Zero voltage ride through control method for self-synchronizing voltage source doubly-fed wind turbine generator

Abstract

The invention provides a zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator, which comprises the following steps that: when the self-synchronizing voltage source doubly-fed wind turbine generator is in a transient state, a grid-side converter adopts vector control, and a rotor-side converter adopts additional virtual impedance and annular current limiting; the transient overcurrent of the grid-side converter and the rotor-side converter can be effectively suppressed, so that the continuous operation capability of the wind turbine generator in the zero-voltage ride-through period can be maintained; meanwhile, by improving the transient capacity and the transient reactive current amplitude of the converter, the transient voltage supporting capacity of the wind turbine generator during the zero voltage ride-through period can be effectively provided; when the self-synchronizing voltage source doubly-fed wind turbine generator set is in a transient state, overvoltage of direct-current bus voltage is limited by a Chopper circuit, active-priority current amplitude limiting control is adopted by a grid-side converter, parameters of a current inner ring PI controller of a rotor-side converter are optimized, energy balance of a direct-current side can be achieved in the zero-voltage ride-through period, and stability of the direct-current bus voltage is maintained.

Description

Technical Field

[0001] This invention relates to the field of doubly-fed induction generator (DFIG) control technology, specifically to a zero-voltage ride-through control method for a self-synchronizing voltage source DFIG wind turbine. Background Technology

[0002] In recent years, with the continuous increase in wind power installed capacity, the impact of large-scale wind power integration on the safe and stable operation of the power grid has become increasingly significant. Voltage dips are a common fault mode in wind power systems. When the grid voltage suddenly drops to zero, wind turbines are required to provide reactive power to the grid to support the system voltage while ensuring their own continuous operation. However, due to their unique structure, doubly-fed induction generators (DFIGs) are extremely sensitive to grid voltage changes and are prone to rotor-side overcurrent problems, which reduces their zero-voltage ride-through capability.

[0003] The emergence of self-synchronizing voltage source control technology and power semiconductor modules with three times the short-term overload capacity has revolutionized the achievement of zero-voltage ride-through for doubly-fed induction generator (DFIG) wind turbines. Existing solutions primarily employ grid-following control during fault periods, but this method heavily relies on strong grid conditions and carries the risk of transient instability in weak grid scenarios, potentially leading to fault ride-through control failure and generator disconnection. Furthermore, to enhance the reactive power support provided by DFIGs to the grid during low-voltage ride-through, grid-side converters typically employ reactive power priority control. However, this control method does not consider the energy balance on the DC side during fault periods, easily leading to DC bus voltage instability. Regarding rotor-side overcurrent issues during DFIG zero-voltage ride-through, existing solutions mainly use Crowbar protection circuits for current limiting, but this causes the wind turbine to lose controllability and absorb a large amount of reactive power from the grid, further deteriorating the grid voltage.

[0004] Therefore, in view of the shortcomings of the existing technology, there is an urgent need in this field to propose a zero-voltage ride-through optimization control method for self-synchronizing voltage source doubly fed wind turbine generators.

[0005] Patent document (application number: 202310910416.6) discloses a low-voltage ride-through method for doubly-fed induction generator (DFIG) wind turbines. The method includes the following steps: S1: After a voltage drop occurs at the DFIG turbine terminals and it enters a low-voltage ride-through state, a fault current limiter connected to the stator side of the DFIG turbine is activated to detect the grid connection voltage. S2: Based on the grid connection voltage and the impedance of the activated fault current limiter, the current control targets for the turbine-side converter and grid-side converter during fault ride-through are determined with the goal of maintaining a constant stator current. S3: The current control targets for the turbine-side and grid-side converters are converted into power control targets and applied to the control of the turbine-side and grid-side converters. This method maximizes the reactive power output of the grid-side converter while maintaining the stator current at the start of the low-voltage ride-through. However, the patent only applies to grid-connected doubly-fed wind turbines and does not test grid-connected units. Furthermore, the patent does not provide a control strategy for doubly-fed wind turbines during zero-voltage ride-through.

