Conventional LCL Research Articles

Design of passive filter based on magnetic integrated technology for single‐phase grid‐connected inverter

AbstractIn response to the need for smaller and lighter power supply equipment, there has been a push towards higher power density in current power electronic converters. This development aligns well with the requirements of photovoltaic grid‐connected inverters. Among various passive filters utilized in these inverters, the LCL filter stands out as a popular choice. Nevertheless, it should be noted that traditional LCL filters have limited core utilization and exhibit significant redundancy. In view of the above problems, this paper proposes a magnetic integrated passive filter based on ripple transfer technology and carries out volume optimization design. Compared to the conventional LCL filter, the magnetic integrated passive filter offers a reduction in size and weight while preserving its capability to ripples attenuate. Finally, a laboratory prototype with a rated power of 2 kW is built to verify the effectiveness of the proposed magnetic integrated passive filter.

Modular Coupler With Integrated Planar Transformer for Wireless EV Charging

A dynamic inductive power transfer (IPT) system is a safe and convenient solution for providing power to electric vehicles (EVs) while they are driving along a roadway. This technology can help reduce the size and cost of the bulky EV batteries without limiting the EV's travelling range. In recent years, practical aspects of dynamic IPT systems have been investigated to advance various IPT technologies from laboratories into roadways. This paper suggest an IPT roadway layout, focusing on a modular IPT system configuration with an integrated semi-loosely coupled planar transformer inside the in-road coupler to mitigate the installation and maintenance concerns of IPT roadways. The proposed configuration keeps the current in the couplers constant and load-independent while providing galvanic isolation between the coupler and the converter, and can be used as a replacement for the conventional LCL and transformer configuration. In order to reduce the number of components used in each module, each in-road coupler is connected to a common H-bridge through a single DC switch to enable individual couplers to be energized independently. Mathematical analysis and simulation results are provided, and validated using a scaled 7.7 kW prototype IPT system employing the proposed configuration.

A New Resonator Design for Wireless Battery Charging Systems of Electric Bicycles

This article presents a new resonator design scheme for wireless battery charging systems of electric bicycles (EBs). The newly designed method is established based on a switched series (S)-series parallel (SP)/S compensation scheme and Helmholtz coils for the transmitting coils. The Helmholtz coils are adopted to ensure that the mutual inductance between the transmitting and receiving coils is invariant. For this reason, the switched S-SP/S compensation scheme can be used to implement load-independent constant current (CC) and constant voltage (CV) charging for the battery loads instead of using the conventional LCL or LCC compensation schemes. The advancements of the proposed design, as compared to the conventional methods for wireless EB charging, are more than constant mutual coupling and elimination of compensated inductors. The communication channel between the transmitter and receiver, additional user-end converter, and complicated control algorithms can also be annihilated. Simulation results using Maxwell verify that the mutual inductance of the proposed resonator is constant. Experimental results validate that the output current and voltage can be well-regulated to track the references at 1.2 A and 24 V, respectively, at different load conditions. Especially, the maximum efficiency can reach 97.17% in the CC charging mode, whereas 91.17% in the CV charging stage. The maximum output power is 115 W on the load side. This design can be generalizable to other power levels to meet different charging demands.

A Current-Fed LCL Resonant Converter for Wide Output-Voltage Applications

This article proposed a novel current-fed LCL resonant converter with a simple structure by multiplexing inductors and switches for wide output voltage applications. With three different pulsewidth modulation methods, the proposed converter can work at three voltage gain modes, namely high gain (HG), medium gain (MG), and low gain (LG). In HG mode, it has a higher voltage gain than the conventional LCL converter by an extra boost energy storage stage. In MG mode, it operates similarly as a conventional LCL converter. In LG mode, it is equivalent to a flyback converter in discontinuous conduction mode (DCM), which achieves higher efficiency and is easier to be controlled than an LCL converter. In these three modes, all power switches and rectifier diodes can obtain soft-switching performance, increasing the power conversion efficiency. The operating principle, design methodology, and control scheme are explained and verified by a laboratory prototype with 520 W output power, 30–150 V output voltage.

