Harmonic Isolation Research Articles

Design and Control of Two-Stage DC-AC Solid-State Transformer for Remote Area and Microgrid Applications

The critical challenges with integrating renewable energy into the grid are smooth power flow control, isolation between the high-voltage and low-voltage networks, voltage regulation, harmonic isolation, and power quality regulation. This paper considers the design and construction of a two-stage DC-AC solid-state transformer based on wide bandgap (WBG) semiconductor technologies, an optimized medium-frequency transformer, and PI and dq controllers for supplying urban area electric drive systems and microgrid applications. The designed SST consists of a dual active bridge (DAB) DC-DC converter followed by a DC-AC three-phase inverter. Each stage of the SST was simulated with independent controllers. The proposed system was initially developed in MATLAB/Simulink and a laboratory prototype was constructed to verify the results experimentally. Resistive and inductive load were used to test the load disturbance to evaluate the voltage regulation performance. This work has comprehensively provided the performance of a double stage (DC-DC and DC-AC converter) by taking into consideration input voltage, load disturbance, and voltage tracking both in simulation and experiment. The dual active bridge with its controller is able to maintain the desired output reference voltage with minimal voltage ripples under input voltage fluctuations and load variations. Similarly, the three-phase DC-AC converter’s controller exhibits better performance in tracking the desired reference voltage and producing well-regulated AC voltage with low harmonic distortion.

Comparison of Control Techniques for Harmonic Isolation in Series VSC-Based Power Flow Controller in Distribution Grids

The application of power electronics equipment in medium voltage (MV) distribution grids can provide new management solutions for power flow control, load balancing and voltage problems. A series MV VSC-based power flow controller has recently been presented to interconnect two radial distribution feeders performing active and reactive power transfers to improve the flexibility and utilization of these circuits in a controlled and secure way. Although not previously explored, this power flow controller can integrate the functionality of a series power filter, accomplishing independent control of the fundamental power flow while isolating the harmonic content between the two interconnected feeders. This prevents harmonic pollution from one feeder from propagating to the other, improving the voltage quality. To implement the harmonic isolation, several control strategies can be used. Therefore, this paper provides a comparative analysis between two of the main harmonic control techniques found in the literature: the Synchronous Reference Frame (SRF) controller and the Proportional Resonant (PR) controller. Assessments are conducted both through simulations and experimental results in a meshed network at 13.8 kV with different types of non-linear loads. In the simulation cases, both algorithms showed similar results; however, in the experimental cases, the PR-based solution exhibited better performance in isolating the harmonics from one feeder to the other.

Damping identification of offshore wind turbines using operational modal analysis: a review

Abstract. To increase the contribution of offshore wind energy to the global energy mix in an economically sustainable manner, it is required to reduce the costs associated with the production and operation of offshore wind turbines (OWTs). One of the largest uncertainties and sources of conservatism in design and lifetime prediction for OWTs is the determination of the global damping level of the OWT. Estimation of OWT damping based on field measurement data has hence been subject to considerable research attention and is based on the use of (preferably operational) vibration data obtained from sensors mounted on the structure. As such, it is an output-only problem and can be addressed using state-of-the-art operational modal analysis (OMA) techniques, reviewed in this paper. The evolution of classical time- and frequency-domain OMA techniques has been reviewed; however, the literature shows that the OWT vibration data are often contaminated by rotor speed harmonics of significantly high energy located close to structural modes, which impede classical damping identification. Recent advances in OMA algorithms for known or unknown harmonic frequencies can be used to improve identification in such cases. Further, the transmissibility family of OMA algorithms is purported to be insensitive to harmonics. Based on this review, a classification of OMA algorithms is made according to a set of novel suitability criteria, such that the OMA technique appropriate to the specific OWT vibration measurement setup may be selected. Finally, based on this literature review, it has been identified that the most attractive future path for OWT damping estimation lies in the combination of uncertain non-stationary harmonic frequency measurements with statistical harmonic isolation to enhance classical OMA techniques, orthogonal removal of harmonics from measured vibration signals, and in the robustification of transmissibility-based techniques.

