Control arrangement of a multi-stator machine

1. A control arrangement of a machine having a first stator and a second stator, comprising:

a first frequency converter for the first stator and a second frequency converter for the second stator, wherein the first frequency converter has a first controller and the second frequency converter has a second controller,

wherein the first controller generates control signals for the first frequency converter based on measured current values relating to the first stator and the second controller generates control signals for the second frequency converter based on measured current values relating to the second stator, and

wherein the first controller generates a first compensation current value for the second controller on the basis of the received measured current values relating to the first stator compared with a first reference current value and the second controller generates a second compensation current value for the first controller on the basis of the received measured current values relating to the second stator compared with a second reference current value;

and a fault diagnosis module realized to detect the occurrence of an open-circuit fault in at least one of the first frequency converter and the second frequency converter, and to generate a compensation current activation signal in the event of the open-circuit fault;

wherein the first controller receives the second compensation current value from the second controller;

wherein, upon receipt of the compensation current activation signal, the first controller computes a voltage reference for a subsequent transform stage of the first controller on the basis of the measured current values and the second compensation current value received by the first controller.

2. A dual-stator machine, wherein said dual-stator machine is a dual-stator permanent magnet synchronous generator, comprising a frequency converter for each of the plurality of stators, and the control arrangement according to claim 1 for controlling the frequency converters.

3. A wind turbine comprising the dual-stator machine according to claim 2 .

4. A current control module in a controller of a frequency converter assigned to one stator of a dual-stator machine, which current control module comprises:

a number of inputs for receiving a measured current value and a reference current value relating to that stator, and a comparator for determining a difference current value on the basis of the received measured current value and the received reference current value;

a compensation current computation module for computing an output compensation current value on the basis of the difference current value, wherein the output compensation current value is equal to the difference current value; and

a reference voltage computation unit realized to compute a voltage reference for a subsequent transform stage on the basis of the difference current value and an output compensation current value received from a current control module of the other frequency converter controller;

wherein the other frequency converter controller only sends a non-zero output compensation current value during an open-circuit fault;

further wherein the voltage reference is used to reduce a torque ripple caused by the open-circuit fault.

5. The current control module according to claim 4 , wherein the compensation current computation module comprises a filter arrangement arranged to process the difference current value.

6. The current control module according to claim 5 , wherein the filter arrangement comprises a number of adaptive filters.

7. The current control module according to claim 5 , wherein the filter arrangement comprises a low-pass filter and/or a notch filter.

8. The current control module according to claim 4 , wherein the compensation current computation module comprises a delay unit for introducing a time delay on the output compensation current value.

9. The current control module according to claim 4 , comprising an input filter realized to filter the reference current value.

10. A method of performing fault-tolerant control of a multiple-stator machine comprising a frequency converter for each of the plurality of stators, and a controller for each frequency converter, which method comprises the steps of:

providing each controller with measured current values relating to its stator;

generating compensation current values on the basis of the measured current values received by each respective controller;

monitoring the frequency converters to detect an occurrence of an open-circuit fault in the frequency converter;

exchanging the compensation current values between the controllers in the event of the open-circuit fault;

computing a voltage reference for a transform stage of the controller on the basis of the received measured current values and the compensation current values; and

operating the multiple-stator machine according to the computed voltage reference for the transform stage to reduce a torque ripple generated by the open-circuit fault.

11. The method according to claim 10 , comprising the step of generating a compensation current activation signal to enable the exchange of the compensation current values between frequency converter controllers in the event of the open-circuit fault.

12. The method according to claim 10 , wherein the steps of performing fault-tolerant control are carried out during uninterrupted operation of the multi-stator machine.

13. The method according to claim 10 , comprising a step of derating a power output of the multi-stator generator in the event of a fault, wherein the power output is de-rated by at most 20% of rated power.