Impedance modeling system and method for energy storage type doubly-fed phase modifier running at non-constant rotating speed

Abstract

The invention discloses an impedance modeling system and method for an energy storage type doubly-fed phase modifier running at a non-constant rotating speed, and belongs to the technical field of power system control. In order to solve the problems that the low-frequency-band precision is insufficient and the design margin of a controller is lacked due to the fact that an existing model neglects the influence of variable-speed operation on impedance characteristics, the method comprises the steps that by analyzing the coupling mechanism of the rotating speed dynamic state and the electromagnetic-electromechanical process, the equation of the controller and a motor is corrected, and a non-constant rotating speed impedance model containing the angular acceleration dynamic state is constructed; an inner and outer ring collaborative analysis method is introduced, an influence rule of variable-speed operation on low-frequency (1Hz-10Hz) and super-synchronous frequency band impedance is quantified, and a design criterion that a controller needs to additionally reserve 3% of margin is provided. According to the method, the limitation of a traditional constant speed model under a complex working condition is solved, the performance of the phase modifier in broadband oscillation suppression is remarkably improved, and the method is suitable for active / reactive coordinated regulation and stability optimization in a high-proportion new energy power grid.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system control, and in particular relates to an impedance modeling system and method for an energy storage type double-fed phase shifter operating at a non-constant speed. Background Art

[0002] As the proportion of renewable energy in the power system continues to increase, the grid's inertia and dynamic regulation capabilities have significantly declined, leading to increasingly prominent system stability issues. As a new type of power equipment, energy storage-based doubly fed phase-shifting condensers (DFSCs) can simultaneously provide active and reactive power support, potentially improving the grid's small-signal stability. Previous literature has analyzed the active power support provided by new DFSCs with energy storage and discussed typical application scenarios, such as high-proportion renewable energy grids and the transmitting and receiving ends of direct current transmission. Energy storage-based DFSCs can effectively support grid voltage and suppress broadband oscillations of renewable energy, thereby improving the grid's security and stability.

[0003] However, existing impedance models for doubly-fed (DFIG) condensers with energy storage are often based on the assumption of constant-speed operation, failing to fully consider the impact of variable-speed operation on impedance characteristics, particularly the coupling effect between rotor speed dynamics and low-frequency impedance during active power support. This deficiency prevents traditional models from accurately characterizing the ability of DFIG condensers to suppress grid oscillations under variable-speed operation, limiting their application in complex operating conditions.

[0004] Therefore, an impedance modeling method for non-constant speed conditions is urgently needed to improve the performance of energy storage doubly fed phase shifters in broadband oscillation suppression. Summary of the Invention

[0005] The present invention proposes an impedance modeling method for an energy storage-type doubly-fed phase-shifting condenser under non-constant speed and an adaptive damping controller design method. By introducing the coupling analysis of rotor speed dynamics and inner and outer loop control, the traditional constant speed model is modified, the accuracy of the impedance model is improved, and the controller design is optimized to enhance the grid oscillation suppression capability.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides an impedance modeling system for an energy storage type doubly fed phase shifter operating at a non-constant speed, comprising a doubly fed asynchronous motor, a flywheel energy storage device, a controller module, and an impedance analysis module.

[0008] The doubly-fed asynchronous motor has its rotor side connected to the grid via a back-to-back converter, and its stator side directly connected to the grid;

[0009] The flywheel energy storage device is coaxially connected to the doubly-fed asynchronous motor to provide inertia support and speed regulation;

[0010] The controller module corrects the speed command and reactive power output in real time;

[0011] The impedance analysis module generates an impedance characteristic curve based on the modified model and outputs optimized parameters of the damping controller.

[0012] Specifically, the controller module includes a cascade control structure, an outer loop for speed control and reactive power control, and an inner loop for rotor current decoupling control.

