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We derive analytically expressions for the probability distribution of the propagation delay time of logic signals through a CMOS inverter when the inverter power supply voltage $V_{{\text{dd}}}$ (more precisely, gate voltage $V_{{\text{GS}}}$) is itself probabilistic for some reason (e.g., system noise or a random external electromagnetic disturbance). Since the propagation delay time is a function of the value of $V_{{\text{dd}}}$ , then some values of $V_{{\text{dd}}}$ may produce values of the inverter propagation delay time that cause the circuit in which the inverter resides to malfunction (e.g., by resulting in an inverter delay time value not conforming with the delay time margins for that circuit). Based upon the derived inverter propagation delay time probability distribution, we then derive a probability for the malfunction of a circuit containing a single inverter subject to such a stochastic $V_{{\text{dd}}}$. In this paper, we present no discussion of the application of our formalism to example probability density functions for $V_{{\text{dd}}}$ ; we rectify this situation by presenting three detailed such examples in a companion paper in this journal. [ABSTRACT FROM AUTHOR]

This paper addresses the resonance problem in a parallel-inverter-based grid-connected system. Harmonic interactions between inverters and the grid exhibit various number of complicated characteristics that threatens the system stability and power quality. In this paper, a method of harmonic resonance analysis is proposed to investigate the resonance problem in a multi-inverter grid-connected system based on resonance modal analysis (RMA) and participation factor (PF) calculations. Initially, an impedance-based analytical approach is employed and expanded to an electricity distribution network that is dominated by multiple inverters with LCL filters and proportional resonant controllers. Then, the RMA is introduced to investigate the resonant interactions among inverters and the grid. Specifically, harmonic resonance characteristics are addressed through transfer functions and the proposed method considering variation of inverter number, different inverter combinations, and critical system components. Finally, time domain simulations on the PSCAD/EMTDC platform are presented. The case study results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Inverter delay is often evaluated as $\textit {CV}_{\text {dd}}/{I}_{\text {eff}}$ , where ${C}$ is the load capacitance, ${V}_{\text {dd}}$ is the supply voltage, and ${I}_{\text {eff}}$ is the effective drive current derived by approximating the inverter switching trajectory with a linear model. The ${I}_{\text {eff}}$ model utilizes high and low drain currents conventionally measured in wafer acceptance tests and does not require extraction of any parameters. Ease of use combined with reasonable accuracy (~15%) is the main reason for wide application of $\textit {CV}_{\text {dd}}/{I}_{\text {eff}}$ delay metrics. However, $\textit {CV}_{\text {dd}}/{I}_{\text {eff}}$ expression produces large errors when applied to another two important basic circuits: NAND and NOR. This is because NAND and NOR circuits contain transistor series connections not accounted for in the inverter model. In this paper, an analytical solution for the transistor series connection influence on the discharge/charge operation in NAND/NOR circuits is provided. The model for NAND/NOR effective drive current (denoted as ${I}_{\text {stack}}$) developed in this paper maintains simplicity of the original ${I}_{\text {eff}}$ expression. It requires only one additional measurement of the linear current. Model accuracy was assessed by comparing to extensive SPICE delay simulations of NAND and NOR circuits designed using state-of-the-art MOS technologies. Comparison results show that $\textit {CV}_{\text {dd}}/{I}_{\text {stack}}$ equation provides ~15% accuracy for NAND/NOR circuits in line with $\textit {CV}_{\text {dd}}/{I}_{\text {eff}}$ accuracy for inverter. In an era of emphasis on low-power design, the developed model presents convenient means of exploring design space when optimizing circuit supply voltage for low-power operation. [ABSTRACT FROM AUTHOR]

This paper analyzes a cost-effective modification of the power topology commonly found in small wind turbine systems based on a passive rectifier and a boost converter. The boost-converter inductor and the input filter capacitor often placed at the rectifier output can be replaced by the generator-phase inductance. Different controller structures have been proposed for this low-cost inverter, but they have been focused on the converter itself rather than the overall turbine control. Moreover, only steady-state behavior has been demonstrated. This paper proposes a control structure only requiring retuning of the boost-current controller found in systems equipped with boost inductance, with other control loops remaining unchanged. The inductorless converter dynamic performance is studied and compared with the conventional topology in terms of current- and torque-control capability. The system efficiency, including the losses’ distribution in the generator, is analyzed. Simulation and experimental results are presented to demonstrate the technical viability of this proposal. [ABSTRACT FROM AUTHOR]

Induction motor loss segregation and efficiency measurement requires loading dynamometers and other equipment, such as a variable voltage sinusoidal power supply. These are expensive and not often available even when a loading device is accessible. Variable frequency drives are now widely used for operating induction machines and are more widely available and less expensive. However, their use in place of a fixed frequency sinusoidal power supply to directly measure machine efficiency is intriguing, but inherently challenging due to the pulsewidth modulation (PWM) output voltage. This paper presents some investigations for using variable frequency drives to perform IEEE 112B and IEC 60034-2-1 tests. The use of the drive, the measurement criteria, and procedures are reported and discussed. The results presented demonstrate the feasibility of the proposed concept for measuring machine efficiency with a PWM power source. [ABSTRACT FROM AUTHOR]

