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This paper investigates and proposes a mitigation strategy for denial-of-service (DoS) cyber-attacks, targeting the most critical distributed energy resource (DER) in an islanded microgrid featuring a high penetration of renewables; the energy storage system (ESS) operating as the isochronous generator that forms and regulates the microgrid voltage and frequency. A rule-based fallback control strategy is proposed to enhance the resiliency of the microgrid to DoS cyber-attacks by managing the ESS state-of-charge in a decentralized manner, such that it can continue operating as the isochronous DER, while dispatching the remaining DERs in a centralized manner. Supplementary control loops are added to the ESS to manage and coordinate, using local frequency signals, with the remaining DERs, whose local controllers are specifically designed to provide frequency support in the event of DoS cyber-attacks. The proposed scheme is applied on a 25 kV islanded microgrid under two configurations, synchronous machine-based and 100% inverter-interfaced, and its effectiveness is validated on a real-time hardware-in-the loop testing platform.

This paper proposes a torque cancelation strategy for a nonisolated three-phase integrated battery charger topology for light and medium duty electric vehicle drives based on six-phase permanent magnet (PM) synchronous machines. The charger requires a three-phase grid interface and utilizes the machine windings as the input filter inductances after minor reconfiguration. The drive power electronics are used to control the currents drawn from the three-phase grid. The current flowing through the machine windings induces a torque on the PM machine rotor which is eliminated by the proposed torque cancelation strategy in battery charging mode. The torque cancelation strategy is general and works with both symmetric and asymmetrically wound six-phase PM machines. The strategy is also capable of eliminating the torque when the rotor is displaced from the stator $d$ -axis. The linear quadratic regulator with the integral action control scheme is used to accommodate for the asymmetry caused by the dependence of winding inductance on the rotor position. Co-simulation results with Finite-Element Analysis and hardware experiments show the topology based on six-phase PM machines can be used to charge or discharge the battery for grid support functions while the torque on the machine shaft remains canceled.

The output current ripple of an inverter shows different variations for sub-fundamental operating cycle and over few fundamental cycles. This paper investigates subfundamental cycle peak-peak current ripple variation of a three-level three-phase inverter over the entire operating modulation index range for the three-level continuous and discontinuous pulsewidth modulation strategies. Furthermore, based on the analytical current ripple variation, a strategy is presented to change the switching frequency within a fundamental cycle while maintaining the peak-peak current ripple similar to the conventional fixed switching frequency strategies. The strategy has been implemented and experimentally validated on a permanent-magnet synchronous motor drive. The results demonstrate that the proposed strategy reduces inverter switching instances and associated losses around 10–30%.

The study proposes a non-isolated three-phase integrated battery charger (IBC) based on electric vehicle drivetrains that have two permanent magnet synchronous motors with shafts coupled via a torque coupler. The windings of both machines are used as input filter inductances after reconfiguration and connected to a three-phase grid in charging mode. Their existing traction inverters are operated as a three-phase charger that controls the charging power from the grid. The total torque produced on the shaft during operation is analysed and a strategy to eliminate it is proposed. The strategy not only maintains a zero-average torque but also eliminates the pulsating torque component on the shaft during operation. The topology allows conversion of the existing drive to an IBC through minor reconfiguration and provides an opportunity to reduce the effective THD injection into the grid via interleaving for machines with low winding inductance. A power balancing control is also proposed to reduce the second harmonic on the DC power output due to machine non-ideality. Simulation and experimental results validate that the topology can be used as both a battery charger and as a distributed resource, while the resultant torque on the shaft remains eliminated by the proposed strategy.

This paper proposes a method to vary the switching frequency within a fundamental cycle to reduce the switching losses of a two-level inverter while maintaining the peak–peak current ripple within a predefined limit. Unlike conventional strategies, the proposed technique utilizes precomputed switching frequency variation factors without relying on prediction or optimization techniques, since the peak–peak current ripple follows a definite trajectory within a fundamental cycle. Moreover, the variation in switching frequency is further controlled based on the operating carrier ratio and modulation index. The proposed strategy has been validated through both the simulation and experimental results on a permanent magnet synchronous motor drive for the space vector and discontinuous pulsewidth modulation patterns, and the results demonstrate that it reduces the two-level inverter switching losses up to 15%.

