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Static Var System (SVS) installations are prevalent and play an important role in voltage regulation and stabilization. A design concern for SVS installations is the introduction of harmonics due to inherent operation and amplification of existing power system harmonic distortion. Analysis of the harmonic interaction between proposed SVS installations and the power system is important. This paper presents information and guidelines for SVS design with specific emphasis on harmonic analysis. The main topics addressed are the design input data, the measurement requirements and the impact on SVS design configuration and component rating.

Future distribution systems are faced with more challenges on islanding detection due to the increasing penetration level of inverter-based distributed generators (DGs). Different DG technologies, inverter control as well as other advanced inverter functions, such as fault ride through are challenging the capability of islanding detection schemes. On the other hand, for multiple feeders network, topological change of feeders and islanding at adjacent feeder increase the vulnerability of islanding detection devices. Furthermore, available islanding detection schemes are suffering from notable non-detection zones (NDZs) under reduced power mismatches. Therefore, to mitigate these issues, this paper proposes an effective methodology for building decision trees-based intelligent relay (IR). This methodology utilizes the NDZ boundaries of existing standard relays and applies a comprehensive training/testing strategy, which effectively reduces the NDZ while maintaining a superior dependability and security performance. To validate the applicability of the proposed methodology, the hardware-in-the-loop simulations are realized by programming the generated IR logics into a real commercial relay.

Compared with multilevel space vector modulation, level-shifted multicarrier sinusoidal pulsewidth modulation (SPWM) for nested neutral point-clamped (NNPC) inverters requires much less calculations and implementation efforts, but the existing conventional SPWM cannot suppress the severe flying-capacitor (FC) voltage ripples under low output-frequency conditions. In order to solve this problem, a multicarrier-based PWM strategy with complete voltage balance control (VBC) capacity is proposed in this paper. For NNPC inverters operating under low output-frequency conditions, two preprocessing steps, the zero-sequence injection and the modulation-signal rearrangement, are proposed before the comparisons between level-shifted carriers and modulating signals. These preprocessing steps make the average currents flowing through FCs zero, which is beneficial to greatly reduce the FC voltage ripples under low output-frequency conditions. Together with additional VBC, the proposed modulation can assure the FC voltages balanced under the entire output-frequency conditions. Principles and implementation processes of proposed modulation techniques and VBC methodsare elaborated in detail and compared with conventional modulation methods. Both simulation results from a 5-MVA system and experimental results based on a 5-kVA platform are presented to verify the effectiveness.

This paper proposes a method to analyze and improve the performance of interconnection protection based on distance relaying for wind power distributed generation (DG) in distribution systems. Of particular importance is distance protection that uses the concept of prefault voltages as reference quantities found to have issues with intermittent behavior of wind power DG. This concept is normally used in different distance protective relaying applications in order to increase the fault resistance coverage capability of the distance relays as well as to ensure selectivity, dependability, and security under extreme undervoltages. The main contributions of this paper are to analyze this issue and propose a method to enhance the performance of distance protection to mitigate this issue. In this methodology, several case studies are investigated with different penetration levels, weather patterns, and configuration topology of DGs under both normal operating conditions as well as fault conditions. Results for a case study are given.

The output current ripple of an inverter shows different variations for sub-fundamental operating cycle and over few fundamental cycles. This paper investigates subfundamental cycle peak-peak current ripple variation of a three-level three-phase inverter over the entire operating modulation index range for the three-level continuous and discontinuous pulsewidth modulation strategies. Furthermore, based on the analytical current ripple variation, a strategy is presented to change the switching frequency within a fundamental cycle while maintaining the peak-peak current ripple similar to the conventional fixed switching frequency strategies. The strategy has been implemented and experimentally validated on a permanent-magnet synchronous motor drive. The results demonstrate that the proposed strategy reduces inverter switching instances and associated losses around 10–30%.

This paper proposes a method to vary the switching frequency within a fundamental cycle to reduce the switching losses of a two-level inverter while maintaining the peak–peak current ripple within a predefined limit. Unlike conventional strategies, the proposed technique utilizes precomputed switching frequency variation factors without relying on prediction or optimization techniques, since the peak–peak current ripple follows a definite trajectory within a fundamental cycle. Moreover, the variation in switching frequency is further controlled based on the operating carrier ratio and modulation index. The proposed strategy has been validated through both the simulation and experimental results on a permanent magnet synchronous motor drive for the space vector and discontinuous pulsewidth modulation patterns, and the results demonstrate that it reduces the two-level inverter switching losses up to 15%.

