A Novel Three-Phase Three-Leg AC/AC Converter Using Nine IGBTs


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.



  1. AC/AC converter
  2. pulse width modulation (PWM)
  3. reduced switch count topology




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




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.



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.



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

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Power Quality Improvement of PMSG Based DG Set Feeding Three-Phase Loads

IEEE Transactions on Industry Applications, 2015

ABSTRACT: This paper presents power quality improvement of PMSG (Permanent Magnet Synchronous Generator) based DG (Diesel Generator) set feeding three-phase loads using STATCOM (Static Compensator). A 3-leg VSC (Voltage Source Converter) with a capacitor on the DC link is used as STATCOM. The reference source currents for the system are estimated using an Adaline based control algorithm. A PWM (Pulse Width Modulation) current controller is using for generation of gating pulses of IGBTs (Insulated Gate Bipolar Transistors) of three leg VSC of the STATCOM. The STATCOM is able to provide voltage control, harmonics elimination, power factor improvement, load balancing and load compensation. The performance of the system is experimentally tested on various types of loads under steady state and dynamic conditions. A 3-phase induction motor with variable frequency drive is used as a prototype of diesel engine with the speed regulation. Therefore, the DG set is run at constant speed so that the frequency of supply remains constant irrespective of loading condition.


  2. VSC
  3. IGBTs
  4. PMSG
  5. PWM
  6. DG Set
  7. Power Quality



Fig. 1 Configuration of PMSG based DG set feeding three phase loads.



Fig. 2. Dynamic performance at linear loads (a) vsab, isa,isb and isc ,(b) vsab, iLa,iLb and iLc (c) Vdc, isa,iLa and iCa


The STATCOM has improved the power quality of the PMSG based DG set in terms voltage control, harmonics elimination and load balancing. Under linear loads, there has been negligible voltage variation (From 219.1 V to 220.9 V) and in case of nonlinear load, the voltage increases to 221 V. Thus, the STATCOM has been found capable to maintain the terminal voltage of DG set within ± 0.5% (220 ±1 V) under different linear and nonlinear loads.

Under nonlinear loads, the load current of DG set is a quasi square with a THD of 24.4 %. The STATCOM has been found capable to eliminate these harmonics and thus the THD of source currents has been limited to 3.9 % and the THD of terminal voltage has been observed of the order of 1.8%. Therefore, the THDs of source voltage and currents have been maintained well within limits of IEEE-519 standard under nonlinear load.

It has also been found that the STATCOM maintains balanced source currents when the load is highly unbalanced due to removal of load from phase ‘c’. The load balancing has  also been achieved by proposed system with reduced stress on the winding of the generator.

The proposed system is a constant speed DG set so there is no provision of frequency control in the control algorithm.

However, the speed control mechanism of prototype of the diesel engine is able to maintain the frequency of the supply almost at 50 Hz with small variation of ±0.2 %.

Therefore, the proposed PMSG based DG set along with STATCOM can be used for feeding linear and nonlinear balanced and unbalanced loads. The proposed PMSG based DG set has also inherent advantages of low maintenance, high efficiency and rugged construction over a conventional wound field synchronous generator based DG set.


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