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This paper investigates the influence of power semiconductor parasitic components on the ground leakage current in the three-phase Current Source Inverter topology, in the literature called H7 or CSI7. This topology allows reducing converter conduction losses with respect to the classic CSI, but at the same time makes the topology more susceptible to the parasitic capacitances of the semiconductors devices. In the present work, a grid-connected converter for photovoltaic power systems is considered as a case study, to investigate the equivalent circuit for ground leakage current. The same analysis can be extended to applications regarding electric drives, since the HF model of electric machines is characterized by stray capacitance between windings and the stator slots/motor frame. Simulation results proved the correctness of the proposed simplified common-mode circuit and highlighted the need of an additional common-mode inductor filter in case of resonance frequencies of the common-mode circuit close to harmonics of the power converter switching frequency. Experimental results are in agreement with the theoretical analysis.

Current source inverter (CSI) is a class of power electronic converters that, thanks to the inherent boost capability and ease of control, is investigated for grid-tied photovoltaic power conversion applications. Traditional CSI and CSI7 topologies are here analyzed and compared with two kind of space vector modulation strategies mainly in terms of ground leakage current both in simulations and experiments. Furthermore, THD of the injected grid current and the computation of conduction and switching semiconductor power losses are also carried out in numerical simulations. The topology comparison is carried out with the use of a different number of PV modules, to analyze the robustness of the topologies to different size of the PV strings. Simulation and experimental results show that the CSI7 topology, with respect to conventional CSI, allows to strongly reduce ground leakage current, phase current THD and semicondutor power losses, at the price of an additional power device.

Voltage Source Inverters (VSIs) are usually adopted for high-speed motor drive applications due to the topology simplicity and the wide availability of control strategies for this topology. An alternative is the Current Source Inverter (CSI) which allows to achieve high speed range with limited DC voltage due to its intrinsic boost capability, and this is of interest in aerospace applications or electrical vehicles (EV), but a pre-stage is necessary to control the DC input current. In this work an hybrid solution is proposed to extend the speed range of a single stage CSI (i.e. CSI without pre-stage) driving a Permanent Magnet Synchronous Machine (PMSM). In fact using a single stage CSI with DC current control, the machine cannot work properly in low speed region, so the control is composed by two different strategies: one is proposed in this work for low speed operations and the other one is already known for high speed.

The current source inverter (CSI) is a power electronics topology that allows for the realization of variable speed drives (VSD). Compared to the most common voltage source inverter (VSI), which can be directly connected to a voltage source, the CSI needs a prestage to generate a constant current bus. This article therefore seeks to challenge this “accepted” consideration that a CSI always needs this precircuit and seeks to remove this circuit by proposing an innovative $i_{dc}$ current control scheme. The proposed scheme is applied to a single stage motor drive driven by a CSI converter. It is shown how implementing this control scheme removes the need for the front-end stage, thus removing an unnecessary converter and optimizing the efficiency at the same time. The CSI state-space equations are presented and the developed models are verified using simulations. Stability analysis of small-signal model is considered through Nyquist criterion with the robustness in presence of variations of the most important system parameters. Experimental results driving a permanent magnet synchronous machine (PMSM) are shown confirming the validity of the proposed control, potentially paving the way to a larger adoption of the CSI topologies for motor drive applications.

The Current Source Inverters (CSIs) are an alternative to Voltage Source Inverters (VSIs) for electric motor applications. Despite the advantageous characteristics of intrinsic voltage boost capability, absence of electrolytic capacitors and reduced machine voltage stress, the increased component count and the need of a pre-stage for the inductor current control have limited the adoption. For some applications which have to operate always above a base speed (e.g. pumps, actuators, fans), single-stage CSI converter with improved efficiencies have been proposed. Owing to the advantage of the direct measurement of the terminal voltage, a simple and robust sensorless control is proposed for a single-stage CSI converter. Simulations on a SiC-based CSI7 converter driving a Permanent Magnet Synchronous Machine (PMSM) confirm the validity of the proposed control, potentially paving the way to a larger adoption of the CSI7 topology for motor drive application.

This paper analyzes the relation between the ground leakage current and the power semiconductor parasitic components of a three-phase Current Source Inverter (CSI) topology named in literature H7 or CSI7. This topology is characterized by the presence of an additional switch which allows to reduce conduction power losses and decouple the DC side from the AC side during the application of the Zero current Vector to reduce ground leakage current. This work deals with the significant variation of this current depending on power converter parasitic capacitors. In this work the analysis is applied to grid-connected converters for a string photovoltaic applications, even if the behavior is the same also in case of electrical drives. The analysis is assessed by numerical simulations and experimental results with different parasitic capacitances that confirm also the validity of the proposed equivalent common-mode circuit.

