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In this article, a self-organizing power electronic converter with control intelligence at the edge of the distribution network is proposed. The proposed converter is called power electronics intelligence at the network edge (PINE), and it has the potential to add intelligence at the network edge to the electricity delivery system of the present and in the future. The proposed approach consists of a power electronic converter (rectifier/dc-link/inverter) termed PINE to supply residential loads. The rooftop solar and battery energy storage system is connected to the dc link. With the bidirectional characteristic of the PINE, the load voltage is regulated via feedback, whereas input distribution voltage can be allowed to vary in a range. This type of configuration allows for control of input power factor to be unity and reactive power to be injected at the grid edge to regulate the voltage and also enable energy budgeting, i.e., limit the amount of power to the residential load under disaster situations. With the PINE converter at the distribution edge that can communicate with other PINEs as well as to the distribution system operator, intelligence at the distribution edge can be established. Such a system has many advantages that are discussed in this article. Furthermore, the impacts of increased penetration levels of PINE are shown using a test feeder based on the IEEE-37 test node feeder. Simulation and experimental results on a laboratory prototype system validate the PINE converter concept.

Countries around the world are setting ambitious goals to achieve carbon neutrality by the mid-21st century. Most plans involve the integration of massive renewable energy resources into the electricity grid. In addition to the large wind and solar farms at the bulk power grid level, there is an increasing number of grid-edge distributed energy resources (DERs) in the queue of installation. Therefore, the role of electricity end users is shifting from passive consumers, who can only purchase electricity, to active prosumers, who can both produce and consume electricity.

This study investigates a novel hybrid cooling method for more weight efficient thermal management of aerospace electric propulsion motors using thermal energy storage (TES) elements. The proposed system utilizes the latent heating of TES in the form of SAPO-34 zeolite slabs hydrated with water to maintain stable operating temperatures during takeoff. The TES operates in parallel with a fluid cooling system comprised of minichannel heatsinks attached to the stator windings and exterior air heat exchanger. Thermoelectric performance benefits of TES inclusion are evaluated using network analysis under assumed flight path load. Complex non-linear thermofluid and electromagnetic behaviors in the network are replaced with lookup table interpolants generated using results of numerical simulations swept across a series of input parameters. Subsequent solution of two-hundred systems with varying TES volume indicated a maximum TMS mass savings of 14.8% compared to the lightest thermal management system without TES inclusion.

There is a growing interest in deploying medium-voltage dc-collection grid technologies in renewable energy applications to improve energy efficiency. Existing dc-collection grids incorporate medium-voltage dc/dc converters that suffer from bulky passive components such as a step-up transformer along with additional conversion stage to incorporate MPPT function. In response to these concerns, this article proposes a new medium-voltage dc-collection grid method for large-scale PV plants with an interleaved modular multilevel (IMMC) dc–dc boost converter. The proposed IMMC converter is synthesized with lower voltage half-bridge SiC inverter blocks connected in series to support medium-voltage dc–dc conversion. The half-bridge blocks of the IMMC employ SiC switches, along with high-frequency PWM operation enable compact size/weight along with high-efficiency conversion. Simulation results are shown for 1500-V (dc) to 16-kV (dc) conversion with four series-connected IMMC inverter blocks powered from two PV plants. A power-sharing stage is an integral part of the proposed converter. This enables two series-connected PV plants to supply unequal power under partial shading conditions. Control of the power-sharing stage for varying insolation from PV (1000–500 W/m2) due to the shading effect is shown. A design example for 1-MW PV power plant block based on the specifications derived from Kuwait Shagaya 60-MW solar power plant is discussed. Experimental results on a scaled-down laboratory prototype are included in this article.