Boost‐integrated LCL resonant converter with high voltage gain

A boost-integrated LCL resonant DC–DC converter is proposed, which is constituted by a full-bridge inverter module, the main transformer and a flyback transformer, resonant unit, and a rectifier module. The primary winding of the flyback transformer is also used as a resonant inductor and a boost inductor to improve the power density and the voltage gain. In order to meet different output environments, the converter can operate in low voltage-gain mode or high voltage gain mode. In low voltage-gain mode, the converter operates in PWM with LCL resonance. In high voltage-gain mode, the converter operates in PWM with boost and LCL resonance, in which boost modulation plays a role before the LCL resonance to increase the output voltage. Compared with the conventional LCL resonant converter, the new converter has higher voltage gain and is more suitable for a wide output range with the same resonant parameters. The operation principles of the proposed converter are clarified. A prototype with 80–140 V output and maximum output current 2.9 A is built, and experimental data shows that the maximum efficiency of the prototype can be 94.5%, verifying the correctness of the theoretical analysis.

LCL Filter Design and Implementation for Improving Transient Position Tracking Control Performance of Voice Coil Motor

Voice coil motor (VCM) is widely used in high precision position servo control for its merits of high linearity and no cogging-torque. There are two conventional driving modes: PWM chopper drive and analog drive. PWM chopper drive usually results in current ripples, which could affect position control precision. Acceptable current ripple limits the increase in the DC bus voltage and could not achieve faster response. On the other hand, analog drive uses power amplifiers, which does not suffer from current ripple but can result in high power loss. Such power loss could also affect precision or result in cooling difficulty, especially for thermal-sensitive applications such as semi-conductor lithography. In this paper, a VCM chopping drive with an LCL filter together with filter design method is proposed. Unlike conventional LCL filter design for grid inverter that only focuses on steady state current quality, the proposed LCL filter design in this paper aims at transient position control, which considers the current ripple, transient position tracking time and additional volume. With the designed filter, position tracking time can be shortened with acceptable current ripple. To compensate the delay caused by LCL filter, the DC drive voltage is increased. And under the same current ripple level, with LCL filter and higher DC voltage can get faster position response speed than without LCL filter and lower voltage. The results are validated by simulation and experimental results.

Integrated Common and Differential Mode Filter With Capacitor-Voltage Feedforward Active Damping for Single-Phase Transformerless PV Inverters

Recently, several publications have discussed the design of LCL filters and current controllers for grid-connected converters. However, the focus was the LCL filter used as a differential mode (DM) filter. Besides its conventional application as DM filter, a modified LCL filter configuration can be used as an integrated common mode (CM) and DM filter, which is particularly interesting for transformerless photovoltaic (PV) inverters, whereby the CM leakage current must be limited to comply with standards. This article proposes the joint design procedure for an integrated CM and DM filter plus the current controller used in single-phase grid-connected transformerless PV inverters. The increased number of components and resonance frequencies, compared to the conventional LCL filter, requires a careful analysis of the location of resonance and anti-resonance frequencies, taking into account parameters variation. The design procedure considers the extended region of stability for the DM resonance frequency allocation provided by the filter capacitor-voltage feedforward active damping with converter-side current feedback. It also considers continuous and discontinuous unipolar pulsewidth modulation. Design examples and simulation results for 1.5 and 10 kVA are presented. The effectiveness of the proposed design procedure is verified by experimental results obtained from a 1.5 kVA inverter.

