Method of controlling an electrical machine

A control system for controlling an electrical machine, wherein the control system comprises:

• processing circuitry, and
• a storage medium having a computer program which when executed by the processing circuitry causes the control system to perform the steps of a method including:
• a) injecting a first voltage waveform (uhx) with a first fundamental frequency into the electrical machine in a first axis of a rotor reference frame, combined with a voltage signal for controlling the electrical machine,
• b) determining a second axis current component (iqhx) of a second axis of the rotor reference frame, having the first fundamental frequency, generated in response to the injection of the first voltage waveform (uhx),
• c) controlling, based on the second axis current component (iqhx), a second axis voltage component (uqhx) of the second axis, having the first fundamental frequency, to obtain an adjusted second axis voltage component (uqhx) for controlling the second axis current component (iqhx) towards zero,
• d) feeding back the adjusted second axis voltage component to combine the adjusted second axis voltage component with the voltage signal and the injected first voltage waveform (uhx), and repeating steps b)-d) until the second axis current component (iqhx) is smaller than a threshold value,
• e) determining a differential cross-coupling parameter of the electrical machine based on the second axis voltage component (uqhx) and a first axis current component (idhx) having the first fundamental frequency, when the second axis current component (iqhx) is smaller than the threshold value, and
• g) controlling the electrical machine based on the differential cross-coupling parameter.

An electrical power system comprising:

• an electrical machine,
• a power converter configured to control the electrical machine, and
• a control system configured to control the power converter, wherein the control system includes:
• processing circuitry, and
• a storage medium having a computer program which when executed by the processing circuitry causes the control system to perform the steps of a method including:
• a) injecting a first voltage waveform (uhx) with a first fundamental frequency into the electrical machine in a first axis of a rotor reference frame, combined with a voltage signal for controlling the electrical machine,
• b) determining a second axis current component (iqhx) of a second axis of the rotor reference frame, having the first fundamental frequency, generated in response to the injection of the first voltage waveform (uhx),
• c) controlling, based on the second axis current component (iqhx), a second axis voltage component (uqhx) of the second axis, having the first fundamental frequency, to obtain an adjusted second axis voltage component (uqhx) for controlling the second axis current component (iqhx) towards zero,
• d) feeding back the adjusted second axis voltage component to combine the adjusted second axis voltage component with the voltage signal and the injected first voltage waveform (uhx), and repeating steps b)-d) until the second axis current component (iqhx) is smaller than a threshold value,
• e) determining a differential cross-coupling parameter of the electrical machine based on the second axis voltage component (uqhx) and a first axis current component (idhx) having the first fundamental frequency, when the second axis current component (iqhx) is smaller than the threshold value, and
• g) controlling the electrical machine based on the differential cross-coupling parameter.