Renewable energy sources; which are abundant in nature and climate friendly are the only preferable choice of the world to provide green energy. The limitation of most renewable energy sources specifically wind and solar PV is its intermittent nature which are depend on wind speed and solar irradiance respectively and this leads to power fluctuations. To compensate and protect sensitive loads from being affected by the power distribution side fluctuations and faults, dynamic voltage restorer (DVR) is commonly used. This research work attempts to withstand and secure the effect of voltage fluctuation of grid connected hybrid PV-wind power system. To do so battery and super magnetic energy storage (SMES) based DVR is used as a compensating device in case of voltage sag condition. The compensation method used is a pre-sag compensation which locks the instantaneous real time three phase voltage magnitude and angle in normal condition at the point of common coupling (PCC) and stores independently so that during a disturbance it used for compensation. Symmetrical and asymmetrical voltage sags scenario are considered and compensation is carried out using Power System Computer Aided Design or Electro Magnetic Transient Design and Control (PSCAD/EMTDC) software.
- Dynamic voltage restorer (DVR)
- Energy storage
- Power quality
- Voltage sag compensation
Figure 1. Wind turbine system and its power curve
EXPECTED SIMULATION RESULTS:
Figure 2. Simulation results and DVR response for 25% symmetrical voltage sag case (a) load voltage without DVR, (b) DVR injected voltage and (c) load voltage with DVR
Figure 3.Simulation results and DVR response for 12% symmetrical voltage sag case (a) load voltage without DVR, (b) DVR injected voltage and (c) load voltage with DVR
Figure 4. Simulation results and DVR response for 25% asymmetrical voltage sag case (a) load voltage without DVR, (b) DVR injected voltage and (c) load voltage with DVR
Figure 5. Simulation results and DVR response for 35% asymmetrical voltage sag case (a) load voltage without DVR, (b) DVR injected voltage and (c) load voltage with DVR
In this paper, a voltage sag enhancement of sensitive load which gets power from grid connected PV-wind power system is demonstrated using HES based DVR. The proposed DVR targets to protect the sensitive load from being affected by any voltage fluctuation which arise either from fault condition or unstable power output of PV-wind system. The control and operations of BES and SMES devices is developed by observing voltage condition of the grid at the PCC and the SOC levels of battery and SMES. In addition to this, for full realization of the proposed DVR system the control and operation of the VSC is developed by observing the voltage level at the PCC. The pre-sag compensation strategy is selected based on the capability of both magnitude and phase jump restoration. Based on the conditions, three operating states of the HES based DVR are defined, which are normal (idle state), charging state and discharging state. The effectiveness of the proposed operating states has been demonstrated in realistic cases. In the simulation, different voltage sag depth scenarios are considered for both symmetrical and asymmetrical voltage imbalances and the HES based DVR works well. A combination of voltage sag, voltage swell and harmonics scenarios will be demonstrated in the future works.
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