[0013] The present invention also provides an impedance modeling method for an energy storage type double-fed phase shifter operating at a non-constant speed, the method comprising the following steps:

[0014] (1) Analyze the coupling mechanism between speed dynamics and electromagnetic and electromechanical processes of the energy storage type doubly fed phase shifter, and determine the influence of the rotor current-speed inner loop dynamics and the rotor angle-measurement outer loop dynamics on the impedance characteristics;

[0015] (2) Establish and modify the small signal model of the motor controller, introduce angular acceleration dynamics into the speed control link, and update the transfer function of the speed controller;

[0016] (3) Establish and modify the small signal model of the doubly-fed asynchronous motor, couple the relationship between speed fluctuation and torque response, and update the rotor voltage equation and speed dynamic equation;

[0017] (4) The phase-locked loop closed-loop transfer function, signal measurement filter model, modified controller and motor equations are combined to construct an impedance model under non-constant speed.

[0018] Specifically, in step (1), the coupling mechanism includes the rotor current acting on the speed through the electromechanical equation, and the speed dynamics is coupled to the closed-loop path of the rotor voltage and current through coordinate transformation, wherein the time scale similarity of the rotor current-speed inner loop dynamics is proportional to the magnitude of the impact on the low-frequency impedance characteristics.

[0019] Furthermore, in step (1), the influence of the rotor current-speed inner loop dynamics and the rotor angle-measurement outer loop dynamics on the impedance characteristics is determined; specifically:

[0020] Establish an equivalent model of the signal measurement link, and measure the current signal through the filter and Park transform T park (θ) is then converted into dq axis components to participate in the control; since the angle signal is obtained through the phase-locked loop, it is regarded as a Park transform T without considering the dynamics of the phase-locked loop. park (θ0), due to the influence of disturbances caused by the phase-locked loop and the motor rotor dynamics T park (θ p -θ r );

[0021]

[0022] Where i D and i Q is the current signal measured on the d-axis and q-axis, i D0 and i Q0 To disregard the park transformation result of the phase-locked loop dynamics, I D and I Q is the steady-state current, θ p The angle disturbance caused by PLL, θ r The angular disturbance caused by the motor rotor.

[0023] Furthermore, the step (2) is specifically as follows:

[0024] The energy storage AC condenser uses the ramp command of the speed loop to achieve energy recovery during the storage process. During the active power support process, the speed is continuously adjusted. The high-order speed command changes are treated as disturbances or noise, and the corresponding system response is:

[0025] ω mtr (t) = ω m0 +ω m +(β0+β)t

[0026] Where, ω mtr is the large signal model of the motor speed, ω m0 is the initial speed of the motor, ω m is the small signal of the motor speed, β0 is the steady-state response of the acceleration command, and β is the small signal of the acceleration response;

[0027] Furthermore, the motor's acceleration response small signal has the following relationship:

[0028]

[0029] Where, L m is the magnetizing inductance, L s is the stator inductance, L r is the rotor inductance, p is the number of rotor pole pairs, ω0 is the synchronous speed of the rotor, β is the small signal of the acceleration response, J is the moment of inertia of the phase regulator, s p is the small signal interference voltage frequency, i D 、i Q is the rotor current, U s is the grid voltage.

[0030] The dynamics of the angular acceleration will be coupled to the speed controller, and the small signal equation that needs to be corrected is:

[0031]

[0032] uq0 =-H iQ H Q Q s -H iQ i Q +K iQ i D

[0033] Where H iD is the rotor side D axis current controller, H ω is the motor speed controller, K iD is the rotor side D-axis current feedforward coefficient, HiQ is the Q-axis current controller, HQ is the Q-axis reactive power controller, s p is the small signal interference voltage frequency, u d0 、u q0 To correct the small voltage signal.

[0034] Furthermore, the small signal equation for correcting the motor rotor voltage is:

[0035] u D =R r i D -(ω0-ω m0 -β0 / s p )ψ Q +(ω m +β / s p )Ψ Q +s p ψ D

[0036] u Q =R r i Q +(ω0-ω m0 -β0 / s p )ψ D -(ω m +β / s p )Ψ D +s p ψ Q

[0037] Where R r is the rotor resistance, ω m0 is the initial mechanical angular velocity of the motor, ω m is the small signal value of the motor's mechanical angular velocity, β0 is the steady-state value of the motor's angular acceleration, and β is the small signal value of the motor's angular acceleration.