Many research works report the use of LCL filters for grid-interfaced PV systems. Indiscreet selection of passive LCL filter parameters may result in poor filtering and increased power losses. LCL filter parameter selection is critical to get a good performance and at the same time ensure that losses and costs stay low. This paper proposes a novel approach to design the LCL filter for a grid-interfaced PV system. A cost-based minimization approach on a cost per joule basis for each of the filter elements is explored to obtain the optimal filter design. Simulation results for a 10-kVA grid-connected inverter with an LCL filter are presented in order to verify the efficacy of the proposed design. The impact of designed filter parameters on the ripple current is also discussed in this paper. The total inductance of the LCL filter is varied and filter parameter values which give lowest cost is identified while meeting harmonic standard requirements and the fundamental voltage drop across the filter. Finally, the proposed design is also experimentally validated via a hardware prototype. Results validate the design method in terms of the harmonic attenuation and total harmonic distortion. [ABSTRACT FROM AUTHOR]

Grid-interactive inverters allow distributed generation units to provide various ancillary services in microgrids. As the linear modulation region of inverters is restricted by the dc-bus voltage, providing ancillary services may drive the fundamental positive-sequence inverter voltage to the overmodulation region. Therefore, to operate in the linear modulation region the maximum active- and reactive-power of the inverter may have to be reduced unless pulsewidth modulation (PWM) references are adjusted. In this paper, an atypical PWM method is proposed for maximizing dc-bus utilization of grid-interactive two-level voltage source inverters (2L-VSI) providing ancillary services. Two important ancillary services, i.e., negative-sequence compensation and harmonic compensation are considered in this paper. The proposed method increases the maximum active- and reactive-power that a 2L-VSI can deliver when providing ancillary services by injecting a common-mode component in the references computed based on instantaneous reference magnitudes. The validity of the proposed technique is verified through simulation, as well as experimental data obtained using a 208-V three phase grid-connected 2L-VSI. [ABSTRACT FROM AUTHOR]

This paper analyzes the configuration, design, and operation of multi-MW grid connected solar photovoltaic (PV) systems with practical test cases provided by a 10-MW field development. In order to improve the capacity factor, the PV system operates at its maximum power point during periods of lower irradiance, and the power output is limited to a rated value at high irradiance. The proposed configuration also incorporates a utility scale battery energy storage system (BESS) connected to the grid through an independent inverter and benefits of the experience gained with a 1-MW 2-MWh BESS large demonstrator. The BESS power smoothing and frequency regulation capabilities are illustrated though combined theoretical and experimental studies. The behavior of the grid connected PV and BESS combined system is studied using a modified IEEE 14 bus test system implemented in PSCAD/EMTDC. This paper also includes a sizing exercise for energy storage in order to provide dispatchable PV power. [ABSTRACT FROM AUTHOR]

In this paper, the theoretical analysis of the position estimation error in position-sensorless operation using pulsating square wave signal injection is presented. The purpose of this paper is to analyze the phenomenon that the position estimation performance varies depending on the injection frequency. Mathematical derivation supported by simulation and experimental results shows that, in no-load condition, the voltage distortion induces position estimation error with 3rd-order harmonics if the frequency of the injected square wave is the same to the switching frequency. While, if the frequency is a half of the switching frequency or heavier load condition in either injection frequency, the effect of nonideal characteristics of inverter disappears and there is no 3rd harmonics in the position estimation error. Therefore, only the effect of cross-coupling inductance is reflected in the estimation error. As the result, the position estimation error appears in the form of 6th-order harmonics due to the spatial harmonics of inductances, and the error is relatively small compared with the switching frequency injection case. The theoretical analysis was verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In a sensorless vector control method, at low speeds and self-commissioning for AC motors, it is necessary to model dead time, rise/fall time, parasitic capacitors, and semiconductors’ voltage drop accurately. In this paper, voltage drop in each phase due to the nonlinear behavior of the inverter from the control system's viewpoint is precisely modeled by using two lookup tables. These lookup tables make the proposed model robust against the dc-link voltage and carrier frequency variations in the entire current range. In conventional methods at standstill, the measured voltage in the dc current test contains the nonlinearity of two phases. Therefore, to obtain the nonlinear voltage of each inverter phase, it is assumed that the values of inverter nonlinearity voltage at both high current and low current are equal. This simplification leads to distortion in measured voltage in the low currents. However, in this paper, the voltage drop equation of each phase is solved by numerical method that is realizable in conventional processors. The results obtained in actual voltage measurement show the superiority of the proposed method over traditional methods in the low currents. The proposed method is verified by using a voltage source inverter feeding a 2.2-kW three-phase induction motor. [ABSTRACT FROM AUTHOR]

This paper proposes a split-capacitor four-wire current source inverter, which is the dual of the split-capacitor four-wire voltage source inverter. Since the midpoint of the dc link is tied to the neutral point of ac filter capacitors, the common-mode voltage (CMV) is reduced significantly. Consequently, the leakage current issue is effectively addressed. The proposed circuit is cost-effective as no extra switch is added. This paper, first, establishes the equivalent common-mode circuit of the proposed inverter. The impact of the neutral line inductance on CMV is also analyzed. Then, a specific modulation is introduced to balance the dc-link voltages/currents. To achieve good input/output performance, a nonlinear control method is developed based on time-domain models. Finally, all the proposed methods and related theoretical analysis are verified by simulations and experimental results. [ABSTRACT FROM AUTHOR]

