 Open Access
 Total Downloads : 365
 Authors : Lakshmi. C. R, Deepa Sankar
 Paper ID : IJERTV5IS051006
 Volume & Issue : Volume 05, Issue 05 (May 2016)
 DOI : http://dx.doi.org/10.17577/IJERTV5IS051006
 Published (First Online): 30052016
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Single Phase ZSource Matrix Converter with BuckBoost Capability
Lakshmi. C. R
M.Tech Student , Dept. of EEE,
Adi Shankara Institute of Engineering & Technology, Kalady,Kerala,India
Deepa Sankar
Asso. Professor, Dept. of EEE,
Adi Shankara Institute of Engineering & Technology, Kalady, Kerala, India
Abstract Matrix converter has been bestknown to offer an " all silicon " solution for ACAC conversion,removing the need for reactive energy storage parts employed in standard rectifier inverter based systems.The matrix converter is a forced commutated converter that uses an array of controlled twoway switches as the main power elements to produce a variable output voltage system with unrestricted frequency.It doesn't have any dc link circuit and does not want any massive energy storage component.
A single phase Zsource matrix converter that is an advancement of the traditional matrix converter can step up and step down the frequency and the voltage can be stepped up or stepped down.A MATLAB simulation of the single phase Zsource buckboost converter at totally different input and output frequencies and voltages that verifies its utility for a number of various applications is given here.
KeywordsZsource matrix converter; Sparse Matrix Converter;shootthrough states; PWM Techniques

INTRODUCTION
A discretionary number of input lines can be associated with a subjective number of output lines specifically utilizing bidirectional semiconductor switches.The various transformation stages and energy storage components of conventional inverter and cycloconverter circuits can be replaced by one exchanging network. A matrix converter is an ac to ac converter prepared to do specifically changing over an ac power supply voltage into an ac voltage of variable amplitude and frequency without a huge energy storage element [1]. The principal portrayal of a matrix converter was distributed in 1976 by Gyugyi and Pelly [2]. In 1980,Venturini and Alesina exhibited the first calculation fit for incorporating output sinusoidal reference voltages [1]. Late research on matrix converters has concentrated for the most part on modulation plans [3][8] and on drive applications. Clearly, all distributed studies have managed mostly with threestage circuit topologies.
The principal investigation of a solitary stage matrix converter was performed by Zuckerberger et al. [9] on a frequency stepup and elementary voltage stepdown converter. Utilisation of singlephase matrix converters has been portrayed for induction motor drives, radiofrequency induction heating, audio power amplification, and compensation voltage sags and swells. It has been accounted for that the use of safecommutation switches with pulsewidth modulation (PWM) control can essentially enhance the performance of ac/ac converters. However, in the conventional singlephase matrix converter topology [9][13],
the ac output voltage cannot exceed the ac input voltage. Furthermore, it is unacceptable to show both twoway switches of one phase leg on at the same time; otherwise, the current spikes generated by this action will destroy the switches. These drawbacks can be overcome by using Z source topology [14].Research on Zsource converters has centered primarily on dc/ac inverters and ac/ac converters.The Zsource ac/ac converters focus on single phase topologies [15][17] and threephase topologies. In applications where solely voltage regulation is required, the group of singlephase Zsource ac/ac converters proposed in [15][17] has a variety of deserves, such as providing a bigger range of output voltages with the buckboost mode, reducing inrush, and harmonic current. However, no one has designed a device primarily based on a Zsource structure and a matrix converter topology that can offer ac/ac power conversion with each a variable output voltage and a stepchanged frequency. Here, we apply the Zsource thought to a single phase matrix converter to produce a new kind of device known as a singlephase Zsource buckboost matrix converter. This singlephase Zsource buckboost matrix converter will offer a wide vary of output ac voltages in buckboost mode with stepdown/stepup frequencies. It is shown from operational principles, analyses and simulation that this singlephase Zsource buckboost matrix converter will buck and boost voltages in stepdown/stepup frequency operation. A safecommutation technique that is very straightforward to implement as a freewheeling path to provide the needed freewheeling operation just like what's offered in alternative device topologies is used. The safe commutation scheme sets up a persistent current way in dead time to wipe out voltage spikes on switches without a snubber circuit.