In this article, an integrated solid-state transformer (I-SST) with high-frequency (HF) isolation for electric vehicle (EV) fast-charging applications is proposed. In the approach proposed in this article, a three-phase I-SST is used as HF galvanic isolation for the system with respect to the medium-voltage grid. A direct multipulse ac–dc rectifier is shown to eliminate low-order harmonics in the input current over a wide range of output dc voltage variation. The proposed approach has the following advantages: no dc link, hence no bulky electrolytic capacitors, galvanic isolation is via a three-phase HF transformer, high-power density, and simple control scheme for regulating output voltage. The approach is easily scalable to several hundreds of kilowatts and is ideal for high-power level-3 EV fast-charging stations. A simplified output voltage regulation scheme for the proposed topology is discussed. Regulating the output voltage enables the circuit to be used as a direct topology for level-3 charge stations with ac bus architecture. Experimental results on a scale down laboratory prototype at 208 V, 1.5 kW are discussed. 1

Realizing a smart Low Voltage Distribution System (LVDS) is essential to realize a smart grid. Restructuring the existing distribution system into microgrids is one important requirement to achieve a smart LVDS. The realization of microgrids in LVDS can take different shapes in different countries. This article discusses the challenges and practical solutions to realize a smart LVDS for radial distribution grids, which are common in India. The network following a distribution transformer can be distinguished as a microgrid for radial low voltage distribution grids. However, this leads to many operational issues. Therefore, this article envisions replacing the Low Voltage distribution transformers with Solid-State Transformers (SSTs). This will enable the LVDS to control the power exchange between the phases within a microgrid as well as power exchange between different microgrids. The architectural design of a smart home in smart LVDS is outlined to complete the discussion. Various unique features required for smart inverters in a smart home and existing grid codes to make them compatible with smart LVDS are also reviewed.

This paper proposes a modular three-phase diode rectifier with high frequency isolation and sinusoidal input currents. The proposed system consists of modular AC-AC converters with 20 kHz transformer isolation on the primary side. A new hybrid pulse width modulation scheme is proposed that combines the high frequency 20kHz with a low frequency selective elimination of 5th, 7th, 11th and 13th current harmonics in the input such that the resulting utility current is nearly sinusoidal. The secondary side consists of a standard three-phase diode rectifier for a high quality dc output voltage suitable for ev-charging/switch mode power supplied in data centers etc. The proposed approach is modular and the output voltage is regulated via simple duty cycle control. Simulation results are discussed in the summary. Experimental results are presented on laboratory 208 V three phase, 1kW prototype hardware.

In this paper an active detection scheme for sensor spoofing (manipulated externally via a cyber attack) in grid-tied PV systems is discussed. The core of the proposed active detection scheme is to introduce a private (secret) watermarking signal into the control inputs of the DC-DC converter and DC-AC inverter stages to detect any malicious spoofing (manipulation) of voltage/current sensor measurements controlling both the DC-DC converter maximum power point tracking (MPPT) stage and the DC-AC inverter of the grid-tied PV system. Several types of possible spoofing mechanisms (attack models) are discussed. The proposed sensor spoofing attack detector system consists of injecting a small magnitude of digital watermarking signal (DWS) and conduct three statistical watermark tests on the reported sensor measurements to determine if a) the proposed system is healthy and operating as expected b) if sensor signals were spoofed (manipulated) externally or c) if a particular sensor is malfunctioning due to a faulty hardware. It is shown via extensive simulations that the proposed DWS approach is robust in detecting malicious external manipulation of sensors controlling the grid tied PV system. A testing platform is currently under development and the experimental results will be discussed in the conference presentation.

In this article, a broad overview of the current research trends in power-electronic innovations in cyber-physical systems (CPSs) is presented. The recent advances in semiconductor device technologies, control architectures, and communication methodologies have enabled researchers to develop integrated smart CPSs that can cater to the emerging requirements of smart grids, renewable energy, electric vehicles, trains, ships, the Internet of Things (IoT), and so on. The topics presented in this article include novel power-distribution architectures, protection techniques considering large renewable integration in smart grids, wireless charging in electric vehicles, simultaneous power and information transmission, multihop network-based coordination, power technologies for renewable energy and smart transformer, CPS reliability, transactive smart railway grid, and real-time simulation of shipboard power systems. It is anticipated that the research trends presented in this article will provide a timely and useful overview to the power-electronics researchers with broad applications in CPSs.

