Lingxiang Wang

Improved Ride-Through Control of DFIG During Grid Voltage Swell

Grid voltage swell causes a transient dc flux component on doubly fed induction generator (DFIG) stator winding even stronger than grid voltage dip, resulting in a much more serious stator, rotor current, and torque oscillation. This paper analyzes the dynamic behavior of DFIG during grid voltage swell. Based on the analysis results, the virtual resistance control strategy manages best to suppress the rotor current and torque oscillation but prolongs the transient duration, resulting in a higher rotor voltage. Thus, this paper proposed a virtual impedance control strategy to enhance the high-voltage ride-through capability of DFIG. In order to improve the dynamic performance, the optimization algorithm of virtual impedance is proposed in the paper. The effectiveness of the proposed control strategy was verified by simulation and experimental results.

Improved Power Pulsation Suppression of DFIG for Wind Shear and Tower Shadow Effects

This paper analyzes and simulates wind shear and tower shadow effects in doubly-fed induction generators, which are known to induce a low-frequency oscillation. Such oscillation is called a 3p oscillation, which can cause shaft torsion load aggravation and shaft torque oscillation, it inevitably lead to electromagnetic torque and power fluctuation in the generator and further affect the whole wind power system. By analyzing a two-mass model, it can be known that a flexible drive train has a low-damping characteristic and an amplification of the input of low-frequency wind torque disturbances. Based on this point, this paper presents a new control scheme to restrain 3p oscillation is presented, which is a damping torque observation. A novel torque observer is designed to ascertain the required damping torque. A small-signal model is established for the system and used to analyze the systems static and dynamic characteristics. The effectiveness of the proposed strategy is finally verified by simulation and experimental results.

Filter design for three-level grid-connected inverter with low switching frequency

Aiming at the problems of poor dynamic control performance and difficult filter design for three-level grid-connected inverter with low switching frequency, a three-level discontinuous PWM strategy and its carrier-based implementation method are introduced. Considering the strategys output harmonic characteristics, an LLCL filter is adopted. Then, aiming at the resonance problem of LLCL filter, two simple passive damping schemes are comparatively analyzed from the aspects of damping effect, filtering performance and damping losses. The conclusion shows that the series resistor structure has better overall performance. Afterwards, the design principle of the filter parameter is proposed based on the bridge-side current ripple analysis and dominant harmonic component attenuation. Correctness and feasibility of the conclusions are validated by experimental results.

Grid fault ride through of a medium-voltage three-level full power wind power converter

According to the fault ride through (FRT) demand to wind generation systems of grid codes, a control scheme of grid FRT under the whole grid change was proposed for a medium-voltage three-level full power wind power converter. This method coordinately controls the generator-side converter (MSC), the grid-side converter (GSC) and the chopper to: 1) reduce the unloading burden of the chopper by limiting the MSC output power during the low voltage ride through (LVRT), 2) insure the controllability of the GSC by adopting the self-adaptive control strategy of dc-link voltage and the carrier-based over-modulation strategy during the high voltage ride through (HVRT), 3) ensure the neutral-point potential (NPP) into the given threshold value by adopting the NP balancing control method based on zero-level elimination during the grid fault. The simulation results validate that the proposed method can fully use the controllability of MSC and GSC to ensure the smooth switching and safe operation, while decrease the unloading burden of the chopper. Thus, the FRT ability of full-scale three-level wind generation converters can be effectively improved.

Super-twisting sliding mode observer based speed sensorless torque control for PMSG used in wind turbines

A speed sensorless torque control method for permanent magnet synchronous generator (PMSG) based on super-twisting sliding mode observer (STSMO) is proposed in this paper. Active back electromotive force (BEMF) can be obtained based on the STSMO. With the observed active BEMF, the rotor position angle and the speed are estimated by a phase-locked loop. Besides, a stator flux and electromagnetic torque (EMT) observation method is proposed based on the observed active BEMF. Compared to the traditional method, the robustness of the proposed one to the parameters of PMSG is improved. Then a speed sensorless EMT closed-loop control system is established. The simulation and experimental results verify the effectiveness of the proposed algorithm.

Notice of Retraction Research on Control Strategy of Direct-drive WPGS Based on Adaptive Resonant Regulator

In MW wind power generation system(WPGS), This paper analyzes the rotor flux oriented vector control theory for permanent magnet synchronous generator (PMSG), a control strategy of grid connected based on adaptive resonant regulator the method described a PLL-based speed and position controller for PMSG drives. 20 KW PMSG wind power system is constructed in the laboratory, which proves the validity and reliability of control strategy by researching and analyzing of results.