Improved Trans-Z-source Inverter for Automobile Application

INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303

Improved Trans-Z-source Inverter for Automobile Application Aiswarya P R1 Calicut University, EEE Aiswarya.kollora@gmail.com Abstract—In this paper a new technology is proposed with a replacement of conventional voltage source/current source inverter with Improved Trans-Z-source inverter in automobile applications. The improved Trans-Z-source inverter has a high boost inversion capability and continues input current. Also this new inverter can suppress the resonant current at the startup; this resonant current in the startup may lead the device to permanent damage. In improved Trans-Z-source inverter a couple inductor is needed, instead of this coupled inductor a transformer is used.

By using a transformer with sufficient turns ratio the size can be reduced. The turn’s ratio of the transformer decides the input voltage of the inverter. In this paper operating principle, comparison with conventional inverters, working with automobiles simulation results, THD analysis, Hardware implementation using ATMEGA 328 P are included.

Index Terms— Boost inversion Capability, Coupled inductor, Improved Trans-Z-Source Inverter, Resonant current suppression, transformer a combination of switching devices and diodes in an antiparallel combination. L1,L2 are separate inductors but proposed system it is a coupled inductor. In figure.1 the DC source is a fuel cell stack[3].

1 INTRODUCTION

T

HE Z-source inverter is a three phase 3 leg 6 switch inverter with an impedance network at the source side of the inverter followed by the DC source. This impedance network may contain several capacitors an inverters, value of this capacitors/inductors are varying the DC input voltage level to the inverter. The Improved trans-Zsource inverter proposed in [1] which can be worked as both voltage source inverter and current source inverter. In addition to that this Improved trans-Z-source inverter is capable of working in both boost and buck conditions. It functions as a buck-boost inverter without making use of DCDC Converter Bridge due to its unique circuit topology.

Different types of Z source inverter topologies using Pulse Width Modulation strategies have been published in [3]-[5] and their applications in [7],[8]. Three level neural-pointclamped topology is published in [9] and[10],direct ac–ac converters [11], [12], and other Z-network topologies [13]– [14]. Quasi-Z-source inverters are used to overcome the disadvantages of the conventional Z-source inverter [15]– [17], and have advantages such as a reduction in the passive component ratings and an improvement in the input profiles.

Some researchers have recently focused on improving the boost factor of the Z-source inverter. This can be achieved using a very high modulation index in order to achieve an improvement in the output waveform [18]–[25].

Fig 1 Conventional Z-source inverter

The conventional Z source can work even the upper and lower switches are active at the same time. This can be for only one leg among three legs or for all three legs. This switching period is known as shoot through (ST).When either 1 switch from a leg is gated then this switching period is known as non- shoot through (NST)[4],[5].The equivalent circuit of figure 1 is redrawn in figure 2 and 3 for shoot through and non shoot through respectively. Non shoot through has 6 switching states depending upon different switching combinations. Z-source inverter shown in figure 1 can be drawn as in figure 2 for shoot through period, the inverter side is acting as a voltage source. The circuit can be redrawn as shown in figure 3 non-shoot through period (for 6 switching combinations).Here the inverter is acting as a current source.

2 CONVENTIONAL Z-SOURCE INVERTER To overcome the drawbacks of the conventional voltage source inverter and current source invert the Z-source inverter is introduced. It consists of a unique impedance network. In figure.1 two inductors L1,L2 and capacitors C1,C2 are connected in X shape which is coupling a three phase inverter and a DC source. The Z source can be used to either connect DC source or another converter circuit. Therefore, the dc source can be a battery, switches used in the converter can be

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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 TABLE 1 COMPARISON OF ZSI WITH CONVENTIONAL VSI&CSI

Fig 2 Equivalent circuit of Z-source inverter during shoot through

ZSI

Conventional Inverter

Can function as both as VSI and CSI Has buck-boost capability

Can function as either VSI or CSI Either Buck or Boost

Shoot through is present

Shoot through is absent

Output Voltage can be varied by varying the boost factor/modulation index

Output voltage depend upon the firing pulses and the input dc voltage

3 IMPROVED TRANS-Z SOURCE INVERTER The Improved trans-Z source inverter is shown in figure 4.

It consists of inductor L1, for the function of coupled inductors L2 and L3 a transformer of turn’s ratio 1: n two capacitors C1 and C2, a main diode D1 are connected.

