In power electronic devices to CVCF pure sine wave inverter s the core of UPS has been widely applied, its output waveform major
technical requirements include low steady-state total harmonic distortion (THD)
and fast dynamic response, since non-linear load, PWM modulation process dead
and inverter system itself weakly damped and other factors, using the general
closed-loop PWM control is not ideal. In this paper, the United States produced
by TI TMS320F240DSP for the control chip, using repetitive control system to
improve steady-state performance with the introduction of integral control pole
configuration to improve the dynamic characteristics of the system, the
experimental results show that the scheme can simultaneously achieve high
quality of homeostasis and dynamic characteristics.
Repeat controller design
The basic idea of repetitive control from control theory internal model principle,
that if you want the control system of a reference instruction to achieve no
static error tracking, then the instruction that generated the reference model
must be included in the stable closed-loop control system internally. First,
the system uses the figure of repetitive control block diagram, the following
analysis and explanation of its various parts.
P (z) is the dc to ac power inverter input and output of
the discrete transfer function, is the system control object. Inverter
switching frequency than the natural frequency of the LC filter is much higher,
the dynamic characteristics determined primarily by the LC filter, obtained by
establishing state equation P (z). In this system, L = 0.88mH, C = 60μF,
inductor series resistance of 0.4Ω, the switching frequency and the sampling frequency
is 10KHz, deduced discrete transfer function is:
Notch filter S1 (z) is mainly used for
cancellation of the inverter resonant peak, a second order filter S2 (z) mainly
provides high frequency attenuation. Zk links lead compensation filter S (z)
and the control target P (z) the total phase lag, Kr is a duplicate control
gain. Compensator C (z) to achieve the purpose of the object to the corrected
low frequency gain close to 1, as soon as the high frequency gain is reduced
to-26dB or less, and the system in the low frequency band prior to the passage
of the total phase shift as small as possible. Take Kr = 0.9, zk = z5, to C (z)
P (z) Bode diagram
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