A method for suppressing oscillation of a new energy grid-connected power generation system containing a network-forming doubly-fed phase-modulation device

Abstract

This invention discloses an oscillation suppression method for a new energy grid-connected power generation system with a grid-type doubly-fed induction generator (DFIG) connected to the grid. A virtual impedance controller is added to the control system of the DFIG, and the output signal Δu of the virtual impedance controller... rd , Δu rq The virtual inductance and virtual resistance are obtained based on optimization. These virtual inductance and virtual resistance are optimized using a dual-variable collaborative iterative method, with phase margin constraints at the system's dominant oscillation frequency and system static stability constraints as dual optimization objectives. During the small-disturbance oscillation instability period of the new energy grid-connected power generation system, feeding the output signal of the virtual impedance controller forward to the output voltage modulation command can reshape the system's impedance characteristics, improve the phase margin at the system's resonant frequency, and enhance the stable operation level of the new energy grid-connected power generation system.

Description

Technical Field

[0001] This invention relates to a method for oscillation suppression in a new energy grid-connected power generation system with a doubly fed phase-modulation device connected to a grid. This method can significantly improve the small-disturbance stability level of the new energy grid-connected power generation system with a doubly fed phase-modulation device connected to a grid, while ensuring that the system does not lack a static stable operating point. It belongs to the field of new energy power generation technology. Background Technology

[0002] The grid connection synchronization and power transmission of new energy power generation systems are highly dependent on phase-locked loop (PLL) synchronization mechanisms, whose synchronization performance is directly affected by voltage amplitude and phase fluctuations at the grid connection point. Under weak grid conditions, traditional PLLs are susceptible to synchronization deviations or even instability due to voltage dips and grid impedance. Furthermore, their control systems are prone to small-disturbance oscillations and instability during interaction with the external grid. To improve the stable operation of new energy grid-connected systems with grid-type phase-locking equipment in weak grid conditions, in-depth research is needed on methods to enhance the system's static stability and small-disturbance stability. Currently, domestic and international scholars have conducted relevant research, as exemplified by the following published literature:

[0003] [1] Qi Xiaoxiao, Cheng Jing, Wang Weiqing, et al. Subsynchronous Oscillation Suppression Method for Photovoltaic Power Generation Grid-connected System Based on SC[J]. Smart Power, 2023, 51(05): 88-95.

[0004] [2] DU N, ZHOU P, YANG D, et al. Research on synchronous condensers to suppress subsynchronous oscillation caused by new energy power generation[C] / / 2021 6th Asia Conference on Power and Electrical Engineering (ACPEE): IEEE Press, Chongqing: 2021, 247-251.

[0005] Reference [1] proposes a method for suppressing subsynchronous oscillations in photovoltaic grid-connected systems based on a new generation of synchronous condensers, which effectively suppresses subsynchronous oscillations in photovoltaic grid-connected systems. Reference [2] uses the eigenvalue analysis method to analyze the influence of synchronous condensers on the damping ratio and eigenvalue distribution of new energy power generation systems, and verifies the feasibility of synchronous condensers suppressing subsynchronous oscillations. However, the above two oscillation suppression schemes are only for traditional synchronous condenser equipment and are difficult to adapt to new energy grid-connected systems with grid-type condenser equipment, and cannot meet the oscillation suppression requirements of this type of new system. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, the present invention aims to propose an oscillation suppression method for new energy grid-connected power generation systems with grid-connected doubly-fed induction generators. This method, through optimization and improvement of the control system of the grid-connected doubly-fed induction generator, can significantly improve the small-interference stability performance of new energy grid-connected power generation systems under weak grid conditions, while ensuring that the system's active power output capability is not affected.

[0007] The technical solution of this invention is implemented as follows:

[0008] A method for suppressing oscillations in a grid-connected renewable energy power generation system with a doubly-fed induction generator (DFIG) connected to a grid-type grid includes the following steps:

[0009] A1) The grid-type doubly-fed phase-modulation equipment uses the conventional method of motor detection to detect the rotor-side current signal I of the doubly-fed motor. r The current signal I is directed by the d-axis voltage orientation method at the grid connection point. r Converted to two-phase DC signal i rd i rq ;

[0010] A2) The two-phase DC signals i obtained in step A1) rd i rq The input is fed into the virtual impedance controller, and the output signal Δu of the virtual impedance controller is calculated according to the following formula. rd , Δu rq :

[0011]

[0012] In the formula, L vsg R vsg These are virtual inductance and virtual resistance, respectively, where ω1 is the system's rated angular frequency, and s slip s is the slip of the doubly fed phase modulation equipment; s is the Laplace operator;

