Showing papers on "Power factor published in 2022"

1.95-kV Beveled-Mesa NiO/β-Ga 2 O 3 Heterojunction Diode With 98.5% Conversion Efficiency and Over Million-Times Overvoltage Ruggedness

Abstract: The technical progress of Ga2O3 power diodes is now stuck at a critical point where a lack of performance evaluation and reliability validation at the system-level applications seriously limits their further development and even future commercialization. In this letter, by implementing beveled-mesa NiO/Ga2O3 p–n heterojunction diodes (HJDs) into a 500-W power factor correction (PFC) system circuit, high conversion efficiency of 98.5% with 100-min stable operating capability has been demonstrated. In particular, rugged reliability is validated after over 1 million times dynamic breakdown with a 1.2-kV peak overvoltage. Meanwhile, superior device performance is achieved, including a static breakdown voltage (BV) of 1.95 kV, a dynamic BV of 2.23 kV, a forward current of 20 A (2 kA/cm2 current density), and a differential specific on -resistance of 1.9 mΩ·cm2. These results indicate that Ga2O3 power HJDs are developing rapidly with their own advantages, presenting the enormous potential in high-efficiency, high-power, and high-reliability applications.

An Overmodulation Algorithm With Neutral-Point Voltage Balancing for Three-Level Converters in High-Speed Aerospace Drives

Abstract: In this article, a virtual space vector based overmodulation algorithm is presented for three-level neutral-point (NP) clamped converters in high-speed aerospace motor drives. With the proposed inscribed polygonal-boundary compression technique, the output voltage capability is enhanced under a lower crossover angle and compression coefficient. As a result, it brings an opportunity for the operation of the studied aircraft electric starter/generator (ESG) systems easily extending from the linear modulation range into the overmodulation region. Furthermore, an active capacitor voltage balancing control method is investigated to recover NP potential imbalance in the case of high modulation index and low power factor operating conditions. To simplify the digital implementation of the algorithm, a fast calculation approach is adopted in this work. The modulation performance of the proposed strategy is verified by both simulation and experimental results with a 45 kW, 32 k r/min ESG prototype system.

High-Efficient Electrolytic-Capacitor-Less Offline LED Driver With Reduced Power Processing

Abstract: In this article, an integrated parallel buck–boost and boost converter (IPB3C) is proposed as an electrolytic-capacitor-less light-emitting diode (LED) driver. The IPB3C provides a high power factor (PF) and low total harmonic distortion (THD). The driver is composed of two converters that are connected in parallel, using just one controlled switch. The buck–boost duty is to deliver constant power to the LED, while ensuring a good PF. The boost converter is employed to cancel the low-frequency ripple at the LED. In return, this decreases the flicker effect and only a relatively small capacitance is needed to fulfill the standard requirements. The buck–boost converter handles the full power of the LED, while the boost converter handles only a portion of the LED power. Thus, better efficiency is ensured by this parallel configuration compared to conventional cascaded integrated converters. Moreover, the voltage across the switch is low, as it is the higher, whether buck–boost or boost converter, but not the addition of both. In this article, the IPB3C is analyzed, and its design methodology is presented. A universal input voltage range prototype of the proposed converter supplying an LED lamp of 108-V/ 0.35-A is presented. The prototype shows high PF, nearly equal to one, very small THD, nearly zero, output voltage ripple of 4.5%, output current ripple of 19%, and high efficiency, equal to 92.4%. Moreover, the converter requires the use of a bulk capacitance of only 68 μF, while the required output capacitance is just 1 μF.

Novel Single-Phase Cuk-Derived Bridgeless PFC Converter for On-Board EV Charger With Reduced Number of Components

Abstract: This article proposes a novel single-phase bridgeless Cuk-derived power factor corrected (PFC) converter with reduced component count for on-board EV charging application. The unique feature of this proposal is to design and operate the output inductor of the converter in discontinuous current mode for the complete power range to attain PFC naturally at ac mains, thereby not requiring the input voltage and input current sensing, which reduces the converter cost, and improves the power density as well as converter robustness to high-frequency noise. The converter control is very simple in operation and easy in implementation with only a single sensor-based voltage control loop. The semiconductor components voltage stress of the proposed power converter is lower when compared to the traditional Cuk converter. The simulation results from PSIM 11 and experimental results are given by testing a proof-of-concept hardware laboratory prototype to demonstrate the high performance of PFC operation of the proposed converter.

