11-04-2012, 11:40 AM
CONTROL OF THE ZERO VOLTAGE TRANSITION CONVERTER
introduction
The objective of the control circuit of any power factor correction canverter is to
make the non-linear rectifier look like a simple resistor with respect to the imput mains. If
this is the case then the input current will track the voltage like it does in case of a simple
resistor and the input power factor shall be 1 .O. An active power factor corrector does this
by prograrnrning the input current to follow the instantaneous input rectified mlfage.
ACTIVEPO WERF ACTOCRO RRECTIOCONN TROL CIRCUIT
An active power factor corrector can program the input current to follow the input
voltage using two methods of current mode control:
(i) Peak current mode control:
CONTROLLO OP DESIGN
In the control loop design of the proposed ZVT converter it is assumed that a PFC
controller like UC - 3855A/B is used. Therefore the following results hold tnie for this
controller although the general design approach will be the same.
SMALLSI GNAL MODEL OF THE CONVERTER
The small signal model of the proposed ZVT converter is the same as that of the
basic PFC boost converter as both of the converters operate similarly during most of their
switching cycle. The only difference is during the tum-on and turn-off transitions of the
main switch and this has no bearing on the design of the control loop,
(ii) Average cwrent mode control
COMPENSATIOOFN T HE VOLTAGE LOOP
The design of the voltage loop is given in 1341. The primary function which the
voltage loop has to meet is to keep the input current distortion to a minimum. The
bandwidth of the voltage hop is typically about 15 Hz and for such a low bandwidth
stability is not a problem. The reason for such a low bandwidth is that the output voltage
on DC bus contains a small 2nd harmonic voltage and if this voltage is fed back to the
conclution
In this chapter the control circuit for the proposed ZVT converter was designed
for PFC application. A compensated current error amplifier was designed for the inner
current loop and a compensated voltage error amplifier was designed for the outer voltage
loop. The closed loop performance is judged on the basis of Bode Plots drawn for each
error amplifier. The frnal design satisfies al1 requirements of minimum THD in input
current.
voltage error amplifier it will modulate the output of the amplifier.
introduction
The objective of the control circuit of any power factor correction canverter is to
make the non-linear rectifier look like a simple resistor with respect to the imput mains. If
this is the case then the input current will track the voltage like it does in case of a simple
resistor and the input power factor shall be 1 .O. An active power factor corrector does this
by prograrnrning the input current to follow the instantaneous input rectified mlfage.
ACTIVEPO WERF ACTOCRO RRECTIOCONN TROL CIRCUIT
An active power factor corrector can program the input current to follow the input
voltage using two methods of current mode control:
(i) Peak current mode control:
CONTROLLO OP DESIGN
In the control loop design of the proposed ZVT converter it is assumed that a PFC
controller like UC - 3855A/B is used. Therefore the following results hold tnie for this
controller although the general design approach will be the same.
SMALLSI GNAL MODEL OF THE CONVERTER
The small signal model of the proposed ZVT converter is the same as that of the
basic PFC boost converter as both of the converters operate similarly during most of their
switching cycle. The only difference is during the tum-on and turn-off transitions of the
main switch and this has no bearing on the design of the control loop,
(ii) Average cwrent mode control
COMPENSATIOOFN T HE VOLTAGE LOOP
The design of the voltage loop is given in 1341. The primary function which the
voltage loop has to meet is to keep the input current distortion to a minimum. The
bandwidth of the voltage hop is typically about 15 Hz and for such a low bandwidth
stability is not a problem. The reason for such a low bandwidth is that the output voltage
on DC bus contains a small 2nd harmonic voltage and if this voltage is fed back to the
conclution
In this chapter the control circuit for the proposed ZVT converter was designed
for PFC application. A compensated current error amplifier was designed for the inner
current loop and a compensated voltage error amplifier was designed for the outer voltage
loop. The closed loop performance is judged on the basis of Bode Plots drawn for each
error amplifier. The frnal design satisfies al1 requirements of minimum THD in input
current.
voltage error amplifier it will modulate the output of the amplifier.