Fig 3 Equivalent circuit of Z-source inverter during non-shoot through

The ratio between the input voltage of the inverter v i and the DC input voltage V0 is defined as the boost factor (B) of the Z-source inverter. Boost ratio can be written as B=

�� �0

Fig 4 Improved trans-Z-source

(1)

Main advantages of improved trans-Z source inverter over conventional z source inverters are the boost inversion capability, continuous input current and resonant current suppression.

This can be rewritten in terms of duty ratio/ turn on time, turn off time 1 1 B = 2đ?‘‡ 0 = (2) 1−

�

1−2đ??ˇ

2.1 Operating Principle The Improved trans-Z-source inverter has shoot through states and non-shoot through states same as that of the Z source inverter. Shoot through state is the condition when both upper and lower switches are gated together, during the shoot-through state, the diode D is OFF[1]. In non shoot through state inverter may be either in six active stages or two zero stage, during non-shoot through diode D is ON. Equivalent circuit of improved trans-Z-source inverter is shown in figure 5. Equivalent circuit for shoot through state is shown in figure 6. Equivalent circuit of non-shoot through state is shown in figure 7. The boost factor is defined as the ratio of input voltage of the inverter to the DC input[1].

The boost factor (B) is given by

Where T0 = turn on time T=turn off time off time D= duty ratio Z-source inverter is compared with conventional inverters and tabulated in table 1.From this comparison it is clear that further studies can result a efficient Z-source

inverter. The voltage boost capability can be changed by changing the boost factor (B) with the help of varying the impedance value of the Z-source network[3]-[6].

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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 đ??ľ= =

with ITZSI a three phase induction motor is represented with a three phase inverter. When the application changes or in other words when the inverter is feeding servo motor or stepper motor a single phase inverter is used. Automobile application with improved trans-Z source inverter arrangement is as shown in figure 8.

1 1− 2+đ?‘› đ??ˇ 1 đ?‘‡ 1−(2+đ?‘› ) 0

(3)

�

Where T0 = turn on time T=turn off time off time D= duty ratio

Fig 8 Arrangement Of Automobile Application With Improved Trans-Z Source Inverter

If an induction motor is used the speed of the induction motor can be controlled by changing the impedance of the Znetwork. In order to make a change in impedance turn’s ratio n is varied [7].

Fig 5 Equivalent Circuit Of Improved Trans-Z-Source Inverter

4 SIMULATION RESULTS To analyze the usage of Improved trans-Z source inverter in automobile application the circuit is simulated using MATLAB R2014a SIMULINK. selected the simulation parameters L3 =1 mH,C1=C2 =1000 ΟF, Lf =1.5 mH, Cf =10 ΟF, and R = 50 Ί/phase. The turn ratio of the transformer is 2. The magnetic inductance measured from the primary side was set to 0.737 mH. The leakage inductance was set to 0.5 ΟH. The switching frequency was 10 kHz, the input was 100 Vdc, and the output phase voltage was 115 Vrms to meet the grid-tied requirement. Constant boost control was used [1].

The simulation diagram is shown in figure 9.

Simulation parameters details are given in table2.Also the simulation of the control circuit providing pulses for the power switching devices are done with ISIS schematic capture. For this the controller ATMEGA 328 P from the manufacturers ATMEL is used. The pulse generated using ISIS schematic capture is shown in figure 10. This is displayed in a digital oscilloscope.

The simulation results are represented in figure 11 and figure 12 respectively. Speed and torque characteristics are represented in figure 11.Phase voltage and phase current are represented in figure 12.