Power Quality Enhancement and Power Flow Analysis of a PV Integrated UPQC System in a Distribution Network

Abstract: Increasing awareness for green energy and sustainable energy management has accelerated the popularity for the incorporation of distributed energy resources and distributed energy storage into the distribution network and microgrid. This has proliferated the use of power electronic-based devices giving rise to a serious issue of deteriorating power quality (PQ) in the distribution system. In this context, this article presents a photovoltaic (PV) integrated unified power quality conditioner (UPQC) operating with an adaptive compensating technique based on variable leaky least mean square (VLLMS) algorithm. It is a soft computing-oriented method that offers quicker convergence to the desired condition in an iterative approach keeping the weight of the updating parameters within the specified limit. The VLLMS-based algorithm eliminates the use of low pass or moving average filter for the extraction of fundamental components from polluted source voltage and load current to generate reference signal for the switching of shunt as well as series voltage source converters (VSC) of the UPQC. Due to the involvement of feed-forward component of PV in the compensating technique of shunt VSC, it efficiently and smoothly manages power balance between grid, load, and PV besides resolving the PQ issues of current harmonics and poor power factor at PCC. It also ensures the regulation of dc-link voltage. The series converter maintains pure sinusoidal voltage at the load terminal irrespective of sag/swell and harmonics present in the grid voltage. The effectiveness of the proposed system is verified through simulation as well as hardware implementation under different static and dynamic operating conditions.

Second Harmonic Current Reduction Schemes for DC–DC Converter in Two-Stage PFC Converters

Abstract: For the two-stage single-phase power factor correction (PFC) converter, its instantaneous input power pulsates at twice the line frequency, generating the second harmonic current (SHC) at the dc-bus port. The dc–dc stage is used to regulate the output voltage or the dc bus voltage in different applications, and the SHC reduction schemes for the dc–dc stage with different control objectives are discussed in this article. When the dc–dc stage regulates the output voltage, it is pointed out that the control bandwidth of the dc–dc stage is required to be high enough and the dc bus capacitor should be large enough to suppress the SHC, and the design of the dc bus capacitor is given. When the dc–dc stage regulates the dc bus voltage, a virtual impedance is added in series with the input/output of the dc–dc stage to suppress the SHC, and a virtual impedance is added in parallel with the dc bus to improve the dynamic performance. The selection and design of the virtual impedances are also given. Based on that, three specific control schemes are proposed for the dc–dc stage to suppress the SHC, and the parameters design method is also presented. Finally, a 3.3-kW two-stage single-phase PFC converter is fabricated and tested in the lab to verify the effectiveness of the proposed SHC reduction schemes.

A Dual Active Bridge DC–DC-Based Single Stage AC–DC Converter With Seamless Mode Transition and High Power Factor

Abstract: In this article, a dual active bridge (DAB) based single-stage isolated ac–dc converter is studied. By analyzing the root mean square value of the leakage inductor current, the high-frequency transformer turns ratio is optimized for higher conversion efficiency. Three operating modes of the DAB converter are utilized in the control strategy. The current and the voltage waveforms of these operating modes are analyzed. The control variables, including the phase-shift ratio ϕ , the primary side duty cycle d 1, and the secondary side duty cycle d 2 are combined based on instantaneous calculation according to achieve boundary zero voltage switching (ZVS). The mode transition is seamless while the switching frequency is constant. Furthermore, the magnetizing inductor of the transformer is designed to help the secondary side switches to achieve ZVS. ZVS conditions and parameter design are given in this article. Besides, a 1 kW prototype was fabricated to verify the effectiveness of the design and the control strategy.

