In recent years, many solar power generation apparatuses for converting direct current power generated by a solar battery into alternating current power by an inverter and supplying the alternating current power to a load in a house (to be simply referred to as a “load” hereinafter) and/or a commercial electric power system (to be simply referred to as a “system” hereinafter) are installed to deal with environmental problems.
These solar power generation apparatuses have also received a great deal of attention as emergency power supplies to be used in the event of disasters such as an earthquake. Even when power outage occurs due to an earthquake, system failure, or maintenance, many recent solar power generation apparatuses can be disconnected from systems and supply a power to loads by isolated operation.
AC modules have also received a great deal of attention as small- or medium-scale solar power generation apparatuses or emergency power supplies, which allow a single solar battery module to output alternating current power by attaching, to, e.g., the lower surface of a solar battery module, a small inverter called a MIC (Module Integrated Converter) for converting direct current power generated by a solar battery into alternating current power.
As disclosed in Japanese Patent Laid-Open No. 10-14111, an AC module is connected to the neutral line and one power line of a single-phase three-wire unit and then connected to a system. In an emergency, a solar power generation apparatus using an AC module uses alternating current power obtained by converting direct current power stored in a storage battery by an emergency inverter.
An AC module is connected to a system in a building through a panel board or the like. In Japan, the voltage of a system in a building is 100 V or 200 V, and an AC module must select a 100-V output or 200-V output in accordance with the connection. Hence, AC module makers must prepare two types of modules for the 100-V and 200-V outputs for domestic supply. For foreign countries, the makers must manufacture AC modules compatible with more system voltages.
If the output voltage changes in switching from interconnected operation to isolated operation, an easier switching method is required for an emergency power supply. Especially in disasters or the like, an AC module need be carried to an arbitrary position together with a load and easily output a desired voltage.