Adaptive control method for transient stability of hybrid synchronous control inverter

Abstract

The invention discloses a self-adaptive control method for transient stability of a hybrid synchronous control inverter, relates to the technical field of transient stability control of a new energy power generation system, and aims at a transient instability phenomenon based on the hybrid synchronous control inverter under a serious asymmetric fault, self-adaptively injecting positive sequence current and negative sequence current of the inverter, and improving the transient stability of the hybrid synchronous control inverter. The transient stability of the hybrid synchronous control inverter under the asymmetric fault is improved; according to the method, the balance of the system after a serious asymmetric fault occurs can be ensured, the transient stability of the flexible interconnection equipment is enhanced, the influence of positive and negative sequence current on the transient stability is analyzed based on a phase diagram, and the safe operation of the system is greatly improved by designing a self-adaptive current injection strategy; practical application is facilitated, and stable operation of new energy grid connection is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of transient stability control of a new energy power generation system, and in particular to an adaptive control method for transient stability of a hybrid synchronous control inverter. Background Art

[0002] With the increasing penetration rate of new energy in modern power grids, the power electronic characteristics of power systems are more prominent, and the grid structure and operation mode of power systems are undergoing profound changes. The access of high-proportion distributed energy has a serious impact on the safety and stability of power systems. The existing new power system lacks support capabilities, and most of the equipment relying on new energy generation is current source-type. Therefore, the active support capacity for the voltage of the power system is insufficient, and the voltage stability problem of the system is more prominent. Voltage source converters (VSG) can realize bidirectional power flow and four-quadrant operation. Compared with the low inertia of grid following control (GFLC), grid forming control (GFMC) technology can give full play to the flexible and controllable advantages of VSG, and show good adaptability and stability to weak and even extremely weak power grids. It can independently and quickly build system voltage in weak power grids, compensate for the inherent inertial damping characteristics of the system, and provide reliable voltage and frequency support for the system. However, GFMC actively establishes frequency by simulating traditional synchronous machines. Therefore, under large interference, GFMC may also experience transient instability similar to synchronous generators. In addition, since power electronic devices cannot withstand large transient currents, the controller must set a current limiting link, which will result in a low transient stability margin of the grid-type VSG and a high risk of system instability.

[0003] In view of the transient instability phenomenon of grid-type control under large disturbances, a large number of literatures have proposed transient stability enhancement strategies. Existing literatures often follow the following two ideas to improve its transient stability: one is to reduce the risk of the converter losing the balance point under faults, such as reducing the active power set value after the fault; the other is to optimize the dynamic response of the converter to avoid transient instability due to crossing the unstable balance point during the dynamic process, such as control parameter optimization design. In order to improve the transient stability of the grid-type VSG control strategy under large disturbance faults, a hybrid synchronous control strategy is proposed. However, when an asymmetric fault occurs, the transient stability of the hybrid synchronous control is affected due to current limitation and the presence of positive and negative sequence components in the grid voltage and current. Summary of the invention

[0004] The purpose of the present invention is to provide an adaptive control method for the transient stability of a hybrid synchronous control inverter. According to the system model of the hybrid synchronous control inverter and its transient instability mechanism under asymmetric faults, an adaptive control module is designed to improve the transient stability of the inverter, thereby solving the problem of poor transient stability of the hybrid synchronous control.

[0005] The present invention is achieved through the following technical solutions:

[0006] An adaptive control method for transient stability of a hybrid synchronous control inverter, comprising:

[0007] Collect the three-phase voltage, three-phase current and frequency of active loop output on the outlet side of the hybrid synchronous control inverter under normal / faulty operation;

[0008] A hybrid synchronous control structure of the inverter is constructed based on a control strategy combining positive sequence control and negative sequence control, and a HSC-VSC hybrid synchronous control inverter system model is constructed according to the hybrid synchronous control structure;

[0009] Based on the three-phase voltage, three-phase current, frequency of active loop output and HSC-VSC hybrid synchronous control inverter system model, the control signal of the inverter is adaptively determined, and the inverter is adaptively controlled according to the control information.

[0010] In a possible implementation, a hybrid synchronous control structure of an inverter is constructed based on a control strategy combining positive sequence control and negative sequence control, and a HSC-VSC hybrid synchronous control inverter system model is constructed according to the hybrid synchronous control structure, including:

[0011] Constructing a positive sequence control substructure, a negative sequence control substructure and a control signal generation substructure, and using the output of the positive sequence control substructure and the output of the negative sequence control substructure as inputs of the control signal generation substructure to obtain a hybrid synchronous control structure;

[0012] The grid simulation structure is constructed and combined with the hybrid synchronous control structure to obtain the HSC-VSC hybrid synchronous control inverter system model.

