Mitigation Voltage sag is a frequently occurring power quality disturbance in the industries equipped with adjustable speed drives (ASD). A detailed investigation of voltage sag effects on ASD performance with the novel mathematical analyses to estimate the ASD parameters during different types of voltage sag is discussed in this article. The effects of voltage sags are mitigated using an enhanced synchronous reference frame (ESRF) theory-based dynamic voltage restorer (DVR).
The working principle of the ESRF theory-based DVR during sag is also described. The investigation of the effects of type A, type B and type F voltage sags on ASD parameters are verified using the simulation and the experimental studies. Further, these effects are mitigated by the ESRF theory-based DVR using the developed simulation and experimental models. The ESRF controller of DVR is working effectively during voltage sags by improving its transient response
which tightly regulates the DC link voltage of ASD around its reference value. Also, the steady state response of DVR is enhanced during severe voltage sag, which further validates the ability of the ESRF theory-based DVR. This type of improved performance of ASD during voltage sags cannot be obtained using other existing SRF theories of the DVR.
- Adjustable speed drives
- DC-link voltage
- Symmetrical sag
- Unsymmetrical sag
- Dynamic voltage restorer
Fig. 1. Circuit diagram of DVR with ASD system.
EXPECTED SIMULATION RESULTS:
Fig. 2. Simulation results of ASD during TAVS, TBVS and TFVS.
Fig. 3. Simulation results (a) ASD performance during severe TBVS and (b) RMS input line current.
Fig. 4. Comparison of the simulation results of the SRF [24,26] and the ESRF controller. (a) DC-link voltage of ASD and (b) Speed of the motor.
Fig. 5. Simulation results of the ESRF theory-based DVR during voltage swell. (a) PCC, DVR and ASD R-phase RMS voltages and (b) DC-link voltage of ASD.
A detailed investigation of ASD performance under TAVS, TBVS and TFVS is presented in this article. A novel mathematical analysis to evaluate the ASD parameters during different types of voltage sag with various sag magnitudes is presented in this article. The initial effect of any voltage sag occurs on ASD is a drop in the DC-link voltage, which results in the fluctuation of stator current, torque and speed of the motor.
From the mathematical analyses, simulation results and experimental results, it is observed that the ASD performance affects more severely due to TAVS. However, the most frequently occurring TBVS can also halt the operation of ASD. It can be inferred from the experimental study that the effects of voltage sag on ASD performance depend on its loading condition, type of sag and sag magnitude. The ESRF theory-based DVR is used to regulate the DC-link voltage of ASD to its reference value during the sag period, which results in the constant speed of the motor.
Moreover, the ESRF controller enhanced the transient response compared to the other SRF theories. Also, the steady-state response of the DVR is improved during severe voltage sag (TAVS), which further validates the ability of the ESRF theory-based DVR to regulate the DC-link voltage of the ASD. The obtained simulation and experimental results proved that the ESRF theory-based DVR is able to regulate the speed of the motor around its reference value during 0.5 p.u. voltage sag for a minute. This proves the effectiveness of the ESRF controller technique over the existing SRF control theories of the DVR.
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