In this paper, validation of a Robust Cyber Shield (RCS) for a grid connected inverter is presented. This paper specifically address the problem of attacks on sensor measurements. When incorrect sensor measurements are used in feedback control loops of the inverter controls, it can lead to incorrect actuation that can cause instabilities or degrade performance. The Robust Cyber Shield (RCS) approach consists of a a defense mechanism termed as dynamic watermarking to detect malicious manipulation of voltage/current sensor measurements feeding inverter control. To prove that the proposed attack detector will not be triggered when there are disturbances present in the grid, such as low-order harmonics, the detector is tested under different conditions on the grid voltage. To test the validity of the proposed approach, a testing platform is developed with a laboratory scale experiment to obtain Hardware results using a real inverter. Simulation results from a grid connected inverter system are also discussed.

In this paper, a single-phase Power Factor Correction (PFC) approach employing a GaN Totem-Pole topology with an H-Bridge Active Power Decoupling (APD) stage is discussed. With the addition of APD stage coupled with closed loop control the DC-Link capacitor size is shown to decrease. The proposed topology is composed of three GaN high switching frequency legs (100 kHz) and one low (line) frequency leg (60 Hz). The H-Bridge APD circuit consists of two of the high switching frequency legs (100 kHz) with four GaN FETs, a decoupling capacitor and an inductor. Simulations and experimental results show the effectiveness of the proposed approach.

This paper introduces an active defense mechanism against cyber attacks in grid-tied Photovoltaic (PV) systems connected at the distribution level. The core of such a defense mechanism dynamic watermarking approach is to detect malicious manipulation of voltage/current sensor measurements feeding inverter control. The defense mechanism is described in detail and several attack possibilities, based on manipulating the current measurements, are described. Three attack models are used to test the validity of the proposed approach on a single-phase, 5 kW, grid-tied inverter, connected at the distribution level.

This paper proposes a new direct three-phase AC-DC rectifier with high-frequency open-delta transformer isolation. The three-phase input voltages are modulated by two AC to AC converters to generate a high-frequency link at 20 kHz. The high-frequency link is then interfaced to a 12-pulse rectifier by means of a high-frequency open-delta transformer arrangement. The resultant output voltage is shown to be high quality and its magnitude is controllable via phase shift modulation. Moreover, the proposed modulation allows the high-frequency converter to achieve soft switching. The output DC voltage can be regulated via a simple duty cycle control. The overall three-phase input currents are of high quality and near unity power factor due to the cancellation of 5th and 7th harmonics. The proposed approach substitutes the bulky line-frequency transformer with a high-frequency transformer, thereby achieving higher power density. Simulation results demonstrate the validity of the concept. Experimental results on a laboratory prototype system demonstrate the feasibility of the proposed approach.

In this paper, a new high-frequency multilevel bridgeless boost power factor correction approach is presented. The proposed topology is a multilevel boost power factor correction circuit that significantly reduces voltage stress on switching devices, the input inductor, and the DC link capacitors. The effective switching frequency of the input current is also multiplied allowing for a significantly smaller input inductor, which improves power density. The design also reduces the voltage rating of all DC link capacitors. Additionally, the design allows access to fractional voltage levels, which can be beneficial for designs which immediately buck the DC link voltage to a lower voltage. A design example and simulation results are presented for a 100 W design and hardware results are presented for a 100 W design.

This paper proposes a new battery charger station architecture based on Integrated Solid-State Transformer (I-SST). The system consists of modular AC-AC converters with 20 kHz isolation and direct three-phase AC- DC Medium Voltage (MV) conversion. Output DC voltage regulation is achieved with a simple control scheme. Zero Voltage Switching (ZVS) is achievable for a wide output voltage range using phase-shift modulation. To comply with IEEE-519 standard, an Active Power Filter circuit block is employed. Simulation and experimental results are discussed.

