Analysis of Z-Source Inverter For Space Vector PWM Fed 3-Phase Induction Motor

This paper presents analysis of operatio n and implementation of Z-source space vector pulse width modulation (SVPWM) inverter fed three phase induction mot or. The Z-source is an alternative power conversion topology that can both buck and boost the input voltage using only passive components. It uses a unique LC impedance network in the DC link between rectifier and inverter fed induction motor . It also allows the use of the shoot-through switching state, w hich el iminates or reduces the dead-times that are used in the conventional inverters. Therefore, the Z-source inverter can buck and boost voltage to a desired o utput voltage that is greater than the available input voltage. In addition, it reduces the harmonics, improves power factor, increases reliability ,lo w cost and highly efficient single-stage structure for buck a nd boost power conversion. Theoretical analysis and simulati on studies using PSIM soft ware have been performed to demonstrate these new features

,where V 1 to V 6 are active vectors and V 0 ,V 7 are zero vectors in the origin.
In SVPWM the space reference voltage moves from state- That led to: Where The time interval T 1 and T 2 satisfy the reference voltage, but T o fills up the remaining gap in T s [1,2].
The representation ,modeling, and implementation of SVPWM technique was given detail in reference [6].

3.Z-Source Inverter(ZSI):
The most important features of Z-Source Accordingly equation (2) become Where T * =T 0 -T The switching time of the upper switches and the lower switches in a ZSI is summarized in Table I.Its clear when the shoot-through duration (T) is equal to zero, the switching time of each power switch for the ZSI is exactly the same as that for the normal one [10].
PDF created with pdfFactory Pro trial version www.pdffactory.com Vi = 0 Case2: non shoot through state Assuming that the average voltage of the inductors over a switching period(0 toTs) is equal to zero in steady state: Where T active =time of non shoot-through active interval.
It is clear that V C can be used to regulate the DC-link voltage.The peak DC-link voltage across inverter bridge can be calculated using ( 7) and ( 8) Vi=B.V dc (10) Where, B = 1 / (1-2T/T s ) i.e. > 1 The peak ac output phase voltage of inverter for Z-source SVPWM is where M is modulation index. The

Z-source impedance calculation:
The Z-impedance network contains Where Vc, ΔI L are the average capacitor voltage and the value of inductor current ripple at peak power.The maximum ripple current was taken as 5%.

Simulation of Proposed System:
The traditional SVPWM inverter fed induction motor was built and detailed analysis in [6].It can be considered as a brief guidelines for the new ZSI which is presented in this research.Also the data of motor,MOSFET bridge ,and single phase rectifier were taken the same.
The performance analysis, system implementation, and simulation has established using PSIM program package.
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5-Results and Discussion:
The analytical and operating principle of the new Z-source inverter has been verified with simulation.
The name plate of the motor shows:

6-Conclusions
This paper has demonstrated that the Z-

3. 1 .
Fig.4(b) when the inductors and input DC source transfer energy to the capacitors and motor.The following equations can be written: Case1: shoot through state Buck -Boost factor (B.M) is determined by the modulation index M and the Boost factor B,which preferably should be set to unity (T/T s = 0) for voltage-buck operation and B > 1 for voltage-boost operation.[10,11] .The linear region in under modulation range of tradional SVPWM is larger than that of other types of PWM techniques, where the modulation index approaches to(90.7).The maximum modulation index can be obtained when V ref equal to the radius of the inscribed circle: ( V ref ) max = V dc ( 30 o ) = 0.577 V dc Therefore, m max = 0.577V dc /(2V dc π) = 0.907 It means that 90.7 percent of the square wave fundamental voltage is available in the linear region of SVPWM.PDF created with pdfFactory Pro trial version www.pdffactory.comAlso the peak ac output phase voltage in traditional SVPWM inverter, Vpac=M.2.V dc / .The SVPWM inverter fed induction motor restricts the drive operation in constant torque region only and also limits its speed because of output voltage limitation.But in ZSI state ,the ac voltage varies from zero to infinity depend on boosting factor B (equation.11 ).

L 1
=L 1 and C 1 =C 2 storage elements .The purpose of the inductor is to limit the current ripple through the devices during boost mode with shoot-through state and the purpose of the capacitor is to absorb the current ripple and maintain a fairly constant voltage .Choosing the parameters of Z-network elements will affect the inverter behavior , performance and harmonic distoration.Also could be optimally designed to lower the cost and size.Therefore, when attempting to size the parametric values of the chosen impedance network, procedures that are well established for traditional SVPWM inverter sizing can be used as brief guides for choosing capacitance and and inductance .Besides that for their second passive values, additional considerations must be taken.A review for calculating these parameters is presented in [12,13].Following the design guidelines presented in paper with a small ripple in capacitor voltage and inductor current, the capacitor and inductor can be calculated as : C≥ (I L .T/Ts) /2.Fs.ΔV c (12) where,I L, T/Ts , Fs, ΔV c are, the average current of the Z-network inductor, the shoot-through duty ratio, the switching frequency and the value of capacitor voltage ripple at peak power.The maximum capacitor voltage ripple was taken as 5% in calculation.And L ≥ (V c .T/Ts) /2Fs.ΔI L

1 - 2 -
control simulation.PSIM's graphic user interface is intuitive and very easy to use.A circuit can be easily setup and edited.The simulation results can be analyzed easily using various post-processing function in the waveform display program .The blocks and their parameters of modified Z-source SVPWM inverter are given in the followings: Space vector calculation, vector location, and time interval calculation blocks are shown in fig.5(a).The shoot through is also setting in the model, that shoot through time (T) can be selected.The maximum value must be T ≤T 0 /2(see mono-stable box in fig.5(a)).The circuit of voltage source Inverter drive induction motor consist of three phase induction motor ,A three -phase voltage source PWM inverter which consist of power bridge devices with three output legs, each consisting of two power switches and two freewheeling diodes, the inverter is supplied from DC voltage Vi through dc link passive Z-impedance .The dc link is supplied by dc voltage V dc from singl phase rectifier as shown in figure 5(b).
Figs.6 show simulation voltage waveforms under the nominal phase voltage of 220Vac.The magnitude of the output voltage is boosted to 175V(phase)

Figure 4 (
Figure 4(b).Equivalent circuit of Z Source in the non shoot through state.

Figure ( 8 )
Figure (8)FFT Results of voltage in ZSI.(a)Input phase voltage of rectifier.(b)Outputphase voltage of inverter.(c)Output line voltage of inverter.

Figure( 10
Figure(10)Current Waveforms in ZSI:(a)Line current of motor.(b)Supply Current

Figure( 9 )
Figure(9)FFT Results of voltage in traditional.(a)Input phase voltage of rectifier.(b)Outputphase voltage of inverter.(c)Output line voltage of inverter.

Figure( 11
Figure(11)Current Waveforms in traditional inverter:(a)Line current of motor.(b)Supply Current

Figure( 13 )
Figure(13)FFT Current Analysis In Traditional Inverter:(a)Line current of motor.(b)Supply Current.

Figure
Figure(15)Voltage Waveforms of ZSI For 20% voltage sag.(a)Input phase voltage to rectifier .(b)Output phase voltage of inverter.(c)Output line voltage of inverter .(d)Inputdc voltage.

com Eng. & Tech. Journal, Vol.28, No.17, 2010 Analysis of Z-Source Inverter For Space Vector PWM Fed 3-Phase Induction Motor 5442
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