Linearity Enhanced Harmonic-Modulated Impedance Inverter Doherty-Like Power Amplifier

In a conventional Doherty Power Amplifier (DPA), harmonic isolation is typically required between the two transistors to prevent them from modulating each other at harmonic frequencies. Normally, the current is clipped at saturation, which results in poor in-band non-linearity, e.g. IMD3. Hence, mutual harmonic interaction is desirable when properly used to prevent current clipping in the active devices, thus improving linearity. In this paper, for the first time, a linearity enhancement technique for Doherty-like power amplifier (DLPA) based on harmonic interaction is presented. The proposed DLPA achieves an excellent trade-off between efficiency and in-band linearity. For demonstration purposes, a DLPA prototype is devised based on two identical 6-Watts gallium nitride HEMTs (CGH 40006P). Within the frequency band of 1.75 to 2.45 GHz, the DLPA achieves a measured power added efficiency (PAE) of greater than 45.0% and 61.9% at 6 dB output back-off and saturation, respectively. An IMD3 below −30 dBc and a PAE of greater than 53% is achieved near saturation under a two-tone signal excitation.

Converter-Based Power System Protection Against DC in Transmission and Distribution Networks

The dc in a power system may be caused by geomagnetic disturbances that are the result of solar storms and high-altitude nuclear detonations. Increased inverter-based generation is also contributing to small dc injection into the power systems. The resultant dc could have serious consequences for the power systems as it may drive power transformers into saturation, cause transformer internal heating, cause large draw of reactive power, and misoperation of protective relays. This letter proposes a novel power electronics-based dc mitigation approach that involves a transformerless series active filter integrated between the neutral point and ground of power transformers serving multiple purposes. The first objective is to surpass the effect of dc injection, the second goal is voltage regulation, and the third is to provide harmonic isolation or impedance balancing. The proposed device is currently being developed on a 7.2-kV/240-V single-phase transformer; however, the solution is also relevant for 24-500-kV networks. The system circuitry, operation, and control are implemented and verified for this letter in a controller hardware-in-the-loop (C-HIL) test setup using a Typhoon HIL-402 simulator. Results indicate that our approach is a promising alternative to traditional neutral capacitor-blocking strategies.

An Inductive Hybrid UPQC for Power Quality Management in Premium-Power-Supply-Required Applications

Voltage sag and harmonic pollution have a serious impact on the medium-voltage premium-power-supply-required park represented by optical semiconductors, data storage, precision instruments and biopharmaceuticals. Which makes existing equipment require higher voltage capacity of power electronics, higher economic cost and compensation performance. In this paper, an Inductive Hybrid Unified Power Quality Conditioner (IH-UPQC), which is characterized as high integration, reduced DC-link voltage and satisfactory harmonic isolation of transformer, is presented to realize the bi-directional power quality improvement for medium-voltage premium-power-supply-required park. First, the three-phase equivalent circuit and mathematical model are established to reveal the mechanism of harmonic suppression and voltage regulation. Based on the theoretical analysis, the compound control strategy of series and shunt Hybrid Active Power Filter (HAPF) as well as the synchronous method sliding Goertzel discrete Fourier transformation-pre-filtering Phase Lock Loop (PLL) are designed. Then, the main circuit components design including Double Resonant Passive Filter (DRPF), L-C-R low pass filter and the special designed filtering winding for implementing inductive filtering method are described. Finally, the performance of IH-UPQC is validated in 10kV distribution network by MATLAB/Simulink. The simulation results demonstrate that the IH-UPQC is effective to perform grid voltage regulation, load harmonic current suppression and reactive power compensation.

Model predictive control‐based smart impedance for harmonic load freewheeling

A novel smart impedance (SI) is introduced for load harmonics (distortion power) freewheeling in microgrids which are called predictive SI (PSI). ‘PSI’ provides solutions to the load harmonics conditioning, reactive power compensation, and parallel resonance suppression. The ‘PSI’ allows for harmonics, sub-harmonics, and inter-harmonics compensation with using only one control loop. The control model, which is used for the ‘PSI’ enables its impedance phasor variation in a wide and continuous range, including inductive and capacitive ones. The ‘PSI’ consumes small active power and can provide reactive power compensation without the need for a separate capacitor bank. The introduced ‘PSI’ does not generate parasitic harmonics and so does not need an additional passive filter in its output. The ‘PSI’ operates such as a harmonic isolator and only compensates for load harmonics and thereby prevents from the source side harmonics flowing into the load. It does not need the phased locked loop for synchronisation to the grid and can be designed for selective harmonic compensation if needed. A droop-boost control strategy is proposed for optimum and prioritised utilising of the SI capacity. At the end of the study, by using simulations in Matlab/Simulink, the figure of merits of the PSI are proved.

