Unity Power Factor Research Articles

A New Hybrid Modular Multilevel Rectifier as MVac–LVdc Active Front-End Converter for Fast Charging Stations and Data Centers

As the power demands from DC energy-storage and loads continue to grow in electric vehicle (EV) fast charging stations and data centers, the power delivery infrastructure faces challenges with the installation of bulky, heavy, and slow responsive line-frequency power transformer (LFT). These transformers are required to step-down the feeder voltage from medium-voltage (MV) ac grid-service to low-voltage (LV) ac, followed by LVac-LVdc rectifiers. This approach results in a large equipment footprint, heavy conductor copper usage, and lower efficiency. Consequently, there is increasing interest in exploring direct interface from MVac to LVdc without the need for LFT. This paper proposed a new solution called MVac-LVdc hybrid modular multilevel rectifier (HMMR). The HMMR serves as a centralized step-down active front-end converter, enabling power delivery to LVdc with a reduced number of dc/dc back-end isolated converters. Compared to the modular multilevel converter (MMC) used as the MVac interface solution, the proposed HMMR could save the submodule number by 40%, reduce losses by 22%, and significantly reduce the footprint area by 37%, effectively increasing the power density and reducing the construction cost. Moreover, the proposed HMMR has the potential to operate in both unity and non-unity power factor modes, allowing it to provide the grid-support functionality. The performance of HMMR is evaluated and compared with full-bridge MMC in the case of 13.8 kV ac to 6 kV dc. The feasibility of the proposed converter is verified by the simulation results with the same specifications. Finally, a scale-down 1.4 kV HMMR prototype is developed to validate the effectiveness of the proposed converter.

A General Purpose Transformerless Charging System Based on Fully Bridgeless Canonical Switching Cell High-Quality Rectifier for LVEVs

A general purpose transformerless charging system (CS) targeted for various class of low voltage electric vehicles (LVEVs) (24 V–72 V), is designed, analyzed, and implemented in this work. The presented CS employs a fully bridgeless canonical switching cell (FBLCSC) improved power quality rectifier (IPQR) at its front end stage, and a high gain buck (HGB) DC-DC converter at its back end stage. At front end, the presented FBLCSC IPQR does not employ diode bridge rectifier (DBR) circuit, and therefore, ensures better conversion efficiency while operating over wide range of AC mains conditions (110 V–265 V). Further, compared to conventional buck-boost derived IPQRs, the presented IPQR employs minimum component count and maintains low current ripples at its AC and DC ends. On one side, the minimum component count shrinks down the cost, size and losses of the complete CS; low current ripples characteristic on the other side lowers the size of AC and DC end filtering elements. Notably, the FBLCSC IPQR exhibits auto unity power factor operation during discontinuous current mode (DCM) design, and thus, facilitates simple and low cost control architecture. Apart from control simplicity, the DCM operation of FBLCSC IPQR leads to negligible switch turn-on and diode reverse recovery losses. Likewise, at the back end stage, the HGB converter realizes a transformerless DC-DC stage to ensure ripple free charging of different classes of LVEVs. Even if, the HGB DC-DC stage accomplishes transformerless steeper step down gain, its simple design and effective operation over wide battery voltages (24 V–72 V), are further ensured through flexible DC link voltage (150 V – 350 V) control of front end FBLCSC IPQR. At last, the design, operation, and performance of the presented CS are validated experimentally, and relevant results are discussed comprehensively in support of the performance validation of the presented CS.

Bridgeless Modified High-Step-Up Gain SEPIC PFC Converter Based Charger for Light EVs Battery

This study presents a two-stage on-board charger for light electric vehicles (LEVs) with low voltage battery (24-72V). The front-end of the charger has characteristics of high voltage conversion ratio and unity power factor operation achieved by a bridgeless high gain modified SEPIC converter. The high voltage conversion ratio enables the front-end to operate over a wide range of input voltages. At the back-end of the charger, an isolated positive output Luo DC-DC converter is employed to regulate the charging profile of the LEV battery under constant current (CC) and constant voltage (CV) charging modes. The presented charger operates in discontinuous conduction mode (DCM), which has dual advantages of having inherent feature of power factor correction (PFC) at the supply end along with significantly reducing the complexity of control mechanism, thereby reducing the cost and effort of control implementation. The operational analysis and design of the presented charger in DCM are covered in detail in this study and the same are further validated by means of simulations. A 650 W test bench setup is developed to authenticate the theoretical performance by means of experimental results. The experimental performance of the front-end is finally compared with other PFC topologies to highlight the merits and demerits of the presented charger.