The increasing penetration level of renewable energy brings new challenges to the field of islanding detection. In this study, a decision-tree (DT)-learning method with hardware-in-the-loop (HIL) simulations is proposed to address the non-detection zone (NDZ) issue of islanding detection in hybrid distributed generation systems including both inverter- and synchronous-machine-based distributed energy resources. This method can effectively reduce the NDZ through advanced relay training strategy and utilise the advantage of real-time simulators on simulation efficiency. In addition, the generated DT can be programmed into a real relay and then get validated through HIL simulations. The HIL implementation adds a practical dimension to the proposed method. With the proposed method, the laboratory testing results indicate promising islanding detection performance in terms of dependability, security, reduced NDZ area and detection time.

Wind power (WP) penetration in weak distribution networks is associated with adverse impacts on voltage quality. The installation of an energy storage system (ESS) is a possible voltage quality remedy in such milieus. This paper proposes a supercapacitor ESS for alleviation of voltage flicker resulting from WP integration. The proposed ESS control and management are tailored to that purpose such that the ESS offsets the flicker-producing fluctuations in the generated WP. The proposed power sizing of the ESS is defined by the estimated turbulence intensity and wind speed average at the installation site. A 2 MW wind generator of the doubly fed induction generator type is employed as a source of WP and simulations are conducted on a simplified test system, as well as a detailed 25 kV distribution network on which results are compared with acknowledged reactive power flicker mitigation approaches and verified by prototyping in a real-time simulation platform. The flicker measurement procedure is conducted per IEC Standard 61000-4-15.

Accelerated developments of renewable energy production technologies and their integration to existing AC microgrids have led to the emergence of several new inverters control schemes. The recently introduced proportional resonant (PR) controllers have the ability to precisely track AC quantities and are increasingly used in grid supporting inverters, especially for current control loops which are at the heart of power transfers. In this paper, the PR-controller action is analyzed and an enhancement is proposed. It is shown that the classical implementation is particularly sensitive to high frequency noises coming from measurements and relocating the proportional action (RPA) on the feedback path can overcome this issue. The proposed improvement was evaluated using bit-true simulations in the Matlab/Simulink® environment. Obtained results show good noise and overshoot suppression using the proposed PR-controller with RPA.

The paper deals with developing and testing frequency-adaptive PMU algorithms with wider linearity range than specified in IEEE Std C37.118-1. This goal is achieved by means of three different concepts encompassing robust state-of-the-art design approaches: 1) FIR bandpass filtering, 2) extended Kalman filtering (EKF), and 3) discrete Fourier transform (DFT) demodulation with FIR low-pass smoothing. While FIR-based PMUs are linear phase with no overshoot in either phase or amplitude step responses, the adaptive EKF PMU is more computer-intensive but allows for a reduced group delay and better out-of-band interference rejection at the cost of a phase step response with overshoot. Frequency measurement performances of the various PMUs are assessed in detail. It turned out that FIR PMUs are best for meeting Std C37-118-1 metrics but they are outperformed by EKF under changing harmonics. Test results on three recent commercial PMU models further confirm that PMU algorithms meeting standard C37-118-1 can behave quite differently under dynamic conditions.

The present paper investigates the effective application of phasor measurement units (PMUs) with different technologies and filtering dynamics to the design of wide-area power system stabilizer (WAPSS). Two frequency-adaptive PMU algorithms shown to exceed the C37.118 class-M requirements based on FIR- and Kalman-bandpass filtering are selected for study. Their sharp dynamic differences are characterized using accurate fourth-order transfer functions derived from step responses using system identification techniques. While FIR-based PMUs have no overshoot in their phase and amplitude step responses, the adaptive Kalman filter allows for better out-of-band interference rejection at the cost of a phase step response with overshoot and a higher computational burden. These PMUs are implemented in Simulink and then embedded in electro-magnetic transients (EMT) simulations to experiment the realistic WAPSS behavior with the discrete-time devices in the loop. It is shown that WAPSSs with optimized settings can improve the damping performance of EMT models of a test system and a simplified Hydro-Quebec network including PMU filtering dynamics and transmission delays. However, WAPSSs based on EKF-PMUs yielded better performances, thanks to their shorter group delay compared with FIR-PMUs. PMU devices and algorithms meeting standard C37-118 can thus behave quite differently under stressed dynamics.