Grid Harmonic Current Correction Based on Parallel Three-Phase Shunt Active Power Filter

Abstract: This article presents a finite-set model predictive control (FS-MPC) applied to the shunt active power filters (SAPF) based on three-phase inverters connected in parallel sharing the same dc-link. The discrete-time model of the system is used to predict the future value of the grid, circulation, and offset currents. The presence of circulation and offset currents occurs due to the connection of the two inverters in parallel sharing the same dc-link. There are 64 switching state vectors for SAPF and, in order to reduce the burden of calculation, only 30 switching states are chosen and applied, however keeping the advantages of the FS-MPC algorithm. The control strategy ensures the sinusoidal shape of the grid current, high power factor, and circulating and offset currents suppression. The FS-MPC has its performance compared to the pulsewidth modulation (PWM) strategy considering the SAPF with two parallel inverters, the conventional SAPF and the neutral-point-clamped SAPF. These comparisons include harmonic distortion, power semiconductor losses, and analysis of dc-link capacitor losses. As a multilevel topology, the SAPF with two parallel inverters using FS-MPC present competitive efficiency and can be applied with a good performance in industrial and residential applications. Simulation results and a laboratory-scale experimental platform is used for corroborating the proposal.

Condition Monitoring of DC-Link Electrolytic Capacitor in Back-to-Back Converters Based on Dissipation Factor

Abstract: Condition-monitoring systems are used to determine the best timing for predictive maintenance of power electronics converters. These monitoring systems can significantly reduce the converter repair time and increase system availability. In this article, an investigation has been conducted on the possibility of using the dissipation factor as a lifetime indicator of electrolytic capacitors. A criterion is also proposed based on the dissipation factor to detect electrolytic capacitors’ end of useful life. A method has been presented for measuring the dc-link capacitor dissipation factor in a back-to-back converter. Using this technique, it is possible to estimate the switching component of the capacitor current by measuring the output currents of the converter without a need to measure the capacitor current directly. The proposed method is simulated, and the impact of various factors, such as switching frequency, capacitor series inductor, and the network filter on the accuracy of the dissipation factor measurement, is discussed. Experimental results are also provided to validate the acceptable accuracy of the proposed method.

A Combined PWM and AEM-Based AC Voltage Controller for Resistive Loads

Abstract: AC voltage controller using PWM technique integrated with equal area digital modulation technique and connected to resistive loads is discussed in this paper. The proposed technique reduces the harmonics in the lower order significantly and improves the power factor compared to the existing conventional line commutated voltage controllers. The voltage and current waveforms are smoothened; therefore, a sinusoidal nature is achieved. The power factor is considerably improved at the low output voltage range when compared to existing methods. The capabilities of the proposed technique are computed mathematically and simulation results are compared with the existing methods.

Dual-Loop Continuous Control Set Model-Predictive Control for a Three-Phase Unity Power Factor Rectifier

Abstract: In this article, a novel cascade model-predictive control for a three-phase unity power factor rectifier is presented. Unlike the traditional control techniques for rectifiers, the proposed method uses a cascade dual-model-predictive control for the inner and outer control loops. The three-phase currents of the rectifier are controlled with the inner control loop, while the desired output voltage is achieved with the outer control loop. In this proposal, the output power is used as a feedforward to enhance the transient dynamics of the output dc voltage. Several advantages can be highlighted such as a fixed switching frequency, and output voltage variations are avoided when a sudden change in the load or a voltage sag appears. The overall control proposal has been fully integrated into a digital signal processor. Selected experimental results are introduced to validate the theoretical contributions of this article.

Fault Tolerant Backstepping Control for Double-Stage Grid-Connected Photovoltaic Systems Using Cascaded H-Bridge Multilevel Inverters

Abstract: This letter introduces a complete DC-AC conversion system fed by photovoltaic (PV) energy. The system consists of $N$ PV panels, $N$ DC-DC boost converters, $N$ cascaded H-bridge inverters, a DC-link composed of $N$ capacitors and an LCL filter. This work aims at reaching threefold control objectives: i) Extracting the available maximum power by regulating the voltages across the PV panels, ii) Ensuring a unitary power factor, iii) Regulating the DC-link voltage to a desired reference. To achieve the mentioned objectives, a multi-loop regulator is designed. The PV panels are individually controlled to track the maximum power point in order to efficiently operate at either the same or different varying climatic conditions without failures. In addition to the maximum power point tracking (MPPT) controller, two cascaded loops guaranteeing a satisfactory power factor and DC-link voltage regulation are developed. The nonlinear backstepping approach combined with Lyapunov theory are used based on the averaged model for the synthesis of the multi-loop controller. The performance of the studied system is tested via MATLAB / SimPowerSystems environment. The obtained simulation results prove that the proposed controller meets its objectives and demonstrate the efficiency of the chosen control strategy under faulty conditions.