[0038] Furthermore, in step (3), the small signal model of the doubly-fed asynchronous motor is corrected, that is, the corrected motor rotor voltage small signal equation is:

[0039] u D =Rr i D -(ω0-ω m0 -β0 / s p )ψ Q

[0040] +(ω m +β / s p )Ψ Q +s p ψ D

[0041] u Q =R r i Q +(ω0-ω m0 -β0 / s p )ψ D

[0042] -(ω m +β / s p )Ψ D +s p ψ Q

[0043] Where R r is the rotor resistance, ω m0 is the initial mechanical angular velocity of the motor, ω0 is the synchronous speed of the rotor, ω m is the small signal value of the motor mechanical angular velocity, β0 is the steady-state value of the motor angular acceleration, β is the small signal value of the motor angular acceleration, u D 、u Q is the actual voltage acting on the motor rotor side after inverse transformation, ψ D is the D-axis magnetic flux small signal, ψ Q is the Q-axis magnetic flux small signal.

[0044] The beneficial effects of the present invention are as follows:

[0045] This column establishes impedance modeling for an energy-storage doubly-fed phase-shifting condenser under non-constant speed conditions. It analyzes the impact of active power support, or the first-order minima of the motor speed regulation process, on the system impedance model within the 1-100 Hz frequency band. This lays the foundation for designing damping controllers for energy-storage doubly-fed phase-shifting condensers under wide-slip operating conditions. Future work will further explore the oscillation suppression potential of energy-storage doubly-fed phase-shifting condensers in scenarios such as active power support in specific frequency bands. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a structural diagram of the rotor-side controller of the energy storage type doubly-fed phase regulator of the present invention;

[0047] Figure 2 This is an impedance model diagram of the energy storage type double-fed phase shifter at a constant speed of the present invention;

[0048] Figure 3 The figure is a coupling mechanism diagram of the speed dynamics of the energy storage type double-fed phase regulator of the present invention;

[0049] Figure 4 This is a comparison and verification diagram of the impedance model measurement and modeling of the energy storage type double-fed phase shifter of the present invention. Specific embodiments

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0051] To achieve the above object, the present invention adopts the following technical solutions:

[0052] (1) Analyze the coupling mechanism between speed dynamics and electromagnetic and electromechanical processes of the energy storage type doubly fed phase shifter, and determine the influence of the rotor current-speed inner loop dynamics and the rotor angle-measurement outer loop dynamics on the impedance characteristics;

[0053] (2) Establish and modify the small signal model of the motor controller, introduce angular acceleration dynamics into the speed control link, and update the transfer function of the speed controller;

[0054] (3) Establish and modify the small signal model of the doubly-fed asynchronous motor, couple the relationship between speed fluctuation and torque response, and update the rotor voltage equation and speed dynamic equation;

[0055] (4) The phase-locked loop closed-loop transfer function, signal measurement filter model, modified controller and motor equations are combined to construct an impedance model under non-constant speed.

[0056] The step (1) is specifically as follows:

[0057] Establish an equivalent model of the signal measurement link, and measure the current signal through the filter and Park transform T park (θ) is then converted into dq axis components to participate in the control. Since the angle signal is obtained through the phase-locked loop, it can be regarded as a Park transform T without considering the dynamics of the phase-locked loop. park (θ0), considering the influence of disturbances caused by the phase-locked loop and the motor rotor dynamics T park (θ p -θ r ).

[0058]

[0059] Where iD0 and i Q0 is the current signal measured on the d-axis and q-axis, i D0 and i Q0 To disregard the park transformation result of the phase-locked loop dynamics, I D and I Q is the steady-state current, θ p The angle disturbance caused by PLL, θ r Angular disturbance caused by the motor rotor

[0060] Furthermore, a small signal model of motor control is established, and the small signal of the motor speed controller's control effect on the motor voltage is as follows: Figure 1 , the expression is:

[0061] u D0 =-H iD H ω ω m -H D i D -K iD i Q

[0062] u Q0 =-H iQ H Q Q s -H Q i Q +K iQ i D

[0063] Where H ω is the speed controller, H iD is the rotor D-axis current controller, K iD is the D-axis current feedforward coefficient, H Q is the reactive power controller, H iQ is the Q-axis current controller, K iQ is the Q-axis current feedforward coefficient.

