Networked PV inverters will face new challenges

As photovoltaic power generation systems are increasingly used around the world, the grid-connected inverter market has played its due role as a key component of solar installations. To achieve stable and reliable operation of the grid, the grid-connected inverter market must be able to guarantee the quality of the power delivered and the stability of the entire grid. To keep pace with these requirements, grid operators will issue new grid operation codes that all manufacturers must follow to monitor the increasing usage. Another challenge facing inverter manufacturers is that the relevant policies and regulations vary from country to country, and in most cases, different projects in the same location must follow different regulations. This article analyzes the various new challenges facing grid-connected photovoltaic inverters in light of these new developments.

One of the pressing issues facing networked inverter manufacturers is that they must comply with the technical requirements for networking PV equipment that are almost different in each country. For example, European countries have different requirements for networking interfaces. Germany implements the "automatic disconnection device between the power generation device and the public low-voltage power grid" regulations under the VDE0126-1 standard; Italy requires each company to comply with the DK5940 standard formulated by Enel (the national power company), the "power plant networking standard", etc. All these national and regional standards have different requirements for the voltage and frequency changes when the inverter is disconnected from the grid. In addition to the necessary adjustments to the parameters of different systems such as fault ride-through, this situation also leads to higher production costs.

From a technical perspective, up to now, common inverter designs are based on the following parameters: temperature range between -25 and 50°C; estimated service life of about 20 years; conversion rate usually above 94%; electromagnetic compatibility; low cost; high reliability; able to withstand all grid faults; power factor approaching 1; and maximum power point tracking (MPPT) capable.

At present, the function of most inverters is to convert the DC voltage produced by photovoltaic equipment into a sinusoidal AC current waveform at the switching converter to ensure the connection and synchronization between the generator and the public grid. However, this function has subsequently changed. The new standards have put forward different requirements for photovoltaic inverters to various degrees: the development of key features such as efficiency, cost and stability; compatibility with new materials such as silicon carbide and gallium nitride; integration with innovative technologies such as microinverters; effective maximum power point tracking control function; and compliance with various new specifications such as "anti-islanding effect" testing.

In terms of the requirements for new materials such as silicon-based MOSFET, SiC technology has undergone significant changes in the carbide field, making the production capacity of MOSFET (metal oxide semiconductor field effect transistor) far exceed that of similar silicon insulated-gate bipolar transistor (IGBT), especially under high voltage and high temperature conditions. This provides a feasible way to improve the efficiency of photovoltaic inverters.