Deep-Investigated Analytical Modeling of a Surface Permanent Magnet Vernier Motor

Abstract: Permanent magnet Vernier motors (PMVMs) possess the advantage of high torque density for high-performance applications. However, the low power factor challenge makes it unacceptable for direct-drive applications. A lack of accurate modeling method based on the motor sizing law, i.e., air-gap flux density, linear current density, and motor geometry parameters, raises difficulties for machine designers to further conduct research on the performance metrics. This article presents a deep investigation into the analytical modeling technique for surface PMVMs (SPMVMs). It can identify an accurate approach to obtain the performance metrics, including electromagnetic torque and power factor. The modeling technique is developed based on the conformal mapping method. By using this, both radial and tangential permeability functions can be calculated to obtain the motor magnetic loading accurately, considering the leakage flux. The slotting effect on both air-gap flux density and armature-winding function is analyzed to achieve a precise formula for torque and power factor computations. The new modeling technique is applied to integral-slot SPMVMs with different slot/pole combinations, gear ratios, slot openings, and magnet thickness to evaluate the impacts of motor parameters on high-power-factor and high-torque-density designs. Finally, an SPMVM with the characteristics of high torque density and power factor is fabricated to verify the analytical model at the power rating of 0.8 kW and the speed of 500 r/min. The experimental results show that the prototype exhibits a high power factor of 0.9 and high torque density 22.5 Nm/L.

New Modulation Technique in Smart Grid Interfaced Multilevel UPQC-PV Controlled via Fuzzy Logic Controller

Abstract: The use of sensitive electronic devices has increased recently; hence, power quality has become an important factor in electrical power systems. The various disturbances occurring in the electrical network (harmonics, voltage swells, sags, etc.) may lead to technical-economic damage that negatively impacts the quality of the supplied power. Therefore, the use of the Unified Power Quality Conditioner (UPQC) is a promising solution to limit such damage. In this paper, a nine-level structure of the proposed standardized power quality conditioner is analyzed. The conditioner is connected between a photovoltaic system (UPQC-PV) and a smart grid. Then, a new approach to generate switches for the switches of both the series and parallel converters is proposed. This modulation technique relies on an adaptive hysteresis band (AHB) that is determined via a fuzzy logic controller in order to obtain the required modified output voltage with minimum distortion. Simulation results, using MATLAB/Simulink, of different disturbance scenarios that may occur in the network are presented to verify the accuracy of the proposed fuzzy-logic-based AHB control system. Compared with the conventional SPWM, it is found that the proposed AHB modulation technique significantly improves the power quality in terms of producing less total harmonic distortion in both the voltage and current waveforms.

Design and performance analysis of three phase solar PV integrated UPQC

Abstract: A renewable energy resource associated with transmission line integrating Unified power quality conditioner (UPQC) accomplishes lossless power transmission. In this compensation, the series and shunt compensator are connected side by side. The solar integrated unified power quality conditioner (PV-UPQC) has gained the benefits of active power filtering and distributed generation. Avoidance of MPPT required for solar power generation to perform maximum power point tracking is replaced by shunt compensation; compensate reactive power and harmonics present at load current. The series compensation evolves voltage swell and sag problems in grid. The system is evaluated using MATLAB to synthesize combined operation, reactive power injection, voltage control, etc. A pulse amplitude controlled voltage source inverter present before transformer can perform active power filtering. A dc link capacitor supplies enough energy needed to the shunt active filter system to impart harmonics at output side. To resolves voltage control in bus by improving power factor. The source current controllability have been executed by DSTATCOM and dynamic voltage restorer (DVR).

