Hassan El-Kishky

On Power Quality of Variable-Speed Constant-Frequency Aircraft Electric Power Systems

In this paper, a comprehensive model of the variable-speed constant-frequency aircraft electric power system is developed to study the performance characteristics of the system and, in particular, the system power quality over a frequency range of operation of 400 Hz to 800 Hz. A fully controlled active power filter is designed to regulate the load terminal voltage, eliminate harmonics, correct supply power factor, and minimize the effect of unbalanced loads. The control algorithm for the active power filter (APF) is based on the perfect harmonic cancellation method which provides a three-phase reference supply current in phase with its positive-sequence fundamental voltage. The proposed APF is integrated into the model of a 90-kVA advanced aircraft electric power system under VSCF operation. The performance characteristics of the system are studied with the frequency of the generators output voltage varied from 400 Hz to 800 Hz under different loading conditions. Several case studies are presented including dc loads as well as passive and dynamic ac loads. The power quality characteristics of the studied aircraft electric power system with the proposed active filter are shown to be in compliance with the most recent military aircraft electrical standards MIL-STD-704F as well as with the IEEE Std. 519.

A novel GSSA method for modeling of controllers in the multi-converter system of an Advanced Aircraft Electric Power System (AAEPS)

This article presents a comprehensive set of Generalized State Space Averaging (GSSA) models for the generation of non-linear control signals in the multi-converter system of an Advanced Aircraft Electric Power System (AAEPS). Due to the switching nature and variation in loading configuration in the aircraft system under study, the pulse-width modulation (PWM) control signals demonstrate inherent time-varying behaviors to keep the systems operation within IEEE/military standard limits. Therefore, the proposed technique can be employed to derive the key features of the non-linear switching signals under investigation, hence, can be treated as an effective method of the feedback control signals approximation. Finally, the GSSA approximated signals corresponding to the PWM switching function of the constant power (CP), constant voltage (CV) and constant current (CC) buck-converters in the DC power electronics system of Boeing 767 aircraft are derived, and the simulation results are obtained from a study model developed in PSIM9 environment. Also, the accuracy of obtained results from GSSA model is verified by developing a study model in PSIM9 environment.

Optimal size and location of distributed generation unit for voltage stability enhancement

This paper presents the analysis of a distribution system connected with distributed generation (DG) units. The developed technique is based on the steady state voltage stability index. The weakest branches in the distribution system which are more likely go to the instability region are selected for DG allocation. Two optimization methods are utilized to find out the size of the DG corresponding to minimum losses or minimum stability index. The Newton-Raphson load-flow is used to find the steady-state solution of the studied distribution system. The AMPL software package is utilized for evaluating the size of the DG units. The developed methods are tested using a 90-bus distribution system with a variety of case studies.

Modeling and characterization of an aircraft electric power system with a fuel cell-equipped APU connected at HVDC bus

A hybrid power source consisting from a fuel cell and a battery is proposed as an auxiliary power unit (APU) for the more electric aircraft (MEA) applications. The output of the fuel cell is controlled using a DC/DC boost converter to provide the voltage of the aircraft 270-VDC bus. The fuel cell and the battery are controlled by using DC/DC converters to provide 270-VDC at their outputs. The output of both fuel cell and battery are connected in parallel at the 270-VDC bus of the aircraft system. Connection at the 270-VDC bus provides several merits for the MEA system; it is simple, feeding DC loads and AC loads through the generator channel 12-pulse inverter, light weight and more economical. The fuel cell/battery hybrid system rating is chosen to be 60-kW to provide power for the aircraft loads in case of the main generator failure or maintenance. To comply with the aircraft standard of MIL-STD-704F and the IEEE Std. 519–1992, an active power filter (APF) is connected at the synchronous generator terminals to reduce or eliminate the harmonics generated from the power converters. The studied aircraft electric power system with the proposed fuel cell/battery hybrid system is simulated without and with the presence of the APF and it is found that the APF reduced the voltage and frequency transients of the system and improves the aircraft electric system performance.

Constant frequency aircraft electric power systems with harmonic reduction

The ever-increasing number of power electronic converters connected to the aircraft electric power system significantly increases harmonic levels and voltage transients in that system. Stringent limits on harmonic current distortion and perturbation of the aircraft electric power supply demands accurate simulation and development of high performance filters for the mitigation of harmonics and minimization of system transients. This paper presents the simulation, modeling, and transient analysis of conventional and advanced aircraft electric power systems with harmonic mitigation using passive harmonic filters. The aircraft electric power system is analyzed considering equivalent passive AC and DC loads under transient and steady state operating conditions. The electric power source is simulated by a controlled motor-generator set to provide a constant frequency and a constant output voltage source. The DC power is generated using 12-pulse converters. Moreover, to mitigate the harmonics generated by the converters a passive input filter is designed to meet the harmonic standards for the AC side of the aircraft electric power system.

