Pulse width modulation has been with us for ages but MPPT has gained massive traction over the last few years as engineers attempt to maximise the efficiency of the PV array. There is sufficient proof to warrant a closer examination of these two topologies as there are users for and against PWM and MPPT.
With the PWM or Pulse Width Modulation circuit the designer originally was specifically looking at the lower voltage panel, typically 18V Max. power voltage open circuit. This would be suitable for a 12V battery. PWM circuits are designed for various battery voltages but do not have the ability to allow for smart power conversion, e.g. when there is a low sun the output of the panel is not optimised.
The PWM circuit will pulse on and off according to whether the battery is in bulk, absorption or floating mode. Because PWM designs have been around for ever and are not unduly sophisticated they are the cheaper alternative. Are they really that much worse than MPPT? Maybe not.
MPPT or Max. Power Point Tracking controllers use what is known as smart technology to allow the panel to deliver maximum power transfer at all times of the day. More often than not they are seen used in inverters which have a very high DC PV input, possibly in the order of 500V. MPPT controllers can be very expensive and at one stage because of this the user was scared off. With the Chinese imports this has changed the playing field, one or more charge regulators are built into the inverter. The importance of the MPPT here is that the array is not matched to the charge controller and battery bank – this system utilises the higher voltage to always ensure that the bank has some sort of charge. The PWM, often found in caravans and RVs, running at a lower voltage, requires the panel to be running at near full output to charge the 12V battery.
The first MPPT was designed and built in Australia by Stuart Watkinson, the founder of a company called AERL.
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