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2 Maszyny Elektryczne : zeszyty problemowe

2 2015

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Discrepancies of the expanded park equations and parameter identification with evolution strategy

Schmuelling Ch., Kreischer Ch., Gołȩbiowski M.

Maszyny Elektryczne : zeszyty problemowe

2015

Nr 3 (107)

81--87

The Park equations are a well known analytic model for describing synchronous machines. Over the years they were consistently extended, like the additional Canay leakage inductance in the rotor circuit. Although, there are newer and more accurate analytic models, the Park equations are still applied by all manufacturers and grid operators. The expanded Park theory [1] derives these equations from the phase-domain model. In this paper at hand, it is shown that this derivation is based on false assumptions for calculating the inductances. Therefore the transformation of the phase-domain parameter does not lead to a decoupled system as it should in the expanded Park theory. It is shown that the new system is more complex and the parameter of this system could not be derived from the phase-domain model. Two different synchronous machines, one with a salient pole rotor and one with a round rotor, are modeled by a finite-element-method (FEM) software and all stator self and mutual inductances are calculated. The model of the round rotor machine is verified by measurements. Due to common application of the Park equations a new method to determine the parameter is also presented. The results of a three-phase sudden short circuit are used in combination with the evolutionary algorithm to derive the Park parameters. All optimized parameters are totally detached from the physics. The found parameters are verified by measurements of other transients, like the twophase short circuit.

Comparison of different methods for excitation of synchronous machines

Schmuelling S., Kreischer Ch., Gołȩbiowski M.

Maszyny Elektryczne : zeszyty problemowe

2015

Nr 3 (107)

89--93

The energy turnaround in Germany leads to new operating conditions for small and medium synchronous generators. Since the electricity generation through renewable energy sources, such as wind or photovoltaic, is highly volatile, generators have to run up from standstill into rated operation within several minutes. Hence, it is necessary to compensate a lack of electricity generation caused by wrong weather forecasts. Usually, gas turbine systems provide this possibility. The generator is used as a starter engine due to the connection to a frequency inverter. The excitation current is often provided by static excitation systems. Thus, it is possible to start from standstill and run up the drive until the gas turbine is able to generate a positive torque. A new excitation concept, based on an induction machine with a 3-phase rotor winding, is able to provide an excitation current at 0 rpm and eliminates the need for brushes. To verify the applicability for power systems, both systems are compared under different aspects. The control of the excitation current at different speeds and the possibility to settle shaft oscillations after electrical faults are aspects researched in the paper at hand. A power system simulation is performed with a synchronous machine connected to a grid. Both excitation systems are modeled by equivalent circuit diagrams in Matlab Simscape.