For the first time, IEEE Std. C37.118.1-2011 now provides metrics for PMU dynamic performance in terms of classes P and M filter designs. This paper attempts to determine whether fulfilling these requirements makes the PMU inherently well suited for stability control applications such as wide-area power system stabilizers (PSSs). In this aim, we considered two different frequency-adaptive approaches for class-P and -M compliance to ensure operation over a wide frequency range. The first is based on a finite-impulse response (FIR) with no overshoot in either the phase or the amplitude step responses, while the second is Kalman filter-based (EKF), which allows for a more refined out-of-band interference rejection at the cost of a phase step response with overshoot. These two approaches are benchmarked against Hydro-Quebec`s existing PSS requirements and the conclusion is that the total vector error-based response time is not indicative of the phase lag within the frequency band of interest, nor of the 3-dB bandwidth under sinusoidal amplitude/frequency modulation phenomena, which are key criteria when specifying PSS PMUs. Using simulated and field-recorded network fault responses, we also show that a class-M PMU is unsatisfactory for wide-area stabilizing control, unless its performance is improved during the fault period, which is not covered by Std. C37.118.1-2011.

The modular multilevel converter (MMC) for single stage DC-DC conversion is emerging as an alternative solution to the two-stage DC-AC-DC conversion. The AC current, that only circulates inside of the MMC, is used to balance the energy between submodules (SMs). However, a high voltage conversion ratio will result in a high AC circulating current that will require high power electronic device ratings and cause high power losses. In this paper, a multiport modular multilevel DC-DC converter, which can have one high voltage port and multiple low voltage ports, is proposed. The power can flow from high voltage to low voltage ports or in the opposite direction. Especially for high voltage conversion ratio applications, the proposed converter needs lower circulating currents compared to the single-port MMC DC-DC converter. The large filtering inductor, which blocks the AC components from presenting at the low voltage DC side, is also eliminated. The proposed topology can be used to connect renewable energy systems or energy storage systems to a medium voltage DC grid.

This paper proposes a topology for the combined frequency/oscillation damping active power control loop for type 4 wind turbines. In order to assess the effects of standard transient network frequency support control loops and the established controller topology on frequency response a quasi steady-state frequency model for the wind turbine equipped with frequency support auxiliary loop is developed. The performance of the proposed controller is then validated on a 14-generator benchmark system with installed wind capacity implemented in an Electromagnetic Transient Program. Positive impacts of the controller on frequency response, long-term frequency stability and inter-area oscillatory mode are demonstrated. The issues of controller tuning with respect to torsional interactions are also discussed.

The Modular Multilevel Converter (MMC) is a newly introduced and attractive converter topology for High Voltage Direct Current (HVDC) transmission system. However, precise modeling of high level MMC is time-consuming in offline simulation. This paper focuses on the dynamic performance of Multi-Terminal MMC-HVDC (MMC-MTDC-HVDC) system. Based on Kirchhoff Law, a Computational-Efficient Model (CEM), including capacitor break-point technique for DC cable, is presented in this paper. Composed of 57 first order Ordinary Differential Equations (ODEs), CEM facilitate the simulation speed significantly without losing accuracy. Time-domain simulations on 12-level 4 terminal Radial MMC-HVDC system based on CEM and detail model (DM) are implemented in RT-LAB. The validation of proposed model has been achieved by comparing steady state and transient state performance.

The high renewable energy penetration level in distribution systems has resulted in an increasing number of inverter-based distributed generators (DGs). Therefore a sophisticated DG interconnection protection relay is required to protect the DGs, overcome the challenges that inverters introduce and respect the new grid requirements. This paper proposes a multifunction intelligent relay (IR) scheme in inverter-based systems, utilizing data-mining method. This protection scheme includes islanding detection, fault detection, fault type recognition and fault ride through (FRT) selective blocking functions. A comprehensive IR modelling strategy is proposed as well to reduce offline computational resource consumption, meanwhile it makes possible the integration of all these functions in the same IR. The proposed multifunction IR scheme is tested in hardware-in-the-loop (HIL) environment. The results show that the proposed scheme is superior to standard islanding and fault protection functions with respect to dependability, security and detection time.

This paper introduces a new three-phase harmonic-decomposition technique to extract voltage/current harmonics for use in grid-connected converters, such as for active power filters (APFs). The main function of this technique is to detect a selective order of harmonics for control purposes. This feature is useful when elimination of certain harmonics is of concern. Moreover, the proposed method can successfully detect and track the variations in the frequency of the signal and extract the time-varying harmonics. A theoretical analysis is presented, and the performance of the method is experimentally evaluated. The methodology is applicable for a wide range of equipment such as uninterruptible power supplies, regenerative converters, APFs, etc., as a basis for the detection of the reference signals.

This paper introduces a new adaptive notch filtering approach to extract the harmonic and reactive current components for power quality purposes in grid-connected converters. The main function of this method is to provide synchronized harmonic and reactive current components for control purposes. The theoretical analysis is presented, and the performance of the method is experimentally evaluated. The methodology is applicable for a wide range of equipment such as uninterrupted power supplies, regenerative converters, active power filters, etc., as a basis for generating the reference signals.

