This paper introduces a novel pulse width modulation (PWM) technique to eliminate common-mode voltage in odd-multilevel inverters using the three zero common-mode vectors principles. Similarly, as in ...conventional PWM for multilevel inverters, this PWM can be properly depicted in an active two-level voltage inverter. With the help of two standardized PWM patterns, the characteristics of the PWM process can be fully explored in that active inverter as a switching time diagram and switching state sequence. Due to an unequal number of commutations of three phases in each sampling period, the switching loss is optimized by a proposed current-based mapping algorithm. The switching loss reduction can be up to 25% compared to the same PWM technique with nonoptimized algorithms. The PWM method has been then generalized as an equipotential PWM control, which is valid to both odd- and even-multilevel inverters . The theoretical analysis is verified by simulation and experimental results.
This paper proposes an asymmetrical switching pattern to eliminate common-mode voltage (CMV) in multilevel converters while reducing switching loss by rearranging the switching sequence to minimize ...the number of level-shifts. In contrast to the existing symmetrical switching pattern, this approach achieves CMV elimination without increasing switching loss. To implement this asymmetrical switching pattern, a simple sawtooth carrier-based PWM scheme is proposed that avoids the need for complicated space vector modulation (SVM) computation, particularly for high-level converters. The proposed method's effectiveness is demonstrated through simulations and experimental results for the three-phase cascaded H-bridge converter and boost seven-level active neutral-point-clamped converter.
Aiming at a class of transformerless three-phase DC/AC inverters with N times of 12 switching-cells, this letter proposes a novel nose-to-tail modulation (NTM) method which can realize zero ...common-mode voltage (CMV). The NTM algorithm places the driving pulses nose-to-tail of the six conversion units in the upper/lower arms, so as to realize the same number of units put into the upper and lower arms at any time. In addition, a dead-time compensation scheme achieving the elimination of narrow pulse CMV caused by dead-time is also proposed for NTM. As a result, the zero CMV can be achieved. Although the proposed NTM slightly increases the modulation complexity, it is of great significance in CMV sensitive systems such as grid-tied and motor drive systems. The effectiveness of the proposal is verified by experiments.
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.
Fast and reliable fault diagnosis is essential for induction motor (IM) drive systems with high-reliability requirements. In this article, we propose a robust open-switch fault-diagnosis method based ...on the common-mode voltages of the inverter in the IM-drive systems. This method makes full use of the characteristics of common-mode voltages. First, the calculated common-mode voltages (CCMVs) are equal to each other under normal operating conditions and the CCMVs represent the other behaviors under fault conditions. Second, average common-mode voltage is a degree of freedom in the modulation of the inverter. Based on the first characteristics, the CCMVs are used to detect and locate the open-switch faults of the inverters. Based on the second one, an active common-mode voltage injection method is proposed to improve the credibility of the diagnosis results and reduce the rate of missed detection. The proposed diagnosis algorithm only uses the measured current information, avoiding the application of extra sensors. And its average detection time is about 300 μs, which is three switching cycles. Simulation and experimental results are presented to demonstrate the feasibility and effectiveness of the proposed fault-diagnosis method.
In the conventional implementations of phase-shifted carrier pulse-width modulation (PSC-PWM) for modular multilevel converters (MMCs), different phases normally adopt identical carrier arrangements, ...neglecting the phase-to-phase carrier phase displacement (P2PCPD). This paper presents a comprehensive analysis of the P2PCPD angles, focusing on their effects on the harmonic characteristics of the line-to-line voltages (LLVs) and common mode voltage (CMV). The selection criteria of the P2PCPD angles are proposed for different conditions in terms of the modulation index and the number of submodules (SMs) per arm of the MMC. It is revealed that the LLV and CMV harmonics cannot be minimized simultaneously, while a trade-off can be achieved between these two control objectives: a proper set of P2PCPD angles can be obtained which minimizes the CMV/LLV harmonic distortion meanwhile keeping the LLV/CMV harmonic distortion below a preset threshold. Simulations and experiments are conducted, and their results validate the theoretical findings.