Conventional three-level discontinuous pulsewidth modulation (DPWM) templates typically provide maximum switching loss reduction capability for load power factor angles in the range from 30° lagging to 30° leading. This paper proposes three space-vector-based DPWM templates for lower power factors and a generalized DPWM strategy for three-level inverters operating with modulation indices lower than 0.5. For different power factors, the proposed strategy adapts the inverter pulse sequence by combining different portions of the proposed and conventional DPWM templates within one operating fundamental cycle and ensures minimum switching instances when changing templates. Consequently, the strategy aligns the PWM clamping intervals with the respective load-current peaks, achieving around 50% switching loss reduction capability extended to all operating power factor angles (90° lagging to 90° leading). The simulation and experimental results demonstrate the effectiveness of the proposed three-level generalized DPWM strategy over the conventional three-level modulation strategies.

This paper proposes a dual three-level, T-type, neutral-point clamped (T-NPC) inverter fed dual permanent magnet synchronous motor topology for low-voltage, high-power traction applications. The switching pulses of the T-NPC inverters are interleaved and controlled, such that they produce equal and opposite three-phase currents at their output. This maintains balanced dc-link voltages in steady-state and transient conditions, even with slight mismatches between two sets of three-phase loads. Thus, the proposed configuration decouples the modulation strategy from the capacitor balancing control. Simulation and experimental results demonstrate that in comparison to the conventional single T-NPC inverter, the proposed topology reduces dc-link capacitors’ voltage deviation and current stress by more than 90% while avoiding additional switching instances to balance capacitor voltages.

The emerging trend for electric utilities to install wind-based generation on a large scale into distribution networks, employing a doubly fed induction generator or full-converter turbine technologies is raising issues for distribution planning engineers with regard to flicker among other power-quality (PQ) issues. This paper investigates dynamic volt/var control, a viable flicker mitigation technique which exploits the reactive power capabilities of modern power-electronic interfaced wind turbine generators. Dynamic volt/var control essentially mitigates flicker by solely dispatching reactive power based on voltage fluctuations within the flicker frequency band. This technique can be incorporated as part of a wind farm multiobjective reactive power-control scheme, which facilitates regulating: 1) the voltage level at the point of common coupling (PCC), employing slow-acting voltage control or power factor control and 2) the flicker level at the PCC with fast-acting dynamic volt/var control. This two-level approach can reduce the wind farm flicker level up to 80% and maintains the voltage level at the PCC well within acceptable bands. The results presented in this paper focus on a typical 25-kV medium-voltage distribution feeder integrating wind-based generation on a large scale. The performance of the two-level controller was tested for varying levels of penetration and wind speed conditions. The applicable standards and utility grid-code requirements are considered throughout.

This paper proposes the real-time implementation of an energy management system (EMS) optimization sequence and enumerates a set of performance metrics for grid-connected microgrids. The operation and performance of the proposed microgrid EMS is validated using a real-time hardware-in-the-loop (HIL) testing platform. The test system emulates the microgrid network, the distributed energy resources (DER) and their corresponding local controllers on a real-time-digital-simulator (RTDS). The microgrid EMS script under evaluation runs on a desktop computer and interfaces the RTDS through a separate digital controller. Real-time simulation results are used to quantify the performance of a grid-connected microgrid EMS in terms of power import constraints, the levelized cost of energy and fuel consumption provided by the DER scheduling algorithms. A utility 25 kV distribution test-line featuring a Type-4 wind turbine generator (WTG), battery energy storage system (BESS), diesel generator and controllable loads has been used for the benchmark test system.