[0064] Furthermore, a small signal model of the doubly-fed asynchronous motor is established, and the voltage equation of the motor is:

[0065] u d =R s i d -ω0ψ q +s p ψ d

[0066] u q =R s i q +ω0ψ d +s p ψ q

[0067] u D =R r i D -(ω0-Ω m )ψ Q +ω m Ψ Q +s p ψ D

[0068] u Q =R r i Q +(ω0-ω m )ψ D -ω m Ψ D +s p ψ Q

[0069] In the formula, according to the stator voltage orientation, u d +ju q is the injected small signal, i d i q is the stator current, i D i Q is the rotor current, Ψ D Ψ Q is the steady-state value of the rotor flux, ψ D is the D-axis magnetic flux small signal, ψ Q is the Q-axis magnetic flux small signal, Ω m is the steady-state value of the motor's mechanical speed.

[0070] In summary, the impedance relationship of the motor can be obtained. Each relationship can be summarized as the controller obtains the control voltage of the motor based on the input and the feedback of the motor, and obtains the actual applied control voltage u of the motor through inverse transformation. D and u Q The motor equation takes the rotor control voltage as input, obtains the rotor and stator current responses of the motor, and sends them to the motor controller through Park transformation and measurement links to form Figure 2 closed-loop structure.

[0071] The step (2) is specifically as follows:

[0072] The energy storage AC condenser uses the ramp command of the speed loop to achieve energy recovery during the storage process. During the active power support process, it can also be considered as a continuous adjustment of the speed. Treating high-order speed command changes as disturbances or noise, the corresponding system response will be:

[0073] ω mtr (t) = ω m0 +ω m +(β0+β)t

[0074] Where, ω mtr is the large signal model of the motor speed, ω m0 is the initial speed of the motor, ω m is the small signal of motor speed, β0 is the steady-state response of acceleration command, and β is the small signal of acceleration response.

[0075] Furthermore, the motor's acceleration response small signal has the following relationship:

[0076]

[0077] Where, L m is the magnetizing inductance, L s is the stator inductance, L r is the rotor inductance, p is the number of rotor pole pairs, and ω0 is the synchronous speed of the rotor.

[0078] like Figure 3 As shown in FIG, the coupling mechanism diagram of the speed dynamics of the energy storage type doubly fed phase regulator of the present invention is shown; specifically, the dynamics of the angular acceleration will be coupled to the speed controller, and the small signal equation that needs to be corrected is:

[0079]

[0080] u q0 =-H iQ H Q Q s -H iQ i Q +K iQ i D

[0081] Where H iD is the rotor side D axis current controller, H Ω is the motor speed controller, K iD is the rotor side D axis current feedforward coefficient, H iQ is the Q-axis current controller, H Q is the Q-axis reactive power controller, u d0 、u q0 To correct the small voltage signal, s p is the small signal interference voltage frequency, i D 、i Q is the rotor current, Q s is the grid-side reactive power, K iQ It is the D-axis current controller.

[0082] Furthermore, the small signal equation for correcting the motor rotor voltage is:

[0083] u D =R r iD -(ω0-ω m0 -β0 / s p )ψ Q +(ω m +β / s p )Ψ Q +s p ψ D

[0084] u Q =R r i Q +(ω0-ω m0 -β0 / s p )ψ D -(ω m +β / s p )Ψ D +s p ψ Q

[0085] Where R r is the rotor resistance, ω m0 is the initial mechanical angular velocity of the motor, ω m is the small signal value of the motor's mechanical angular velocity, β0 is the steady-state value of the motor's angular acceleration, and β is the small signal value of the motor's angular acceleration.

[0086] The key parameters of the energy storage type double-fed phase regulator analyzed in this invention are shown in Table 1.

