The excellent steady state and dynamic performance are also required. Therefore, high-performance PMSM control in the focus of comprehensive research during the last decades, and still continues to receive a great attention from the researchers.The most established control strategy for PMSMs consists of cascaded control loops, typically with an inner loop for current regulation and an outer loop for speed control. It can be argued that the current control loop has a major effect on the overall system performance [7,8]. Therefore, many studies that investigate various current control (CC) schemes are reported in [9][10][11] . In general, it can be stated that the field of CC is dominated by synchronous reference frame (SRF) proportionalintegral (PI) CCs. Their success is mainly due to the inherent simplicity in their design and implementation.The main challenge with SRF PI CCs deals with the fact that their optimal operation depends heavily on the accurate knowledge of the machine parameters, required to design and tune the PI CCs correctly [8,12,13]. Any errors or uncertainties in machine parameters significantly affect the drive performance.The challenge is that the machine parameters may significantly vary during the operation, especially in harsh environment such as in aircrafts. These parameters depends on various effects including temperature, pressure, load, saturation, cross saturation and operating frequencies [14,15]. Manufacturing processes may introduce discrepancies in the machine parameters with respect to the nominal values [16]. It is therefore clear that all these internal disturbances, in addition to the external disturbances, can lead to degradations of a PMSM drive performance [3,16,17].Currently, several methods to estimate and address disturbances are known. State observers (SO) and disturbance observers (DOB) have a long history of being used to overcome the effects of external disturbances [16,18]. Traditionally, these have been implemented to address the effects due to external disturbances, however a SO can also be used to estimate internal disturbances such as variations of machine parameters. An "extended state observer" (ESO) is proposed in [19] introducing active disturbance rejection control (ADRC). The basic idea of the ADRC is to consider uncertainties, unmodeled dynamics and external disturbances as a total disturbance which is estimated in real time by ESO. Then, an ESO-based feedback control is used to compensate the total disturbance and to keep the system output matching the

Multilevel converters have been used for aircraft electric starter/generator (ESG) systems due to their high power qualities. One of the desirable topologies is the three-level neutralpoint-clamped (3L-NPC) converter. Our studied ESG system operates at a high speed during its generation mode, which results in high modulation index (MI) and puts some specific challenges on neutral-point (NP) voltage balance, especially under low power factor (PF) load conditions. Moreover, common-mode voltage (CMV) needs to be addressed properly as it leads to irreversible damage of motor shaft bearings, thereby degrading the efficiency and reliability of the entire system. Compared with the conventional nearest-three virtual space vector (NTV 2 ) technique, the proposed modulation scheme employs three adjacent medium vectors to synthesize a new medium vector and two pairs of large vectors to compose new small vectors. This allows the presented modulation scheme to achieve balanced capacitor voltage and reduced CMV at the same time. In addition, the torque ripple of the proposed modulation strategy is thoroughly compared and analyzed. Meanwhile, in order to overcome the heavy computational burden, a fast calculation approach is adopted to simplify the algorithm. Simulation results obtained from Simulink/PLECS and experimental results obtained from a 45 kW, 32 krpm aircraft ESG system verify the effectiveness of the proposed strategy in more-electric-aircraft (MEA) applications.

Synchronous reference frame proportional-integral (PI) current controller (CC) is considered the most well-established solution for the current regulation in electrical drives. However, the gain selection of the PI CC is still regarded to be poorly reported, particularly in relation to the effect of the inevitable execution time taken by the controller and inverter. Mostly, tuning process of PI CC is done by trial and error or using simple rules based on pole zero cancelation and pole placement methods which ignore time delays through the controller and inverter. Hence, PI CC delivers significantly different performance compared to the expected one during the digital implementation, especially if high bandwidth or low ratio between the switching and operational frequency are required. Therefore, this paper firstly addresses and analyses the common tuning rules of PI CC which ignore the existence of time delays followed by a rigorous analysis for PI CCs' robustness to the influence of computational and modulation delays. Based on this analysis, generic recommendations have been proposed to select the PI CCs' gains as a function of the electrical drive switching frequency considering the delay effect. A set of simple, generic, and fast tuning rules were derived that guarantee fast dynamic performance with reasonable stability margins. Moreover, the effects of model uncertainties on these developed rules have been analyzed and reported. Comprehensive experimental results are provided to prove the key analytical results of this study and to validate the proposed design recommendations.

This paper presents the operating characteristics of surface-mounted permanent magnet synchronous machine taking into account the influence of stator resistance and inductance variation at high frequencies, whose effect are always neglected in the previous research papers which deal with the operating limits during the flux weakening. First, the machine dynamic equations in d-q reference frame considering the effect of high operating frequency on stator resistance and inductance is discussed based on experimental data. Then, the stator voltage constraint is deduced in the current plane as a function of the stator resistance to study the influence of parameters variation on the operating characteristics. Finally, results are compared with the case of neglecting the resistance and inductance variation at high frequencies. Keywords -Flux weakening control, permanent magnet synchronous machines, high frequency operation, voltage and current constraints NOMENCLARURE , d-q axis component of stator voltage , d-q axis component of stator current Stator resistance Permanent Magnet flux Linkage , d-q axis component of stator selfinductance Electric rotor speed in rad/s Electromagnetic Torque Maximum phase stator voltage Maximum phase stator current I.

In this paper, a virtual space vector (VSV)-based overmodulation algorithm is presented for three-level neutralpoint-clamped (3L-NPC) converters in high-speed aerospace motor drives. With the proposed inscribed polygonal-boundary compression technique, the output voltage capability is enhanced under a lower crossover angle and compression coefficient. As a result, it brings an opportunity for the operation of the studied aircraft electric starter/generator (ESG) systems easily extending from the linear modulation range into the overmodulation region. Furthermore, an active capacitor voltage balancing control method is investigated to recover neutral-point (NP) potential imbalance in the case of high modulation index and low power factor operating conditions. To simplify the digital implementation of the algorithm, a fast calculation approach is adopted in this work. The modulation performance of the proposed strategy is verified by both simulation and experimental results with a 45 kW, 32 krpm ESG prototype system. Index Terms-High-speed motor drives, more-electric-aircraft (MEA), neutral-point voltage, overmodulation, three-level.

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Recently, Active Disturbance Rejection Control (ADRC) Scheme has been widely used for current regulation in AC drive systems owing to its robustness to system uncertainties and its high disturbance-rejection capability. However, it has not been considered as an option for high-speed drives usually operated at limited switching and sampling frequencies. Therefore, this paper thoroughly analyses and discusses the effects of high operating speed, modulation, and computational delays on the conventional ADRC. Based on this analysis, an enhanced ADRC for the current control is proposed to operate the drive system at low sampling time ratio with high robustness to the internal and external disturbances. Effect of model uncertainties on the proposed scheme has also been analytically analyzed and reported. Comprehensive simulation and experimental results have been presented to demonstrate the improved performance of the proposed ADRC scheme and to support the analytical studies.

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