[0013] In a possible implementation manner, the positive sequence control substructure includes a power processing unit, a voltage inner loop, a first current inner loop and a first conversion unit;

[0014] The power processing unit includes a hybrid synchronization ring and a reactive droop controller;

[0015] The hybrid synchronization ring is used to generate positive sequence active power and positive sequence active power reference value P ref +The input and output positive sequence voltage reference phase θ HSC ;

[0016] The reactive power droop controller is used to control the positive sequence reactive power Q and the positive sequence reactive power reference value Q ref + is the input and output positive sequence voltage reference value E dref ;

[0017] Among them, the positive sequence reactive power Q and the positive sequence active power The acquisition method is as follows: the three-phase voltage and three-phase current output at the inverter outlet side are decoupled by positive and negative sequence to obtain the positive sequence component and negative sequence component of the voltage, and the positive sequence component and negative sequence component of the current; according to the positive sequence component of the voltage and the positive sequence component of the current, the positive sequence reactive power Q and the positive sequence active power are determined.

[0018] The voltage inner loop is used to reference the positive sequence voltage phase θ HSC With positive sequence voltage reference value E dref The input and output d-axis positive sequence current reference value I drefp1 And the q-axis positive sequence current reference value I qrefp1 ;

[0019] The first current inner loop is used to use the d-axis positive sequence current reference value I drefp1 And the q-axis positive sequence current reference value I qrefp1 is the input, and the output d-axis positive sequence voltage m dp And the q-axis positive sequence voltage m qp ;

[0020] The first conversion unit is used to use the positive sequence voltage reference phase θ HSC , d-axis positive sequence voltage m dp And the q-axis positive sequence voltage m qp As input, synthesize the voltage in the dq coordinate system to obtain the positive sequence synthesized voltage m abcp .

[0021] In a possible implementation manner, the data processing flow of the hybrid synchronization ring includes:

[0022] The collected three-phase voltage is processed by the first DSOGI module and the first PNSC module in turn to obtain the positive sequence voltage component

[0023] The positive sequence voltage component After being processed by the first PARK conversion module and the proportional regulator, the angular velocity deviation Δω of the PLL is obtained. PLL ;

[0024] The active power reference value P ref + Positive sequence active power Subtract and process through transfer function to get the angular velocity deviation value Δω of VSG. VSG ;

[0025] The angular velocity deviation of the PLL is Δω PLL Angular velocity deviation from VSG Δω VSG After addition and processing by the first integrator, the positive sequence voltage reference phase θ is obtained. HSC ;

[0026] Among them, the positive sequence voltage reference phase θ HSC is fed back to the first PARK conversion module so that the positive sequence voltage reference phase θ HSC With positive sequence voltage component Perform joint processing.

[0027] In a possible implementation manner, the negative sequence control substructure includes a phase locked loop, a second current inner loop and a second conversion unit;

[0028] The phase-locked loop is used to generate the negative-sequence voltage d-axis component U qn is the input, output negative sequence voltage phase θ n ;

[0029] The second current inner loop is used to use the d-axis negative sequence voltage reference value I drefn1 And the q-axis negative sequence voltage reference value I qrefn1 is the input, and the output d-axis negative sequence voltage m dn And the q-axis negative sequence voltage m qn ;

[0030] The second conversion unit is used to convert the negative sequence voltage phase θ n , d-axis negative sequence voltage m dn And the q-axis negative sequence voltage m qn As input, synthesize the voltage in the dq coordinate system to obtain the negative sequence synthesized voltage m abcn .

[0031] In a possible implementation manner, the data processing flow of the phase-locked loop includes:

[0032] The collected three-phase voltage is processed by the second DSOGI module and the second PNSC module in turn to obtain the negative sequence voltage component

[0033] The negative sequence voltage component After being processed by the second PARK conversion module, the negative sequence voltage d-axis component U is obtained. qn;

[0034] The negative sequence voltage d-axis component U qn After the proportional integral processing, subtraction from the angular velocity reference value ω0 and the second integrator processing, the negative sequence voltage phase θ is obtained. n ;

[0035] Among them, the negative sequence voltage phase θ n is fed back to the second PARK conversion module so that the negative sequence voltage phase θ n With negative sequence voltage component Perform joint processing.

[0036] In a possible implementation manner, the control signal generation substructure includes a signal synthesis unit and a PWM modulation unit;

[0037] The signal synthesis unit is used to synthesize the positive sequence voltage m abcp Combined with negative sequence voltage m abcn Add together to get the desired voltage modulation signal m abc ;

[0038] The PWM modulation unit is used to modulate the desired voltage signal m abc Perform PWM modulation to generate control signals for the switching tubes in the inverter.