[0006] Patent document (application number: 202311508969.5) discloses a cooperative control method for doubly-fed induction generator (DFIG) wind turbines (doubly-fed induction generators) under low-voltage ride-through, relating to the field of DFIG technology. The method includes: constructing a cooperative control strategy for the rotor converter and the grid-side converter, wherein the cooperative control strategy includes adding a voltage control outer loop to the grid-side converter control for coordinated voltage control with the rotor converter; switching the DFIG control to the cooperative control strategy during the voltage recovery phase until the turbine terminal voltage recovers to a steady state. This invention, employing the above scheme, can accelerate reactive power retraction, suppress DFIG overvoltage, and reduce the risk of consecutive faults following low-voltage ride-through to high-voltage ride-through. However, this patent only applies to grid-connected DFIGs and does not test grid-connected units. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a zero-voltage ride-through control method for self-synchronizing voltage source doubly fed wind turbine generators.

[0008] The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine provided by the present invention includes:

[0009] Rotor-side converter control steps include: active power / frequency control, reactive power / voltage control, virtual admittance control, loop current limiting control, and inner current loop control.

[0010] Grid-side converter control steps include vector control and active power priority current limiting.

[0011] During transient conditions, the self-synchronous voltage source doubly-fed wind turbine adopts vector control for the grid-side converter and suppresses transient overcurrents in both the grid-side and rotor-side converters by adding virtual impedance and ring current limiting, enabling the wind turbine to maintain continuous operation during zero-voltage ride-through. At the same time, by increasing the transient capacity and transient reactive current amplitude of the converter, the transient voltage support capability of the wind turbine is provided during zero-voltage ride-through.

[0012] During the transient state of a self-synchronous voltage source doubly fed wind turbine, the DC bus voltage is limited by the Chopper circuit to prevent overvoltage. By adopting active power priority current limiting control for the grid-side converter and optimizing the parameters of the rotor-side converter current inner loop PI controller, energy balance on the DC side is achieved during zero voltage ride-through, thus maintaining the stability of the DC bus voltage.

[0013] Preferably, the active power / frequency control includes:

[0014] The rotor-side converter uses virtual synchronous control to generate the phase information required for rotor-side converter control. The angular frequency ω of the output modulation voltage vector of the rotor-side converter is... vsg and phase angle θ s The active power setpoint and feedback value of the doubly-fed generator unit are obtained through closed-loop control, and can be obtained by solving the following expression:

[0015]

[0016] In the formula, P s,ref and P s These are the commanded and actual active power values, respectively; ω vsg The control output synchronous angular frequency of the rotor-side converter; θ vsg ω1 is the phase angle of the output modulation voltage vector of the rotor-side converter; H is the grid angular frequency; D is the inertial time constant of the doubly-fed generator; and D is the damping coefficient of the doubly-fed generator.

[0017] Preferably, the reactive power / voltage control includes:

[0018] The rotor-side converter uses the sum of the grid connection point voltage deviation and reactive power deviation as an error signal, and generates a reference value for the internal potential amplitude through the control equation, expressed as:

[0019]

[0020] In the formula, E m V is the amplitude of the internal potential. s and V s,ref These are the amplitudes of the commanded and actual stator voltage values, respectively; Q sref and Q s These are the stator reactive power command value and the actual value, respectively; D q and D uThese are the reactive power and voltage droop coefficients, respectively.

[0021] Preferably, the virtual admittance control includes:

[0022] The static circuit relationship simulating virtual admittance, and the circuit equations in the synchronously rotating dq coordinate system are as follows:

[0023]

[0024] In the formula, E ref V is the internal potential reference value. s I is the stator voltage phasor. s,cmd and I r,cmd These are the stator and rotor current command value phasors, respectively; X v and R v These are virtual inductive reactance and virtual resistance, respectively; L m For mutual inductance between stator and rotor magnetic flux; L s For stator flux linkage self-inductance.

[0025] Preferably, the annular current limiting control includes:

[0026] When I r,cmd Greater than the limit value I lim Subsequently, the loop current limiting control scales I according to the method of equal scaling of the dq-axis current. r,cmd Limit the amplitude so that it does not exceed the limit value; before and after limiting, the current reference value I r,ref With the I output from the virtual admittance control r,cmd The angle between them remains constant, and the expression for the ring current limiting control is as follows:

[0027]

[0028] In the formula, I r,ref I is the phasor of the rotor current reference value; r,cmd I is the phasor of the rotor current command value; lim This is the rotor current limiting value.

