Improving magnetic gear overload torque with cage rotor bars

This paper introduces a coaxial magnetic gearbox with a new high-speed rotor configuration. The proposed configuration optimizes magnet volume and employs cage rotor bars in the high-speed rotor. The resulting proposed gear improves torque performance at overload condition, and utilises 5% less magnet volume in the high¬speed rotor

Convergence analysis and tuning of a sliding-mode ripple-correlation MPPT

The development of fast Maximum Power Point Tracking (MPPT) algorithms for photovoltaic (PV) systems with high bandwidth and predictable response to irradiation transients is attractive for mobile applications and installations under fast changing weather conditions. This paper proposes the convergence analysis of a sliding-mode version of the MPPT based on ripple correlation control (RCC). The contribution of the paper is a dynamic model, useful to derive a set of design guidelines to tune the sliding-mode RCC-MPPT and achieve a desired dynamic performance under irradiation transients, without a dedicated commissioning phase. The research is based on sliding control theory and it includes both the chattering phenomena analysis and a discussion on the effects of reactive parasitic elements in the PV module. The proposed analysis and design have been validated by Matlab simulations first and then with experimental tests on a 35 W panel with a boost converter charging a 24 V battery. The results support the effectiveness of the proposed modelling procedure and design guidelines, showing good agreement between the model prediction and the experimental transient response

Speed control for multi-three phase synchronous electrical motors in fault condition

The growth of electrification transportation systems is an opportunity for delving into new feasible solutions for more reliable and fault tolerant arrangements. So far, many investigations distant from the market have been carried out. Most of the works are looking at new control strategies adding extra components increasing manufacturing efforts and costs. Considering a nine phase synchronous multi-three phase electrical motor with disconnected neutral points, this manuscript compares the common speed reference configuration (where all the drives are configured in speed mode) and the torque follower configuration (where one drive is in speed mode and all the others are in torque mode). Furthermore, a post-fault operation in open-circuit condition is proposed. Analytical equations and experimental validation in nominal and fault condition are given by means of Matlab/Simulink simulations and by experimental on a 22kW test rig

Harmonic reduction methods for electrical generation: a review

This paper provides a comprehensive literature review of techniques for harmonic related power quality improvement of electrical generation systems. An increasing interest in these aspects is due to the ever more stringent power quality requirements, deriving from new grid codes and compliancy standards, aimed at limiting waveform harmonic distortion at all points of the distribution network. Although a wealth of literature is available for such techniques, it has never been compiled into a handbook incorporating all the solutions aimed at both electrical machine and power systems engineers

A new AC/AC power converter

The Future Electrical Network will be based on the integration of different renewable energy sources. In this regard, modular bidirectional power converter architectures will get special attention. Galvanic isolation in such power converter architectures plays a vital role in confining faults. This paper presents a new AC/AC converter concept suitable for Solid State Transformer (SST) applications. The basic operation of the topology is first presented, followed by the development of suitable modulation, commutation and protection methods. The proposed idea is validated in simulation with PLECS

Distributed speed control for multi-three phase electrical motors with improved power sharing capability

This paper proposes a distributed speed control with improved power sharing capability for multi-three phase synchronous machines. This control technique allows the speed to be precisely regulated during power sharing transients among different drives. The proposed regulator is able to control the time constant of the current within the dq0 reference frame to a step input variation. If compared to current set-point step variations, the proposed droop controller minimises device’s stress, torque ripple, and thus mechanical vibrations. Furthermore, since distributed, it shows improved fault tolerance and reliability. The design procedure and the power sharing dynamic have been presented and analysed by means of Matlab/Simulink and validated in a 22kW experimental rig, showing good agreement with the expected performances

Stability assessment of power-converter-based AC systems by LTP theory: eigenvalue analysis and Harmonic Impedance estimation

