Performance characteristics of photovoltaic cold storage under composite control of maximum power tracking and constant voltage per frequency

Abstract

A direct-driven photovoltaic refrigeration compressor usually operates in an unstable working state in the long term due to the fact that it is affected by intermittent solar irradiance. Hence, it is essential to control the compressor efficiently and appropriately. To ensure energy-saving and stable operation of photovoltaic refrigeration, we adopted a control method of photovoltaic maximum power point tracking combined with constant voltage per frequency for off-grid photovoltaic cold storage to achieve dynamic matching between the photovoltaic system and the load. A matching model of the optimum photovoltaic array output power and the optimized power with a certain temperature irradiance and standard test conditions was established. Based on the collaborative control method proposed herein, a 5.4-kW direct-driven cold storage system with a distributed photovoltaic system was established, and the performance characteristics of the photovoltaic cold storage were analysed. The results showed that the refrigeration system controlled using maximum power point tracking combined with constant voltage per frequency can efficiently track the optimal output power of the photovoltaic array and improve compressor utilisation in the direct-driven mode. The photoelectric conversion efficiency of the photovoltaic system reached 15.33%, which was closer to the nominal efficiency of the photovoltaic modules. Compared to the conventional maximum power point tracking control, the performance ratio of the photovoltaic system under the maximum power point tracking combined with constant voltage per frequency control improved by 9.18%. Such a typical off-grid solar photovoltaic cold storage system can use energy instantaneously, with optimal energy-saving effect.