Four novel architectures of wideband five-port single-ended-to-balanced power dividers with broadband common-mode suppression are proposed in this paper. The bandpass filtering capability with/without close-to-passband transmission zeros are also incorporated in some of them to obtain multifunctional single-ended-to-differential-mode filtering/power division operation. Two ideal 180° phase inverters are used to replace the conventional half-wavelength transmission line-based inverters in the basic power divider structure so that wideband common-mode rejection and a smaller circuit size are achieved. Quarter-wavelength transmission lines and coupled-line sections are exploited to simultaneously realize the bandpass filtering and wideband power division functionalities. Each five-port power divider exhibits broadband 3-dB single-ended-to-balanced power division, high in-band input–output power-matching levels, high in-band power isolation levels between the two balanced outputs and wideband common-mode rejection. The theoretical analysis, parametric study, and design procedure for the conceived single-ended-to-differential-mode power dividers are provided. Furthermore, for experimental and demonstration purposes, four microstrip prototypes designed at 1 GHz are manufactured and characterized. [ABSTRACT FROM AUTHOR]

Islanded grids operate isolated from the main grid and they allow the use of ac with a different frequency from the main grid. In this paper, it is proposed to use more than one frequency at the same time in such autonomous systems. The grid voltage amplitude at the fundamental frequency can be increased while the voltage peak is constant by adding odd harmonics to the voltage waveform. The grid currents and the power converter currents are decreased for the same power level, which leads to reduced losses in the system. The currents can be minimized if waveform shaping is additionally applied to the current waveforms. The approach also offers the possibility of mitigating the influence of low power factor in single-phase systems. This paper presents the impact of multifrequency power transfer on single-phase converters and grid components such as power cables and protection, and verifies the results with analysis, simulations, and experiments. [ABSTRACT FROM AUTHOR]

This paper proposes a new high-efficiency photovoltaic (PV) converter for grid connection through a high-leg delta transformer. The converter is composed of a symmetrically connected boost converter and three half-bridge inverters. One of the three half-bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. As a result, this circuit configuration enables to reduce the power losses in both boost converter and inverters. This paper also proposes a new cooperative control method between the symmetrically connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in the switching power loss. Experimental results confirm that the proposed circuit configuration makes it possible to improve its European efficiency from 91.6% to 94.5%. Moreover, system performance is evaluated on the assumption of maximum power point tracking operation. [ABSTRACT FROM AUTHOR]

A multifunctional grid-connected inverter (MFGCI) has been a promising solution to mitigate power quality problems in distributed generation system and microgrid applications. However, the capability of a conventional MFGCI is limited when compensating a voltage-based power quality problem. In this paper, a new configuration of MFGCI is proposed to improve both voltage-based and current-based power quality issues and is named shunt-series-switched MFGCI (SSS-MFGCI). The SSS-MFGCI can be connected in series or parallel to the grid by implementing bidirectional switches to provide different modes of operation depending on various grid disturbances. The required compensating current and voltage are analytically derived considering the grid and load conditions for voltage regulation. This paper also presents the compensation strategies, control scheme, and transition scheme between different modes of the proposed SSS-MFGCI. Simulation results to prove the concept are also included for unbalanced sag and swell cases. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the variation in performance of variable speed induction motors fed by inverters with grades of core materials used for stators and rotors from both results of measurement and finite element analysis. Identical shaped stator/rotor cores are manufactured by using several kinds of electrical steel sheets from low to high grades. Then, the characteristics of these motors are measured. Finite element analysis is applied to these motors to understand the measured results by separating losses and torques according to origins. The measured motor characteristics are found to be in good agreement with the results of the analysis. The analysis reveals the variation in each loss component with electrical steel sheets. Finally, the strong and weak points of the application of high-grade electrical steel sheets to the variable speed induction motors are discussed. [ABSTRACT FROM AUTHOR]

Magnetically coupled resonant (MCR) wireless power transfer (WPT) is one of the most promising WPT technologies for its remarkable capability of simultaneous noncontact power transfer for multiple independent loads. Nevertheless, diverse energy requirements of different loads and efficiency quota make it difficult to design and optimize the multiload system. In this paper, a novel driver configuration for the MCR WPT system with multiple loads is proposed, in which the transmitting resonant tank is driven synchronously by multiple inverters operating at multiple switching frequency and sharing a common dc voltage source, then a multifrequency superposition methodology is presented to achieve high efficiency and targeted power distribution. The dominant features of the methodology are listed as follows: 1) the multifrequency power components from multiple inverters can be simultaneously delivered to multiple loads through a single transmitter; 2) the receiving coils are elaborately designed at different resonant frequencies that correspond to the operating frequencies of multiple inverters to achieve targeted power transfer and high efficiency; 3) the resonant frequency of the transmitter can be modulated within the adjacent area of multiple operating frequencies, and the power distribution to meet the requirements of selective loads will be realized; and 4) the resonant frequencies of receivers can also be adjusted to effectively realize the power distribution. In this paper, a double-frequency MCR WPT system with two loads is comprehensively investigated as a representative example, and the studied methodology has been experimentally verified by two prototypes of the proposed circuit configurations. [ABSTRACT FROM AUTHOR]

This paper proposes a zero-voltage ride-through (ZVRT) method and an LCL filter design method to meet the fault ride-through (FRT) requirements for a single-phase grid-connected inverter with a minimized LCL filter. A high inverter output current overshoot occurs at a grid voltage sag and a grid voltage recovery, when a low-inductance LCL filter design is employed in order to minimize the filter volume. In order to suppress the current overshoot, a high-speed gate-block operation and the design method of the minimized LCL filter are proposed. In particular, the filter design considers the delay time in the gate-block operation in order to clarify the reduction limitation of the inductance in the LCL filter. As a result, the maximum inverter output current overshoot is suppressed to 146% by the high-speed gate-block operation and the designed LCL filter, where the impedances of an interconnected inductor and a filter inductor are 1.0% and 0.78% of the inverter normalized impedance, respectively. Therefore, it is possible to meet the FRT requirements with the proposed ZVRT method even with the minimized LCL filter. [ABSTRACT FROM AUTHOR]