The FFT analysis is also done to understand the Total Harmonic Distortion of the circuit. The total harmonic distortion is defined as the measure of closeness of the

Fig 6 Equivalent Circuit Shoot-Through State

Fig 7 Equivalent Circuit Non-Shoot-Through State

2.2 Automobile Application The boost factor of improved trans-Z-source inverter is higher as compared to the conventional Z-source inverter.

The boost capability depends upon the term n in equation (3) which is representing the turn’s ratio of the transformer which is replacing the coupled inductor[7]. As discussed earlier the boost inversion capability and the continues input current are the reason for opting the improved tans-Source inverter for an automobile application. This new inverter technology can drive several motors in an automobile which is running under AC condition. Servomotor driving the power window and stepper motor driving the power steering commonly found in electric vehicles are example for them.

For the purpose of explaining the working with motor along

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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303

Fig 9 simulation diagram of improved trans-Z source inverter

TABLE 2 SIMULATION TABLE OF IMPROVED TRANS-ZSOURCE INVERTER FOR SPEED CONTROL OF INDUCTION MOTOR Input DC voltage

100V

Output phase voltage

115 Vrms

Capacitors

1000ÂľF

Turn ratio

1:2

Primary Transformer

0.737mH

inductance

Fig 10 Pulses For Six Switching Devices

Leakage

0.5ÂľH

inductance Inductor L3

1mH

Switching Frequency

10kHz

Three-Phase

Lf

1.5mH

output Filter

Cf

10¾F 50Ί/phase

Three-phase resistive load

Fig 11 Speed And Torque Characteristics

obtained waveform to the shape of its fundamental waveform. And is given by the equation 1 đ?‘‡đ??ťđ??ˇ = đ?‘‰1

∞

��2 �=1,2,3‌.

Where, �1 =voltage of the fundamental voltage �� =voltage of the nth wave The amount of Total Harmonic Distortion (THD) is found 2.15% which is an appreciably low value for such a circuit with six power switching devices and an impedance network.

FFT analysis for the circuit is shown in figure 13. So this improved trans-Z source inverter has a very fair value for THD. Along with other advantages like boost inversion

Fig 12 Phase Voltage And Phase Current

capability, continuous input current, suppression of startup current this can be added.

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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 5 ISSUE 2 – MAY 2015 - ISSN: 2349 - 9303 the speed and torque characteristics, phase voltage and current.

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Fig 13 FFT Analysis for the Circuit

5 HARDWARE IMPLEMENTATION The prototype of improved trans-Z source inverter for automobile application is shown in figure 15. The switching devices are commercially available 600-V MOSFET (IRFZ44N) modules. The controller used for giving gate pulses to the switching device is ATMEGA 328 P from the manufacturers ATMEL. And other parameter values are same as that mentioned in simulation result’s session. The proto type is running a 6V servo motor.

Fig 14 Prototype Of Improved Trans-Z Source Inverter For Automobile Application

6 FUTURE SCOPE This technology can also be used for driving the main motor drive in an electric vehicle which is using a three phase induction motor instead of driving auxiliary drives like power window, power steering, and wipers. This technology can also be used with a matrix converter. Trans-Z source with matrix converter for automobile application this can reduce DC link and the power conversion can be done in a single stage.

7 CONCLUSION A new topology was proposed to improve the trans-Zsource inverter for automobile application, which is driving auxiliary drives in automobiles with the following main advantages: high boost voltage inversion ability, continuous input current, and resonance suppression at start-up.

The experimental results for dc 100 V input and ac 115 Vrms phase output verified the high step-up inversion ability, and the simulation and experimental results show that the proposed inverter has high boost inversion ability with continuous input current. Also the simulation results shows

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Author’s Profiles Aiswarya P R has obtained B.Tech degree in Electrical and Electronics Engineering from Veda Vyasa institute of Technology,Malappuram,Kerala .She is pursuing 4th semester,M.Tech in Power Electronics at Veda Vyasa institute of Technology Malappuram,Kerala.Life time Member in ISTE M.no: LM86920. Her current research interests are in Z source inverters applications in Electric vehicles, Multi Level inverters simulation and modelling

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