devices with low harmonic content, can compensate for reactive power deficits in real time when connected in parallel to the inverter bus of an LCC-HVDC system, effectively mitigating commutation failures. However, STATCOMs under traditional control have a slow response speed, insufficient to raise the reactive current to the required level within the critical time; furthermore, their command tracking capability is limited under extreme operating conditions. Therefore, STATCOMs under traditional PI control are not very effective at suppressing commutation failures.

[0004] Current research focuses on optimizing the coordination process between STATCOM and DC transmission systems to improve the operational performance of the combined system and suppress commutation failure, but it neglects the optimization of STATCOM's own control. Furthermore, when dealing with strong disturbances that lead to commutation failure in LCC-HVDC, the dynamic response speed and anti-interference capability of a single, traditionally controlled STATCOM are limited, restricting its ability to reach its full potential and quickly, accurately, and reliably stabilize the AC bus voltage of the LCC-HVDC. Summary of the Invention

[0005] This invention provides a method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC. The method introduces sliding mode control and a disturbance observer design to the current inner loop control of the STATCOM control circuit to construct a STATCOM with SMC-SMDO coordinated control, which is then connected to an LCC-HVDC to suppress commutation failure in LCC-HVDC.

[0006] The technical solution of this invention is:

[0007] According to a first aspect of the present invention, a method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC is provided, comprising: employing sliding mode control for the inner current loop control of the STATCOM control circuit; the sliding mode control including a sliding surface, an exponential reaching law, and a sliding mode control law; introducing a sliding mode disturbance observer to estimate the actual disturbance; and adding the actual disturbance estimated from the sliding mode disturbance observer to the sliding mode control law to construct a modified sliding mode control law.

[0008] Furthermore, the sliding mode control specifically involves designing the sliding surface as independent sd and s q The integral sliding surface is derived; an exponential reaching law is designed; the derivative of the integral sliding surface is obtained; and the mathematical models of the exponential reaching law and STATCOM are substituted into the derivative expression of the integral sliding surface to obtain the sliding mode control law.

[0009] Furthermore, the sliding mode control law is expressed as follows:

[0010]

[0011] In the formula: u sd_SMC u sq_SMC These are the d-axis and q-axis output voltages when sliding mode control is used in the STATCOM current inner loop; u d u q These are the d-axis and q-axis voltage components of the three-phase voltage of the grid-connected bus, respectively; R sh and L sh These are the equivalent resistance and equivalent inductance of the bus from STATCOM to the inverter side of the HVDC transmission system, respectively; ω is the synchronization angular frequency of the inverter side of the HVDC transmission system; i d i q These are the d-axis and q-axis current components of the three-phase reactive power compensation current on the AC side of the STATCOM, respectively; k pd k pq These are the scaling factors for the sliding surfaces of the d and q axes, respectively; λ d , λ q The switching gains of the d-axis and q-axis sliding surfaces are respectively; sd, s q The sliding surface functions of the d-axis and q-axis currents, respectively; φ d φ q The boundary layer thicknesses of the sliding surface saturation functions on the d and q axes are respectively; η d η q , respectively, are the exponents of the sliding surfaces on the d and q axes; k id k iq These are the integral coefficients of the sliding surfaces on the d and q axes, respectively; i dref This is the reference value for the d-axis current of the inner ring; i qrefThis is the reference value for the q-axis current of the inner loop.

[0012] Furthermore, the introduction of a sliding mode disturbance observer to estimate the actual disturbance specifically involves: designing a sliding mode disturbance observer; and adjusting the e in the sliding mode disturbance observer. d e q Taking the derivative, we obtain the error dynamic equation; where ed and e q The current errors are denoted as d-axis and q-axis, respectively. Based on the error dynamic equation, the equivalent compensation amount of the disturbance is derived to approximate the actual disturbance. Based on the approximate actual disturbance amount of the disturbance, low-pass filtering is used to extract the estimated values ​​of the actual disturbance of the d-axis and q-axis of the inner current loop.

