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This paper proposes a new reduced switch-count power cell for a regenerative Cascaded H-Bridge (CHB) motor drive that reduces the number of switching devices per power cell from ten switches to six switches. The proposed power cell employs a Four-Switch Three Phase Inverter (FSTPI) at the front-end and a half-bridge inverter at the output of the power cell. The new configuration introduces four challenges: cell input current unbalance, input low order harmonics, DC-link voltage capacitor balancing, and switching harmonics. This paper analyzes and addresses these issues to ensure proper operation, control, and compliance with grid connection standards. The solutions are verified through simulation studies of a 3kV CHB motor drive and experimental validation with a single power cell setup. The results show the possibility of replacing the traditional power cell with a proposed cell, effectively reducing the required number of switches from ten to six.

Cascaded H-Bridge (CHB) topology is one of the attractive topologies in high-power medium-voltage motor drive applications due to its modularity and scalability. Research in high power regenerative motor drives has gained significant attention with the increasing demand for efficient energy use. In a cascaded H-Bridge (CHB) converter, the regenerative capability can be introduced by replacing diode front end (DFE) with active front end (AFE) topologies. However, this results in a huge increase in the number of power semiconductors, gate drivers, and heat sink size and thus increases the overall size and cost of the regenerative CHB motor drives. To overcome the aforementioned challenges, different power cell designs have been introduced to reduce the switch count, allowing the design of more suitable-sized and more economical drives. This paper comprehensively reviews the reduced switch-count power cell designs, including single-phase and three-phase grid connections. Each reduced switch-count cell design is analyzed, and its advantages and disadvantages are studied in detail. The challenges that arise with each design and the method to address the challenges are discussed.

More demanding harmonic limits of future grid standards are likely to aggravate the disadvantages associated with the use of passive filters in high-power converters. These include substantial additional losses, a large footprint, and a considerable, power factor dependent voltage drop. For this reason, active filters (AFs) are an increasingly attractive alternative for reducing converter-induced harmonics; however, their performance is often subject to a limited frequency range and a frequency-dependent attenuation. To further improve the potential of AFs for use with grid-connected power converters, this article presents a novel control scheme for a parallel voltage-source AF integrated into a high-power main converter. A detailed converter analysis shows that, due to the advantageous converter configuration, the AF requires only fundamental frequency current control to mitigate converter-induced current harmonics. In contrast to conventional AF applications, this avoids tuning to specific frequencies, identification of individual harmonics, and measurement of high-frequency current ripple and high control bandwidth. The control design is carried out with the aim of minimizing the AF current load in steady state and transient operation. As shown by simulation results, the AF thus allows the mitigation of harmonics up to frequencies above the switching frequency of the main converter at only a small share of the total power and with small passive components. Finally, the hybrid converter is compared to LCL-filter based converter systems and the effectiveness of the presented control scheme is verified experimentally using a silicon carbide demonstrator. [ABSTRACT FROM AUTHOR]

Installation and operation of rail vehicles powered by multiple system voltages forces the construction of multi-system traction substation. The article describes a traction substation power supply with 15 kV output voltage and frequency Hz and 25 kV at 50 Hz. The topology of the power electronics system and the control structure of the power supply enables parallel connection of several power supplies. The selected topology and control structure ensures minimizing the rms value of the LCRL filter capacitor current used at the output of the inverters. The article analyses the influence of harmonics consumed by the active front end (AFE) rectifier used in traction vehicles on the rms current of the LCRL filter capacitor.

Installation and operation of rail vehicles powered by multiple system voltages forces the construction of multi-system traction substation. The article describes a traction substation power supply with 15 kV output voltage and frequency Hz and 25 kV at 50 Hz. The topology of the power electronics system and the control structure of the power supply enables parallel connection of several power supplies. The selected topology and control structure ensures minimizing the rms value of the LCRL filter capacitor current used at the output of the inverters. The article analyses the influence of harmonics consumed by the active front end (AFE) rectifier used in traction vehicles on the rms current of the LCRL filter capacitor. [ABSTRACT FROM AUTHOR]

Nowadays, the increasing number of non-linear loads influences the grid, causing grid voltage disturbances. These disturbances may be very dangerous for the equipment and can create faults in converter behaviour. However, the right control algorithm can improve the reliability of the work. For a current source rectifier, the finite control set model predictive control has been proposed. This method is very flexible because of the variety of the possible cost function forms. It has been examined under grid voltage disturbed by the higher harmonics and the voltage drop. Simulation results prove the ability to damp the distortions and to ensure the unity power factor. Summing up, the algorithm is a very good solution for use in applications such as battery charging, active power filtering and low-voltage direct current load feeding.

