Xiaoyu Lang

Dual-Generator power systems have attracted increased attention in recent years as it can significantly reduce the fuel assumption of aircraft engines allowing power transfer between different engine shafts. In such a system, two generators supply a common DC bus together. A DC-bus capacitor is required to filter switching harmonics to ensure that the DC-bus voltage satisfying MIL-STD-704F standard. Due to the high current rating, this capacitor is normally bulky and heavy. This paper aims to introduce a switching harmonic cancellation method which can effectively reduce harmonics at the DC bus. This, in return, will extend the lifetime and reduce the weight of the dc-bus capacitor. With the assumption that power converters connected to the DC bus are modulated with the commonly used space vector pulse width modulation (SVPWM) technique, a simplified mathematical model to estimate both first and second switching harmonics is developed. Based on the proposed models, an advanced method of switching harmonic cancellation scheme is proposed through an adaptive phase shift of carrier signals for different power output of converters. Both simulation and experimental results are used to validate the proposed model and the suppression method.

Wide-speed range operation capabilities in both motoring and generation modes are essential for an aircraft electrical starter/generator (ESG) drive system for more-electric aircraft applications. When running as a generator, the ESG is supplying power to the main HVdc bus within the onboard electrical system. A fast and robust dc bus voltage would be beneficial to electrical loads connected to it. In this article, an active disturbance rejection control (ADRC) is proposed to realize a fast and robust regulation of onboard dc bus voltages. The ADRC is achieved with a second-order extended state observer (ESO) to generate torque reference for the ESG. All the key characteristics, such as the stability of ESO, dc voltage tracking performance, and disturbance rejection capability of the ADRC for aircraft ESG applications, are thoroughly analyzed. To enhance system stabilities, an innovative and simple design method for the ADRC and ESO gains is introduced based on the gain-margin and phase-margin criteria. Experimental results have shown that, compared with the conventional PI-based dc voltage control, the proposed method can realize a faster and more robust dc voltage control.

This article presents an instantaneous power control (IPC) to regulate the power flow of a back-to-back converter (BTB converter) within an advanced power generation center (APGC) for more-electric aircraft applications. The APGC essentially is composed of two power generation channels (each channel is with a permanent magnet generator driven by two different engine shafts and an ac/dc converter) with a BTB converter connected in between. The BTB converter allows power transfer between these two channels and thus two different shafts of an aircraft engine. Control of the power transfer was achieved using the phase current synchronization (PCS) method where current flowing through the BTB converter is controlled to be in phase with that of one generator within the APGC. In this article, we propose an improved IPC technique. Compared with the previously proposed PCS method, the IPC method enables independent control of active power and reactive transferred from one channel to the other. The IPC also allows improved dynamic response in power control and elimination of tedious tuning of control parameters. The effectiveness and performance of the proposed IPC method are compared with those of the PCS method in terms of power control within the APGC in both simulation and experiments.

In the high-power settings of engine, such as maximum take-off, more power should be extracted from the high-pressure spool of engine (HPS) than the low-pressure spool of engine (LPS) to avoid the overspeed and potential instability of the HPS. However, as revealed in this article, extracting more power from the HPS will degrade the onboard high-voltage direct current (HVdc) grid stability for the conventional single dc bus power generation center. To address this conflict, in this article, an advanced power generation center (APGC) incorporating an extra back-to-back (BTB) converter is introduced to improve the stability for both engine and HVdc grid. The BTB converter connects the HP power generation channel and the LP channel, providing an additional power flow path between the HP channel and LP channel. A transfer function-based impedance model and a state-space model of the HVdc grid are proposed to study the HVdc grid stability. The analytical findings of the HVdc grid stability and stability improvement using the APGC architecture have been verified through simulation and experimental results.

This article presents a control scheme for a recently reported aircraft advanced power generation center (APGC) during postfault operation conditions. Within the APGC, two electrical generators extract power from two separate engine shafts and supply electrical power to a common high-voltage direct current (HVDC) bus through their dedicated main ac/dc power converters. An extra back-to-back (BTB) converter is also used to connect the ac terminals of the two generators. This architecture provides merits of fault tolerance capabilities of the APGC. In the case of main ac/dc power converter failure, the system can be reconfigured and the BTB converter provides an extra power flow path from the generators to the HVDC bus. This ensures electrical power generation capabilities onboard. This article discusses in detail about the control of the APGC under fault conditions with one main ac/dc converter failure. A seamless transition scheme from normal operation to postfault conditions is proposed using a voltage command initialization technique within the BTB converter. Both experimental and simulation results have verified the fault tolerance improvement and control performances of the APGC.