Design of Solar Pv Based Shunt Active Filter for Nonlineasr Load

Elevation of power electronics technology, converter are the main causes for power quality issues, because of their high switching characteristics.so to reduce the harmonics injected by the nonlinear load, the filters are play a major role to improve a power quality improvement, particularly shunt active filter is more reliable for reduce a harmonic in power system network. This novel technique proposed for design a shunt active filter with solar photovoltaic array integrated into nonlinear load using a Point of Common Coupling (PCC) technique. Zero crossing detection technique are used to extract the magnitude of a fundamental active components of distorted load currents. The estimation of harmonic isolator and current compensation are controlled by Field Programmable Gate Array (FPGA) controller, different types of compensation techniques are used in this work Synchronous reference frame theory, instantaneous reactive power theory (PQ) and hysteresis current control technique. These techniques enable extraction of active power, regulates a load voltage and maintain a phasor sequence at PCC under the voltage sag and swell. Simulation is carried out by MATLAB/SIMULINK for different compensations techniques and Total Harmonics Distortion (THD) values are tabulated.

A controllable inductive power filtering system: modeling, analysis and control design

This paper presents a controllable inductive power filtering (CIPF) system with the novel filtering mechanism. Due to the zero-impedance design of the power transformer, the harmonic magnetic flux between the secondary load winding and the customized filtering winding can be balanced each other. Hence, the contaminated area of harmonics is reduced. The addition of the active filter contributes to further improve the filtering performance with the task of harmonic isolation between the power grid and the load. First, the three-phase unified equivalent circuit model and the mathematical model are given out at the harmonic domain. Based on the deduced transfer matrix, the filtering evaluation criterion of CIPF system is established, and the filtering principle is revealed, as well. According to the special operational law, an improved virtual impedance control strategy is designed to prevent the potential harmonic amplification, and the relationship between the phase/magnitude of the virtual impedance and the filtering performance is discussed. Finally, the experimental results based on the laboratory scaled prototype show the validity of the CIPF system with improved virtual impedance control.

Improved series active power filter with fundamental and harmonic magnetic flux hybrid compensation

The filtering performance of series hybrid active power filter (SHAPF) based on fundamental magnetic flux compensation positively correlates with the magnetising impedance of the transformer. However, excessive magnetising impedance will decrease reliability while increasing capacity and costs of the whole system. In order to reduce the magnetising impedance while ensuring the same filtering performance of SHAPF, an improved series active power filter (ISAPF) with fundamental and harmonics magnetic flux hybrid control is presented here. The equivalent impedances to fundamental and harmonics in ISAPF are firstly analysed to explain the principle of ‘harmonic isolation’. Then the range of compensation coefficients is investigated in detail based on the complete control block diagram and the open-loop function of ISAPF. Moreover, stability conditions of an overall system with non-linear loads are deduced. Finally, a set of single-phase prototype with two kinds of special transformer has been constructed; the related experiments results showed that ISAPF can ensure the filtering performance while applying a transformer with smaller capacity, thus resulting in the reduction in capacity and the costs while increasing the reliability.

Study and Analysis of Performance of 3-Phase Shunt Active Filter in Grid-tied PV-Fuel Cell System Employing Sinusoidal Current Control Strategy

This paper describes about mitigation of power quality issues using Shunt active filter in a Grid connected hybrid energy system consisting of PV-Battery-Fuel Cell. The Shunt active filter control is based on Sinusoidal Current Control Strategy. Shunt Active Power Filters (ShAPF) is implemented in the hybrid systems to mitigate the harmonic current component as well as to recompense the imaginary or reactive power owing to their exact and reckless operation. Sinusoidal current based controller used in a ShAPF has been focused over here. Sinusoidal current control strategy is utilized to extricate sinusoidal current commencing from the source. The sinusoidal Currents in addition with a stout synchronizing circuit (Phase Locked Loop or PLL circuit), custom a brief controller meant for ShAPF which is precise by a sinusoidal current control based controller in order to perform like a harmonic isolator amid supply and load. Action of the ShAPF under passive load conditions using non-linear load, the performance of the sinusoidal current control technique is evaluated using MATLAB R2016a. MATLAB simulation results validate the efficiency of the power filter system to mitigate harmonic, it also offered to validate the control strategy. Total Harmonic Distortion (THD) of voltage as well as of current determines the practical feasibility of controller designed for ShAPF to deliver a harmonic separation of passive loads.

