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This article presents internal model control (IMC) based decentralized reinforce‐control of renewable dynamic virtual power plant (DVPP) so that, it can be integrated into the power system as a substitution of fuel‐based conventional generators. Such grid integration towards net‐zero targets could not be possible without providing additional ancillary service (AS) to the power system, as the traditional AS would fall short with the retirement/substitution of conventional generators. The theory of DVPP from a technical perspective (i.e., TDVPP) is presented in a detailed and simplified manner, including the formulation of a generalized control objective (desired specification) for DVPP integration. The solution approach includes two steps: (1) disaggregation of desired specification and (2) decentralized reinforce‐control to match the disaggregated specification. The theory and solution approach for DVPP integration is presented in a generalized manner enabling the DVPP to offer multiple ASs, but the case study is limited only to frequency control AS (FCAS) in this article. The study is performed on the 'western system coordinating council (WSCC)' test system, in which an attempt is made towards net‐zero targets by substituting the largest thermal generator with renewable DVPP ensuring the grid's operation or dynamics safe. [ABSTRACT FROM AUTHOR]

Medium‐/High Voltage DC grids are interesting for the integration of renewable energy sources. DC‐DC conversion systems are highly needed for the development of DC grids. Recently, Modular Multilevel Converter (MMC) is the most promising technology for medium‐/high‐voltage applications, but employing the conventional MMC with DC output voltage leads to diversion in the Submodule (SM) capacitor voltages, that is energy drift. This paper proposes a modified modular multilevel DC‐DC converter with self‐energy equalization, which ensures successful DC‐DC conversion with balanced capacitors voltages. In the modified topology, clamping Insulated Gate Bipolar Transistors (IGBTs) are employed in each arm to enable parallel‐connection of the capacitors in the same arm. During the operation (equalization period), the parallel‐connected upper capacitors are connected to the parallel‐connected lower capacitors in each leg through a small limiting inductor to transfer energy between the arms to ensure balanced capacitor voltages. The proposed configuration, along with the operational concepts, mathematical analysis, and design, are presented. Finally, simulation and experimental results are presented for validation. [ABSTRACT FROM AUTHOR]

Conventional modular multilevel converters (MMCs) are promising converters for high-voltage high-power applications. Unlike DC-AC conversion, DC-DC conversion of MMCs suffers from unbalanced capacitor voltages due to the energy drift problem. In this study, a new modular DC-DC converter is proposed, which consists of front-end half-bridge MMC with half-bridge submodules followed by full-bridge MMC with full-bridge submodules. The proposed modular multilevel DC-DC converter can be used effectively for connecting two different DC voltage levels in high-/medium-voltage DC grids. The proposed architecture provides successful DC-DC conversion with balanced capacitor voltages throughout the arm interchange concept. It also provides a high conversion ratio, bidirectional power flow, low losses, low current stresses, reduced number of submodules, and DC fault blocking capability. Detailed illustration, operational concept, and design of the proposed architecture with the arm interchange concept are presented. Simulation results for a high-voltage high-power DC-DC converter with the suggested approach are presented to demonstrate the system performance during different normal as well as abnormal operating conditions. Finally, a scaled-down prototype has been implemented for validation. The extracted simulation and experimental results elucidate the presented claims. [ABSTRACT FROM AUTHOR]

In electric drive applications that are based on high‐speed induction motors (IMs) with an extended speed range, stator winding pole‐changing is a possible technique to avoid oversizing the driving motor. The electronic pole changing employed in multiphase IMs has gained recent interest because it avoids physical winding reconfiguration. The effective number of poles of the air gap flux distribution can be electronically altered by simply changing the applied current sequence to a multiphase stator. The main problem associated with this technique is the significant increase in machine magnetising current with the increase in effective pole number when conventional multiphase distributed windings are employed. This study proposes a new fractional‐slot concentrated winding layout with a special stator connection suitable for pole‐amplitude modulated IMs that offers a 2:1 pole ratio while maintaining equal magnetising current for both winding pole pairs. Moreover, constant power operation can be achieved for a speed range of over 4 pu. The main concept is discussed and verified through simulations and experimentally. The machine mathematical model and the required vector space decomposition‐based controller are also presented. [ABSTRACT FROM AUTHOR]