This paper introduces an approach for the real-time extraction of the frequency, phase angle, and symmetrical components of the grid signal, which is of great importance for many applications in power systems such as power quality and protection. The proposed method is based on the concept of the adaptive notch filter that provides a fast and accurate estimation of the symmetrical components in the presence of frequency and amplitude variations. In addition, the system offers a high degree of immunity and insensitivity to power system disturbances, harmonics, and other types of pollutions that exist in the grid signal. The simplicity of the structure makes the method suitable for both software and hardware implementations. Moreover, this very simple and very powerful tool can be used as a synchronization technique, which further simplifies the control issues currently challenging the integration of distributed energy technologies into the electricity grid. Mathematical derivations are presented to describe the principles of operation, and experimental results confirm the validity of the analytical work.

This paper has developed a direct power control (DPC) structure to improve the performance of an active filter. A control algorithm directly uses the instantaneous power terms as control variables to replace the current and voltage variables that are commonly used in proportional-integral (PI) control systems. Compared to the other DPC schemes that have been reported so far, the proposed algorithm is oriented to harmonic current compensation, for which the switching functions are redefined, the bandwidths of the two hysteresis comparators are dynamically adjusted, and consequently, the pulsewidth modulation (PWM) switching frequencies are regulated to eliminate the unnecessary short switching pulses, and the control system can be used directly and effectively for various types of nonlinear load compensation. With the proposed control scheme, full control of the active filter, including the line current and the DC bus voltage, can be realized within an integrated power control loop. The advantages of the proposed control strategy have been verified by simulation and experimental results on a 2-kVA laboratory prototype.

This letter introduces a new adaptive notch filtering (ANF) approach as a powerful tool for synchronization of converter-interfaced distributed generation systems that can potentially stimulate much interest in the field and provide improvement solutions for both grid-connected and stand-alone (islanding operation) modes of micro-grids. The proposed technique is simple and offers a high degree of immunity and insensitivity to power system disturbances, harmonics and other types of pollution that exist in the grid signal. A modified structure of the ANF-based synchronization technique is capable of decomposing three-phase quantities into symmetrical components, extracting harmonics, tracking the frequency variations, and providing means for voltage regulation and reactive power control. A prominent advantage of the proposed scheme is that it does not require a phase-locked loop for the synchronization. In addition, this very simple and very powerful power signal processor will simplify the control issues currently challenging the integration of distributed energy technologies onto the electricity grid. All converter-interfaced equipment, such as flexible AC transmission systems, custom power controllers, and active power filters, will benefit from this technique. Theoretical analysis is presented and the performance of the method is evaluated through simulation.

Pulsewidth-modulated (PWM) techniques equip power converters with unique features such as input-output linearity and control flexibility. Nevertheless, frequent switching of semiconductor switching devices causes considerable switching loss, and therefore makes traditional two-level PWM converters inappropriate for high-power applications. Two alternatives for building modular structures, namely multipulse and multimodule PWM converters were introduced to provide not only voltage and current sharing among the semiconductor switching devices, but also a high-quality output voltage at a much lower switching frequency. While multipulse converters offer minimal switching losses, low-order harmonic neutralization, and the best utilization of the inverter, multimodule PWM converters give control flexibility and power structure simplicity. This paper combines these two, and preserves the advantages of both multipulse and multimodule PWM converters. This not only provides an additional degree of freedom for voltage control, but also enables the converter to operate in PWM mode during transient and in single-pulse mode during the steady state. For the PWM switching mode, a special space vector strategy of 3 p.u. switching frequency is presented to maximize the voltage utilization and maintain a linear transfer characteristic. The power structure and control methods are analyzed, and validated by simulation and experimentally.

This paper addresses implementation issues associated with secondary voltage control in a doubly-fed induction generator based wind farm. The effects of different system parameters on the performance of the control are considered, namely the short circuit ratio of the interconnection and the inherent communication delay between the wind park and the remote bus. In addition, a strategy for allocation reactive power requirements to each of the generators within the wind park is proposed. The system is developed and simulated for a wind park consisting of six wind generators connected to a typical transmission system. The paper proposes an optimal tracking secondary voltage control method developed to achieve effective voltage regulation, enhance the network voltage profile and provide optimal reactive power compensation to the interconnected power system. The performance of the controller is compared with secondary voltage control at one selected bus, primary voltage control and the optimal voltage profile obtained from the optimal power flow analysis. The performance of the controllers is tested for steady state operation and in response to system contingencies, taking into account the impact of communication time delays and short circuit ratio (SCRs). Simulation results are presented to demonstrate the capability of the controllers to provide the desired reactive power compensation and voltage support to the electric power grid.