The conventional finite control-set model predictive control (FCS-MPC) methods need a cost function with weighting factors to minimize the common-mode voltage (CMV) in the multilevel inverter (MLI) ...fed electric drive systems. Moreover, these methods require a higher sampling time for real-time implementation, resulting in a rich harmonic content in the inverter ac currents. This article addresses these concerns by proposing a low-complexity FCS-MPC with CMV minimization for a five-level inverter (FLI). The per-phase philosophy is adopted in the design and implementation of the proposed FCS-MPC for an FLI, resulting in a maximum number of predictions of 6 per phase only (a total of 18 predictions in a three-phase FLI system). Moreover, the proposed FCS-MPC minimizes the CMV without using a cost function, leading to superior current harmonic performance. Additionally, Heun's integration method is introduced in the formulation of discrete-time models of the FLI, and they are used in real-time implementation of the proposed FCS-MPC. The superiority of the proposed method is demonstrated through a dSPACE-controlled FLI laboratory prototype. Furthermore, a comparative analysis of the proposed and the conventional FCS-MPC methods is presented in terms of total demand distortion (TDD) of the current, inverter CMV, and the computational burden.
The problem of common-mode voltage (CMV) in current source converter (CSC) has been concerned with the development and application of CSC, such as in the transformerless motor drive system. Using a ...common-mode choke is a popular solution to suppressing CMV. The high-frequency harmonics of the CMV can be eliminated by the common-mode filter. However, the low-order harmonics cannot be eliminated effectively, especially at low modulation index, which may cause common-mode resonance and increase the size of the choke. In this paper, a novel virtual space vector modulation (VSVM) method is proposed, which constructs virtual space vectors by the original vectors. The average value of the CMV produced by each virtual vector is zero. The proposed method can reduce the amplitude and third-order harmonic component of the CMV. In addition, the number of switching transitions in a switching sequence of the proposed method is the same as the conventional 5-segment SVM. The suppression effects of different methods on the low-order harmonics of CMV are compared through simulation and experiments, and the effectiveness of the proposed methods is verified.
Zero-sequence current exists in five-phase open-winding permanent magnet synchronous motors (FPOW-PMSMs) with a common DC bus, resulting in harmonic current and system losses. Besides, the use of the ...dual-inverter increases inverter losses and induces a high-frequency common-mode voltage, damaging the bearing. This paper proposes a novel zero-sequence current suppression method for the FPOW-PMSM, which can reduce the inverter losses while decreasing the common-mode voltage. First, the average zero-sequence voltage equal to zero is considered a restriction to calculate the duration time of basis vectors. Five active vectors are selected to synthesize the reference voltage vector in each sector. Then, benefiting from abundant switching states redundancy, a novel switching states combination with minimum switching actions is proposed to reduce the common-mode voltage and inverter losses. Furthermore, the modulation range of the proposed modulation method is analyzed, indicating that the proposed method achieves considerable DC bus voltage utilization. Finally, the experimental results verify the effectiveness of the proposed method.
Literature reviews affirm the constructive influence of the Intelligent Predictive Multi-objective Control (IPMOC) on the power quality, power ancillary services, efficiency, and reliability expected ...from grid-tide Transformerless Multilevel Converters (TMLC). Regarding, this paper contributes to developing the Intelligent Predictive Multi-objective Control (IPMOC) concept in terms of training, Autonomous Power Management (APM), and real-time harmonic mitigation. In the proposed IPMOC, Model Predictive Control (MPC) adjusts the power, regulates the dc-link capacitors' voltages, reduces the switching transitions, suppresses CMV, and alleviates harmonics using a novel real-time Selective-Predictive Harmonic Mitigation (SPHM) objective. As the intelligent part, two Artificial Neural Networks (ANN) trained by a novel data-free, Fast, Self-Training Strategy (FSTS) reinforce the MPC to handle the multi-objective task. The first one adapts the weighting factors of the MPC dynamically, while the second one as a model-free controller autonomously adjusts the active and reactive power references of the MPC to assure the unity power factor of the grid in the presence of unknown loads. The proposed IPMOC has been applied to a three-phase neutral point clamped converter and evaluated via various test scenarios run by dSPACE 1202 and MATLAB to verify its effectiveness and feasibility.
