8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 1/12

Z - SOURCE CONVERTERS 

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 2/12

•What is Z source Converter? Why Z source ? 

•V- Source converter and its limitations 

•I - Source Converter and its limitations 

V-Source inverter:

ac output voltage is < the dc voltage or the dc-voltage > the ac input voltage.

The V-source inverter is a buck inverter for dc-to-ac power conversion and is

a boost (step-up) rectifier for ac-to-dc power conversion. 

Additional dc-dc boost converter is needed for higher ac voltages. 

The upper and lower devices of each phase leg cannot be gated on to avoid

shoot through fault EMI may cause shoot through; and to avoid dead time is

needed between upper and lower devices adding to cost and controlcomplexity. 

An LC output filter is needed to provide sinusoidal output voltage. 

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 3/12

Additional dc –dc buck (or boost) converter is needed for applications requiring

ide voltage range, increasing system cost and lower efficiency. 

At least one of the upper devices and one of the lower devices have to be

ted on and maintained on at any time. Otherwise, an open circuit of the dc inductor

uld occur and destroy the devices. The open-circuit problem by EMI noise’s

isgating-off is a major concern. Overlap time for safe current commutation is needed

the I-source converter, which also causes waveform distortion, etc. The main switches have to block reverse voltage that requires a series diode to

used in combination with high-speed and high-performance devices such as IGBTs. 

I source inverter 

output voltage > dc voltage that feeds the dc

ductor or the dc voltage < than the ac input

ltage.

ource inverter is a boost inverter for dc-to-acwer conversion and is a buck rectifier (or buck

nverter) for ac-to-dc power conversion. 

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 4/12

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 5/12

Z-source converter structure using the antiparallel combination of switching device

and diode. 

Z-source converter structure using the series combination of switching device and

diode. 

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 6/12

Traditional two-stage power conversion for fuel-cell applications. 

Z-source inverter for fuel-cell applications. 

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 7/12

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 8/12

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 9/12

Modified carrier-based PWM control with shoot-through zero states that are evenly

distributed among the three phase legs, while the equivalent active vectors are unchanged. 

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 10/12

For the inverter bridge in the shoot-through zero state for an interval of T0

during a switching cycle, one can write v L = VC and v d = 2VC and v out = 0 (2) 

and for the non shoot through six states we can write: 

v L = Vin – VC, v d= Vin, vout = VC – v L = 2VC – Vin (3) 

Where, Vin is the dc source voltage and T = T0 + T1. 

Avg voltage of the inductor over one switching period in steady state should be zero 

or

Similarly, avg dc link voltage is given by: 

Peak dc link voltage of eqn (3) can be expressed as: 

Where, B is boost factor

CIRCUIT ANALYSIS AND OBTAINABLE OUTPUT VOLTAGE 

Assuming L1=L2=L and C1=C2=C 

VC1 = VC2 = VC, and v L1 = v L2= v L (1) 

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 11/12

The output peak phase voltage of the inverter can be expressed as

Where, M is the modulation index can be rewritten using (7) and (9) as 

Eqn (10) shows that the output voltage can be boosted up and down by

choosing an appropriate buck-boost factor BB given by 

From (1) (5) and (8) the capacitor voltage can be expressed as: 

The buck-boost factor BB is determined by the modulation index M and boost factor B. B can be controlled by

duty cycle of the shoot through of the inverter state PWM.

8/10/2019 Z Source Converter

http://slidepdf.com/reader/full/z-source-converter 12/12

•References: 

•Fang Zheng Peng “Z-Source Inverter” IEEE trans. On Industry

Applications, Vol. 39, No.2 March/April 2003 pp.504-510.