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Energy saving by Voltage Optimisation – reduce carbon emissions and electricity bill by using PWM technology
13 April 2011
There are several voltage optimisation products in the market but most of them are based on obsolete technologies like automatic tap switching transformer, electro-mechanical stabilisers etc.
In the UK the electricity supply is 230V +10% /-6% (216V – 253V) and the average voltage is usually 240V. Most of the electrical equipment is designed to work in 220V.
If there is a 10% increase in the supply voltage, there will be 15% to 20% more power consumption in the equipment.
This will generate heat resulting in energy loss, CO2 emission, and will substantially reduce the life of the equipment.
The latest technology in voltage optimisation is IGBT based PWM type Static Voltage Regulators / Static Voltage Stabilizers. This is an SMPS type voltage stabiliser for mains voltage where PWM is made directly in AC-to-AC switching, without any harmonic distortion.
In this topology there is no need to convert the AC input to DC and again convert it back to regulated AC output.
This simplifies the design, reduces the component count and improves the efficiency and reliability. The power stage is an IGBT chopper control.
The chopping frequency is around 20KHz which ensures absolute silent operation and pure sine wave output.
In the block diagram (top), the DSP based control circuit will give the PWM drive to the IGBT by sensing the AC output voltage.
If the AC output voltage is more, the DSP will reduce the duty cycle of the PWM and if the AC output voltage is less, the DSP will increase the duty cycle of the PWM. When the input is above 220V, the output is maintained at 220V constant, +/-1%.
When the input is below 220V the PWM duty cycle will be 100% so the output voltage is same as input.
The second and third images show PWM and output WAVEFORMs (Black = PWM, Red = Output waveform). The figures show the PWM and the output waveforms. Note that the PWM frequency is not to scale.
The actual PWM will be much denser. When the PWM duty cycle decreases, the AC output will decrease and when the PWM duty cycle increases the AC output will increase.
In the IGBT chopper, the IGBTs are connected in anti-series mode so it can switch in both directions. In this way AC to AC PWM is possible. During turn-off, another set of IGBTs will be turned on for freewheeling. So the fly-back energy will go back to the load.
Because the PWM frequency is 20KHz, a small amorphous or ferrite core inductor and a small filter capacitor are sufficient to integrate the chopped waveform to a pure sine wave.
There is no need for a transformer. Hence the stabiliser will be compact and light weight.
The same can be used for three phase balancing and save further energy.
Interleaved switching in this topology can be used for mega-watts application. By cascading the switches, this topology can be used for buck and boost operation.
P.A. Martin Xavier
Hardware designer and Managing Partner
MEDI Electronics
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