**ABSTRACT:**

This paper proposes a novel three-phase nine-switch ac/ac converter topology. This converter features sinusoidal inputs and outputs, unity input power factor, and more importantly, low manufacturing cost due to its reduced number of active switches. The operating principle of the converter is elaborated; its modulation schemes are discussed. Simulated semiconductor loss analysis and comparison with the back-to-back two-level voltage source converter are presented. Finally, experimental results from a 5-kVA prototype system are provided to verify the validity of the proposed topology.

**KEYWORDS:**

- AC/AC converter
- pulse width modulation (PWM)
- reduced switch count topology

**SOFTWARE: **MATLAB/SIMULINK

**CIRCUIT DIAGRAM:****Fig: 1 B2B 2L-VSC.**

Fig: 2 Proposed nine switch ac to ac converter with a quasi dc link

**EXPECTED SIMULATION RESULTS:**

Fig. 3. Measured rectifier and inverter waveforms (CF-mode operation). (a) Input and output voltages. (b) Voltage spectrum. (c) Input and output currents.

Fig. 4. Measured waveforms and spectrum (VF mode operation). (a) Input and output voltages. (b) Spectrum.

Fig. 5. Measured waveforms when the inverter output frequency has a step increase from 30 to 120 Hz, while the rectifier input frequency remains at 60 Hz. (a) Input and output voltages. (b) Input and output currents.

**CONCLUSION:**

A novel nine-switch PWMac/ac converter topology was proposed in this paper. The topology uses only nine IGBT devices for ac to ac conversion through a quasi dc-link circuit. Compared with the conventional back-to-back PWM VSC using 12 switches and the matrix converter that uses 18, the number of switches in the proposed converter is reduced by 33% and 50%, respectively. The proposed converter features sinusoidal inputs and outputs, unity input power factor, and low manufacturing cost. The operating principle of the converter was elaborated, and modulation schemes for constant and VF operations were developed. Simulation results including a semiconductor loss analysis and comparison were provided, which reveal that the proposed converter, while working in CF mode, has an overall higher efficiency than the B2B 2L-VSC at the expense of uneven loss distribution. However, the VF-mode version requires IGBT devices with higher ratings and dissipates significantly higher losses, and thus, is not as attractive as its counterpart. Experimental verification is carried out on a 5-kVA prototype system.

**REFERENCES:**

** **Wu, High-power Converters and AC Drives. Piscataway, NJ: IEEE/Wiley, 2006.

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