High efficiency can be achieved in grid-connected converters by implementing a zero-voltage switching mechanism, such as the integrated triangular current mode (iTCM) modulation, which reduces the switching losses in the semiconductors. The iTCM can be readily adapted to a three-phase three-wire voltage-source converter (VSC) with the help of virtual ground (VG), which decouples the operation of three-phase switching cells. However, conventional methods of VG have all the zero-sequence currents flowing through the dc-link capacitors, resulting in an increase in the rms current, hence, extra loss for those passive components. This article, thus, introduces a capacitor-split VG topology that can relieve this issue by excluding the dc-link capacitors from the circulating path of the main zero-sequence currents, helping to reduce current stress for the dc-link capacitors. This topology is characterized by its filter capacitors being split into two halves and connected to the top and the bottom dc rails, respectively. Herein, the working principles of the proposed iTCM-operated three-phase three-wire VSC are comprehensively explained, and a detailed design guideline for the LC branch and LCL filter is offered. Analytical models for component stresses and the reverse current waveform have been developed and corroborated through PLECS simulations. A 3-kW, heatsink-less VSC system was constructed and tested, confirming both the system's effective functionality and the enhanced power efficiency of the proposed capacitor-split VG connection. Therein, the studied system demonstrated a significant efficiency improvement, ranging from 0.51% to 2% across the entire operating power spectrum, as compared to the conventional VG connection in iTCM-operated VSCs.

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Active power decoupling circuits are used in bidirectional single-phase grid-connected systems to enhance the circuit lifetime by creating an alternative path for the typical dc-side power pulsating ripple. Therefore, this reduces the requirement of smoothing dc capacitors allowing compact designs even with the implementation of long life metalized film technology. However, with the necessary addition of auxiliary components, extra power losses in the added switching devices and passive components will be introduced, which will inevitably reduce the system power conversion efficiency. To relieve this issue, a new discontinuous pulsewidth modulation (PWM) strategy with minimum switching losses is proposed in this article. This method detects the converter current and reference voltages synchronously to determine the optimum clamped duration of each circuit phase-leg. With such a characteristic, the proposed strategy can realize the minimum switching losses at any instant, thus improving the power conversion efficiency and potentially the power density of the converter. The proposed modulation method is described, analyzed, validated, and compared with different PWM methods on a 2-kVA bidirectional single-phase ac-dc converter with active power decoupling circuit.

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The implementation of finite-control-set model predictive control (FCS-MPC) in voltage source inverters (VSIs) can make the system suffer from poor current harmonics performance, which may complicate the design of the required AC filter. To overcome this shortcoming, a carrier-based modulated model predictive control (CB-MMPC) strategy is proposed in this paper. This method enables the utilization of existing PWM modulation techniques with FCS-MPC, where a modulation waveform with zero-sequence signal injection is generated and compared to a triangular carrier wave, while optimizing the selection of the switching states. As it is shown, the studied CB-MMPC strategy not only considerably improves the current total harmonic distortion (THD) but also attains the performance of fast current dynamic response and robustness as the traditional FCS-MPC. Herein, the detailed implementation of the CB-MMPC control strategy is given, while considering its application to the current feedback control loop of a three-phase three-wire two-level VSI modulated at constant switching frequency. Finally, PLECS circuit simulation and a 3-kW VSI prototype are used to verify the superiority and the effectiveness of the presented CB-MMPC strategy. This is also benchmarked to the FCS-MPC and dead-beat based controllers.

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In the applications of three-phase two-level voltage source inverters (VSIs) relatively large energy storage capacitors are used to absorb the high DC-link current ripples mainly caused by the circulating reactive power, the switched AC phase current flowing to the DC-link, and other dynamic and/or asymmetric operating conditions. Especially for electrolytic capacitor technology the typically high current stress and consequent losses is known to limit the power electronics lifetime, thus the design and selection of this component is critical for the whole system. To alleviate this problem, a new model predictive control (MPC) cost function which enables DC-link capacitor current ripple reduction is proposed in this paper. Based on the DC-link current mathematical model and the available VSI switching states, the future DC current ripple can be predicted, and then the optimized space vectors that best tracks the sinusoidal output current and minimizes the DC-link current ripple are chosen. Compared with conventional DC-link capacitor current reduction methods, the proposed approach has the advantage to incorporate an outstanding fast current control dynamics as well as being of relatively simple implementation because there is no need to adjust the switching signals or space vectors in the modulation as function of operational conditions of the system. Simulation and experimental results are presented verifying the effectiveness of the proposed MPC method.@en

The implementation of traditional finite-control-set model predictive control (FCS-MPC) with variable switching frequency in voltage source rectifiers (VSRs) can make the system suffer from poor current harmonics performance. In fact, the resulting wide-spread voltage harmonic generated at the AC terminals makes the design of the typical multi-order AC filtering bulky and prone to control instabilities. This paper proposed a fixed frequency carrier-based modulated model predictive control (CB-MMPC) which is able to overcome these issues. This control strategy aims to improve the total harmonic distortion (THD) of the AC current waveform without introducing any additional weight factor in the cost function of the optimization routine, while maintaining the typical performance of fast current dynamic response of the FCS-MPC. Herein, the detailed implementation of the proposed CB-MMPC is given, while considering its application to the current feedback control loop of a three-phase three-level Vienna rectifier. Finally, PLECS based simulation results are used to verify the feasibility and the effectiveness of the proposed control strategy and to benchmark its performance to the classical FCS-MPC strategy and the conventional application of a current closed loop implementing a proportional-integral(PI)-controller.@en

The implementation of finite-control-set model predictive control (FCS-MPC) in grid-tied inverters can make the system to suffer from poor harmonics performance, which may complicate the AC filter design for compliance with strict harmonic standards. To overcome this shortcoming, a simplified modulated model predictive control strategy is proposed in this paper. This control strategy not only improves current waveform total harmonic distortion (THD) without introducing additional weight factor in the cost function but can also shorten running/computational time without compromising the performance of fast current dynamic response. Herein, the detailed implementation of this control strategy is given, while considering its application to the current feedback control loop of a three-phase three-level T-type inverter modulated at constant switching frequency. Finally, PLECS circuit simulations are used to verify the feasibility and effectiveness of the proposed control strategy and to benchmark its performance to the classical FCS-MPC strategy and the application of a PI-controller.

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