Electrical – How to regulate PWM to control a boost converter

boostduty cyclepwm

I am creating a simple boost converter following the classic circuit diagram just for learning purpose.

The switch is a power transistor controlled by PWM output of an Arduino (with additional necessary components). I want to implement a feedback mechanism to control or regulate the output voltage. I am a novice, but I know how to use a voltage divider to read the output voltage as an analog input to Arduino. What I am not very sure is – what to increase or decrease based on the input. For example if I need to increase the output voltage to maintain desired output voltage level, should I

  1. Just increase the duty cycle and keep the frequency constant?
  2. Increase duty cycle, and decrease frequency?

I want to achieve higher 'On' time on the switch, but what is the right way to do it?

If only toggling duty cycle is the answer, how does the frequency impact the output parameters? Does it also allow controlling the output voltage (but not the right way)? Or does it determine how much current I allow the output load to draw? Or something else? Please help.enter image description here

Best Answer

Think about what happens. There are two parts to the switching cycle. The first part is when the switch is closed and the input supply voltage is placed across the inductor. This causes the current to ramp positively: -

$$\dfrac{di}{dt} = \dfrac{V}{L}$$

The longer the switch is closed the higher the current becomes. More current means more energy (W) stored in the magnetic field: -

$$W = \dfrac{1}{2}\cdot LI^2$$

When the switch opens that energy is transferred to the load via the diode. If that is done 100,000 times per second then the power to the load is 100,000 x W.

So you can use duty cycle increases to send more power to the load and you modify the duty cycle to regulate the voltage at the load. If you kept duty cycle constant and increased frequency, the "charge time" reduces as frequency increases and, the energy transferred per cycle reduces as a square of the frequency but, because frequency is increasing more packets of reduced energy are delivered per second hence, increasing frequency whilst keeping duty constant will reduce power to the load proportionately.

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