Development of Advanced MPPT Algorithms and Power Management
Scheme for Standalone PV Systems

Abstract

The present emphasis on harvesting solar energy through Photovoltaic (PV) power generation has motivated researchers to develop more efficient methods of extracting maximum available power from the PV panels and effectively utilising it. This thesis introduces two new Maximum Power Point Tracking (MPPT) algorithms based on the popular Perturb and Observe (P&O) method, which primarily aim to stop the steady state oscillations thus providing a steady power output. A Power Management Scheme (PMS) is also introduced for the Standalone Photovoltaic System (SPVS) with battery storage. The new PMS tries to seamlessly balance the power flow between the PV panel, battery and the load by controlling the DC-link voltage.

Among the various MPPT algorithms the P&O algorithm, being simple and easy to implement over any digital platform, is widely used. In the P&O algorithm, the operating point oscillates around the Maximum Power Point (MPP) resulting in lower power output at every alternate perturbation, thus reducing the overall efficiency. Now if the oscillations around the MPP are stopped once the steady state is reached, a steady maximum power output can be achieved which would also improve the efficiency.

Two new MPPT algorithms have been introduced here, namely the Steady Output and Fast Tracking MPPT algorithm (SOFT – MPPT) and the Steady Output Power MPPT algorithm (SOP-MPPT). While the SOFT-MPPT is developed based on the Direct Duty Ratio based P&O algorithm (DDR-P&O), the SOP-MPPT is designed based on the Voltage Reference based P&O (VR-P&O) method. Both the algorithms identify the steady state and then stop the artificial perturbations, providing a steady power output from the PV panel at the corresponding MPP value. Any change in irradiance is quickly identified without using any additional sensors and the artificial perturbations are restarted to track the new MPP. The SOFT-MPPT algorithm additionally uses a truly adaptive step-size updation rule, which takes into account the effect of change in irradiance as well as the slope of the P-V curve, thus providing a fast tracking performance.

In a SPVS with battery storage, the various modes of power flow from the PV panel to the load, and to & fro the battery require a complex supervisory control. Now if the DC-link voltage is controlled while allowing the MPPT controller to work independently, then the load power demand would be automatically distributed between the PV panel and the battery. This would provide a simple way of controlling the various modes of power flow, an idea that has been used to develop the DC-Link Voltage Control based Power Management Scheme (DVC-PMS) proposed here. A bidirectional controller (BDC), used as an interface between the battery and the DC-Link side of the SPVS, is used to control the DC-Link voltage with the help of a PI controller. This automatically distributes the power flow between the PV array, battery and the load, providing a simple and flexible power management scheme.

The proposed SOFT-MPPT and SOP-MPPT algorithms and the DVC-PMS have been simulated on the MATLAB-SIMULINK (Ver. 2016a) platform. The performance of the proposed methods have been observed for wide variations in load and operating conditions. Hardware prototypes have been developed and used to validate the performance the proposed methods experimentally. The results of the experimental studies have been captured and presented here. Both the simulation as well as the experimental results exhibit proper functioning of the methods and the performance improvements claimed in the design are also clearly visible.