High-resistance grounding (HRG) is preferred in many industrial applications where continual operation during ground fault conditions is critical. However, there are some drawbacks for the traditional HRG detection methods to locate a ground fault in adjustable speed drive systems. The existing methods cannot detect or identify which phase faulted once the drive has HRG fault. A leakage flux linkage detection-based method for HRG fault identification is proposed in this paper. It will be used to identify the faulted phase of the drive. [ABSTRACT FROM AUTHOR]

This paper presents a novel digital control strategy for the islanding mode operation of a power electronics-based energy management system (EMS). Thanks to the use of a high-performance repetitive controller combined with active damping, the EMS is capable of supplying a high-quality sinusoidal voltage to critical loads when the ac grid is not available. The proposed control scheme is analyzed and implemented in a field-programmable gate array-based control platform; it achieves a very low output voltage total harmonic distortion and holds a large stability margin for a wide range of load conditions. Analysis and simulations demonstrate the superiority of the proposed controller versus open-loop control. Laboratory experiments with linear and nonlinear loads validate the model used for the simulations that demonstrate the excellent performance of the new control strategy. [ABSTRACT FROM AUTHOR]

In this paper, a new class of compact Chebyshev differential-mode (DM) bandpass filters with intrinsic common-mode (CM) rejection is proposed and demonstrated on $\lambda$ /4 coplanar stripline (CPS) resonators with an improved unloaded quality factor ($Q_{u}$). The distinct advantage of the proposed $\lambda$ /4 CPS resonator with higher $Q_{u}$ than slotline resonator, together with intrinsic CM rejection of CPS line, can demonstrate that $\lambda$ /4 CPS resonator is more suitable for the design of narrowband DM filter than others on slotline resonator. Then, the underlying physics why CPS resonator possesses higher $Q_{u}$ than slotline resonator is numerically studied and further interpreted by the radiation loss. To facilitate the design process, an analytical design approach is introduced by using alternative J/K inverters and a tailored method is used to extract J/K inverter values with their associated effective electrical lengths based on their equivalent circuit models. Finally, two design examples, a second-order and a fourth-order DM Chebyshev bandpass filter, are designed and implemented, operating at the center frequency of 1.8 GHz with the fractional bandwidths of 6% and 19%, respectively. The simulated and measured DM/CM frequency responses match well with each other. The proposed DM filters based on $\lambda$ /4 CPS resonators have demonstrated the claimed superior performances in terms of intrinsic CM rejection, improved unloaded quality factor, easy implementation of J/K inverter, inherent suppression of first DM harmonic, and compact size. [ABSTRACT FROM AUTHOR]

This paper presents a center frequency and bandwidth reconfiguration mechanism for waveguide microwave bandpass filters. The filters are designed to be used in the output section of a satellite communication system. While the center frequency of a bandpass filter can be tuned by changing the lengths of the filter resonators, the coupling irises as practical realizations of the impedance inverters cannot easily be adapted to a new value. The novel approach chosen in this paper is to replace the impedance inverters by a novel type of coupling structure. This coupling structure allows adjustment of the coupling by changing the length of a transmission line, which is equivalent to changing the resonant frequency of a coupling resonator. Design equations are presented to transform an impedance inverter into the proposed coupling structure. A synthesis procedure for bandwidth reconfigurable filters is proposed. The feasibility of coupling adaptation is proven based on a full-wave model of the coupling structure. The synthesis process is applied to a four-pole Chebyshev sidewall-coupled circular waveguide filter with 54- and 72-MHz bandwidth settings. The filter is built up and measured. The measured results prove that the filter can be tuned to both bandwidths over a center frequency range of 200 MHz with excellent return loss and insertion loss. [ABSTRACT FROM PUBLISHER]

A circuit configuration, a circuit topological family, a buck-mode active clamped circuit, and an instantaneous output voltage feedback control strategy of combined bidirectional buck–boost dc–dc chopper-mode inverter with high-frequency (HF) link (HFL) were proposed and fully investigated in this paper. The steady principle characteristic and the design criteria for the key circuit parameters were given in this paper. The circuit configuration is composed of two identical isolated bidirectional buck–boost dc–dc choppers with the same input and output filters. These two choppers in parallel at input end and in series at output end generate unipolarity sinusoidal pulsewidth modulation current waveforms with positive and negative half low-frequency cycles separately. The circuit topological family includes four circuit topologies, such as one-transistor mode. Taking the one-transistor mode circuit topology as an example, the 750VA48VDC/220V50HzAC prototype is designed and implemented. The theoretical analysis and principle test show the inverters have excellent performance. [ABSTRACT FROM PUBLISHER]