[0029] Preferably, the current inner loop control includes:

[0030] The rotor-side converter current setpoint and feedback value are processed by a PI controller to output the d-axis and q-axis components of the rotor-side converter modulated voltage vector, expressed as follows:

[0031] V r =k pi (I r,ref -I r )+k ii ∫(I r,ref -I r )dt+j(ω1-ω r)ψ r

[0032] In the formula, V r For rotor voltage phasor; k pi and k ii ω represents the proportional gain and integral time constant of the inner-loop PI controller for the rotor current; r ψ is the rotor angular frequency. r I is the rotor flux linkage phasor. r Represents the rotor current phasor; j represents the imaginary unit;

[0033] Based on the d-axis and q-axis components and phase angle of the rotor-side converter modulation voltage vector, the three-phase modulation voltage value of the rotor-side converter is obtained. After pulse width vector modulation, the trigger signal of the rotor-side converter is obtained. The expression for the three-phase modulation voltage of the rotor-side converter is:

[0034]

[0035] In the formula, v ra ,v rb ,v rc These are the components of the rotor voltage in the three-phase stationary coordinate system; v rd and v rq These are the components of the rotor voltage in the synchronously rotating dq coordinate system; θ slip This is the slip angle.

[0036] Preferably, the parameters of the inner current loop PI controller of the rotor-side converter are optimized. The inner current loop control adopts a PI controller with the following transfer function:

[0037]

[0038] In the formula, s is the Lagrange operator;

[0039] The transfer function of the actual controlled object is:

[0040]

[0041] In the formula, L f and R f These are the filter inductor and the filter resistor, respectively.

[0042] Internal model control is used to tune the parameters of the PI controller. This involves canceling out the zeros of the PI controller with the poles of the controlled object, leaving the remaining gain at the cutoff frequency. The expressions for the proportional gain and integral time constant of the PI controller are as follows:

[0043] k pi =α c L f ,k ii =αc R f

[0044] In the formula, α c The bandwidth of the inner current loop;

[0045] The ranges of the proportional coefficient and integral time constant of the PI controller are obtained based on the range of the current inner loop bandwidth, and are denoted as set B. p and B i The state-space equations for a doubly-fed wind power system, taking into account the control of both the rotor-side and grid-side converters, are established as follows:

[0046]

[0047] In the formula, x is the state variable of the system, and A is the characteristic matrix;

[0048] The stability of a doubly-fed induction generator (DFIG) wind power system is determined by whether the characteristic matrix A contains eigenvalues ​​in the right half of the complex plane. This yields the stability regions of the proportional gain and integral time constant of the PI controller, denoted as sets S, respectively. p and S i By taking the intersection, we can finally obtain the range of values ​​for both, as shown in the following expression:

[0049] C p =B p ∩S p C i =B i ∩S i

[0050] In the formula, C p and C i These represent the final value ranges of the proportional coefficient and integral time constant of the PI controller, respectively.

[0051] I lim When = 3p.u., in order to suppress the oscillation of the stator flux linkage during the fault, the proportional coefficient and integral time constant of the PI controller are respectively taken as: k pi =min{C p},k ii =max{C i}

[0052] Preferably, the vector control includes:

[0053] The active current command value of the grid-side converter is obtained from the DC voltage closed loop, and the expression is:

[0054]

[0055] In the formula: k pd and k idThese are the proportional and integral coefficients of the DC voltage loop, respectively; U dc,ref and U dc These are the reference and actual DC voltage values, respectively; i gd,cmd The current command value for the d-axis of the grid-side converter; s is the Laplace operator;

[0056] The reactive current command value of the grid-side converter is obtained from the reactive power closed-loop control, and the expression is:

[0057]

[0058] In the formula: k pq and k iq These are the proportional and integral coefficients of the grid-side reactive power loop, respectively; Q g,ref and Q g These are the reference and actual values ​​of reactive power output from the grid-side converter, respectively; i gq,cmd This is the command value for the q-axis current of the grid-side converter.

