Abstract
This article presents the converter circuit analysis, mathematical modeling followed by deriving its average state space equations. The model so obtained is simulated in MATLAB in open loop and closed loop configuration and changes in the output are observed. Specifically, Buck & Boost converters with & without its controller at steady state and study of their transient responses to the changing inputs with a controller design and its implementation on SIMULINK model is presented here. The method used to control the output of the converter is Proportional and Integral error correction that is a PI controller which is used to reduce errors and stabilize the variable input fed to the Buck or Boost converters. The tool used to design the controller parameters is PID Tuner application in in MATLAB. The analyses plots derived using the tool lets us examine the controller performance in time and frequency domain. The advantage of the tool used is, it allows user to interactively refine the performance of the controller to adjust loop bandwidth and phase margin or to favor a set-point tracking or disturbance rejection. The designed converters are analyzed in current mode control and voltage mode control to switch on/off. The long term goal is to have a sophisticated controller design for buck & boost converters for the application where variable input is fed to them, so as to allow its simulation to fully understand how the converters behave when controller is implemented. The model tested here are of the similar nature that are being used in standalone solar or wind energy generation & distribution systems. The variable nature of the input tested here with Buck & Boost converters reflects the variable nature of the output of the renewable energy sources and that broaden the scope of these converters to be implanted with such standalone energy systems
Highlights
The voltage-mode controlled regulator, the PWM signal is generated by applying a control voltage to one comparator input and a saw-tooth voltage of fixed frequency, generated by the clock, to the other
Results for Buck Converter in Closed loop with variable input are given in figure 19
When the figure is compared with figure 18, it can be concluded that with the variable input voltage supply, the resulting output voltage remains constant
Summary
The voltage-mode controlled regulator, the PWM signal is generated by applying a control voltage to one comparator input and a saw-tooth voltage of fixed frequency, generated by the clock, to the other. PI controller is used here to reduce the errors These DC-to-DC power converters steps up/down the voltage (while stepping down/up the current) from its input (supply) to its output (load). A simplified circuit diagram is shown in figure below In this type of control the peak of the output filter inductor current is controlled to a set point value. The output of the controller is the new value of the duty cycle which is used as an input to the power stage and modulates the switching devices so as to close the control loop and provide a regulated and stable output voltage. Figure shows the schematic of the boost converter with current-mode control: Energy equations during ON condition: EIN = VIN tON Energy equations during OFF condition: EOUT = (VOUT-VIN)tOFF a) Voltage control mode. Voltage-mode control which is called as the duty-cycle control contains a single loop and adjusts the duty cycle directly in response to changes in output voltage
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