This paper presents a single-phase ac power supply circuit that based on modified voltage-fed quasi-Z-source inverter topology; it suits to the light or the heavy load and is fit for the resistive, inductive, or capacitive load. The topology, operating principle, voltage gain, control method, and its realization by DSP are described in this paper. The feasibility and rationality of the system is verified by the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents an algorithm for the economical design of a utility-scale photovoltaic (PV) power plant via compromising between the cost of energy and the availability of the plant. The algorithm inputs are the plant peak power and the price of inverters with respect to their power ratings. The outputs are the optimum inverter ratings and the interconnection topology of PV panels. This paper introduces the effective levelized cost of energy (LCOE) (ELCOE) index as the core of the proposed design algorithm. ELCOE is an improved index based on the conventional LCOE that includes the availability of a power plant in economical assessments. The conventional LCOE index determines centralized topology (e.g., 1-MW inverter for a 1-MW PV power plant) for minimizing the energy generation cost, whereas based on ELCOE, a multistring topology (e.g., a 1-MW PV plant consists of fifty 20-kW inverters) despite of higher investment cost becomes the economically winning topology. Given the price of commercially available PV inverters at present, the case studies in this paper show that, for 0.1–100-MW PV power plants, the economical ratings of inverters range from 8 to 100 kW. The recently installed PV power plants confirm the feasibility of the calculations based on the suggested algorithm. [ABSTRACT FROM PUBLISHER]

There are several ways to model three-phase gridconnected voltage-source inverters (VSIs) with an $LCL$ filter. Such models often use simplifications like constant dc-link voltage or averaging over a switching period. These simplifications remove transistor switching and dc-link capacitor dynamics from the model. In this paper, a comprehensive modeling of a three-phase VSI, including an $LCL$ filter, is described and compared to models using one or more of the aforementioned simplifications. Advantages and disadvantages of different models are discussed. All simulations are verified by comparing with experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a methodology to evaluate the potential of submicrometer organic thin-film transistors (OTFTs) with nanoimprinted gate and self-aligned source and drain contacts. In the first step, the dedicated static model we previously reported is updated to account for the subthreshold regime and is used to simulate a zero- $V_{{\rm GS}}$ inverter (one of the most basic unipolar logic gate). Based on the extracted noise margins, two methodologies were studied to assess the potential of this technology in terms of p-logic digital circuits. The first one is De Vusser's V_{T} -based method that we adapted to our OTFT model. The second one relies on statistical modeling and takes into account the actual worst case scenario for an inverter in terms of noise margins. It better represents the experimental distribution because of specific corner models. The different analysis studied in this paper shows that these OTFTs, in the current state of the technology, are still not ready for complex digital circuits as the throughput is expected to be quite low. In addition, the proposed methodology and related interpretation are technology-independent therefore this analysis may serve as a basis to characterize unipolar-logic printed electronics and can be further extended to complementary-logic circuits. [ABSTRACT FROM PUBLISHER]

This paper presents a complete wave-to-wire approach to the modeling of wave energy farms. It captures all the main peculiarities of such applications, from the variability of sea waves to the issues related to the grid integration of a multi-MW wave farm, including the hydrodynamic modeling of wave energy converters (WECs). The paper specifically discusses the different levels of control of a wave farm and their integration and coordination. These are crucial to meet the power quality requirements at the point of common coupling (PCC) and ensure the efficiency of the power transfer from the waves to the main electric grid. A specific real-time technique for the centralized control of a wave farm is also proposed, which is exemplified with reference to the PCC voltage control in the real test case of bimep. Critical cases of weaker grids are also considered to extend the validity of the analysis. [ABSTRACT FROM PUBLISHER]

The power system, including variable-speed drives (VSDs), transformers, and long subsea power cables, is one of the main building blocks in the development of subsea gas compression. This paper presents results from full-scale technology qualification testing of a power system onshore where the VSD is controlling a 188-Hz 7.8-MW gas compressor motor over a simulated distance of 47 km. The extensive testing shows that it is possible to control the compressor/motor speed from start-up throughout the whole load envelope without the need for motor voltage and current feedback. By the use of estimator-based control, it is also possible to provide motor overcurrent protection. This paper shows how resonances in the long cable system can be handled by the use of optimization of the generated voltage waveform instead of using a VSD sine filter. The successful technology qualification shows applicability for subsea compressors with a rated frequency of up to 200 Hz, at least 8-MW shaft power, and a step-out distance of at least 50 km. [ABSTRACT FROM PUBLISHER]

This paper presents a modular push–pull PWM converter (MPC) for a battery energy storage system, which is intended for grid connections to medium- or high-voltage power systems. The converter per phase consists of a center-tapped transformer and two arms based on a cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. This paper discusses the operating performance and control method of the MPC, focusing on voltage balancing of all the floating dc capacitors. Moreover, a comparison is made between the MPC and a modular multilevel converter (MMC), under an assumption that both are used as the same battery energy storage system. The validity of the operating performance and control method is confirmed by both computer simulation using the “PSCAD/EMTDC” software package and experiment using a three-phase, 200-V, 5-kW downscaled model. [ABSTRACT FROM PUBLISHER]

The introduction of communication systems to power system controllers has brought in another layer of complexity in their design and operation. In this paper, a plug-in hybrid electric vehicle charging facility is studied. A linearized model of the facility is built, including both the dc/dc and dc/ac converters of the distributed energy resources. In addition, a control strategy that includes both local and networked loops is proposed to monitor and control the dc bus voltage of a local energy storage unit. This dc bus voltage is crucial to the self-sustaining capabilities of the system. A review of challenges and opportunities in networked control systems is presented, and the impacts of communication factors to the charging facility stability are analyzed. Finally, a real-time simulation platform which combines both electrical and communication networks is presented to validate the small-signal model, control strategy, and stability analysis including the communication effects. [ABSTRACT FROM PUBLISHER]

This paper deals with the setting-parameter optimization procedure for a multiphase induction heating system considering transverse flux heating. This system is able to achieve uniform static heating of different thin/size metal pieces without movable inductor parts, yokes, or magnetic screens. The goal is reached by the predetermination of the induced power-density distribution using an optimization procedure that leads to the required inductor supplying currents. The purpose of the paper is to describe the optimization program with the different solution obtained and to show that some compromise must be done between the accuracy of the temperature profile and the energy consumption, with the calculation of the losses. [ABSTRACT FROM PUBLISHER]

