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ACKNOWLEDGEMENTS

This study was supported by the Spanish Ministerio de Economía y Competitividad under the project

ENE2012-33043

First, a the detailed mathematical model of the multiphase machine, assuming non-

zero mutual couplings between the three stators [3-6] is developed. Once the model

is defined, the current controller of the machine is designed based on the obtained

system equations, considering that no communications are available between the

different stator controllers. For this reason, the torque control is divided in three

independent controllers, each performed by the converter connected to each stator.

Each converter carries out its own controller in the machine reference frame,

regulating the active and reactive current flowing through its circuit. The controllers

are designed to show a reduced interaction between the stators during the

operation.

A distributed torque control of a nine-phase wind turbine generator is proposed in

this paper. Specifically, the generator is compounded by three different three-phase

stators embedded in the same machine yoke. Due to this configuration, the

machine couplings between stators are present during the operation [1], fact that

complicates the design of the current controllers. Multiphase machines usually

require a centralized controller to achieve a good performance during the operation

[2]. However, the control proposal presented here deals with the implementation of

a decentralized controller, considering that each stator only knows its own

measurements, in order to increase the machine operation possibilities.

Different simulations and experiments have been performed to test the behavior

of the machine distributed current control, considering different possible

scenarios. These tests have validated the concept viability and the controller

design methodology with satisfactory results. These experiments also have

shown that a triple three-phase permanent magnet generator configuration, along

with the designed controller, could be an interesting proposal to be installed in

future offshore wind power plants, because it has additional capabilities in

comparison with the classical three-phase structures, in terms of redundancy,

fault operation and control possibilities.

Abstract

Distributed control of a nine phase permanent magnet

generator and scaled platform validationE. Prieto-Araujoa / D. Lavèrniab / A. Junyent-Ferréc / O. Gomis-Bellmunta,b

aCITCEA-UPC / bIREC / cC&P Imperial College

PO. ID

338

Experimental results

Control design methodology

Conclusions

Simulations

References

EWEA 2014, Barcelona, Spain: Europe’s Premier Wind Energy Event

To validate the controller, a simulation model representing the operation of a nine-

phase wind turbine generator has been developed. The simulated scenario

consists on introducing a step change to the active current reference of the stator 1

(q axis), to observe the performance of the controller of this stator along with the

interaction between stators.

Summary

Magnitude -

𝑖𝑠1𝑞∗

reference 0 to 500 A - 0.5 s.

𝑖𝑠1𝑑∗reference Constant at 0 A

𝑖𝑠2𝑞∗

reference Constant at 0 A

𝑖𝑠2𝑑∗reference Constant at 0 A

𝑖𝑠3𝑞∗

reference Constant at 0 A

𝑖𝑠3𝑑∗reference Constant at 0 A

Controllers

time response

10 ms

Speed Constant (rated)

The controller shows a good

performance during the current step

change. The time response defined

during the controller design stage is

accomplished because the stator 1

active current reaches the steady

state in 10 ms. Also, as the

controllers do not compensate the

effects between stators, currents of

stators 2 and 3 are affected by the

current change in stator one.

However, these effects are

compensated in a few milliseconds

by their respective controllers.

The control algorithms have been

validated in a scaled wind turbine test

rig. This rig is composed by two 30

kW permanent magnet machines,

one acting as a motor and the other

as a generator, joined mechanically

by their axes. The motor is connected

to a frequency converter and the

generator is a nine-phase generator

with three independent stators,

connected to the grid by means of

three back-to-back converters.

Two different experiments are performed to show the behavior of the designed

controller. The first test is performed to validate the decentralized controller of

the machine, setting the active current reference of the three stators to the same

value. Then a second experiment is developed to validate that the current

regulator is able to operate the machine with different current references for

each stator. The results shown below have validated the performance of the

controller during the developed experiments.

Machine phase ‘a’

current waveforms

flowing through each

of the machine

stators during the

experimental tests.