Showing papers by "Yan-Fei Liu published in 2016"

An Accurate Design Algorithm for LLC Resonant Converters—Part II

Abstract: This paper proposes a new approach to optimally design LLC converters. The core of the proposed approach is an accurate algorithm that can find all the possible designs satisfying the peak-gain requirement. Designers can conveniently evaluate several design results and find the optimal one for their respective applications. Part II of this paper discusses design considerations and procedure using the proposed algorithm. Case studies reveal different design tradeoffs in different application scenarios. A 384-V nominal 300-V minimum input voltage range 12-V/50-A output LLC converter prototype with 97.3% peak efficiency is built to verify the proposed design algorithm.

A Distributed Architecture Based on Microbank Modules With Self-Reconfiguration Control to Improve the Energy Efficiency in the Battery Energy Storage System

Abstract: This paper proposes a new distributed battery energy architecture based on the microbank module (MBM) for dc microgrids. The benefits of the proposed architecture include: 1) no voltage sharing problem and no overcharge/overdischarge problem; 2) high compatibility and reliability; 3) high energy utilization efficiency; 4) reduced volume and weight of the battery management system (BMS). The proposed MBM consists of a microbidirectional dc/dc converter, a micro-BMS and a cell bank. Moreover, taking advantage of the battery recovery effect, a self-reconfiguration discharge strategy is also proposed to further enhance the battery performance and discharge efficiency of the new battery energy storage system (BESS). To optimize the proposed control, an efficiency analytical model considering the battery recovery effect is proposed using the curve fitting method. Owing to the bidirectional capability, soft switching capability and high efficiency, the dual active bridge (DAB) converters are chosen as the microbidirectional dc/dc converters. A hybrid modulation strategy with variable switching frequency combining the conventional phase-shift modulation and triangular current modulation is proposed for the DAB converter to reduce the dominant loss and improve the efficiency in wide load range based on the minimum loss model. A 1.5-kW experimental testing platform consisting of four MBMs and four 12 V/100 Ah lithium battery modules was built to verify the proposed architecture with the control and the proposed model. The experimental results show that the discharge time of the proposed distributed BESS is increased significantly under wide operation condition with the self-reconfiguration control. The discharge efficiency of the BESS is improved by 7.1% with the idling time of 5 min under the power level of 1.5 kW.

Digitally Controlled Energy Harvesting Power Management System

Abstract: Intermittent energy harvesting devices often have difficulties in harvesting the peak energy generated due to battery power limitations, which increase the size and cost of the device. This paper discusses a power electronics module (PEM) that is used to extract power from a human energy harvesting device according to the user’s desired difficulty level while maximizing energy transfer into a battery. The PEM can temporarily store the peak power produced by the generator, allowing a reduction in the battery size required to regulate the average power produced by the harvester. A two-stage prototype (a digitally controlled average current mode boost converter and an average current mode buck converter) has been designed, and the experimental waveforms were captured to validate the control theories used in the PEM. The peak efficiencies of the boost and buck are measured to be 93% and 93.7%, respectively. The total PEM system efficiency is measured at 87.9% at an average input power level of 10 W. The PEM design was able to extract 50% more power than the single-stage converter without energy storage capability. The PEM is also used to demonstrate the flexible resistance control scheme capabilities of the device for broader usage in bioenergy harvesting research.

A hierarchical active balancing architecture for Li-ion batteries

Abstract: This paper proposes a hierarchical battery balancing architecture for the series connected lithium-ion batteries. The battery cells are grouped into different packs and the bottom layer is the Adjacent Cell-to-Cell structure consisting of the packs. The top layer is connected to different packs and can deliver the energy from one pack to any other pack bi-directionally, leading to high flexibility. A multi-directional multi-port converter is proposed to serve as the top layer. With the hierarchical architecture, the balanced energy transfer of the cells in different packs can be decoupled, which avoid the repeated charging and discharging during the balancing process. This is beneficial for lengthening the battery lifetime and increasing the State-of-Health (SOH). Moreover, the proposed architecture can lower the current rating of the balancing circuits, which helps decrease the required cost and improve the system efficiency. The experimental results verified the benefits of the proposed architecture.