A dual two-level voltage source inverter (VSI) can synthesize a three-level voltage space vector employing an open-end winding induction motor. Space-vector-based pulsewidth modulation (PWM) variants for this dual VSI are proposed in this paper that offer the dual advantage of limiting the switching power loss to a single VSI at all instants and also reducing the switching commutations in the dual VSI by 50%. The influence of different error volt seconds (affected with different PWM variants) on the motor phase current in the dual VSI is critically analyzed. To this end, two analytical approaches (one using error-voltage trajectory information and the other using switching state information of the dual VSI) are also proposed in this paper to predict the current trajectory and the ripple content in the drive system. Expressions for rms ripple current are developed with different PWM variants. The efficacy of the proposed analytical approaches to predict the current trajectory and the ripple content is confirmed from the experimental results. All the PWM variants are first simulated using MATLAB and verified experimentally by conducting tests on a three-phase open-end winding induction motor drive controlled with volts per hertz control. The implementation of the PWM algorithms only requires instantaneous magnitudes of three-phase reference voltages and completely avoids the sector identification and lookup tables. [ABSTRACT FROM PUBLISHER]

Maintaining balanced voltages across distribution networks is becoming more challenging with increasing deployment of single-phase distributed generation and larger single-phase loads. The paper develops a reactive power compensation strategy that uses distributed solar photovoltaic (PV) inverters to mitigate such voltage unbalance. The proposed strategy takes advantage of Steinmetz design and is implemented via both decentralized and distributed control. The latter coordinates PV inverters through a communication network. We demonstrate the performance of the controllers on the IEEE 13-node feeder and a much larger taxonomy feeder (617 nodes and 1196 triplex nodes), and consider different connections of loads and PV systems. Simulation results demonstrate the trade-offs between the controllers. It is observed that the distributed controller achieves greater voltage unbalance reduction than the decentralized controller, but requires communication infrastructure. [ABSTRACT FROM AUTHOR]

The connection of distributed energy resources (DERs) to distribution feeders can significantly increase the operational flexibility of system operators. Local feedback control schemes (such as Volt/VAr droop curves) are a cheap, scalable, and communication-free solution to control DERs in active distribution grids. However, these controllers can interfere detrimentally with each other when they act on multiple DERs connected to the same grid. We show that even the standardized curves recommended in the most recent grid codes may exhibit an unstable behavior. In this paper, we investigate the stability of local incremental DER control laws in three-phase active distribution grids with balanced, and unbalanced loading, and we bound the resulting rate of convergence. The use of low-pass filters on the DER set-points allows us to achieve closed-loop stability even for high-gain local control laws that would otherwise destabilize the grid. This feature is particularly relevant in data-driven approaches that yield optimal DER local control schemes, often in the form of steep customized piece-wise linear Volt/VAr curves. [ABSTRACT FROM AUTHOR]

With the growing penetration of distributed renewable energy, distributed control approaches are widely utilized in voltage control of active distribution networks (ADNs), suffering from limited applicability for control devices or heavy communication burden. This paper develops an innovative distributed voltage control strategy of ADNs with global sensitivities (DVC-GS), which integrates network information from a global optimization view to coordinate energy storages, PV inverters and the OLTC with little communication and computing time. The global sensitivities of voltage violations across all buses with respect to nodal voltage and active/reactive power injection are formulated to quantify the ability of each controllable resource for alleviating voltage violations in the entire ADN. The back-and-forth communication combined with the modified DistFlow model is newly developed for the real-time update of global sensitivities at each bus with high accuracy and no iteration. Then the coordinated control of various devices is implemented on basis of global sensitivities to effectively ensure voltage security of ADNs. Comprehensive simulations based on modified 11-bus and 123-bus systems demonstrate the significant efficiency and superiority of the global sensitivities and DVC-GS. [ABSTRACT FROM AUTHOR]

Commutation failures (CFs) including repetitive CFs (RCFs) are frequently occurring faults in line commutated converter based high voltage direct current (LCC-HVDC) systems. Consequently, sending end system will suffer transient voltage disturbances (TVD) with a characteristic of “first reduce then rise and may repeat”. Due to the complex interaction process of TVD, the electromagnetic process behind this phenomenon cannot be easily explained, which imposes great challenges on the development of mitigation strategies. Given this, this paper provides a deep insight into the mechanism and the impact factors of the TVD caused by CFs and RCFs. The numerical relationship between the transmitting power and the TVD is derived. Research results revealed that the transient process after fault can be segmented into five stages. In each stage, the control interactions among HVDC controllers and power interactions at the PCC are analyzed. Besides, we discussed the TVD under RCFs in detail. Several indices are further proposed to facilitate the characterization of the TVD, and main control loops of HVDC that have impacts on the characteristics of TVD are thereby studied. Finally, the mathematical relationship between wind farm power and the TVD is derived to quantify the impact of wind farms on the TVD. [ABSTRACT FROM AUTHOR]