This paper introduces a new intelligent-based approach for detecting islanding in distributed generation (DG). This approach utilizes and combines various system parameter indices in order to secure the detection of islanding for any possible network topology, penetration level and operating condition of the DG under study. Hence, every parameter index displays characteristics for a given set of events. The proposed technique uses the data-mining technology to extract information from the large data sets of these indices after they are screened off-line via massive event analyses using network simulations. The technique is tested on a typical DG with multiple distributed resources and the results indicate that this technique can successfully detect islanding operations. In addition, this technique can also overcome the problem of setting the detection thresholds inherent in the existing techniques by optimizing their settings

This paper investigates various random PWM (RPWM) techniques for conventional two-level inverter-fed traction drives and proposes a discrete RPWM technique for acoustic noise reduction. The proposed RPWM technique randomizes within a set of predefined switching frequencies compared with the continuous nature of randomization in conventional RPWM techniques. The proposed method was compared with conventional SVPWM and other RPWM techniques with respect to the A-weighted IEC 61672-2013 standard acoustic noise profile. The proposed RPWM method spreads the narrowband harmonic clusters effectively and, compared to the conventional RPWM techniques, reduces broadband noise by 2–6 dB over the full modulation index range, thus producing a better acoustic noise profile.

Modular multilevel converter (MMC) is a promising topology for medium and high power applications. The MMC system consists a large number of sub-modules (SMs), which take long time to simulate. In a real-time simulator, the MMC model is optimized to have a fast simulation speed for real-time applications, such as hardware-in-the-loop (HIL) tests. The methodology to evaluate model fidelity is important. In this paper, a methodology is proposed to validate an MMC model capable of real time simulation and implemented in central processing unit (CPU) and field-programmable gate array (FPGA). The model is validated in both open-loop and closed-loop control in a simple MMC test system, and compared to a reference detailed model made with SimPowerSystems (SPS) blocks. The effect of the model sampling time on the accuracy is also studied. The results indicate the MMC model optimized for real time simulation with a time step of 25 μs is as accurate as an SPS model with a time step of 0.2 μs.

The interconnection of Type-4 wind farms into weak distribution feeders may result in voltage rise and flicker concerns. This paper investigates a wind farm control scheme employing a slow-acting reactive power controller to regulate the steady-state voltage at the point of common coupling (PCC) and a fast-acting active power controller, streaming from an embedded energy storage system (ESS) to mitigate flicker at the wind turbine terminals. Real-time hardware-in-loop (HIL) results have been obtained for the proposed power control strategy, emulating the distribution-feeder and wind turbines on a real-time digital simulator (RTDS) and the power control loops on a digital controller, communicating using the IEC 61850 GOOSE Messaging protocol. Flicker studies are conducted on a 25 kV distribution feeder using a flickermeter compliant to the IEC 61000-4-15 standard. Results demonstrate a short-term flicker level reduction up to 83%. Applicable utility grid codes and standards are considered throughout.

This paper proposes reduced switching random PWM (RPWM) techniques based on Space Vector PWM (SVPWM) technique for conventional two-level inverters. In the proposed RPWM techniques, the switching frequency is randomized within a band lower than the nominal switching frequency at and around the peaks of the three-phase output currents. For the rest of the fundamental cycle, the switching frequencies are randomly selected within a band higher than the nominal switching frequency. The proposed method is able to spread the narrowband harmonic clusters similar to the conventional RPWM techniques and additionally produce less inverter output current distortion than conventional spread spectrum techniques. The proposed technique has been analyzed and has been verified using experimental results.

This paper presents a new interpolation–reinitialization method for transient simulations in both forced commutation and natural commutation conditions occurring in power electronic circuits. Recently published methods in this field are also discussed. The objectives are to provide generalization and to increase the precision level of numerical methods used for the computation of transients due to switching events in Electromagnetic Transients Program (EMTP) type applications.

Force-commutated multiconverter systems have been proposed and recently implemented for high power applications, particularly high-voltage direct current (HVDC) transmission and flexible ac transmission systems (FACTS) devices, including STAtic var COMpensators (STATCOM). This paper demonstrates that pulse-width modulation (PWM) based on space vector modulation (SVM), and using low switching frequencies (a few hundred Hertz) can be implemented in multimodule power converter systems. The proposed scheme is based on a delayed sampling technique and allows output voltage control and minimization of harmonic components. Pattern generation options are analyzed and system waveforms are presented for different switching frequencies and number of modules. Results are validated by simulation and confirmed by experiments on a 5-kVA prototype unit.

