MEPPI’s SVC-Diamond® STATCOM design begins with the Insulated Gate Bipolar Transistor (IGBT), which is the fundamental power electronic device. IGBT sub-modules or cells are the “building blocks” of MMC technology that enable STATCOM systems to deliver superior performance which results in higher operating efficiencies with lower losses. Mitsubishi Electric manufactures its own IGBT’s and has provided more than 50,000 IGBTs for STATCOM and HVDC applications worldwide.
These IGBT sub-modules are connected in a Full-Bridge configuration within the sub-module. A number of these submodules are connected in series depending on the reactive power output rating of the STATCOM.
By connecting a large number of submodules in series, the STATCOM is able to reconstruct an output waveform that is nearly sinusoidal in shape. This means that the STATCOM produces a low level of harmonics, so additional filtering is unnecessary. The STATCOM submodules also operate at a relatively low switching frequency, which reduces switching losses and improves overall efficiency.
As the following competitive comparison illustrates, the Mitsubishi Electric STATCOM MMC approach provides an ability to reduce the harmonic content measured on the transmission system through its inherent and active filtering functionality. During normal operation the STATCOM controls the fundamental voltage magnitude to adjust reactive power output. With Active Filtering functionality, the SSD STATCOM controls harmonic current in addition to the fundamental current. Additional sub-modules are used to superimpose the harmonic current and fundamental current. The end result is an overall reduction in the harmonic levels seen on the high voltage transmission system
As illustrated in the technical comparison, the losses are very small, the harmonic distortion is minimal, and the need for disconnecting switching is eliminated. The Vac Waveform is perfectly controlled, with equal ability, in both voltage lagging and voltage leading conditions.