[0013] Furthermore, the sliding mode disturbance observer is as follows:

[0014]

[0015] In the formula: Currents observed along the d and q axes, respectively. Rate of change over time; R sh and L sh These are the equivalent resistance and equivalent inductance of the STATCOM to the inverter-side bus of the high-voltage direct current transmission system; u d u q These are the d-axis and q-axis voltage components of the three-phase voltage of the grid-connected bus, respectively; u sd_SMC u sq_SMC These are the d-axis and q-axis output voltages when the STATCOM current inner loop uses sliding mode control, respectively; ω is the synchronization angular frequency on the inverter side of the high-voltage direct current transmission system; z d z q These are the equivalent compensation amounts for d-axis and q-axis disturbances, respectively; λ od , λ oq These are the gain coefficients of the d-axis and q-axis sliding mode disturbance observers, respectively; η od η oq These are the auxiliary coefficients for the d-axis and q-axis sliding mode disturbance observers, respectively; φ od φ oq , respectively, are the boundary layer thicknesses of the saturation functions in the d-axis and q-axis sliding mode perturbation observers.

[0016] Furthermore, the modified sliding mode control law is as follows:

[0017]

[0018] In the formula: u sd_SMC ′、u sq_SMC ′ represents the d-axis output voltage and q-axis output voltage after adding the disturbance voltage compensation from the sliding mode disturbance observer to the d-axis and q-axis of the sliding mode control law, respectively; u d u qThese are the d-axis and q-axis voltage components of the three-phase voltage of the grid-connected bus, respectively; R sh and L sh These are the equivalent resistance and equivalent inductance of the bus from STATCOM to the inverter side of the HVDC transmission system, respectively; ω is the synchronization angular frequency of the inverter side of the HVDC transmission system; i d i q These are the d-axis and q-axis current components of the three-phase reactive power compensation current on the AC side of the STATCOM, respectively; k pd k pq These are the scaling factors for the sliding surfaces of the d and q axes, respectively; λ d , λ q The switching gains of the d-axis and q-axis sliding surfaces are respectively; sd, s q The sliding surface functions of the d-axis and q-axis currents, respectively; φ d φ q The boundary layer thicknesses of the sliding surface saturation functions on the d and q axes are respectively; η d η q , respectively, are the exponents of the sliding surfaces on the d and q axes; k id k iq These are the integral coefficients of the sliding surfaces on the d and q axes, respectively; i dref This is the reference value for the d-axis current of the inner ring; i qref This is the reference value for the q-axis current of the inner loop; This represents the estimated value of the actual d-axis disturbance of the inner current loop by the sliding mode disturbance observer; This represents the estimated value of the actual disturbance on the q-axis of the inner current loop by the sliding mode disturbance observer.

[0019] According to a second aspect of the present invention, a terminal device is provided, including a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the method described in any one of the above.

[0020] According to a third aspect of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described above.

[0021] The beneficial effects of this invention are:

[0022] This invention constructs a novel STATCOM based on SMC-SMDO collaborative control, which incorporates a multi-objective sliding mode surface and achieves comprehensive optimization through exponential reaching laws. A sliding mode disturbance observer is introduced to mitigate the impact of disturbances, enabling rapid reactive power injection and enhanced commutation failure defense capabilities. Furthermore, the introduction of the sliding mode disturbance observer allows for the estimation and accurate compensation of system disturbances, significantly improving the accuracy of the STATCOM, effectively shortening fault recovery time, and significantly enhancing anti-interference capabilities. Further, the proposed SMC-SMDO collaborative control STATCOM was verified using the PSCAD / EMTDC simulation platform. It successfully suppressed the first commutation failure during a single-phase-to-ground short-circuit fault on the inverter side of a HVDC transmission system and successfully suppressed subsequent commutation failures during a three-phase short-circuit fault. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the principle of implementing this invention;

[0024] Figure 2 It is the time-domain model of STATCOM;

[0025] Figure 3 This is a diagram illustrating the implementation of sliding mode control in this invention;

[0026] Figure 4 This is a diagram of the STATCOM control strategy for SMC-SMDO collaboration of the present invention;

[0027] Figure 5 This is a simulation topology diagram of the STATCOM-HVDC co-system of the present invention;

[0028] Figure 6 It is the dynamic reactive power response of STATCOM under different control strategies;

[0029] Figure 7 It is a real-time disturbance observation of SMDO;

[0030] Figure 8 This is a diagram illustrating the effect of the present invention on suppressing commutation failure under a single-phase ground fault;

[0031] Figure 9 This is a diagram illustrating the effect of the present invention on commutation failure suppression under three-phase short-circuit faults;

[0032] Figure 10 This invention relates to the number of commutation failures under single-phase grounding short-circuit faults with different grounding resistances;

[0033] Figure 11 This invention measures the number of commutation failures under three-phase short-circuit faults with varying grounding resistances. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be arbitrarily combined with each other.