Current harmonics generated by adjustable‐speed drives (ASDs) are one of the main power quality concerns in commercial and industrial distribution networks due to a high number of ASDs. These harmonics affect the grid power quality, instability, resonances, and power losses. Therefore, different harmonic mitigation strategies using active front end have been proposed to tackle this issue. However, due to the cost‐effectiveness, conventional front end such as diode rectifier is still recommended in industries for a broad range of three‐phase power electronics systems. Thus, in this study, a new DC modulation method is proposed using three‐phase diode rectifier with controlled DC‐link current (boost converter) for grid harmonic elimination approach. Simulations and experiments have been carried out to validate the proposed concept that a selective harmonic can be eliminated from the grid using the developed strategy. [ABSTRACT FROM AUTHOR]

Emerging wide bandgap (WBG) semiconductors, such as silicon carbide (SiC), will enable chargers to operate at higher switching frequencies, which grants the ability to deliver high power and enhances efficiency. This paper addresses the modeling of a double-sided cooling (DSC) SiC technology-based off-board charger for battery electric buses (BEBs) and the design of its control and real-time (RT) implementation. A three-phase active front-end (AFE) rectifier topology is considered in the modeling and control system design for the active part of the DC off-board charger. The control system consists of a dual-loop voltage–current controller and is used to ensure AC to DC power conversion for charging and to achieve the targeted grid current total harmonic distortion (THD) and unity power factor (PF). Linear and nonlinear simulation models are developed in MATLAB/Simulink for optimum control design and to validate the voltage and current control performances. Four types of controllers (i.e., proportional–integral (PI), lead–lag, proportional–resonant (PR), and modified proportional–resonant (MPR)) are designed as current controllers, and a comparative analysis is conducted on the simulation model. In addition, the final design of the dual-loop controller is implemented on the RT–FPGA platform of dSpace MicroLabBox. It is then tested with the charger to validate the control performance with experimental data. The simulation and experimental results demonstrate the correct operation of the converter control performance by tracking the reference commands.

In the present pre-conceptual design, the base converters to supply the main DEMO poloidal magnets are rated for 45 kA and about 10 kV. If the traditional design approach, based on thyristor bridges, was adopted, this would result in very large reactive power exchanged when low voltage values are required by the load. To satisfy the limitations imposed by National Grid Operators, the reactive power should be compensated inside the DEMO Plant Electrical System by means of a Reactive Power Compensation and Harmonic Filtering system. This could represent an additional cost and takes up a large area of the plant. This paper shows that the reactive power demand, estimated with an analytical model starting from the current/voltage waveforms foreseen in DEMO magnets, is huge. Therefore, an innovative approach, based on Active Front End converters, is proposed and compared with the traditional solution for coil power supplies. [ABSTRACT FROM AUTHOR]

The size of back-to-back converters with active front end is significantly determined by the size of the passive filter components. This paper presents a new complete EMC filter concept for this type of converter system that is effective on the input and the output. This involves filtering the main common mode interferences from the grid and motor sides with a single CM choke. Since only the difference of the generated common mode voltage-time areas of both converters is absorbed by this component, the size of the required filter can be greatly reduced compared to conventional filter concepts. The concept is validated on a grid feeding inverter that can be connected to the public distribution network with an output power of 63 kW. The size reduction is demonstrated by means of a design example on a system with the same power and electrical requirements. It is elaborated why, applying the new filter concept, the impedance of the DC link potentials to ground and other electrical potentials should be as high as possible and therefore associated parasitic capacitances should be minimized. From this requirement, rules for the design of the power modules of PFC and motor converters for the application of this filter concept are derived.

