This paper presents a voltage-controlled DSTATCOM-based voltage regulator for low voltage distribution grids. The voltage regulator is designed to temporarily meet the grid code, postponing unplanned investments while a definitive solution could be planned to solve regulation issues. The power stage is composed of a three-phase four-wire Voltage Source Inverter (VSI) and a second order low-pass filter. The control strategy has three output voltage loops with active damping and two dc bus voltage loops. In addition, two loops are included to the proposed control strategy: the concept of Minimum Power Point Tracking (mPPT) and the frequency loop. The mPPT allows the voltage regulator to operate at the Minimum Power Point (mPP), avoiding the circulation of unnecessary reactive compensation. The frequency loop allows the voltage regulator to be independent of the grid voltage information, especially the grid angle, using only the information available at the Point of Common Coupling (PCC). Experimental results show the regulation capacity, the features of the mPPT algorithm for linear and nonlinear loads and the frequency stability.
- DSTATCOM, Frequency Compensation
- Minimum Power Point Tracker
- Power Quality
- Static VAR Compensators
- Voltage Control
- Voltage Regulation
Fig. 1. Low voltage distribution grid under analysis with the voltage regulator
EXPECTED SIMULATION RESULTS:
Fig. 2. Dc bus voltages during the DSTATCOM initialization
Fig. 3. PCC voltages without compensation for linear loads
Fig. 4. PCC voltages with compensation for linear loads
Fig. 5. Voltage regulator currents for linear loads
Fig. 6. Grid, load and voltage regulator currents for linear loads
Fig. 7. PCC voltages without compensation for nonlinear loads
Fig. 8. PCC voltages with compensation for nonlinear loads
Fig. 9. Voltage regulator currents for nonlinear loads
Fig. 10. Grid, load and voltage regulator currents for nonlinear loads
Fig. 11. PCC rms value with linear loads
Fig. 12. Processed apparent power with linear loads
Fig. 13. Voltage regulator currents with mPPT enabled for linear loads
Fig. 14. PCC rms value with nonlinear loads
Fig. 15. Processed apparent power with nonlinear loads
Fig. 16. Voltage regulator currents with mPPT enabled for nonlinear loads
Fig. 17. Total dc bus voltage, PCC voltage, grid voltage and voltage regulator current waveforms of a-phase with mPPT enabled with grid swell
Fig. 18. (a) Total dc bus voltage, PCC voltage, grid voltage and voltage regulator current waveforms of a-phase and (b) detail of total dc bus voltage performance with mPPT enabled with grid sag
This paper presents a three phase DSTATCOM as a voltage regulator and its control strategy, composed of the conventional loops, output voltage and dc bus regulation loops, including the voltage amplitude and the frequency loops. Experimental results demonstrate the voltage regulation capability, supplying three balanced voltages at the PCC, even under nonlinear loads.
The proposed amplitude loop was able to reduce the voltage regulator processed apparent power about 51 % with nonlinear load and even more with linear load (80%). The mPPT algorithm tracked the minimum power point within the allowable voltage range when reactive power compensation is not necessary. With grid voltage sag and swell, the amplitude loop meets the grid code. The mPPT can also be implemented in current-controlled DSTATCOMs, achieving similar results. The frequency loop kept the compensation angle within the analog limits, increasing the autonomy of the voltage regulator, and the dc bus voltage regulated at nominal value, thus minimizing the dc bus voltage steady state error. Simultaneous operation of the mPPT and the frequency loop was verified. The proposed voltage regulator is a shunt connected solution, which is tied to low voltage distribution grids without any power interruption to the loads, without any grid voltage and impedance information, and provides balanced and low-THD voltages to the customers.
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