This paper proposes a new dual modular multilevel converter (MMC) topology as a medium-voltage drive for adjustable-speed applications incorporating open-end stator winding machines. A novel concept of sharing one capacitor between each two adjacent-arm sub-modules (SMs) of MMC phase-legs, operating with out-of-phase modulation, is realised through new SM arrangement. This concept allows the MMC to utilise half the number of the SM capacitors, compared to a traditional MMC topology. Additionally, the sizing requirement of the shared capacitor is diminished, which significantly reduces the volume of the drive system and its stored energy. The switching scheme of the shared capacitor between two oppositely modulated SMs eliminates the problem of capacitor wide-voltage fluctuations, independent of the operating frequency. Further, the proposed MMC can efficiently operate at near zero frequency; therefore, a machine speed-range from zero speed to the rated speed is possible under rated torque operating condition. The proposed MMC topology is elucidated in detail, and its effective performance is verified through simulation. [ABSTRACT FROM AUTHOR]

This paper presents a modular multilevel converter (MMC) configuration that utilises energy exchange between sub-modules (SMs) of upper and lower arms, for energy rebalancing. The configuration is applicable to medium-voltage high-power variable-speed drives with any number of motor phases, where the traditional MMC topology experiences challenging shortcomings. With the out-of-phase alternation of the fundamental ripple power in upper and lower arms, the proposed MMC configuration decouples this ripple power by employing dual half-bridge modules linking opposite SMs in upper and lower arms of the same MMC-leg. This counter-balances arm ripple-power through bidirectional power transfer between opposite SMs, resulting in a reduction in the SM capacitance and the MMC system stored energy. The proposed MMC configuration solves the problem of wide SM capacitor voltage fluctuation, especially at low operating frequencies, where the SM capacitor voltage ripple profile is almost constant, independent of the operating frequency. Therefore, the configuration is able to drive multi-megawatt machines from stand-still to the rated speed, at rated torque. The operation of the proposed converter topology is elucidated in detail, and its effectiveness is verified through simulation and experimentation. [ABSTRACT FROM AUTHOR]

This paper proposes a new high-voltage pulse generator (PG) fed from a low-voltage DC supply Vs, which charges one arm of N series-connected full-bridge (FB) modular multilevel converter (MMC) sub-module (SM) capacitors sequentially, through a resistive-inductive branch. By utilising FB-SMs, the proposed PG is able to generate bipolar rectangular pulses of peak NVs and unipolar rectangular pulses of either polarity, at high repetition rates. Asymmetrical pulses are also possible. The proposed topology is assessed via simulation and scaled-down experimentation, which establish the viability of the topology for water treatment applications. [ABSTRACT FROM AUTHOR]

In this study, a cost‐effective HVDC shunt tap with low‐number of relatively low‐voltage semiconductor devices and small‐sized passive components is proposed. The proposed architecture is based on employing three single‐phase half‐bridge Modular Multilevel Converters (MMCs), where the DC sides of MMCs are connected in series across the total DC‐link voltage. The MMCs are adopted instead of conventional Two‐Level Voltage Source Converters (2L‐VSCs) to avoid the complications of series connection of Insulated Gate Bipolar Transistors (IGBTs). The involved MMCs in the suggested architecture are operated with the conventional 2L modulation, which results in insignificant arm inductors and Sub‐Modules (SMs) capacitances (in range of µH and µF, respectively). This, in turn, affects positively the converter cost and footprint. Each arm of the involved MMCs can be considered as a high‐voltage valve of a 2L‐VSC. To maintain the balance of SMs capacitors, each arm of the involved (N + 1)‐level MMC has an extra SM (a balancing SM) to select N out of N + 1 SMs during the turn‐off condition. The operational concept, design, and assessment of the proposed architecture are presented in this study. Simulation results are provided for substantiation of the proposed concept. Finally, a scaled down single‐phase prototype is used for experimental validation. [ABSTRACT FROM AUTHOR]

Pulse forming networks and Marx generators are the classical rectangular waveform pulse generators (PGs). They are inflexible and their capacitors must be fully charged to the required voltage from 0 V before delivering each high-voltage (HV) pulse. They are only able to generate unipolar pulses; if bipolar pulses are sought another generator fed from a negative supply voltage is added. Recently, several power electronics based PGs have been proposed. This study presents an HV power electronics based PG, which is based on half-bridge modular multilevel converter (MMC) sub-modules (SMs) charged sequentially in a voltage-boost mode. Each SM capacitor and main switch form a boost converter with the charging input supply and inductor. As a result, all SM capacitors are charged to a voltage greater than the input. During the discharging process, the SM capacitors are connected in series, producing a rectangular HV pulse across the load. The proposed charging method allows a reduction in the converter footprint in comparison with recently proposed MMC sequentially charged PG topologies. Although only rectangular pulse waveforms are sought in this study, an SM-capacitor voltage balance method allows multilevel pulse generation. The viability of the proposed converter is confirmed by MATLAB/Simulink simulation and scaled-down experimentation. [ABSTRACT FROM AUTHOR]

