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UC3854A-based PFC control simulation of bifurcation

In Electronic Infomation Category: U | on April 26,2011

Abstract: To better understand the UC3854A control of PFC converter based on the dynamic characteristics of system parameters on the bifurcation phenomena in the converter, Boost PFC Converter in the establishment of two-loop mathematical model based on the use of Matlab software converter slow time scale such as bifurcation and TDA7264 datasheet and chaos instability is simulated. PFC converter in the slow time scale bifurcation in the simulation, based on the analysis of system parameters on the bifurcation point of impact, and TDA7264 price and simulation verification. The simulation results clearly show the amplitude of the input rectifier voltage change on the point of bifurcation.

Recent years, the power factor correction technology has been in power in power electronic circuits is widely used, switching power supply Power Factor Correction (Power Factor Correction, PFC) technology as used to suppress harmonic pollution and TDA7264 suppliers and reduce the effective electromagnetic pollution means of power electronics technology is becoming the focus of the study.

Present, based on the UC3854A control of PFC converters has been widely used, has been shown that this converter can exhibit rich dynamic behavior, including bifurcation and chaos. Once the system into the bifurcation, there will be serious harmonic distortion, power factor correction to achieve the purpose can not. Therefore, the bifurcation of converter parameters on the point of impact on the stability of the system is necessary. In this paper, the UC3854A chip as the core of the Boost PFC converter is simulated and analyzed the bifurcation point of the converter (ie, into period-2 state) factors. This will increase understanding of the dynamics in the PFC converter has some help, but also for the design of converter provides a theoretical guidance.

1 PFC converter modeling

Figure 1 shows the average based UC3854A Boost PFC converter current control schematic work.


Figure 1 Average Current Controlled Boost PFC converter principle diagram

In Boost PFC converter circuit, the rectified input voltage vg (t) = Vin | sin (lt) | is a periodic time-varying voltage, cycle, half of the input AC voltage, for Tl = / l, the effective value.

According to Figure 1, the control circuit of the mathematical model can be described as follows:

1) voltage controller output voltage dynamic equation


Where


2) Vff feedforward filter output voltage equation of state


3) in the current command signal multiplication Lu


Minus 1.5 is a chip design requirements, and when Vvea 1.5, the multiplier output iref = 0, the rectifier input current iL tracking function, so that iL in the saturated limit 0 A, the system is saturation.

4) current controller feedback loop capacitor Cp, Cz voltage equation of state


5) current controller output voltage


Vcea compared with the sawtooth signal to generate PWM control signal, the control of Boost PFC converter, sawtooth signal


which VL and VU are the minimum potential and maximum sawtooth potential signal, Ts is the carrier cycle, when vcea> vramp, the switch Q turns on, or off.

2 PFC converter simulation analysis

According to formula (1) to (7), have Boost PFC Converter Matlab simulation model shown in Figure 2. Take Vin = 100V, Tl = 0.02 s, Ts = 0.00001 s, Vref = 3 V, L = 1 mH, Rs = 0.22, other control parameters can refer to the UC3854A technical indicators. By changing the output capacitor C0 and the size of the load resistor RL, Boost PFC converter can be run in different states of the phase diagram and the bifurcation diagram.


Figure 2 based on average current control simulation model of Boost PFC converter

1) When RL = 550, C0 = 400 F, the voltage loop output voltage and output voltage V0 vvea phase diagram shown in Figure 3 (a) shows, the system steady state in period 1, this time has been great vvea at 1.5 V, the system does not run into saturation boundary.

2) when RL = 1 200 , C0 = 100 F, the system is still running in period 2, but vvea in some time less than 1.5 V, from the literature analysis, then the multiplier output iref = 0 A, resulting rectifier input current iL period of time in a saturated boundary 0 A, the final system will be saturated and unsaturated constantly switch between, so Figure 3 (b) shows the phase diagram is no longer an ellipse.

3) When RL = 4000 , C0 = 65F, by Figure 3 (c) shows the same part of the time vvea of ??less than 1.5 V, the system in the saturated and unsaturated constantly switch between the phase diagram vvea and V0 in the dense orbit, but do not coincide, the system running in a chaotic state.

