Inverter with switch control and a method of controlling an inverter
A control device ( 8 ) for an inverter ( 2 ) that feeds an electric machine ( 3 ), wherein the control device ( 8 ) is configured to provide pulse-width-modulated switching signals ( 15 ) at a carrier frequency to drive switching elements ( 12 ) of the inverter ( 2 ), wherein the control device ( 8 ) is configured to ascertain the carrier frequency within at least one operating range ( 22, 23 ) depending on a piece of operating point information that describes an operating point defined by a rotation speed and a torque of the electric machine ( 3 ) in such a way that the carrier frequency is reduced within the at least one operating range ( 22, 23 ) compared to a maximum carrier frequency operating point at which a maximum carrier frequency is specified in the operating range.
1. A control device for an inverter that feeds an electric machine, wherein the control device comprises:
a computer; and
a computer program comprising commands which, when executed by the computer, cause the control unit to:
provide pulse-width-modulated switching signals at a carrier frequency to drive switching elements of the inverter, and
ascertain the carrier frequency within at least one operating range depending on a piece of operating point information that describes an operating point defined by a rotation speed and a torque of the electric machine in such a way that the carrier frequency is reduced within the at least one operating range compared to a maximum carrier frequency operating point at which a maximum carrier frequency is specified in the operating range,
wherein an operating range has a full-load operating point, at which a maximum torque that is specified in terms of absolute value for its rotation speed is present, as the maximum carrier frequency operating point and extends into partial-load operation, and
wherein the control device is configured to reduce the carrier frequency as the distance from the maximum carrier frequency operating point increases.
2. The control device as claimed in claim 1 , wherein the rotation speed of the full-load operating point deviates by a maximum 30 percent, from the rotation speed at a corner operating point, which describes a transition from a basic rotation speed operation to a power-limiting operation or to a field-weakening operation.
3. The control device as claimed in claim 1 , wherein an operating range lies within a torque interval limited by an upper torque limit and a lower torque limit and the control device is configured to reduce the carrier frequency in the operating range as the rotation speed decreases, in particular independently of the torque.
4. The control device as claimed in claim 3 , wherein the operating ranges are defined without overlapping and/or specifiable carrier frequencies run continuously at boundaries at which the operating ranges adjoin one another.
5. The control device as claimed in claim 1 , which is configured to specify the carrier frequency with a fixed value within a further operating range defined without overlapping with respect to the at least one operating range and comprising operating points above a rotation speed threshold value.
6. The control device as claimed in claim 1 , which is configured not to ascertain the carrier frequency below a specified or specifiable minimum value.
7. The control device as claimed in claim 1 , which is configured to:
select the carrier frequency from a characteristic map that assigns carrier frequency values to pairs of rotation speed values and torque values, or
ascertain the carrier frequency by means of an analytical calculation specification from which the carrier frequency can be ascertained depending on the operating point.
8. The control device as claimed in claim 1 , which is configured to ascertain an updated carrier frequency in each case
upon receipt of an updated piece of operating point information,
after a specified or specifiable period of time has elapsed,
after completion of an electrical period of the electric machine,
after completion of a period of a respective switching signal.
9. The control device as claimed in claim 1 , which is configured to ascertain the operating point information from a piece of torque information received at an input and/or a piece of rotation speed information received at an input and/or depending on a piece of current information describing phase currents feeding the electric machine received at an input, and/or to estimate the operating point information in the context of a control process for ascertaining the switching signals.
10. An inverter, comprising:
a DC link capacitor;
switching elements which are interconnected to convert a DC link voltage applied to the DC link capacitor into a single-phase or multi-phase AC voltage depending on switching signals that drive the switching elements; and
a control device as claimed in claim 1 .
11. An assembly comprising:
an inverter as claimed in claim 10 ; and
an electric machine operated by the AC voltage.
12. The assembly as claimed in claim 11 , wherein the ascertainment of the carrier frequency represents the relationship
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during operation of the assembly, wherein
f PWM describes the carrier frequency to be ascertained,
f PWM,max describes a maximum carrier frequency,
f PWM,min describes a minimum value of the carrier frequency,
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describes a peak-valley value of the DC link voltage at the maximum carrier frequency that is dependent on the torque and on the rotation speed,
u DC,pp,max describes a specified maximum value of the peak-valley value of the DC link voltage,
f rot describes the rotation speed and
f rot,max describes a maximum rotation speed.
13. A method for operating an inverter for the supply of an electric machine, comprising:
ascertaining a carrier frequency of pulse-width-modulated switching signals for driving the inverter within at least one operating range depending on a piece of operating point information that describes an operating point defined by a rotation speed and a torque of the electric machine in such a way such that the carrier frequency is reduced within the at least one operating range compared to a maximum carrier frequency operating point at which a maximum carrier frequency is specified in the at least one operating range; and
providing the switching signals for switching elements of the inverter,
wherein an operating range has a full-load operating point, at which a maximum torque that is specified in terms of absolute value for its rotation speed is present, as the maximum carrier frequency operating point and extends into partial-load operation, and
wherein the control device is configured to reduce the carrier frequency as the distance from the maximum carrier frequency operating point increases.
14. A computer program, comprising commands which, when executed by a computer, cause the computer to execute the method as claimed in claim 13 .