Single-Phase AC–AC Converter Based on Quasi-Z-Source Topology


[46104]


Abstract

This paper dealswith a new family of single-phase ac–
ac converters called single-phase quasi-Z-source ac–ac converters.
The proposed converter inherits all the advantages of the traditional
single-phase Z-source ac–ac converter, which can realize
buck–boost, reversing, or maintaining the phase angle. In addition,
the proposed converter has the unique features that the input
voltage and output voltage share the same ground and the operation
is in the continuous current mode. The operating principles
of the proposed converter are described, and a circuit analysis
is provided. In order to verify the performance of the proposed
converter, a laboratory prototype was constructed with a voltage
of 84 Vrms /60 Hz. The simulation and experimental results verified
that the converter has a lower input current total harmonic
distortion and higher input power factor in comparison with the
conventional single-phase Z-source ac–ac converter.

INTRODUCTION

FOR ac–ac power conversion, the most popular topologies
are indirect ac–ac converters with a dc link [1]–[3], matrix
converters [4]–[6], and direct pulsewidth modulation (PWM)
ac–ac converters [7]–[16]. The indirect ac–ac converters and
matrix converters can provide variable output voltage and variable
frequency. However, for applications, where only voltage
regulation is needed, the direct PWM ac–ac converters are used
to perform as ac choppers or power line conditioners with
the following features: the provision of a better power factor
and efficiency, low harmonic current in line, single-stage
conversion, simple topology, ease of control, smaller size, and
lower cost [8], [14]–[16].

CIRCUIT ANALYSIS

Circuit analysis of the proposed single-phase quasi-Z-source
ac–ac converter begins with the following assumptions: 1) all
capacitors and switches are ideal and lossless; 2) the parasitic
resistances of L1 and L2 are the same and equal and denoted
by r and due to the parasitic resistance of LLf is much smaller
than the load impedance, it is neglected in the analysis; 3) the
converter is operating in the continuous conduction mode; and
4) the switching frequency is more than the cutoff frequency
of the output filter and the frequency of the input and output
voltages.
The proposed converter has two operational states in one
switching period, which are denoted as state 1 and state 2, as
shown in Fig. 4(a) and (b), respectively. In state 1, S1 is turned
ON and S2 is turned OFF, as shown in Fig. 4(a). The time interval
in this state is (1−D)T, where D is the equivalent duty ratio of
S2 and T is the switching period.

SIMULATION RESULTS

In order to verify the advantages of the proposed single-phase
quasi-Z-source ac–ac converter, the PSIM simulation is used in
comparison with the conventional single-phase Z-source ac–
ac converter presented in [15]. We selected the simulation parameters
L1 = L2 = 1 mH, C1 = C2 = 6.8 μF, Lf = 1.4 mH,
Cf = 10 μF, and R = 20 Ω. The bidirectional switches were
implemented with two IGBTs connected oppositely. The diode
voltage drop was set to 2 V and the switching frequency was
set to 20 kHz. The input voltage was 84 Vrms/60 Hz. In the
simulation, the parasitic resistances of L1 and L2 were set to
zero (r = 0 Ω). Table II provides a list of the parameters used
in the simulation of the conventional converter in Fig. 1 [15]
and the proposed converter in Fig. 2.

EXPERIMENTAL VERIFICATIONS

We have constructed a laboratory prototype based on
TMS320F2812 DSP to verify the properties described earlier.
The same parameters were used in the prototype as in the simulation.
The input voltage was produced by an ES2000S singlephasemaster
(NF Corporation). The bidirectional switches were
implemented with two FAIRCHILD G60N90D IGBTs connected
oppositely. The input power and input power factor were
measured by the ES2000S; the output power was measured by
a WT210 digital power meter (YOKOGAWA).

CONCLUSION

A kind of quasi-Z-source converter for ac–ac power conversion
has been presented in this paper. The proposed converter
inherits all the advantages of the traditional single-phase
Z-source ac–ac converter, which can realize buck–boost as well
as reversal or maintenance phase angle. In addition, the proposed
single-phase quasi-Z-source ac–ac converter has unique
advantages in that the input voltage and output voltages share the
same ground and the operation of the input current is in CCM.
Comparison of the principles of operation and the simulation
results with those for the conventional single-phase Z-source
ac–ac converter are presented.