Single Stage Solar PV Fed Brushless DC Motor Driven Water Pump

Abstract

In order to optimize the solar photovoltaic (PV) generated power using a maximum power point tracking (MPPT) technique, a DC-DC conversion stage is usually required in solar PV fed water pumping which is driven by a brushless DC (BLDC) motor. This power conversion stage leads to an increased cost, size, complexity and reduced efficiency. As a unique solution, this work addresses a single stage solar PV energy conversion system feeding a BLDC motor-pump, which eliminates the DC-DC conversion stage. A simple control technique capable of operating the solar PV array at its peak power using a common voltage source inverter (VSI), is proposed for BLDC motor control. The proposed control eliminates the BLDC motor phase current sensors. No supplementary control is associated for the speed control of motor-pump and its soft start. The speed is controlled through the optimum power of solar PV array.

Existing System

Cuk Converter.

Proposed System

The proposed BLDC motor driven water pumping based on a single stage solar PV generation has been validated through a demonstration of its various steady state, starting and dynamic performances. The topology of the proposed system has provided a DC-DC converter-less solution for PV fed brushless DC motor driven water pumping. Moreover, the motor phase current sensing elements have been eliminated, resulting in a simple and cost-effective drive. The proposed solution as a BLDC motor driven solar water pumping system, offers a high efficiency power conversion in comparison with that of an induction motor driven system. The efficiency of an induction motor diminishes under light loading as the excitation losses dominate. Thus, it causes reduced volume of water delivery under bad weather condition as compared to a BLDC motor, wherein no excitation loss takes place owing to its permanent magnet excitation. A high efficiency BLDC motor substantially reduces the size of PV array and hence its installation cost. In other words, the number of required PV modules is less with a BLDC motor as compared to that with an induction motor. The BLDC motor has high power factor, which leads to a reduced capacity of the used VSI. This feature helps in cost-minimization of PV pumping systems. Being a rectangular current fed motor, the BLDC motor offers a high DC bus voltage utilization, in comparison with an induction motor. This feature also reduces the voltage rating of DC bus capacitor and the switching devices of VSI. Unlike an induction motor, the speed of a BLDC motor is not limited by power frequency. Therefore, the rated speed of a BLDC motor can be designed higher, which is beneficial to increase the capacity and decreasing the size. This leads to a compact solar PV water pumping system. The proposed speed control technique for BLDC motor is much simpler than that of an induction motor. No additional VSI and phase current sensing are involved in the proposed control, unlike the speed control of an induction motor.

Architecture

Proposed water pumping based on a single stage solar PV energy conversion system