Operating an inverter for coupling an electric machine, designed for operation on ac voltage, with an ac voltage network

A method for operating an inverter which couples an electric machine designed for operation on AC voltage to an AC voltage network, wherein the inverter is coupled to a network-side converter connected to the AC voltage network by means of a DC intermediate circuit, the method comprising

• controlling the network-side converter with a network control signal and controlling conversion of electric energy by the machine-side converter with a machine control signal from a control unit:
• determining a torque-related machine current component from electric machine currents of the electric machine,
• detecting an actual value for a magnetic flux,
• determining an actual value of a machine torque of the electric machine by linking the detected magnetic flux to the torque-related machine current component,
• determining a torque difference between the actual value of the machine torque and a setpoint value of the machine torque of the electric machine,
• filtering the torque difference with a bandpass filter tuned to a machine-side natural frequency to determine a filter output signal,
• processing the filter output signal with a Park transformation to determine a d-component and a q-component, and determine therefrom a compensation signal,
• determining mean values for the determined d-component and q-component,
• regulating the mean values to zero with a PI controller,
• determining the compensation signal with an inverse Park transformation, and
• superimposing the compensation signal determined with the inverse Park transformation on the network control signal or the machine control signal, or both.

A computer program product residing on a non-transitory computer readable medium and comprising a program having program code sections, wherein the program code sections, when read into a memory of a processor of a control unit and executed by the processor of the control unit, causes the control unit to:

• control the network-side converter with a network control signal and controlling conversion of electric energy by the machine-side converter with a machine control signal:
• determine a torque-related machine current component from electric machine currents of the electric machine,
• detect an actual value for a magnetic flux,
• determine an actual value of a machine torque of the electric machine by linking the detected magnetic flux to the torque-related machine current component,
• determine a torque difference between the actual value of the machine torque and a setpoint value of the machine torque of the electric machine,
• filter the torque difference with a bandpass filter tuned to a machine-side natural frequency to determine a filter output signal,
• process the filter output signal with a Park transformation to determine a d-component and a q-component, and determine therefrom a compensation signal,
• determine mean values for the determined d-component and q-component,
• regulate the mean values to zero with a PI controller,
• determine the compensation signal with an inverse Park transformation, and
• superimpose the compensation signal determined with the inverse Park transformation on the network control signal or the machine control signal, or both.

A control unit for operating an inverter coupling an electric machine operating on AC voltage to an AC voltage network, wherein the inverter comprises a network-side converter connected to the AC voltage network and a machine-side converter connected to the electric machine and electrically coupled are connected to the network-side converter by way of a DC intermediate circuit, the control unit comprising

• a network-side connector configured for connection to the network-side converter and providing a network control signal to control the network-side converter, and
• a machine-side connector configured for connection to the machine-side converter and providing a machine control signal to control the machine-side converter the control unit further configured to
• determine a torque-related machine current component from electric machine currents of the electric machine,
• detect an actual value for a magnetic flux,
• determine an actual value of a machine torque of the electric machine by linking the detected magnetic flux to the torque-related machine current component,
• determine a torque difference between the actual value of the machine torque and a setpoint value of the machine torque of the electric machine,
• filter the torque difference with a bandpass filter tuned to a machine-side natural frequency to determine a filter output signal,
• process the filter output signal with a Park transformation to determine a d-component and a q-component, and determine therefrom a compensation signal,
• determine mean values for the determined d-component and q-component,
• regulate the mean values to zero with a PI controller,
• determine the compensation signal with an inverse Park transformation, and
• superimpose the compensation signal determined with the inverse Park transformation on the network control signal or the machine control signal, or both.