This paper studies the impact of optimal sizing of photovoltaic distributed generators (PV-DGs) on a distribution system using different static load models (i.e., constant power, constant current, and constant impedance) and various power factor (PF) operations. A probabilistic approach with Monte Carlo simulation is proposed to obtain the optimal size of PV-DG. Monte Carlo simulation is applied to predict the solar radiation, ambient temperatures, and load demands. The objective is to minimize average system real power losses, with the power quality constraints not exceeding the limits, i.e. voltage and total harmonic voltage distortion (THDv) at the point of common coupling (PCC). A modified Newton method and a classical harmonic flow method are employed to calculate the power flow and THDv values, respectively. An actual 51-bus, medium-voltage distribution system in Thailand is employed as a test case. Results demonstrate that the proposed method performs well to provide the optimal size of PV-DG based on technical constraints. Further, the results show that the three static load models do not affect the optimal PV-DG size but the model has a different impact for various PF operations. PV-DGs may improve the voltage regulation and decrease the losses in distribution systems practically, but the THDv values could increase.
Abstract. This paper presents the particle swarm optimization based equivalent circuit estimation (PSOBECE) method for three-phase induction motor efficiency analysis, during on-service condition. The prominent point of the paper is to accurately estimate the three-phase induction motor efficiency without disturbing motor operation, using basic electrical instruments, which are clamp-on power meter and non-contact tachometer. The proposed method estimates the parameters of induction motor equivalent circuit (EC) using motor current, real power, voltage, and speed, which can be measured without interrupting the motors operations. Afterward, the motor's efficiency can be nonintrusively determined from the EC. In this paper, the 1.5, 11 and 30 kW motors are used for test and verify the accuracy of the proposed method. The motor efficiency test results, by shaft torque method, compliance to IEC60034 standards, are used as references to verify the accuracy of the proposed method compared to the conventional slip and current methods. The proposed method resulted in the reasonable mismatch in efficiency estimation for three-phase induction motor. The root-mean square mismatch of the proposed method, comparing to those of obtained by CM and SM, is shown to be minimum. Therefore, the proposed method could effectively and conveniently be applied for the on-service three-phase induction motor efficiency estimations.
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