This paper introduces a new methodology for settings of transmission system distance protection based on an intelligent analysis of events and their consequences. The output of the proposed methodology is comprehensive distance relay settings which include not only the zone reaches and zone time delays, as in the existing approaches, but also the optimal impedance operating characteristics, the fault detection settings, and the required relay sensitivities in terms of voltage and current. The need for this methodology is the result of the increased complexity of interconnected power systems protected with a large number of relays with different relay technologies, such as electromechanical, static, and numerical as well as diversity in their operating algorithms. The relay settings are automatically updated after every major change in the state of the network topology. Since it is not possible to include all design details of the proposed system, sample design events and rules are given to illustrate the proposed methodology.

This paper shows that when load centers require Static VAR Systems (SVS) for regulated voltage control, the strategy of using many, small, distributed SVS located at distribution buses is more advantageous than a few large bulk SVS located at the transmission or sub-transmission bus. The advantages are (i) standby to meet N-1 reliability criterion is reduced; (ii) costly high voltage transformers are no longer needed because the SVS can be connected directly to the low voltage distribution buses; (iii) distribution-side voltage support is more effective so that the total MVAr requirement of the distributed SVS is less. Simulation studies have demonstrated that the distributed SVS units operate harmoniously together.

This paper presents a zero-voltage-transition (ZVT) boost converter using a soft switching auxiliary circuit for power factor correction (PFC) applications. The improvement over existing topologies lies in the positioning of the auxiliary circuit capacitors and the subsequent reduction in the resonant current and therefore the conduction losses as compared to other similar topologies. The proposed converter operates in two modes - Mode 1 and Mode 2. It is shown in the paper that the converter should be designed using the constraints obtained in Mode 1 to achieve low-loss switching. The converter is analyzed and characteristic curves presented which are then used in a detailed design example. Experimental results from a 250 W, 127 V input laboratory prototype switching at 100 kHz verify the design process and highlight the advantages of the proposed topology. The proposed converter is suitable for single-phase, two stage power factor correction circuits with universal input voltage range and power levels up to 3 kW.

Four distinct uninterruptible power supply topologies are presented here for powering hybrid fiber/coaxial (HFC) networks. Topologies based on a low frequency isolation transformer are found to have better efficiency than the topologies with high frequency transformer. However, the latter topologies have much better performance in terms of transient response, quality of the output voltage, input power factor, total harmonic distortion of the input current, size and weight. The series-parallel resonant based UPS topology is found to have best overall performance for the emerging HFC applications.

This paper studies the sensitivity of flicker severity to flicker mitigation planning solutions that can be adopted by distribution network operators. More specifically, the paper studies the flicker mitigation capacity under different bandwidths of direct voltage control stipulated by the network operator and implemented by a distributed wind farm, different MV/HV substation transformer ratings, series compensation of the distribution line and finally, the change of the wind farm connection point. The purpose of this paper is to provide results that help in the understanding of the feasibility and effectiveness of flicker mitigation solutions in the planning phase of a wind farm. A detailed typical North-American 25 kV distribution network is employed as the test network and a 10 MW DFIG-based wind farm is employed as the source of wind power. The flicker measurement is carried out for a 10-minute time frame according to the guidelines of IEC standard 61000-4-15. All studies are conducted on a multi-processor real-time simulator for its superior computational capacity.

This paper introduces a new method of IGBT switching loss reduction on the system level, while leaving the PWM scheme completely unchanged. The switching loss reduction is achieved by designing an IGBT gate driver that dynamically sets the IGBT gate current depending on feedback signals from IGBT current, IGBT voltage, phase load current, and DC link voltage if it is not constant in the application. Factors influencing switching losses will be demonstrated for two types of output driver stages: one with discrete switching speed setting and one with continuously variable switching speed. Comparing to other gate driver types with or without feedback aimed at keeping constant dv/dt, di/dt, and overshoots of IGBT voltage and current, the proposed gate driver not only ensures the operation of an IGBT in the safe operating area (SOA), but also improves the SOA utilization density by tracking the programmed voltage and current limits using peak-detection circuitry while minimizing the switching losses. Adaptive feedback control algorithms have been developed and verified by simulations. Keywords—gate driver; variable current output stage; IGBT switching loss; adaptive control algorithm I. INTRODUCTION Discrete IGBTs and IGBT modules are used in high- voltage applications mainly to perform DC to AC power conversion and vice-versa. The conversion losses dissipated by devices in form of heat consist of three sources: conduction losses, leakage current losses, and switching losses. The first two sources usually cannot be varied as long as appropriate extreme levels of gate-emitter voltage are applied to the IGBT. The switching losses, on the contrary, can be widely varied by using different modulation schemes, switching frequencies, and gate drivers. The topic of this paper is about development of a closed-loop gate driver with the task of minimizing switching losses while keeping the IGBT in the SOA.