A Mathematical Design Approach to Volumetric Optimization of EMI Filter and Modeling of CM Noise Sources in a Three-Phase PFC

Abstract: Designing an efficient, compact, and optimized electromagnetic interference (EMI) filter for the next generation high-frequency switched mode power converter while maintaining a small form factor with high power density, requires adequate research and development effort. This article presents a systematic as well as unified approach to design the EMI filter for any power electronic converter, particularly for three-phase ac–dc active boost rectifier systems. Since the differential mode (DM) filter stage consumes a major part of the EMI filter volume and weight, DM filter design optimization is a necessary yet challenging task to attain a higher power density. This article theoretically demonstrates the design steps for choosing the appropriate filter component values and number of filter stages to achieve the smallest volume of the DM EMI filter. Furthermore, to design an optimized common mode (CM) filter stage, a research effort has been made for estimation of the CM noise corner frequencies followed by multiconstraint volume optimization through a detailed mathematical noise modeling of the converter. While the validation of the proposed design methodology is done through MATLAB simulation, an experimental verification is also performed by designing the optimized EMI filter for a 2.3-kW proof of concept of a three-phase boost power factor correction converter to comply with the stringent EMI requirements of DO-160F standard.

Peak and Valley Current Control for Cuk PFC Converter to Reduce Capacitance

Abstract: Traditional power factor correction (PFC) converters usually employ a large electrolytic capacitor to ensure a stiff output voltage. However, the electrolytic capacitor is not expected in terms of the reliability and the size of the system. This article proposes a peak and valley current control for Cuk PFC converter to remove the bulky electrolytic capacitor. The proposed control is realized by a combination of analog and digital circuits. The analog circuits are used to accomplish the real-time comparison between the actual currents and their reference values. And the digital circuits are employed to deal with simple logical judgement. Different from the existing full digital control technique, which needs a high-quality digital signal processor (DSP) to process complex arithmetic operation, the proposed control concept even can only require a low performance microcontroller unit. Besides, the control delay is avoided. This article first analyzes the operation stages of the Cuk PFC converter. Then, design considerations of main circuit and control circuit are introduced. Finally, the experimental results from 200W Cuk PFC converter are presented to verify the effectiveness of the proposed control.

Buck–Boost Common Ground Bridgeless PFC (CGBPFC) Rectifies With Positive/Negative Output

Abstract: This article proposes new common ground bridgeless power factor correction rectifiers suitable for use in any application which requires a positive or negative dc power supply. The main advantage of the proposed rectifiers, compared to previous works, is the provision of the common ground between input and output, which eliminates electromagnetic interference (EMI) associated with high rates of change of voltage and consequently reduces the need for EMI common mode filtering. The converter also provides step-down and step-up operation, and facilitates positive or negative output voltages with a low number of semiconductor devices operating simultaneously. High power factor, acceptable grid-side current quality, and high efficiency are also achieved. Two variants are presented, referred to as type-I and type-II, which offer common ground positive and negative dc voltages, respectively. Closed-loop control of the converters is provided by a dead-beat current controller in the inner loop. Experimental results are presented for a 500-W prototype, operating from 220 and 110 Vrms input to $\pm$ 48 and $\pm$ 200 Vdc output. The experimental results demonstrate the capability for step-down and step-up ac-to-dc power conversion with a peak efficiency of 96.8% and 96.6% in the positive and the negative outputs, respectively.

Single-Receiver Multioutput Inductive Power Transfer System With Independent Regulation and Unity Power Factor

Abstract: Inductive power transfer (IPT) systems with multiple output voltages are potential to supply a variety of loads simultaneously. This article proposes an IPT system with multiple semiactive rectifier cells (SARCs) connected in series at the receiver (Rx) side. These SARCs are independent of each other and their output voltages can be regulated individually with single receiver coil, which reduces the cost and volume. The proposed IPT configuration has the advantages of high flexibility, simple control, and no cross regulation. Considering that the SARC may cause additional reactance and lead to detuning of the Rx side, variable inductor is introduced to ensure the full tuning condition. Thus, the proposed IPT system can maintain zero phase angle operation with unity power factor in the whole load range, minimizing the reactive power losses. In addition, both primary inverter and the SARCs can achieve zero voltage switching. To verify the feasibility and validity of the proposed IPT system, an experimental prototype with two outputs of 640 W/150 V and 400 W/120 V is built.

A novel starting method with reactive power compensation for induction motors

Abstract: This paper investigates several traditional startup methods for induction motors. Since a large starting current and a reactive power may lead to a deep voltage drop and cause a potential damage to induction motors and other devices in the same power grid, a novel starting method is proposed for induction motors based on the autotransformer and the magnetically controlled reactor (ATMCR). Then, a reactive power dynamical compensation strategy is developed to improve the power factor and overcome the voltage drop effectively. The main advantage of the proposed approach is that the starting current of induction motors is reduced in the starting period and compensate the reactive power simultaneously. In simulation, a parameter identification method is presented to deal with simulation parameters and the motor's nameplate parameters inconsistencies problem. Finally, simulation and experiment are provided to verify the effectiveness of the proposed approaches.

