Three-phase Current Source Inverter Research Articles

Modulation and control scheme for DC-link current minimization of an improved current source inverter

The traditional three-phase current source inverter (CSI) cannot maintain a constant DC-link current, the charging and discharging process under different operating modes will lead to the DC-link current being discontinuous or continuously increasing. To address this issue, the topology of CSI is improved, and a modulation scheme without additional losses is proposed in this paper to control the DC-link current. Then, based on the analysis of the DC-link ripple under all switching states, the calculation expression for the optimal reference of the DC-link current is derived, under the premise of meeting the current demand for the AC load, the minimum loss and harmonic distortion can be obtained by reducing the DC-link current. Finally, the math model of the AC-side is established, and the closed-loop control system including the voltage outer loop and the current inner loop is designed. The feasibility and correctness of the proposed modulation strategy and control method are validated by the simulation and experimental results, the minimum and stable DC-link current with the ripple below ± 1 A is obtained, and the high steady-state and dynamic control performances are achieved. The total harmonic distortion of the load current is less than 4 %, and the dynamic response time is 0.3 s.

Torque Ripple Reduction in Brushless Wound Rotor Vernier Machine Using Third-Harmonic Multi-Layer Winding

This article aims to realize the brushless operation of a wound rotor vernier machine (WRVM) by a third-harmonic field produced through stator auxiliary winding (X). In the conventional model, a third-harmonic current is generated by connecting a 4-pole armature and 12-pole excitation windings serially with a three-phase diode rectifier to develop a pulsating field in the airgap of a machine. However, in the proposed model, the ABC winding is supplied by a three-phase current source inverter, whereas the auxiliary winding (X) carries no current due to an open circuit. The fundamental MMF component developed in the machine airgap creates a four-pole stator field, while the third-harmonic MMF induces the harmonic current in the specialized rotor harmonic winding. The rotor on the other side contains the harmonic and the field windings connected through a full-bridge rectifier. The electromagnetic interaction of the stator and rotor fields generates torque. Due to the open-circuited winding pattern, the proposed machine results in a low torque ripple. A 2D model is designed using JMAG-Designer, and 2D field element analysis (FEA) is carried out to determine the output torque and machine’s efficiency. A comparative performance analysis of both the conventional and proposed topologies is discussed graphically. The quantitative analysis of the proposed topology shows better performance as compared to the recently developed third-harmonic-based brushless WRVM topology in terms of output torque and torque ripples.

A Power-Decoupled Three-Phase Current Source Inverter with Model Predictive Control in An Unbalanced Grid

The current source inverter (CSI) is a promising interface between the Photovoltaic (PV) panel and the three-phase AC grid. It boosts the PV panel voltage by a DC-link inductor and converts the maximum available PV power. In an unbalanced grid, double-line-frequency pulsating powers will be generated in the CSI, increasing the rating of the DC-link inductor and impeding the maximum power point tracking (MPPT) operation. To address this issue, a power decoupling (PD) circuit for a three-phase CSI is proposed in this paper. By using the DC-link inductor and active switches multiplex, the proposed PD circuit can reduce the current rating of the DC-link inductor with fewer active switches, and no detrimental power components are introduced to the utility grid. Moreover, to concurrently control multiple objectives without multiple loops, a model predictive control (MPC) method is further proposed for the PD-CSI, achieving a rapid response of PD-CSI. Besides, a space vector pulse width modulation (SVPWM) method is proposed for the PD-CSI to enhance the utilization of DC voltage, helping to reduce the voltage stress of the ripple storage capacitor. The priorities of the proposed topology and the corresponding control and modulation methods are finally verified by comparative experimental results.