[0039] In a possible implementation manner, the control signal output by the hybrid synchronous control structure is connected to the switch tube of the inverter in the power grid simulation structure.

[0040] In a possible implementation manner, based on the three-phase voltage, the three-phase current, the frequency of the active loop output and the HSC-VSC hybrid synchronous control inverter system model, the control signal of the inverter is adaptively determined, including:

[0041] It is determined whether the frequency of the active loop output is greater than the preset frequency threshold. If so, the three-phase voltage and the three-phase current are processed as the input of the HSC-VSC hybrid synchronous control inverter system model to determine the control signal of the inverter output by the hybrid synchronous control structure in the HSC-VSC hybrid synchronous control inverter system model. Otherwise, the system is determined to be transiently unstable, and the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value are adaptively adjusted. The HSC-VSC hybrid synchronous control inverter system model is controlled according to the adjusted d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value to adaptively determine the control signal of the inverter and pull the inverter back to a transient stable state.

[0042] In a possible implementation, adaptively adjusting the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value, and the q-axis negative-sequence voltage reference value includes:

[0043] The state space equation of the system before and after the fault is established, and the stability domain of the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value is determined by the phase diagram method, and the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value are adjusted back to the boundary of the stability domain.

[0044] The present invention provides an adaptive control method for the transient stability of a hybrid synchronous control inverter. Aiming at the transient instability phenomenon based on the hybrid synchronous control inverter under severe asymmetric faults, the positive sequence current and negative sequence current of the inverter are adaptively injected, thereby improving the transient stability of the hybrid synchronous control inverter under asymmetric faults; it can ensure the balance of the system after a severe asymmetric fault occurs, enhance the transient stability of the flexible interconnected equipment, analyze the influence of positive and negative sequence currents on transient stability based on phase diagrams, and design an adaptive current injection strategy, which greatly improves the safe operation of the system; it is easy to apply in practice, thereby ensuring the stable operation of new energy grid connection. 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 A flow chart of an adaptive control method for transient stability of a hybrid synchronous control inverter provided by an embodiment of the present invention;

[0047] Figure 2 A schematic diagram of the structure of a HSC-VSC hybrid synchronous control inverter system model provided by an embodiment of the present invention;

[0048] Figure 3 A block diagram of a hybrid synchronous ring control provided by an embodiment of the present invention;

[0049] Figure 4 A negative sequence phase locked loop control block diagram provided by an embodiment of the present invention;

[0050] Figure 5 An adaptive control block diagram provided by an embodiment of the present invention;

[0051] Figure 6(a) is a flow chart of the embodiment of the present invention showing the injection of I after a fault occurs. qp =0,I dn =0,I qn =0, different I dp Phase diagram waveform when ;

[0052] Figure 6 (b) After the fault is provided in the embodiment of the present invention, when I is injected dp =57A,I dn =0,I qn =0, different I qp Phase diagram waveform when ;

[0053] Figure 6 (c) After the fault is provided in the embodiment of the present invention, when I dp =57A,I qp =0,I qn =0, different I dn Phase diagram waveform when ;

[0054] Figure 6 (d) After the fault is provided in the embodiment of the present invention, when I is injected dp =57A,I qp =0,I dn =0, different I qn Phase diagram waveform when ;

[0055] Figure 7 (a) is a simulation waveform of the frequency and the dq-axis components of the positive and negative sequence current when there is no adaptive control module after a fault provided by an embodiment of the present invention;

[0056] Figure 7 (b) is the simulated waveform of the frequency and the dq-axis components of the positive and negative sequence current when the adaptive control module is added after a fault provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0057] 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.

[0058] like Figure 1 As shown, an embodiment of the present invention provides an adaptive control method for transient stability of a hybrid synchronous control inverter, comprising:

[0059] S101, collecting the three-phase voltage, three-phase current and frequency of the active loop output at the outlet side of the hybrid synchronous control inverter under normal / faulty operation;

[0060] S103, constructing a hybrid synchronous control structure of the inverter based on a control strategy combining positive sequence control and negative sequence control, and constructing a HSC-VSC hybrid synchronous control inverter system model (Hybrid Synchronous Control converter, HSC-VSG) according to the hybrid synchronous control structure;

[0061] S103, based on the three-phase voltage, three-phase current, frequency of active loop output and HSC-VSC hybrid synchronous control inverter system model, adaptively determine the control signal of the inverter, and adaptively control the inverter according to the control information.

[0062] The present invention provides an adaptive control method for the transient stability of a hybrid synchronous control inverter. Aiming at the transient instability phenomenon based on the hybrid synchronous control inverter under severe asymmetric faults, the positive sequence current and negative sequence current of the inverter are adaptively injected, thereby improving the transient stability of the hybrid synchronous control inverter under asymmetric faults; it can ensure the balance of the system after a severe asymmetric fault occurs, enhance the transient stability of the flexible interconnected equipment, analyze the influence of positive and negative sequence currents on transient stability based on phase diagrams, and design an adaptive current injection strategy, which greatly improves the safe operation of the system; it is easy to apply in practice, thereby ensuring the stable operation of new energy grid connection.

