A Modified Active Power Control Scheme for Enhanced Operation of PMSG Based WGs

 ABSTRACT:

This paper emphasises the development of a simplified active power control scheme for enhanced operation of grid integrated permanent magnet synchronous generator (PMSG) based wind-driven generators (WGs). An active power reference generation scheme is proposed for the machine side converter (MSC) to inject active power into the grid even under grid disturbances, without violating system components rating. In this scheme, the controller employed for MSC adjusts the active power captured proportionate to the drop in the grid voltage upon considering wind speed and rotor speed. Furthermore, unlike dual vector control scheme, the grid side converter (GSC) controller is implemented in a positive synchronous frame (PSF) with the proposed current oscillation cancellation scheme to suppress the oscillations in dc-link voltage, active and reactive power of the grid and to obtain symmetrical sinusoidal grid current. Extensive analytical simulation has been carried out in PSCAD/ EMTDC to validate the superiority of proposed control scheme over the conventional schemes when WG is subjected to various grid disturbances. The reduced percentage of oscillation in the system parameters such as dc-link voltage and grid active power confirms the efficacy of the proposed method when compared with the conventional control techniques.

KEYWORDS:

1.      Fault ride through

2.      Grid disturbances

3.      Positive synchronous frame

4.      Permanent magnet synchronous generator

5.      Wind-driven generator

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1 PMSG based grid integrated WG.

 EXPECTED SIMULATION RESULTS:

Fig.2 Behavior of PMSG based WG during step change in wind speed (a) wind speed profile, m/s; (b) rotor speed, rad/s; (c) dc-link voltage, V; (d) grid active power, W; (f) grid current, A.

Fig.3 Performance evaluation of proposed controller for the voltage profile of IEGC during symmetrical fault: (a) grid phase voltage, V; (b) MSC active power reference and grid power, W; (c) rotor speed, rad/s; (d) electromagnetic torque, N-m; (e) dc-link voltage, V; (f) grid current, A.

Fig.4 Performance of controllers (I, II and proposed controller) during Type – F fault of 50% voltage sag with -12.5o phase-angle jump (a) dc-link voltage, V; (b) grid active power, W; (c) grid current, A. (d) grid current loci in stationary reference frame during fault period

Fig.5 Performance of controllers (I, II and proposed controller) under distorted utility (a) grid active power, W; (b) grid current, A (zoomed in view).

CONCLUSION:

A modified active power control and current oscillation cancellation scheme are proposed for the MSC and GSC, respectively to strengthen the FRT compliance of the PMSG based WG. A 1.5 MW system is considered to validate the performance of proposed controller. Reduced active power regulation proportionate to retained grid voltage during fault conditions guarantees the dc-link voltage and GSC peak current are within its operating limits. Unlike dual vector control scheme, the GSC is implemented in PSF with oscillation cancellation terms and positive sequence grid angular frequency to suppress the oscillation in system parameters and to obtain symmetrical sinusoidal grid current. The control scheme is validated for various types of fault and distorted grid conditions. The reduced percentage of oscillation in the system parameters as recorded in Table I confirms the efficacy of the proposed method when compared with the controllers (I) and (II). As a future work, the proposed control scheme can be deployed to address weak grid condition with an improvised design.

REFERENCES:

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