PI Passivity-based Control of a Stand-alone Three-phase Current Source Inverter

This paper presents the design of a Proportional-Integral Passivity-based Controller (PI-PBC) for a current source inverter feeding a resistive load. Thanks to the definition of a new passive output, the closed-loop system is shown to be globally asymptotically stable. This result solves the internal stability problem reported for these power converters. To robustify the control algorithm, the paper also includes the design of a parameter estimation scheme for the parasitic resistances and the load conductance. Numerical simulations are carried out to validate the control algorithm. The simulation stage compares the behaviour using the averaged model of the power converter and a more realistic switching model, including the three-phase implementation.

Impacts of SiC-MOSFET Gate Oxide Degradation on Three-Phase Voltage and Current Source Inverters

In this paper, the performance variations of SiC MOSFET-based voltage and current source inverters under gate oxide degradation are studied. It is confirmed that the turn-on and turn-off delays of SiC MOSFETs change significantly by high electric field stress, which accelerates the gate oxide degradation. Variations in the turn-on and turn-off delays of switching devices extend or reduce the duty error of voltage source inverters and current source inverters. The performance variations of the voltage and current source inverter due to the duty error changes caused by the gate oxide degradation are analyzed through simulations. As a result, the gate oxide degradation worsens the performance of the voltage source inverter. Furthermore, the negative gate oxide degradation, which lowers the threshold voltage, decreases the performance of the current source inverter.

High-Frequency Common-Mode Voltage Reduced Space Vector Modulation for Grid-Connected Current-Source Inverter

Suitable space vector modulation (SVM) with reduced high-frequency common-mode voltages (HF-CMVs) for grid-connected current-source inverters (CSIs) have not been well investigated yet. In this study, the potential of active zero-state SVM (AZS-SVM) to suppress high frequency common-mode voltages (HF-CMVs) is revealed and theoretically analyzed, which is different from existing approaches of modifying topology. A special five-segment sequence with an optimally selected third active space vector for AZS-SVM is proposed and applied for CSIs. Simulation and experiments were completed on a (2.5 kW/208 V/6.94 A) grid-connected three-phase CSI. The results indicate that the proposed AZS-SVM mitigates HF-CMVs around unity and double control frequency by a factor of at least four times in contrast to that by conventional SVM, which validates the effectiveness of the proposed AZS-SVM to mitigate HF-CMVs generated by a grid-connected CSI.

Modified SVPWM for Three-Phase Six-Switch Switching-Cell Current Source Inverter

This article proposes a three-phase six-switch switching-cell current source inverter (H6-SC-CSI) and a modified switching scheme of space vector pulsewidth modulation (SVPWM). Compared to the conventional three-phase six-switch current source inverter, the H6-SC-CSI has no open-circuit possibility, thus, the inverter reliability is greatly enhanced. In addition, the overlap-time can be minimized; hence, the output waveform quality can be considerably improved. Due to the presence of switching-cell capacitors, a conventional switching sequence of the SVPWM is modified for the inverter to operate properly. A 2.2 kW hardware prototype is built and tested to verify the effectiveness of the proposed PWM.

Comparative Study of Conducted Common-Mode EMI in WBG-Enabled DC-Fed Three-Phase Current-Source Inverter

In pulsewidth-modulated (PWM) inverters, common-mode (CM) voltage and associated conducted CM electromagnetic interference (EMI) can cause motor bearing failures, ground leakage current, and audio susceptibility issues. When wide bandgap (WBG) devices are used to construct a voltage-source inverter (VSI), the CM EMI issues become more challenging. The current-source inverter (CSI) is an alternative, which produces more sinusoidal output voltage waveforms, making it a promising topology for reducing CM EMI in power converters. However, there is little systematic and comprehensive analysis of CSI’s CM EMI, especially when using WBG devices. The conducted CM EMI generation mechanisms of dc-fed two-level VSIs and CSIs are compared in this article. The analytical derivation and the circuit analysis are performed to identify the CM EMI generation mechanisms in both inverters, including CM voltage sources and the resulting CM current flowing paths. The effects of WBG devices on the CM EMI of both inverters are discussed. New CM EMI equivalent circuits (EQCs) of both inverters are analytically derived to reduce the computational time of full-circuit CM EMI simulation. Different filtering schemes and inverter topology variations’ impacts on CSI’s CM EMI are evaluated using the derived EQC. An effective CM EMI filter is designed to suppress the CSI’s CM EMI to be lower than EMI standards.

