Wind Energy This paper presents an improvement technique for the power quality of the electrical part of a wind generation system with a self-excited induction generator (SEIG) which aims to optimize the utilization of wind power injected into weak grids. To realize this goal, an uncontrolled rectifier-digitally controlled inverter system is proposed. The advantage of the proposed system is its simplicity due to fewer controlled switches which leads to less control complexity. It also provides full control of active and reactive power injected into the grid using a voltage source inverter (VSI) as a dynamic volt ampere reactive (VAR) compensator.
A voltage oriented control (VOC) scheme is presented in order to control the energy to be injected into the grid. In an attempt to minimize the harmonics in the inverter current and voltage and to avoid poor power quality of the wind energy conversion system (WECS), an filter is inserted between VOC VSI and the grid. The proposed technique is implemented by a digital signal processor (DSP TMS320F240) to verify the validity of the proposed model and show its practical superiority in renewable energy applications.
- Grid connected systems
- Self-excited induction generator (SEIG)
- Voltage oriented control (VOC)
- Voltage source inverter (VSI)
- Wind energy conversion systems (WECSs)
Fig. 1. Proposed SEIG-based WECS with VOC VSI.
EXPECTED SIMULATION RESULTS:
Fig. 2. Line voltage of theVSI in frame (400 V/div–5ms). (a) Simulation. (b) Experiment.
Fig. 3. Phase voltage of the VSI in frame (400 V/div–5 ms). (a) Simulation. (b) Experiment.
Fig. 4. Grid phase voltage (50 V/div–10 ms) and injected current (1 A/div–10 ms). (a) Simulation. (b) Experiment.
Fig. 5. Inverter phase voltage to be connected to the grid with only filter (50 V/div–10 ms). (a) Simulation. (b) Experiment.
Fig. 6. Harmonic spectrum of (a) injected current; (b) phase voltage
Fig. 7. Grid voltage (50 V/div–25 ms) and injected current (1 A/div–25 ms) under step change in the reactive power injected into grid. (a) Simulation. (b) Experiment.
Fig. 8. VSI response with filter for the grid and capacitor voltage (100 V/div–10 ms) with the injected line current (5 A/div–10 ms). (a) Simulation. (b) Experiment.
Fig. 9. Harmonic spectrum analysis with filter. (a) Injected current harmonic content. (b) Filter capacitor voltage harmonic content.
In this paper, the SEIG-based WECS dynamic model has been derived. The VOC grid connected VSI has been investigated for high performance control operation. The test results showed how the control scheme succeeded in injecting the wind power as active or reactive power in order to compensate the weak grid power state. An filter is inserted between VOC VSI and grid to obtain a clean voltage and current waveform with negligible harmonic content and improve the power quality. Also, this technique achieved unity power factor grid operation (average above 0.975), very fast transient response within a fraction of a second (0.4 s) under different possible conditions (wind speed variation and load variation), and high efficiency due to a reduced number of components (average above 90%) has been achieved.
Besides the improvement in the converter efficiency, reduced mechanical and electrical stresses in the generator are expected, which improves the overall system performance. The experimental results obtained from a prototype rated at 250 W showed that the current and voltage THD (2.67%, 0.12%), respectively, for the proposed WECS with filter is less than 5% limit imposed by IEEE-519 standard. All results obtained confirm the effectiveness of the proposed system feasible for small-scale WECSs connected to weak grids.
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