Integrated power electronics for photovoltaic applications has attracted increasing interest, due to the possibility of having grid-connected photovoltaic modules with independent maximum power point tracking and high reliability. In this paper, a single-phase Current Source Inverter (CSI) is discussed for a photovoltaic application. The basic CSI topology will be explained for the sake of completeness, highlighting its main features and analyzing the ground leakage current problem, an important benchmark for photovoltaic application. A novel topology, called CSI5, is proposed in this work. The main feature is the presence of additional switches for ground leakage current reduction. The performance of the proposed topology is assessed by numerical simulation, and the experimental results confirm that this solution is able to strongly reduce the ground leakage current and conduction power losses.

Modern electrical machines, such as those employed in transportation applications are required to provide very high performance in terms of power (and torque) density and efficiency. The reality, however, is that the more these machines are “pushed” in relation to power density, the more is the probability of failure of their insulation systems, through enhanced electrical and thermal stresses. On the other hand, regardless the power density level, the electrical machine still needs to respect the certification processes set by the international standards and procedures. Unfortunately, today reliability and lifetime are still not considered as main design objective functions right from the start of the design process. This is a direct result of a gap in knowledge in terms of the precise understanding of failure mechanisms. If physics of failure models are available, then reliability can be included at all design stages. Therefore, this article proposes a method that shortens the time demanded for the thermal lifetime evaluation procedure or qualification of low-voltage electrical machines. The theory behind the method is presented and, then, experimentally validated on custom designed specimens.

Electrical motors are required to perform reliably for a certain number of hours/cycles. Assuming the insulation breakdown as the predominant source of failure, then the lifetime of an electrical machine can generally be said to correspond to that of its weakest insulation sub-system. Among all the insulation stressing factors, thermal aging is a primary source of progressive deterioration, and, eventually, failure. In order to guarantee a satisfactory lifetime, motors are designed to have thermal operational points which are always lower than their insulation thermal class. However, this design choice does not allow to maximize the exploitation of the insulation lifetime capability. Technical standards report methods for the thermal qualification of electrical machines based on accelerated thermal aging tests. Such assessment, despite enabling the insulation lifetime estimation, might require several thousand hours of testing. This paper, therefore, proposes and validates a new methodology which considerably shortens the thermal qualification of electric motors.

It is well known and widely accepted that the voltage source inverter (VSI) now dominates the world of electrical drives. Its success is probably due to its simplicity, high efficiency, and the widespread availability of VSs. This popularity has, in turn, influenced the evolution of the semiconductor industry, which has focused in recent years on devices tailored for VSIs. Thus, products such as depletion devices (normally off) and those without reverse voltage blocking have been widely marketed and used.

This paper analyzes in detail the effect of a simple solution for ground leakage current mitigation applicable to transformerless three-phase current source inverter (CSI). The circuit modification solution is assessed for both traditional CSI topology and for CSI with an additional seventh switch, in literature named CSI7 (or H7), in particular with the splitting of the dc input inductance. In the present work, the solution is applied to grid-connected converters for string photovoltaic applications: scope of the circuit modification is to provide an internal return path from the wye connected capacitors of the output CL filter. This additional return path is able to significantly reduce the ground leakage current without adversely affecting THD. The performance of the proposed solution is assessed by the numerical simulations in case of a string of photovoltaic (PV) modules and the different behavior of CSI and CSI7 topologies is thoroughly investigated. Furthermore, the definition of V-{cmZC} is assessed by applying it to the common mode equivalent circuits for CSI7 with additional return path and their validation by means of a two-step simulation. The simulation results and experimental validation shows good agreement and confirm that the proposed solution is able to strongly reduce the ground leakage current. © 2013 IEEE.

Wireless power transfer systems are characterized by a loosely coupled magnetic circuit and a power electronics interface. For the optimization of the system power factor, a compensation circuit composed of capacitors is adopted to form a resonant tank with the power coil. The behavior of the overall circuit in terms of power transfer and current/voltage waveform depends on several parameters, which can make the analysis and optimization of the system complex. This paper proposes an analytical derivation of an equivalent RLC system that greatly simplify the design in terms of Zero Voltage Switching (ZVS) regions. In addition to this, the RLC equivalent circuit allows an easy analytic calculation of the output power depending on all WPT system parameters. The analytical model will be validated by simulation results.