VSCF aircraft electric power system performance with active power filters

A three-phase three-wire shunt active power filter (APF) is presented to regulate the load terminal voltage, eliminate harmonics, correct supply power-factor and balance the nonlinear unbalanced loads. A three-phase based current controlled voltage source inverter is used as an active power filter. The control algorithm for the APF is based on the perfect harmonic cancellation method which provides a three-phase reference supply current in phase with its positive sequence fundamental voltage component. The APF is used in the 90-kVA advanced aircraft electric power system under variable-speed constant-frequency (VSCF) operation. The generator output voltage frequency is varied from 400-Hz to 800-Hz for different loading case-studies. Non-linear DC loads are included in the simulation of the aircraft system in addition to the different passive and dynamic loads. The power quality of the studied aircraft electric system is shown to comply with the newly aircraft electrical standards MIL-STD-704F and the IEEE-std 519.

Power quality investigations of VSCF aircraft electric power systems

A model of the advanced aircraft electric power system is developed and studied under variable-speed constant-frequency (VSCF) operation. The frequency of the generators output voltage is varied from 400-Hz to 800-Hz for different loading case-studies. Non-linear DC loads in addition to the different passive and dynamic AC loads are included in the simulation of the VSCF aircraft electric power system. Power conversions are obtained using 12-pulse converters. Moreover, two high-pass passive filters are designed and compared according to their loss and effectiveness in reducing the harmonic contents of the generator output waveforms. The power quality characteristics of the studied VSCF aircraft electric power system are presented and the effectiveness of the proposed filters is demonstrated through compliance with the newly published aircraft electrical standards MIL-STD-704F.

Modeling and characterization of an aircraft electric power system with a fuel cell-equipped APU paralleled at main AC bus

In this paper a More Electric Aircraft (MEA) electric power system is modeled and simulated with a fuel cell/battery hybrid Auxiliary Power Unit (APU). Fuel cell/battery hybrid power source is connected at the AC-load bus bar of 200-VAC and 400-Hz. Due to the DC output of the hybrid power source, a 12-pulse inverter is used at the output of the APU. The two output voltages of the generator-channel inverter and the hybrid-source inverter must be synchronized. The output of the fuel cell is controlled using a DC/DC boost converter to provide the aircraft DC bus voltage of 270-V. The battery is controlled by using a bidirectional DC/DC converter to provide the excess load when necessary and be charged from the fuel cell during normal operating conditions. To make the aircraft electric power system compatible with the aircraft standards, an active power filter (APF) is connected at the synchronous generator terminals. The APF reduced the total harmonic distortion (THD) of the generator voltage and current to be within the standard values. The studied aircraft electric power system with the proposed fuel cell/battery hybrid system is simulated without and with the presence of the APF and it is found that the APF reduced the voltage and frequency transients of the system and improves the aircraft electric system performance

Voltage stability modeling and analysis of unbalanced distribution systems with wind turbine energy systems

This paper presents a new method to asses voltage stability of unbalanced distribution systems with wind turbine generation systems (WTGSs). In the voltage tracing process, the Lagrange linear and quadratic interpolations have been applied to predict voltage magnitudes and phase angles. The predicted solutions are then corrected using the unbalanced three-phase forward/backward power flow solver. The solution process continues until the maximum loading conditions of the system under study are reached. The salient advantage of the method is avoiding construction of massive augmented three-phase Jacobian matrix of the classical Newton-Raphson method. The direct connected WTGSs have been modeled with sufficient details to account for distribution system unbalances and slip variations. Substation transformer tap-setting for voltage regulation is also considered. Voltage collapse scenarios are investigated for unbalanced systems using various unbalanced radial feeders. The results show the robustness of the proposed continuous power-flow method for voltage stability of power distribution networks. Assessment of the obtained results shows that WTGSs of synchronous generator types are more robust than those equipped with induction generators from the point of view of voltage stability.

Characterization and Performance Evaluation of Advanced Aircraft Electric Power Systems

A model of an advanced aircraft electric power system is developed and studied under variable-speed constant-frequency (VSCF) operation. The frequency of the generator’s output voltage is varied from 400-Hz to 800-Hz for different loading scenarios. Power conversions are obtained using 12-pulse power converters. To reduce the harmonic contents of the generator output waveforms, two high-pass passive filters are designed and installed one at a time at the generator terminals. The performance of the two passive filters is compared according to their losses and effectiveness. The power quality characteristics of the studied VSCF aircraft electric power system are presented and the effectiveness of the proposed filter is demonstrated through compliance with the newly published aircraft electrical standards MIL-STD-704F.