[0087] Table 1

[0088] Performance parameters Numerical unit Stator resistance@115℃ 0.031 Ω Stator leakage reactance 0.429 Ω Rotor resistance @115℃ 0.026 Ω Rotor leakage reactance 0.409 Ω Excitation reactance 24.71 Ω Rated active power 10 MW Rated reactive power 11 MVar Slip range -0.2～0.3 pu Pole pairs 2 /

[0089] This study uses electromagnetic transient simulation to perform swept-frequency measurements on the impedance model of a doubly-fed phase-shifting condenser (DFSC). This measurement is compared with theoretical analysis to verify the model's validity. After the motor enters steady-state operation, a voltage disturbance is injected at the motor's grid connection point. Fourier analysis is used to calculate the response current at a specific frequency, thereby determining the impedance of the energy storage DFSC at that specific frequency.

[0090] The impedance characteristics of a doubly-fed (DFIG) condenser with energy storage are primarily influenced by three key operating point parameters: active power support, reactive power support, and motor slip. A typical operating state for a DFIG is outputting inductive reactive power Q = -0.8 pu, with no active power support P = 0 pu, and the motor operating at a supersynchronous speed s = -0.05 pu. In this case, the introduction of non-constant speed has no effect on the system's impedance characteristics; the theoretically calculated impedance characteristics remain consistent regardless of active power support considerations. The waveforms of the impedance measured using the voltage injection method and those calculated using simulation are shown in the figure. The waveforms overlap within the 1-500 Hz range, demonstrating that the model is effective and can accurately represent the impedance characteristics of the DFIG.

[0091] The real part of the impedance model indicates the contribution of the phase-shifting system to the oscillation. When the real impedance is less than 0, it indicates that there is an oscillation risk in this frequency band. When the imaginary impedance is less than 0, it indicates that capacitive current may exist in this frequency band, and there may be a resonance risk.

[0092] Those skilled in the art will readily conceive of other embodiments of the present application after considering the specification and practicing the contents disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of this application and include common knowledge or customary techniques in the art that are not disclosed in this application.

[0093] It will be understood that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. An impedance modeling system for a non-constant speed energy storage type double-fed phase shifter, characterized in that: Including doubly-fed asynchronous motor, flywheel energy storage device, controller module and impedance analysis module: The doubly-fed asynchronous motor has its rotor side connected to the grid via a back-to-back converter, and its stator side directly connected to the grid; The flywheel energy storage device is coaxially connected to the doubly-fed asynchronous motor to provide inertia support and speed regulation; The controller module corrects the speed command and reactive power output in real time; The impedance analysis module generates an impedance characteristic curve based on the modified model and outputs optimized parameters of the damping controller.

2. The system according to claim 1, wherein: The controller module includes a cascade control structure, an outer loop for speed control and reactive power control, and an inner loop for rotor current decoupling control.

3. A modeling method for an impedance modeling system of an energy storage type double-fed phase shifter operating at a non-constant speed according to any one of claims 1-2, characterized in that: The method comprises the following steps: (1) Analyze the coupling mechanism between speed dynamics and electromagnetic and electromechanical processes of the energy storage type doubly fed phase shifter, and determine the influence of the rotor current-speed inner loop dynamics and the rotor angle-measurement outer loop dynamics on the impedance characteristics; (2) Establish and modify the small signal model of the motor controller, introduce angular acceleration dynamics into the speed control link, and update the transfer function of the speed controller; (3) Establish and modify the small signal model of the doubly-fed asynchronous motor, couple the relationship between speed fluctuation and torque response, and update the rotor voltage equation and speed dynamic equation; (4) The phase-locked loop closed-loop transfer function, signal measurement filter model, modified controller and motor equations are combined to construct an impedance model under non-constant speed.

4. The impedance modeling method for a non-constant speed energy storage type double-fed phase shifter according to claim 3 is characterized in that: In step (1), the coupling mechanism includes the rotor current acting on the speed through the electromechanical equation, and the speed dynamics being coupled to the closed-loop path of the rotor voltage and current through coordinate transformation, wherein the time scale similarity of the rotor current-speed inner loop dynamics is proportional to the magnitude of the impact on the low-frequency impedance characteristics.