[0035] Example 1:

[0036] like Figures 1-11 As shown, a method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC includes: maintaining the voltage outer loop control of the STATCOM control circuit as PI control, and adopting sliding mode control (SMC) for the current inner loop control; the sliding mode control includes a sliding surface, an exponential reaching law, and a sliding mode control law; introducing a sliding mode disturbance observer to estimate the actual disturbance; and adding the actual disturbance estimated by the sliding mode disturbance observer to the sliding mode control law to construct a modified sliding mode control law.

[0037] Furthermore, the sliding mode control specifically involves designing the sliding surface as an independent s d and s q The integral sliding surface is derived; an exponential reaching law is designed; the derivative of the integral sliding surface is obtained; and the mathematical models of the exponential reaching law and STATCOM are substituted into the derivative expression of the integral sliding surface to obtain the sliding mode control law.

[0038] Furthermore, the introduction of a sliding mode disturbance observer to estimate the actual disturbance specifically involves: designing a sliding mode disturbance observer; and adjusting the e in the sliding mode disturbance observer. d e q Taking the derivative, we obtain the error dynamic equation; where ed and e q The current errors are denoted as d-axis and q-axis, respectively. Based on the error dynamic equation, the equivalent compensation amount of the disturbance is derived to approximate the actual disturbance. Based on the approximate actual disturbance amount of the disturbance, low-pass filtering is used to extract the estimated values ​​of the actual disturbance of the d-axis and q-axis of the inner current loop.

[0039] The following describes optional embodiments of the present invention:

[0040] S01: This study investigates the mathematical model of STATCOM and the mechanism by which STATCOM suppresses commutation failure on the inverter side of a high-voltage direct current (HVDC) transmission system. As a dynamic reactive power compensation device with low harmonic content, STATCOM, when connected in parallel to the inverter bus of an LCC-HVDC system, can compensate for reactive power deficits in real time, thus mitigating commutation failure. The time-domain model of STATCOM is as follows: Figure 2 As shown. Figure 2 in, udc and i dc These are the actual values ​​of the DC side voltage and current of the STATCOM; R sh and L sh These are the equivalent resistance and equivalent inductance of the STATCOM to the inverter-side bus of the high-voltage direct current transmission system; e a e b e c These are the AC phase voltages of the STATCOM, namely phases a, b, and c; i a i b i c These are the reactive power compensation currents for phases a, b, and c on the AC side of the STATCOM; u a u b u c These are the a, b, and c phase voltages of the grid-connected bus, respectively.

[0041] By transforming the STATCOM time-domain model in the dq0 rotating coordinate system and ignoring the 0 axis, the mathematical model of STATCOM is obtained as follows:

[0042]

[0043] In the formula: The d-axis current i d Rate of change with time, q-axis current i q Rate of change over time, DC side voltage u of STATCOM dc Rate of change over time; R sh and L sh These are the equivalent resistance and equivalent inductance of the STATCOM to the inverter-side bus of the high-voltage direct current transmission system; u d u q respectively for u a u b u c The d-axis and q-axis voltage components obtained by performing the Parker transform; u sd u sq respectively for e a e b e c The d-axis and q-axis voltage components obtained by performing the Park transform; i d i q For i respectively a i b i c The d-axis and q-axis current components obtained by Parker transformation; ω is the synchronization angular frequency on the inverter side of the LCC-HVDC transmission system; C is the DC-side capacitance of the STATCOM; u dc This refers to the DC side voltage of the STATCOM.

[0044] When a STATCOM is connected in parallel to the inverter side of an LCC-HVDC integrated STATCOM-HVDC system, the turn-off angle during the commutation process is as follows:

[0045]

[0046] In the formula, γ is the switching failure angle of the thyristor on the inverter side of the LCC-HVDC system; β is the firing angle of the thyristor on the inverter side of the LCC-HVDC system; X c I is the equivalent commutation reactance of the inverter-side commutation circuit in an LCC-HVDC system. d For the DC current of the LCC-HVDC system, U L ΔU represents the rated line voltage amplitude of the inverter-side bus in the LCC-HVDC system. ΔU is the voltage compensated by the STATCOM to the inverter-side bus in the LCC-HVDC system. That is, the connection of the STATCOM allows for rapid response to changes in the system's AC voltage, dynamically adjusting the transfer of reactive power. When the AC bus voltage on the inverter side decreases, the STATCOM quickly supplies inductive reactive power to increase the AC bus voltage, thereby preventing the turn-off angle from falling below the critical value and causing commutation failure.

