High Voltage Ride Through Control Method Introducing Active Disturbance Rejection Control

Abstract

The present invention discloses a high voltage ride-through control method that introduces an auto-disturbance rejection control, which specifically includes the following steps: analyzing the voltage, current, and flux transient process on the rotor side when a DFIG fails; introducing an auto-disturbance rejection control to control the inner loop transfer function in the double closed loop; designing an extended observer to observe and estimate the total disturbance f of the system in real time, using a disturbance compensation link to perform active feedback compensation, performing pole configuration on the auto-disturbance rejection control, and calculating the controller bandwidth, observer bandwidth, and controller gain. The auto-disturbance rejection control is introduced into the inner loop of the rotor side current, and the simulation results show that the proposed high voltage ride-through control method can effectively reduce the rotor side current and reduce the fluctuation time.

Description

Technical Field

[0001] The invention belongs to the technical field of wind power generation grid connection, and relates to a high voltage ride through control method introducing active disturbance rejection control. Background Art

[0002] Environmental pollution, climate change, energy security and sustainable development are becoming increasingly prominent. Most countries in the world have included new energy in their national energy priority development strategies, and new energy power generation has ushered in development opportunities. The large-scale grid connection of wind turbines with a high proportion has accelerated the construction of low-carbon power grids, but more and more complex faults often occur, which has put forward more stringent requirements for the development of wind power generation technology and wind power system fault ride-through. Continuous fault ride-through includes low voltage ride-through and high voltage ride-through technology. Low voltage ride-through technology started relatively early, the technology is more mature, and the national standards are more detailed. However, the high voltage ride-through control technology is not yet mature, and the national standards still need to be supplemented. Therefore, more efforts need to be invested in the research of DFIG high voltage ride-through control technology.

[0003] The existing high voltage ride-through control methods for doubly-fed wind turbines are mainly: 1. Traditional control vector strategy, which has relatively simple control logic but weak interference resistance and does not inject reactive current into the power grid. 2. High voltage ride-through technology considering reactive support. When a fault occurs, the active and reactive power on the rotor side and the grid side are configured so that the doubly-fed wind power generation system can inject inductive reactive power into the power grid. 3. Control strategy based on dynamic voltage command value changes to solve transient fluctuations and time at the time of fault occurrence and end. 4. Control strategy considering dynamic changes in stator flux to solve the rotor overcurrent problem caused by changes in stator flux when a fault occurs. 5. Reverse current tracking control: The current tracking coefficient is designed according to the relationship between the stator and rotor current changes. When the tracking coefficient is negative, the rotor current can reversely track the changes in the stator current, thereby effectively suppressing rotor overvoltage and overcurrent. Summary of the invention

[0004] The purpose of the present invention is to provide a high voltage ride through control method introducing active disturbance rejection control, which solves the problem of excessive transient current of the rotor in the prior art.

[0005] The technical solution adopted by the present invention is: a high voltage ride through control method with an auto-disturbance rejection control is introduced, which specifically comprises the following steps:

[0006] Step 1: Collect the d-axis active current, q-axis reactive current, d-axis voltage, q-axis voltage, and stator flux data of the doubly-fed wind turbine rotor side at the time of the fault, and design an outer loop control strategy;

[0007] Step 2, analyzing the data collected in step 1, the voltage, current, and flux transient process on the rotor side when the DFIG fails, and calculating the inner loop transfer function;

[0008] Step 3: introduce the anti-disturbance control to control the inner loop transfer function in the double closed loop.

[0009] Step 1 is as follows:

[0010] The reference value of the outer loop is the stator active power P s and reactive power Q s :

[0011]

[0012] According to formula (1), a PI controller is designed to control the power outer loop:

[0013]

[0014] i rd is the d-axis current on the rotor side, i rq is the q-axis current on the rotor side, is the d-axis reference current on the rotor side, is the q-axis reference current on the rotor side;

[0015] is the stator reactive power reference value, P s ref is the stator active power reference value,

[0016] U s is the stator voltage, ω1 is the synchronous angular velocity, L s is the stator side inductance, L m is the mutual inductance between stator and rotor, k p is the proportional coefficient of the PI controller, k i is the integral coefficient of the PI controller;

[0017] In order to make the doubly fed wind turbine work at full power, the active power reference value P is usually set. s ref 1, reactive power reference value is 0; the dq axis current reference value is obtained by PI controlling the power outer loop, which is used as the input of the current inner loop transfer function, and finally the high voltage ride through control capability is improved.