A Bidirectional Five-Level Buck PFC Rectifier With Wide Output Range for EV Charging Application

Abstract: AC-to-DC conversion is integral to the two-stage charging interface of electric vehicle (EV) batteries. For such chargers, the use of multilevel rectifiers (MLRs) reduces voltage ratings of power switches, while achieving a high-quality input voltage waveform. Balancing of capacitors in MLRs, however, is an important challenge. In this work, a power factor correction (PFC) five-level rectifier with self-balanced switched capacitors is proposed. Each leg of the presented topology comprises five power switches and one switched capacitor, where the voltage ratings of power switches are equal to the output dc voltage. It does not require an additional filter capacitor on the dc side, as the load appears in parallel always with a switched capacitor of one of the legs. The five-level operation with continuous conduction leads to the elimination of the capacitive filter on the ac-side and inductive filter on the dc-side. This article presents the operating principle, modulation strategy, closed-loop control, and design aspects of the proposed rectifier. The proposed topology is validated through experimental results and a comparison is made with other topologies. Following three features of the proposed topology make it suitable for EV battery charging applications—buck operation with a wide output regulation, the possibility of bidirectional flow of power needed for vehicle-to-grid systems, and easy realization of its three-phase version by simply adding one more leg. These features too have been demonstrated with experimental results.

Vibrating Coordinates Frame Transformation Based Unity Power Factor Control of a Three-Phase Converter at Grid Voltage Imbalance and Harmonics

Abstract: This article proposes a control system of a three-phase grid-connected power converter, operating in the rectifier mode, which achieves the unity power factor target, i.e., unbalanced and distorted current instead of sinusoidal one for grid voltage imbalance and harmonics. Such a target is known from active power filters control, but it has not been used for power supply devices yet. Thanks to that, the three-phase converter is seen as resistive load by the utility grid, and active power is consumed with minimal possible rms current, keeping current asymmetry corresponding to the voltage asymmetry during unbalanced dips. Intentional introduction of current harmonics is not trivial from the point of view of both reference signals calculation and control system structure, because in the classical approach, it would require resonant terms in controller structure. Additionally, grid voltage asymmetry introduces another oscillating component, which imposes other resonant terms in the controller. The transformation presented in this article allows to achieve desirable current harmonics and asymmetry with the use of two proportional-integral controllers, one in each controlled axis. This article presents theoretical principles of the new transformation, control system structure as well as simulation and experimental tests of a three-phase converter utilizing this idea.

Airgap Magnetic Field Harmonic Synergetic Optimization Approach for Power Factor Improvement of PM Vernier Machines

Abstract: Permanent magnet (PM) vernier machine has excellent prospects because of its high torque density, whereas its power factor is lower than conventional PM counterpart. At present, power factor of PM vernier machine is mainly analyzed and improved from the perspective of either PM magnetic field or armature magnetic field individually. Also, synergetic effect of both PM and armature fields is rarely considered, thus limiting the power factor improvement. In this article, a synergetic optimization approach considering both PM and armature airgap harmonics simultaneously is proposed to improve the power factor of PM vernier machine. First, the power factor is analyzed from the both PM and armature airgap harmonics. Second, the proposed optimization framework is interpreted and implemented. Meanwhile, a PM vernier machine with rotor flux barriers is selected as a design example to investigate the effectiveness of the proposed optimization approach. Finally, a prototype machine is manufactured and experimented to verify the effectiveness of the proposed optimization approach.

