The main contribution of this paper is the derivation rules summarized from existing high-performance inverters with H6-type configuration, which makes novel topologies possible. In addition, a novel ...high-efficiency single-phase transformerless photovoltaic inverter with hybrid modulation method is also proposed and evaluated as an example. Without input split capacitors, common-mode voltage and leakage current issues in a nonisolated system with H6-type configuration are eliminated, and the feature of a three-level output voltage in the inverter bridge's middle point helps inductors and power quality optimization. The detailed operation principles with hybrid modulation strategy combined with unipolar and bipolar pulsewidth modulation schemes are presented. Experimental results of a 2200VA prototype verify the proposed topology with hybrid modulation method.
Modular multilevel converters (MMC) have revolutionized the voltage-sourced converter-based high-voltage direct current transmission, but not yet got widespread application in medium-voltage ...variable-speed motor drives, because of the large capacitor voltage ripples at low motor speeds. In this paper, a novel hybrid MMC topology is introduced, which significantly reduces the voltage ripple of capacitors, particularly at low motor speeds. Moreover, this topology does not introduce any motor common-mode voltage; as a result, there are no insulation and bearing current problems. Additionally, the current stress can remain at rated value throughout the whole speed range; thus, no device needs to be oversized and converter efficiency can be ensured. Operating principle of this hybrid topology is explained, and control schemes are also developed. Validity and performance of the proposed topology are verified by simulation and experimental results.
Transformerless inverters, most of which are H-bridge inverters, have been widely used and studied in grid-connected power systems in the last decades. However, the H-bridge inverter is affected by ...the low- and high-frequency common-mode voltage between the input and output terminals, resulting in a large common-mode leakage current. An alternative solution is to connect the ground of the input terminal to the output load or grid, that is, the dual-grounded inverter. In this case, the low- and high-frequency common-mode voltages can be mitigated or eliminated. As a matter of fact, scholars have made several research results on dual-grounded inverters. However, as of now, there is still no literature that comprehensively and systematically summarizes these research results. To fill this gap, this article classifies different types of dual-grounded inverters from the perspective of topology for the first time, and compares and summarizes their advantages and disadvantages. More than 60 works of literature have been reviewed to identify the practical implementation challenges and research opportunities in the application of dual-grounded inverters.
This paper presents a pulse width modulation (PWM) technique for the minimization of the leakage current in the grid-connected/stand-alone transformerless photovoltaic (PV)-cascaded multilevel ...inverter (CMLI). The proposed PWM technique is integrated with the MPPT algorithm and is applied to the five-level CMLI. Furthermore, using the proposed PWM technique the high-frequency voltage transitions in the terminal and common mode voltages are minimized. Thus, the proposed PWM technique minimizes the leakage current of the PV array and electromagnetic interference filter requirement in the system without addition of any extra switches. Furthermore, this paper also presents the analysis for the terminal voltage across the PV array and the common mode voltage of the inverter based on the switching function. Using the given analysis, the effect of the PWM technique can be analyzed, as it directly links the switching function with the common mode voltage and leakage current. Also, the proposed PWM technique requires reduced number of carrier waves compared to the conventional sinusoidal pulse width modulation technique for the given CMLI. Complete details of the working principle and analysis with the support of simulation and experimental results of the proposed PWM technique are presented in this paper.
The paralleled configuration of three-phase two-level (3P2L) inverters has been put forward to increase the output power rating, operating efficiency, and system reliability. Nevertheless, this ...architecture brings about the serious circulating current problem, which distorts the quality of output currents, results in additional power losses, and reduces the system efficiency. Another problem is the common-mode voltage (CMV), which causes electromagnetic interference and threatens the safe operation of the system. There exists interconnection between these two issues in the paralleled 3P2L inverters. To suppress the CMV and circulating current simultaneously, an improved control method is presented. At first, the discrete model of paralleled 3P2L inverters is established, based on which the improved control method is designed to restrain the circulating current, while the parameter tuning is avoided. In addition, the zero-sequence component injection associated with the optimized configuration of carrier phase is conducted, and the CMV magnitude of each inverter is limited within one-sixth of dc-side voltage. When comparing with the traditional space vector modulation (SVM) approach, the CMV magnitude is restrained by two-thirds by the presented method. The hardware-based evaluation results have been provided to validate the presented approach.
•This article investigates a control method for paralleled three-phase inverters.•The control parameters are directly obtained by the discrete model.•The configuration of carrier phase is optimized to reduce common-mode voltage.