Optimal Volt/VAR control (VVC) in distribution networks relies on an effective coordination between the conventional utility-owned mechanical devices and the smart residential photovoltaic (PV) inverters. Typically, a central controller carries out a periodic optimization and sends setpoints to the local controller of each device. However, instead of tracking centrally dispatched setpoints, smart PV inverters can cooperate on a much faster timescale to reach optimality within a PV inverter group. To accommodate such PV inverter groups in the VVC architecture, this paper proposes a bi-level optimization framework. The upper-level determines the setpoints of the mechanical devices to minimize the network active power losses, while the lower-level represents the coordinated actions that the inverters take for their own objectives. The interactions between these two levels are captured in the bi-level optimization, which is solved using the Karush-Kuhn-Tucker (KKT) conditions. This framework fully exploits the capabilities of the different types of voltage regulation devices and enables them to cooperatively optimize their goals. Case studies on typical distribution networks with field-recorded data demonstrate the effectiveness and advantages of the proposed approach. [ABSTRACT FROM AUTHOR]

Low-voltage grid-connected microgrids rely on the exploitation of inverter-interfaced distributed energy resources (DERs) in order to feed loads and to achieve bidirectional power flow controllability at their point of common coupling (PCC) with the upstream grid. However, adverse operational conditions, such as the existence of DERs of different operation natures, DERs of non-equal power ratings, as well as the occurrence of non-steady and non-sinusoidal grid voltage scenarios, bring complications to microgrid energy management. Consequently, control strategies employed to coordinate DERs in dispatchable microgrids need to be resilient to such non-ideal conditions. Hence, this paper demonstrates that a multi-purpose strategy, so-called the Generalized Current-Based Control (GCBC) approach, is capable of steering DERs under such adverse operational scenarios, ensuring proportional current sharing among them while also regulating the microgrid power dispatchability at the PCC. The discussions are supported by an extensive experimental validation on a laboratory-scale single-phase microgrid prototype, demonstrating that the GCBC approach allows DERs of different operational natures to be coordinated, respecting their power ratings, and allowing the single-controllable microgrid to endure operation under distorted voltages and support voltage ride-through conditions. [ABSTRACT FROM AUTHOR]

This paper presents a multiphase induction system modeling for a metal disc heating and further industrial applications such as hot strip mill. An original architecture, with three concentric inductors supplied by three resonant current inverters, leads to a reduced element system, without any coupling transformers, phase loop, mobile screens, or mobile magnetic cores as it could be found in classical solutions. A simulation model is built, based on simplified equivalent models of electric and thermal phenomena. It takes into account the data extracted from Flux2D finite-element software, concerning the energy transfer between the inductor currents and the piece to be heated. It is implemented in a versatile software PSIM, initially dedicated to power electronics. An optimization procedure calculates the optimal supply currents in the inverters in order to obtain a desired power density profile in the work piece. This paper deals with the simulated and experimental results which are compared in open loop and closed loop. This paper ends with a current control method which sets rms inductor currents in continuous and digital conditions. [ABSTRACT FROM PUBLISHER]

This paper addresses the problem of predictive diagnostic in high-power transformers. Particularly, this paper is focused on their use in uninterruptible power supply systems for safety critical applications, such as railway interlocking signaling installations. With respect to the state of the art, where typically only thermal and electrical faults are monitored, this work proposes a distributed network of measuring nodes where also vibration-based mechanical stress diagnosis is implemented. Mechanical degradation is tracked through vibration measures, using multichannel accelerometers, with sensitivity down to 0.5 mg and local signal processing in the transformed frequency domain, up to 1 kHz. A compact hardware-software implementation of the nodes is also presented. The performances of the diagnostic system are assessed through experimental measurements on real three-phase high-power transformers used in railway applications. [ABSTRACT FROM AUTHOR]

This paper investigates both the fundamental and harmonic losses of permanent magnet synchronous motor (PMSM) in conjunction with inverter losses for a wide range of switching frequencies (SFs) and different direct-axis currents (Ids) under full power range. The effects of SFs and Ids on the total losses, including fundamental loss and harmonic loss in the windings and lamination core, conduction loss, and switching loss in IGBTs, are described through analytical models. Meanwhile, the loss models of the motor are modified and validated by the 2-D finite-element analysis. Furthermore, the efficiency improvement of the overall PMSM-inverter system for different operation conditions benefits from an artificial bee colony (ABC) algorithm proposed in this paper. The optimal SF and Id, in terms of PMSM-inverter overall efficiency, are preferred for every operation point, thanks to the proposed ABC and the precise calculation of losses. Experimental results validate the proposed methodology. [ABSTRACT FROM PUBLISHER]

As the number of renewable energy generation units and, consequently, solid-state based converters increases in the power grid, many power electronics concepts should be integrated into power system analysis and design. Thus, a power laboratory course with emphasis on the nexus between power electronics and power system is desired. However, the flexibility of instructors in designing a wide range of educational experiments is limited by the use of specialized educational setups. This problem can be resolved by allowing students to assemble their setups using laboratory scaled-down devices; however, implementation times can limit students to focus on the main concepts of the experiments. In particular, lacking experience with hardware description languages to develop switching patterns and control schemes for solid-state based converters further increases the implementation times. In this paper, a technique for rapidly implementing switching patterns and control schemes for power converters is proposed. This technique provides an easy-to-use laboratory allowing students to focus on reinforcing the theory learned in energy conversion, motor-drive, power electronics, and power system classes while still providing instructors with the flexibility to design a wide range of educational experiments. [ABSTRACT FROM PUBLISHER]