[0018] Step 2 is as follows:

[0019] The rotor dq axis voltage is expressed as follows:

[0020]

[0021] In formula (3), u rd is the rotor d-axis voltage, u rq is the rotor q-axis voltage; L ris the rotor inductance, R r is the rotor resistance;

[0022] ω slip ——Slip angle frequency

[0023] ω1——synchronous angular velocity

[0024] U s ——Stator voltage

[0025]

[0026] According to formula (3), it can be seen that there is a coupling phenomenon between the d-axis and q-axis components. Therefore, it is necessary to decouple them through feedback input to realize that the d-axis component of the rotor current controls the active power of the DFIG, and the q-axis component controls the reactive power transmitted from the DFIG to the grid.

[0027]

[0028] u dcomp Indicates the d-axis feedback input, u qcomp It represents the dq axis feedback input quantity. The feedback input quantity is compensated before the signal is input into the SVPWM signal generator. Therefore, the feedback compensation is ignored when calculating the inner loop transfer function.

[0029]

[0030] According to formula (4), the inner loop transfer function of the dq axis control strategy can be derived:

[0031]

[0032] G d (s) is the d-axis inner ring transfer function, G q (s) is the q-axis inner loop transfer function, R r Rotor resistance, L r is the rotor inductance.

[0033] Step 3 is as follows:

[0034] Step 3.1: All nonlinear factors and disturbance factors in the system are attributed to the system disturbance f, and an extended observer is designed to observe and estimate the total disturbance f of the system in real time. The state variables are selected and their state equations are calculated.

[0035] Formula (7) is used to calculate the relationship between the system output y and the total disturbance f:

[0036]

[0037] b is the control quantity gain, f is the total disturbance, and u is the system control quantity;

[0038] State variable selection:

[0039]

[0040] Using formula (8), the state equation (9) of the extended state observer is designed:

[0041]

[0042] Simplify formula (9):

[0043]

[0044] β1 and β2 are two parameters of the state observer, b0 is the estimated value of the control gain, and z1 is the output value of the extended state observer, which is used to track y and z. 2 is the output value of the expanded observer, used to track the total disturbance f, A, B, C are all constant matrices;

[0045] Step 3.2: Perform pole configuration for the ADRC, calculate the controller bandwidth, observer bandwidth, and controller gain to control the high voltage ride-through capability;

[0046] Formula (11) is obtained by calculating according to formula (8) and formula (10):

[0047]

[0048] Only when the eigenvalue of A-LC is less than 0, xz can be delayed over time and approach 0; the bandwidth method is used to configure:

[0049] β1=2ω0

[0050] Where y is the system output, w is the external disturbance, t is the time-varying disturbance, z is the output of the extended observer, β1 and β2 are two parameters of the state observer, L is the transpose of [β1β2], and ω0 is the controller bandwidth;

[0051] Since the system is first-order

[0052]

[0053] Simple PD control of the integrator series system:

[0054] u0=k p (ref-z1) (13)

[0055] k p =ω c (14)

[0056] ω cis the PD controller gain, u0 is the current error value after amplification, and ref is the current reference value obtained by the power outer loop through the PI controller;

[0057] Therefore, the parameters that need to be adjusted in the ADRC are as follows:

[0058] β1=2ω0 k p =ω c .

[0059] The active disturbance rejection control adopted by the present invention attributes all nonlinear factors and disturbance factors in the system to the system disturbance f, and does not rely on the precise mathematical model of the controlled object. The mathematical model of the doubly-fed wind turbine is a complex system with strong coupling and nonlinearity, so the active disturbance rejection control is very suitable for the doubly-fed wind turbine. Compared with the traditional PI control, ADRC has stronger anti-interference ability and simpler parameter setting.