Comparative evaluation and analysis of GaN-based VSIs and CSIs

In this paper, a SPICE-based assessment platform for fast-switching Gallium Nitride (GaN) devices-based voltage source inverters (VSIs) and current source inverters (CSIs) is presented. VSI has long been the dominant topology for motor drive systems. The previous research found enormous problems caused by the direct replacement of WBG switches in VSIs. As a viable alternative, the intrinsic properties of CSI topology make it suitable for WBG-based devices. The GaN device is selected in this paper as one of the most promising candidates among all WBG devices. Tailored double pulse test (DPT) is used to characterize the GaN switch in VSI and CSI topologies. VSI-DPT and CSI-DPT printed circuit boards (PCBs) are fabricated to experimentally evaluate the GaN switch, and to further modify the SPICE model. Moreover, the way to realize a dedicated SVPWM modulation scheme for three-phase CSI is introduced. The parasitic elements associated with the DPT-PCB layout are considered for the purpose of accuracy. VSI and CSI circuits are built in LTspice with a modified SPICE model of the GaN switch, enabling more precise analysis of GaN-based VSI and CSI under a wide range of operating conditions.

High‐frequency common‐mode voltage mitigation for current‐source inverter in transformerless photovoltaic system using active zero‐state space vector modulation

Space vector modulation (SVM) schemes with leakage current mitigation capability for current-source inverters (CSIs) in transformerless photovoltaic (PV) systems have not been well explored yet. In this study, the advantage of a special SVM scheme, called active zero-state SVM (AZS-SVM), on suppressing high-order harmonics in the common-mode voltage (CMV) is revealed and theoretically analysed, since the high-frequency components in the CMV have decisive impacts on the generated leakage current. A five-segment sequence is proposed for AZS-SVM applied for CSIs. Both simulation and experiments are conducted on a (2.5 kW/208 V/6.94 A) grid-connected three-phase CSI, which validates the effectiveness of the designed AZS-SVM to mitigate the CMV high-order harmonics when compared to that by conventional SVM under different operating conditions.

New Powertrain Configurations Based on Six-Phase Current-Source Inverters for Heavy-Duty Electric Vehicles

In this paper, new powertrain configurations for heavy-duty electric vehicles (HDEV) are proposed based on current-source inverters (CSI) and asymmetrical six-phase motors. Voltage-source inverters (VSI) are widespread in many applications; however, VSI-based powertrains require a bulky bank of capacitors with a limited lifetime. Recently, powertrains based on the current-source inverter (CSI) are getting more attention to be a more reliable structure for EVs by replacing the dc-link capacitor with a choke inductor. To the authors’ best knowledge, a six-phase CSI-based powertrain is not fully addressed yet. Since the six-phase CSI comprises two three-phase CSIs, multiple configurations can arise based on the connection between the two CSIs. In this context, the proposed powertrain configurations are based on parallel, cascaded, and standalone six-phase CSIs. The standalone topology is based on separating the two three-phase converters by supplying each converter with a dedicated dc-dc converter. All the proposed configurations are studied from the perspective of structure, modulation, and stresses/sizing. A case study highlights the differences and compares the three structures. The comparison is backed by experimental results, and a detailed discussion is provided for concluding a suggested selection of the best-suited topology.

Effect of Semiconductor Parasitic Capacitances on Ground Leakage Current in Three-Phase Current Source Inverters

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.