Comparative Study between Shunt Active Filter and Hybrid Filter

This paper presents an comparative study between shunt active filter and shunt hybrid filter based on configuration system and harmonic isolation. The harmonic isolator isbased on Self Tuning Filters (STF) (it can be tuned at any frequency). The study of the active filter control is divided in two parts. The first part deals with the harmonic isolator which generates the harmonic reference currents. The second part focuses on the generation of the switching pattern of the IGBTs of the inverter by the modulated hysteresis current controller. The studied hybrid active filter consists of an active filter and three phase tuned LC filters for 7th harmonic frequency. The nonlinear load is a diode rectifier feeding a (R, C) parallel load. The use of STF's simplifies the control scheme by reducing the number of extraction filters. The use of STFs instead of classical extraction filters allows extracting directly the voltage and current fundamental components. The effectiveness of this study has been verified by computer simulation and comparing the results.

A Broadband Doherty Power Amplifier Based on Continuous-Mode Technology

In this paper, a novel broadband Doherty power amplifier based on the continuous-mode technique (C-DPA) is proposed. The amplifier is focused on manipulating harmonic components in a Doherty power amplifier (DPA) structure to achieve improved bandwidth and efficiency. In a conventional DPA, harmonic isolation is typically required between the two transistors to prevent them from modulating each other at harmonic frequencies. However, as presented in this paper, such isolation is not actually necessary. On the contrary, by allowing the two transistors to modulate each other at harmonic frequencies with the help of a properly designed postharmonic tuning network, a series of highly efficient DPA modes can be created over a continuous frequency band, leading to a broadband C-DPA. Based on the proposed method, an example of a C-DPA working from 1.65 to 2.75 GHz was designed. According to the measured results, the designed C-DPA exhibits a 52%–66% efficiency at a −6 dB power backoff and a power utilization factor higher than 1.08 over the 1.1-GHz band. In addition, when simulated by a 7.5-dB peak-to-average power ratio 20-MHz LTE signal, the example C-DPA exhibits an efficiency of 46%–62% while maintaining an adjacent channel power ratio below −45 dBc after linearization over the full 1.1-GHz band. To the best of our knowledge, this is the first proposed C-DPA and a state-of-the-art performance for broadband DPAs.

Three Phase Grid Connected PV System for Mitigation of Voltage and Current Harmonics Compensation Using SRF Method

Power quality is an all-encompassing concept for a multitude of individual types of power system disturbances. The presence of harmonics in power supply network poses a severe power quality problem that results in greater power losses in the distribution system, interference problems in communication systems and, sometimes, in operation failures of electronic equipment. This paper presents a three -phase active power filter for harmonic compensation which is consists of a series active power filter and a shunt active filter. The active filter connected in series to a source acts as a harmonic isolator between the sources and loads whereas the shunt active filter is connected in parallel with a load and suppresses the harmonic current produced by the load and. reduce the total harmonic distortion (THD). The voltage source inverter (VSI) is the core of an active power filter. The hysteresis current control is a method of controlling the VSI. Hysteresis control can be either of fixed band type or adaptive band type. In this paper, Synchronous Reference Frame (SRF) theory is implemented for the generation of reference current signals for the controller. Mat lab /Simulink and are used for simulation. From the simulation results it is confirmed that the filter topology is capable of compensating the load current and voltage harmonic distortion within the stipulated limits laid down by the IEEE 519 standard.

A Single-Phase Active Device for Power Quality Improvement of Electrified Transportation

A transformerless hybrid series active filter is proposed to enhance the power quality in single-phase systems with critical loads. This paper assists the energy management and power quality issues related to electric transportation and focuses on improving electric vehicle load connection to the grid. The control strategy is designed to prevent current harmonic distortions of nonlinear loads to flow into the utility and corrects the power factor of this later. While protecting sensitive loads from voltage disturbances, sags, and swells initiated by the power system, ridded of the series transformer, the configuration is advantageous for an industrial implementation. This polyvalent hybrid topology allowing the harmonic isolation and compensation of voltage distortions could absorb or inject the auxiliary power to the grid. Aside from practical analysis, this paper also investigates on the influence of gains and delays in the real-time controller stability. The simulations and experimental results presented in this paper were carried out on a 2-kVA laboratory prototype demonstrating the effectiveness of the proposed topology.