Revamped System Performance of Grid-Interactive Hybrid DFIG-PV System Using WSO Based Dual Layer MRFKMP Adaptive Control

Due to the stochastic characteristicsof wind, keeping high-quality power into the grid-dependent hybrid wind energy systems is important for effective energy utilization, especially when there are non-linear loads involved. In this paper, a dual layer random features kernel mean p-power (MRFKMP) adaptive control for the grid interfaced converter of a DFIG-PV based hybrid energy system is implemented for the purpose of maintaining power balances and quality power at both the source and grid ends while operating at unity power factor. The introduced control extracts the weight of stator and load current components with finer convergence and lower computational complexity, excluding complex reference transformations. The dual layer adaptive control improves grid side converter functionality by improving power quality, interruption of loads, taking into account reactive power and harmonic remediation under steady-state and dynamic scenarios.In the secondary step, to achieve optimal DFIG-PV control response, the stability of the DC-link, which is themain coupling element for power transfer between DFIG, solar PV, and battery energy storage (BES), is reinforced by tuning the DC link voltage controller with the white shark optimization (WSO) algorithm. Under the worst-case scenario of large step wind change, the primacy of the envisaged WSO algorithm for tuning DC-link PI controller has been evidenced. It is discovered that WSO tuning positively affects the settling time and oscillatory response of the DC-link voltage not just at the outset, but also throughout the subjugated dynamic wind speedchange.Power flow to the grid is stable due to optimized DC-link voltage performance. WSO parameter tuning improved efficiency is validated using MATLAB simulation results and compared to GA and PSO techniques in this study.

Assessment of Energy Conversion in Passive Components of Single-Phase Photovoltaic Systems Interconnected to the Grid

This paper presents a mathematical analysis of how energy return in grid-connected single-phase photovoltaic systems affects the sizing of passive components. Energy return affects the size of the link capacitor, making it larger than reported in the literature. One of the main points of this article is that an inverter connected to the grid using a DC–DC converter with an appropriate link capacitor is analyzed. The energy return is caused by the value (in Henry units) of the L-filter, which is also analyzed in this paper. The analysis shows that there is a link between the value of the L-filter and the voltage of the DC bus. The analysis assumes two conditions: (1) the DC bus voltage is always higher than the peak value of the grid sinusoidal voltage, and (2) there is a unity power factor at the connection point between the grid and the L-filter. To operate in an open loop, a compensation phase angle is calculated and introduced in the single-phase inverter modulation; this phase angle compensates the phase shift caused by the L-filter, avoiding the use of a phase-locked-loop (PLL) control system. The L-filter ripple current is evaluated by Fourier analysis, and the DC bus ripple voltage is evaluated by considering the energy returned to the link capacitor. The results of the analyses are compared with existing methods reported in the literature. The results also show that, to minimize the value of the L-filter, the DC voltage must be almost equal to the maximum voltage of the grid. Equations to assess the value of the DC-link capacitor and the L-filter in function of their ripples are developed. The results were verified with simulations in Simulink and experimentally.

Balanced Dual-Side LCC Compensation in IPT Systems Implementing Unity Power Factor for Wide Load Range and Misalignment Tolerance