[0059] Preferably, the active power priority current limiting includes:

[0060] The grid-side converter adopts an active-priority current-limiting mode, in which the reference value of the active current i is... gd,ref and the reference value i of reactive current gq,ref The expression is as follows:

[0061]

[0062] In the formula, i g,lim Indicates the grid-side current limit value;

[0063] During a fault, the output voltage vector of the grid-side converter is generated by the PI controller based on the grid-side converter current setpoint and feedback value, and its expression is:

[0064]

[0065] In the formula, i gd and i gq The d-axis and q-axis components of the actual value of the grid-side converter current; u gd and u gq For the d-axis and q-axis components of the grid voltage; k pg and k ig These are the proportional and integral coefficients of the grid-side converter current loop, respectively; u td and u tq represents the d-axis and q-axis components of the modulation voltage of the grid-side converter; s represents the Laplace operator;

[0066] The expression for the three-phase modulation voltage of the grid-side converter is:

[0067]

[0068] In the formula, u ta ,u tb ,u tc These are the components of the grid-side converter output voltage in the three-phase stationary coordinate system; u td and u tq These are the components of the grid-side converter output voltage in the synchronously rotating dq coordinate system; θ g The phase information of the grid voltage vector is obtained from the phase-locked loop circuit.

[0069] Preferably, it also includes a Chopper circuit control step:

[0070] The Chopper circuit employs hysteresis control; when the DC bus voltage exceeds the DC voltage setpoint C... H When the DC bus voltage is less than the DC voltage set value, the DC Chopper circuit activates; when the DC bus voltage is less than the set value of the DC voltage, the Chopper circuit activates. L When the current frequency is doubled, the DC Chopper circuit exits operation;

[0071] Among them, C H C L All are empirical values; C H Take 1.09, C L Take 1.02.

[0072] Compared with the prior art, the present invention has the following beneficial effects:

[0073] (1) The self-synchronous voltage source doubly fed wind turbine generator provided by the present invention adopts vector control for the grid-side converter during transients, and the rotor-side converter can effectively suppress transient overcurrents of the grid-side converter and the rotor-side converter by adding virtual impedance and ring current limiting, so that the wind turbine generator can maintain continuous operation during zero voltage ride-through; at the same time, by increasing the transient capacity and transient reactive current amplitude of the converter, the transient voltage support capability of the wind turbine generator can be effectively provided during zero voltage ride-through.

[0074] (2) The DC bus voltage of the self-synchronous voltage source doubly fed wind turbine provided by the present invention is limited by the Chopper circuit during transients. By adopting active power priority current limiting control through the grid-side converter and optimizing the parameters of the rotor-side converter current inner loop PI controller, the DC side energy balance can be achieved during zero voltage ride-through, thus maintaining the stability of the DC bus voltage. Attached Figure Description

[0075] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0076] Figure 1 This is a structural diagram of a self-synchronizing voltage source doubly fed wind turbine system.

[0077] Figure 2 This is a block diagram of the transient control of the grid-side converter;

[0078] Figure 3 This is a control block diagram of the rotor-side converter; where, Figure 3 (a) in the diagram is the active power-frequency control block diagram; Figure 3 (b) in the diagram is the reactive power-voltage control block diagram; Figure 3 (c) in the diagram represents the inner loop control block diagram;

[0079] Figure 4 This is the control block diagram of a DC Chopper circuit. Detailed Implementation

[0080] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0081] Example

[0082] like Figure 1 The present invention provides a zero-voltage ride-through control method for a self-synchronizing voltage source doubly fed wind turbine, comprising: a rotor-side converter control step, a grid-side converter control step, and a Chopper control step.

[0083] like Figure 3 The rotor-side converter control steps include:

[0084] 1) Active power / frequency control module

[0085] The rotor-side converter uses virtual synchronous control to generate the phase information required for rotor-side converter control. The angular frequency ω of the output modulation voltage vector of the rotor-side converter is... vsg and phase angle θ s It can be obtained by closed-loop control of the active power setpoint and feedback value of the doubly-fed generator unit, and can be obtained by solving the following expression:

[0086]

[0087] In the formula, P s,ref and P s These are the commanded and actual active power values, respectively; ω vsg The control output synchronous angular frequency of the rotor-side converter; θ vsg ω1 is the phase angle of the output modulation voltage vector of the rotor-side converter; H is the grid angular frequency; D is the inertial time constant of the doubly-fed generator; and D is the damping coefficient of the doubly-fed generator.

