This paper presents the use of pulse-width modulated voltage source converter (PWM-VSC) for power quality improvement of a wound field synchronous generator-based diesel generator (DG) set realising standalone supply system. The system consists of a diesel engine driven wound field synchronous generator, a three-leg PWM-VSC with a capacitor on the DC link and linear/non-linear loads. The PWM-VSC supplies the leading kilo volt-amphere reactive (kVAR) to the loads and maintains the unity power factor of the DG set. In addition, it eliminates the harmonics from the source currents and provides load balancing. The terminal voltage is controlled by field excitation control of the generator and the supply frequency is controlled by the speed regulating system of the diesel engine. A variable step size filter-x least mean square-based control algorithm is used for estimation of reference currents for control of VSC.

Synchronous machines with brushless excitation have the disadvantage that the field winding is not accessible for the de-excitation of the machine. This means that, despite the proper operation of the protection system, the slow de-excitation time constant may produce severe damage in the event of an internal short circuit. A high-speed de-excitation system for these machines was developed, and this study presents the continuation of a previously published study. This study presents the design by computer simulation and the results of the first commissioning of this de-excitation system in a commercial 20 MVA hydro-generator. The de-excitation is achieved by inserting resistance in the field circuit, obtaining a dynamic response similar to that achieved in machines with static excitation. In this case, a non-linear discharge resistor was used, making the dynamic response even better.

The need for models that represent the behaviour of transformers operating in steady state or submitted to transient events is of great importance in studies involving power systems. In this context, this study presents a model used to represent the impedance frequency response of transformers at no load and under nominal conditions. In the model, networks of parameters with RLC cells are employed to reproduce the resonances present in the frequency responses and also RL network sections are used to represent the frequency-dependent effects in the core, which aid in the current damping during transient events. The parameter values of these networks are determined with the least-squares numerical method. To evaluate the model as well as the methodology to determine the parameter values, data originating from measurements of the frequency responses with frequency range from 10 Hz to 2 MHz of two single-phase transformers (16 kVA and 55 MVA) are used. Validations of the model are carried out in the frequency and time domains. The model can be used to simulate transformer operation under nominal conditions of voltage and frequency and also for a broad frequency spectrum.

This paper proposes a driving-scenario oriented design of an axial-flux permanent-magnet synchronous motor for a pedal electric cycle (Pedelec). Traditional motors are usually designed according to a torque and speed (TN) curve with two operation zones – constant torque and constant power, without being closely related to a driving scenario. The proposed design method defines the TN curve with three operation zones – constant torque, maximum DC current and maximum voltage, which are specified by a driving scenario, the modulation method of motor drive and basic torque and voltage equations of motors. This target TN curve provides admissible ranges for the back electromotive force constant and phase resistance of the motor to be designed. A systematic design procedure is introduced by a quasi-three-dimensional (3D) magnetic circuit model, a multi-objective optimisation process for sizing the motor and a finite element analysis for verifying and refining the design. The resulting TN curve of the proposed Pedelec motor is proved to be very close to the target TN curve that is prescribed by the driving scenario, and motor and drive parameters.

Ultra-high-speed permanent magnet synchronous motors (PMSMs) usually use bipolar rotors with ring permanent magnets (PMs) or cylindrical PMs which are magnetised in parallel. The stator of the motor is first simplified as a slotless stator, and an analytical solution to the flux density distribution in the motor is obtained by solving the Laplace's equation in the regions of PM and airgap. Then, by introducing the two-dimensional relative permeance function, the slotting effects on the radial flux density are also included. Finally, rotors with different types of PMs are studied by the presented analytical method and the finite-element analysis. In addition, experiments are also performed to verify the results of the analysis. This analytical solution can be used to determine the open-circuit flux density of PMSMs which have a parallel magnetised rotor with cylindrical or ring-type PM. With the analytical solution, the dimensionless magnetic flux density in the airgap could also be derived and can be used to calculate the sizes of different rotors with the same airgap flux density easily.