LITERATURE SURVEY

Basic Matrix Converter(MC) Topologies
Broadly,the existing frequency converter designs can be classified into 2 categories:direct and indirect converters.To reduce number of switches in the conventional matrix converter, major step was taken with regard to the further development of matrix converter topologies which occurred in 2001 as Indirect matrix converter topologies known as Sparse Matrix Converters as shown in Fig.1 by Kolar et al followed by the first experimental results of a Very Sparse Matrix Converter (Fig.2.). Ziegler et al in 2004 advocated possible circuit topologies referred as SAX converters. The same concept was proposed in 2002 by Kolar et al for the Sparse Matrix Converters known as Ultra Sparse Matrix Converter as shown in (Fig.3).
The ultrasparse matrix converter (USMC), shown in Fig.3, is the most simple form of the IMC, comprising only 9 individual switches and 18 diodes. The Ultra Sparse MC itself is a variant of the sparse matrix converter (SMC), shown in Fig.1. The USMC and SMC operate by creating a dc link,with the input stage and by using the output stage to provide inversion. The main variation between the IMC and SMC is that the USMC only permits unidirectional power flow due to the arrangement of the input switches.
Fig 1. Sparse Matrix Converter
Figure 2.Very Sparse Matrix Converter
Fig 3.Ultra Sparse Matrix Converter

Single phase Matrix Converter(MC) Topologies
Fig.4.(a) and (b) shows a singlephase Zsource, PWM voltagefed, buckboost converter and currentfed buckboost converter, respectively.The output voltage of the proposed acac converter can be bucked or boosted by controlling the duty ratio D. In addition, the output voltage can be inphase or outofphase with the input voltage depending on operating regions . This is a unique feature of the Zsource converter[16]
Fig 4. Singlephase Zsource acac converter:(a)voltagefed and (b)currentfed.

Bidirectional switch topologies
A true bidirectional switch must be realized by the combination of conventional unidirectional semiconductor devices. Fig.5.shows diverse bidirectional switch setups which have been utilized as a part of model and/or proposed in [18], [19], [20].
Another problem, tightly related to the bidirectional switches implementation is the commutation problem. The absence of static freewheeling paths gives rise to commutation issues . As a consequence it becomes a difficult task to safely commutate the current, since a particular care is required in the timing and synchronisation of the switches command signals.
Fig.5.Basic input filter configurations used in matrix converter prototypes(.a)Capacitorsstar or delta connected.(b)Second order LC filter (c)LC filter with parallel damping reistor

The input filter
The input filter design for static power converters operating from an ac power system has to meet three main requirements:

carry out the required switching noise attenuation;

having a low input displacement angle between filter input voltage and current;

guaranty overall system stability.
In addition to these requirements, a set of considerations related to cost, system efficiency,voltage attenuation, and filter parameter variation have to be made for an optimized input filter design [21], [22]