Figure 3 (d) the time when C0 = 100 F, the load resistance RL as a bifurcation parameter bifurcation diagram obtained by simulation, from which the system state can be observed clearly with the parameters from cycle 1 to cycle 2, cycle 4, ... ..., chaotic process, bifurcation from the normal operation of the system whether or not the border. Therefore, bifurcation analysis of factors affect the system operating state of the system is very necessary.


Figure 3 PFC Converter vvea and V0 state phase diagram and bifurcation diagram of the load resistor RL

3 factors affect the system bifurcation

From the previous simulation results in Figure 3 can be seen that the reduction of C0 with the output capacitor and load resistance RL increases, the voltage loop output vvea part time in less than 1.5 V, resulting in the system between the saturated and unsaturated constantly switch into a segment of the nonlinear system. The saturation causes bifurcation, chaos and other traditional non-linear phenomena, allowing the system to become unstable.

Bifurcations do not occur, however the system because the system ran into saturation boundary. Figure 3 (d) of the bifurcation diagram shown in the vicinity of RL = 350, the system from the period 1 to period 2, the occurrence of bifurcation. This bifurcation is the traditional bifurcation is not met by the system caused by saturation boundary, such as taking RL = 400 , C0 = 100F when the simulation was vvea and V0 of the phase diagram shown in Figure 4, two elliptic phase diagram, the system runs in cycle 2 though, but vvea has been greater than 1.5 V, the system does not meet saturation boundary. Therefore, the analysis of bifurcations of the system, the need is met according to the system are two saturation boundaries were analyzed.


Figure 4, the system does not touch the saturation boundary bifurcation occurs when the vvea and V0 of the phase diagram

1) the voltage loop output voltage is less than 1.5 V based on UC3854A vvea chip design features, when the voltage loop output voltage Vvea less than 1.5 V, the system encountered the saturation boundary, runtime

Between the saturated and unsaturated constantly switching, which in the saturated and unsaturated constantly switching between the bifurcation will cause the system to occur. Factors that affect the vvea less than 1.5 may also affect the production of bifurcation, the detailed analysis of these factors, see the literature.

From Figure 3 (d) bifurcation diagram and Figure 4 vvea state phase diagram and V0 can be seen, the voltage loop output voltage vvea the value of the Hengda at 1.5 V, the system does not meet Saturation boundary bifurcation can also occur under the circumstances. This shows that the PFC converter, the system produces only the bifurcation of factors to consider factors that affect the vvea less than 1.5 are not sufficient, the need for other factors were analyzed. Vvea below only less than 1.5 but did not affect the impact of system to produce bifurcation analysis of the factors.

2) is greater than the voltage loop output voltage vvea The simulation results show that 1.5 V, PFC converter period-doubling bifurcation occurs PFC converter with input voltage amplitude Vm change. Figure 5 (a) shows take Vin = 80 V, other parameters unchanged and Figure 3 (d) under the same circumstances, in order to load resistor RL is the bifurcation parameter bifurcation diagram obtained by simulation, we can see, the input voltage amplitude decrease the value of Vin, the system from the period 1 to period 2 bifurcation point into the RL = 350 RL = 600 nearby.

Figure 5 (b) other parameters remain unchanged for the system, take C0 = 100F, RL = 350 , the amplitude of the input voltage Vin as the bifurcation parameter bifurcation diagram obtained by simulation, with the increase of Vin , the system bifurcation occurred. Shows the amplitude of the input rectified voltage of the system have significant effect on bifurcation.


Figure 5, the input voltage amplitude bifurcations of the system

4 Conclusion

Based on the core composition of the UC3854A Boost PFC converter simulation, the system is running in different states and the bifurcation diagram of state of the phase diagram, the simulation results show that the converter output voltage for the voltage loop is not saturation boundary conditions encountered, the system will enter the bifurcation state. By analyzing the factors that affect the availability of bifurcation, in addition to the factors that affect the system into saturation, the change in the amplitude of the input rectified voltage of the system have significant effect on bifurcation. Because the conditions are limited, this is analyzed from the simulation and experiment is not from the hardware to verify the system, so the parameters on the system into the bifurcation phenomena to be further verify the analysis.

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