A Misalignment-Tolerant Series-Hybrid Wireless EV Charging System With Integrated Magnetics

Electric vehicles (EVs) are becoming increasingly popular as a mean of mitigating issues associated with fossil fuel consumption in transportation systems. A wireless inductive power transfer (IPT) interface between EV and the utility grid has several key advantages, such as safety, convenience, and isolation. However, physical misalignments between the pads of IPT charging systems used in EVs are unavoidable and cause variations in key system parameters, significantly increasing losses and affecting power throughput. This paper presents a novel series-hybrid topology in which the series inductors of the primary and pick-up inductor–capacitor–inductor ( LCL ) networks are integrated into polarized magnetic couplers to improve the system performance under pad misalignment. A mathematical model is developed to investigate the behavior of the proposed system under misalignment. To demonstrate the viability of the proposed method, the results of a 3.3-kW prototype series-hybrid IPT system are presented, benchmarked against a conventional IPT system. Experimental results clearly indicate that the proposed system maintains the output power within ±5% of its rated power despite the pad misalignment. The proposed system is efficient, reliable, and cost effective in comparison to conventional LCL- and CL -compensated IPT systems.

Robust Design of LCL Filters for Single-Current-Loop-Controlled Grid-Connected Power Converters With Unit PCC Voltage Feedforward

The point of common coupling (PCC) voltage feedforward control is widely employed for LCL-type grid-connected converters to prevent large inrush current during startup, reduce steady-state tracking error, and suppress disturbances of grid voltage. Generally, this feedforward loop is ignored in the system modeling and stability analysis for simplicity. However, the grid impedance would be introduced to the control system through the feedforward loop under practical power grids, leading to a different current loop model from the original one, then conventional LCL filter design for single-current-loop control may be inappropriate. In this paper, the detailed modeling of current control loop with unit PCC voltage feedforward is presented. Based on the established model, it is found that unstable open-loop poles may appear under grid impedance variation, which thus may cause system instability. Therefore, the robust design regions of LCL filters against grid impedance variation are proposed for single-current-loop control schemes. Moreover, another interesting finding is that the feedforward control can help maintain a high current control bandwidth under grid impedance variation. This feature is highly desirable if multiple resonant controllers are employed for harmonic compensation. Experimental results are finally presented to verify the theoretical analysis and robust design presented in this paper.

High Power Density Three-Phase Shunt Active Power Filter Design Based on Multiple Magnetic Integrations of LCL Filter

The LCL filter has been widely used in inverter design due to its excellent attenuation capability for the switching harmonics. Nevertheless, the large cost associated with the conventional three-phase LCL filter has limited its usage. This paper proposes a multiple magnetic integration strategy of the LCL filter to reduce the cost while increasing power density. In the new design, an EIE-type magnetic core is put forward for the single-phase LCL filter, where the magnetic fluxes generated by the two discrete inductors cancel out mostly and the residual flux is mainly related to the small capacitor branch current. The magnetic integration is then extended to three-phase by adopting the three-phase three-limb core. Due to the coupling among phases, the equivalent inductance is much larger than the self-inductance such that the self-inductance can be reduced dramatically. An experimental prototype is developed which demonstrates the validity of the proposed method.

A Grid Voltage Feed-forward Control Strategy Based on The Virtual Impedance

This paper initially investigates the conventional LCL filter grid-connected inverts system, which introduces the control strategy with inverter-side current feedback, and analyzes the deficiencies within the strategy. The stability of the controller can be improved by adopting the active damping scheme. However, the output current of the inverter is severely influenced by the external grid voltage distortion and the grid low-order harmonic voltage. In order to reduce this impact and gain high-quality power, a novel control strategy is proposed in this paper, in which the virtual complex impedance is introduced to feed grid voltage forward. By using the proposed control strategy, the total harmonic distortion can be greatly decreased, allowing the grid current to synchronize the reference current well. In addition, the modulation of the virtual complex impedance by controller can also quantificationally regulate the equivalent output impedance, which brings great convenience for inverters system designers to calculating and devising. Simulation results are presented to prove the validity and improvements achieved by the proposed controller.

