Converter for synchronous motor starting

A converter for starting a three phase synchronous motor from a three phase input power source wherein said motor has a first phase winding, a second phase winding and a third phase winding and further wherein said power source has a first mainline carrying a first phase of said power, a second mainline carrying a second phase of said power, a third mainline carrying a third phase of said power and a neutral line, said converter comprising:

• a star point neutral termination coupling said first phase winding, said second phase winding, and said third phase winding to said neutral line;
• means for rectifying said first phase, said second phase and said third phase of said input power and for summing each of said rectified phase to develop a starting current having a substantial DC component;
• means for applying said starting current sequentially to each of said first phase winding, said second phase winding, and said third phase winding at a continuously increasing frequency so that an angular velocity of said motor synchronously increase with said increasing frequency, said starting current being removed when said angular velocity is synchronous with the constant frequency of said input power.
• said applying means including a plurality of second thyristors, each of said second thyristors having a n anode, a cathode, and a gate, said anode of each of said second thyristors being electrically coupled in common to which said starting current is applied, said cathode of each of said second thyristors being coupled to a respective one of said first phase winding, said second phase winding and said third phase winding;
• means for developing a plurality of second gate control signals, each of said second gate signals being applied to said gate of a respective one of said second thyristors to fire said respective one of said second thyristors, said second gate signals being developed sequentially at said continuously increasing frequency so that each of said second thyristors couples said starting current to said respective one of said first phase winding, said second phase winding, and said third phase winding to increase said angular velocity synchronously with said frequency;
• and
• said developing means including a plurality of filters, each of said filters developing a filtered voltage in response to a respective voltage difference between said first phase windings, said second phase winding and said third phase winding, a plurality of first gates, said filtered voltage of each of said filters being applied to a respective one of said first gates, said first gates developing a gate voltage when said filtered voltage is positive, and a plurality of second gates, each of said second gates having a non-inverting input coupled to a respective one of said first gates for application of said gate voltage thereto and an inverting input coupled to a prior sequential one of said first gates for application of said gate voltage thereto, said second gates each developing one of said gate signals when said gate voltage of said respective one of said first gates is high and said gate voltage of said prior sequential one is low.