Misalignment tolerance and wide load range capability are necessary for a practical inductive power transfer (IPT) system. In pursuit of high-performance, input unity power factor and high efficiency are expected. In this paper, a balanced design method of dual-side LCC compensation is proposed to achieve input unity power factor over wide misalignment and load ranges. With the proposed method, dual-side LCC compensation is in a balanced state where zero phase angle frequencies coincide with designed voltage gain frequencies under coupling and load variations. Unity power factor can be implemented while maintaining voltage gain with frequency control. Possible output power versus frequency characteristics of this balanced dual-side LCC compensation are categorized and fully analyzed. One of them, with strong power regulation capability and high misalignment adaptability, is selected as the design target. Coil currents are optimized using a surplus degree of design freedom while selecting parameters. Unity power factor and coil current optimization ensure low losses in devices and coils, which benefits system efficiency. Thus, a wide load range, high misalignment tolerance, nearly zero reactive power, and high efficiency can be simultaneously implemented. The proposed method is verified on a 2.1kW prototype. The coil size of both primary and secondary sides is 600mm <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">×</i> 600mm, and the air gap is 150mm. Load power varies from 10% to 100% within the coupling range from 0.15 to 0.35. Nearly unity power factor is realized under various working conditions. The maximum dc-dc efficiency reaches 96.4%.

A Novel High-Frequency Inverter With ZVT in a Wide Range of Duty Cycles and PFs

This paper presents a wide-range zero-voltage-transition (ZVT) high-frequency single-phase inverter. The proposed inverter consists of a full-bridge inverter and two auxiliary switches that are magnetically coupled to the output filter inductor via an additional winding. The auxiliary circuit provides zero-voltage switching (ZVS) for the full-bridge converter switches, while the auxiliary switches are turned on and off with zero current switching (ZCS). A combination of unipolar and bipolar modulation is used as the modulation technique to ensure soft-switching over a wide range of duty cycles and power factors. The proposed auxiliary circuit has a simple structure and does not require floating gate drives for the auxiliary switches. A 1.5 kW-400 kHz prototype has been developed to verify the theoretical analysis, demonstrating a significant increase in efficiency for both unity and non-unity power factors.

Flexible Power Control for Extending Operating Range of PV–Battery Hybrid Cascaded H-Bridge Converters Under Unbalanced Power Conditions

Due to the nonuniform solar irradiance, different temperature and inconsistent module features, the output power among each photovoltaic (PV) module in a single-phase cascaded H-bridge (CHB) inverter is unequal. The H-bridge module with higher power generation faces the risk of overmodulation. To further extending the operating range of the CHB PV inverter under unity power factor condition, a battery module is connected with the system in series to form a PV-battery hybrid CHB converter in this paper. Meanwhile, the corresponding flexible power control strategy is proposed. The injected power of the battery module is controlled adaptively according to the maximum modulation index (MI) of all PV modules. With the proposed approach, all PV modules are free from overmodulation even with severe power imbalance and thus more energy are harvested. The effectiveness of the proposed control method is verified by experimental results.

O Splines-Based Fixed-Frequency Integral Sliding-Mode Controller for PFC Rectifier

This paper proposes a fast-response sliding mode controller (SMC) for a semi-bridgeless boost converter under large and quick load fluctuations to ensure tight output voltage regulation and unity power factor correction (PFC) at the line side. In this sense, a novel approach for estimating the reference current profile is presented focusing on the real-time phasor estimation via the O-splines of the discrete-time Taylor-Fourier transform (DTTFT). This method allows for improving the computational efficiency and dynamic performance of the estimations of amplitude, frequency and phase of the network voltage used for the generation of the reference current profile. Several aspects of the controller design are discussed, including the choice of the sliding surface, the existence and stability conditions, and the implementation of an adaptive hysteresis band to fix the switching frequency and reduce zero-crossing distortion. Experimental results of a GaN-based prototype validate the theoretical predictions, exhibiting a PF close to 1 and a total harmonic distortion lower than 3.2% in presence of load changes of up to 50% and changes in the output voltage set point. Several comprehensive experimental comparisons between the proposed framework and the most widely used methods recently reported in the literature are accomplished in terms of transitory and steady-state responses. The robustness of the proposed control approach is experimentally demonstrated under sag conditions and a wide operating range of the input voltage.

