Inverter drives having a controlled power output

1. An electromechanical system comprising:

an inverter drive;

a component arranged during operation to generate a variable force having one or more periodic frequency components, a frequency of the one or more periodic frequency components being between about 1.6 Hz and about 25 Hz; and

processing circuitry arranged to:

determine the power output of the inverter drive;

measure a difference between the power output and a reference power output; and

control an output frequency of the inverter drive as a function of the measured difference, so as to stabilise the power output during operation of the component.

2. A inverter drive comprising processing circuitry arranged to cause the inverter drive, when the inverter drive is operably connected via an electrical machine to a component arranged during operation to generate a variable force having one or more periodic frequency components, to:

determine the power output of the inverter drive;

measure a difference between the power output and a reference power output; and

control an output frequency of the inverter drive as a function of the measured difference, so as to stabilise the power output during operation of the component;

wherein a frequency of the one or more periodic frequency components is between about 1.6 Hz and about 25 Hz.

3. A method of controlling a power output of an inverter drive operably connected via an electrical machine to a component arranged during operation to generate a variable force having one or more periodic frequency components, comprising:

determining the power output of the inverter drive;

determining a difference between the power output and a reference power output; and

controlling an output frequency of the inverter drive as a function of the difference, so as to stabilise the power output during operation of the component;

wherein a frequency of the one or more periodic frequency components is between about 1.6 Hz and about 25 Hz.

4. The method of claim 3 , wherein the electrical machine is an electric motor, and wherein the output power is delivered by the inverter drive to the component so as to cause the component to generate the variable force.

5. The method of claim 3 , wherein the component is arranged during operation to generate a pulsating force.

6. The method of claim 3 , wherein the variable force is a variable torque.

7. The method of claim 3 , wherein the stabilised power output is substantially constant over one period of the variable force.

8. The method of claim 3 , wherein an average output frequency of the inverter drive is substantially constant one period of the variable force.

9. The method of claim 3 , wherein controlling the output frequency of the inverter drive comprises controlling the output frequency substantially over one period of the variable force.

10. The method of claim 3 , wherein the reference power output is determined by:

determining an output frequency of the inverter drive;

determining a difference between the output frequency and a reference output frequency; and

controlling the reference power output as a function of the difference between the output frequency and the reference output frequency.

11. The method of claim 3 , wherein determining the power output of the inverter drive comprises determining an output voltage and an output current of the inverter drive.

12. The method of claim 3 , wherein determining the power output of the inverter drive comprises determining an output frequency and an output torque of the electrical machine.

13. The method of claim 3 , wherein stabilising the power output results in stabilising an input current of the inverter drive.

14. The method of claim 3 , wherein the variable force generated by component during operation is expressed as q=Q av +Q cyc sin(ω cyc t), wherein: q is a magnitude of the force; Q av , Q cyc and ω cyc are constants; and t is time.

15. The method of claim 3 , wherein an input current of the inverter drive is connected to a mains power supply.

16. A machine-readable medium having instructions stored thereon and configured, when read by a machine, to cause the steps of claim 3 to be carried out.