In this paper, a high frequency integrated solid state transformer (SST) for utility interface of solar PV / battery energy storage system is proposed. The primary side consists of three 1-phase AC-AC converter blocks with a weak dc-link interfaced to a high frequency transformer. The secondary side of the transformer is connected to the three-phase PWM current source converter (CSC). The input AC-AC converters are modulated using high frequency square wave 20 kHz with 50% duty cycle. CSC is controlled with selective harmonic elimination (SHE) PWM technique with 5th, 7th, 11th, 13th harmonics elimination. It is shown that the utility line currents are of high quality with the elimination of lower order harmonic currents. The proposed approach has the advantages of higher power density, absence of electrolytic capacitors, higher frequency isolation. Simulation results are presented on a 120kW solar PV system employing 1500V DC. Experimental results for a scale down laboratory prototype are discussed to verify the concept.

In this paper a transformer-less hybrid PV inverter with integrated battery energy storage is proposed. The proposed converter integrates both solar PV and battery sources with the ability to control for maximum power transfer as well as control the charge discharge functions of a battery energy storage system. The proposed control employs a single current and single voltage sensor with perturb and observe based method to achieve maximum solar power and battery state of charge control. The proposed interleaved modular multilevel converter boosts the dc link voltage to suitable value to enable transformer-less interface to the electric commercial utility grid. It is shown that ZVS operation will yield higher conversion efficiency. Simulation results validate the concept over a wide operation range. Preliminary experimental results are discussed.

This paper proposes a medium-frequency (MF) solid-state transformer (SST) based grid interface for high-power multipulse rectifiers. In the proposed approach, the low-frequency ac (grid) voltage is transformed to MF voltage via front-end converters. The three single-phase MF outputs from these converters are fed to the primary side of a three-phase, five-limb multiwinding isolation transformer (or alternately three one-phase transformers). The secondary side windings from the transformer are configured in a certain “zig-zag” arrangement, which are connected to the inputs of three-phase diode rectifier modules as in a typical multipulse system. The proposed topology can better than double the power density by reducing volume (or weight) of the required front-end isolation transformer while maintaining the same input current quality as a conventional low-frequency transformer based approach. Usage of an open-loop square wave pulse width modulation for the front-end converters makes this approach simple to implement. This paper explains the proposed concept taking an adjustable speed drive application's perspective using modeling, simulation, and experimental results from a scaled down laboratory prototype.

This paper investigates a dc collection grid architecture to process energy from offshore wind turbine generators (WTGs), which can be further interfaced with the shore via a high-voltage dc network. In the proposed approach, WTG output voltage is rectified and converted to medium frequency (MF). Then, a transformer isolation stage is used, followed by a boost rectification stage. The boost rectification stage is controlled to emulate a resistive load, forming a medium voltage dc (MVDC) interconnection. This type of control is simple for varying wind conditions. The operating principles and unique advantages of the proposed approach are documented along with comparison with a conventional benchmark, assuming the turbines are fitted with direct drive technology. System design example, loss/size analysis and transformer finite element analysis are shown in this paper. Simulation results demonstrate the functional capability of the system. Experimental results from a scaled down prototype prove the operation of proposed concept.

This paper presents a reduced switch count multipulse rectifier with medium-frequency (MF) transformer isolation. The proposed topology consists of a three-phase push–pull based ac to dc rectifier with a MF ac link employing two active switches. A three-phase, five-limb, multiwinding MF transformer is employed for isolation. The secondary side of the transformer is connected in a zig-zag configuration and is fed to two six-pulse diode rectifiers, achieving 12-pulse rectifier operation. The primary advantage of the proposed system is reduction in size/weight/volume compared to the conventional 60 Hz magnetic transformer isolation rectifier system. Operating the transformer at 600 Hz is shown to result in three times reduction in size. Furthermore, the proposed system employs only two active semiconductor switching devices operating under a simple pulse width modulation scheme. Also, the zig-zag transformer connection helps to balance leakage inductance on the secondary side. Detailed analysis, simulation, and experimental results on a 208Vl-l, 3.15 kW laboratory prototype are presented to validate the performance of the proposed approach.