The voltage-source inverter with pulsewidth modulation (PWM) is widely used in motor drive applications owing to the technical maturity and simplicity. However, the inverter operating in the discrete ...and impulse state generates the high-frequency common-mode voltage (CMV) in the neutral point terminal of stator winding, which induces the negative effects. This article proposes a CMV elimination modulation scheme for the dual two-level inverter-fed asymmetrical six-phase permanent magnet synchronous motor, which has two sets of three-phase windings spatially shifted by 30° electrical degrees. The modulation algorithm shifts the PWM signals with the designed end-to-end cyclic sequence, which can retain the zero-voltage vectors for each sub-CMV of dual three-phase windings and theoretically eliminate the total CMV for the motor drive system. The validation of the proposal is verified by simulations and experiments.
This letter presents a three-phase voltage source inverter (VSI) topology to reduce the common mode (CM) voltage and electromagnetic interference (EMI) of electric motor drives. Instead of using ...filters, active or passive, or specific pulse width modulated (PWM) techniques to reduce the CM voltage, the proposed topology has inherently less CM voltage generation. With the addition of two switches placed in series on the dc lines, this topology effectively reduces the CM voltage during zero switching states by "floating" the inverter from the dc source. This topology can be implemented with any PWM method and does not add any additional complexity to the standard control techniques. The operation and CM reduction capability of the topology is first demonstrated in simulation and then verified with experimental results. A comparison of both common mode voltage and EMI is made to a conventional three-phase VSI to demonstrate the effectiveness of the proposed topology.
Modular multilevel converters (MMCs) have emerged as an attractive converter topology for renewable energy integration systems. A smooth operation of an MMC depends on the proper regulation of ...multiple control variables, e.g., phase current, circulating current, capacitor voltage, etc. The model predictive control (MPC) is an excellent candidate for such a scenario since different control objectives can be simultaneously handled in a unified cost function. Although extensive research has been conducted in the literature, a computationally efficient MPC implementation capable of regulating the common-mode voltage (CMV) of the ac-side neutral point of an MMC as a control target has not been properly investigated. This article proposes such an MPC strategy that can flexibly regulate the CMV by incorporating the CMV tracking error into the cost function. The biggest challenge is the dramatically increased number of available control actions and the consequent computational burden as the three phases are controlled as a whole, which are addressed employing a quadratic programming technique, leading to only 64 cost-function evaluations per control period regardless of the number of submodules of the MMC. Several experiments and simulations are carried out considering the regulation of the CMV in different scenarios, and the results validate the effectiveness of the proposed method.
Common-mode voltage (CMV) produces serious reliability and electromagnetic interference (EMI) issues in modern pulse-width modulated (PWM) electric drives. Such issues will become more prominent in ...the near future, as industry moves towards the introduction of wide-bandgap (WBG) semiconductor technologies operating at higher switching frequencies and also with greater dvdt. In this context, multiphase electric drive technologies can be of great interest, as their additional degrees of freedom can be exploited to reduce CMV. This work aims to study the potential of multiphase electric motor drive systems for CMV mitigation. To do so, a comprehensive review of the most recent scientific literature is conducted, mainly focusing on high impact works published recently. As a result, a clear and up-to-date picture of the most common multiphase technologies, i.e., (m+1)-leg, multiple three-phase, open-end and star-connected multiphase systems is provided along with their CMV reduction potential. Not only the topologies themselves but also modulation techniques are analysed and presented, mainly focusing on star-connected systems. As a conclusion, it can be stated that such multiphase systems are promising candidates to substitute conventional three-phase motor drives as, apart from their well-known advantages (efficiency, power density, power splitting, and fault tolerance), their CMV reduction potential is confirmed. The technical information provided in this work will help researchers and field engineers to design and develop high-performance multiphase electric drives.
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•Multiphase configurations are becoming popular in motor drive systems.•Device switching and pulse-width modulation produce common-mode voltage (CMV).•CMV leads to motor/drive failures and, eventually, complete breakdown.•The additional degrees-of-freedom of multiphase converters help reduce the CMV.•This paper provides a thorough review of the many works published on this topic.
Grid-tied inverters are the key components of distributed generation system because of their function as an effective interface between renewable energy sources and utility. Recently, there has been ...an increasing interest in the use of transformerless inverter for low-voltage single-phase grid-tied photovoltaic (PV) system due to higher efficiency, lower cost, smaller size and weight when compared to the ones with transformer. However, the leakage current issues of transformerless inverter, which depends on the topology structure and modulation scheme, have to be addressed very carefully. This review focuses on the transformerless topologies, which are classified into three basic groups based on the decoupling method and leakage current characteristics. Different topologies under the three classes are presented, compared and evaluated based on leakage current, component ratings, advantages, and disadvantages. An examination of demand for the inverter, the utility grid, and the PV module are presented. A performance comparison in MATLAB/Simulink environment is done among different topologies. Also an analysis has been presented to select a better topology. Finally, based on the analysis and simulation results, a comparison table has been presented. Furthermore, some important experimental parameters have been summarized.
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