Novel Reduced Switches Single-Phase to Three-Phase On-line Uninterruptible Power Supply

Abstract - This paper describes the design considerations and performance analysis of a new on-line single-phase to three-phase uninterruptible power supply (UPS) with fewer switches. Compared with the traditional 10-switch topology, the proposed topology uses only 5 active switches, thus reducing system cost. The proposed UPS includes single phase rectifier / charger, bipod / three phase inverter connected to the load, battery pack, DC link capacitor, and AC inductor. Detailed circuit operation and analysis and simulation results are also provided to verify its feasibility.

Three-phase inverters are used for variable frequency drive applications and high power applications such as HVDC transmission. The basic three-phase inverter consists of three single-phase inverter switches, each connected to one of the three load terminals. In the most basic control scheme, the operation of the three switches is adjusted so that one switch operates at each 60 degree point of the basic output waveform. This creates a 6-step line-to-line output waveform. The 6 step waveform has a zero voltage step between the positive and negative parts of the square wave and tripled third harmonic as described above. When applying carrier-based PWM technology to a six step waveform, the basic overall shape or envelope of the waveform is maintained to offset the third harmonic and its multiple.

By functioning as a rotary generator, the rotary phase converter converts the single phase energy supply to three phase power. The rotary phase converter uses a single-phase 2-wire power source from a utility company and generates a tertiary power supply. Three wires, also called phases, are usually more accurate than three-phase power supplies provided by power companies because they are indistinguishable from a practical three-phase power source. All three lines will move 120 degrees. When the rotary phase converter is of the correct magnitude, it produces a true three phase power supply, and each of the three output voltages is balanced across the connected load range.