A Wind and Solar Power Generation Data Collection System for Public Buildings

In view of the high power current source inverter (CSI) switching frequency is limited and system load parameter is variable, system output performance is affected. An interconnection and damping assignment of passivity-based control (IDA-PBC) for three-phase CSI is proposed. The lumped-parameter model of three-phase CSI with independent storage unit is established, and its port-controlled Hamilton (PCH) model in Park coordinate is proposed. The control rate of the closed-loop system is obtained by solving the parametric partial differential equation based on interconnection and damping assignment. The controller is designed, and the system stability is analysed by Lyapunov function. The Simulation and experiment results show that the inverter can output a good sinusoidal voltage, which has strong anti-interference ability to the load disturbance. The stability and robustness of the system are also improved.

CSI7: Novel Three-Phase Current-Source Inverter With Improved Reliability

Unlike voltage-source inverters (VSI), the power decoupling element in current-source inverters (CSI) is inductor. Inductor has a long lifetime and makes the CSI more reliable. However, the traditional CSIs suffer from open-circuit problem and dangerous voltage spikes are generated if the input inductor current is intermitted. Therefore, to avoid the voltage spikes, overlap-time should be inserted in the gate signals. But these intervals distort the output currents and reduce the current source utilization. To address these issues, a novel three-phase CSI is proposed in this article. The proposed inverter is originated from the conventional seven-switch CSI named CSI7 by adding only two small film capacitors. The film capacitors along with the pre-existing diodes of the CSI7 ensure that there is always a path for the inductor current, and thus the open-circuit issue is resolved. The elimination of open-circuit issue enhances the reliability and allows to minimize the overlap-time. This will improve the quality of output currents as well. Moreover, simulation and experimental results are provided at the output power of 950 W to verify the effectiveness of the proposed inverter.

Multivariable Model Predictive Control for a Virtual Synchronous Generation-Based Current Source Inverter

Three-phase current-source inverters are an alternative solution for interfacing photovoltaic modules to the utility thanks to its voltage boosting ability. This paper presents a virtual synchronous generator strategy for a three-phase current-source inverter using a multivariable model predictive control. The proposed method can ensure operations in both grid-connected and islanded modes while achieving virtual inertia features to stabilize the grid frequency and active damping to reduce grid current distortions caused by an output CL filter included on the grid side of the system. The obtained simulation results in the PSCAD/EMTDC environment software verify the effectiveness and the excellent performance of the proposed method.

Voltage boosting capability of three phase current source inverter for standalone system

This paper presents a three-phase current source inverter (CSI) topology with voltage boosting capability for standalone system. Current source inverter (CSI) and voltage source inverter (VSI) are two competitive options to be used as an interfacing unit between variable dc input resource and ac output fed into on-grid, off-grid and industrial used. Among the two topologies, VSI is widely used due to its variable controllable output voltage and ability to operate steadily with open loop V/Hz control. Yet, it suffers circuit complexity due to the need of extra converter stage to meet the required output. On the other hand, CSI has an advantage of voltage boosting capability and better quality of output waveshape, thus no extra converter stage is needed. Most of research works were focusing on studying the suitability and practicality of CSI, along with the advancement using silicon carbide-based power switches and improved modulation techniques to minimize the harmonics suffer by CSI. There is lack of research in investigating the boosting capability particularly on how high CSI able to boost the fundamental output and its impact to overall performance in both open and closedloop standalone system. Thus, this work is intended to highlight in detail the boosting capability of CSI and compare with VSI based on the several circuity and operational features. To support the work, three modulators are implemented namely sinusoidal pulse width modulation (SPWM), third harmonic injection PWM (THIPWM) and space vector modulation (SVM). A dedicated synchronous frame proportional-integral (PI) control in used in closed-loop condition. Result shows that CSI topology able to boost the fundamental output voltage by 52% to 58% by using smaller modulation index as compared to VSI. Interestingly, CSI able to achieve comparable quality and harmonic minimization of output voltage and current as in VSI but with smaller PI control gain. All works are analyzed and verified using MATLAB/Simulink platform.