Here, a new bi‐directional hybrid modular non‐isolated DC–DC converter is proposed where it consists of a boost converter (BC) fed from the high‐voltage (HV) side. At the BC output stage, a certain number of half bridge submodules (HB‐SMs) is connected across the BC switch. During the turn‐on period of BC switch, the HB‐SMs are connected sequentially to the low‐voltage (LV) side, which results in charging/discharging their capacitors from/into the LV side. While, during the turn‐off period, the LV side is bypassed and the HB‐SMs capacitors are connected in series across the BC output stage, which results in discharging/charging them into/from the HV side. The power flow is controlled in both directions by controlling the duty cycle. The proposed configuration provides self‐balancing operation thanks to the sequential connection of HB‐SMs capacitors, and it also provides the ability to operate with high conversion ratios. Illustration and analysis of the proposed converter and its closed‐loop controller are presented. A full design of the values and ratings of the involved components are presented. Simulation study for a 2.5 MW (25 kV/10 kV) DC–DC converter is presented. Finally, experimental results for a downscaled prototype are presented for validation. [ABSTRACT FROM AUTHOR]

This study proposes an isolated on‐board integrated battery charger using an interior permanent magnet (IPM) machine with a nine‐slot/eight‐pole combination or its multiples, and equipped with a non‐overlapped fractional slot concentrated winding. The proposed winding layout comprises three three‐phase winding sets that are connected in such a way as to provide six motor terminals. Hence, a six‐phase or two three‐phase converters will be required for propulsion. Under motoring mode, the machine can be effectively regarded as a six‐phase machine, which provides a high fault‐tolerant capability, and allows for a 'limp home' mode of operation. Additionally, all magneto motive force subharmonics are eliminated, which significantly reduces the induced rotor eddy current losses, when compared with a conventional three‐phase motor having the same slot/pole combination. In battery charging mode, the winding is reconfigured, so that the machine is considered as a three‐phase to six‐phase rotating transformer. A 40 kW IPM machine is designed and simulated under different modes of operation using two‐dimensional finite element analysis to validate the proposed concept. A small‐scale prototype machine is also used for experimental validation. [ABSTRACT FROM AUTHOR]

In this study, a new transformerless wind energy conversion system to integrate high‐power multi‐phase permanent magnet wind generators to medium‐voltage local grids is presented. The proposed converter topology consists of multi‐half‐bridge modules with a high ac–direct current (dc) boosting capability. Each phase of an open winding multi‐phase generator is connected to the ac side of a half‐bridge module, whereas the dc sides of the half‐bridge modules are connected in series forming the high‐voltage dc‐link output. The proposed architecture facilitates the employment of semiconductor switches with a relatively low‐voltage rating, which equals the dc‐link voltage divided by the number of generator phases. A detailed analysis of the proposed architecture along with the required closed‐loop control is presented. The proposed architecture is simulated under different operating conditions using a typical 2 MW system, while the experimental validation is carried out using a low‐scale prototype converter. [ABSTRACT FROM AUTHOR]

The half‐bridge modular multilevel converter (HB‐MMC) is one of the most promising topologies for high‐voltage direct current (HVDC) systems. Unlike full‐bridge MMC (FB‐MMC) and clamp double sub‐module MMC (CDSM‐MMC), HB‐MMCs are defenceless against DC side faults. Different types of DC circuit breakers (DC CBs) assisted with arrester banks/damping resistors such as solid‐state CB and hybrid DC CBs can be used to interrupt the DC fault current. Arrester banks are used to protect against overvoltage after interrupting the fault current and in turn to demagnetise the circuit inductors. The main disadvantage of the arresters is that they forcibly break apart when they are overloaded. In this study, an arrester‐less fault current limiter is proposed for HB‐MMC configuration, which provides an opposing voltage during the DC side fault. This is achieved by inserting external pre‐charged capacitors in the DC current path during the fault. The selection of these external capacitors, their suitable initial voltages, and their charging stations are also presented in this study. A comparison between the proposed scheme and the CDSM‐MMC has been held as well. The proposed protection scheme is assessed using a simulation study for a point‐to‐point nine‐level HB‐MMC‐based HVDC system. [ABSTRACT FROM AUTHOR]