[0088] 2) Reactive power / voltage control module

[0089] The rotor-side converter uses the sum of the grid connection point voltage deviation and reactive power deviation as an error signal, and generates a reference value for the internal potential amplitude through the control equation. Its expression is written as:

[0090]

[0091] In the formula, E m V is the amplitude of the internal potential. s and V s,ref These are the amplitudes of the commanded and actual stator voltage values, respectively; Q sref and Q s These are the stator reactive power command value and the actual value, respectively; D q and D u These are the reactive power and voltage droop coefficients, respectively.

[0092] 3) Virtual admittance control module

[0093] The purpose of virtual admittance control is to simulate synchronous electromechanical reactance, but here we only simulate the static circuit relationship of virtual admittance, ignoring the dynamic part. Its circuit equations in the synchronous rotating dq coordinate system are:

[0094]

[0095] In the formula, E ref V is the internal potential reference value. s I is the stator voltage phasor. s,cmd and I r,cmd These are the stator and rotor current command value phasors, respectively; X v and R v These are virtual inductive reactance and virtual resistance, respectively; L m For mutual inductance between stator and rotor magnetic flux; L s For stator flux linkage self-inductance.

[0096] 4) Ring current limiting control module

[0097] When I r,cmd Greater than the limit value I lim Subsequently, the loop current limiting control scales the current reference value I according to the method of equal scaling of the dq-axis current. r,cmd Limit the amplitude so that it does not exceed the limit value. Before and after limiting, the current reference value I... r,ref With the current command value I output from the virtual admittance control r,cmd The angle between them remains constant. The expression for the ring current limiting control is as follows:

[0098]

[0099] In the formula, I r,ref I is the phasor of the rotor current reference value; r,cmd The magnitude of the rotor current command; I lim The rotor current limiting value is set to 3p.u.

[0100] 5) Current inner loop control module

[0101] The rotor-side converter current setpoint and feedback value are processed by the PI controller to output the d-axis and q-axis components of the rotor-side converter modulated voltage vector, whose expressions are as follows:

[0102] V r =k pi (I r,ref -I r )+k ii ∫(I r,ref -I r )dt+j(ω1-ω r )ψ r

[0103] In the formula, V r For rotor voltage phasor; k pi and k ii ω represents the proportional gain and integral time constant of the inner-loop PI controller for the rotor current; r ψ is the rotor angular frequency. r For rotor flux linkage phasor.

[0104] The three-phase modulation voltage value of the rotor-side converter can be obtained from the d-axis and q-axis components of the modulation voltage vector and the phase angle. After pulse width vector modulation, the trigger signal of the rotor-side converter is obtained. The expression for the three-phase modulation voltage of the rotor-side converter is:

[0105]

[0106] In the formula, v ra ,v rb ,v rc These are the components of the rotor voltage in the three-phase stationary coordinate system; v rd and v rq These are the components of the rotor voltage in the synchronously rotating dq coordinate system; θ slip This is the slip angle.

[0107] The parameters of the PI controller for the inner current loop of the rotor-side converter are optimized below. The inner current loop control uses a PI controller, whose transfer function is:

[0108]

[0109] The transfer function of the actual controlled object is:

[0110]

[0111] In the formula, L f and R f These are the filter inductor and the filter resistor, respectively.

[0112] Internal model control is used to tune the parameters of the PI controller. This means the zeros (numerator) of the PI controller cancel out the poles (denominator) of the controlled object, leaving the remaining gain at the cutoff frequency. The expressions for the proportional gain and integral time constant of the PI controller are as follows:

[0113] k pi =α c L f ,k ii =α c R f

[0114] In the formula, α c This represents the bandwidth of the inner current loop.

[0115] Based on the range of values ​​for the current inner loop bandwidth, the ranges of values ​​for the proportional coefficient and integral time constant of the PI controller can be obtained, denoted as set B. p and B i The state-space equations for a doubly-fed wind power system, taking into account the control of both the rotor-side and grid-side converters, are established as follows:

[0116]

[0117] In the formula, x is the state variable of the system, and A is the characteristic matrix.