Indirect Sliding Mode Power Control associated to Virtual Resistor based Active Damping Method for LLCL-Filter-based Grid-Connected Converters

LLCL filters are becoming an attractive solution for Grid connected Converters (GcCs) due to their ability to reduce the filter cost and size while meeting new grid codes and power quality requirements. Compared to the conventional LCL filter, the LLCL filter inserts a small inductor in the capacitor branch to compose a series LC circuit that resonates at the GcC switching frequency. The LC branch has a very low impedance at the switching frequency, which can strongly suppress the harmonic current around switching frequency and therefore reduce the filter grid side inductor. However, the LLCL filter resonance phenomenon and the large changes in the grid inductance (typically under weak grid conditions and in rural areas) may compromise the system stability. In order to address these concerns, this paper proposes an Indirect Sliding Mode Power Control associated to Virtual Resistor based Active Damping method (ISMPC-VRAD) for LLCL -filter-based Grid-connected Converters ( LLCL-GcCs ) . The LLCL filter design parameters as well as the ISMPC-VRAD gains are carefully tuned in order to ensure stable operation under severe grid inductance variations while taking into account the influence of LLCL filter parameters changes on the system stability. Simulation results are presented and discussed in order to prove the efficiency and the reliability of the proposed ISMPC-VRAD for LLCL-GcCs as well as the high filtering performances of the designed LLCL-GcCs .

Double resonant output filter to eliminating the tradeoff between bandwidth and switching ripple in shunt active power filters

Since shunt active power filters (SAPFs) are designed to inject harmonic current, its bandwidth should be much wider compared to regular inverters. LCL filters are commonly employed in regular inverters. However, it cannot completely meet the requirements of SAPF due to its filtering performance and the impact on system stability. This study proposes a novel double resonant LCL (DR-LCL) filter for SAPFs. Derived from the conventional LCL filters, one RC damping circuit and two LC resonant circuits are employed in the proposed filter. Meanwhile, a resistor is connected in parallel with the grid-side inductor. The mutual impact among different components of the filter is discussed, and the stability of SAPF with DR-LCL filter is studied. This DR-LCL filter can not only inherit the advantages of LCL filters, but also eliminate the tradeoff between bandwidth and switching ripple in SAPFs. Finally, the design principle of the proposed output filter is presented and the parameters of the filter are applied to a 66 kW three-phase three-wire SAPF prototype. Simulation and experimental results verify the feasibility of DR-LCL filter.

Modified Filter for Enhancement of Power Quality in Distribution Networks

The recent rise in renewable energy sources has brought with it a corresponding rise in the utilization of Voltage Source Converters (VSCs). These typically contain a Pulse Width Modulation (PWM) switched element that can introduce harmonics into the power grid, resulting in equipment damage and failure. In order to suppress excessive harmonics and improve performance, various lowpass filters are inserted between the VSC and grid. This paper presents a comparative and systematic analysis of the LCL filter and its derivatives based on both theoretical and simulation results. The paper details the impact of each parameter on the system behaviour, as well as a performance analysis between different filter structures such as the conventional LCL filter, LLCL filter, LCL-LC filter and others. Then a design process of the modified filter is introduced with particular focus on development of a formal model which allows the filter components to be determined while maintaining filter performance and reducing damping loss.

변압기 영향을 포함한 고정주파수 LCL형 DC-DC 컨버터 해석

An LCL-type Isolated dc-dc converter operating for constant output voltage is analyzed, including the effect of a high frequency transformer using ac complex circuit approximation. Its solution is derived and is used to obtain the characteristics of the proposed converter. The analyses show through converter modeling, phasor diagram and gain comparison that inclusion of a high frequency transformer results in introduction of magnetizing inductance and leakage inductances at conventional LCL dc-dc converter with ideal transformer. The theoretical and simulation results are presented in case of the wide variations in input voltage and load current in detail. Analysis and simulation results observed that introduction of a transformer in the dc-dc converter had considerable effect on the performance, especially in the case of low output voltage and large load.