This paper presents a series voltage regulator for a distribution transformer which addresses power quality issues in the electrical power distribution system. The proposed system is comprised of a line frequency transformer connected to a power electronic converter which is autoconnected on the secondary side. This autoconnection is facilitated by use of a high-frequency or medium-frequency transformer. A simplified strategy to compensate for voltage sags and swells on the grid side, by providing continuous ac voltage regulation, is discussed. When a voltage sags or swells occur, the power electronic converter generates a compensating voltage, which is vector-added to the grid voltage in order to regulate the output voltage supplied to the load. The proposed system satisfies needs of smart distribution grids in terms of improved availability, equipment protection, and resilience. Detailed analysis is provided with experimental results in order to validate the effectiveness of the proposed system.

Reports on the mission and activities of the PELS Digital Media and Education Committee. It’s primary objective is to contribute, support, and lead this mission by disseminating knowledge, fostering engagement, and creating excitement among IEEE PELS members, the engineering and scientific community, and the general public. In keeping with the mission, the Committee organized a number of activities this year.

In this paper we present a methodology to compare DC-AC or AC-DC power conversion topologies by calculating their indirect power $(\mathbf{P}_{\mathbf{ind}})$ . It is shown that $\mathbf{P}_{\mathbf{ind}}$ impacts on volume and losses of passive components, therefore by comparing this factor, high-level comparison of various circuits can be made. DC-AC or AC-DC topologies are modeled as quasi-static DC-DC converters at each working point along the line cycle, and continuous power models are used as the basic tool. Since this modeling methodology is bi-directional, in this paper only the DC-AC inverting is discussed as example. Several DC-AC inverter topologies such as: conventional 1-phase half/full bridge and the interconnected modular multi-level converter (IMMC) are examined from the perspective of $\mathbf{P}_{\mathbf{ind}}$ . While each type of DC-AC inverter topology has found its place in applications, the proposed analysis draws attention to the fact that certain inverter configuration process nearly twice the amount of power in passive components. With the emergence of wide band gap devices and their availability in higher power ranges, an examination of indirect power processed by passive components to accomplish the DC-AC or AC-DC topologies can open new doors for further optimization and topology selection to suite particular applications.

This paper proposes a medium voltage (MV) DC collection grid concept for large-scale PV power plant with a line commutated 12-pulse SCR converter and an integrated solid-state transformer (SST) for utility interface. DC power from the PV power plant sections is first processed via a line commutated 12-pulse converter employing an inverter grade SCR’s is interfaced to a SST powered by a higher frequency AC-AC converter. The objective of this paper is having the SST operate at medium frequency (360Hz or 720Hz), to reduce the transformer size/weight to 1/3rd to 1/5th. It is shown due to 12-pulse operation a high-quality utility line current can be achieved with the cancellation of 5th and 7th harmonic currents. The proposed approach is a robust current fed system, that improves power density, is simple to control with an integrated solid-state transformer. Simulation results presented on an example 150 kW PV power plant to validate the concept. Experimental results from a scale down laboratory type 1kW system are also discussed.

This paper proposes a single stage transformer-less (SSTL) microinverter with integrated battery storage system (BSS). This topology is envisioned as a high switching frequency power semiconductor unit with compact size passive elements that realizes 120/240V/50-60Hz AC output. The proposed system establishes a common ground between solar PV and battery storage. Both MPPT function for PV along with charge/discharge controller function for storage battery is enabled by the power sharing stage. The power-sharing unit is followed by a two-stage twin DC-DC interleaved modular multilevel converter (IMMC) units to boost the PV/battery output to 400VDC. Due to 180 degrees phase shift control and symmetry of upper and lower DC- DC IMMC units voltage ripple is cancelled. The DC-AC inverter stage has a built-in active decoupling stage to eliminate twice the line frequency ripple in the dc-link capacitor. This function along with the 180-degree phase shift control of the DC-DC IMMC stage drastically reduces the size of the dc-link capacitor value. Various Modes of operation are simulated to show the performance of the proposed system under different insolation conditions demonstrating battery charge/discharge functions. Preliminary experimental results from a prototype laboratory converter is presented in the paper.