This paper studies the dual three-phase inverter configuration for an electric vehicle drive feeding a dual three-phase permanent magnet synchronous machine. Employing interleaved SVPWM and DPWM modulation techniques with the proposed configuration, the input capacitor ripple current has been substantially reduced to 50–60 % compared to that of a conventional 2-level VSI. The optimal interleaving angles have been identified for capacitor ripple reduction considering both modulation indexes and power factors pertaining to the traction motor's operating range. The dual three-phase inverter's switching losses have been analyzed for two different DC-link voltages and output power levels and a 15–20% reduction in switching loss has been noted.

This paper presents a unified approach for generating pulsewidth-modulated patterns for three-phase current-source rectifiers and inverters (CSR/Is) that provides unconstrained selective harmonic elimination and fundamental current control. The approach uses the chopping angles or gating patterns developed for voltage-source rectifiers and inverters in combination with a logic circuit to generate the gating patterns for CSR/Is. The circuit also includes naturally and symmetrically distributed shorting pulses. Thus, the approach avoids the hassle of positioning the shorting pulses and defining and solving a set of nonlinear equations dedicated to CSR/Is. Moreover, the approach can eliminate an even or odd arbitrary number of harmonics (e.g., fundamental current control and elimination of the 5th, 7th, and 11th harmonics). This is an improvement over existing techniques and a new approach to pattern generation. Simulated and experimental results for both static and dynamic operating conditions are presented in order to validate the effectiveness of the approach.

Shunt-type static VAr compensators have been shown to be an effective means of increasing the transmission capability of power systems and of increasing the power factor of industrial loads. This paper presents an alternative to the shunt connection consisting of a series-connected transformer-coupled pulsewidth modulation (PWM) inverter. The scheme consists of a current source inverter (CSI) fed from a self-controlled DC current bus and presents the following features: (1) instantaneous series injected voltage control through online PWM of the DC link current; and (2) steady-state modulation index of the PWM pattern near unity through DC link current minimization. The first feature results in fast dynamic response, while the second feature ensures low and fixed injected voltage harmonic distortion and reduced steady-state compensator losses. Operation of the compensator and of the two-loop control scheme are presented. Simulation and experimental results on a 2 kVA laboratory prototype unit confirm the feasibility of the proposed VAr compensator structure.

Summary form only given. This paper offers a novel topology for the implementation of a shunt STATCOM based on a grouping of four 3-level, diode-clamped converters, switching at line frequency and coupled to the AC system through wye/wye and wye/delta phase-shifting transformers. Advantages include direct voltage control through the gating pattern and reduced size of DC capacitor. The dominant harmonic on the AC side is the 11/sup th/ and on the DC side the 12/sup th/. The proposed STATCOM can meet typical harmonic distortion requirements.

This paper presents the analysis and design of a single-phase single-stage high-power-factor AC/DC converter employing a series-parallel resonant topology operating in self-sustained oscillating mode. A control approach is proposed to achieve low total harmonic distortion of the input current. This approach does not require sensing of the input current. In addition, the inverter output current is limited during transients, and the converter operates with zero voltage switching for all operating conditions including open and short circuit. The performance of the proposed scheme is verified experimentally on a 500 W prototype.

This article has demonstrated the feasibility of a three phase active filter based on a half-bridge topology. Design guidelines for the power circuit have been derived and applied to a 5 kVA IGBT laboratory prototype. In the single phase mode, the active filter can reduce the low frequency harmonic content in the AC line to below 1% excluding the harmonics due to switching action of the converter. In the three phase mode, line currents are corrected under balanced and unbalanced conditions. The neutral current is reduced significantly.

Pulsewidth modulated (PWM) current-source rectifiers (CSR), among other alternatives, offer marked improvements over thyristor line-commutated rectifiers as a source of variable DC power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including unity displacement power factor operation. However, due to nonlinearities of the PWM-CSR model, their control has usually been carried out using direct line current control in a three-phase stationary frame (abc). This paper proposes the application of a nonlinear control technique that introduces more flexibility in the control of the rectifier and results in a more straightforward approach to controller design. The proposed technique is based on a nonlinear state variable feedback approach in the rotating frame (dq). The approach allows the independent control of the two components of the line current (active and reactive) with the same dynamic performance, regardless of the operating point. The control strategy also eliminates the need for input damping resistors and rejects the effect of supply voltage variations. Furthermore, a space vector modulation (SVM) technique is used to maximize the supply voltage utilization. This paper includes a complete formulation of the system equations and a controller design procedure. Experimental results on a 2 kVA digital-signal-processor-controlled prototype confirm the validity of theoretical considerations.

