To improve the utilization of the DC-bus voltage and solve the problem of neutral-point voltage (NP-V) unbalance and high common-mode voltage (CMV) in the overmodulation region of three-level NPC ...inverters, a virtual space vector overmodulation (VSV-OVM) strategy considering NP-V balance and CMV suppression is proposed. Based on the hybrid vector correction method, the utilization of DC-bus voltage in the overmodulation region is improved, the computational burden of overmodulation algorithm is alleviated by means of fitting and establishing lookup table (LUT). Meanwhile, an effective active NP-V control method with switch states Misalignment protection is designed for the proposed VSV-OVM strategy. Furthermore, the implementation details of the proposed VSV-OVM strategy is elaborated. The experimental results verify that the proposed VSV-OVM has excellent NP-V balance and CMV suppression ability in the overmodulation region, and has higher DC-bus voltage utilization.
In this paper, a suitable long prediction horizon (multistep) model predictive control (MPC) formulation for cascaded H-bridge inverters is proposed. The MPC is formulated to include the full ...steady-state system information in terms of output current and output voltage references. Generally, basic single-step predictive controllers only track the current references. As a distinctive feature, the proposed MPC also tracks the control input references, which in this case is designed to minimize the common-mode voltage (CMV). This allows the controller to address both output current and CMV targets in a single optimization. To reduce the computational effort introduced by a long prediction horizon implementation, the proposed MPC formulation is transformed into an equivalent optimization problem that can be solved by a fast sphere decoding algorithm. Moreover, the benefits of including the control input references in the proposed formulation are analyzed based on this equivalent optimization problem. This analysis is key to understand how the proposed MPC formulation can handle both control targets. Experimental results show that the proposal provides an improved steady-state performance in terms of current distortion, inverter voltages symmetry, and CMV.
To reduce the common-mode voltage (CMV) and eliminate the CMV spikes for two-level voltage source inverters (2L-VSIs), an improved model predictive control (MPC) based CMV reduction method is ...proposed in this paper considering dead-time effects. First, an improved voltage vector (VV) preselection strategy is proposed to reduce the CMV spikes caused by the dead time. Second, a new hybrid VV preselection strategy based on a delay compensation strategy and a modified current sector division strategy is proposed to completely eliminate the CMV spikes. As the proposed hybrid VV preselection based MPC strategy makes full use of the six nonzero VVs of the 2L-VSI, the current total harmonic distortions and ripples are reduced. The simulation and experiments are carried out to verify the effectiveness of the proposed strategy.
The transformerless cascaded H-bridge (CHB) inverter is a potential topology for low-cost, high-efficiency photovoltaic (PV) systems. The leakage current problem caused by parasitic capacitors ...between the PV panels and the earth, on the other hand, remains a challenge in constructing a reliable PV system. The distinctive properties of the CHB inverter's leakage current paths are investigated in this research. A new multicarrier pulse width modulation method and topology are presented to suppress the leakage current. Simulations in the MATLAB/Simulink environment are used to verify the validity of the suggested solution. An experimental prototype with a power rating of 600W is also produced and tested, with the experimental findings confirming the theoretical and simulation results
Model predictive control (MPC) has emerged as a promising approach to control a modular multilevel converter (MMC). With the help of a cost function, the control objectives of an MMC are achieved ...easily by using an MPC approach. However, the MPC has several technical challenges and issues including the need of accurate system models, computational complexity, and variable switching frequency operation and weighting factor selection, when it comes to the control of an MMC. In the past few years, several research studies are conducted to address some of the challenges and issues in an MPC and developed several model predictive algorithms for an MMC. In this paper, the importance of each challenge and its impact on the system performance is discussed. Also, the MMC mathematical models used in the implementation of MPC are presented. Furthermore, some of the popular MPC algorithms are discussed briefly, and their features and performance are highlighted through case studies. Finally, summary and future trends of MPC for an MMC are presented.