In this paper, a direct three phase multi-pulse AC-DC rectifier topology with high frequency isolation for fast-charging stations for electric vehicles (EV) is proposed. By using a multi-pulse approach, low order harmonics in the input current are eliminated. The proposed topology has the following advantages: no DC-link energy storage capacitor, high frequency galvanic isolation, higher power density (due to high switching frequency) and simple control scheme. The novelty of the proposed topology is its low complexity, ease of control and robust operation due to it’s inherit 12-pulse rectifier behavior. The approach is easily scalable to several hundred kilowatts and is ideal for driving high power Level 3 fast EV battery chargers. Experimental results on scale down laboratory prototype 208V, 2kW unit are discussed.

This paper presents a comparison between mitigation techniques for double line frequency ripples in single-phase microinverters based on wide-bandgap FETs. A topology based on an auxiliary dc–ac stage is adopted based on optimizing both power density and efficiency to achieve the pressing needs of the next generation of microinverters as announced by Google’s little box challenge. An accurate yet simple control algorithm is proposed that provides a ripple-free dc current. Experimental results demonstrate the effectiveness of the presented topology and control algorithm in achieving a high-power-density microinverter rated at 2 kW.

In this paper, a self-organizing power electronic converter with control intelligence at the edge of the electric distribution network is proposed. The proposed framework, termed Power Electronics Intelligence at the Network Edge (PINE), has the potential to make the future electricity delivery system more internet-like (i.e., intelligence at the network edge). This approach addresses the need to mobilize distributed energy resources, as well as to endow the power grid with edge-based intelligence to provide local communities with at least the critical portion of their electricity needs, hence improving the overall resiliency of the electric grid. The proposed concept has many advantages including: a) energy budgeting is possible and can be enabled remotely, b) power flow is bidirectional, c) output voltage is regulated via PWM control, d) distribution voltage can vary over a wider range, e) input current is harmonic free at unity power factor. Simulation and hardware results validate the proposed concept.

In this paper, a modified Angle Droop Control (ADC) scheme is presented with added flexibility for accurate peer-to-peer Transactive Energy (TE) control in an interconnected microgrid system. The proposed scheme enables TE (i.e., energy transfer on demand) between two or more microgrids with simultaneous guaranteed stable operation due to overlaid ADC. To enable such a scheme, the concept of a power router (PR) for power flow control is introduced. The PR is realized by augmenting a fractionally rated transformer with AC-AC converter blocks (also fractionally rated). This leads to a topology which is named as Power Electronics Transformer with Dynamic Voltage and Angle Droop Control (PET-DVADC). The interface of the proposed topology resides at distribution voltage level of the micro-grid interface point before the step-up transformer. Extensive simulations on a five interconnected microgrid architecture are presented. Energy transactions between two and three microgrid examples are discussed with the proposed PET-DVADC control.

This paper presents a new two-stage differential mode power converter to enable higher energy yield for large-scale solar power plants. The proposed topology is characterized by its fractional power rating, higher efficiency, scalability and lower cost. The approach consists of dividing a given solar field to several zones, employing a center point ground with ±1500V DC collection grid and interconnecting them with fractional rated current/voltage balancing converter topology to achieve maximum power point tracking (MPPT) thereby mitigating the effects of partial shading and temperature differences. The proposed system is shown to be scalable to suite large-scale solar PV power plants. A design example along with simulation results are discussed for a wide range of insolation/temperature levels for a 1.1 MW power plant.

In this paper, a new medium voltage DC collection grid method for large-scale PV plants is proposed. An Interleaved Modular Multilevel (IMMC) DC-DC boost converter is proposed in order to enable medium voltage DC power collection grid followed by a central medium voltage class DC-AC inverter for utility interface. The proposed IMMC converter is synthesized with lower voltage half-bridge SiC inverter blocks connected in series to support medium voltage DC conversion. The half-bridge blocks of the IMMC employ SiC switches, along with high frequency PWM operation enable compact size/weight along with high efficiency conversion. Simulation results are shown for 1500V (DC) to 16kV (DC) conversion with four series connected IMMC inverter blocks powered from two PV plants. A power sharing stage is an integral part of the proposed converter. This enable two series connected PV plants to supply unequal power under partial shading conditions. Control of the power sharing stage for varying insolation from PV (1000-500W/m2) due to shading effect is shown. A design example for 1MW PV power plant block based on the specifications derived from Kuwait Shagaya 60MW solar power plant is discussed. Experimental results on scale down laboratory prototype is included in the paper.