[0047] S02: The STATCOM control circuit is designed with an outer voltage loop and an inner current loop. The outer voltage loop control remains a PI control. To avoid cross-coupling interference, control strategies are designed for active and reactive components respectively. The inner current loop control uses sliding mode control (SMC). The implementation of sliding mode control is as follows: Figure 3 As shown. The sliding mode control includes a sliding surface, an exponential reaching law, and a sliding mode control law. The sliding surface is designed as an independent s d and s q The integral sliding surface enhances the multi-objective cooperative suppression capability; when the system fails to commutate, the integral term corrects the control quantity through accumulated error, enhancing the adaptability to transient processes. Simultaneously, the integral action can compensate for system parameter uncertainties, reducing the dependence on model accuracy, which aligns with the application requirements of STATCOM in complex power grid environments. The integral sliding surface is as follows:

[0048]

[0049] In the formula: sd, s q These are the sliding surface functions of the d-axis current and the q-axis current, respectively; i dref The current reference value for the inner loop d-axis is derived from the DC-side voltage reference value U of the STATCOM. dcref Compared with the actual value u dc The difference is obtained after voltage outer loop PI control; i qref The current reference value for the inner loop q-axis is derived from the grid connection point voltage reference value U. pccref Compared with the actual value Upcc The difference is obtained through PI control; k pd k pq These are the scaling factors for the sliding surfaces of the d and q axes, respectively; k id k iq These are the integral coefficients of the sliding surfaces on the d and q axes, respectively.

[0050] The exponential reaching law, through its two-stage characteristics of "rapid reaching-smooth convergence" and the chattering suppression capability of the saturation function, balances the dynamic response speed and control smoothness required for STATCOM to suppress commutation failure. Its parameter adjustability and decoupling design further enhance the flexibility of multi-objective cooperative control. The exponential reaching law is designed as follows:

[0051]

[0052] In the formula: For s d s q The first derivatives of λ and q represent the exponential reaching laws of the d-axis current and the q-axis current, respectively. The exponential reaching law is the rate of change of the sliding surface; d , λ q The switching gains of the d-axis and q-axis sliding surfaces are respectively; sat is the saturation function; sd and s q The sliding surface functions of the d-axis and q-axis currents, respectively; φ d φ q The boundary layer thicknesses of the sliding surface saturation functions on the d and q axes are respectively; η d η q These are the exponential coefficients of the sliding surfaces on the d and q axes, respectively.

[0053] Differentiating the integral sliding surface yields its derivative expression; substituting the exponential reaching law and the mathematical model of STATCOM into this derivative expression, we obtain the sliding mode control law, which is expressed as follows:

[0054]

[0055] In the formula: u sd_SMC u sq_SMC These are the d-axis and q-axis output voltages when sliding mode control is used in the STATCOM current inner loop; u d u q respectively for u a u b u c The d-axis and q-axis voltage components obtained by performing the Parker transform; R sh and L sh These are the equivalent resistance and equivalent inductance of the STATCOM to the inverter-side bus of the high-voltage direct current transmission system; i d iq For i respectively a i b i c The d-axis and q-axis current components obtained by performing the Park transform; k pd k pq These are the scaling factors for the sliding surfaces of the d and q axes, respectively; λ d , λ q The switching gains for the d-axis and q-axis sliding surfaces are respectively; s d s q The sliding surface functions of the d-axis and q-axis currents, respectively; φ d φ q The boundary layer thicknesses of the sliding surface saturation functions on the d and q axes are respectively; η d η q , respectively, are the exponents of the sliding surfaces on the d and q axes; k id k iq These are the integral coefficients of the sliding surfaces on the d and q axes, respectively; i dref The current reference value for the inner loop d-axis is obtained by PI control of the difference between the STATCOM DC-side voltage reference value and the actual value; i qref ω is the reference current value of the inner loop q-axis, which is obtained by PI control from the difference between the reference voltage value and the actual value at the grid connection point; ω is the synchronous angular frequency of the inverter side of the high voltage direct current transmission system (LCC-HVDC).