A Novel Integrated Power Quality Controller for Microgrid

A novel variable reactor based on magnetic flux control is proposed in this paper. The system configuration of the novel variable reactor is presented, while its operational principle and dynamic performance are analyzed. Based on the developed variable reactor, a novel integrated power quality controller (IPQC) suitable for microgrid is proposed, which can cater for the peculiar requirements of microgrid power quality, such as the harmonic high penetration, frequent voltage fluctuation and overcurrent phenomenon, and bidirectional power flow and small capacity. For the fundamental, the equivalent impedance of the primary winding is a variable reactor or capacitor. For the nth-order harmonic, the equivalent impedance is very high impedance and acts as a “harmonic isolator.” The system control strategy is also analyzed in detail. A set of three-phase IPQC has been constructed. The experimental test results verify the validity of the novel variable reactor and the IPQC.

New Method to Harmonic Isolation Based on High Selectivity Filter to Control of Shunt Active Filter with Experimental Validation Using DSPACE System

This paper presents a new control method of a parallel active power filters based on improved harmonic isolation with hardware implementation. The harmonic isolator is based on High Selectivity Filters (it can be tuned at any frequency) and the current control technique consists in a modulated hysteresis current controller. This active filter is intended for harmonic compensation of a diode rectifier feeding a RL load. The study of the active filter control is divided in two parts. The first part deals with the harmonic isolator which generates the harmonic reference currents and is implemented into a DSPACE DS1104 prototyping card. The second part focuses on the generation of the switching pattern of the IGBTs of the inverter by the modulated hysteresis current controller, implemented into an analogue card. The use of High Selectivity Filters instead of classical extraction filters allows extracting directly the voltage and current fundamental components in the α-β axis at high performances. The effectiveness of the new proposed method is verified by computer simulation and by experimental study.

Optimization of Phase jump angle of Series Active Power Filter (SAPF)

This paper deals with the optimization of phase jump angle of series active power filter by using particle swarm optimization technique and series active power filter compensates supply voltage distortions/unbalance, supply voltage harmonics in a view as such they do not reach at the load end with very low THD in load voltage. SAPF operates mainly as voltage regulator and harmonic isolator between the non-linear load and the utility system. The main aim of this project is to design the dynamic model of the Series Active Power Filter and minimization of VA rating of the Series Active Power Filter by using practical swarm optimization (PSO). Hence the results are obtained by using the Matlab/Simulink.

Application of Adaptive Tabu Search Algorithm in Sinusoidal Fryze Voltage Control based Hybrid Series Active Power Filter

A novel hybrid series active power filter to eliminate harmonics and compensate reactive power is presented and analyzed. The proposed active compensation technique is based in a hybrid series active filter using adaptive Tabu search (ATS) algorithm in the conventional Sinusoidal Fryze voltage (SFV) control technique. Optimization of the conventional Sinusoidal Fryze voltage control technique has been done using adaptive tabu search algorithm. This paper discusses about the comparative performances of conventional Sinusoidal Fryze voltage control strategy and ATS-optimized controllers. ATS algorithm has been used to obtain the optimum value of Kp and Ki. Analysis of the hybrid series active power filter system under non linear load condition and its impact on the performance of the controllers is evaluated. Effectiveness of the hybrid series active power filter to provide harmonic damping is demonstrated by MATLAB/Simulink results. Total harmonic distortion (THD) demonstrates the practical viability of the controller for hybrid series active power filter to provide harmonic isolation of non-linear loads and to comply with IEEE 519 recommended harmonic standards.

Dual Z-Source Three Level Inverter Topology with Triplen Harmonic Elimination Employing Clamping Capacitor for Impedance Network for Open End Stator Winding Induction Motor

In open end stator winding three phase induction motor the two ends of all the phases of stator windings are connected to separate supplies. Open-end winding motors require either harmonic filters or isolation transformers to prevent currents of the triplen harmonic order flowing in the motor phases and the semiconductor devices. Separate dc supply is used for each inverter to block the flow of third harmonic currents. Z-Source Inverter will act as a booster inverter and also due to the presence of source impedance network, it provides ride through shoot through faults. A novel configuration of three level Neutral Point Clamped (NPC) Multi level Inverter with source impedance network, in which impedance network is formed by using the capacitors of the NPC inverter is proposed in this paper. Therefore the numbers of capacitors are reduced and voltage unbalancing of capacitor can be minimized. The proposed configuration offers reduced size and better throughput. The simulation results for the same are presented in this paper.