This paper presents an active decoupling technique for a dual phase output inverter with an integrated power optimizer for off-grid applications. The proposed method employs a half bridge with passive elements (L-C) to balance the output and actively compensate for twice the frequency power ripple in the dc-link, The closed loop control adjusts for varying load conditions. Further, an integrated power optimizer (PO) provides interface of solar-pv and battery to the dc-link, The PO stage (half bridge) is controlled such that maximum power point tracking (MPPT) is achieved for the connected pv-array and independent charge/discharge functions of the battery. Simulation and experimental results verify the performance of the proposed technique under balanced, unbalanced load, non-linear conditions as well as fault condition.

A new Interconnected Modular Multilevel Converter (IMMC) for photovoltaic (PV) applications is proposed in this paper. The proposed IMMC is a high power density converter that produces a sinusoidal output voltage. The sinusoidal output voltage and high power density of the converter makes it suitable to be proposed as a micro-inverter for PV applications. The IMMC has the following advantages: low EMI; sinusoidal output voltage; low voltage GaN switches can be employed due to its multilevel structure. The proposed system is modular in construction employing high frequency L-C components. Simulation results of a single-phase grid-connected IMMC micro-inverter including the Maximum Power Point Tracking (MPPT) operation and grid-tie control. Experimental results are presented to demonstrate the feasibility of the proposed micro-inverter.

A new voltage and current balancing topology is introduced to enable a better energy yield from central inverters for large-scale solar power plants. The proposed balancing topology is characterized by its fractional power rating, high efficiency, scalability and low cost. The approach uniquely locates the maximum power point (MPP) for the system using a new developed algorithm such that it will increase the overall system efficiency. The proposed approach would be using a two staged differential power converter where the PV voltage and current are measured during each period of operation and the power converter will keep adjusting itself to maintain operation at the maximum power point. The two stages differential power converter is not a substitute for the central inverter; a central inverter would still be required to achieve maximum power point by matching the maximum available current and voltage seen by the inverter. The proposed two stages differential power converter is a new concept which addresses various needs of the present and future power generation units in the grid. The main advantages for the multistage differential power converter are: 1- The MPP is efficiently distributed on system level and each stage will match both voltage and current to reduce circulating power and maximize harvested power. 2- The controls are less complex than other existing solutions. 3- Less number of blocks, passive components, and switches used to run the new system for full integration with the grid. 4- Commercially practical solution since it requires simple control techniques and optimizes overall system efficiency. The first stage of the power differential converter is called the power sharing converter (PSC), and the second stage is voltage balancing converter (VBC). The PSC is a half H-Bridge circuit that has two PV groups are connected to it as an input to the converter; the PSC will adjust the total current between the two PV groups such that the current difference will be created between them equal to the maximum current available by one group subtracted from the other PV group by using passive element such as inductor between the two groups. VBC is also in the form of half H-bridges connected in parallel. Therefore, it would see all the available voltages by the connected strings such that each of the VBC would balance the voltages between the different strings. The voltage balancing is done by adjusting the switching duty ratio of the half H-Bridge switches. The proposed design gave an extra degree of freedom in creating better power matching conditions within each PV group as well as on the system level. The modeling equations for the proposed system was derived and proved the robustness of the proposed system. The simulation results showed the effectiveness of the proposed circuitry along with the newly proposed MPPT design, and it showed the system energy harvesting efficiency was 98% in comparison to the traditional method with 63% efficiency designed for a PV power plant with capacity of 160 KW. The circuit would be implemented in hardware design using Gallium Nitride (GaN) switches with switching frequency of 100 KHz which can endure high voltage rating and moderate current levels.

