Method of controlling an electrical machine

A non-transitory computer-readable medium storing a computer program comprising computer executable components which when executed by processing circuitry of a control system causes the control system to perform the following steps:

• inputting an initial rotor angle, in a known reference frame, into a power converter controlling the electric machine, injecting a first voltage waveform into the power converter, wherein the first voltage waveform has a first fundamental frequency and includes a component along a first axis of the reference frame and a component along a second axis being orthogonal to the first axis, and wherein the first voltage waveform is such that it effects the torque from the machine to vary between at least one positive torque value and at least one negative torque value and that the mean output torque is zero,
• injecting a second voltage waveform into the power converter, wherein the second voltage waveform has a second fundamental frequency and includes a component which is offset with an offset angle δθ with respect to the first axis in the reference frame,
• determining a resulting second axis current in the power converter at the second fundamental frequency,
• adjusting, for each torque value, the offset angle δθ so that the resulting second axis current at the second fundamental frequency becomes zero, and storing a respective plurality of offset angle δθ values, and
• estimating the position of the rotor based on the plurality of offset angle values.

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 following steps:
• inputting an initial rotor angle, in a known reference frame, into a power converter controlling the electric machine,
• injecting a first voltage waveform into the power converter, wherein the first voltage waveform has a first fundamental frequency and includes a component along a first axis of the reference frame and a component along a second axis being orthogonal to the first axis, and wherein the first voltage waveform is such that it effects the torque from the machine to vary between at least one positive torque value and at least one negative torque value and that the mean output torque is zero,
• injecting a second voltage waveform into the power converter, wherein the second voltage waveform has a second fundamental frequency and includes a component which is offset with an offset angle δθ with respect to the first axis in the reference frame,
• determining a resulting second axis current in the power converter at the second fundamental frequency,
• adjusting, for each torque value the offset angle δθ so that the resulting second axis current at the second fundamental frequency becomes zero, and storing a respective plurality of offset angle δθ values, and
• estimating the position of the rotor based on the plurality of offset angle values.

An electrical power system comprising:

• an electrical machine,
• a power converter configured to control the electrical machine,
• a control system configured to control the power converter, and
• a control system for controlling the electrical machine, wherein the control system for controlling the electrical machine 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 following steps:
• inputting an initial rotor angle, in a known reference frame, into a power converter controlling the electric machine,
• injecting a first voltage waveform into the power converter, wherein the first voltage waveform has a first fundamental frequency and includes a component along a first axis of the reference frame and a component along a second axis being orthogonal to the first axis, and wherein the first voltage waveform is such that it effects the torque from the machine to vary between at least one positive torque value and at least one negative torque value and that the mean output torque is zero,
• injecting a second voltage waveform into the power converter, wherein the second voltage waveform has a second fundamental frequency and includes a component which is offset with an offset angle δθ with respect to the first axis in the reference frame,
• determining a resulting second axis current in the power converter at the second fundamental frequency,
• adjusting, for each torque value, the offset angle δθ so that the resulting second axis current at the second fundamental frequency becomes zero, and storing a respective plurality of offset angle δθ values, and
• estimating the position of the rotor based on the plurality of offset angle values.