TMEIC: Pioneer of Large-capacity PV Inverter (1) (page 3)
Advanced power electronics technology improves power generation capacity
Fig. 4: The "3-level converter circuit" has four power semiconductors (IGBTs). Switching loss is substantially smaller compared with conventional circuits, leading to improvement in efficiency. (source: TMEIC)
TMEIC's PV inverters retain their high market share not only because the company commercialized the products and established the production system earlier than others by taking advantage of the knowhow obtained through development of UPS technologies and UPS production. The company leads the industry having introduced its own design in the power converter circuits that incorporate the IGBT to improve conversion efficiency. This is another reason for the high market share.
Conventionally, sine wave alternating current was generated by switching two IGBTs for conversion of direct current to alternating current. Using this method, however, current loss, called switching loss, occurs, and this current loss is the major cause of the decline in the conversion efficiency of PV inverters.
Under such circumstances, TMEIC adopted the "3-level conversion circuit" (advanced multi-level inverter), where four IGBTs are used to generate sine wave alternating current (Fig. 4). According to the company, the loss is reduced due to the decrease of stress in each switching operation because the waveform is divided into three parts for conversion by four IGBTs.
The idea of this circuit design had been known for years, but commercialization was delayed because of issues regarding the materials, etc. TMEIC released the PV inverter that incorporates the "3-level" ahead of other companies in the industry in 2010. The PV inverter featured a maximum 98.6% (630kW model) conversion efficiency (Fig. 5).