IEEE Transactions on Power Delivery, 2013
The dynamic voltage restorer (DVR) is a series compensator for distribution system applications, which protects sensitive loads against voltage sags by fast voltage injection. The DVR must estimate the magnitude and phase of the measured voltages to achieve the desired performance. This paper proposes a phasor parameter estimation algorithm based on a recursive variable and fixed data window Least Error Squares (LES) method for the DVR control system. The proposed algorithm, in addition to decreasing the computational burden, improves the frequency response of the control scheme based on the fixed data window LES method. The DVR control system based on the proposed algorithm provides a better compromise between the estimation speed and accuracy of the voltage and current signals and can be implemented using a simple and low cost processor. The results of the studies indicate that the proposed algorithm is insensitive to noise, harmonics, interharmonics and DC offset unlike the LES method, while both methods estimate the phasor parameters within 5 ms. The performance of the control scheme based on the proposed method is evaluated by multiple case studies in the PSCAD/EMTDC environment and experimentally validated based on a laboratory setup.
- Dynamic voltage restorer
- Phasor estimation
- Least Error Squares
- Minimum energy
- Four-leg inverter
Fig. 1 Power circuit schematic of the four-wire DVR
EXPECTED SIMULATION RESULTS:
Fig. 2. Sag compensation during SLG fault in the presence of zero sequence component, (a) Grid voltages (V), (b) Estimated grid voltage magnitude of phase A by the improved phasor estimation method, LES, RLS and ADALINE (V), (c) Compensated load voltages (V)
Fig. 3 Sag compensation under nonlinear load conditions, (a) Grid voltages (V), (b) Load currents (A), (c) Compensated load voltages (V)
Fig. 4. Comparison between the improved estimation method, LES, RLS and ADALINE under nonlinear load conditions, (a) Estimated grid voltage magnitude of phase A (V), (b) Estimated grid voltage angle of phase A (rad), (c) Estimated load current angle of phase A (rad)
Fig. 5. Comparison between the improved estimation method, LES, RLS and ADALINE under interharmonics and DC offset conditions, (a) Input signal (p.u.), (b) Estimated magnitude (p.u.), (c) Estimated phase angle (rad)
This paper proposes an improved phasor estimation method for DVR control system using a recursive Least Error Squares (LES) method with fixed and variable data window lengths. The proposed algorithm improves the frequency response of the control scheme based on the fixed data window LES in additional to decreasing the computational burden. Thus, it provides a desirable compromise among the speed, accuracy and the amount of computations for the phasor estimation of DVR signals. The experimental and simulation results confirmed that:
1) The estimation time is less than 5 ms and its accuracy increases gradually and it is not sensitive to noise, harmonics, interharmonics and DC offset. Consequently, it is fast and accurate.
2) The proposed algorithm is able to estimate several signal phasors simultaneously in real-time using a low cost processor.
3) The proposed scheme can compensate balanced and unbalanced sag scenarios accurately and within the required time under linear and nonlinear load conditions.
Moreover, during voltage sag compensation, the minimum energy is used and the voltage sags can be compensated without any additional energy storage.
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