Single Phase Z Source Half Bridge Inverter

Single Phase Z Source Half Bridge Inverter

Reeto Jose K, Anisha Shivanandan, Vani Venugopal

PG Students(Power Electronics): EEE dept. Vidya Academy Of Science&Technology Thrissur,India

AbstractThe novel Single phase Z source half bridge inverter is presented as applying Z network in the half bridge inverter.The inverter can convert dc to ac.The proposed converter can solve limited voltage and shoot through problem.By using the Z network voltage source converter in the main circuit can be used as current source and vice versa.The proposed converter can solve the midpoint balance of the input capacitors.By using the Z source half bridge inverter it can improve the voltage as compared to the conventional half bridge inverter.The z network can overcome the disadvantage of voltage source inverter and the current source inverter.The Z network can be applied to dc-dc,dc-ac,ac-ac and ac-dc.The Z source half bridge inverter is working in the duty ratio of 1.2.It is a special case and it can act as buck boost converter by interchanging the duties of the switches. The proposed inverter is increases the efficiency. Total harmonics distortion in conventional half bridge inverter and the single phase z source half bridge inverter is 7.03% and 0.88% respectively.The proposed converter is simulated using MATLAB/Simulink.

Keywords-Half Bridge Inverter,MATLAB/Simulink,THD,Z network

1. INTRODUCTION

   Inverter is used to convert dc to ac.In single phase half- bridge converters have their switches in series,[1] as shown in Fig. 1. Here shoot-through can occur which means that when a strong current flowing through the switches in the same leg makes them break down. Also, the ac output voltage is less than the dc voltage, which is called as the limited voltage problem, since, in practice, ac output voltage is sometimes required to be higher than the dc voltage. Still, an unbalanced midpoint ofinput capacitors in conventional half-bridge converters leads to large ripples.Thismaking the system unstable.

   In order to overcome the disadvantages of voltage source inverter(VSI) and the current source inverter(CSI),Z network is proposed [2].It can act as buck boost converter,voltage source inverter in the main circuit can be interchanged to current source and vice versa.

   The recently developed new inverter is Z-source inverter. It can produce any preferred output ac voltage, even better than the line voltage, irrespective of the input voltage, improves the reliability of the inverter greatly because the shoot-through states that might be caused by EMI noise can no longer destroy the inverter, and reduce the in-rush current and harmonics in the current owing to the Z-source network.

   Furthermore it can solve the unbalanced midpoint voltage problem.

   Fig.1 Conventional Half Bridge Inverter

2. EQUIVALENT CIRCUIT

   Fig.2. Consisting of single phase z source half bridge inverter [3].The diode D is used to prevent the current from flowing backto the source. The inductors is used in the Z-networkis to eliminate strong current, when the switches are inthe shoot- through state.

   Fig.2 Proposed Inverter

   The following conditions are assumed for simplicity

   1. Entire components in the circuit are ideal

   2. The dead time in the driving pulses is ignored

   3. C1 = C2 and L1 = L2 in the Z-network

   4. C1, C2, Cb1, and Cb2 has large value

   5. The freewheeling diodes present in the switches are ignored.

3. MODES OF OPERATIONS Duties of the switch S1and S2 by d1 and d2.

   Case; d1+d2>1

   There are three modes ofoperations.The switching period T. T0 as the beginning of one period.

   T1 as mode of transition instant from mode1 to mode2.

   T1=T0+{d2+d1-1}T

   T2 as the mode of transition instant from mode2 to mode3 T2=T1+{1-d2}T

   T3 as the end of the period.

   T3=T Mode1;T[T0,T1]

   Fig.3 Equivalent Circuit For S1ON And S2ON

   From Fig.3,In the loop1 C1 discharges the energy to the L1, then IL1 increases Vc1=VL1 (1)[3].

   the loop2 C2discharges the energy to the L2,then IL2increase, then Vc2=VL2 (2)

   The voltage across the diode VD is negative because the anode voltage is less than the cathode voltage.

   VD=-{Vc1+Vc2-Vi}

   The energy of C2 is delivered to R load and Cb2 through theloop C2-R-Cm2.Therefore, Cb2 charges and Cb1 discharges.

   Output voltage,V0=Vc2-Vcb2(3)

   Mode2;T[T1,T2]

   As shown in Fig.4 S1is ON,S2 is OFF. In the loop1 Vin and L1 discharges the energy to the C2.

   Vc2=Vi-VL1(4)

   The energy of C2 is delivered to the load R and Cb2through the loopC2-R-Cb2. Therefore,Cb2 charges and Cb1discharges. Output voltage,

   V0=Vc2-Vcb2

   Fig.4Equivalent Circuit for S1ON And S2OFF

   Mode3;T[T2,T3]

   Fig.5 Equivalent Circuit For S1 OFF And S2 ON

   Fig.5 consist of S1 is OFF,S2is ON. In the loop1 Vi and L1discharges the energy to C2.Vc2=Vi-VL1

   In loop2 Vi and L2 discharges the energy to the C1.The energy of L2 and Cb2delivered to load R.So Cb1 charges and Cb2 is discharges.

   From the loop Vin-D1-C1-R-Cm2,the output voltage is V0=Vi-Vc1-Vcb2 (5)

   Vc1=Vc2={2-d1-d2}Vi /{3-2{d1+d2}} (7)

   Vcb2={2Vc2-Vi}d1-Vc2+Vi (8)

   When d1=0.5 the proposed converter act as the single phase inverter but it exceed the output voltage (Vin/2 and Vin/2)than the conventional one[3].

4. Simulation Result

TABLE1.Simulation parameters and values

Fig.6 SimulationFor S1=0.5 and S2=0.7

Fig.7 Simulation Results

Fig.9 Frequency Domain Response Of Inverter

Fig.10 Harmonics Order Analysis Of Inverter

CONCLUSION

The proposed single phase Z source half bridge inverter is improved the output voltage than the conventional one.The voltage across Cb1 and Cb2 are Vcb1=Vcb2=20V .So midpoint voltages are balanced. The proposed converter is simulated using MATLAB/Simulink.Total harmonics distortion in conventional half bridge inverter and the single phase z source half bridge inverter inverter is 7.03% and 0.88% respectively.

Fig.8 Simulated Output Voltage Waveform

REFERENCES

1. Muhammad H.Rashid, Power Electronics Circuits,

   Devices and Applications, Third Edition, Pearson Education 2004.

2. F. Z Peng, "Z-Source Inverter" IEEE Trans. Ind. Appl., vol. 39, no. 2, Mar./Apr. 2003

3. Guidong Zhang, ZhongLi, Bo Zhang,DongyuanQiu, Wenxun Xiao, and Wolfgang A. Halang "A Z-Source Half-Bridge Converter" IEEE Trans on industrial electronics,Vol. 61, no.3,March 2014

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