In view of problem of harmonic pollution and system loss of active front end of 10 kV high voltage mine hoist, MSHE-PWM harmonic suppression method was proposed. ANPC five-level topology mathematical model was established to analyze MSHE-PWM harmonic suppression principle and solve MSHE-PWM nonlinear equations under constraint conditions. Voltage balance control method of suspended capacitor was also given. The results of MSHE-PWM performance test based on 1 MW industrial prototype show that SHE-PWM technology achieves grid side low-order harmonic control of 10 kV high voltage mine hoist, and comparison experiment with SV-PWM further demonstrates superiority of MSHE-PWM in solving problems of temperature-rise and loss of 10 kV high voltage inverter system.

Modular multilevel converters (MMCs) have emerged in response to increasing the demands of converter in high-power applications. Because of the modularity, MMC structures are ideal in order to use in high voltage and current applications. Increasing the number of semiconductors and passive components made it so bulky and expensive. On the other hand, high number of variables and the circular interaction between the components values and electrical quantities of the MMCs make it difficult to analyze and design. In this paper, an accurate steady-state analytical model of modular multilevel active front end has been presented and developed. The proposed steady-state model provides more precise analytical expressions for capacitor voltage ripple and circulating current based on the input and output specifications. Then, a novel optimization approach has been proposed and integrated to determine the passive component values in order to maximize the performance and minimize the total volume using analytical model with respect to the technical and mechanical constraints. The optimization procedure uses a nonlinear numerical solver to calculate the optimal values of sub-module capacitor and arm inductance in order to minimize the total energy stored in the converter which is directly related to the total converter mass. [ABSTRACT FROM AUTHOR]

The global consumerism trend and the increase in worldwide population is increasing the need to improve the efficiency of marine container transportation. The high operating costs, pollution and noise of the diesel yard equipment is leading sea ports to move towards replacing diesel RTG cranes with electric Rubber Tyre Gantry (RTG) cranes which offer reduced environmental impact and higher energy efficiency. However, ports will require smarter solutions to meet the increased demand on the electrical distribution network due to the electrification of RTGs. This paper aims to highlight the peak demand problem in the two electrical cranes network and attempts to increase the energy saving at ports by using two different technologies: Energy Storage System (ESS) and Active Front End (AFE). This article introduces one of the first extensive investigations into different networks of RTG crane models and compares the benefits of using either AFE or ESS. The proposed RTG crane models and network parameters are validated using data collected at the Port of Felixstowe, UK. The results of the proposed RTG cranes network show a significant peak demand reduction and energy cost saving.

An active front end (AFE) is required for a three-phase induction motor (IM) fed by a voltage source inverter (VSI), because of the increasing need to derive quality current from the utility end without sacrificing the power factor (PF). This study investigates a proportional-plus-integral (PI) controller based AFE topology that uses a super-lift converter (SLC). The significance of the proposed SLC, which converts rectified AC supply to geometrically proceed ripple-free DC supply, is explained. Variations in several power quality parameters in the intended IM drive for 0% and 100% loading conditions are demonstrated. A simulation is conducted by using MATLAB/Simulink software, and a prototype is built with a field programmable gate array (FPGA) Spartan-6 processor. Simulation results are correlated with the experimental results obtained from a 0.5 HP IM drive prototype with speed feedback and a voltage/frequency (V/f) control strategy. The proposed AFE topology using SLC is suitable for three-phase IM drives, considering the supply end PF, the DC-link voltage and current, the total harmonic distortion (THD) in supply current, and the speed response of IM. [ABSTRACT FROM AUTHOR]

The paper deals with the control of three-phase voltage source rectifiers (VSRs) with an arbitrary number of voltage levels. By means of an approach borrowed from the “Direct Torque Control” of AC drives, the paper presents an enhanced direct power control (DPC) strategy for VSRs which directly controls both active ( P ) and reactive ( Q ) line power by considering the values of their time derivatives. This control strategy can be applied both to the Neutral Point Clamped and to Cascaded H-bridge multilevel converters. In every sampling interval the proposed control technique is able to select the most suitable converter voltage vector to obtain good dynamic response and to maintain P and Q within their respective reference bands. This result is achieved in the different operating conditions by means of a Dynamic Look-Up Table (D-LUT) of the converter voltage vectors, which are ordered on the basis of their influence on P and Q time derivatives. The mentioned D-LUT depends on the instantaneous operating point and is not predetermined. Some significant operating conditions are numerically investigated in order to show the capability of the modified DPC technique to ensure good values of power quality indexes for the grid. Experimental results on a laboratory setup based on a three-level VSR show good accordance with the simulation ones. [ABSTRACT FROM AUTHOR]

