This paper presents a reference current generation scheme for improved dynamic performance of a doubly fed induction generator (DFIG) subjected to unbalanced grid voltage. The power and torque oscillations induced due to the unbalance in grid voltage are minimized using additional compensatory terms in the reference currents. The focus is on estimating the reference currents and control implementation without the need for dual vector control. Real and reactive power control is implemented in the positive d-q reference frame using stator flux-oriented vector control. The rotor-side converter (RSC) is controlled to enable effective reduction of oscillations in torque and active and reactive power. The dc-link voltage oscillation is minimized and the grid-side power factor is maintained unity using the grid-side converter (GSC). Unlike the previously reported techniques, the proposed scheme enables effective reduction of oscillations in torque, active, and reactive power, and the dc-link voltage, all in a single target. The performance of DFIG is investigated in consideration with the Indian Electricity Grid Code (IEGC). Numerical simulations are carried out in power system computer aided design/electromagnetic transients including direct current (PSCAD/EMTDC) for the laboratory 3-hp DFIG test setup. The results establish that the performance of DFIG is notably enhanced with the proposed scheme.

A versatile method to compute the rotor position of a three-phase induction machine under balanced or unbalanced grid voltage is proposed in this paper. The rotor position of a doubly fed induction machine (DFIM) is computed in closed loop using R-PLL with the q-axis stator flux as the reference signal and the computed rotor speed as feed forward input. A PI controller is used to reduce the phase error while the updated feed forward input (rotor speed) eliminates the frequency error, thereby facilitating a quick and accurate response. Furthermore, the rotor speed is computed directly using only the measured stator voltages and currents, independent of any measurement of rotor current or position. Also, the speed computation process is free from voltage or flux integration or heuristic mathematical calculations. Starting on the fly and accurate computation near and through the synchronous speed even under unbalanced grid voltage are the attractive features. The effectiveness of the scheme is validated through PSCAD/EMTDC simulations and laboratory experiments. Excellent results demonstrate the efficacy of the proposed scheme.

In the context of a Doubly-Fed Induction Generator (DFIG) connected to the utility grid under unbalanced voltage conditions, the controller design needs to ensure additional challenges such as restricting the THD in grid current, minimizing the pulsations in generated power, torque, dc link voltage etc. apart from facilitating the generator power control. In this study, a negative sequence compensation scheme for the magnetizing current in a DFIG is investigated. The reference currents are modified to include the negative sequence compensating component for the magnetizing current. Rotor Side Converter (RSC) is employed to compensate the pulsations in magnetizing current thereby minimizing the ripple in power and torque. Grid Side Converter (GSC) is used to maintain unity power factor and a constant dc link voltage. It is revealed that, controlling the magnetizing current as a single control target enables simultaneous reduction of pulsations in torque, power and dc link voltage and also minimizes unbalance in currents. The effectiveness of the scheme is validated through detailed analysis and numerical simulations in PSCAD/EMTDC for a practical 250kW DFIG wind generation system and further, through experimental results for a 2.3kW DFIG test setup. Typical experimental results for the laboratory test setup show improved performance.

—India is faced with the major challenges of (a) providing energy access to all its citizens, (b) heavy dependence on fuel imports for energy security, and (c) complying with international protocols on climate change mitigation, although the economic and social development is the foremost priority. The increase in energy demand due to growing population and industrialization in the face of depleting fossil fuel resources has stimulated the country's efforts in adopting power generation from renewable energy sources. Starting with 0.34 GW (2%) out of 17 GW of the country's total installed capacity in the year 2002, the share of renewable power generation has reached 31.7 GW (12.5%) of 250 GW as of 2014. In the aspect of total installed renewable power generation, India occupies the fifth position in the world today. While the governmental policies have steadily encouraged the adoption of renewable power generation, there is need and potential for more vigorous engagement in pursuit of achieving power for all citizens along with economic development. This article presents a brief review of emergence and growth of renewable power generation in India, wind and solar sectors in particular.

Maximum power extraction and constant power generation in a smooth and uninterrupted manner are challenging control tasks for the robust operation of DFIG under grid voltage dips, owing to severe power and torque pulsations. Thus, necessitating tailored power control strategies while curtailing the undesirable effects on DFIG performance under voltage dips. The crux of this paper is to compute the angular stator flux frequency for precise reference power generation and control of DFIG subjected to grid voltage unbalance especially during MPPT operation. The angular frequency of stator flux is computed with the stator voltage and current components in the positive sequence stationary α-β reference frame without the need for a PLL and differentiation of stator voltage vector. Further, the computed stator flux frequency signal is employed for rotor speed computation, and reference power generation for maximum power extraction from DFIG. The efficacy of the proposed method in enabling precise power control of DFIG under unbalanced grid voltage is demonstrated using simulations in PSCAD/EMTDC and further through test results on a 3 hp DFIG test set up. The overall results show enhanced performance of DFIG under MPPT with the proposed scheme.