Fractional fuzzy PI controller using particle swarm optimization to improve power factor by boost converter

The power circuit of AC voltage controller capable of operating at a leading, lagging, and unity power factor is studied by a lot of researchers in the literature. Circuits working with high switching frequency are known as power factor correctors (PFCs). The single-phase boost converter has become the most popular topology for power factor correction (PFC) in general purpose power supplies. Power factor correction circuit provides conventional benefits to electric power systems. The benefits are the reduction of power factor penalty and utility bill and power loss. Therefore, a boost converter power factor correction scheme is presented in this paper. A PI, fuzzy logic PI and fractional order PI (FOPI) controllers are used to fix an active shaping of input current of the circuit and to improve the power factor. The controller parameters (coefficients) are optimized using the Particle Swarm Optimization (PSO) algorithm. Average current mode control (ACMC) method is used in the circuit. The converter circuit consists of a single-phase bridge rectifier, boost converter, transformer and load. A mathematical model of the plant is required to design the PI controller. A model for power factor correction circuit is formed in MATLAB/Simulink toolbox and a filter is designed to reduce THD value. The proposed model is simulated using a combination of PI, fuzzy logic and FOPI controllers. The control scheme is applied to 600 Watt PFC boost converter to get 400 Volt DC output voltage and 0.99 power factor. The input voltage is 230 VRMS with 50 Hz. The combination of FOPI and PI controller has the best solution to control the power factor according to PI and fuzzy controllers.

Efficient Day-Ahead Scheduling of PV-STATCOMs in Medium-Voltage Distribution Networks Using a Second-Order Cone Relaxation

This paper utilizes convex optimization to implement a day-ahead scheduling strategy for operating a photovoltaic distribution static compensator (PV-STATCOM) in medium-voltage distribution networks. The nonlinear non-convex programming model of the day-ahead scheduling strategy is transformed into a convex optimization model using the second-order cone programming approach in the complex domain. The main goal of efficiently operating PV-STATCOMs in distribution networks is to dynamically compensate for the active and reactive power generated by renewable energy resources such as photovoltaic plants. This is achieved by controlling power electronic converters, usually voltage source converters, to manage reactive power with lagging or leading power factors. Numerical simulations were conducted to analyze the effects of different power factors on the IEEE 33- and 69-bus systems. The simulations considered operations with a unity power factor (active power injection only), a zero power factor (reactive power injection only), and a variable power factor (active and reactive power injections). The results demonstrated the benefits of dynamic, active and reactive power compensation in reducing grid power losses, voltage profile deviations, and energy purchasing costs at the substation terminals. These simulations were conducted using the CVX tool and the Gurobi solver in the MATLAB programming environment.

Grid-Connected Solar PV Fed BLDC Motor Drive for Water Pumping System

This article proposes a unidirectional power flow of a grid-connected brushless DC motor powered water pumping system fed by a photovoltaic array using a bridgeless power factor corrected (PFC) boost converter. The system consists of a bridgeless PFC converter, a boost converter, and a voltage source inverter to drive a brushless DC motor coupled with a pump. As a backup source, the grid is used. This system allows the water pump to run at maximum capacity regardless of the weather conditions. The grid will provide power if the photovoltaic array is unable to fulfil the required power demand. The unidirectional power flow through a conventional power factor corrected (PFC) boost converter causes conduction loss in the input bridge rectifier, thereby hurting efficiency, power factor, and THD. This paper presents a bridgeless PFC boost converter topology to reduce the conduction losses, thereby increasing the efficiency and obtaining a nearly unity power factor as well as lower total harmonic distortion (THD) of input current. The system is simulated using MATLAB /Simulink. The proposed system’s real-time validation is realized through the OPAL-RT simulator OP5700. The THD results obtained are well within the specified standard of IEC 61000-3-2 and IEEE 519-1992.

Design and Implementation of Single-Phase Boost PFC Converter

In this paper, a single-phase boost type ac-dc converter with power factor correction (PFC) technique is designed and implemented. A current mode control at a constant switching frequency is used as a control strategy for PFC converter. The PFC converter is a single-stage singleswitch boost converter that uses a current shaping technique to reshape the non-sinusoidal input current drawn by the bulky capacitor in the conventional rectifier. This technique should provide an input current with almost free-harmonics, comply with the IEC61000-3-2 limits, and a system operates with near unity power factor. The other function of the boost converter that should beaccomplished is to provide a regulated DC output voltage. The complete designed system is simulated in MATLAB/SIMULINK and a hardware prototype has been built using analog devices. Simulation results and experimental results are presented to validate the proposed system.