[0056] Proof of the stability of sliding mode control:

[0057] Choosing Lyapunov functions Taking its derivative and substituting it into the exponential reaching law, we get:

[0058]

[0059] In the formula: V SMC Represented as a Lyapunov function; It is expressed as the derivative of the Lyapunov function.

[0060] Due to λ d >0, η d >0, λ q >0, η q >0, and by the definition of the saturation function, s d ·sat(s d / φ d )≥0(i=d,q), therefore If and only if s d =s q When = 0, According to Lyapunov's stability theorem, sliding mode control is asymptotically stable.

[0061] S03: The STATCOM system is affected by model uncertainties, external disturbances, and unmodeled dynamic disturbances. Considering the core cause of commutation failure in HVDC transmission after introducing unknown disturbances, the current loop dynamic equation of the STATCOM with sliding mode control acting as the inner current loop control is as follows:

[0062]

[0063] In the formula, d d d q These represent the actual disturbance along the d-axis and the actual disturbance along the q-axis, respectively. sd_SMC u sq_SMC These are the d-axis output voltage and q-axis output voltage for sliding mode control, respectively.

[0064] To ensure that the STATCOM outputs more accurate reactive current i during grid faults. q To maintain a rapid recovery of the grid voltage to normal, further reduce the inherent chattering of sliding mode control, and protect the power electronic devices of the STATCOM from high-frequency stress damage, a Sliding Mode Disturbance Observer (SMDO) is introduced to estimate disturbances and compensate for them to the sliding mode control input in real time. The design of the SMDO is as follows:

[0065]

[0066] In the formula: Currents observed along the d and q axes, respectively. Rate of change with respect to time; z d z q These are the equivalent compensation amounts for d-axis and q-axis disturbances, respectively; λ od , λ oq λ represents the gain coefficients of the d-axis and q-axis sliding mode disturbance observers, respectively, where λ od >|d d | max , λ oq >|d q | max ,|d d | max 、|d q | max These represent the maximum amplitudes of the actual disturbances along the d and q axes, respectively; η od η oq These are the auxiliary coefficients for the d-axis and q-axis sliding mode disturbance observers, respectively; φ od φ oq The boundary layer thicknesses of the saturation function in the d-axis and q-axis sliding mode perturbation observers are respectively; ed and e q These represent the d-axis and q-axis current errors, respectively. ( (The currents observed along the d and q axes are respectively).

[0067] For each of the sliding mode perturbation observers, e d e q Taking the derivative, we obtain the following dynamic equation for the error:

[0068]

[0069] When the STATCOM's inner current loop control enters the sliding mode surface, e d →0,e q →0, the equivalent compensation for the disturbance approximates the actual disturbance, hence d d ≈z d d q ≈z q Because of z d z q If it is a high-frequency switching signal, then a low-pass filter is needed to extract the estimated values ​​of the actual disturbances on the d and q axes of the inner current loop, as shown in the following formula:

[0070]

[0071] In the formula, This represents the estimated value of the actual d-axis disturbance of the inner current loop by the sliding mode disturbance observer; denoted as the sliding mode disturbance observer's estimate of the actual disturbance on the q-axis of the current inner loop; LPF(·) represents the low-pass filter; τ represents the time constant of the low-pass filter, which is much smaller than the dynamic response time of the STATCOM system; s represents the Laplace operator.

[0072] S04: The sliding mode control law incorporates disturbance compensation from SMDO to form a modified sliding mode control law, which is as follows:

[0073]

[0074] In the formula: u sd_SMC ′、u s q_SMC′ represents the d-axis output voltage and q-axis output voltage after adding the disturbance voltage compensation from the sliding mode disturbance observer to the d and q axes of the sliding mode control law, respectively.

[0075] SMC-SMDO coordinated STATCOM control strategy implementation as follows Figure 4 As shown, Figure 4 The upper part is the main circuit of the STATCOM, and the lower part is the control circuit. The control circuit consists of an outer voltage control loop and an inner current control loop. The main circuit requires the control circuit to drive it. The simulation topology of this new STATCOM, co-driven by SMC-SMDO, connected in parallel to the inverter side of a high-voltage direct current transmission system is shown below. Figure 5 As shown.