[0118] The stability of a doubly-fed induction generator (DFIG) wind power system can be determined by whether the characteristic matrix A has eigenvalues ​​in the right half of the complex plane. From this, the stability regions of the proportional gain and integral time constant of the PI controller can be obtained, denoted as sets S, respectively. p and S i By taking the intersection, we can finally obtain the following range of values ​​for both:

[0119] C p =B p ∩S p C i =B i ∩S i

[0120] In the formula, C p and C i These represent the final value ranges of the proportional coefficient and integral time constant of the PI controller, respectively.

[0121] in I limUnder the premise of 3p.u., in order to suppress the oscillation of stator flux linkage during faults, the proportional coefficient and integral time constant of the PI controller are respectively taken as:

[0122] k pi =min{C p},k ii =max{C i}

[0123] like Figure 2 The grid-side converter control steps include:

[0124] 1) Vector Control Module

[0125] The active current command value of the grid-side converter is obtained from the DC voltage closed loop, and its expression is:

[0126]

[0127] In the formula: k pd and k id These are the proportional and integral coefficients of the DC voltage loop, respectively; U dc,ref and U dc These are the reference and actual DC voltage values, respectively; i gd,cmd This is the commanded value for the d-axis current of the grid-side converter.

[0128] The reactive current command value of the grid-side converter is obtained from the reactive power closed-loop control, and its expression is:

[0129]

[0130] In the formula: k pq and k iq These are the proportional and integral coefficients of the grid-side reactive power loop, respectively; Q g,ref and Q g These are the reference and actual values ​​of reactive power output from the grid-side converter, respectively; i gq,cmd This is the command value for the q-axis current of the grid-side converter.

[0131] 2) Active power priority current limiting module

[0132] The grid-side converter adopts an active-priority current-limiting mode. The reference values ​​for active and reactive currents in this mode are expressed as follows:

[0133]

[0134] During a fault, the output voltage vector of the grid-side converter is generated by the grid-side converter current setpoint and feedback value through a PI controller, and its expression is:

[0135]

[0136] In the formula, i gd and i gq The d-axis and q-axis components of the actual value of the grid-side converter current; u gd and u gq For the d-axis and q-axis components of the grid voltage; k pg and k ig These are the proportional and integral coefficients of the grid-side converter current loop, respectively; u td and u tq These are the d-axis and q-axis components of the modulated voltage of the grid-side converter.

[0137] The expression for the three-phase modulation voltage of the grid-side converter is:

[0138]

[0139] In the formula, u ta ,u tb ,u tc These are the components of the grid-side converter output voltage in the three-phase stationary coordinate system; u td and u tq These are the components of the grid-side converter output voltage in the synchronously rotating dq coordinate system; θ g The phase information of the grid voltage vector is obtained from the phase-locked loop circuit.

[0140] like Figure 4 The Chopper circuit control steps include:

[0141] The Chopper circuit employs "Bang-Bang control," which activates when the DC bus voltage exceeds the DC voltage setpoint C. H When the DC bus voltage is less than the DC voltage set value, the DC Chopper circuit activates; when the DC bus voltage is less than the set value of the DC voltage, the Chopper circuit activates. L When the current value is doubled, the DC Chopper circuit exits operation. Among them, C... H C L All are empirical values; C H Take 1.09, C L Take 1.02.

[0142] This invention proposes a zero-voltage ride-through control method for the rotor-side converter of a self-synchronizing voltage source doubly-fed wind turbine. The rotor-side converter employs virtual synchronous control, utilizing virtual admittance and a ring current limiter to suppress transient overcurrents in the rotor-side converter. By increasing the converter's capacity and reactive current support coefficient, the transient voltage support capability of the unit can be effectively improved, thereby contributing to grid voltage recovery.

[0143] This method improves the stability of the DC bus voltage by suppressing stator flux oscillations and reducing DC bus voltage fluctuations. The grid-side converter employs active power priority control to maintain the energy balance of the DC bus, with remaining capacity used for reactive power output. This method not only achieves zero-voltage ride-through for the doubly-fed induction generator (DFIG) in weak grid environments but also fully utilizes the capacity of the grid-side converter to further enhance the unit's transient voltage support capability. The DC-side Chopper circuit uses Bang-Bang control to prevent DC voltage overvoltage issues.

