Low cost variable input voltage inverter with reliable commutation

Claim 2

In a variable input voltage inverter comprising at least two load current carrying solid-state switching means connected in a series circuit between a first pair of variable input voltage supply terminals, gating means for alternately rendering conductive said solid-state switching means, and commutating means for respectively turning off said solid-state switching means after desired intervals of conduction, wherein said commutating means includes commutating inductor means and a commutating capacitor effectively coupled in parallel circuit relationship with each of said solid-state switching means, a point on said series circuit between said solid-state switching means being an output terminal connectable to a load, the improvement which comprises: commutating capacitor recharging circuit means effectively coupled between a second pair of supply terminals; said commutating capacitor recharging circuit means comprising the series combination of an impedance and a controllable semiconductor switch connected in series circuit relationship with each of said commutating capacitors for recharging each commutating capacitor to a predetermined voltage sufficient to reliably commutate its associated parallel-connected load current carrying solid-state switching means over the entire range of variable input voltage; means for rendering conductive each controllable semiconductor switch for desired intervals of conduction during intervals of nonconduction of the respective aforementioned associated solid-state switching means; and further including rectifier means connected in said series circuit in series circuit relationship with each of said solidstate switching means and respectively operative to block when the voltage on the recharging commutating capacitor exceeds the voltage supplied to the load at said output terminal.

Claim 3

An inverter according to claim 1 wherein each impedance and controllable semiconductor switch in said commutating capacitor recharging circuit means comprises a resistor and a transistor.

Claim 4

An inverter according to claim 1 wherein the interval of conduction of each controllable semiconductor switch is coextensive with the interval of nonconduction of the respective associated load current carrying solid state switching means.

Claim 5

An inverter according to claim 3 wherein said gating means for said load current carrying solid-state switching means and said means for rendering conductive said controllable semiconductor switches is provided by a single gating circuit.

Claim 6

An inverter according to claim 1 wherein said first pair of variable voltage input supply terminals are connected to a source of variable unidirectional voltage comprising a solid-state phase controlled full wave bridge rectifier and an electrical filter, and said second pair of supply terminals are connected to a source of fixed unidirectional voltage comprising a solid-state fixed output full wave bridge rectifier and an electrical filter; said phase controlled and fixed output bridge rectifiers having common components so that one of the supply terminals in each pair is common.

Claim 7

A variable input voltage inverter comprising: a load current carrying series circuit connected between a pair of variable input voltage supply terminals comprised by a first gate controlled thyristor, a first commutating inductor, a first blocking diode, a second gate controlled thyrisTor, a second commutating inductor, and a second blocking diode, said commutating inductors being inductively coupled, the junction between said first blocking diode and second gate controlled thyristor being an output terminal connectable to a load; feedback means for circulating reactive load current and excess commutating energy; first and second commutating capacitors respectively connected in parallel circuit relationship with said first gate controlled thyristor and commutating inductor, and said second gate controlled thyristor and commutating inductor; first and second commutating capacitor recharging circuits each effectively coupled between a pair of fixed voltage supply terminals, said first commutating capacitor voltage supply terminals, said first commutating capacitor recharging circuit comprising the series combination of an impedance and a first controllable semiconductor switch connected in series with said first commutating capacitor, said second commutating capacitor recharging circuit comprising the series combination of an impedance and a second controllable semiconductor switch connected in series with said second commutating capacitor; and gating circuit means for simultaneously rendering conductive said first gate controlled thyristor and second controllable semiconductor switch, and for alternately and simultaneously rendering conductive said second gate controlled thyristor and first controllable semiconductor switch; whereby the commutating capacitors are recharged prior to commutation to the value of the fixed voltage appearing in said second pair of fixed voltage supply terminals and reliable commutate said gate controlled thyristors over the entire range of variable input voltage.