[0076] The invention will be described below with reference to the data:

[0077] I. Performance Verification of STATCOM (SMC-SMDO) Based on Sliding Mode Control and Disturbance Observer Coordination for Suppressing Commutation Failure in LCC-HVDC Proposed in This Invention

[0078] Experiments were conducted on three different controlled STATCOMs (where "Traditional" indicates that the inner loop of the STATCOM uses PI control; "SMC" indicates that the inner loop of the STATCOM uses sliding mode control; and "SMC-SMDO" indicates that the inner loop of the STATCOM uses sliding mode control in conjunction with a sliding mode disturbance observer, while the voltage outer loop control uses PI control). At 2.0s, the capacitive reactive power output of the STATCOM was set to 200Mvar for 1s. After it recovered to zero reactive power output and stabilized for 1s, the inductive reactive power output was set to 200Mvar at 4.0s for 1s. Then, the inductive reactive power output of the STATCOM was increased to 300Mvar for 1s. Finally, after 6s, the STATCOM stabilized at zero reactive power output. The dynamic response of the STATCOM under the three control conditions was compared, and the results are as follows: Figure 6 As shown. By Figure 6 It is evident that when PI control is used in the inner loop of the STATCOM, the reactive power response exhibits overshoot, slow response speed, and severe oscillation. When sliding mode control is used in the inner loop, the reactive power response speed is significantly improved, and the overshoot phenomenon is markedly reduced, but some oscillation still exists. When the inner loop uses sliding mode control in conjunction with a sliding mode disturbance observer, the sliding mode disturbance observer estimates system disturbances in real time and compensates for them in the sliding mode control. The dynamic reactive power response is rapid and overshoot-free, improving the response speed and compensation accuracy of the STATCOM's reactive power output, making the actual reactive power output of the STATCOM closer to its maximum output limit.

[0079] II. Performance Verification of the Sliding Mode Disturbance Observer

[0080] In the STATCOM-HVDC system, a fault disturbance is introduced at 2s and disappears at 2.2s. The real-time observation effect of the sliding mode disturbance observer on the disturbance is tested. The observation of the disturbance on the d-axis of the inner current loop by the sliding mode disturbance observer is as follows: Figure 7 As shown in the left figure, the observation of the perturbation on the q-axis of the inner current loop is as follows: Figure 7 As shown in the right figure ( Figure 7 The actual disturbance d in the middle left figure d The actual disturbance d in the right figure q ; Figure 7 The disturbance observed in the middle left figure The right figure shows the observed disturbance. ).Depend on Figure 7It can be seen that the disturbance observation curves of the sliding mode disturbance observer designed in this invention for the d-axis and q-axis basically coincide with the actual disturbance curves, indicating that the observer can accurately estimate the actual disturbance and achieve precise compensation.

[0081] III. Verification of Commutation Failure Suppression

[0082] Single-phase ground fault and three-phase short-circuit fault were set on the inverter side of the LCC-HVDC, and the commutation failure of the two schemes was compared. It is assumed that the AC bus on the inverter side has a fault at 2.0s, the fault duration is 0.3s, the fault resistance is 100Ω, the sampling frequency is 20kHz, and the total simulation time is 5s.

[0083] Option 1: The inverter-side AC bus is not connected to STATCOM.

[0084] Option 2: Connect the inverter-side AC bus to the STATCOM for SMC-SMDO collaborative control.

[0085] When a single-phase ground fault occurs in Scheme 1 and Scheme 2 respectively, the waveforms of each electrical quantity are as follows: Figure 8 As shown.

[0086] Depend on Figure 8 It is known that in high-voltage direct current transmission systems without STATCOM, when a minor fault such as a single-phase ground fault occurs, the DC voltage drops significantly to below 0, resulting in initial commutation failure. However, after connecting the STATCOM with SMC-SMDO coordinated control as designed in this invention, the voltage drop is effectively mitigated, increasing from -0.165 pu to 0.73 pu, and the turn-off angle increases from 0° to 8.198°, successfully suppressing initial commutation failure.

[0087] When a three-phase short-circuit fault occurs in Scheme 1 and Scheme 2 respectively, the changes in various electrical quantities are as follows: Figure 9 As shown.