A common capacitor multi-phase LLC resonant converter

Abstract: In this paper, a new common capacitor current sharing method is proposed for multi-phase LLC resonant converter. Automatic current sharing is achieved by using a common resonant capacitor for all the LLC resonant stages, by connecting the resonant capacitors in each phase in parallel. The proposed method can automatically share the load current without any additional circuits and control strategy. The current sharing performance of the proposed common capacitor current sharing method is analyzed under Fundamental Harmonic Analysis (FHA) assumption. A 600W two-phase LLC converter prototype based on the proposed method is built to verify the feasibility. Excellent current sharing performance (6.5% current sharing error at a wide load range) has been achieved.

Thermal analysis of a magnetic packaged power module

Abstract: Power density of converters have been dramatically increased through the innovations of packaging and integration technologies. Meanwhile, it also imposes more challenges on the thermal performances. An integrated power module packaged with magnetic component is proposed to improve both electrical and thermal performances. This paper presents the thermal analysis of the proposed power module. The magnetic component acts as both the filter inductor in the converter and the package of the power module. Benefiting from this package technology, the inductor can be designed with a bigger winding of lower resistance, thus generating less heat. The magnetic material has better thermal conductivity than plastic material used in conventional plastic packaged power modules; therefore, the power module has better thermal performance. Simulation is executed to show thermal effect of winding configurations. A thermal evaluation board is built to compare thermal performances of the proposed power module and two other commercial products. The proposed power module has 11°C lower than the other part with the same size.

Automatic current-sharing method for multi-phase LLC resonant converter

Abstract: An automatic current sharing method is proposed for multi-phase LLC resonant converter for high power application. There are two types, one is common inductor, and the other is common capacitor. Automatic current sharing is achieved by using a common component for all LLC resonant stages. The proposed method can automatically share the load current without any additional circuit and control strategy. The current share performance of the proposed method is analyzed under Fundamental Harmonic Analysis (FHA) assumption. A 600W two-phase LLC converter prototype based on the proposed method is built to verify the feasibility. Excellent current sharing performance has been achieved.

New low-cost five-level active neutral-point clamped converter

Abstract: Multilevel converters are a popular solution for medium-voltage and high-power applications, including renewable energy conversion. Five-level active neutral-point-clamped converter (5L-ANPC) is one of the most advantageous topologies among five-level multilevel converters. A six-switch 5L-ANPC (6S-5L-ANPC) topology is proposed, which can achieve low-cost because several fast recovery diodes are employed to replace the body-diodes and active switches. However, the power branches including the diode can only provide active current path. Special modulation strategy is proposed to achieve reactive power operation. The simulation analysis shows the proposed 6S-5L-ANPC is suitable for unity power factor application such as photovoltaic (PV) application. A 500W single-phase inverter prototype is built to verify the validity and flexibility of proposed topology and modulation.

LLC converter with auxiliary switch for hold up mode operation

Abstract: This paper proposes a new half bridge (HB) LLC resonant converter with pulse width modulated (PWM) auxiliary switch (sLLC converter) for hold-up mode operation. The proposed sLLC converter works with synchronous rectifier (SR), which is suitable for low output voltage applications. The magnetizing inductor can be designed with large value to reduce the circulation loss. In the proposed sLLC converter, the auxiliary switch and diode branch will provide charging path for the resonant inductor. For nominal 400V input, sLLC achieves same performance as conventional LLC converter, and all the good features such as soft switching are naturally retained. For slight input voltage fluctuation, frequency modulation is used to regulate the output voltage. When the input voltage drops further, HB switches will operate at constant minimum frequency, and the auxiliary switch will operate in PWM mode to energize the resonant inductor with 400V bus directly during hold up period, thus the output voltage can be maintained at desired level. To verify the effectiveness of the proposed sLLC converter, operational principle and equivalent circuit will be carefully explained and analyzed in this paper. A 300W prototype is built for 250V–400V input, 12V output application.