[0060] The beneficial effect of the present invention is that the high voltage ride-through control method of the present invention introduces self-disturbance rejection control. When a fault occurs in the power grid and the voltage at the machine end rises, its rotor current undergoes transient fluctuations, and the fluctuation time is too long. If the current continues to be too large, it will cause damage to the power electronic device. To solve this problem, self-disturbance rejection control is introduced into the inner loop of the rotor side current. The simulation results show that the proposed high voltage ride-through control method can effectively reduce the rotor side current and reduce the fluctuation time. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a block diagram of the rotor side control strategy of the present invention;

[0062] 2(a)-(c) are respectively waveform diagrams of the terminal voltage, rotor side current and reactive power when a fault occurs in the present invention. DETAILED DESCRIPTION

[0063] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0064] The present invention provides a high voltage ride through control method introducing active disturbance rejection control, which specifically comprises the following steps:

[0065] Step 1: Collect the d-axis active current, q-axis reactive current, d-axis voltage, q-axis voltage, and stator flux data of the doubly-fed wind turbine rotor side at the time of the fault, and design an outer loop control strategy;

[0066] The present invention adopts stator voltage orientation on the rotor side. Figure 1 It can be seen that the outer loop reference value is the stator active power P s and reactive power Q s :

[0067]

[0068] Design the outer loop power control according to formula (1):

[0069]

[0070] i rd ——D-axis current on the rotor side

[0071] i rq ——Q-axis current on the rotor side

[0072] i rd is the d-axis current on the rotor side, i rq is the q-axis current on the rotor side, is the d-axis reference current on the rotor side, is the q-axis reference current on the rotor side;

[0073] is the stator reactive power reference value, P s ref is the stator active power reference value,

[0074] U s is the stator voltage, ω1 is the synchronous angular velocity, L s is the stator side inductance, L m is the mutual inductance between stator and rotor, k p is the proportional coefficient of the PI controller, k i is the integral coefficient of the PI controller;

[0075] In order to make the doubly fed wind turbine work at full power, the active power reference value is usually set to 1 and the reactive power reference value is set to 0. The dq axis current reference value is obtained by controlling the power outer loop through PI, which is used as the input of the current inner loop transfer function, and finally the high voltage ride through control capability is improved.

[0076] Step 2, analyzing the data collected in step (1) to obtain the transient process of voltage, current and flux linkage on the rotor side when the DFIG fails, and calculating the inner loop transfer function;

[0077] The rotor dq axis voltage is expressed as follows:

[0078]

[0079] In formula (3), u rd is the rotor d-axis voltage, u rq is the rotor q-axis voltage; L r is the rotor inductance, R r is the rotor resistance;

[0080] ω slip ——Slip angle frequency

[0081] ω1——synchronous angular velocity

[0082] U s ——Stator voltage

[0083]

[0084] According to formula (3), it can be seen that there is coupling between the d-axis and q-axis components. Therefore, it is necessary to decouple them through feedback input to realize that the d-axis component of the rotor current controls the active power of the DFIG and the q-axis component controls the reactive power transmitted from the DFIG to the grid.

[0085]

[0086] u dcomp Indicates the d-axis feedback input, u qcomp Indicates the dq axis feedback input quantity, according to Figure 1 It can be seen that the feedback input is compensated before the signal is input to the SVPWM signal generator. Therefore, the feedback compensation is ignored when calculating the inner loop transfer function.

[0087]

[0088] According to formula (4), the inner loop transfer function of the dq axis control strategy can be derived:

[0089]

[0090] G d (s) is the d-axis inner ring transfer function, G q (s) is the q-axis inner loop transfer function, R r Rotor resistance, L r is the rotor inductance.

[0091] Step 3, introduce the anti-disturbance control to control the inner loop transfer function in the double closed loop;

[0092] 3.1 All nonlinear factors and disturbance factors in the system are attributed to the system disturbance f, and an extended observer is designed to observe and estimate the total disturbance f of the system in real time, select state variables and calculate their state equations;

[0093] Formula (7) is used to calculate the relationship between the system output y and the total disturbance f:

[0094]

[0095] b is the control quantity gain, f is the total disturbance, and u is the system control quantity;

[0096] State variable selection:

[0097]

[0098] Using formula (8), the state equation (9) of the extended state observer is designed:

[0099]

[0100] Simplify formula (9):

[0101]

[0102] β1 and β2 are two parameters of the state observer, b0 is the estimated value of the control gain, and z1 is the output value of the extended state observer, which is used to track y and z. 2 is the output value of the expanded observer, used to track the total disturbance f, A, B, C are all constant matrices;

[0103] 3.2. Perform pole configuration for the ADRC, calculate the controller bandwidth, observer bandwidth, and controller gain to control the high voltage ride-through capability.