[0088] Depend on Figure 9 It is known that in a high-voltage direct current transmission system without a STATCOM, when a relatively serious fault such as a three-phase short circuit occurs, the DC voltage drops to -0.84 pu at 2.32 seconds, and the LCC-HVDC system experiences subsequent commutation failure. However, after connecting the STATCOM with SMC-SMDO coordinated control designed in this invention, the voltage rises to 0.95 pu, effectively suppressing the occurrence of subsequent commutation failure. Furthermore, the voltage drop of the first commutation failure increases from -0.275 pu to 0.26 pu. The STATCOM designed in this invention has the potential to suppress the first commutation failure caused by a large degree of fault.

[0089] Single-phase ground faults and three-phase short-circuit faults with different fault resistances were set at the inverter side bus of the LCC-HVDC inverter. The ground resistance ranged from 50Ω to 150Ω, with a step size of 5Ω. The smaller the ground resistance, the more severe the fault level. The number of commutation failures under the same fault conditions was compared between the two schemes.

[0090] The number of commutation failures for the two schemes under a single-phase ground fault is as follows: Figure 10 As shown. Blue indicates the number of commutation failures when using Scheme 1, orange indicates the number of commutation failures when using Scheme 2, and gray indicates that the number of commutation failures is the same for both schemes. Figure 10 It is known that when a single-phase ground fault with a fault resistance of 50Ω-150Ω occurs on the AC bus of the inverter side, the system experiences initial commutation failure when the LCC-HVDC is not connected to the STATCOM. However, after connecting the STATCOM designed in this invention, the initial commutation failure is successfully suppressed, and no commutation failure occurs. The STATCOM designed in this invention effectively suppresses commutation failure caused by single-phase ground faults.

[0091] The number of commutation failures under two schemes in a three-phase short-circuit fault is as follows: Figure 11 As shown. Blue indicates the number of commutation failures when using Scheme 1, orange indicates the number of commutation failures when using Scheme 2, and gray indicates that the number of commutation failures is the same for both schemes. Figure 11 It is known that when a three-phase short-circuit fault with a fault resistance of 50Ω-150Ω occurs on the AC bus of the inverter side, and the LCC-HVDC is not connected to the STATCOM, the number of commutation failures decreases as the fault resistance increases. When the fault resistance is between 50Ω and 95Ω, the LCC-HVDC system experiences multiple commutation failures. When the fault resistance is between 95Ω and 150Ω, the system experiences only two commutation failures. When the AC bus of the inverter side is connected to the STATCOM designed in this invention, only the first commutation failure occurs. The STATCOM designed in this invention effectively suppresses subsequent commutation failures caused by three-phase short-circuit faults.

[0092] Example 2:

[0093] A terminal device includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps of any of the methods described in Embodiment 1. When the processor executes the program, it implements the following steps: adopting sliding mode control for the inner current loop of the STATCOM control circuit; introducing a sliding mode disturbance observer to estimate the actual disturbance; and adding the actual disturbance estimated from the sliding mode disturbance observer to the sliding mode control law to construct a modified sliding mode control law.

[0094] Example 3:

[0095] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described in Embodiment 1.

[0096] Optionally, in this embodiment, the computer-readable storage medium may be located in any computer terminal in a group of computer terminals in a computer network, and / or in any mobile terminal in a group of mobile terminals, and the computer-readable storage medium includes a stored program.

[0097] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0098] In the above embodiments of the present invention, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0099] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC, characterized in that, include: The current inner loop control of the STATCOM control circuit adopts sliding mode control; The sliding mode control includes the sliding surface, the exponential reaching law, and the sliding mode control law; A sliding mode disturbance observer is introduced to estimate the actual disturbance; By incorporating the actual disturbance estimated from the sliding mode disturbance observer into the sliding mode control law, a modified sliding mode control law is constructed.

2. The method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC according to claim 1, characterized in that, The sliding mode control specifically refers to: Design the sliding surface as independent sd and s q Integral sliding surface; Design index convergence law; By taking the derivative with respect to the integral sliding surface, we obtain the expression for the derivative of the integral sliding surface; Substituting the exponential reaching law and the mathematical model of STATCOM into the integral sliding surface derivative expression, the sliding mode control law is obtained.