[0063] In a possible implementation, a hybrid synchronous control structure of an inverter is constructed based on a control strategy combining positive sequence control and negative sequence control, and a HSC-VSC hybrid synchronous control inverter system model is constructed according to the hybrid synchronous control structure, including:

[0064] Constructing a positive sequence control substructure, a negative sequence control substructure and a control signal generation substructure, and using the output of the positive sequence control substructure and the output of the negative sequence control substructure as inputs of the control signal generation substructure to obtain a hybrid synchronous control structure;

[0065] The grid simulation structure is constructed and combined with the hybrid synchronous control structure to obtain the HSC-VSC hybrid synchronous control inverter system model.

[0066] like Figure 2 As shown, the positive sequence control substructure includes a power processing unit, a voltage inner loop, a first current inner loop and a first conversion unit;

[0067] The power processing unit includes a hybrid synchronization ring and a reactive droop controller;

[0068] The hybrid synchronization ring is used to generate positive sequence active power and positive sequence active power reference value P ref + The input and output positive sequence voltage reference phase θHSC ;

[0069] The reactive power droop controller is used to control the positive sequence reactive power Q and the positive sequence reactive power reference value Q ref + is the input and output positive sequence voltage reference value E dref ; Among them, the positive sequence reactive power Q and the positive sequence active power The acquisition method is as follows: the three-phase voltage and three-phase current output at the inverter outlet side are decoupled by positive and negative sequence to obtain the positive sequence component and negative sequence component of the voltage, and the positive sequence component and negative sequence component of the current; according to the positive sequence component of the voltage and the positive sequence component of the current, the positive sequence reactive power Q and the positive sequence active power are determined.

[0070] The voltage inner loop is used to reference the positive sequence voltage phase θ HSC With positive sequence voltage reference value E dref The input and output d-axis positive sequence current reference value I drefp1 And the q-axis positive sequence current reference value I qrefp1 ;

[0071] The first current inner loop is used to use the d-axis positive sequence current reference value I drefp1 And the q-axis positive sequence current reference value I qrefp1 is the input, and the output d-axis positive sequence voltage m dp And the q-axis positive sequence voltage m qp ;

[0072] The first conversion unit is used to use the positive sequence voltage reference phase θ HSC , d-axis positive sequence voltage m dp And the q-axis positive sequence voltage m qp As input, synthesize the voltage in the dq coordinate system to obtain the positive sequence synthesized voltage m abcp .

[0073] The constructed system model of HSC-VSG connected to infinite power grid is as follows: Figure 2 As shown, it includes the main circuit part and the control circuit part. The main circuit part, V dc is the DC bus voltage; L f is the filter inductor; C f is the filter capacitor; X g1 , X g2 and R g is the reactance and resistance on the grid side; u abc and i abc are the three-phase voltage and current at the PCC (Point of Common Coupling); u gabcis the grid voltage; the control loop includes a positive sequence control loop and a negative sequence control loop. The positive sequence loop mainly includes a hybrid synchronous control loop with positive and negative sequence decoupling, a reactive droop control loop, a voltage inner loop and a current inner loop. Among them, the positive sequence active power P output by the inverter at the grid connection point is calculated based on the grid connection point voltage and current measured in step 1. e + and reactive power Q, a hybrid synchronous control loop with positive and negative sequence decoupling is Figure 3 As shown, based on the voltage at the PCC measured in step 1, the positive sequence voltage component is obtained through the DSOGI and PNSC modules. is the component of the positive sequence PCC voltage in the αβ coordinates. After PARK transformation, the positive sequence q-axis voltage component combined with the active power reference value P is obtained. ref + And the output active power P e + As the input of the hybrid synchronization loop, the output positive sequence voltage reference phase θ HSC .

[0074] like Figure 3 As shown, the data processing flow of the hybrid synchronization ring includes:

[0075] The collected three-phase voltage is processed by the first DSOGI (based on dual second-order generalized integrator) module and the first PNSC (positive and negative sequence calculation) module to obtain the positive sequence voltage component.

[0076] The positive sequence voltage component After being processed by the first PARK (Park transform) conversion module and the proportional regulator, the angular velocity deviation Δω of the PLL is obtained. PLL ;

[0077] The active power reference value P ref + Positive sequence active power Subtract and process through transfer function to get the angular velocity deviation value Δω of VSG. VSG ;

[0078] In the embodiment of the present invention, the reference value is obtained by presetting.