This article presents a family of 1-φ transformerless switched-capacitor based five-level inverter (TSC5LI) topologies for photovoltaic (PV) applications. The proposed family comprises four inverter ...topologies: H8, H8-UPF, H10, and H10-UPF capable of mitigating the leakage current by having continuous grid frequency voltage at PV parasitic capacitor in spite of considering switch terminal capacitances. A distinctive attribute of the TSC5LI is that 100% dc-bus utilization, symmetrical operation, and constant total common-mode voltage (TCMV) are achieved together. H8 variant of the proposed inverter family is studied extensively. The control strategy used is a simple level-shifted sine-triangle pulsewidth modulation followed by the synthesis of the gate pulses utilizing logical functions. Switching function based TCMV analysis, switched capacitor design, and loss analysis are presented. Simulation and experimental results of H8 variant are presented to validate the theoretical claims. Proposed topology is also compared with the existing five-level transformerless inverters to prove its various advantages.
This paper proposes a balanced inverter topology for canceling the common-mode (CM) voltage of motor drives, and thus reducing or eliminating the ground leakage current, bearing current, and CM ...electromagnetic interference. The proposed topology splits one of the switches on each phase-leg of a conventional inverter into two half-voltage rated switches, and creates two complementary sets of balanced three phase output voltages, whose CM voltages cancel each other in the driven motor. The balanced inverter topology does not involve filter components, modification of the modulation strategy, or increase of the total device rating. Theoretical analysis and testing results are presented to verify this concept.
Model predictive current control (MPCC) is widely studied and applied in five-phase VSIs, and virtual voltage vectors (V 3 s) are constructed to improve steady state performance and simplify ...computation complexity. However, V 3 s in five-phase VSIs were initially constructed using one large and one medium voltage vectors, and all existing works employed this method, which goes against the common-mode voltage (CMV) reduction. To address this problem, two improved MPCC (IMPCC) methods are proposed in this article. Firstly, the V 3 s are constructed in a new way using four adjacent large vectors, which enables the proposed IMPCC methods to reduce CMV and low-order harmonic currents inherently. Thus, there are no harmonic and CMV terms in the cost function. Secondly, the duty ratio optimization is introduced and dwell time of the optimal V 3 is estimated to reduce current ripples. Then, in order to achieve superior steady state performance, two switching patterns are designed, namely the asymmetrical and symmetrical ones. The asymmetrical pattern aims to reduce the switching frequency while the symmetrical one focuses on harmonics suppression. Finally, experimental comparisons between the proposed IMPCC methods and conventional methods are presented. Experimental results have verified that the proposed schemes can mitigate CMV, suppress current harmonics and reduce computation complexity, simultaneously.
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 neutral-point-clamped ...converter. Our studied ESG system operates at a high speed during its generation mode, which results in high modulation index and puts some specific challenges on neutral-point voltage balance, especially under low power factor 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 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 kr/min aircraft ESG system verify the effectiveness of the proposed strategy in more-electric-aircraft applications.
•The paper presents a new transformer-less step-up switched-capacitor topology that utilizes twelve switches to create nine different voltage levels.•The salient features of the proposed topology are ...the least switching components, zero leakage current, boosting capability, and reduced voltage stresses.•The capacitors possess inherent self-balancing properties, eliminating the requirement for an extra circuit to achieve capacitor self-balancing.•The theoretical concept and feasibility of the proposed topology have been verified through simulations and experimental results.
The paper introduces a new transformer-less step-up switched capacitor topology that utilizes twelve switches to create nine different voltage levels. The salient features of the proposed topology are the least switching components, zero leakage current, boosting capability and reduced voltage stresses. Furthermore, the capacitors possess inherent self-balancing properties, eliminating the requirement for an extra circuit to achieve capacitor self-balancing. The paper provides concise explanations of the operational principle, modulation scheme, and loss analysis. A brief comparative analysis of the existing topologies demonstrates the advantages and superiority of the proposed approach. Additionally, the theoretical concept and feasibility of the new topology are verified through simulations and experimental results. Without a filter, the THD at the output voltage and current of the proposed inverter has been measured at 16.48 % and 0.88 %, respectively.
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