Surge current suppression in power-factor-corrected AC-to-DC converter with capacitive load
A power supply for a capacitive-resistive load includes plural paralleled phase correcting modules together with current sharing controllers for tending to equalize their currents. Each module is provided with a diode, poled to prevent forward current from flowing in the return current path, for aiding in equalizing module currents. Surge currents are reduced by a single saturable reactor coupled to the combined outputs of current sharing controllers, thereby avoiding the need for soft-start in each controller. A precharging path extends from a source of pulsating direct voltage to the load, for precharging the load capacitance at turn-on.
1. An electrical apparatus for powering a load including a resistive and a capacitive component, said electrical apparatus comprising:
a source of pulsating direct voltage;
a first plurality of power factor correction units coupled to said source of pulsating direct voltage, each for converting said pulsating direct voltage into a direct voltage at an output port and for tending to maintain the current through said source of pulsating direct voltage in-phase with said pulsating direct voltage;
a plurality equal to said first plurality of current sharing controllers, each of which includes a port coupled to said output port of one of said power factor correction units, and each of which also includes an output port in common with all output ports of said current sharing controllers, said current sharing controllers being subject to a surge current when said direct voltage of the associated one of said power factor correction units is coupled to said capacitive component of said load at turn-on; and
a saturable reactor coupled between said common output port of said current sharing controllers and said load.
2. An apparatus according to claim 1 , wherein said power factor correction units are boost power factor correction converters.
3. An apparatus according to claim 1 , further comprising a plurality, equal to said first plurality, of ground current equalizing impedances coupled between a common reference terminal and a current return port of each of said power factor correction units.
4. An apparatus according to claim 3 , wherein said ground current equalizing impedances comprise unidirectional current conducting means poled to prevent the flow of forward current from the return current terminal of the associated one of said power factor correction units.
5. An apparatus according to claim 1 , further comprising a controllable path coupled to said source of pulsating direct voltage and to said load, for tending to charge said capacitive component of said load at turn-on, said controllable path ceasing said charge after turn-on.
6. An apparatus according to claim 5 , wherein said controllable path includes a controllable switch.
7. An apparatus according to claim 6 , wherein said controllable switch includes a unidirectional current conducting device which conducts when pulsating direct voltage is greater than the voltage on said capacitive component and which ceases conduction when said pulsating direct voltage is less than said voltage on said capacitive component.
8. An apparatus according to claim 7 , wherein said power factor correction units are voltage-boosting units which produce a direct voltage greater than the peak value of said pulsating direct voltage.