Dual three-phase permanent magnet synchronous machines (DTP-PMSMs) have received increasing attention from the industry and academia due to their advantages in lower burden on power inverters when operating in high power applications compared to the three-phase counterparts and low torque ripples. In this article, it reveals that the favorable low torque ripple characteristic of DTP-PMSM is undermined in the high power and overload operating mode. To solve this problem, this article proposes a novel torque ripple suppression strategy based on optimal harmonic current injection. A mathematical torque ripple model of DTP-PMSM considering the cross-coupling effects between d–q axis and dq - z ₁ z ₂ axis is built. And based on this model, a detailed analysis is carried out to obtain the optimal harmonic current. The theoretical analysis also guarantees that the induced machine loss is minimum. Moreover, the proposed strategy has good dynamic performance since the algorithm involves no iterative computation and is computationally effective, which is proved on a laboratory DTP-PMSM system. The effect of parameter variation is also discussed and tested. The experiment results prove that the influence of magnetic saturation on torque ripple can be effectively suppressed.

Conventional finite control set model-predictive control (FCS-MPC) presents a high computational burden, especially in three-level neutral-point-clamped (NPC) converters. This article proposes a low-complexity optimal switching time-modulated model-predictive control (OST-M2PC) method for a three-level NPC converter. In the proposed OST-M2PC method, the optimal switching time is calculated using a cost function. Compared with the conventional FCS-MPC, the proposed OST-M2PC method has a fixed switching frequency as well as better power quality. The proposed OST-M2PC can operate at a 20-kHz sampling frequency, reducing the computational burden of the processor. Simulation and experimental results validate the operation of the proposed method.

One of the main areas of research for the More Electric Aircraft (MEA) is mounting a generator on the low-pressure shaft in addition to the starter/generator mounted on the high-pressure shaft. Given that there are electrical machines on both the low-and high-pressure shafts, there is an “electrical bridge” to establish power exchange between the shafts. Potential improvements in the engine performance in terms of fuel consumption, engine stability and compatible thrust with flight mission at various flight scenarios under such transfer, have been studied and discussed in the literature. To prove the concept and demonstrate the practicality of power transfer, an engine emulator has been constructed. The emulator will replicate basic behavior of the engine by using similarity analysis to allow for conducting tests in a scaled environment without the need for an actual physical engine. A unique time-scaling technique is implemented to synchronize the time of the engine model and the test rig for transient studies. This enables scalable flexible engine emulation at different power generation ratings. A new criterion composed of shaft inertia, time and speed scaling factors, is also introduced to assess the validity of shaft inertia emulation. The experimental results are reported to demonstrate and further discuss the feasibility of electric power transfer between the engine shafts.

This paper proposes an improved power generation architecture (PGA) for future more electric aircraft (MEA) applications. In the proposed architecture, a starter/ generator is connected to the high-pressure (HP) shaft, and a generator is connected to the low-pressure (LP) shaft. Their outputs supply a common DC bus via active rectifiers. A back-to -back (B2B) converter is deployed to link the AC terminals of the two generators. The proposed topology embraces three main advantages. Firstly, with the B2B converter, the HP generator can operate at a high speed without flux weakening, thus the magnitude of stator current will be decreased when output same active power. This will lead to the reduction of power losses on the generators and the active rectifiers. Secondly, the proposed architecture allows power transfer from the LP and to HP shafts. This can potentially reduce the fuel consumption and increase aircraft engine compressor surge margins when engine is at low speed setting. Thirdly, the B2B converter provides an additional power flow path to the generators under converter fault scenarios, hence improving the post fault operation ability. For the proposed PGA, engine benefits, modelling, control design and efficiency improvements are illustrated in detail. The control performances of the proposed PGA, engine performance improvement by transferring power from the LP to HP shaft, and power loss reduction are verified through simulations and experimental results collected from a twin-shaft aircraft power generation test rig.