Battery chargers for plugin electric vehicles can be costly and add to the weight and volume of the vehicle when designed to be on-board. Conversely, integrated battery chargers not only re-use the already available components on-board but also provide a higher charging power capability than their dedicated counterparts. Such chargers use the traction motor's windings as input filter when connected to the three-phase supply. Surface mounted permanent magnet motors have not been used for integrated battery chargers for the apparent risk of rotor movement while charging. This paper demonstrates the use of a surface mounted permanent magnet motor to charge the battery while identifying the limiting factors of its implementation. The maximum torque (70Nm) developed on the rotor while charging is calculated using an FEA model of the motor and is found to be within the limits that a vehicle can withstand. Efficiencies up to 97% with an acceptable THD was achieved with a scaled down power version of the charger.

This paper investigates various random PWM (RPWM) techniques for conventional two-level inverter-fed traction drives and proposes a discrete RPWM technique for acoustic noise reduction. The proposed RPWM technique randomizes within a set of predefined switching frequencies compared with the continuous nature of randomization in conventional RPWM techniques. The proposed method was compared with conventional SVPWM and other RPWM techniques with respect to the A-weighted IEC 61672-2013 standard acoustic noise profile. The proposed RPWM method spreads the narrowband harmonic clusters effectively and, compared to the conventional RPWM techniques, reduces broadband noise by 2–6 dB over the full modulation index range, thus producing a better acoustic noise profile.

The interconnection of Type-4 wind farms into weak distribution feeders may result in voltage rise and flicker concerns. This paper investigates a wind farm control scheme employing a slow-acting reactive power controller to regulate the steady-state voltage at the point of common coupling (PCC) and a fast-acting active power controller, streaming from an embedded energy storage system (ESS) to mitigate flicker at the wind turbine terminals. Real-time hardware-in-loop (HIL) results have been obtained for the proposed power control strategy, emulating the distribution-feeder and wind turbines on a real-time digital simulator (RTDS) and the power control loops on a digital controller, communicating using the IEC 61850 GOOSE Messaging protocol. Flicker studies are conducted on a 25 kV distribution feeder using a flickermeter compliant to the IEC 61000-4-15 standard. Results demonstrate a short-term flicker level reduction up to 83%. Applicable utility grid codes and standards are considered throughout.

The use of six-phase motors is an attractive option for electric and hybrid electric vehicles due to its modularity. Demand for high power density and lower costs for electric traction drives has led to the idea of integrating the battery charging function into the traction drive. When the main battery for dual motor type electric and hybrid electric vehicles is being charged, the equivalent power converter system is two converters that act as rectifiers and are connected in parallel. Feeding these converters from the AC grid with interleaved discontinuous PWM schemes can result in the appearance of a significant amount of circulating current flowing between the converters. Such circulating current increases converter component stresses and reduces battery-charging efficiency. In the paper, a PWM scheme based on discontinuous PWM methods is proposed to mitigate this circulating current. The proposed scheme does not require additional passive elements and maintains the benefits of discontinuous PWM. Simulation and experimental results are presented to validate the proposed scheme.

This paper proposes reduced switching random PWM (RPWM) techniques based on Space Vector PWM (SVPWM) technique for conventional two-level inverters. In the proposed RPWM techniques, the switching frequency is randomized within a band lower than the nominal switching frequency at and around the peaks of the three-phase output currents. For the rest of the fundamental cycle, the switching frequencies are randomly selected within a band higher than the nominal switching frequency. The proposed method is able to spread the narrowband harmonic clusters similar to the conventional RPWM techniques and additionally produce less inverter output current distortion than conventional spread spectrum techniques. The proposed technique has been analyzed and has been verified using experimental results.

The deployment of modern DFIG or full converter turbine technologies on a large scale into distribution networks is raising issues for electric utilities with regard to voltage rise and flicker amongst other power quality issues. This paper proposes an real-time reactive power coordination scheme employed with the voltage control technique, the concurrent means for achieving both voltage regulation and flicker mitigation at the wind farm point of common coupling (PCC). Noting that each wind turbine generator (WTG) comprising the wind farm operates in a different state, wind condition dependant, the instantaneous reactive power capabilities of each WTG differ. Based on the estimated real-time instantaneous reactive power available from each WTG, a wind farm Q dispatcher is proposed to fully utilize the DFIG turbine power converter capabilities in order to avoid active power curtailment and maximize energy production. Exploiting the reactive power capabilities of the rotor side converter (RSC) and grid side converter (GSC), the proposed control strategy regulates the voltage level within acceptable bands and reduces the flicker level by up to 90%. The real-time simulation results presented in this paper focus on a 6 MW wind farm being connected to a rural 25 kV distribution feeder, considering the applicable utility grid code requirements.