A novel solar photovoltaic powered grid interactive battery charging system for electric vehicle applications

ABSTRACT In this work, a novel Solar Photo Voltaic (SPV) powered grid interactive Electric Vehicle (EV) battery charging system has been proposed and validated. The objective of the proposed system is to provide seamless battery charging facility that includes a high capacity station battery system. The grid interactions like integration of SPV energy, station battery charging and reactive power support are included through the DC link of aShunt Active Power Filter (SAPF). The SAPF maintains unity power factor on the source side grid current. The objectives of the proposed system are ensuring the source side power factor nearly unity with minimal THD of source current, an SPV grid integration system with Maximum Power Point Tracking (MPPT), a comfortable charging point for EVs with a reliable charging station supported by a back up station battery. The novelty of the proposed work is that the common DC bus bar maintains a high DC link voltage when the utility source is available and the SAPF is active. The regulation of the DC link voltage is achieved by a PI controller tuned by the Gravitational Search Algorithm. The proposed system has been validated using simulations in the MATLAB SIMULINK environment as well using an experimental prototype. The proposed GSA controller outperforms in terms of THD (%) of source and load currents are 2.4 and 17.87, respectively.

Enhancing Single-Phase Grid Integration Capability of PMSG-Based Wind Turbines to Support Grid Operation under Adverse Conditions

The proposed work delivers a robust control solution for a single-phase permanent magnet synchronous generator-based wind power conversion system (PMSG-WPCS) to enhance grid integration capability. The proposed control approach also offers an extended facility to fulfill low-voltage fault ride-through (LVRT) requirements under adverse grid conditions. Unlike the conventional observer-based PLL (O-PLL) approach, the proposed improved Lyapunov theory-based prefilter (ILP) is helpful in yielding a quadrature signal to solve the single-phase grid synchronization problem. Moreover, the proposed prefilter can leverage delayed signal operation, which improves the harmonic and the DC-offset component rejection abilities while eliminating the need for internal feedback-based submodule blocks for the case of an O-PLL. Consequently, the proposed ILP-PLL exhibits better dynamic behavior to rapidly synchronize a grid-tied power converter and can accurately track the fundamental amplitude information that is required for inverter control to meet the fault ride-through requirements. In addition, the suggested LVRT controller ensures smooth transition between the unity and non-unity power factor modes for superior converter control over reactive current injection into the grid to recover the grid from faults while maintaining a lower amount of total harmonic current distortions. The dynamic performance of the proposed control scheme is experimentally validated in view of the existing O-PLL approach for lower-rating wind-turbine-based PMSG-WPCS.

Backstepping Based Grey Wolf and DPC for Power Quality Improvement and Active Power Injection in PV Grid-connected System Based on Interleaved Boost Converter

This research offers the backstepping based grey wolf control design for a multifunctional PV grid-connected system (MPGC) based on four phases interleaved boost converter. This work proposes a solution to the issues of harmonic mitigation, reactive power compensation, and PV-generated power injection into the grid-based MPGC. The interleaved boost converter (IBC), controlled using maximum power point tracking (MPPT), is utilized to harvest the photovoltaic (PV) system's peak power and overcome the conventional topology's drawbacks. Direct power control (DPC) based on space-vector pulse width modulation (SVPWM) is used to control the instantaneous power of the MPGC, and the backstepping control (BSC) is applied to the whole system to maintain the robustness and stability of the suggested method. The Grey Wolf Optimizer (GWO) optimized the system's dynamic response by adjusting the BSC parameters. The results were obtained using MATLAB/Simulink software. The suggested work shows excellent performance based on the obtained results, achieving the sinusoidal waveform of the currents and a unity power factor. Total harmonic distortion (THD) has been decreased below 5% in accordance with IEEE 519-2014 standard.