[0013] Among them, the virtual inductance L vsg and virtual resistance R vsg Tuning is performed as follows; using the system's dominant oscillation frequency f x The phase margin constraint and the system static stability constraint are the dual optimization objectives, and a two-variable collaborative iterative method is used for optimization: First, L is configured. vsg R vsg The initial value of the iteration is L, which is fixed in each iteration. vsg R vsgOne parameter is used to perform a one-dimensional optimization update of the other parameter along the phase margin improvement direction, while simultaneously verifying whether the current parameter combination satisfies the static stability constraint. Then, the updated parameter is fixed, and the other parameter, which was fixed in the previous iteration, is iteratively updated. This process is repeated until the phase margin meets the preset convergence threshold and the system satisfies the static stability requirement, ultimately yielding a virtual inductor L that simultaneously satisfies both the small-disturbance stability constraint and the static stability constraint. vsg and virtual resistance R vsg Small disturbance stability constraints and static stability constraints are expressed as follows:

[0014]

[0015] In the formula, Z p Z n Z represents the positive and negative sequence equivalent impedances of the new energy grid-connected power generation system, respectively. zp Z zn These are the positive and negative sequence impedances of the power grid, respectively; P pm I pm These represent the transmitted power and output current of the new energy grid-connected power generation system, respectively. Ipv pm0 represents the maximum output current value that satisfies the static power stability of the system without additional control strategies; where P pm It can be expressed by the following formula:

[0016]

[0017]

[0018] In the formula, E s U z L represents the equivalent voltage of the grid-type doubly-fed induction generator and the grid voltage, respectively. v L z These represent the equivalent series inductance and line inductance of a grid-type doubly-fed phase-modulation device, respectively. , , , It is an intermediate variable with no clear physical meaning;

[0019] A3) During the small-disturbance oscillation instability period of the new energy grid-connected power generation system, the output signal Δu of the virtual impedance controller will be... rd , Δu rq Feedforward to output voltage modulation command, that is, to reshape the impedance characteristics of the system, improve the phase margin at the system resonant frequency point, and improve the stable operation level of the new energy grid-connected power generation system.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention adds a virtual impedance control loop to the control system of a grid-type doubly fed phase modulation device. During the period of small disturbance oscillation instability, the virtual impedance control strategy is implemented. Under the premise of ensuring that the static stable operating point of the system is not lost, the impedance characteristics of the system can be reshaped, the phase margin of the system at the resonant frequency point can be improved, the stability level of the system under small disturbances can be improved, and the active power output capability of the system can be ensured to remain unaffected. Attached Figure Description

[0022] Figure 1 A schematic diagram of a new energy grid-connected power generation system with a doubly fed phase-modulation device connected to a grid-type grid.

[0023] Figure 2 This is a schematic diagram of the virtual impedance control strategy proposed in this invention.

[0024] Figure 3 The simulation waveforms are shown after the system is subjected to virtual impedance control strategies designed with different parameters during small disturbance oscillation instability. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0026] This invention is used to improve the stable operation capability of new energy grid-connected power generation systems with grid-type doubly fed phase-modulation equipment. Figure 1 A schematic diagram of a new energy grid-connected power generation system with a doubly fed phase-modulation device connected to a grid-type grid. Figure 2 This is a schematic diagram of the virtual impedance control strategy proposed in this invention. During the period of system instability due to small disturbances, the virtual impedance control strategy can reshape the impedance characteristics of the system, improve the phase margin at the system's resonant frequency, and thus improve the system's stable operation.

[0027] The specific implementation steps of this invention are as follows:

[0028] A1) The grid-type doubly-fed phase-modulation equipment uses the conventional method of motor detection to detect the rotor-side current signal I of the doubly-fed motor. r The current signal I is directed by the d-axis voltage orientation method at the grid connection point. r Converted to two-phase DC signal i rd i rq ;

[0029] A2) The two-phase DC signals i obtained in step A1) rd i rq The input is fed into the virtual impedance controller, and the output signal Δu of the virtual impedance controller is calculated according to the following formula. rd , Δu rq :

[0030]

[0031] In the formula, L vsg R vsg These are virtual inductance and virtual resistance, respectively, where ω1 is the system's rated angular frequency, and s slip s is the slip of the doubly fed phase modulation equipment; s is the Laplace operator;

[0032] Among them, the virtual inductance L vsg and virtual resistance R vsg Tuning is performed as follows; using the system's dominant oscillation frequency f x The phase margin constraint and the system static stability constraint are the dual optimization objectives, and a two-variable collaborative iterative method is used for optimization: First, L is configured. vsg R vsg The initial value of the iteration is L, which is fixed in each iteration. vsg R vsg One parameter is used to perform a one-dimensional optimization update of the other parameter along the phase margin improvement direction, while simultaneously verifying whether the current parameter combination satisfies the static stability constraint. Then, the updated parameter is fixed, and the other parameter, which was fixed in the previous iteration, is iteratively updated. This process is repeated until the phase margin meets the preset convergence threshold and the system satisfies the static stability requirement, ultimately yielding a virtual inductor L that simultaneously satisfies both the small-disturbance stability constraint and the static stability constraint. vsg and virtual resistance R vsg Small disturbance stability constraints and static stability constraints are expressed as follows:

[0033]

[0034] In the formula, Z p Z n Z represents the positive and negative sequence equivalent impedances of the new energy grid-connected power generation system, respectively. zp Z zn These are the positive and negative sequence impedances of the power grid, respectively; P pm I pm These represent the transmitted power and output current of the new energy grid-connected power generation system, respectively. Ipv pm0 represents the maximum output current value that satisfies the static power stability of the system without additional control strategies; where P pm It can be expressed by the following formula:

[0035]

[0036]

[0037] In the formula, E s U z L represents the equivalent voltage of the grid-type doubly-fed induction generator and the grid voltage, respectively. v L zThese represent the equivalent series inductance and line inductance of a grid-type doubly-fed phase-modulation device, respectively.