A Soft-Switching Current-Source-Inverter-Fed Motor Drive With Reduced Common-Mode Voltage

This article proposes a common-mode voltage (CMV) attenuation method for the three-phase current source inverter (CSI)-fed permanent-magnet synchronous machine drive. The key of this method is to introduce an auxiliary circuit branch connected in parallel with the dc link. Based on the dedicated switching strategy, the zero-voltage-switching conditions are provided for the main switches in the CSI. In particular, the zero current vector is newly constructed without utilizing shoot-through operation in the CSI. Thus, the CMV in the traditional CSI drives is attenuated significantly. Compared with the existing research on CMV suppression, the proposed method will not compromise the modulation index range or increase output current harmonics. Meanwhile, the overshoot voltage can be clamped by the auxiliary power circuit in the dc link under open-circuit fault in the power switches. The system configuration, operating principle, analysis of operation modes, as well as the control scheme are described in detail. Both simulation and experimental results are presented to verify the performance of the proposed method.

Provision of Balanced Voltages Under Severe Unbalanced Load Currents in a Microgrid Using a 3D-SVM Technique

The current source inverter (CSI) is more suitable for use in photovoltaic applications than the voltage source inverter (VSI), but this structure has two main constrains: inability to feed unbalanced load and high common mode voltage (CMV). Despite the merits, use of CSI is limited due to these constrains. A three-phase CSI with a neutral-leg is presented in this paper, compared to the conventional three-phase CSI to overcome mentioned limitations, in which load unbalance under a PV system is dealt in a microgrid. An innovative three-dimensional space vector modulation (3D-SVM) is suggested for the four-leg CSI inverter. This novel 3D-SVM technique is very simple compared to the existing methods and computational complexity is too low. Operating principles, equivalent circuit and SVM is discussed for the four-leg inverter. Then, a balancing technique is applied to the four-leg inverter using the developed 3D-SVM, where simulations validate the capability of the inverter in supplying balanced load voltages; 4-leg inverter generates balanced sinusoidal voltages even under severe unbalanced load current.

Comparative Evaluation of Three-phase Voltage and Current Source Inverter in Renewable Energy System

In the renewable energy power generation system, voltage source inverters (VSIs) are commonly used due to its stable operation, high efficiency and low cost. However, a dc-dc boost converter is necessary for VSI to operate has increased the system complexity. Thus, current source inverters (CSIs) has become an alternative of VSI due to its ability of voltage boosting and can provide a better output waveform. This paper presents a comparative evaluation of VSI and CSI focusing on topological circuits and basic operational parameters of these inverters. The performances of VSI and CSI are analyzed in MATLAB/Simulink focusing on two operational characteristics which are modulation index, ma and switching frequency, fsw. The performance of VSI and CSI are dependent on the modulation index, increasing ma increase the inverter efficiency. In term of switching frequency, it does not affect much on the efficiency of inverters, yet a normalized switching frequency of odd multiple of three provides better fundamental output and harmonic minimization. Furthermore, CSI presents its voltage boosting capability which can boost 6-27% within ma of 0.05-1.0 and using the same modulation technique, VSI and CSI have present duality relationship in term of output voltage and current wave shapes.

Voltage-controlled of a three-phase current source inverter in islanded operation

This paper presents the performance of a three-phase current source inverter (CSI) in island mode voltage-controlled operation. Simple converter structure, low switching count and inherent boosting capability among the features offered by CSI. However, less investigation has been done with regards to the performance of CSI especially on its control system for island and grid-connected photovoltaic system. Thus, this study aims to investigate the suitability of proportional-integral (PI) and proportional-resonant (PR) control including their dynamic equations and state-space modeling. The results show that both controllers able to perform satisfactory in achieving zero steady-state error and balanced sinusoidal output voltage and current. PI control is superior in fast response time and excellent harmonic rejection than inverter using PR control PR control on the other hand, able to give more robust performance during imbalance occur than PI control due to individual control of the phases. This study may becomes one of the references with regard to current source inverter for early career researchers. as All results presented in this paper are verified with varying operational parameters in MATLAB/ SIMULINK platform.