SINGLE PHASE ZSOURCE MC TOPOLOGY
A.GENERAL DESCRIPTION
The basic system is that of a single phase Zsource buckboost matrix converter whose general block diagram is as shown in Fig.6.The ac voltage across the singlephase matrix converter va is boosted by the ac/ac Zsource converter with the input voltage vi . Then, the singlephase matrix converter modulates the frequency of va. The output voltage is obtained with a variable amplitude and stepchanged frequency .Fig.7 shows the singlephase Zsource buckboost matrix converter. It employs a Zsource network,an LC input filter, bidirectional switches, and an RL load. The LC input filter is required to reduce switching ripple in input current. The single phase Zsource buckboost matrix converter discussed here requires four bidirectional switches S1j , S2j
,S3j , and S4j (j = a, b) to work as a singlephase matrix converter and one source bidirectional switch,Ssj (j = a, b), where a and b refer to drivers 1 and 2, respectively. All the bidirectional switches used are common emitter backtoback switch cells.
Fig 6. General block diagram of the existing topology
Fig 7. Singlephase Zsource buckboost matrix converter topology
B. MODES OF OPERATION
The frequency of input voltage fi is assumed to be 50 Hz, and the desired output frequency fo is decided to be 100 Hz (i.e.stepup frequency), 50 Hz (i.e.same frequency), or 25 Hz (i.e.stepdown frequency). To double the output frequency of the input voltage, the operation of the converter is divided into four stages, as shown in the Fig.8.
Fig.8. defines stage 1 in the boost mode when both input voltage and output voltage are positive. The switches Ssa; S1a; S2b, and S4a are completely turned on (S2b is turned on for commutation purposes, while Ssa and S4a are turned on for continuous current flow);
S1b,S3b,and S4b are modulated complementary to the dead time. In state 1, as shown in Fig.8(a),S4b is turned on and it conducts current flow during the increasing positive cycle of input voltage;Ssband S1b turn on and conducts negative current flow from the load to the source, if possible;S2b turns on for commutation purposes. Then, Ssb and S4b turn off, and S3b has not yet turned on, and there are two commutation states that occur.If iL1 + iL2 + io > 0, the current flows along a path which is from from Ssa , as shown in Fig. 8(b); if – iL1 – iL2 + io > 0 , the current flows along a path which is from S4a and S2b, as shown in Fig.8(c). Because switch S2b must be conducting, the current condition for this state is given as – iL1 – iL2 + io > 0. In state 2, as shown in Fig.8(d), S3b turns on and conducts current flow as a shootthrough path; the positive load current may be freewheeled through S2b and S1a; the negative load current may be freewheeled through S3b and S4a. In these switching patterns, the current path is always continuous whatever the current direction be. Thus, the voltage spikes are eliminated during switching and commutation processes. The analysis for stages 2, 3, and 4 is identical to that for stage 1. The dotted line in Fig.8.indicates the safecommutation switch during each stage. The operations at other output frequencies of 50Hz and 25 Hz are performed by varying the switching strategies. The operation for an output frequency of 50 Hz is implemented by omitting stage 2 and stage 3 and making the time intervals for stage 1 and stage 4 twice . Similarly, the operation for an output frequency of 25 Hz is carried out by interchanging stage 2 and stage 3 and doubling the time intervals of all stages. In the operations for output frequencies of 50Hz and 25 Hz, the time interval of each stage is 8.33 ms.
Fig 8. Stage1 for the boost mode for a frequency of 100 Hz. (a) State 1. (b) Commutationstate when iL1+iL2+io > 0(c) Commutation state when iL1 – iL2 + io > 0(d) State 2.
Fig 9. Switching pattern of the singlephase Zsource buckboost matrix converter for a 100 Hz output frequency in boost mode
C.OBSERVATIONS AND OUTCOMES OF STUDY
From the survey of different topologies of matrix converters the following observations are made:
Converter
No:of active device
No:of diodes
Isolated driver potentials
Simultaneous buckboost capability
MC
18
18
6(CC),9(CE)
NO
IMC
18
18
8
NO
SMC
15
18
7
NO
VSMC
12
30
10
NO
USMC
9
18
7
NO
ZSMC
21
21
6(CC),9(CE)
YES
Converter
No:of active device
No:of diodes
Isolated driver potentials
Simultaneous buckboost capability
MC
18
18
6(CC),9(CE)
NO
IMC
18
18
8
NO
SMC
15
18
7
NO
VSMC
12
30
10
NO
USMC
9
18
7
NO
ZSMC
21
21
6(CC),9(CE)
YES
Table.1. Comparison of different topologies
An Zsource structure and a matrix converter topology that can provide ac/ac power conversion with both a variable output voltage and a stepchanged frequency is opted.Zsource concept is applied to a singlephase matrix converter to create a new type of converter called a single phase Zsource buckboost MC.
From the observations made we decide to use a safe commutation technique that is very simple to implement as a freewheeling path to provide the freewheeling operation required identical to what is available in other converter topologies. The safecommutation scheme gives a continuous current path in dead time to eliminate voltage spikes on switches without a snubber circuit.
Four bidirectional switches to serve as a singlephase matrix converter and one source bidirectional switch can be selected for the topology discussed.All bidirectional switches selected are common emitter backtoback switch cells.