[0079] The angular velocity deviation of the PLL is Δω PLL Angular velocity deviation from VSG Δω VSG After addition and processing by the first integrator, the positive sequence voltage reference phase θ is obtained. HSC ;

[0080] Among them, the positive sequence voltage reference phase θ HSCis fed back to the first PARK conversion module so that the positive sequence voltage reference phase θ HSC With positive sequence voltage component Perform joint processing.

[0081] In a possible implementation manner, the negative sequence control substructure includes a phase locked loop, a second current inner loop and a second conversion unit;

[0082] The phase-locked loop is used to generate the negative-sequence voltage d-axis component U qn is the input, output negative sequence voltage phase θ n ;

[0083] The second current inner loop is used to use the d-axis negative sequence voltage reference value I drefn1 And the q-axis negative sequence voltage reference value I qrefn1 is the input, and the output d-axis negative sequence voltage m dn And the q-axis negative sequence voltage m qn ;

[0084] Among them, the d-axis negative sequence voltage reference value I drefn1 And the q-axis negative sequence voltage reference value I qrefn1 It is the default value and is 0 in normal operation.

[0085] The second conversion unit is used to convert the negative sequence voltage phase θ n , d-axis negative sequence voltage m dn And the q-axis negative sequence voltage m qn As input, synthesize the voltage in the dq coordinate system to obtain the negative sequence synthesized voltage m abcn .

[0086] like Figure 4 As shown, the data processing flow of the phase-locked loop includes:

[0087] The collected three-phase voltage is processed by the second DSOGI module and the second PNSC module in turn to obtain the negative sequence voltage component

[0088] The negative sequence voltage component After being processed by the second PARK conversion module, the negative sequence voltage d-axis component U is obtained. qn ;

[0089] The negative sequence voltage d-axis component U qn After the proportional integral processing, subtraction from the angular velocity reference value ω0 and the second integrator processing, the negative sequence voltage phase θ is obtained. n ;

[0090] Among them, the negative sequence voltage phase θ nis fed back to the second PARK conversion module so that the negative sequence voltage phase θ n With negative sequence voltage component Perform joint processing.

[0091] In a possible implementation manner, the control signal generation substructure includes a signal synthesis unit and a PWM modulation unit;

[0092] The signal synthesis unit is used to synthesize the positive sequence voltage m abcp Combined with negative sequence voltage m abcn Add together to get the desired voltage modulation signal m abc ;

[0093] The PWM modulation unit is used to modulate the desired voltage signal m abc Perform PWM modulation to generate control signals for the switching tubes in the inverter.

[0094] In a possible implementation manner, the control signal output by the hybrid synchronous control structure is connected to the switch tube of the inverter in the power grid simulation structure.

[0095] In a possible implementation manner, based on the three-phase voltage, the three-phase current, the frequency of the active loop output and the HSC-VSC hybrid synchronous control inverter system model, the control signal of the inverter is adaptively determined, including:

[0096] It is determined whether the frequency of the active loop output is greater than the preset frequency threshold. If so, the three-phase voltage and the three-phase current are processed as the input of the HSC-VSC hybrid synchronous control inverter system model to determine the control signal of the inverter output by the hybrid synchronous control structure in the HSC-VSC hybrid synchronous control inverter system model. Otherwise, the system is determined to be transiently unstable, and the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value are adaptively adjusted. The HSC-VSC hybrid synchronous control inverter system model is controlled according to the adjusted d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value to adaptively determine the control signal of the inverter and pull the inverter back to a transient stable state.

[0097] like Figure 5 As shown, the frequency value collected in step 1 is compared with the frequency threshold 53.6Hz. When the frequency is greater than 53.6Hz, the reference value I of the injected positive and negative sequence dq axis current component is adaptively adjusted. drefp1 ,I qrefp1 ,I drefn1 and I qrefn1 , pulling the system “back” to the transient stable state.

[0098] When the system frequency is less than 53.6Hz, the system positive sequence current input is the output value of the voltage loop I drefp1 and I qrefp1 , the negative sequence current input is i drefn1 and i qrefn1 That is, in normal state, the three-phase voltage and three-phase current are input normally and controlled by the HSC-VSC hybrid synchronous control inverter system model. When the system frequency is greater than 53.6Hz, the system is transiently unstable and it is necessary to inject positive and negative sequence currents into the system to enhance the system stability. After the adaptive control link, the positive sequence current input is adaptively adjusted to I drefp2 and I qrefp2 , the negative sequence current is adaptively adjusted to I drefn2 and I qrefn2 .

[0099] In a possible implementation, adaptively adjusting the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value, and the q-axis negative-sequence voltage reference value includes:

[0100] The state space equation of the system before and after the fault is established, and the stability domain of the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value is determined by the phase diagram method, and the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value are adjusted back to the boundary of the stability domain.