Current-source-inverter-based uninterruptible power supplies and V/f-controlled induction motor drives require sensing of two or more load voltages in addition to the DC voltage sensors used for protection purposes. This paper proposes a digital-signal-processor (DSP)-based load voltage control scheme that requires only information provided by the DC-bus voltage sensor. Load voltage estimation is based on AC line voltage reconstruction by means of a recursive least-square error algorithm that uses the information available on the DC bus and knowledge of the pulsewidth modulation gating pattern. Thus, the system minimizes the transducer count and, therefore, enhances reliability and ruggedness. Experimental results show that the load voltage can be reconstructed and its RMS value controlled for a wide range of operating conditions with errors of at most 4%. Moreover, the use of the space-vector modulation technique ensures a reduced load voltage harmonic distortion, which remains within the 5% range at nominal voltage and for all load conditions. The paper presents the DSP algorithms required for the operation of the system and key experimental results obtained on a three-phase 208-V 60-Hz 2-kVA prototype unit.

Static var compensators have been, for many years, an essential component in the operation of power transmission systems. They are part of a family of devices known as Flexible AC Transmission System (FACTS) devices. The advent of large capacity force-commutated semiconductor switches allows many developments in power electronic converters to be applied to the implementation of high power compensators. This paper describes the principles of controlled reactive power compensation, particularly in the context of power systems. It focuses on active static power converter-based compensators and discusses issues related to the power circuit topology and control techniques, including the impact of Pulse Width Modulation (PWM) techniques. Compensators based on current and voltage source converters and onac controllers, both in the shunt and series configurations, are covered. Methods to enhance power capacity using multi-level and multi-pulse arrangements are discussed.

Standard pulsewidth modulation (PWM) techniques assume a ripple-free DC-link voltage at the inverter input terminals and ideal switches. Most techniques proposed in the literature to compensate the nonideal characteristics require additional and complex circuitry. This paper proposes and analyzes a simple method of generating PWM switching patterns which ensures a high-quality output voltage and inherently compensates for a nonideal DC bus and switching delays. The method is based on maintaining a sinusoidal volt-second distribution at the inverter output by sensing the output voltage and generating the gating pattern online. The principles of operation are explained, and a design procedure is presented. Simulation results illustrating the features of the proposed modulator are verified experimentally on a 3 kVA prototype unit.

Output harmonic minimization in standard pulse width modulation (PWM) pattern generators is based on the assumption that the input DC bus voltage is ripple-free. However, in a practical converter system, a nonideal DC bus deteriorates the quality of the inverter output voltage by introducing undesirable low-order harmonics that may be difficult to filter. The existing compensation techniques often use additional and complex circuitry to eliminate the effect of this ripple on the output voltage. This paper presents an online PWM pattern generator that inherently takes into account the DC bus ripple and generates gating signals required to produce high-quality sinusoidal output voltages. The technique is based on integrating the output voltage at a constant frequency on a pulse-by-pulse basis to ensure a sinusoidal volt-sec (V/s) distribution, irrespective of the input DC bus. The principles of operation are explained, and design equations are derived. The features of the proposed PWM pattern generator are illustrated. Comparison of the output voltage waveforms of those standard sinusoidal PWM (SPWM) techniques illustrate, in particular, the effectiveness of the ripple-rejection mechanism. Experimental results obtained on a 3-kVA laboratory prototype confirm the feasibility and features of the proposed pattern generator.

The conventional structures used for phase shifters employ quadrature voltage injection controlled by means of on-load tap changers that require considerable maintenance. Line-commutated thyristor structures have been proposed to replace tap changers, but problems related to filter requirements or the number of switches have limited their utilization. This paper proposes a pulse width modulation (PWM) quadrature-booster phase shifter based on a force-commutated AC controller. It offers features such as fast dynamic response, continuous variation of the phase angle with low harmonic injection, and it requires a simple power structure and can be controlled by adjusting the duty cycle of the switches. The operating principles of the proposed phase shifter are analyzed and their feasibility is demonstrated through digital simulation and experimental implementation.

A Power Electronic Transformer (PET) performs the tasks of a conventional transformer by means of power electronic converters and medium-frequency transformers. A three-stage PET has high- and low-voltage AC and low-voltage DC output terminals. In this work, employing a Modular Multilevel Converter (MMC) at the first stage of a three-stage topology, a PET configuration is proposed, which not only has the common terminals, but also features a high-voltage DC terminal, enabling interfacing a DC distribution grid. Furthermore, the proposed configuration is readily scalable to high-voltage and power ratings. Besides, in the third stage of the proposed configuration, a simple two-leg inverter is used to supply a split-phase distribution system.