Modular high power induction heating and melting system

A system for melting metal and holding molten metal at a selected temperature, comprising:

• a plurality of induction furnaces, each furnace of said plurality of induction furnaces having a maximum power consumption, and each furnace of said plurality of induction furnaces arranged to be supplied with AC electric power from a respective one of a plurality of AC connections;
• a rectifier unit arranged to output a DC electric power to a DC common connection;
• and
• a plurality of inverter units equal in number to said plurality of induction furnaces, each inverter unit of said plurality of inverter units arranged to deliver AC electric power to a respective one of said plurality of AC connections for delivering the AC electric power to one of said plurality of induction furnaces;
• each inverter unit of said plurality of inverter units further comprising a plurality of inverter modules selectively connected in parallel, each inverter module having a selectively connectable input to said DC common connection for receiving said DC electric power and each inverter module having a selectively connectable output to the one of said plurality of AC connections that is respective to the inverter unit comprising such inverter module;
• wherein said AC electric power from each inverter unit of said plurality of inverter units is used to selectively melt metal or hold molten metal at a selected temperature in the respective induction furnace.

A system for melting metal and holding molten metal at a selected temperature, comprising:

• a plurality of induction furnaces, each furnace of said plurality of induction furnaces having a maximum power consumption;
• a plurality of rectifier modules selectively connected together to form a rectifier unit, each module of said plurality of rectifier modules having a selectively connectable input to a multi-phase supply of AC power and a selectively connectable output to a DC common connection to supply a DC electric power, each module of said plurality of rectifier modules further comprising:
• means for transforming said multi-phase supply of AC power, said means for transforming selectively phase shifting said multi-phase supply of AC power to provide a selective phase-shifted output;
• and
• means for rectifying said selective phase-shifted output;
• and
• a plurality of inverter units, equal in number to said plurality of induction furnaces, each inverter unit of said plurality of inverter units dedicatedly delivering an AC electric power to a respective furnace of said plurality of induction furnaces, and each inverter unit of said plurality of inverter units further comprising a plurality of inverter modules selectively connected in parallel, each module of said plurality of inverter modules having a selectively connectable input to a DC common connection for receiving said DC electric power and a selectively connectable output to an AC common connection for delivering an AC electric power to the respective furnace of said plurality of induction furnaces;
• wherein said AC electric power from each inverter unit of said plurality of inverter units is used to selectively melt metal or hold molten metal at a selected temperature in the respective dedicated furnace of said plurality of induction furnaces.

A system for melting metal and holding molten metal at a selected temperature, comprising:

• a plurality of induction furnaces, each furnace of said plurality of induction furnaces having a furnace maximum holding power to hold a substantially full charge of metal in the molten state at a pre-selected temperature and a maximum power consumption;
• a rectifier unit outputting a magnitude of DC electric power wherein said magnitude of DC electric power is less than the sum of the maximum power consumption for each furnace for all of said plurality of induction furnaces, and said magnitude of DC electric power exceeds the sum of said furnace maximum holding power for each furnace for all of said plurality of induction furnaces;
• a plurality of inverter units, equal in number to said plurality of induction furnaces, each inverter unit of said plurality of inverter units dedicatedly delivering an AC electric power to one of said plurality of induction furnaces, and each inverter unit of said plurality of inverter units further comprising a plurality of inverter modules selectively connected in parallel, each module of said plurality of inverter modules having a selectively connectable input to a DC common connection for receiving said DC electric power and a selectively connectable output to an AC common connection for delivering an AC electric power to one of said plurality of induction furnaces;
• and
• a control means operatively connected to each inverter unit of said plurality of inverter units, said control means further comprising:
• means for inputting a power set point, P.sub.i, for each furnace of said plurality of induction furnaces;
• means for reducing the power set point, P.sub.i, for each furnace of said plurality of induction furnaces for which said power set point, P.sub.i, exceeds said furnace maximum holding power, if the sum of said power set point, P.sub.i, for each furnace for all of said plurality of induction furnaces is greater said than said magnitude of DC power;
• means for determining a total available power to the system from the product of a percentage of demand limitation, D%, and a total maximum power, P.sub.total, available to the system;
• means for determining a total power required for holding, .SIGMA.P.sub.hold, by summing the power set point, P.sub.i, for each furnace of said plurality of induction furnaces having said power set point, P.sub.i, less than or equal to said furnace maximum holding power;
• means for determining a total power required for melting, .SIGMA.P.sub.melt, by summing the power set point, P.sub.i, for each furnace of said plurality of induction furnaces having said power set point, P.sub.i, greater than said furnace maximum holding power;
• means for determining a total power available for melting, P.sub.available, from the equation:
• P.sub.available =[D%.circle-solid.P.sub.total ]-.SIGMA.P.sub.hold ;
• means for determining a power availability coefficient, k.sub.available, from the equation:
• k.sub.available =[P.sub.available ]/[.SIGMA.P.sub.melt ];
• and
• means for adjusting said power set point, P.sub.i, for each furnace of said plurality of induction furnaces for which said power set point, P.sub.i, is greater than said furnace maximum holding power to a value substantially equal to the product of said power availability coefficient, k.sub.available, and said power set point, P.sub.i, if said power availability coefficient, k.sub.available, is less than unity.