3. The method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC according to claim 1, characterized in that, The sliding mode control law is expressed as follows: In the formula: u sd_SMC u sq_SMC These are the d-axis and q-axis output voltages when sliding mode control is used in the STATCOM current inner loop; u d u q These are the d-axis and q-axis voltage components of the three-phase voltage of the grid-connected bus, respectively; R sh and L sh These are the equivalent resistance and equivalent inductance of the bus from STATCOM to the inverter side of the HVDC transmission system, respectively; ω is the synchronization angular frequency of the inverter side of the HVDC transmission system; i d i q These are the d-axis and q-axis current components of the three-phase reactive power compensation current on the AC side of the STATCOM, respectively; k pd k pq These are the scaling factors for the sliding surfaces of the d and q axes, respectively; λ d , λ q The switching gains of the d-axis and q-axis sliding surfaces are respectively; sd, s q The sliding surface functions of the d-axis and q-axis currents, respectively; φ d φ q The boundary layer thicknesses of the sliding surface saturation functions on the d and q axes are respectively; η d η q , respectively, are the exponents of the sliding surfaces on the d and q axes; k id k iq These are the integral coefficients of the sliding surfaces on the d and q axes, respectively; i dref This is the reference value for the d-axis current of the inner ring; i qref This is the reference value for the q-axis current of the inner loop.

4. The method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC according to claim 1, characterized in that, The introduction of a sliding mode disturbance observer to estimate the actual disturbance is specifically as follows: Design a sliding mode perturbation observer; e in the sliding mode perturbation observer d e q Taking the derivative, we obtain the error dynamic equation; where ed and e q These are the d-axis and q-axis current errors, respectively. Based on the error dynamic equation, the equivalent compensation amount for the disturbance is derived to approximate the actual disturbance; Based on the approximation of the actual disturbance by the equivalent compensation amount, low-pass filtering is used to extract the estimated values ​​of the actual disturbances on the d and q axes of the inner current loop.

5. The method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC according to claim 4, characterized in that, The sliding mode disturbance observer is as follows: In the formula: The observed currents along the d and q axes are respectively. Rate of change over time; R sh and L sh These are the equivalent resistance and equivalent inductance of the STATCOM to the inverter-side bus of the high-voltage direct current transmission system; u d u q These are the d-axis and q-axis voltage components of the three-phase voltage of the grid-connected bus, respectively; u sd_SMC u sq_SMC These are the d-axis and q-axis output voltages of the STATCOM current inner loop when sliding mode control is used, respectively; ω is the synchronization angular frequency on the inverter side of the HVDC transmission system; zd, z q These are the equivalent compensation amounts for d-axis and q-axis disturbances, respectively; λ od , λ oq These are the gain coefficients of the d-axis and q-axis sliding mode disturbance observers, respectively; η od η oq These are the auxiliary coefficients for the d-axis and q-axis sliding mode disturbance observers, respectively; φ od φ oq , respectively, are the boundary layer thicknesses of the saturation functions in the d-axis and q-axis sliding mode perturbation observers.

6. The method for constructing a STATCOM that combines sliding mode control and a disturbance observer to suppress commutation failure in LCC-HVDC according to claim 1, characterized in that, The modified sliding mode control law is as follows: In the formula: u sd_SMC ′、u s q_SMC′ represents the d-axis and q-axis output voltages after adding disturbance voltage compensation from the sliding mode disturbance observer to the d and q axes of the sliding mode control law, respectively; u d u q These are the d-axis and q-axis voltage components of the three-phase voltage of the grid-connected bus, respectively; R sh and L sh These are the equivalent resistance and equivalent inductance of the bus from STATCOM to the inverter side of the HVDC transmission system, respectively; ω is the synchronization angular frequency of the inverter side of the HVDC transmission system; i d i q These are the d-axis and q-axis current components of the three-phase reactive power compensation current on the AC side of the STATCOM, respectively; k pd k pq These are the scaling factors for the sliding surfaces of the d and q axes, respectively; λ d , λ q The switching gains for the d-axis and q-axis sliding surfaces are respectively; s d s q These are the sliding surface functions of the d-axis and q-axis currents, respectively; φ d φ q The boundary layer thicknesses of the sliding surface saturation functions on the d and q axes are respectively; η d η q , respectively, are the exponents of the sliding surfaces on the d and q axes; k id k iq These are the integral coefficients of the sliding surfaces on the d and q axes, respectively; i dref This is the reference value for the d-axis current of the inner ring; i qref This is the reference value for the q-axis current of the inner loop; This represents the estimated value of the actual d-axis disturbance of the inner current loop by the sliding mode disturbance observer; This represents the estimated value of the actual disturbance on the q-axis of the inner current loop by the sliding mode disturbance observer.

7. A terminal device, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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