Power Electronics and Energy Systems
Core concepts
Understand rectification (half-wave, full-wave, bridge), smoothing, and ripple. Know switching converters-buck, boost, buck-boost-and their duty-cycle relationships, plus linear regulator trade-offs (efficiency versus noise). Study power semiconductor devices: diodes, thyristors, MOSFETs and IGBTs, including switching losses and thermal management. Candidates should understand transformers, three-phase systems, power factor, and the difference between real, reactive and apparent power. Battery technologies, charge and discharge characteristics, and renewable sources such as photovoltaic panels and inverters are relevant. Safety earthing, isolation and protection devices complete the picture.
Traps
A common mistake is applying the buck duty-cycle formula to a boost converter. Remember buck: V_out = D × V_in; boost: V_out = V_in/(1 − D). Another trap is confusing power factor with efficiency. Questions may ask about ripple frequency-full-wave rectified ripple is twice the supply frequency. Watch thermal calculations: junction temperature depends on power dissipation and thermal resistance. Do not assume a linear regulator is efficient at large voltage drops.
Worked example
A boost converter with 12 V input and duty cycle 0.5 gives V_out = 12/(1 − 0.5) = 24 V (ideal). Rule of thumb: in any converter, duty cycle between 0 and 1 sets the ideal ratio; real losses reduce output, so always check device ratings and thermal margins.