A method for selectively melting metal and holding molten metal at a selected temperature in a plurality of induction furnaces, each furnace of said plurality of induction furnaces having a furnace maximum holding power to hold a substantially fall charge of metal in the molten state and a furnace maximum power consumption, the method comprising the steps of:

• supplying an AC electric power to said plurality of induction furnaces from a plurality of inverter units equal in number to said plurality of induction furnaces, wherein each inverter unit of said plurality of inverter units dedicatedly supplies said AC electric power to a respective furnace of said plurality of induction furnaces, and each inverter of said plurality of inverter units further comprises a plurality of inverter modules;
• supplying a magnitude of DC electric power from at least one rectifier module receiving a magnitude of AC electric supply power to all of said plurality of inverter units, said magnitude of DC electric power equal to less than the sum of the furnace maximum power consumption for each furnace for all of said plurality of induction furnaces, and greater than or equal to the sum of said furnace maximum holding power for each furnace of all of said plurality of induction furnaces;
• establishing a power set point for each furnace of said plurality of induction furnaces;
• reducing said power set point for each furnace of said plurality of induction furnaces for which the power set point exceeds said furnace maximum holding power if the summation of said power set point for each furnace for all of said plurality of induction furnaces is greater than said magnitude of DC electric power;
• and
• sharing a magnitude of available melting power among each furnace of said plurality of induction furnaces having a power set point greater than said furnace maximum holding power wherein said magnitude of available melting power is determined by the difference between said magnitude of AC electric supply power and a total power required for holding determined by summing the power set point for each furnace of said plurality of induction furnaces wherein said power set point is less than or equal to said furnace maximum holding power for each furnace of said plurality of induction furnaces.

A method for selectively melting metal and holding molten metal in a plurality of induction furnaces, each furnace of said plurality of induction furnaces having a furnace maximum holding power to hold a substantially full charge of metal in the molten state and a furnace maximum power consumption to melt a substantially full charge of metal, comprising the steps of:

• supplying an AC electric power to said plurality of induction furnaces from a plurality of inverter units equal in number to said plurality of induction furnaces, wherein each inverter unit of said plurality of inverter units dedicatedly supplies said AC electric power to a respective furnace of said plurality of induction furnaces, and each inverter of said plurality of inverter units further comprises a plurality of inverter modules;
• supplying a magnitude of DC electric power from at least one rectifier module receiving a magnitude of AC electric supply power to all of said plurality of inverter units, said magnitude of DC electric power equal to less than the sum of the furnace maximum power consumption for each furnace for all of said plurality of induction furnaces, and greater than or equal to the sum of said furnace maximum holding power for each furnace of all of said plurality of induction furnaces;
• establishing a power set point, P.sub.i, for each furnace of said plurality of induction furnaces;
• reducing said power set point, P.sub.i, for each furnace of said plurality of induction furnaces for which the power set point, P.sub.i, exceeds said furnace maximum holding power if the summation of said power set point for each furnace for all of said plurality of induction furnaces is greater than said magnitude of DC electric power;
• inputting a percentage of demand limitation, D%, and a total maximum power, P.sub.total, available to the system;
• determining a total power required for holding, .SIGMA.P.sub.hold, by summing the power set point, P.sub.i, for each furnace of said plurality of induction furnaces having said power set point, P.sub.i, less than or equal to said furnace maximum holding power;
• determining a total power required for melting, .SIGMA.P.sub.melt, by summing the power set point, P.sub.i, for each furnace of said plurality of induction furnaces having said power set point, P.sub.i, greater than said furnace maximum holding;
• determining a total power available for melting, P.sub.available, from the equation:
• P.sub.available =[D% .circle-solid.P.sub.total ]-.SIGMA.P.sub.hold ;
• determining a power availability coefficient, k.sub.available, from the equation:
• k.sub.available =[P.sub.available ]/[.SIGMA.P.sub.melt ];
• and
• adjusting said power set point, P.sub.i, for each furnace of said plurality of induction furnaces for which said power set point, P.sub.i, is greater than said furnace maximum holding power to a value substantially equal to the product of said power availability coefficient, k.sub.available, and said power set point, P.sub.i, if said power availability coefficient, k.sub.available, is less than unity.