AC–DC–AC converter-fed induction motor (IM) drive is mainly realized by back-to-back three-phase converters. However, fault in a single semiconductor switch will make it inoperative. To enable continued controllable operation in case of the faults occurring in the converter, the five-leg converter with a shared leg between the grid and load sides is a possible solution. However, this topology poses an inherent two-objective control problem, because its grid and load sides should be controlled simultaneously. More importantly, the potential increase of the shared-leg current may destroy the converters. In this paper, a new control scheme based on the FCS-MPC combined with intrinsic characteristic of the five-leg converter is proposed for independent control of the rectifier and inverter subsystem with the shared-leg overcurrent constraint. The condition for independent control is analyzed. In order to give a complete evaluation of the proposed control scheme, the conventional pulsewidth modulation (PWM) control scheme is conducted for comparison. Experimental results are provided to validate the effectiveness of the proposed scheme. [ABSTRACT FROM PUBLISHER]

This paper presents an application of model predictive control to a variable-speed drive system operating in the multi-megawatt range. The variable-speed drive system comprises a synchronous machine fed by a line-commutated rectifier and a load-commutated inverter. The control task is to regulate the dc-link current, and hence the machine torque, to ensure the machine speed follows a given reference. The proposed control approach is model predictive control, where both the rectifier- and inverter-firing angles are considered as control inputs. The nonlinear model predictive torque controller has been implemented on an embedded system and applied in an industrial-scale pilot plant installation. The experiments show the successful operation of model predictive control on a plant with more than 48 MW power. [ABSTRACT FROM PUBLISHER]

This paper extends the previous virtual synchronous generator (VSG) control for voltage-source converters to modular multilevel converters (MMCs). Compared with the ac synchronous generator (SG), the VSG-based MMC is embedded with a power-angle characteristic. Starting from this feature and with reference to the existing ac system coherency-based equivalence methods, this paper proposes a novel coherency equivalence method for MMC used in large-scale renewable energy systems connected to the ac grid. This novel method mainly focuses on the coherency criterion and parameter aggregation methods which have significant differences compared with the ac system methods. The proposed equivalence method is validated on PSCAD/EMTDC and the study results indicate that: 1) the VSG-based MMC model does show the power-angle characteristic similar to the SG model; 2) the proposed coherency criterion can accurately and efficiently classify the paralleled MMC into coherent groups; and 3) the dynamic behaviors of the external systems are preserved after the aggregations of all previous coherency MMC groups. [ABSTRACT FROM AUTHOR]

Unbalanced load currents not only give rise to unbalanced voltages but also adversely affect the performance of the conventional current-limiting mechanisms. The latter might result in overcurrent stress on the distributed energy resources (DERs) or current harmonics. In this paper, a novel decentralized control method is proposed to improve the power quality and protect DERs from overload. The proposed controller makes use of the model predictive control (MPC) technique to minimize the voltage unbalance, improve current limiting, and prevent active power overload. The MPC is combined with the V-I droop method to realize coordinated operation with fast dynamic response. The proposed method is tested on the CIGRE benchmark microgrid. Simulation results demonstrate that the proposed method improves power quality but also allows for operation close to the maximum load capacity without imposing DERs to overload. [ABSTRACT FROM PUBLISHER]

The Sandia frequency-shift method, among all frequency-based active islanding detection methods (IDMs), is one of the most effective methods for inverter based distributed generators (DGs). The nondetection zone (NDZ) of the Sandia frequency shift (SFS) highly depends on its design parameters. If the design parameters are not properly tuned, they may result in failure of the method or deterioration of the system power quality (PQ) through injection of a high amount of harmonics. The main objective of this paper is to propose a new algorithm for SFS method parameter determination, which would add precision to the previous parameter design criterion. In this paper, also a new formula for multi-DG applications is proposed which results in optimally setting of all SFS parameters to eliminate NDZ. Using the new criterion, the negative impact of the conventional criterion on PQ is reduced, and the efficiency of the SFS IDM is increased. The simulation results show that the proposed algorithm results in more accurate detection of the islanding phenomenon in the shortest possible time. All of the simulations and NDZ analysis are carried out in the MATLAB environment. [ABSTRACT FROM PUBLISHER]

This paper addresses theoretical calculation of a single-phase multilevel pulsewidth modulation (PWM) inverter current total harmonic distortion (THD). Analytical approach introduced in late 1980s for a two-level inverter is generalized for an arbitrary level count for a single-phase inverter. Although the obtained closed-form piecewise analytical solutions assume (infinitely) large ratio of switching and fundamental frequencies and pure inductive load, they are practically very accurate for the ratios of (apparent) switching and fundamental frequencies larger than 25–30 and inductance-dominated loads. Along with strict mathematical solutions, simple accurate Bessel function approximation and hyperbolic average trend one are suggested. The formulas clearly reveal a single-phase PWM inverter current THD dependence on modulation index for an arbitrary voltage level count and are easily modified to cover grid-connected cases. [ABSTRACT FROM PUBLISHER]

This paper proposes a hybrid static synchronous compensator (hybrid-STATCOM) in a three-phase power transmission system that has a wide compensation range and low dc-link voltage. Because of these prominent characteristics, the system costs can be greatly reduced. In this paper, the circuit configuration of hybrid-STATCOM is introduced first. Its V–I characteristic is then analyzed, discussed, and compared with traditional STATCOM and capacitive-coupled STATCOM (C-STATCOM). The system parameter design is then proposed on the basis of consideration of the reactive power compensation range and avoidance of the potential resonance problem. After that, a control strategy for hybrid-STATCOM is proposed to allow operation under different voltage and current conditions, such as unbalanced current, voltage dip, and voltage fault. Finally, simulation and experimental results are provided to verify the wide compensation range and low dc-link voltage characteristics and the good dynamic performance of the proposed hybrid-STATCOM. [ABSTRACT FROM PUBLISHER]