1
Digital-Controlled Single-Phase TransformerBased Inverter for Non-Linear Load
Applications
Abstract:
The paper presents a new digital-controlled single-phase transformer-based inverter for
non-linear load applications. A capacitive full-bridge circuit is added to provide instant
current under non-linear load condition and thereby reducing the harmonics significantly
to meet the required harmonic standard, IEEE 519-1992, even under non-linear load
condition. The redundant capacity, cost, size and weight of line frequency transformer can
therefore be dramatically reduced. Moreover, a new integrated controller for inverter
control is proposed to eliminate both DC current component and steady state error even
under heavy load condition. The proposed integrated controller consists of a Proportional
(P) controller acts as voltage controller, DC offset canceller, an RMS compensator and nonlinear load compensator.
INTRODUCTION:
N recent years, single phase inverter [1]-[3] has been widely used in various
I applications, such as UPS [4]-[9], renewable energy conversion [10]-[15], power source,
etc. The circuit structure [1] of the single-phase inverter can be divided into half-bridge,
full-bridge, and three-level structures. The main function of the inverter is to provide an
AC output voltage with less voltage distortion [3] while meeting the codes of safety and
harmonics (power quality) under both linear and non-linear loads [6], [15]-[18]. The
inverter can be divided into transformer-based and transformer-less types [19], [20] to
fulfill the requirement of safety standards and the field applications [19]-[22]. Although the
transformer-less inverter, without line-frequency transformer installed in front of load for
isolation, provides the merits of compact size, lower cost, less voltage harmonics yielded by
the saturation of line frequency linear loaded converter for power source. A higher
harmonic compensator [33], which is using synchronously rotating frame to eliminate the
same order’s harmonic, is proposed to reduce the total current harmonics from 16.5% to
5% for a three phase power grid.
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Architecture Diagram:
CONCLUSION
The contributions of this paper include:
Proposal of a new transformer-based single-phase inverter which can significantly
1.
reduce the harmonic distortion to meet the related code even under non-linear load
condition
Proposal of a new integrated controller to eliminate the DC component, steady state
2.
error and mitigate the inverter output distortion contributed by non-linear load
Presentation of digital-controlled transformer-based single-phase inverter to
3.
confirm the above-mentioned claims
Experimental results are carried out on a 1.5 kVA and 45-400 Hz single-phase inverter
controlled by digital signal processor (TMS320F2809) to confirm the effectiveness of the
proposed inverter and integrated controller. The results show that the THD of output
voltage can be reduced from 7.95% to 3.82% which meets the requirement of IEEE-519
standard under the same non-linear load conditions. The input peak current of the
transformer is also decreased from 30 A to 20 A. Moreover, both DC current component
and steady state error can be eliminated to confirm the topology and controller.
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