[0144] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0145] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator, characterized in that, include: Rotor-side converter control steps include: active power / frequency control, reactive power / voltage control, virtual admittance control, loop current limiting control, and inner current loop control. Grid-side converter control steps include vector control and active power priority current limiting. During transient conditions, the self-synchronous voltage source doubly-fed wind turbine adopts vector control for the grid-side converter and suppresses transient overcurrents in both the grid-side and rotor-side converters by adding virtual impedance and ring current limiting, enabling the wind turbine to maintain continuous operation during zero-voltage ride-through. At the same time, by increasing the transient capacity and transient reactive current amplitude of the converter, the transient voltage support capability of the wind turbine is provided during zero-voltage ride-through. During the transient state of a self-synchronous voltage source doubly fed wind turbine, the DC bus voltage is limited by the Chopper circuit to prevent overvoltage. By adopting active power priority current limiting control for the grid-side converter and optimizing the parameters of the rotor-side converter current inner loop PI controller, energy balance on the DC side is achieved during zero voltage ride-through, thus maintaining the stability of the DC bus voltage.

2. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, The active power / frequency control includes: The rotor-side converter uses virtual synchronous control to generate the phase information required for rotor-side converter control. The angular frequency ω of the output modulation voltage vector of the rotor-side converter is... vsg and phase angle θ s The active power setpoint and feedback value of the doubly-fed generator unit are obtained through closed-loop control, and can be obtained by solving the following expression: In the formula, P s,ref and P s These are the commanded and actual active power values, respectively; ω vsg The control output synchronous angular frequency of the rotor-side converter; θ vsg ω1 is the phase angle of the output modulation voltage vector of the rotor-side converter; H is the grid angular frequency; D is the inertial time constant of the doubly-fed generator; and D is the damping coefficient of the doubly-fed generator.

3. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, The reactive power / voltage control includes: The rotor-side converter uses the sum of the grid connection point voltage deviation and reactive power deviation as an error signal, and generates a reference value for the internal potential amplitude through the control equation, expressed as: In the formula, E m V is the amplitude of the internal potential. s and V s,ref These are the amplitudes of the commanded and actual stator voltage values, respectively; Q sref and Q s These are the stator reactive power command value and the actual value, respectively; D q and D u These are the reactive power and voltage droop coefficients, respectively.

4. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, The virtual admittance control includes: The static circuit relationship simulating virtual admittance, and the circuit equations in the synchronously rotating dq coordinate system are as follows: In the formula, E ref V is the internal potential reference value. s I is the stator voltage phasor. s,cmd and I r,cmd These are the stator and rotor current command value phasors, respectively; X v and R v These are virtual inductive reactance and virtual resistance, respectively; L m For mutual inductance between stator and rotor magnetic flux; L s For stator flux linkage self-inductance.

5. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, The ring current limiting control includes: When I r,cmd Greater than the limit value I lim Subsequently, the loop current limiting control scales I according to the method of equal scaling of the dq-axis current. r,cmd Limit the amplitude so that it does not exceed the limit value; before and after limiting, the current reference value I r,ref With the I output from the virtual admittance control r,cmd The angle between them remains constant, and the expression for the ring current limiting control is as follows: In the formula, I r,ref I is the phasor of the rotor current reference value; r,cmd I is the phasor of the rotor current command value; lim This is the rotor current limiting value.

6. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, The current inner loop control includes: The rotor-side converter current setpoint and feedback value are processed by a PI controller to output the d-axis and q-axis components of the rotor-side converter modulated voltage vector, expressed as follows: V r =k pi (AND r,ref -AND r )+k ii ∫(I r,ref -AND r )dt+j(ω1-ω r )ψ r In the formula, V r For rotor voltage phasor; k pi and k ii ω represents the proportional gain and integral time constant of the inner-loop PI controller for the rotor current; r ψ is the rotor angular frequency. r I is the rotor flux linkage phasor. r Represents the rotor current phasor; j represents the imaginary unit; Based on the d-axis and q-axis components of the modulated voltage vector of the rotor-side converter and the phase angle, the three-phase modulated voltage value of the rotor-side converter is obtained. After pulse width vector modulation, the trigger signal of the rotor-side converter is obtained. The expression for the three-phase modulated voltage of the rotor-side converter is: In the formula, v ra ,v rb ,v rc These are the components of the rotor voltage in the three-phase stationary coordinate system; v rd and v rq These are the components of the rotor voltage in the synchronously rotating dq coordinate system; θ slip This is the slip angle.

7. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, The parameters of the PI controller for the inner current loop of the rotor-side converter are optimized. The inner current loop control uses a PI controller with the following transfer function: In the formula, s is the Lagrange operator; The transfer function of the actual controlled object is: In the formula, L f and R f These are the filter inductor and the filter resistor, respectively. Internal model control is used to tune the parameters of the PI controller. This involves canceling out the zeros of the PI controller with the poles of the controlled object, leaving the remaining gain at the cutoff frequency. The expressions for the proportional gain and integral time constant of the PI controller are as follows: k pi =a c L f ,k ii =a c R f In the formula, α c The bandwidth of the inner current loop; The ranges of the proportional coefficient and integral time constant of the PI controller are obtained based on the range of the current inner loop bandwidth, and are denoted as set B. p and B i The state-space equations for a doubly-fed wind power system, taking into account the control of both the rotor-side and grid-side converters, are established as follows: In the formula, x is the state variable of the system, and A is the characteristic matrix; The stability of a doubly-fed induction generator (DFIG) wind power system is determined by whether the characteristic matrix A contains eigenvalues ​​in the right half of the complex plane. This yields the stability regions of the proportional gain and integral time constant of the PI controller, denoted as sets S, respectively. p and S i By taking the intersection, we can finally obtain the range of values ​​for both, as shown in the following expression: C p =B p ∩S p ,C i =B i ∩S i In the formula, C p and C i These represent the final value ranges of the proportional coefficient and integral time constant of the PI controller, respectively. I lim When = 3p.u., in order to suppress the oscillation of the stator flux linkage during the fault, the proportional coefficient and integral time constant of the PI controller are respectively taken as: k pi =min{C p },k ii =max{C i } 8. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, The vector control includes: The active current command value of the grid-side converter is obtained from the DC voltage closed loop, and the expression is: In the formula: k pd and k id These are the proportional and integral coefficients of the DC voltage loop, respectively; U dc,ref and U dc These are the reference and actual DC voltage values, respectively; i gd,cmd The current command value for the d-axis of the grid-side converter; s is the Laplace operator; The reactive current command value of the grid-side converter is obtained from the reactive power closed-loop control, and the expression is: In the formula: k pq and k iq These are the proportional and integral coefficients of the grid-side reactive power loop, respectively; Q g,ref and Q g These are the reference and actual values ​​of reactive power output from the grid-side converter, respectively; i gq,cmd This is the command value for the q-axis current of the grid-side converter.

9. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, The active power priority current limiting includes: The grid-side converter adopts an active-priority current-limiting mode, in which the reference value of the active current i is... gd,ref and the reference value i of reactive current gq,ref The expression is as follows: In the formula, i g,lim Indicates the grid-side current limit value; During a fault, the output voltage vector of the grid-side converter is generated by the PI controller based on the grid-side converter current setpoint and feedback value, and its expression is: In the formula, i gd and i gq The d-axis and q-axis components of the actual value of the grid-side converter current; u gd and u gq For the d-axis and q-axis components of the grid voltage; k pg and k ig These are the proportional and integral coefficients of the grid-side converter current loop, respectively; u td and u tq represents the d-axis and q-axis components of the modulation voltage of the grid-side converter; s represents the Laplace operator; The expression for the three-phase modulation voltage of the grid-side converter is: In the formula, u ta ,u tb ,u tc These are the components of the grid-side converter output voltage in the three-phase stationary coordinate system; u td and u tq These are the components of the grid-side converter output voltage in the synchronously rotating dq coordinate system; θ g The phase information of the grid voltage vector is obtained from the phase-locked loop circuit.

10. The zero-voltage ride-through control method for a self-synchronizing voltage source doubly-fed wind turbine generator according to claim 1, characterized in that, It also includes the Chopper circuit control steps: The Chopper circuit employs hysteresis control; when the DC bus voltage exceeds the DC voltage setpoint C... H When the DC bus voltage is less than the DC voltage set value, the DC Chopper circuit activates; when the DC bus voltage is less than the set value of the DC voltage, the Chopper circuit activates. L When the current frequency is doubled, the DC Chopper circuit exits operation; Among them, C H C L All are empirical values; C H Take 1.09, C L Take 1.02.

Images