Three phase charge pump brigde rectifier

This circuit represents a three phase motor/generator whose output is rectified and 'boosted'. This setup sometimes called a 'voltage doubler' but in this case the voltage isn't doubled as there is significant voltage drop across the diodes of the rectifier. It is very clear, however that the voltage (with reference to ground) of the first rectifier output is significantly boosted. This setup includes just two rectifiers but more rectifiers can be added in the same configuration to boost the voltage even further but costing more energy dissipation across the diodes. A (theoretical) application may be in microwind turbines where some generators require considerbly high RPM to produce a usable voltage. This setup allows the turbine to rotate at lower RPM so that a turbine can work more safely. Higher voltages through a fixed load produce higher current and therefore a higher back EMF which slows the turbine down. A wind turbine therefore regulates it's own RPM as long as a load is attached and a current can flow. Open contacts would rapidly produce too high RPM which could in turn damage the turbine. Increasing the output voltage at a constant RPM could be done by rewinding the generator or through this circuit which would allow larger blades to be fitted to the turbine to produce more torque at lower RPM. As stated before, There is a voltage drop accross the diodes of the bridge rectifier causing power dissipation to occur. If the RPM of the turbine drops too low, the open contact voltage will also drop low enough so that the voltage drop accross the diodes nullify the voltage gain through the circuit. Notice that, when the load infcreases (the resistance through the load drops) the effect will cease. This turning point also depends on the back EMF which in turn is determined by the winding resistance in the generator. Rewinding the generator to produce equal voltage at lower RPM (or higher voltage at equal RPM) would inevitably also cause the winding resistance to increase. To use the output usefully a charge controller would be required to trickle current into a battery. The current could also by pumped into a battery directly so that the battery voltage will determine the RPM of the turbine. Notice that to increase the usefull load one must also use larger capacitors. Play around with the generator output (higher frequencies equal higher open contact voltage in the real world). Real world application would also require control circuitry that dumps excess load into a dummy load (e.g. heating element). Do not use this circuit in the real world if no dump load is attached since it could cause runnaway of the rubine and potentially catastrophic failure!!! As the load increases the central capacitors may reverse polarity considerably. If using polarized capacitors (chances are you would in these power applications). an extra, forward biased diode may reduce the ammount of reverse voltage (one less voltage drop to overcome...) This approach, however does not guararantee a good output.

published 4 years ago