Methods for Investigating Interactions between Multiple Maximum Power Point Trackers in Photovoltaic Systems

Power loss due to photovoltaic (PV) module mismatch is a well-known problem for PV systems. The ability to recuperate the power lost has increased the popularity of distributed maximum power point tracking (DMPPT) systems using per-module ‘power optimisers’; DC-DC converters that track the maximum power point (MPP) of each module. There are concerns over systems with multiple maximum power point trackers (MPPTs) incurring unwanted interactions between MPPT controllers. A method for electrical engineers to analyse such systems is required. A lack of in-depth evaluation in literature has been addressed in this work through practical testing and development of a computer model for simulating various DMPPT systems. To achieve acceptably accurate models of DMPPT power conditioning devices (PCDs) practical testing systems were employed: a solar emulator with real PV module, a real outdoor DMPPT test system and a PV emulator (PVE) developed during this work. A fast and dynamically stable PV module emulator (PVME) was developed for testing a power optimiser. The PVME consists of a linear regulator and an analogue computation circuit for speed and flexibility. The steady-state operation of the power optimiser was tested with the PVME whereas the solar emulator obtained the true dynamic response. The extension of the PVME into a PV array emulator (PVAE) through the addition of a switched-mode controllable DC voltage source and a digital lookup table was considered. PSpice ‘block models’ of PCDs were created for ease of reconfiguration using averaged equations of the switching power electronics and an equation for inverter ripple derived in this work. An MPPT model was developed in Simulink for co-simulation with the PSpice electrical models using SLPS. The overall DMPPT model showed similar behaviour to the outdoor test system. A number of proposed scenarios for investigating DMPPT system interactions have been suggested for further work.