[0104] Formula (11) is obtained by calculating according to formula (8) and formula (10):

[0105]

[0106] Only when the eigenvalue of (A-LC) is less than 0, can xz be delayed over time and approach 0.

[0107] The bandwidth method is used for configuration:

[0108] β1=2ω0

[0109] Where y is the system output, w is the external disturbance, t is the time-varying disturbance, Z is the output of the extended observer, β1β2 are the two parameters of the state observer, L is the transpose of [β1β2], and ω0 is the controller bandwidth

[0110] Since the system is first-order

[0111]

[0112] Simple PD control of the integrator series system:

[0113] u0=k p (ref-z1) (13)

[0114] k p =ω c (14)

[0115] ω c is the PD controller gain.

[0116] In summary, the parameters that need to be adjusted in the ADRC are as follows:

[0117] β1=2ω0 k p =ω c .

[0118] The principle of the high voltage ride through control method of the present invention which introduces the active disturbance rejection control is as follows:

[0119] Doubly-fed wind turbine generators use wound induction generators, with the stator side directly connected to the grid and the rotor side connected to the grid through back-to-back converters, namely the rotor-side converter (RSC) and the grid-side converter (GSC). Both the rotor and the stator can feed power to the grid, so they are called "doubly-fed" generators. The part studied in this paper is the rotor-side control strategy, such as Figure 1 As shown, the inner loop uses active disturbance rejection to replace traditional PI control.

[0120] When a grid fault occurs, causing the machine-end voltage to rise instantaneously, the stator flux of the doubly-fed wind turbine cannot change suddenly, resulting in excessive current on the rotor side, which can cause damage to the power electronic devices. A high voltage ride-through control strategy is proposed to solve this problem.

[0121] Example 1

[0122] In order to verify the performance of the proposed high voltage ride through control method, an electromagnetic transient model of a doubly fed wind power generation system was established in Simulink. The doubly fed wind turbine and line parameters were referenced to the actual line and were reasonably modified to meet the simulation requirements.

[0123] The design steps of high voltage control strategy with ADRC are as follows:

[0124] 1) Collect the d-axis active current, q-axis reactive current, d-axis voltage, q-axis voltage, and stator flux data of the doubly-fed wind turbine rotor side at the time of the fault;

[0125] 2) Analyze the data collected in step (1) to find out the transient process of voltage, current and flux linkage on the rotor side when the DFIG fails, and calculate the inner loop transfer function;

[0126] 3) Introduce active disturbance rejection control (ADRC) to control the inner loop transfer function in the double closed loop: attribute all nonlinear factors and disturbance factors in the system to the system disturbance f, design an extended observer to observe and estimate the total disturbance f in real time, select state variables and calculate their state equations; use the disturbance compensation link to perform active feedback compensation; perform pole configuration on the ADRC, calculate the controller bandwidth, observer bandwidth, and controller gain

[0127] Simulink is used to perform simulation tests and verify the performance of the high voltage ride-through control method for different voltage rise levels.

[0128] Figure 2(a) is the waveform of the voltage rise at the machine end. Figure 2(b) is the waveform of the rotor side current. Figure 2(c) is the waveform of the reactive power output of the doubly-fed wind power generation system.

[0129] From Figure 2(a), we can find the instantaneous rise of the terminal voltage;

[0130] From Figure 2(b), it can be seen that the overcurrent on the rotor side does not exceed 1.2pu;

[0131] From Figure 2(c), we can see that when the generator terminal voltage rises instantaneously, the system injects reactive power into the grid to restore the grid voltage.

