Abstract: A three-phase dc to-ac power inverter includes a dc power source with a first dc node for positive voltage, a second dc node for negative voltage, and a third dc node for zero voltage. A set of three-level pole circuits are connected to the first dc node, the second dc node, and the third dc node of the dc power source. A control circuit, responsive to an inverter voltage vector reference demand signal with a voltage magnitude reference demand component and a voltage phase reference demand component, generates pole control signals for the three-level pole circuits using logic circuitry which combines phase indexed digital waveform values stored in a pair of lookup tables. The pole control signals force the three-level pole circuits to generate a set of phase-shifted waveforms with zero voltage components. The phase-shifted waveforms are combined by a set of transformers to produce a three-phase output voltage with a harmonic content lower than the harmonic content of the phase-shifted waveforms.

Abstract: A unified power flow controller has a dc-to-dc converter which uses the dc voltage produced by a first static inverter, connected in shunt with a transmission line and providing parallel reactive compensation, to establish the magnitude of a series compensation voltage injected into the transmission line by a second static inverter. The second static inverter then only has to regulate the phase angle of the series injected voltage. With the dc-to-dc converter turned off, the two inverters are decoupled and can be operated independently even if the other inverter is not operational.