System and method of controlling an inverter based on a calculated capacitance of a DC link capacitor

1. A system ( 100 ), comprising:

a control regulation system ( 50 );

an inverter ( 10 );

a DC link capacitor ( 2 ), which is coupled to input connections of the inverter ( 10 );

at least one control apparatus ( 4 ), which is coupled to semiconductor switches ( 1 ) of a half-bridge of the inverter ( 10 ), wherein the control apparatus ( 4 ) is configured to actuate the semiconductor switch ( 1 ) on the basis of a control signal ( 5 ) from the control regulation system ( 50 );

at least one temperature sensor ( 52 ), which is configured to determine a change in temperature of the semiconductor switches ( 1 ) in the half-bridge of the inverter ( 10 ); and

a voltage sensor ( 51 ), which is configured to determine the voltage at the DC link capacitor ( 2 ),

wherein the control regulation system ( 50 ) is configured to generate the control signal ( 5 ) as a series of control signal pulses, a pulse length of the control signal pulses having a duration that results in the semiconductor switches ( 1 ) in the half-bridge of the inverter ( 10 ) not becoming completely conductive during the control signal pulse,

wherein the control regulation system ( 50 ) is configured to calculate a present capacitance of the DC link capacitor ( 2 ) on the basis of a determined change in temperature of the temperature sensor ( 52 ) between the beginning and the end of the control signal pulse and a determined change in voltage of the voltage sensor ( 51 ) between the beginning and the end of the control signal pulse, and

wherein the operation of the system ( 100 ) is altered if the calculated capacitance of the DC link capacitor ( 2 ) indicates the DC link capacitor ( 2 ) is not functioning properly.

2. The system ( 100 ) according to claim 1 , wherein the control apparatus ( 4 ) has:

an actuation circuit ( 16 ), which is configured to generate a driver signal ( 18 ) depending on the switching signal ( 5 ) generated by the control regulation system ( 50 );

a driver circuit ( 15 ), which is coupled between the actuation circuit ( 16 ) and a control input ( 13 ) of the semiconductor switches ( 1 ), and which is configured to receive the driver signal ( 18 ), to generate a switch control signal ( 7 ) depending on the driver signal ( 18 ), and to feed the switch control signal ( 7 ) into the control inputs ( 13 ) of the semiconductor switches ( 1 ).

3. The system ( 100 ) according to claim 2 , wherein the actuation circuit ( 16 ) is configured to generate the driver signal ( 18 ) as a series of driver signal pulses with an adjustable pulse length so that the semiconductor switches ( 1 ) are not completely conductive during the pulse length on actuation by the switch control signal ( 7 ).

4. The system ( 100 ) according to claim 3 , wherein the pulse length is adjustable such that the semiconductor switches ( 1 ) have a predetermined current value on actuation by the switch control signal ( 7 ).

5. The system ( 100 ) according to claim 1 , wherein the semiconductor switches ( 1 ) are IGBT switches.

6. The system ( 100 ) according to claim 1 , further comprising:

an n-phase electric machine ( 3 ), where n≧1, which is coupled to output connections of the inverter ( 10 ).

7. A method (M) for actuating an inverter ( 10 ), comprising the following steps:

actuating (M 1 ) semiconductor switches ( 1 a , . . . , 1 f ) in a half-bridge of an inverter ( 10 ) by a control signal ( 5 ) which has a series of control signal pulses having a pulse length such that the semiconductor switches ( 1 a , . . . 1 f ) in the half-bridge of the inverter ( 10 ) are not completely conductive during an on actuation of the pulse length in accordance with the control signal ( 5 );

determining (M 2 ) a voltage of a DC link capacitor ( 2 ) feeding the inverter ( 10 ) between the beginning and the end of the actuation of the semiconductor switches ( 1 a , . . . , 1 f );

determining (M 3 ) a change in temperature of the semiconductor switches ( 1 a , . . . , 1 f ) in the half-bridge of the inverter ( 10 ) during between the beginning and the end of the actuation of the semiconductor switches ( 1 a , . . . , 1 f );

calculating (M 4 ) a present capacitance of the DC link capacitor ( 2 ) on the basis of the determined change in temperature and the determined voltage; and

altering the actuation of the inverter ( 10 ) if the calculated capacitance of the DC link capacitor ( 2 ) indicates the DC link capacitor ( 2 ) is not functioning properly.