Synchronous stability control method for permanent magnet direct-driven wind power grid-connected system based on double-sequence current self-adaptive controller

Abstract

The invention discloses a synchronous stability control method for a permanent-magnet direct-driven wind power grid-connected system based on a double-sequence current adaptive controller, which comprises the following steps of: firstly, measuring the voltage of a common coupling point of the system as positive and negative sequence phase-locked loop input signals, and obtaining positive and negative sequence phase-locked loop output frequencies after passing through a band-pass filter; calculating an additional reference value of d-axis positive and negative sequence current by using the positive and negative sequence phase-locked loop output frequency and the power grid rated frequency; in the asymmetric short-circuit fault stage of the power grid, if positive-sequence synchronous instability occurs in the permanent magnet direct-driven wind power grid-connected system, the d-axis positive-sequence current additional reference value is superposed to the input of a current loop, and if negative-sequence synchronous instability occurs, the d-axis negative-sequence current additional reference value is superposed to the input of the current loop; therefore, synchronous and stable control of the permanent magnet direct-driven wind power grid-connected system is realized. According to the method, extra device investment is not needed, only the positive and negative sequence current control loop of the permanent magnet direct drive wind power system is optimized and adjusted, and the synchronous stability performance of the system during the asymmetric short-circuit fault period of the power grid can be effectively improved.

Description

Technical Field

[0001] The present invention relates to a synchronous stability control method for a permanent magnet direct drive wind power grid-connected system based on a dual-sequence current adaptive controller. This technology can effectively improve the synchronous stability of the permanent magnet direct drive wind power grid-connected system under the scenario of grid asymmetric short-circuit faults, and belongs to the technical field of clean energy power generation grid connection. Background Technique

[0002] With the progress of wind power generation technology, traditional synchronous power generation equipment has been gradually replaced, and wind power generation will become one of the important supporting forces in the new power system. This will lead to the synchronous stability problem dominated by wind power grid-connected equipment becoming a key issue affecting the safe and stable operation of the power system. In addition, wind power generation bases are mostly located at the end of the power grid, the strength and anti-interference ability of the power grid are weak, and the risk of synchronous instability of the wind power system increases after the power grid fails, thus posing a serious threat to the safe and stable operation of large-scale wind farms connected to the power grid. In the actual power system, compared with symmetric short-circuit faults, the probability of the power grid suffering from asymmetric short-circuit faults is higher. When dealing with asymmetric short-circuit faults, special attention needs to be paid to the synchronous stability problems under positive and negative sequences. To enhance the synchronous stability of the permanent magnet direct drive wind power grid-connected system and improve the safe and stable operation ability of the new power system, it is urgent to deeply explore the synchronous stability control technology of the permanent magnet direct drive wind power grid connection under the condition of grid asymmetric short-circuit faults. Current scholars at home and abroad have carried out relevant research on this issue. The following are some of the published literatures:

[0003] [1] WU H, WANG X F. Design-Oriented Transient Stability Analysis of GridConnected Converters with Power Synchronization Control[J]. IEEE Transactionson Industrial Electronics, 2019, 66(08): 6473 - 6482.

[0004] [2] Suul J A, D'Arco S, Rodríguez P, et al. Impedance-compensated gridsynchronisation for extending the stability range ofweak grids with voltagesource converters[J]. IET Generation, Transmission&Distribution, 2016, 10(6): 1315 - 1326.

[0005] Reference [1] characterized the transient synchronization process of the converter and the infinite bus using the phase-plane diagram, revealing the transient synchronization performance superiority of the converter over the traditional synchronous machine. On this basis, by changing the structure of the phase-locked loop and proposing a control strategy to block the integral controller of the phase-locked loop under faults, this control strategy cannot be applied to systems without an equilibrium point. Reference [2] analyzed the maximum static power transmission limit and stability range of the system when a voltage-source converter is connected to a weak grid. Further, by introducing an impedance regulation term in the phase-locked loop to compensate for the impedance voltage drop, the stable operation of the wind power generation system during faults is achieved. However, this control strategy depends on the actual parameters of the line impedance and has poor applicability in engineering applications. Summary of the Invention

[0006] Aiming at the above deficiencies in the existing technology, the object of the present invention is to propose a synchronous stability control method for a permanent magnet direct-drive wind power grid-connected system based on a dual-sequence current adaptive controller. This method does not require additional device investment. Only by optimizing and adjusting the positive and negative sequence current control loops of the permanent magnet direct-drive wind power system can the synchronous stability performance of the system during grid asymmetric short-circuit faults be effectively improved.