Line Filter Design of Parallel Interleaved VSCs for High-Power Wind Energy Conversion Systems

The voltage source converters (VSCs) are often connected in parallel in a wind energy conversion system to match the high power rating of the modern wind turbines. The effect of the interleaved carriers on the harmonic performance of the parallel connected VSCs is analyzed in this paper. In order to achieve low-switching losses, the $60^\circ$ clamp discontinuous pulsewidth modulation (DPWM1) is used to modulate the VSCs. A step-by-step design procedure of the line filter, which ensures the desired harmonic performance under all operating conditions, is presented. The analytical harmonic solution for the two parallel interleaved VSCs is derived in order to obtain the worst case voltage magnitude of the individual harmonic components. The required value of the filter admittance for the specific harmonic component is obtained by using the worst case voltage magnitude and the allowable harmonic injection limit. In order to achieve the desired filter performance with optimal values of the filter parameters, the use of an LC trap branch with the conventional LCL filter is proposed. The expressions for the resonant frequencies of the proposed line filter are derived and used in the design to selectively choose the values of the line filter components. The analysis and design methodology are also verified experimentally.

A Modified LLCL Filter With the Reduced Conducted EMI Noise

For a transformerless grid-tied converter using pulse width modulation, the harmonics of grid-injected current, the leakage current, and the electromagnetic interference (EMI) noise are three important issues during designing of the output filter. In this paper, the common mode and the differential mode EMI noises are investigated for the LCL- and LLCL-filter-based single-phase full-bridge grid-tied inverters. Based on this, a modified LLCL-filter topology is proposed to provide enough attenuation on the conducted EMI noise as well as to reduce the dc-side leakage current. The parameter design method of the filter is also developed. The comparative analysis and discussion on four filter cases (the conventional LCL filter, the conventional LLCL filter, the modified LCL filter, and the modified LLCL filter) are carried out and verified through simulations and experiments on a 0.5-kW, 110 V/50 Hz single-phase full-bridge grid-tied inverter prototype.

A New Design Method for the Passive Damped LCL and LLCL Filter-Based Single-Phase Grid-Tied Inverter

A higher order passive power filter (LLCL filter) for the grid-tied inverter is becoming attractive for industrial applications due to the possibility to reduce the cost of the copper and the magnetic material. However, similar to the conventional LCL filter, the grid-tied inverter is facing control challenges. An active or a passive damping measure can be adopted to suppress the possible resonances between the grid and the inverter. For an application with a stiff grid, a passive damping method is often preferred for its simpleness and low cost. This paper introduces a new passive damping scheme with low power loss for the LLCL filter. Also, a simple engineering design criterion is proposed to find the optimized damping resistor value, which is both effective for the LCL filter and the LLCL filter. The control analysis and the power loss comparison for different filter cases are given. All these are verified through the experiments on a 2-kW single-phase grid-tied inverter prototype using proportional resonant controllers. It is concluded that, compared with the LCL filter, the proposed passive damped LLCL filter can not only save the total filter inductance and reduce the volume of the filter but also reduce the damping power losses for a stiff grid application.

계통연계형 인버터의 LCL필터 최적 설계기법

The conventional LCL filter design method of the utility interactive inverter considers only harmonics attenuation of the current injected to the grid. However, in case of utility-interactive inverter with critical load the voltage quality of the critical load should also be considered for LCL filter design. Also, considering cost and volume of LCL filters. it is important to have minimum values of inductance and capacitance as far as the harmonic standards are satisfied. In this paper a LCL filter design method is proposed to satisfy not only the harmonic standards of the grid current during the grid-connected mode but the voltage quality of the critical load during grid-connected mode and stand-alone mode. With the proposed method optimized values of LCL filters could be obtained by applying weighting factor to voltage ripple across the critical load, inductor volume, amount of reactive current and system bandwidth.