[0101] Based on the established adaptive control link, a mathematical model of hybrid synchronous control for normal operation and after a fault occurs is constructed and a state space equation is created, where the initial quantity x1=δ=0 during normal operation, x3=U=311V, (where δ is the virtual power angle, is the first-order derivative of the hybrid synchronous control output angular velocity deviation / δ, and U is the voltage amplitude at the PCC. ) The initial value of the state variable after the fault occurs is the value just before the fault. With the help of the phase diagram method, the mathematical boundary of positive and negative sequence currents to ensure transient stability is quantitatively analyzed.

[0102] Based on the established system model, a mathematical model of pre-fault hybrid synchronous control is constructed, with virtual power angle δ and angular velocity deviation as The state space equation before the fault occurs is constructed with the voltage amplitude U as the state variable, where the initial quantity x1=δ=0, =0, x3=U=311V. Before the fault occurs, the inverter operates normally and there is no negative sequence component. The q-axis component U of the voltage at PCC is qpAs a feedback quantity added to the active loop of VSG control, the added voltage-based synchronization loop uses the phase angle difference to resist the frequency deviation. Its control law can be expressed as:

[0103]

[0104] Where δ = θ HSC -θ g ,θ HSC and θ g are the phase angle of the hybrid synchronous loop output and the phase angle of the power grid during normal operation, ω HSC is the HSC-VSG output angular velocity, ω0 is the angular velocity reference value, Δω VSG is the angular velocity deviation of VSG, Δω PLL is the angular velocity deviation of PLL. J is the virtual inertia, D is the damping coefficient, K p Instead of representing the proportional coefficient of the PI controller in the PLL, P ref is the active power reference value during normal operation, U qp is the q-axis component of the PCC voltage, s is the differential operator, and 1 / s is the integral operator.

[0105] Due to the normal operation, it can be considered that U qp =0, so the hybrid synchronous loop is approximately equivalent to the VSG control mode during normal operation, and the control law of the reactive loop is:

[0106]

[0107] Where U is the voltage amplitude at PCC, K Q is the reactive integral coefficient; Q ref is the reactive power reference value; Q is the system output reactive power; U0 is the voltage amplitude reference value at PCC. Figure 1 It can be calculated that the system output active power and reactive power during normal operation are:

[0108]

[0109] Among them, U g For the amplitude of the grid voltage, define a three-dimensional state variable x1 = δ, x3=U, and substituting equation (3) into equation (1) and equation (2) yields the state space equation before the fault:

[0110]

[0111] Among them, the initial values ​​of the state variables are x1=δ=0, x3=U=311V.

[0112] Based on the system model established in step 3, the mathematical model of hybrid synchronous control when an asymmetric fault occurs (taking a single-phase grounding fault as an example) is derived. Figure 2 As shown, the control law of the hybrid synchronization loop under asymmetric fault can be obtained:

[0113]

[0114] Among them, δ p is the positive sequence virtual power angle after the fault, and the positive sequence active power is U dp and U qp are the dq axis components of the PCC positive sequence voltage, I dp and I qp are the dq axis components of the PCC positive sequence current respectively. According to the superposition principle, U p and U n The voltage is:

[0115]

[0116] Among them, Z i =|Z i |∠Φ i , i=1,2,3,4,5,6,|·| represents the modulus value, Φ i represents the angle, and the specific expression is shown in Table 1.

[0117] Table 1Z i Expressions under different asymmetric faults

[0118]

[0119]

[0120] |I p |and|I n | are the amplitudes of the positive sequence current and negative sequence current at PCC, respectively, θ Ip and θ In are the phases of the positive sequence current and the negative sequence current, θ HSCp and θ gp are the phase angle of the positive sequence control hybrid synchronous loop output and the phase angle of the power grid when a fault occurs, θ n -θ gn are the phase angle of the negative sequence phase locked loop output and the negative sequence phase angle of the grid voltage when a fault occurs, respectively. According to the principle of PARK transformation, equation (6) is transformed into a rotating coordinate system to obtain equation (7).

[0121]

[0122] In the formula, δ p =θHSCp -θ gp , δ n =θ n -θ gn is the negative sequence virtual power angle after the fault, and the q-axis components U of the positive and negative sequence voltage at the PCC can be obtained. qp , U qn They are:

[0123]

[0124] Substituting equation (8) into equation (5), we can obtain the positive sequence HSC kinetic equation:

[0125]

[0126] in, is δ p The second-order derivative, X1 = Z1sinΦ1, R1 = Z1cosΦ1, X2 = Z2sinΦ2, R2 = Z2cosΦ2, I dn and I qn are the components of the negative sequence current at PCC in dq coordinates. In order to simplify the calculation of the output active power, the line resistance is not considered, and the equation (8) ignoring the positive and negative sequence coupling terms is substituted into We can get:

[0127]

[0128] Combining equations (7), (9) and (10), we can obtain the state space equation after the fault occurs:

[0129]

[0130] Where U p is the positive sequence voltage amplitude at PPC, d(·) / dt represents the first-order derivative, d 2 (·) / dt 2 Indicates the second-order derivative. Based on the established state equation, the system parameters are shown in Table 2.