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

[0008] A synchronous stability control method for a permanent magnet direct-drive wind power grid-connected system based on a dual-sequence current adaptive controller, the steps are as follows:

[0009] A1) Measure the voltage at the point of common coupling of the system as the input signal of the positive and negative sequence phase-locked loops. After passing through a band-pass filter, obtain the output frequency ω PLL+ of the positive sequence phase-locked loop and the output frequency ω PLL- of the negative sequence phase-locked loop;

[0010] A2) During the grid asymmetric short-circuit fault period, calculate the additional reference values of the d-axis positive and negative sequence currents through the following formula and

[0011]

[0012] where k p_c+ and k i_c+ are the proportional coefficient and integral coefficient used to calculate the additional reference value of the d-axis positive sequence current respectively, k p_c- and k i_c- are the proportional coefficient and integral coefficient used to calculate the additional reference value of the d-axis negative sequence current respectively, and ω n is the rated angular frequency of the grid;

[0013] A3) During the grid asymmetric short - circuit fault stage, if the positive - sequence synchronous instability occurs in the permanent - magnet direct - drive wind power grid - connected system, then the positive - sequence current additional reference value of the d - axis obtained in step A2) is superimposed on the input of the current loop If the negative - sequence synchronous instability occurs in the permanent - magnet direct - drive wind power grid - connected system, then the negative - sequence current additional reference value of the d - axis obtained in step A2) is superimposed on the input of the current loop That is, the synchronous stable control of the permanent - magnet direct - drive wind power grid - connected system is realized; the calculation formula is as follows,

[0014]

[0015] where and are the actual reference values of the positive and negative - sequence currents of the d - axis respectively.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] By designing an additional positive - and negative - sequence current adaptive regulation controller, the present invention can enable the permanent - magnet direct - drive wind power grid - connected system to control the output d - axis current in real - time according to the positive - and negative - sequence phase - locked loop frequencies during the grid asymmetric fault, thereby offsetting the positive - and negative - sequence impedance voltage drop effects generated by the line impedance, enabling the permanent - magnet direct - drive wind power grid - connected system to automatically transition to new positive - and negative - sequence balance points during the asymmetric short - circuit fault, thus ensuring the synchronous stable operation of the permanent - magnet direct - drive wind turbine and the grid during the grid asymmetric short - circuit fault and improving the transient synchronous stability of the permanent - magnet direct - drive wind power grid - connected system under the asymmetric short - circuit fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic structural diagram of a permanent - magnet direct - drive wind turbine connected to the power system.

[0019] Figure 2 is a schematic control structural diagram of the dual - sequence current adaptive controller proposed by the present invention.

[0020] Figure 3 are the simulation waveform diagrams of the permanent - magnet direct - drive wind turbine under the system asymmetric short - circuit fault when using the conventional control strategy and the control strategy based on the dual - sequence current adaptive controller respectively. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention is used to improve the synchronous stable operation ability of the permanent - magnet direct - drive wind power system under the grid asymmetric short - circuit fault. Figure 1 is a schematic structural diagram of a permanent - magnet direct - drive wind turbine connected to the power system. Figure 2This is a schematic diagram of the control structure of the dual-sequence current adaptive controller proposed by the present invention. During the grid short-circuit fault, by adopting the dual-sequence current adaptive controller, the permanent magnet direct-drive wind power system can automatically transition to new positive and negative sequence balance points, thereby improving the transient synchronous stability operation ability of the permanent magnet direct-drive wind power grid-connected system under asymmetric faults.

[0022] A synchronous stability control method for a permanent magnet direct-drive wind power grid-connected system based on a dual-sequence current adaptive controller according to the present invention specifically comprises the following implementation steps:

[0023] A1) Measure the voltage at the point of common coupling of the system as the input signal of the positive and negative sequence phase-locked loops. After passing through the band-pass filter, obtain the output frequency ω PLL+ of the positive sequence phase-locked loop and the output frequency ω PLL- ;

[0024] A2) During the grid asymmetric short-circuit fault period, calculate the additional reference values of the d-axis positive and negative sequence currents through the following formula and

[0025]

[0026] where k p_c+ and k i_c+ are respectively the proportional coefficient and integral coefficient used to calculate the additional reference value of the d-axis positive sequence current, k p_c- and k i_c- are respectively the proportional coefficient and integral coefficient used to calculate the additional reference value of the d-axis negative sequence current, ω n is the rated angular frequency of the grid;

