A ZVS Grid-Connected Three-Phase Inverter

ABSTRACT:

A six-switch three-phase inverter is widely used in a high-power grid-connected system. However, the anti parallel diodes in the topology operate in the hard-switching state under the traditional control method causing severe switch loss and high electromagnetic interference problems. In order to solve the problem, this paper proposes a topology of the traditional six-switch three-phase inverter but with an additional switch and gave a new space vector modulation (SVM) scheme. In this way, the inverter can realize zero-voltage switching (ZVS) operation in all switching devices and suppress the reverse recovery current in all anti parallel diodes very well. And all the switches can operate at a fixed frequency with the new SVM scheme and have the same voltage stress as the dc-link voltage. In grid-connected application, the inverter can achieve ZVS in all the switches under the load with unity power factor or less. The aforementioned theory is verified in a 30-kW inverter prototype..

KEYWORDS:

  1. Grid connected
  2. soft switching
  3. space vector modulation (SVM)
  4. three-phase inverter
  5. zero-voltage switching (ZVS)

 SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 Fig. 1. ZVS three-phase inverter.

 EXPECTED SIMULATION RESULTS:

 

 Fig. 2. Inverter output current and grid voltage (10 ms/div): (a) φu = φi , (b), φuφi = π/6, (c) φuφi = π/6.

Fig. 3. CE voltage and current of S6 (IGBT on) (5 μs/div).

Fig. 4. CE voltage and current of S6 (diode on) (2.5 μs/div).

 

 Fig. 5. CE voltage and current of S7 (25 μs/div).

Fig. 6. CE voltage and current of S7 , ibus, and iLr (10 μs/div).

 

Fig. 7. VCc and iLr (50 μs/div).

Fig. 8. Efficiency curve.

CONCLUSION:

In order to speed up the market acceptance of EVs/HEVs, the capital cost in charging infrastructure needs to lower as much as possible. This paper has presented an improved asymmetric half-bridge converter-fed SRM drive to provide both driving and on-board DC and AC charging functions so that the reliance on off-board charging stations is reduced.  The main contributions of this paper are: (i) it combines the split converter topology with central tapped SRM windings to improve the system reliability. (ii) the developed control strategy enables the vehicle to be charged by both DC and AC power subject to availability of power sources. (iii) the battery energy balance strategy is developed to handle unequal SoC scenarios. Even through a voltage imbalance of up to 20% in the battery occurs, the impact on the driving performance is rather limited. (iv) the state-of-charge of the batteries is coordinated by the hysteresis control to optimize the battery performance; the THD of the grid-side current is 3.7% with a lower switching frequency.  It needs to point out that this is a proof-of-concept study based on a 150 W SRM and low-voltage power for simulation and experiments. In the further work, the test facility will be scaled up to 50 kW.

REFERENCES:

[1] B. K. Bose, “Global energy scenario and impact of power electronics in 21st Century,” IEEE Trans. Ind. Electron., vol. 60, no. 7, pp. 2638- 2651, Jul. 2013.

[2] J. de Santiago, H. Bernhoff, B. Ekergård, S. Eriksson, S. Ferhatovic, R. Waters, and M. Leijon, “Electrical motor drivelines in commercial all-electric vehicles: a review,” IEEE Trans. Veh. Technol., vol. 61, no. 2, pp. 475-484, Feb. 2012.

[3] A. Chiba, K. Kiyota, N. Hoshi, M. Takemoto, S. Ogasawara, “Development of a rare-earth-free SR motor with high torque density for hybrid vehicles,” IEEE Trans. Energy Convers., vol. 30, no. 1, pp.175-182, Mar. 2015.

[4] K. Kiyota, and A. Chiba, “Design of switched reluctance motor competitive to 60-Kw IPMSM in third-generation hybrid electric vehicle,” IEEE Trans. Ind. Appl., vol. 48, no. 6, pp. 2303-2309, Nov./Dec. 2012.

[5] S. E. Schulz, and K. M. Rahman, “High-performance digital PI current regulator for EV switched reluctance motor drives,” IEEE Trans. Ind. Appl., vol. 39, no. 4, pp. 1118-1126, Jul./Aug. 2003.

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