Methods of inverter voltage control by superimposed chopping

Claim 2

In a variable speed polyphase a-c motor drive: a primary speed control means comprising an adjustable frequency polyphase inverter having the inverter output coupled to the motor; and, means for time ratio controlling the output power of individual phases of said inverter in response to a command signal that additionally controls the fundamental output frequency thereof, said controlling being applied individually to said phases sequentially in 60 electrical degree intervals.

Claim 3

In a three-phase series inverter having two main power switching means per phase, the combination of: means for alternately rendering the switching means of each phase conductive in a permutated sequence wherein during successive 60 electrical degree intervals switching means of two phases are connected to a source of electrical potential of one polarity and a switching means of the remaining phase is connected to a source of electrical potential of the other polarity; and means for time ratio control switching only the switching means of said remaining phase during said intervals to control the average power delivered.

Claim 4

In a three-phase series inverter having two main power switching means per phase, the combination of: means for alternately rendering the switching means of each phase conductive in a permutated sequence wherein during successive 60 electrical degree intervals switching means of two phases are connected to a source of electrical potential of one polarity and a switching means of the remaining phase is connected to a source of electrical potential of the other polarity; and means for time ratio control switching only the switching means of said remaining phase during said intervals to control the average power delivered.

Claim 5

The inverter of claim 2 wherein the frequency of operation of said permutated sequence is variable to provide adjustable frequency polyphase power.

Claim 6

The inventer of claim 3 including means for sensing the average voltage supplied by said inverter and means responsive to said sensing means to provide time ratio control adapted to maintain the ratio of average voltage to frequency of operation substantially constant.

Claim 7

A conversion circuit for conducting electrical power between a power supply and a load, with the power supply having at least first and second sources of potential; three output phases for said conversion circuit with the amount of power conducted by said conversion circuit being controlled by time ratio controlled switching of the phase-to-phase voltage of the load, comprising in combination: a. means including electrical switching means for carrying load current for each of said three phases of said conversion circuit, and means for connecting said switching means between the power supply and the load; b. first control means operatively connected to said switching means for causing said switching means of one of said phases normally to connect said phase to one of the sources of potential during a selected period of time, said first control means simultaneously causing said switching means of both the other two phases normally to be connected to another of the sources of potential during the selected period of time; and c. second control means operatively connected to said switching means of said one phase to cause said switching means to time ratio control switch the voltage of said one phase during the aforesaid selected period of time, said second control means causing said switching means of each of the other phases to time ratio control switch the voltage of these phases during selected periods of time when each of these phases is normally connected to one of the sources of potential while the other two phases are both connected to another of the sources of potential.

Claim 8

A conversion circuit for conducting electrical power between a power supply and a load, with the power supply having at least first and second sources of potential; three output phases for said conversion circuit with the amount of power conducted by said conversion circuit being controlled by time ratio controlled switching of the phase-to-phase voltage of the load, comprising in combination: a. means including electrical switching means for carrying load current for each of said three phases of said conversion circuit, and means for connecting said switching means between the power supply and the load; b. first control means operatively connected to said switching means for causing said switching means of one of said phases normally to connect said phase to one of the sources of potential during a selected period of time, said first control means simultaneously causing said switching means of both the other two phases normally to be connected to another of the sources of potential during the selected period of time; and c. second control means operatively connected to said switching means of said one phase to cause said switching means to time ratio control switch the voltage of said one phase during the aforesaid selected period of time, said second control means causing said switching means of each of the other phases to time ratio control switch the voltage of these phases during selected periods of time when each of these phases is normally connected to one of the sources of potential while the other two phases are both connected to another of the sources of potential.

Claim 9

An a-c adjustable speed electric motor drive comprising: a source of unidirectional electric power; static power conversion means including a plurality of selectively conductive switches for converting said unidirectional electric power to polyphase electric power having a controllably variable fundamental frequency, said switches including positive and negative switches for each output phase; a polyphase a-c motor coupled to the output of said conversion means and energized thereby; and means for controlling the power supplied by said conversion means including means effective during sequential 60 electrical degree intervals to connect one switch only to one polarity of said source and all of the opposite polarity switches of the other phases to the other polarity of said source, said one switch only being time ratio controlled switched during such intervals to control all of the phase-to-phase voltages.

Claim 10

An a-c adjustable speed electric motor drive comprising: a source of unidirectional electric power; static power conversion means including a plurality of selectively conductive switches for converting said unidirectional electric power to polyphase electric power having a controllably variable fundamental frequency, said switches including positive and negative switches for each output phase; a polyphase a-c motor coupled to the output of said conversion means and energized thereby; and means for controlling the power supplied by said conversion means including means effective during sequential 60 electrical degree intervals to connect one switch only to one polarity of said source and all of the opposite polarity switches of the other phases to the other polarity of said source, said one switch only being time ratio controlled switched during such intervals to control all of the phase-to-phase voltages.

Claim 11

The drive of claim 6 wherein said time ratio controlled switching provides a substantially constant available voltage per cycle of polyphase power applied to said motor.