[0131] Table 2 System parameters

[0132]

[0133]

[0134] The system operates normally within t = 0 ~ 0.5s, executing the state equation shown in equation (4), with the initial quantity x1 = δ = 0, x3=U=311V. At t=0.5s, a single-phase ground fault occurs, and the state equation shown in equation (11) is executed. The initial state of equation (11) is the state of equation (4) at t=0.5s. The result is Figure 6 As shown by Figure 6 (a) It can be seen that increasing I dp It is detrimental to the stability of the system. dp When it increases to 54A, the system becomes unstable. Figure 6 (b) indicates that the reduction of I qp It is conducive to system stability. qp When it is reduced to -5A, the system is stable. Figure 6 (c) indicates an increase in I dn It is beneficial to improve the stability of the system. qp Increased to 11A, the system became stable. Figure 6 (d) indicates that the increase of I qn It is conducive to the stability of the system and the stability boundary is when I qn When increased to 13A.

[0135] Among them, the solved I dp As I drefp , solve for I qp As I qrefp2 , solve for I dn As I drefn2 , solve for I qn As I qrefn2 .

[0136] Based on the above analysis method, simulation verification was carried out. Figure 7 is the simulation result, Figure 7 (a) is the simulation result without adaptive control module. It can be seen that the system becomes unstable after the fault. Figure 7 (b) shows the positive-sequence dq-axis current and negative-sequence dq-axis current of the adaptive control system after the fault, which are 54A, -1A, 7A and 7A. It can be seen from the figure that the system does not suffer from transient instability. Therefore, when a fault occurs, the transient stability of the system can be enhanced by adaptively adjusting the size of the injected current through real-time detection of the frequency.

[0137] 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 control method for transient stability of a hybrid synchronous control inverter, characterized in that: include: Collect the three-phase voltage, three-phase current and frequency of active loop output on the outlet side of the hybrid synchronous control inverter under normal / faulty operation; A hybrid synchronous control structure of the inverter is constructed based on a control strategy combining positive sequence control and negative sequence control, and a HSC-VSC hybrid synchronous control inverter system model is constructed according to the hybrid synchronous control structure; Based on the three-phase voltage, three-phase current, frequency of active loop output and HSC-VSC hybrid synchronous control inverter system model, the control signal of the inverter is adaptively determined, and the inverter is adaptively controlled according to the control information.

2. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 1, characterized in that: A hybrid synchronous control structure of the inverter is constructed based on a control strategy combining positive sequence control and negative sequence control, and a HSC-VSC hybrid synchronous control inverter system model is constructed according to the hybrid synchronous control structure, including: Constructing a positive sequence control substructure, a negative sequence control substructure and a control signal generation substructure, and using the output of the positive sequence control substructure and the output of the negative sequence control substructure as inputs of the control signal generation substructure to obtain a hybrid synchronous control structure; The grid simulation structure is constructed and combined with the hybrid synchronous control structure to obtain the HSC-VSC hybrid synchronous control inverter system model.

3. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 2, characterized in that: The positive sequence control substructure includes a power processing unit, a voltage inner loop, a first current inner loop and a first conversion unit; The power processing unit includes a hybrid synchronization ring and a reactive droop controller; The hybrid synchronization ring is used to generate positive sequence active power and positive sequence active power reference value P ref + The input and output positive sequence voltage reference phase θ HSC ; The reactive power droop controller is used to control the positive sequence reactive power Q and the positive sequence reactive power reference value Q ref + is the input and output positive sequence voltage reference value E dref ; Among them, the positive sequence reactive power Q and the positive sequence active power The acquisition method is as follows: the three-phase voltage and three-phase current output at the inverter outlet side are decoupled by positive and negative sequence to obtain the positive sequence component and negative sequence component of the voltage, and the positive sequence component and negative sequence component of the current; according to the positive sequence component of the voltage and the positive sequence component of the current, the positive sequence reactive power Q and the positive sequence active power are determined. The voltage inner loop is used to reference the positive sequence voltage phase θ HSC With positive sequence voltage reference value E dref The input and output d-axis positive sequence current reference value I drefp1 And the q-axis positive sequence current reference value I qrefp1 ; The first current inner loop is used to use the d-axis positive sequence current reference value I drefp1 And the q-axis positive sequence current reference value I qrefp1 is the input, and the output d-axis positive sequence voltage m dp And the q-axis positive sequence voltage m qp ; The first conversion unit is used to use the positive sequence voltage reference phase θ HSC , d-axis positive sequence voltage m dp And the q-axis positive sequence voltage m qp As input, synthesize the voltage in the dq coordinate system to obtain the positive sequence synthesized voltage m abcp .

4. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 3, characterized in that: The data processing flow of the hybrid synchronization ring includes: The collected three-phase voltage is processed by the first DSOGI module and the first PNSC module in turn to obtain the positive sequence voltage component The positive sequence voltage component After being processed by the first PARK conversion module and the proportional regulator, the angular velocity deviation Δω of the PLL is obtained. PLL ; The active power reference value P ref + Positive sequence active power Subtract and process through transfer function to get the angular velocity deviation value Δω of VSG. VSG ; The angular velocity deviation of the PLL is Δω PLL Angular velocity deviation from VSG Δω VSG After addition and processing by the first integrator, the positive sequence voltage reference phase θ is obtained. HSC ; Among them, the positive sequence voltage reference phase θ HSC is fed back to the first PARK conversion module so that the positive sequence voltage reference phase θ HSC With positive sequence voltage component Perform joint processing.

5. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 3, characterized in that: The negative sequence control substructure includes a phase locked loop, a second current inner loop and a second conversion unit; The phase-locked loop is used to generate the negative-sequence voltage d-axis component U qn is the input, output negative sequence voltage phase θ n ; The second current inner loop is used to use the d-axis negative sequence voltage reference value I drefn1 And the q-axis negative sequence voltage reference value I qrefn1 is the input, and the output d-axis negative sequence voltage m dn And the q-axis negative sequence voltage m qn ; The second conversion unit is used to convert the negative sequence voltage phase θ n , d-axis negative sequence voltage m dn And the q-axis negative sequence voltage m qn As input, synthesize the voltage in the dq coordinate system to obtain the negative sequence synthesized voltage m abcn .

6. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 5, characterized in that: The data processing flow of the phase-locked loop includes: The collected three-phase voltage is processed by the second DSOGI module and the second PNSC module in turn to obtain the negative sequence voltage component The negative sequence voltage component After being processed by the second PARK conversion module, the negative sequence voltage d-axis component U is obtained. qn ; The negative sequence voltage d-axis component U qn After the proportional integral processing, subtraction from the angular velocity reference value ω0 and the second integrator processing, the negative sequence voltage phase θ is obtained. n ; Among them, the negative sequence voltage phase θ n is fed back to the second PARK conversion module so that the negative sequence voltage phase θ n With negative sequence voltage component Perform joint processing.

7. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 5, characterized in that: The control signal generation substructure includes a signal synthesis unit and a PWM modulation unit; The signal synthesis unit is used to synthesize the positive sequence voltage m abcp Combined with negative sequence voltage m abcn Add together to get the desired voltage modulation signal m abc ; The PWM modulation unit is used to modulate the desired voltage signal m abc Perform PWM modulation to generate control signals for the switching tubes in the inverter.

8. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 7, characterized in that: The control signal output by the hybrid synchronous control structure is connected to the switch tube of the inverter in the power grid simulation structure.

9. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 5, characterized in that: Based on the three-phase voltage, three-phase current, frequency of active loop output and HSC-VSC hybrid synchronous control inverter system model, the control signal of the inverter is adaptively determined, including: It is determined whether the frequency of the active loop output is greater than the preset frequency threshold. If so, the three-phase voltage and the three-phase current are processed as the input of the HSC-VSC hybrid synchronous control inverter system model to determine the control signal of the inverter output by the hybrid synchronous control structure in the HSC-VSC hybrid synchronous control inverter system model. Otherwise, the system is determined to be transiently unstable, and the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value are adaptively adjusted. The HSC-VSC hybrid synchronous control inverter system model is controlled according to the adjusted d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value to adaptively determine the control signal of the inverter and pull the inverter back to a transient stable state.

10. The adaptive control method for transient stability of hybrid synchronous control inverter according to claim 9, characterized in that: Adaptively adjust the d-axis positive sequence current reference value, the q-axis positive sequence current reference value, the d-axis negative sequence voltage reference value, and the q-axis negative sequence voltage reference value, including: The state space equation of the system before and after the fault is established, and the stability domain of the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value is determined by the phase diagram method, and the d-axis positive-sequence current reference value, the q-axis positive-sequence current reference value, the d-axis negative-sequence voltage reference value and the q-axis negative-sequence voltage reference value are adjusted back to the boundary of the stability domain.

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