Differential-mode inverter topologies are promising for renewable energy generation since they offer advantages such as passive elements sizes reduction, having decreased power losses and reduced total cost. Single phase buck-boost differential-mode current-source inverters (DMCSIs) can deliver wider range of output voltage above or below the input dc voltage, which is necessary for high-efficiency modern renewable energy applications. Since these inverters have continuous input currents, they are suitable for maximum power point tracking (MPPT) operation of photovoltaic systems. Yet, the investigation, operation and implementation of these types of inverters have not been extensively discussed. As a drawback, the total dc side input current of a single-phase inverter consists of a dc component and an undesirable ac component. This ac component frequency is double the output voltage frequency and thus it affects MPPT resulting in reduced total efficiency. In this study, five promising DMCSIs are proposed and compared in terms of their total efficiencies, high-frequency ripple current in the dc side, total harmonic distortion, devices sizes and ratings. Moreover, the sliding mode controller's design and possible methods of eliminating the input second harmonic current are discussed. 2.5 kW bidirectional inverters are implemented to confirm the design flexibility of the proposed DMCSIs. [ABSTRACT FROM AUTHOR]

In many applications, interior permanent magnet synchronous machines (IPMSMs) with fractional slot concentrated windings (FSCWs) are considered promising candidates in terms of higher power density and efficiency. In addition, employing a multiphase stator winding improves the drive train availability and increases reliability. This study investigates the effect of applying stator shifting to five‐phase FSCW winding IPMSMs to suppress the effect of the slot harmonics by doubling the number of slots. In this case, the winding coil pitch will be two, which stands as a compromise between single‐tooth and distributed winding topologies. This highly improves the air gap flux distribution, significantly reduces both rotor core and magnet eddy current losses, and increases saliency ratio and reluctance torque component. Moreover, an improved performance under fault conditions, in terms of lower torque ripple, and core and magnet losses, adds to the main advantages of this technique. Various slot/pole combinations suitable for five‐phase machines are investigated. A full simulation case study based on two‐dimensional finite element analysis is applied to the 20‐slot/18‐pole stator with single‐tooth winding under both healthy and open‐circuit phase fault cases. [ABSTRACT FROM AUTHOR]

This study proposes a new architecture of flywheel energy storage system (FESS) which can be implemented at generating unit (GU) level (e.g. wind turbine) or scaled up for application in grid‐side converter (GSC) stations of a multi‐terminal direct current (MTDC) system. The proposed architecture suppresses DC voltage leaps under grid faults, and performs power levelling duty at grid connection points. When implemented at GU level, the proposed FESS features a doubly‐fed induction machine (DFIM) – the flywheel machine – where its six stator winding terminals are connected in series between the grid and the GSC. The flywheel converter is of partial power rating, and is connected to the DFIM rotor. When employed at an MTDC GSC station, several submodules are connected to build an FESS station. The study proposes the control concept and the general topology of the FESS station. The performance parameters of the system are tested under normal and abnormal operating conditions. Results and analyses indicate smooth dynamic operation, the economic advantage and the improved fault ride‐through capability because of the proposed system. [ABSTRACT FROM AUTHOR]

The growing penetration of renewable energy resources and distributed generation (DG) has raised significant interest in power quality issues. Achieving low total harmonic distortion of exported current using low switching frequency inverters such as current source inverters (CSI) is a challenge, especially under conditions of severe utility voltage distortion. This study presents a control structure for a CSI-based DG system, based on a multi-synchronous reference frame (MSRF) architecture that rejects the effect of utility voltage distortion and helps attain high-quality output current. The proposed solution is applicable for low switching frequency inverters with limited passive filter bandwidth. The MSRF architecture presented confines two stages; one for harmonics extraction and another for harmonics rejection. A state-space-based stationary frame equivalent model of the proposed MSRF architecture is presented; this substantially reduces the computational load while preserving system performance. Experimental results validate the proposed technique against the conventional harmonic rejection controller. [ABSTRACT FROM AUTHOR]