Current grid standards largely require that low-power (e.g., several kilowatts) single-phase photovoltaic (PV) systems operate at unity power factor (PF) with maximum power point tracking (MPPT), and disconnect from the grid under grid faults by means of islanding detection. However, in the case of wide-scale penetration of single-phase PV systems in the distributed grid, disconnection under grid faults can contribute to 1) voltage flickers, 2) power outages, and 3) system instability. This article explores grid code modifications for a wide-scale adoption of PV systems in the distribution grid. In addition, based on the fact that Italy and Japan have recently undertaken a major review of standards for PV power conversion systems connected to low-voltage networks, the importance of low voltage ride-through (LVRT) for single-phase PV power systems under grid faults is considered, along with three reactive power injection strategies. Simulations are presented for a PV power system with a LVRT capability and ancillary services. An example of a full-bridge single-phase grid-connected system is tested experimentally to demonstrate the potential benefits. Additionally, grid codes for advanced PV systems with the discussed features are summarized.

A multilevel topology with medium-frequency ac link for medium-voltage grid integration of utility photovoltaic (PV) plants is discussed in this paper. A megawatt-scale PV plant is divided into many zones, each comprising of two series-connected arrays. Each zone employs a medium-frequency transformer with three secondaries, which interface with the three phases of the medium voltage grid. An insulated-gate bipolar transistor full-bridge inverter feeds the MF transformer. The voltages at the transformer secondaries are then converted to three-phase line frequency ac by three full-bridge ac-ac converters. Second line frequency harmonic power does not appear in the dc bus, thereby reducing the dc capacitor size. Cascading several such cells, a high-quality multilevel medium-voltage output is generated. A new control method is proposed for the cascaded multilevel converter during partial shading while minimizing the switch ratings. The proposed topology eliminates the need for line frequency transformer isolation and reduces the dc bus capacitor size, while improving the power factor and energy yield. This paper presents the analysis, design example, and operation of a 10-MW utility PV system with experimental results on a scaled-down laboratory prototype.

A fault-tolerant adjustable speed drive (ASD) topology is introduced in this paper. A conventional ASD topology is modified to address: 1) drive vulnerability to semiconductor device faults; 2) input voltage sags; 3) motor vulnerability to effects of long leads; and 4) minimization of common-mode (CM) voltage applied to the motor terminals. These objectives are attained by inclusion of an auxiliary IGBT inverter leg, three auxiliary diodes, and isolation-reconfiguration circuit. The design and operation of the proposed topology modifications are described for different modes: 1) fault mode, 2) active CM suppression mode, and 3) auxiliary sag compensation (ASC) mode. In case of fault and sag, the isolation and hardware reconfiguration are performed in a controlled manner using triacs/antiparallel thyristors. In normal operation, the auxiliary leg is controlled to actively suppress CM voltage. For inverter IGBT failures (short circuit and open circuit), the auxiliary leg is used as a redundant leg. During voltage sags, the auxiliary leg, along with auxiliary diodes, is operated as a boost converter. A current-shaping control strategy is proposed for the ASC mode. A detailed analysis of CM performance of the proposed topology is provided, and a new figure of merit, CM distortion ratio (CMDR), is introduced to compare the attenuation of CM voltage with that of a conventional ASD topology. The output filter design procedure is outlined. A design example is presented for an 80 kW ASD system, and simulation results validate the proposed auxiliary leg based fault-tolerant scheme. Experimental results from a scaled prototype rated at 1 hp are discussed in this paper.

This paper presents a family of new multiport power-sharing converter (PSC) topologies for utility-scale fuel cell (FC) power generation. The proposed system connects multiple FC sources to a medium-voltage grid via a single multilevel neutral point clamp (NPC) inverter interface with high-frequency isolation. High-voltage series-connected inputs are achieved, despite safely referencing each source to ground. Also, unique power-sharing technology decouples series-connected source currents and enables control of each FCs individual power level. Multidimensional modeling and analysis of the proposed system's PI- and PV-behavior is presented. Then, system topology and design considerations are discussed. Case study simulations show how this topology can operate four 250-kW FCs at separate power levels between 20% and 100%, while connecting to a single three-level NPC utility-interface. Correspondingly, a reduced-scale hardware prototype provides further proof of concept. Altogether, the proposed family of multiport PSC topologies realizes independent power control per source as well as increased output power, operational flexibility, thermal balancing, source availability, and cost effectiveness for utility FC power generation.