[0038] A3) During the small-disturbance oscillation instability period of the new energy grid-connected power generation system, the output signal Δu of the virtual impedance controller will be... rd , Δu rq Feedforward to output voltage modulation command, that is, to reshape the impedance characteristics of the system, improve the phase margin at the system resonant frequency point, and improve the stable operation level of the new energy grid-connected power generation system.

[0039] Description of the effects of this invention:

[0040] Figure 3 Time-domain simulation results are presented for a doubly-fed induction generator (DFIG) with different control parameters under small-disturbance oscillations in the system. The system experiences small-disturbance oscillation instability at 2 seconds, and the virtual impedance control strategy with different control parameters is implemented at 3 seconds. When using the control strategy proposed in this invention, the control parameter design simultaneously satisfies both small-disturbance stability constraints and static stability constraints. The time-domain simulation results are as follows: Figure 3 As shown in (1) above, i.e., the two figures on the left, it can be seen that the system can recover stable operation after adopting the control strategy of the present invention, which significantly improves the stability level of the system. When using the existing virtual impedance control strategy, the control parameter design only satisfies the small disturbance stability constraint, but does not satisfy the static stability constraint. Its time-domain simulation results are as follows: Figure 3 As shown in (2) of the figure, i.e. the two figures on the right, it can be seen that after adopting the existing control strategy, the system changes from small disturbance oscillation instability to static instability due to the lack of a stable operating point.

[0041] Therefore, the strategy proposed in this invention can significantly improve the stability level of the system under small disturbances and reduce the risk of small disturbance instability and static instability of the new energy grid-connected power generation system, while ensuring that the system does not lose its stable operating point.

[0042] Finally, it should be noted that the above examples of the present invention are merely illustrative and not intended to limit the implementation of the invention. Although the applicant has described the present invention in detail with reference to preferred embodiments, those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for suppressing oscillations in a new energy grid-connected power generation system with a doubly fed induction generator (DFIG) connected to a grid-type grid, characterized in that: The specific steps are as follows: A1) The grid-type doubly-fed phase-modulation equipment uses the conventional method of motor detection to detect the rotor-side current signal I of the doubly-fed motor. r The current signal I is directed by the d-axis voltage orientation method at the grid connection point. r Converted to two-phase DC signal i rd i rq ; A2) The two-phase DC signals i obtained in step A1) rd i rq The input is fed into the virtual impedance controller, and the output signal Δu of the virtual impedance controller is calculated according to the following formula. rd , Δu rq : In the formula, L vsg R vsg These are virtual inductance and virtual resistance, respectively, where ω1 is the system's rated angular frequency, and s slip s is the slip of the doubly fed phase modulation equipment; s is the Laplace operator; Among them, the virtual inductance L vsg and virtual resistance R vsg Tuning is performed as follows; using the system's dominant oscillation frequency f x The phase margin constraint and the system static stability constraint are the dual optimization objectives, and a two-variable collaborative iterative method is used for optimization: First, L is configured. vsg R vsg The initial value of the iteration is L, which is fixed in each iteration. vsg R vsg One parameter is used to perform a one-dimensional optimization update of the other parameter along the phase margin improvement direction, while simultaneously verifying whether the current parameter combination satisfies the static stability constraint. Then, the updated parameter is fixed, and the other parameter, which was fixed in the previous iteration, is iteratively updated. This process is repeated until the phase margin meets the preset convergence threshold and the system satisfies the static stability requirement, ultimately yielding a virtual inductor L that simultaneously satisfies both the small-disturbance stability constraint and the static stability constraint. vsg and virtual resistance R vsg Small disturbance stability constraints and static stability constraints are expressed as follows: In the formula, Z p Z n Z represents the positive and negative sequence equivalent impedances of the new energy grid-connected power generation system, respectively. zp Z zn These are the positive and negative sequence impedances of the power grid, respectively; P pm I pm These represent the transmitted power and output current of the new energy grid-connected power generation system, respectively. Ipv pm0 represents the maximum output current value that satisfies the static power stability of the system without additional control strategies; where P pm It can be expressed by the following formula: In the formula, E s U z L represents the equivalent voltage of the grid-type doubly-fed induction generator and the grid voltage, respectively. v L z These represent the equivalent series inductance and line inductance of a grid-type doubly-fed phase-modulation device, respectively. , , , It is an intermediate variable with no clear physical meaning; A3) During the small-disturbance oscillation instability period of the new energy grid-connected power generation system, the output signal Δu of the virtual impedance controller will be... rd , Δu rq Feedforward to output voltage modulation command, that is, to reshape the impedance characteristics of the system, improve the phase margin at the system resonant frequency point, and improve the stable operation level of the new energy grid-connected power generation system.

Images