[0027] A3) During the grid asymmetric short-circuit fault stage, if the positive sequence synchronous instability occurs in the permanent magnet direct-drive wind power grid-connected system, then superimpose the additional reference value of the d-axis positive sequence current obtained in step A2) on the input of the current loop. If the negative sequence synchronous instability occurs in the permanent magnet direct-drive wind power grid-connected system, then superimpose the additional reference value of the d-axis negative sequence current obtained in step A2) on the input of the current loop, that is, realize the synchronous stability control of the permanent magnet direct-drive wind power grid-connected system; the calculation formula is as follows,

[0028]

[0029] where, and are respectively the actual reference values of the d-axis positive and negative sequence currents.

[0030] Description of the effects of the present invention:

[0031] Figure 3 They are respectively the simulation waveform diagrams of the permanent magnet direct drive wind turbine adopting the conventional control strategy and the control strategy based on the dual-sequence current adaptive controller proposed herein. The power grid experiences an asymmetrical short-circuit fault at 0.5 s. From Figure 3 (1), it can be seen that when the wind power generation equipment adopts the conventional control strategy during the fault, the negative-sequence instability phenomenon occurs in the permanent magnet direct drive wind power system. From Figure 3 (2), it can be known that after the permanent magnet direct drive wind turbine adopts the control strategy based on the dual-sequence current adaptive controller proposed in the present invention, under the action of the dual-sequence current adaptive controller, the permanent magnet direct drive wind turbine can adaptively find a negative-sequence balance point, enabling the system to quickly recover to the synchronous stable operation state, effectively improving the transient synchronous stability of the permanent magnet direct drive wind power grid-connected system.

[0032] Thus, it can be seen that the synchronous stability control strategy of the wind power system based on the dual-sequence current adaptive controller proposed in the present invention can enable the permanent magnet direct drive wind power grid-connected system during the fault to autonomously find the balance point, so that the wind power generation equipment can quickly recover to the synchronous operation state with the power grid under the asymmetrical short-circuit fault, effectively enhancing the synchronous stability of the permanent magnet direct drive wind power grid-connected system under the asymmetrical short-circuit fault of the power grid.

[0033] It should be emphasized that the embodiments provided in the present invention are intended to elaborate on the core concepts and principles of the invention and do not represent limitations on the implementation manners. Although the applicant has elaborated on the present invention in detail based on the embodiments, for those skilled in the art of this technology, after understanding the basic principles of the present invention, various forms of adjustment and improvement can be made according to this principle. Given the diversity of the implementation manners, it is impossible to list all potential variants in detail one by one. All change or adjustment schemes directly or indirectly derived from the technical solution of the present invention shall be regarded as part of the protection scope of the present invention.

Claims

1. A synchronous stability control method for a permanent magnet direct drive wind power grid-connected system based on a dual-order current adaptive controller, characterized in that, The steps are as follows: A1) Measure the voltage at the common coupling point of the measurement system as the input signals of the positive- and negative-sequence phase-locked loops. After passing through a band-pass filter, obtain the output frequency ω of the positive-sequence phase-locked loop PLL+ and the output frequency ω of the negative-sequence phase-locked loop PLL- ; During the period of asymmetric short-circuit fault in the power grid, the additional reference values of the positive and negative sequence currents on the d-axis are calculated by the following formula and where k p_c+ and k i_c+ are the proportionality coefficient and the integral coefficient used to calculate the additional reference value of the d-axis positive-sequence current respectively, and k p_c- and k i_c- are the proportionality coefficient and the integral coefficient used to calculate the additional reference value of the d-axis negative-sequence current respectively, and ω n is the rated angular frequency of the power grid; A3) During the asymmetric short - circuit fault stage of the power grid, if the positive - sequence synchronous instability occurs in the permanent - magnet direct - drive wind power grid - connected system, then the additional reference value of the d - axis positive - sequence current obtained in step A2) is superimposed on the input of the current loop If the negative - sequence synchronous instability occurs in the permanent - magnet direct - drive wind power grid - connected system, then the additional reference value of the d - axis negative - sequence current obtained in step A2) is superimposed on the input of the current loop That is, the synchronous stability control of the permanent - magnet direct - drive wind power grid - connected system is realized. The calculation formula is as follows: Among them, and are the actual reference values of the positive and negative sequence currents on the d-axis, respectively.

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