Noise-immune, clamped, resonant link inverter

Claim 1

A method of driving a multiphase induction motor by means of a high frequency resonant link inverter having a DC bus with switches for connecting each phase of said motor to each side of said DC bus, said resonant link causing the voltage across said DC bus to reduce to zero volts twice in each cycle at said high frequency, comprising: sampling the current in each phase of current supplied to said induction motor in each cycle at said high frequency; and momentarily closing at least two of said switches to totally short circuit said bus each time that said bus reaches zero volts and immediately thereafter selectively operating said switches so as to provide current to said induction motor in accordance with a reference current and in response to the current sampled in said sampling step; characterized by the improvement comprising: said sampling step comprising sampling the current in each phase of current supplied to said induction motor at a point in time immediately prior to each time that the voltage across said bus reduces toward zero volts.

Claim 2

A method of driving a multiphase induction motor by means of a high frequency resonant link inverter having a DC bus with switches for connecting each phase of said motor to each side of said DC bus, said resonant link causing the voltage across said DC bus to reduce to zero volts twice in each cycle at said high frequency, comprising: sampling the current in each phase of current supplied to said induction motor in each cycle at said high frequency; and momentarily closing at least two of said switches to totally short circuit said bus each time that said bus reaches zero volts and immediately thereafter selectively operating said switches so as to provide current to said induction motor in accordance with a reference current and in response to the current sampled in said sampling step; characterized by the improvement comprising: said sampling step comprising sampling the current in each phase of current supplied to said induction motor at a point in time immediately prior to each time that the voltage across said bus reduces toward zero volts.

Claim 7

A method of driving a multiphase induction motor by means of a high frequency resonant link inverter having a DC bus with feed switches for connecting each phase of said motor to each side of said DC bus, said resonant link including a frequency determining tank circuit having an inductor in series with said DC bus and a source of DC power and a capacitor in parallel with said DC bus, said resonant link having an active clamp circuit connected across said inductor, said clamp including an electronic switch having an anti-parallel diode connected thereacross, said electronic switch and diode in series with a pre-charged clamp capacitor, comprising: turning off said electronic switch at a point in time when the current in said inductor is sufficient to drive said bus completely to zero volts thereby causing said DC bus to reduce toward zero volts twice in each cycle at said high frequency; sampling the current in each phase of current supplied to said induction motor in each cycle of said high frequency; and momentarily closing at least two of said feed switches to totally short circuit said bus each time that said bus reaches zero volts and immediately thereafter selectively operating said feed switches so as to provide current to said induction motor in accordance with a reference current and in response to the current sampled in said sampling step; characterized by the improvement in which said step of turning off comprises: turning off said electronic switch in response to a first magnitude of current flow through said clamp capacitor which bears a first predetermined relationship to the voltage across said clamp capacitor and which also bears a second predetermined relationship to the voltage of said source of DC power.

Claim 8

A method of driving a multiphase induction motor by means of a high frequency resonant link inverter having a DC bus with feed switches for connecting each phase of said motor to each side of said DC bus, said resonant link including a frequency determining tank circuit having an inductor in series with said DC bus and a source of DC power and a capacitor in parallel with said DC bus, said resonant link having an active clamp circuit connected across said inductor, said clamp including an electronic switch having an anti-parallel diode connected thereacross, said electronic switch and diode in series with a pre-charged clamp capacitor, comprising: turning off said electronic switch at a point in time when the current in said inductor is sufficient to drive said bus completely to zero volts thereby causing said DC bus to reduce toward zero volts twice in each cycle at said high frequency; sampling the current in each phase of current supplied to said induction motor in each cycle of said high frequency; and momentarily closing at least two of said feed switches to totally short circuit said bus each time that said bus reaches zero volts and immediately thereafter selectively operating said feed switches so as to provide current to said induction motor in accordance with a reference current and in response to the current sampled in said sampling step; characterized by the improvement in which said step of turning off comprises: turning off said electronic switch in response to a first magnitude of current flow through said clamp capacitor which bears a first predetermined relationship to the voltage across said clamp capacitor and which also bears a second predetermined relationship to the voltage of said source of DC power.