DYNAMIC ONLINE HW-OVERCURRENT-THRESHOLD-REDUCTION DEPENDENT ON THE OPERATION POINT
A method of setting an AC overcurrent shutoff limit for an inverter of an electric motor and an inverter for an electric motor. The inverter includes power switches and output terminals for providing multiple AC currents for windings of the electric motor. A maximal allowed AC current or at least one measurement or estimation quantity based on which the maximal allowed AC current depends is determined. The overcurrent shutoff limit for the inverter is adapted in dependency of the maximal allowed AC current or the at least one measurement or estimation quantity.
1 . A method of setting an AC overcurrent shutoff limit for an inverter of an electric motor, the inverter comprising power switches and output terminals for providing multiple AC currents for windings of the electric motor, the method comprising the steps of:
a) Determining a maximal allowed AC current or at least one measurement or estimation quantity based on which the maximal allowed AC current depends, and
b) Adapting the overcurrent shutoff limit for the inverter in dependency of the maximal allowed AC current or the at least one measurement or estimation quantity.
2 . The method of claim 1 , wherein the measurement or estimation quantity based on which the maximal allowed AC current depends is a DC voltage of the inverter.
3 . The method of claim 2 , wherein the overcurrent shutoff limit is constant at a first level for a first voltage range of the DC voltage wherein the overcurrent shutoff limit is constant at a second level for a second voltage range of the DC voltage and wherein the overcurrent shutoff limit varies within a transition range of the DC voltage which is located between the first voltage range and the second voltage range.
4 . The method of claim 3 , wherein the overcurrent shutoff limit varies linearly within the transition range of the DC voltage.
5 . The method of claim 1 , wherein the inverter comprises a nominal maximal allowed AC current to be outputted and a nominal overcurrent shutoff limit depending on the nominal maximal allowed AC current, and wherein a ratio of an altered maximal allowed AC current divided by the nominal maximal allowed AC current equals a ratio of the overcurrent shutoff limit adapted divided by the nominal overcurrent shutoff limit.
6 . The method of claim 1 , wherein the measurement or estimation quantity based on which the maximal allowed AC current depends is a temperature of the electric motor or at least one magnet thereof.
7 . An inverter for an electric motor, the inverter comprising power switches and output terminals for windings of the electric motor, wherein the inverter also comprises a control device for controlling the operating states of the power switches and wherein the control device is configured to:
a) determine a maximal allowed AC current or at least one measurement or estimation quantity based on which the maximal allowed AC current depends,
b) adapt an overcurrent shutoff limit for the inverter in dependency of the maximal allowed AC current or the at least one measurement or estimation quantity.
8 . The inverter according to claim 7 , wherein the overcurrent shutoff limit is provided by at least one hardware component.
9 . (canceled)
10 . An electric system comprising an inverter according to claim 7 .
11 . The method of claim 2 , wherein the inverter comprises a nominal maximal allowed AC current to be outputted and a nominal overcurrent shutoff limit depending on the nominal maximal allowed AC current, and wherein a ratio of an altered maximal allowed AC current divided by the nominal maximal allowed AC current equals a ratio of the overcurrent shutoff limit adapted divided by the nominal overcurrent shutoff limit.
12 . The method of claim 2 , wherein the measurement or estimation quantity based on which the maximal allowed AC current depends is a temperature of the electric motor or at least one magnet thereof.
13 . An electric system comprising an inverter according to claim 8 .
14 . The method of claim 3 , wherein the inverter comprises a nominal maximal allowed AC current to be outputted and a nominal overcurrent shutoff limit depending on the nominal maximal allowed AC current, and wherein a ratio of an altered maximal allowed AC current divided by the nominal maximal allowed AC current equals a ratio of the overcurrent shutoff limit adapted divided by the nominal overcurrent shutoff limit.
15 . The method of claim 3 , wherein the measurement or estimation quantity based on which the maximal allowed AC current depends is a temperature of the electric motor or at least one magnet thereof.
16 . The method of claim 4 , wherein the inverter comprises a nominal maximal allowed AC current to be outputted and a nominal overcurrent shutoff limit depending on the nominal maximal allowed AC current, and wherein a ratio of an altered maximal allowed AC current divided by the nominal maximal allowed AC current equals a ratio of the overcurrent shutoff limit adapted divided by the nominal overcurrent shutoff limit.
17 . The method of claim 4 , wherein the measurement or estimation quantity based on which the maximal allowed AC current depends is a temperature of the electric motor or at least one magnet thereof.
18 . The method of claim 5 , wherein the measurement or estimation quantity based on which the maximal allowed AC current depends is a temperature of the electric motor or at least one magnet thereof.