A Review of Series-Connected Partial Power Converters for DC–DC Applications

Abstract: This article presents a review of series-connected partial power converters (S-PPCs) for dc–dc applications, which allows carrying out the partial power processing (PPP), whose main goal is to achieve a reduction of the power processed by the converters. An analysis of the S-PPCs’ characteristics, topologies, and applications concerning the active and nonactive power processing is presented. The power processing factor (PPF) is then defined, which refers to the active power and depends exclusively on the voltage regulation range. The so-called Fryze power factor (PF) is used to evaluate the nonactive power processed, which depends on the topology voltage and current waveforms. Due to the lack of research around step-up/-down S-PPCs, this article presents the restrictions and requirements for the design of this type of S-PPCs. Finally, it is demonstrated that the turns ratio of magnetic devices can be optimized to reduce the nonactive power and improve the converter Fryze PF, ensuring PPP. In order to validate the analyses, two 2200-W prototypes were built and evaluated for a photovoltaic (PV) application example. Experimental results show that the reduction of both the active and nonactive power processed by the S-PPCs results in lower component ratings and higher efficiencies.

A More Efficient Single-Phase AC/DC Converter With Automatic PFC and Power Decoupling Capability

Abstract: Reducing power transmission path is a new trend to increase the whole efficiency. Moreover, the electrolytic capacitors (E-caps) are another essential criterion for judging the performance of converters. Based on this, a novel single-stage ac/dc converter is proposed in this article, which demands fewer power semiconductors compared to previous works due to the time-sharing power devices; thus lower cost and higher power density are achieved. The power flow of the decoupling circuit is further optimized, where most of the energy is designed to transfer directly to the load, reducing the intermediate link and only absorbing pulsating power with the film capacitor, thus higher efficiency is guaranteed. Additionally, a simple control scheme is presented, where near perfect power factor (PF) is obtained. Finally, all the superior performances of the proposed light-emitting diode (LED) driver are verified by an experimental prototype with a rated output power of 100 W.

Fault Tolerant Backstepping Control for Double-Stage Grid-Connected Photovoltaic Systems Using Cascaded H-Bridge Multilevel Inverters

Abstract: This letter introduces a complete DC-AC conversion system fed by photovoltaic (PV) energy. The system consists of N PV panels, N DC-DC boost converters, N cascaded H-bridge inverters, a DC-link composed of N capacitors and an LCL filter. This work aims at reaching threefold control objectives: i) Extracting the available maximum power by regulating the voltages across the PV panels, ii) Ensuring a unitary power factor, iii) Regulating the DC-link voltage to a desired reference. To achieve the mentioned objectives, a multi-loop regulator is designed. The PV panels are individually controlled to track the maximum power point in order to efficiently operate at either the same or different varying climatic conditions without failures. In addition to the maximum power point tracking (MPPT) controller, two cascaded loops guaranteeing a satisfactory power factor and DC-link voltage regulation are developed. The nonlinear backstepping approach combined with Lyapunov theory are used based on the averaged model for the synthesis of the multi-loop controller. The performance of the studied system is tested via MATLAB / SimPowerSystems environment. The obtained simulation results prove that the proposed controller meets its objectives and demonstrate the efficiency of the chosen control strategy under faulty conditions.

Adaptive Power Control Strategy for Smart Droop-Based Grid-Connected Inverters

Abstract: Grid-connected inverters play an important role in the integration of renewable energy sources such as solar and wind. However, due to the unneglectable grid impedance value seen by the inverters at the point of common coupling (PCC), especially in the weaks and resistive low voltage distribution networks, there is an inherent strong coupling between active and reactive power flow. This power coupling causes significant power quality problems including 1) voltage fluctuation of the common AC bus resulted from high penetration of intermittent renewable generation systems, 2) non-optimal control of neither power flow nor power factor of the delivered power by inverters to the common AC bus, and 3) unintended/uncompensated transmission losses, where the flow of active power through the transmission/distribution lines will cause unintended reverse reactive power flow from the grid-side and vice versa with the reactive power flow. To solve these issues, this paper proposes an adaptive mechanism for droop-based grid-connected inverters to decouple the power flow by compensating the associated unintended active and reactive power losses flowing through the transmission line (or any desired segment of it). This control strategy relies on modifying the power command provided to the frequency and voltage droop loops by considering the effects of both the transmission line resistance and inductance components on the power flow between the inverter and the grid. It uses only the local current and voltage measurements to first perform an online estimation of the transmission line resistance and inductance and then to calculate the proposed adaptive power terms. The performance of the proposed control is validated in MATLAB/Simulink and HIL experiment for a 350 kW droop-based grid-connected inverter system. The proposed control strategy can be utilized to provide ancillary services to the grid such as accurate frequency and voltage support at the location of interest.