In an Electric Vehicle a galvanically insulated auxiliary power module of suitable power size is employed to interface the high-voltage main energy storage battery to the low voltage auxiliary loads. Such converter must be reliable, efficient and compact. Resonant converters have reached widespread application as they are characterized by high efficiency and low Electromagnetic Interference (EMI). Resonant converters are usually operated in Pulse Frequency Modulation (PFM) with fixed duty cycle. In case of high power applications characterized by wide output voltage regulation, Pulse Width Modulation (PWM) can be beneficially adopted to extend the continuous modulation operation at low output voltage / low output power. This work analyses drawbacks and critical aspects of use of PWM along with some modulation strategies able to minimize hard switching commutations in this operating condition. After a first analytical comparison, different PWM strategies are evaluated by means of numerical simulations and experimentally assessed. A Quasi-Resonant control is proposed and assessed by means of simulation, resulting in an effective solution to hard switching commutation.

This paper presents a simple solution for ground leakage current mitigation applicable to transformerless three-phase Current Source Inverter (CSI). The proposed solution is addressed only for CSI topology with an additional seventh switch, in literature named CSI7 (or H7), in particular with the splitting of the DC input inductance. In this paper the solution is applied to grid-connected converters for string photovoltaic applications. The proposed approach is to provide an internal return path from the wye-connected capacitors of the output CL filter. Thanks to CSI7 topology and modulation technique, this additional return path is able to significantly reduce the ground leakage current without adversely affecting power conversion efficiency and THD. The performance of the proposed solution is assessed by numerical simulations in case of strings with a different number of PV modules. Simulation results and preliminary experimental validation show that the proposed solution is able to strongly reduce the ground leakage current.

Current source inverter (CSI) is a family of power converters which has been recently investigated for photovoltaic power conversion in grid-tied operation, due to the inherent boost capability and ease of control. This paper assess Photovoltaic three-phase Current Source Inverters by two different CSI topologies and space vector modulation commutation strategies. Different CSI solutions are therefore analyzed by means of numerical simulations and the results are compared in terms of ground leakage current and THD of the injected grid currents. Extensive simulation results show that the CSI7 topology can improve the common mode performance while at the same time increasing the efficiency of the conventional CSI, at the price of a negligible added complexity.

This paper analyzes the performance of a grid-tied, wide power range, transformerless, modified three-phase current-source inverter (CSI), named CSI7. The CSI7 topology is here analyzed along with a suitable space vector modulation strategy able to attenuate the excitation of the output CL filter. The theoretical analysis and simple analytic expressions highlighted the performance and limitations of the topology when employed as a single-stage photovoltaic (PV) inverter, with a particular emphasis on injected grid current distortion and ground leakage current values. The inverter wide input range allows interfacing PV strings of different module count with a simple closed-loop control. The principle of operation and control is described; the viability of the CSI7 topology was assessed with simulations and extensive experiments on a full-size laboratory prototype.

The recent advanced solution in Marino, Tomei, and Verrelli (2013) to the tracking control problem for sensorless IMs with parameter uncertainties is translated on the basis of letter swap connections between the models of (nonsalient-pole surface) permanent magnet synchronous motors (PMSMs) and induction ones (IMs). The (stability proof-based) nonlinear adaptive position/speed tracking control for sensorless PMSMs (with simultaneous estimation of uncertain constant load torque and stator resistance), which is accordingly obtained by exploring and decoding the design paths in Marino et al. (2013) and which surprisingly represents a simple generalization of the controller in Tomei and Verrelli (2011) , constitutes an innovative solution to the related open problem. Illustrative experimental results are included.

This paper presents a grid-tied single phase photovoltaic microinverter based on Current Source Inverter (CSI) topology. The main topic of this work is related to the identification of a topology and a PWM strategy able to minimize the obvious issues of the basic CSI solution: efficiency and ground leakage current. The strong reduction of this last issue allows the use of the proposed solution in conjunction with Photovoltaic module in building integrated installations. Simulation results and a low voltage experimental validation present the effectiveness of the proposed solution in mitigating ground leakage currents.

On board electrical power generation continue to increase as more aircraft systems are being electrified. Increasingly power converters are the interface of power generation and electrical loads in aircrafts. Reliability of aircraft power electronics is essential for high reliability and mission critical applications. Along with wear-out failure mechanisms, random failure modes must also be addressed to realize high reliability aerospace power converters. A dominant random failure mode in aerospace environment is due to cosmic rays (CR). In this work, a thermal management approach is proposed to maximize reliability of the converters considering CR failure mode. The proposed thermal controller is validated with an experimental setup. In the discussion, the trade-off involved between wear-out and CR induced failure mode is addressed.