Claims

1. A high voltage ride through control method using active disturbance rejection control is introduced, characterized in that: The specific steps include: Step 1: Collect the d-axis active current, q-axis reactive current, d-axis voltage, q-axis voltage, and stator flux data of the doubly-fed wind turbine rotor side at the time of the fault, and design an outer loop control strategy; Step 2, analyzing the data collected in step 1, the voltage, current, and flux transient process on the rotor side when the DFIG fails, and calculating the inner loop transfer function; Step 2 is as follows: The rotor dq axis voltage is expressed as follows: In formula (3), u rd is the rotor d-axis voltage, u rq is the rotor q-axis voltage; L r is the rotor inductance, R r is the rotor resistance; L s is the stator side inductance, L m is the mutual inductance between the stator and the rotor, i rd is the d-axis current on the rotor side, i rq is the q-axis current on the rotor side; ω slip ——Slip angle frequency ω1——synchronous angular velocity U s ——Stator voltage According to formula (3), it can be seen that there is a coupling phenomenon between the d-axis and q-axis components. Therefore, it is necessary to decouple them through feedback input to realize that the d-axis component of the rotor current controls the active power of the DFIG, and the q-axis component controls the reactive power transmitted from the DFIG to the grid. u dcomp Indicates the d-axis feedback input, u qcomp It represents the dq axis feedback input quantity. The feedback input quantity is compensated before the signal is input into the SVPWM signal generator. Therefore, the feedback compensation is ignored when calculating the inner loop transfer function. According to formula (4), the inner loop transfer function of the dq axis control strategy can be derived: G d (s) is the transfer function of the inner ring of the d-axis, G q (s) is the q-axis inner loop transfer function, R r Rotor resistance, L r for Rotor inductance; Step 3, introduce the anti-disturbance control to control the inner loop transfer function in the double closed loop; Step 3 is as follows: Step 3.1: All nonlinear factors and disturbance factors in the system are attributed to the system disturbance f, and an extended observer is designed to observe and estimate the total disturbance f of the system in real time. The state variables are selected and their state equations are calculated. Formula (7) is used to calculate the relationship between the system output y and the total disturbance f: b is the control quantity gain, f is the total disturbance, and u is the system control quantity; State variable selection: Using formula (8), the state equation (9) of the extended state observer is designed: Simplify formula (9): β1 and β2 are two parameters of the state observer, b0 is the estimated value of the control gain, z1 is the output value of the extended state observer, used to track y, z2 is the output value of the extended observer, used to track the total disturbance f, A, B, C are all constant matrices; Step 3.2: Perform pole configuration for the ADRC, calculate the controller bandwidth, observer bandwidth, and controller gain to control the high voltage ride-through capability; Formula (11) is obtained by calculating according to formula (8) and formula (10): Only when the eigenvalue of A-LC is less than 0, xz will be delayed over time and approach 0; the bandwidth method is used to configure and obtain: β1=2ω0 Where y is the system output, w is the external disturbance, t is the time-varying disturbance, z is the output of the extended observer, β1 and β2 are two parameters of the state observer, L is the transpose of [β1β2], and ω0 is the controller bandwidth; Since the system is first-order Simple PD control of the integrator series system: u0=k p (ref-z1) (13) k p =ω c (14) ω c is the PD controller gain, u0 is the current error value after amplification, and ref is the current reference value obtained by the power outer loop through the PI controller; Therefore, the parameters that need to be adjusted in the ADRC are as follows: β1=2ω0 k p =ω c 。 2. The high voltage ride through control method with active disturbance rejection control according to claim 1, characterized in that: Step 1 is as follows: The reference value of the outer loop is the stator active power P s and reactive power Q s : According to formula (1), a PI controller is designed to control the power outer loop: i rd is the d-axis current on the rotor side, i rq is the q-axis current on the rotor side, is the d-axis reference current on the rotor side, is the q-axis reference current on the rotor side; is the stator reactive power reference value, P s ref is the stator active power reference value, U s is the stator voltage, ω1 is the synchronous angular velocity, L s is the stator side inductance, L m is the mutual inductance between stator and rotor, k p is the proportional coefficient of the PI controller, k i is the integral coefficient of the PI controller; In order to make the doubly fed wind turbine work at full power, the active power reference value P is set. s ref 1, reactive power reference value is 0; the dq axis current reference value is obtained by PI controlling the power outer loop, which is used as the input of the current inner loop transfer function, and finally the high voltage ride through control capability is improved.

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