Stability analysis of power-converter-based AC systems poses serious challenges not only because of the non-linear nature of power converters, but also because linearisation is not generally applied around a steady-state operating point, as in the DC case, but around a time-periodic operating trajectory. Typical examples are single-phase and unbalanced three-phase systems. In this paper, two general methods to assess stability of the aforementioned systems are presented. Both are based on the Linear Time Periodic (LTP) systems theory. The first is model-based and relies on the evaluation of the eigenvalues of the linearised model, assuming a complete knowledge of the parameters. By contrast, the second proposes a set of small-signal current injections to measure the Harmonic Impedances and applies the LTP Nyquist Criterion, so that stability of the system can be assessed with a black-box approach, without relying on knowledge of the system parameters. The basic LTP systems theory is reviewed in order to provide a mathematical justification for the second method. As case study, a simple network, consisting of a source full-bridge converter in AC voltage-control mode and a load full-bridge converter in AC current-control mode including PLL, is considered. Analytical results based on average modelling and simulations based on both average and switching models are presented, showing good accuracy in the identification of the stability thresholds for both the proposed methods

Active Magnetic Bearing system design featuring a Predictive current control

Active Magnetic Bearing (AMB) technology is becoming attractive for several reasons such as high speed operations, high reliability and vibrations exemption. Moreover, AMB can behave as active vibration dampers and provide a real-time control of the shaft. For all these advantages, AMBs are particularly attractive for high power - high speed applications. These desirable features come at the cost of an increased complexity of the system, which now includes a power electronic converter and a control system dedicated to the AMBs. This paper focus on the overall system design, from the AMB design, to the power electronic converter design and control, for an AMB featuring Wheatstone bridge winding configuration. The magnetic design has been developed analytically and validated by means of Finite Elements simulation, to generate up to 2kN of axial forces. The power conversion system is based on three full bridges, one to magnetize the bearing and two to control the axial forces independently on the x and y axes. In order to achieve high bandwidth current control able to generate the desired orthogonal forces, a predictive control strategy has been proposed, for the several advantages it can provides such as fast dynamic response, no need of modulation, easy inclusion of nonlinearities and constraints of the system, possibility of incorporating nested control loops in only one loop and the flexibility to include other system requirements in the controller. The control system has been validated in Matlab/PLECS simulation, including the effect of parameters mismatches in the coils

Control design and voltage stability analysis of a droop-controlled electrical power system for more electric aircraft

This paper focuses on the analysis of a single DC bus multi-generator Electrical Power System (EPS) for future More Electric Aircrafts (MEA). Within such a single bus paradigm, the paper proposes a detailed control design procedure and provides a stability analysis based on the derivation of the output impedance of the source subsystem and input impedance of the load subsystem, including control dynamics. The single bus characteristic is analyzed and the stability properties of the EPS are investigated when supplying constant power loads. In addition, the paper highlights the impact on stability of the number of parallel sources and of the power sharing ratio. The theoretical analysis is instrumental in designing an optimally stable single DC bus EPS. The key findings are validated by experimental results

Stability assessment of high-bandwidth DC voltage controllers in single-phase active-front-ends: LTI vs LTP models

In recent years, a considerable effort has been made to minimise the size of DC-link capacitors in single-phase activefront-ends (SP-AFE), to reduce cost and to increase power density. As a result of the lower energy storage, a high-bandwidth outer DC voltage control loop is required to respond to fast load changes. Linearised modelling is usually performed according to the power-balance method and the control is designed using LTI techniques. This is done assuming negligible voltage ripple at twice the grid frequency, and the model is considered valid up to the grid frequency. However, its precise validity limits are usually unknown and the control design becomes empirical when approaching these boundaries. To overcome this drawback, Linear Time Periodic (LTP) theory can be exploited, defining the range of validity of the LTI model and providing precise stability boundaries for the DC-link voltage loop. The main result is that LTP models more accurately describe the system behaviour and provide superior results compared to the LTI ones. Theoretical analysis, simulations and extensive experimental tests on a 10 kW converter are presented to validate the claims