SIMULATION RESULTS
iiIV. SIMULATION RESULTS
iiIV. SIMULATION RESULTS
Fig.10. Simulation diagram for single phase Zsource buckboost matrix
Simulated waveform of single phase Zsource buckboost MC for boost operation at 25Hz
Fig.11. Simulation diagram for single phase Zsource buckboost matrix converter for boost operation at 25Hz
Fig.11. shows the input voltage whose amplitude was 40V rms,50 Hz which was boosted to 138.4V at a frequency of 25 Hz.The input current was observed to be 3.02A
Simulated waveform of single phase Zsource buckboost MC for boost operation at 50Hz
Fig.12. Simulation diagram for single phase Zsource buckboost matrix converter for boost operation at 50Hz
Fig.12.shows the input voltage whose amplitude was 40V rms,50 Hz and was boosted to 130.5V at a frequency of 50 Hz.The input current was observed to be 2.12A.
Simulated waveform of single phase Zsource buckboost MC for boost operation at 100Hz
Fig.13. Simulation diagram for single phase Zsource buckboost matrix converter for boost operation at 100Hz
Fig.13. shows the input voltage whose amplitude was 40V rms,50 Hz and was boosted to 180.2V at a frequency of 100 Hz.The input current was observed to be 3.519A.
Simulated waveform of single phase Zsource buckboost MC for buck operation at 25 Hz
Fig.14. Simulation diagram for single phase Zsource buckboost matrix converter for buck operation at 25Hz
Fig.14.shows the input voltage whose amplitude was 40V rms,50 Hz and was bucked to 27.18V at a frequency of 25 Hz.The input current was observed to be 0.3105A.
Simulated waveform of single phase Zsource buckboost MC for buck operation at 50 Hz
Fig.15. Simulation diagram for single phase Zsource buckboost matrix converter for buck operation at 50Hz
Fig.15.shows the input voltage whose amplitude was 40V rms,50 Hz and was bucked to 31.14V at a frequency of 50 Hz.The input current was observed to be 0.245A
Simulated waveform of single phase Zsource buckboost MC for buck operation at 100 Hz
Fig.16. Simulation diagram for single phase Zsource buckboost matrix converter for buck operation at 100Hz
Fig.16. shows the input voltage whose amplitude was 40V rms,50 Hz and was bucked to 50.54V at a frequency of 100 Hz.The input current was observed to be 0.413A
Table.2. Output voltage with stepchanged frequency in buck and boost mode
25Hz
50Hz
100Hz
Boost mode
138.4V
130.5V
180.2V
Buck mode
27.8V
31.8V
50.54V
Table.3. Input current with stepchanged frequency in buck and boost mode
25Hz
50Hz
100Hz
Boost mode
3.024A
2.12A
3.51A
Buck mode
0.31A
0.24A
0.41A
Table.4. THD of input current
25Hz
50Hz
100Hz
Boost mode
9.04%
9.70%
12.19%
Buck mode
12.87%
11.23%
11.57%

CONCLUSION
A new singlephase Zsource buckboost MC that can buck and boost the desired output voltage frequency which is stepchanged was studied. The output frequency is either an integer multiple or an integer fraction of the input frequency. A continuous current path by using a commutation strategy is used. The use of this safecommutation strategy is a significant enhancement as it makes it possible to avoid voltage spikes on the switches without the use of a snubber circuit. A steadystate circuit analysis was presented and the operational stages were described. Based on the simulation results, the performance of the existing system were analyzed.

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