P. Kulsangcharoen

Assessing the accuracy of loss estimation methods for supercapacitor energy storage devices operating under constant power cycling

This paper assesses different energy loss estimation methods using the supercapacitor model parameters extracted from the electrochemical impedance spectroscopy (EIS). Two energy loss estimation methods are applied to two similar supercapacitors from different manufacturers operating under constant power charge-discharge cycling. The simpler loss method uses only the impedance data that corresponds to the cycle frequency and the instantaneous current data whilst the more complex method uses the detailed impedance versus frequency dependency and the corresponding current harmonics available from the FFT. The experimental loss data (the benchmark) uses integration of instantaneous power processed by the supercapacitor. By comparing the difference between the estimated and the experimental losses, the performance of each method is assessed and the factors that influence the accuracy of the two loss estimation methods as well as their limitations are highlighted.

A Modified Neutral Point Balancing Space Vector Modulation for Three-Level Neutral Point Clamped Converters in High-Speed Drives

This paper describes a high-performance neutral point voltage balancing technique for a neutral point clamped (NPC) converter. Conventional neutral point voltage balancing methods do not function well under low power factor, low pulse ratio, and near-unity modulation index operation conditions. These conditions are essentially dominant operation conditions for aircraft starter/generator systems. This paper introduces an alternative space vector modulation technique for three-level NPC converters in an aircraft starter generator system. The selection of voltage space vectors is optimized for high modulation index and low power factor operation. Disturbances caused by a low pulse ratio are also compensated. The proposed method maintains neutral point voltage balance and ripple minimization over the full range of operating conditions. This paper also provides a detailed analysis of the sources of neutral point voltage imbalances and ripples in high-speed drives with deep flux weakening. Simulation results obtained from a Simulink/PLECS model and experimental results obtained from a 45 kVA, 32 krpm aircraft starter generator test rig prove that the proposed method eliminates the neutral point voltage imbalance and significantly reduces the neutral point voltage ripple.

Nonlinear aircraft engine model for future integrated power center development

Aircraft engines, the prime source of on-board power, play a vital role within the electrical power generation system. In literature these are considerably simplified to rudimentary engine speed. In this paper, a nonlinear zero-dimension (0-D) order turbofan engine model has been developed for use with an integrated power center. By analyzing the compressor maps in detail, the results reveal a limit on the amount power off-take from each engine shaft at different altitudes.

Minimization of electro-mechanical interaction with posicast strategies for more-electric aircraft applications

This paper studies strategies to minimize the electromechanical interaction (EMI) within aircraft power systems. With the growth of electrical power on-board aircraft, the interaction between the electrical systems and the engine core will become significant. The behaviour of electrical loads (on/off, transient etc.) will have significant impacts on the engine shaft, such as producing transient vibrations, creating stability problems and reducing the efficiency etc. To avoid these problems, an advanced electrical power management system (PMS) is required. This paper introduces novel loading methods for PMS applications to minimize the interactions between electrical and mechanical systems. The strategies, referred as Single Level Multi-edge Switching Loads (SLME), Multilevel Loading (MLL), and Multi-load Single Level Multi-edge Switching Loads (MSLME) are developed based on the Posicast method. An insight look of the developed technique has been studied using the zero-pole root locus. It is demonstrated that the excited poles in the system are cancelled by the addition of zeros, and thus suppressed the EMI vibrations.

Characterization of energy storage devices for constant power applications

In this paper, a few known characterization techniques for supercapacitors have been evaluated with the purpose of being able to predict the roundtrip efficiency of an energy storage system under constant power application. It is found that the user cannot rely on a single characterization method since the methods based on small signal disturbance are not very precise when the model is subjected to large signal variations. Also, methods based on large signal disturbance will not be very precise when subjected to small signal tests. By comparing the analytically estimated constant power round trip efficiency with experimental data, it is concluded that both models can give acceptable accuracy if a relevant DC bias is used.