Synthesis and Analysis of Primary High-Order Compensation Topologies for Wireless Charging System Applying Sub-Harmonic Control

Sub-harmonic control (SHC) is an excellent method for wireless charging system because it is easy to achieve full-load range soft switching and unity power factor. However, in existing works, SHC is only applied to the system with primary series compensation topology (PSCT), which has the drawbacks of low degrees of design freedom, high sensitivity to misalignments and no open-circuit protection. To overcome these issues, in this paper, systematic synthesis of primary high-order compensation topology (PHCT) for WPT is identified in terms of general T-branch structure. Afterwards, the applicability of PHCT to SHC is explored by gaining insight into their filter characteristics. It reveals that when SHC is applied, four kinds of PHCTs are superior over other candidates in performance because the unity power factor and soft switching can be achieved without limitation on pulse distribution. Then, six kinds of PHCTs exhibit a moderate performance as they may nullify the strengths of SHC under some specific pulse distributions. The rest of PHCTs are not applicable to SHC no matter what the pulse distribution. Finally, the experimental results on prototype with jointly applying SHC and PHCT are examined.

Novel bidirectional universal 1‐phase/3‐phase‐input unity power factor differential AC/DC converter

AbstractA common 400 V dc bus for industrial motor drives advantageously allows the use of high‐performance 600 V power semiconductor technology in the inverter drive converter stages and to lower the rated power of the supplying rectifier system. Ideally, this supplying rectifier system features unity power factor operation, bidirectional power flow and nominal power operation in the three‐phase and the single‐phase grid. This paper introduces a novel bidirectional universal single‐/three‐phase‐input unity power factor differential ac‐dc converter suitable for the above mentioned requirements. The basic operating principle and conduction states of the proposed topology are derived and discussed in detail. Then, the main power component voltage and current stresses are determined and simulation results in PLECS are provided. The concept is verified by means of experimental measurements conducted in both three‐phase and single‐phase operation with a 6 kW prototype system employing a switching frequency of 100 kHz and 1200 V SiC power semiconductors.

An Enhanced Hybrid Grid Connected Photovoltaic System Using Voltage Oriented Controller and Class D Chopper

The performance of a shunt interconnection made from a PV system, a three phase grid voltage supply, and a DC shunt motor (DC load) is investigated The PV system participates with maximum powers to the overall interconnection active power flow. It uses a class D chopper circuitry controlled properly by a typical maximum power point tracker (MPPT) controller. The grid has the role of supplying active power in case of any power deficiency needed by the DC motor load. Similarly, it has also the role of absorbing active power in case of any additional power generated by the PV system and not needed by the DC load. This is done by using an AC/DC power electronic converter. The AC/DC power electronic converter operates either under rectifier or inverter modes. The AC/DC power electronic converter is also operated under the next two conditions: 1-the reactive power expected at the grid voltage bus should be nearly null, 2-harmonics currents often encountered in the grid line currents waveforms should be tolerable. The two latter conditions are fulfilled by using the principle of voltage oriented control (VOC) technique. The performance of the investigated interconnection is simulated in Matlab/Simulink platform. Quite satisfactory results are obtained. The satisfaction about the obtained simulation results persists on being able to integrate easily the PV system with the AC grid while extracting maximum power from the PVG and having a unity power factor at the AC grid bus and less encountered harmonics in the ac line currents.

Power Quality Improvement in Fifteen Level PUC Converter for Solar PV Grid-Tied Applications

A fifteen-level packed U cell (FLPUC) converter with eight active switch counts for the grid-connected solar photovoltaic (GCSPV) application is introduced in this work. This converter has eight active switches with a PV source and two floating capacitors. This topology takes an edge over conventional configurations in terms of components required to achieve fifteen levels in converter output voltage. The mode of operation and switching states of the fifteen-level PUC converter are presented in detail. The active and reactive powers (PQ) control is incorporated for a grid-connected PV configuration, which in turn helps in an independent control over power injection into the grid. The maximum power operation is achieved for the first source connected to the PV array with the perturb and observe (P&O) MPPT technique and unity power factor is attained at the AC side. The voltages of floating capacitors are balanced at reference values using proportional-integral (PI) controllers to attain proper achievement of desired output voltage levels. Performance of the FLPUC based single-phase grid-tied system is analyzed under a constant and variable solar environment. This topology is modeled in MATLAB/Simulink, and test results are validated using real-time emulator to meet the IEEE-519 standard for power quality improvement.