Analysis and control of unified active power filter
Date
2017-11-06
Authors
Muthu, Subramanian
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Abstract
The combined series and shunt active filters have been proposed to alleviate the power
quality problems at the demand-side power systems. They provide compensation for
load reactive power, load harmonics, unbalanced loads, utility harmonics, utility disturbances
and utility imbalance. However, the conventional approach for the control
of the combined active filter systems have resulted in large operating capacity of the
shunt active filter because reactive power compensation involves only the shunt active
filter. Furthermore, the harmonic mitigation problems are handled mainly by indirect
harmonic compensation schemes rather than direct harmonic isolation schemes.
This thesis presents the analysis and control of Unified Active Power Filter(UAPF)
and proposes a novel concept of load reactive power compensation involving both the
series active filter and the shunt active filter. This new control strategy of the combined
active filter is to achieve the reduction in KVA rating of the shunt active filter
and the optimal operation with increased efficiency. The thesis also applies discretetime
sliding-mode control technique to enhance the performance of the combined
active filter system in terms of fast dynamic response and effective solution to harmonic
mitigation problems. The thesis also presents simulation and experimental
results to provide verification of the proposed UAPF concept.
In this thesis, the involvement of series active filter for reactive power compensation
is achieved by controlling the phase difference between the load voltage and
the utility voltage. The complete steady-state operating characteristics of UAPF are
analyzed with the identification of the different operating modes of UAPF and the
analysis of active and reactive power handled by the active filter components. The
results of the analysis are shown to provide an insight about the load reactive power
compensation by the series and shunt active filter. The reduction in ratings of the
shunt active filter is demonstrated by an apparent power analysis of active filter components.
The results of the analysis are also useful to design and select the optimal
operating point for UAPF.
The performance of UAPF to meet the stringent power quality standards are
realized by applying discrete-time sliding-mode control schemes for the load voltage regulation and the active power factor correction. Various voltage and current control
techniques used for three-phase voltage-source inverters are surveyed to identify the
discrete-time sliding mode control technique as the suitable one. A generalized design
procedure is derived for the control of power converter systems and the control scheme
is extended to the load voltage control of shunt active filter and the line current control
of series active filter. The control algorithms are developed to track a given load
voltage and line current reference signals respectively. The effect of computational
delay in DSP implementation is studied extensively and the control law is designed
with the consideration for the computational delay. The systematic approach for the
design of DC link voltage regulation is also presented in this thesis.
A prototype experimental setup including the power circuit for UAPF and DSP
based control circuit is built to implement the control and to verify the performance
characteristics of UAPF. A real-time control algorithm is developed and is implemented
on a DSP TMS320C40 system with PWM implementation by DMA without
the intervention of CPU.
The steady-state operating characteristics of UAPF is investigated by experiments.
The operation of UAPF at the optimal operating point is shown to reduce the
ratings of the shunt active filter and to improve the efficiency. The steady-state operation
and the dynamic response of discrete-time sliding mode load voltage control
and utility line current control are examined by simulation and experiments. The
invariance property and the robustness property of the discrete-time sliding mode
control are also demonstrated by the experimental results. With the discrete-time
sliding mode control, the compensation characteristics of UAPF are shown to meet
the stringent power quality standards.
Description
Keywords
Electric filters