The demand for higher power density in electric traction applications has led to compact design requirements for traction drives complicating its thermal management. Therefore, the traction drive's thermal management has to be addressed by its design and/or control. Normally, the traction inverter becomes the bottleneck in providing the transient rated peak torque at zero and near zero speeds due to peak current conduction for longer fundamental frequency cycles. This paper presents thermal management strategies based on both current limitation and on an alternate modulation scheme that redistributes the losses between the IGBTs and diodes of the highest current carrying leg at very low modulation indices. The presented strategies avoid or delay the over-temperature junction failure due to high conduction losses. The proposed strategies enable the drive to provide the rated peak torque at zero or near zero speeds while avoiding or delaying thermal failure.

This paper introduces a new method of IGBT switching loss reduction on the system level, while leaving the PWM scheme completely unchanged. The switching loss reduction is achieved by designing an IGBT gate driver that dynamically sets the IGBT gate current depending on feedback signals from IGBT current, IGBT voltage, phase load current, and DC link voltage if it is not constant in the application. Factors influencing switching losses will be demonstrated for two types of output driver stages: one with discrete switching speed setting and one with continuously variable switching speed. Comparing to other gate driver types with or without feedback aimed at keeping constant dv/dt, di/dt, and overshoots of IGBT voltage and current, the proposed gate driver not only ensures the operation of an IGBT in the safe operating area (SOA), but also improves the SOA utilization density by tracking the programmed voltage and current limits using peak-detection circuitry while minimizing the switching losses. Adaptive feedback control algorithms have been developed and verified by simulations. Keywords—gate driver; variable current output stage; IGBT switching loss; adaptive control algorithm I. INTRODUCTION Discrete IGBTs and IGBT modules are used in high- voltage applications mainly to perform DC to AC power conversion and vice-versa. The conversion losses dissipated by devices in form of heat consist of three sources: conduction losses, leakage current losses, and switching losses. The first two sources usually cannot be varied as long as appropriate extreme levels of gate-emitter voltage are applied to the IGBT. The switching losses, on the contrary, can be widely varied by using different modulation schemes, switching frequencies, and gate drivers. The topic of this paper is about development of a closed-loop gate driver with the task of minimizing switching losses while keeping the IGBT in the SOA.

This paper studies the dual three-phase inverter configuration for an electric vehicle drive feeding a dual three-phase permanent magnet synchronous machine. Employing interleaved SVPWM and DPWM modulation techniques with the proposed configuration, the input capacitor ripple current has been substantially reduced to 50–60 % compared to that of a conventional 2-level VSI. The optimal interleaving angles have been identified for capacitor ripple reduction considering both modulation indexes and power factors pertaining to the traction motor's operating range. The dual three-phase inverter's switching losses have been analyzed for two different DC-link voltages and output power levels and a 15–20% reduction in switching loss has been noted.

This paper describes possible incorporation of a modular multilevel inverter (MMI) for a low voltage low-medium power electric vehicle drive. The main focus of this work is essentially to justify the MMI topology as a viable alternative to the classical 2-level voltage source inverter in an electric vehicle drive due to its highly efficient operation. MMIs are viable alternatives for use in low and medium power applications due to lower power dissipations in the switches, low harmonic contents, modularity and outputs with lower electromagnetic interference (EMI). The MMI discussed is based on the half-bridge topology. The modes of operation and different control features have been reviewed. The capacitive voltage unbalance phenomenon is discussed and few balancing techniques are reviewed. Different PWM techniques and switch utilization of the half-bridge topology are also reviewed. A comparative study of two level VSI and 3, 5 level MMI is discussed in the context of conduction and switching loss reduction.