Claim 8

A variable input voltage inverter comprising: a load current carrying series circuit connected between a pair of variable input voltage supply terminals comprised by a first gate controlled thyristor, a first commutating inductor, a first blocking diode, a second gate controlled thyrisTor, a second commutating inductor, and a second blocking diode, said commutating inductors being inductively coupled, the junction between said first blocking diode and second gate controlled thyristor being an output terminal connectable to a load; feedback means for circulating reactive load current and excess commutating energy; first and second commutating capacitors respectively connected in parallel circuit relationship with said first gate controlled thyristor and commutating inductor, and said second gate controlled thyristor and commutating inductor; first and second commutating capacitor recharging circuits each effectively coupled between a pair of fixed voltage supply terminals, said first commutating capacitor voltage supply terminals, said first commutating capacitor recharging circuit comprising the series combination of an impedance and a first controllable semiconductor switch connected in series with said first commutating capacitor, said second commutating capacitor recharging circuit comprising the series combination of an impedance and a second controllable semiconductor switch connected in series with said second commutating capacitor; and gating circuit means for simultaneously rendering conductive said first gate controlled thyristor and second controllable semiconductor switch, and for alternately and simultaneously rendering conductive said second gate controlled thyristor and first controllable semiconductor switch; whereby the commutating capacitors are recharged prior to commutation to the value of the fixed voltage appearing in said second pair of fixed voltage supply terminals and reliable commutate said gate controlled thyristors over the entire range of variable input voltage.

Claim 9

An inverter according to claim 6 wherein the impedances and controllable semiconductor switches in said commutating capacitor recharging circuits comprise resistors and transistors.

Claim 10

An inverter according to claim 6 wherein said variable voltage and fixed voltage supply terminals have a common terminal, and said first commutating capacitor recharging circuit is connected between said common terminal and the other fixed voltage supply terminal, and said second commutating capacitor recharging circuit is connected between said output terminal and the other fixed voltage supply terminal.

Claim 11

A three-phase inverter including three of the inverters as defined in claim 6 connected between common pairs of variable and fixed voltage supply terminals, and an alternating current motor connected across the output terminals of the three inverters.

Claim 12

A single phase inverter including two of the inverter circuits as defined in claim 6 connected between a single pair of variable and fixed voltage supply terminals, and an alternating current load connected between the output terminals of the two inverter circuits.

Claim 13

In a variable input voltage inverter comprising at least two load current solid-state switching devices connected in a series circuit between a first pair of variable input voltage supply terminals, gating means for alternately rendering conductive said solid-state switching devices for the conduction of load current, and commutating means for respectively turning off said solid-state switching devices after desired intervals of conduction, wherein said commutating means includes commutating inductor means and also includes commutating capacitors each effectively coupled in parallel circuit relationship with a respective one of said solid-state switching devices, a point on said series circuit between said solid-state switching devices being an output terminal connectable to a load, the improvement which comprises: a pair of independent commutation capacitor recharging circuits effectively coupled between a second pair of supply terminals; each commutation capacitor recharging circuit comprising the series combination of a resistor and a controllable semiconductor switch connected in series circuit relationship with a respective one of said commutating capacitors for recharging each commutating capacitor to a predetermined voltage sufficient to reliably commutate its associated parallel-connected load current switching device over the entire range of variable input voltage; and means for rendering conductive each controllable semiconductor switch only during intervals of nonconduction of the respective associated load current switching device.

Claim 14

In a variable input voltage inverter comprising at least two load current solid-state switching devices connected in a series circuit between a first pair of variable input voltage supply terminals, gating means for alternately rendering conductive said solid-state switching devices for the conduction of load current, and commutating means for respectively turning off said solid-state switching devices after desired intervals of conduction, wherein said commutating means includes commutating inductor means and also includes commutating capacitors each effectively coupled in parallel circuit relationship with a respective one of said solid-state switching devices, a point on said series circuit between said solid-state switching devices being an output terminal connectable to a load, the improvement which comprises: a pair of independent commutation capacitor recharging circuits effectively coupled between a second pair of supply terminals; each commutation capacitor recharging circuit comprising the series combination of a resistor and a controllable semiconductor switch connected in series circuit relationship with a respective one of said commutating capacitors for recharging each commutating capacitor to a predetermined voltage sufficient to reliably commutate its associated parallel-connected load current switching device over the entire range of variable input voltage; and means for rendering conductive each controllable semiconductor switch only during intervals of nonconduction of the respective associated load current switching device.