Experimental Verification of Isolated DC-AC Converterwith Matrix Converter using Pulse Density Modulation Method
Ryo Oshima*

Hiroki Takahashi*

Jun-ichi Itoh**Nagaoka University of Technology
Abstract:- This paper verifies an isolated DC-AC power converter using a single phase to three phase matrix converter inexperiments. The matrix converter does not require large reactors and large smoothing capacitors in the DC-link part. Furthermore,
the proposed control method enables zero voltage switching (ZVS) by implementing the phase shift control on the inverter andthe pulse density modulation (PDM) on the matrix converter. In this paper, the fundamental operation of the converter isconfirmed by experimental results. From the experimental results, the total harmonic distortion (THD) of the output voltage is
7.53%.
Keywords : DC-AC converter, Matrix converter, Pulse density modulation, Zero voltage switching1.

Introduction

Recently, battery energy storage systems actively have spreadand need a DC-AC converter for connecting the grid and battery.
Such converters need to be isolated by a transformer in order toprotect from failure and noises. However, the transformer ofcommercial frequency is large and heavy. In consequence, a highfrequency AC link converter has been researched for down-sizing
the transformer [1]-[2].
The authors have proposed an isolated DC-AC converter which
adopts the matrix converter using the pulse density modulation inorder to improve the efficiency [3]. This proposed circuit achieves
ZVS by using the pulse density modulation.
This paper provides the fundamental operation of the proposed
circuit with no load experiment under the condition of the input
DC voltage of 200 V and AC link frequency of 50 kHz. From theresults, it is confirmed that the output voltage THD is obtained to
7.53% and ZVS can be achieved on the matrix converter at thesecondary side of the transformer.

2.

Fig.1. DC-AC converter with the matrix converter.

Fig.2. Control block diagram of the inverter.

Circuit configuration

Fig. 1 shows the main circuit configuration of the proposed
DC-AC converter with the matrix converter using the pulse
density modulation method. This circuit is divided into a fullbridge inverter by a phase shift control at the primary side of thetransformer and the matrix converter at the secondary side.
The proposed system achieves high efficiency because thenumber of power conversion at secondary side of the transformer
is once only due to the direct AC-AC conversion. In addition, thematrix converter promises to achieve long lifetime and to reducethe volume of the DC-AC converter because the bulky DC-link
capacitors and an initial charge circuit are not required. However,
it is difficult to reduce the switching loss when the pulse widthmodulation (PDM) is applied to the matrix converter.
Therefore, in the proposed system, the zero voltage periods aregenerated by the primary inverter with phase-shift control in orderto achieve ZVS in the matrix converter. Then, the output voltageof the matrix converter is generated by PDM at the zero voltage
period.

Fig.3. Control block diagram of the matrix converter.

3. Control Strategies
3.1 Phase shift control
Fig. 2 shows a control block
diagram of the phase shift control for the inverter. The inverter
outputs 3-level voltage which includes zero voltage by the phaseshift control. Therefore, the matrix converter achieves ZVS whenthe matrix converter turns at the zero voltage period provided bythe inverter.
3.2 Pulse density modulation method based on space
vector modulation [4]Fig. 3 and Fig. 4 shows a control
block diagram and the operation waveforms of the pulse density
modulation which enables ZVS of the matrix converter. The PDM
1controls the density and the pole of the constant width pulse, andthen these pulse signals are used as the minimum unit of theoutput voltage waveform. The input voltage of the matrix
converter consists of the high frequency square waveform because
the inverter outputs square waveform to the matrix converter withthe phase shift control. Therefore, a half cycle of the input voltage
is used as 1 pulse of the PDM. Then, in order to yield the gate
signals by the PDM, the control block diagram includes a D typeflip-flop to quantize the duty references generated by a space
vector modulation (SVM). The clock (CLK) to drive the D typeflip-flop is synchronized with the zero voltage period owing to thephase shift control. As a result, the PDM and the ZVS of thematrix converter are implemented.

4.

Fig.4. Operation principle of the pulse density modulation
for the matrix converter.
Table 1. Experimental conditions.

Experimental Results

Table 1 shows the experimental conditions. The experiments ofthe proposed system are implemented in order to confirm thefundamental operation and the ZVS.
Fig. 5 shows the input and output waveforms of the matrix
converter. It should be noted that the cut-off frequency of the low
pass filter for the output voltage is 1 kHz. The filtered output
voltage is sinusoidal and the output voltage THD is obtained to7.53%. Therefore, the proposed system can be connected to thegrid if the interconnection inductors are set to several percent of
the rated power capacity.
Fig. 6 shows the enlarged waveform of Fig. 5. From thesecondary voltage waveform of the transformer, the 50-kHz and3-level voltage which has the zero voltage periods is confirmed. Inaddition, the output voltage waveform consists of the secondary
voltage pluses of the transformer and the density of the pulses arecontrolled by the PDM. Thus, the PDM of the matrix converter isconfirmed.
Fig. 7 shows the ZVS operation of the matrix converter in theproposed system. From the results, when the secondary voltage ofthe transformer is in a zero voltage period, the switching of thematrix converter is implemented and the ZVS is achieved.

5.

Fig.5. Experimental waveforms of the secondary voltage of thetransformer and output voltage of the DC-AC converter with no load.

Conclusion

This paper verifies an isolated DC-AC converter using a matrix
converter experimentally. The matrix converter in the proposedsystem is applied the PDM and achieves ZVS by combination
with the high frequency inverter with the phase shift control. Fromthe experimental results, the ZVS operation and the PDM of thematrix converter are confirmed in the experiment with no load.
Moreover, the output voltage THD of 7.53% is obtained.
Therefore, the validity of the proposed system is confirmed.
In the future work, the load characteristics, efficiency andperformance of the proposed circuit will be evaluated inexperiments.

Fig.6. Enlarged waveforms of Fig.5

References
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[2]

[3]

[4]

K. Inagaki, T. Furuhashi, A. Ishiguro, M. Ishida, S. Okuma, Y. Uchikawa :“A Waveform Control Mehod of AC to DC converters with High-Frequency
Links”, IEEJ Trans. D,Vol.110, No.5, pp.525-533 (1990)
K. Inagaki, S. Okuma : “A High Frequency Link DC/AC Converter using aThree Phase Output PWM Controlled Cycloconverter”, IEEJ Trans.
D,Vol.112, No.6, pp.545-552 (1992)
R. Oshima, H. Takahashi, G.T.Chiang, J. Itoh: "Basic Study of 6-kW
isolated DC to AC Matrix Converter using Pulse Density Modulation
method", IEEJ JIASC, No. 1-24 (2013)
Y. Nakata, J. Itoh : “Pulse Density Modulation Control using Space VectorModulation for a Single-phase to Three-phase Indirect Matrix Converter”,
IEEE ECCE 2012, Raleigh, P3905, pp. 1753-1759 (2012)

Fig.7. Experimental waveforms when the gate signals are turnedin the zero voltage period.

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