5. The impedance modeling method for a non-constant speed energy storage type double-fed phase shifter according to claim 3 is characterized in that: In the step (1), the influence of the rotor current-speed inner loop dynamics and the rotor angle-measurement outer loop dynamics on the impedance characteristics is determined; specifically: Establish an equivalent model of the signal measurement link, and measure the current signal through the filter and Park transform T park (θ) is then converted into dq axis components to participate in the control; since the angle signal is obtained through the phase-locked loop, it is regarded as a Park transform T without considering the dynamics of the phase-locked loop. park (θ0), due to the influence of disturbances caused by the phase-locked loop and the motor rotor dynamics T park (θ p -θ r ); Where i D and i Q is the current signal measured on the d-axis and q-axis, i D0 and i Q0 To disregard the park transformation result of the phase-locked loop dynamics, I D and I Q is the steady-state current, θ p The angle disturbance caused by PLL, θ r The angular disturbance caused by the motor rotor.

6. The impedance modeling method for a non-constant speed energy storage type double-fed phase shifter according to claim 3 is characterized in that: The step (2) is specifically as follows: The energy storage AC condenser uses the ramp command of the speed loop to achieve energy recovery during the storage process. During the active power support process, the speed is continuously adjusted. The high-order speed command changes are treated as disturbances or noise, and the corresponding system response is: oh mtr (t)=ω m0 +oh m +(β0+β)t Where, ω mtr is the large signal model of the motor speed, ω m0 is the initial speed of the motor, ω m is the small signal of the motor speed, β0 is the steady-state response of the acceleration command, and β is the small signal of the acceleration response; Furthermore, the motor's acceleration response small signal has the following relationship: Where, L m is the magnetizing inductance, L s is the stator inductance, L r is the rotor inductance, p is the number of rotor pole pairs, ω0 is the synchronous speed of the rotor, β is the small signal of the acceleration response, J is the moment of inertia of the phase regulator, s p is the small signal interference voltage frequency, i D 、i Q is the rotor current, U s is the grid voltage. The dynamics of the angular acceleration will be coupled to the speed controller, and the small signal equation that needs to be corrected is: u q0 =-H iQ H Q Q s -H iQ i Q +K iQ i D Where H iD is the rotor side D axis current controller, H ω is the motor speed controller, K iD is the rotor side D-axis current feedforward coefficient, HiQ is the Q-axis current controller, HQ is the Q-axis reactive power controller, s p is the small signal interference voltage frequency, u d0 、u q0 To correct the small voltage signal. Furthermore, the small signal equation for correcting the motor rotor voltage is: you D =R r I D -(ω0-ω m0 -β0 / s p )ψ Q +(ω m +b / s p )Ψ Q +s p ψ D you Q =R r I Q +(ω0-ω m0 -β0 / s p )ψ D -(oh m +b / s p )Ψ D +s p ψ Q Where R r is the rotor resistance, ω m0 is the initial mechanical angular velocity of the motor, ω m is the small signal value of the motor's mechanical angular velocity, β0 is the steady-state value of the motor's angular acceleration, and β is the small signal value of the motor's angular acceleration.

7. The impedance modeling method for a non-constant speed energy storage type double-fed phase shifter according to claim 3 is characterized in that: In step (3), the small signal model of the doubly-fed asynchronous motor is corrected, that is, the corrected motor rotor voltage small signal equation is: you D =R r I D -(ω0-ω m0 -β0 / s p )ψ Q +(ω m +b / s p )Ψ Q +s p ψ D you Q =R r I Q +(ω0-ω m0 -β0 / s p )ψ D -(oh m +b / s p )Ψ D +s p ψ Q Where R r is the rotor resistance, ω m0 is the initial mechanical angular velocity of the motor, ω0 is the synchronous speed of the rotor, ω m is the small signal value of the motor mechanical angular velocity, β0 is the steady-state value of the motor angular acceleration, β is the small signal value of the motor angular acceleration, u D 、u Q is the actual voltage acting on the motor rotor side after inverse transformation, ψ D is the D-axis magnetic flux small signal, ψ Q is the Q-axis magnetic flux small signal.

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