This paper studies a regenerative cascaded multilevel converter that substitutes active front ends for the diode-based front ends only in part of cells, and proposes a power tracking control strategy that does not need any motor parameters. During the induction motor's deceleration, by controlling the two kinds of cells' output voltages according to the motor's power factor angle, the converter makes the motor-generated energy wholly collected by regenerative cells; thus, other cells' dc-link voltages remain stable. Regeneration limitation is analyzed. The simulation results of a 6-kV six-cell cascaded converter and experiments on a laboratory cascaded converter verify that the converter can transfer the motor power back to the grid and allows the motor to decelerate more quickly. Moreover, the control strategy is suitable for the drive systems whose regenerated power cannot be estimated or is varying. [ABSTRACT FROM PUBLISHER]

The area of harmonic line current formation by an active front end was established. The theoretic dependence of boundary characteristic for active front end operation with a set value of reactive power consumed from the network (outputted to the network) was obtained. The operating mode for various tasks on the line current displacement angle relative to the supply voltage, as well as tasks of measuring the active front end output voltage were investigated. [ABSTRACT FROM AUTHOR]

This paper introduces a new iterative design procedure of L and LCL filters for low-voltage active-front-end PWM two-level voltage source converters. The analytical expression of the converter harmonic voltages by Bessel functions is applied to design the filter parameters for defined maximum grid current harmonics. Different filter designs are derived for various resonance frequencies and inductance split factors of LCL filter. The minimum amount of stored energy of passive components is used to select a final filter design. A voltage-oriented control scheme, including active damping, is applied in the (400 V and 50 kVA) experimental setup. Both simulation and experimental investigations are presented to verify the accuracy of the filter design procedure. Finally, the steady state and transient performance of the active front end with different LCL filters are depicted. [ABSTRACT FROM AUTHOR]

In this paper, a single phase inductance-capacitance-inductance (LCL) output stage for grid coupled inverters is designed and built. An accurate model and observer of the output filter and the distorted grid voltage are implemented. The paper deals with the construction of a 14-state model, and the feedback control loop to obtain adequate closed loop response. Simulations indicate a good performance of the controller, with a total harmonic current distortion (THD) below 1%. Experimental results confirm simulations, and illustrate the correct operation of the Kalman observer to estimate the distorted grid voltage (THD 3%). The observer only uses the inverter current measurement as input. The output filter effectively reduces the pulsewidth modulation harmonics in the grid current. [ABSTRACT FROM AUTHOR]

Emerging wide bandgap (WBG) semiconductors, such as silicon carbide (SiC), will enable chargers to operate at higher switching frequencies, which grants the ability to deliver high power and enhances efficiency. This paper addresses the modeling of a double-sided cooling (DSC) SiC technology-based off-board charger for battery electric buses (BEBs) and the design of its control and real-time (RT) implementation. A three-phase active front-end (AFE) rectifier topology is considered in the modeling and control system design for the active part of the DC off-board charger. The control system consists of a dual-loop voltage–current controller and is used to ensure AC to DC power conversion for charging and to achieve the targeted grid current total harmonic distortion (THD) and unity power factor (PF). Linear and nonlinear simulation models are developed in MATLAB/Simulink for optimum control design and to validate the voltage and current control performances. Four types of controllers (i.e., proportional–integral (PI), lead–lag, proportional–resonant (PR), and modified proportional–resonant (MPR)) are designed as current controllers, and a comparative analysis is conducted on the simulation model. In addition, the final design of the dual-loop controller is implemented on the RT–FPGA platform of dSpace MicroLabBox. It is then tested with the charger to validate the control performance with experimental data. The simulation and experimental results demonstrate the correct operation of the converter control performance by tracking the reference commands. [ABSTRACT FROM AUTHOR]