An innovative power module with power-system-in-inductor structure

Abstract: This paper presents an integrated power module with the features of high power density and high efficiency. A multi-functional integrated magnetic component is designed. The component has the roles of both the filter inductor and the case of the whole power module. With the assist of finite element analysis (FEA), design and optimization of the proposed inductor are demonstrated. It has higher inductance value than the inductor used in conventional designs. It has bigger coil winding and larger surface area, leading to lower DCR and better thermal performances than plastic packaging. Benefiting from these advantages, the power module constructed based on the inductor can achieve higher efficiency and lower temperature than those based on traditional plastic packaging solutions. Design of the inductor is demonstrated through the combination of analytical and simulation methods. An inductor prototype is built and used in an integrated power module to do experimental tests. Loss breakdown of the power module is executed to show the loss of the magnetic component. The proposed power module shows better performances than the plastic packaging solution.

An algorithm to analyze circulating current for multi-phase resonant converter

Abstract: An algorithm based on new circulated current model is proposed to analyze the circulating current in the multiphase LLC converter. First of all, a virtual-open concept is introduced and LLC phases are decoupled from each other, Thus, A circulating current model can be achieved from fundamental harmonic approximation (FHA). Secondly, the ac voltages on the equivalent resistor of different phases are assumed same magnitude but different angle viewing from the primary-side. From mentioned above, current sharing error can be calculated, two types calculated results are shown under two-phase independent LLC converter and two-phase common inductor LLC converter. Simulation results from different input voltage levels, different resonant component tolerances, and different total load are compared. A two-phase 600W prototype is built to verify the effectiveness of the proposed analysis method

A passive-impedance-matching concept for multiphase resonant converter

Abstract: A passive impedance matching (PIM) concept is proposed for multi-phase resonant converters application. The new concept can achieve load current sharing between every unit automatically. A passive element such as an inductor or a capacitor is connected in the common branch of the two units (or multi-units), such that several sets of equivalent positive resistors and negative resistors are distributed into these units accordingly. The equivalent virtual resistors are of variable value, which automatically adjust the DC gain in each unit to achieve load sharing. Three equivalents LLC resonant converters with virtual variable resistor are analyzed. The theoretical analysis result shows that the first and third types have good load current sharing performance. A 600W, 12V two-phase LLC converter prototype is built based on the first type. The prototype verified the feasibility and demonstrated advantages of PIM multiphase resonant converter.

Efficiency-wise optimal design methodology of LCLC converter for wide input voltage range applications

Abstract: LCLC converter is an LLC-based, four-element resonant topology, which has been proved to achieve high voltage gain and high efficiency. Such trait makes LCLC converter specifically suitable for wide-input-voltage-range DC/DC applications. Currently, LCLC converter lacks a design method targeting at optimal efficiency over a wide input voltage range. In fact, due to the complexity, efficiency itself is seldom used as optimization criterion even for LLC designs. In this paper, a systematic methodology is proposed to optimize the efficiency at different input voltage levels for LCLC converter. Three mathematical programs (developed in MATLAB) are employed respectively to find all resonant parameter combinations that critically achieve the required voltage gain; precisely analyze the current stress in time domain; and comprehensively calculate the losses in the power circuit including magnetic components. The programs will automatically generate the optimal parameter design with highest weighted efficiency at desired input voltage levels, as well as the magnetic components construction with specified types and sizes of core and conductor. Besides, this method can be extended to other topologies for wide voltage range applications. To verify the effectiveness of the proposed optimal design method, the function of the mathematical tools will be carefully explained in this paper; and a step-by-step design will be demonstrated as an example. Simulation will be included to verify the accuracy of the method.

Modulation method for single-phase six-switch five-level ANPC inverter

Abstract: The Five-Level Active-Neutral-Point-Clamped (5L-ANPC) inverter is one of the most popular topologies among five-level inverters since it combines the features of Flying-Capacitor (FC) type and Neutral-Point-Clamped (NPC) type inverters and was commercially used for industrial applications. This paper proposes a novel modulation strategy for a Six-Switch 5L-ANPC (6S-5L-ANPC) topology to keep voltages of DC-link capacitors and FC balanced. The equations to calculate the FC capacitance in active and reactive power conditions are also provided. Simulation and experiment have been carried out to demonstrate the effectiveness of the proposed modulation technique.

Unified model of high step-up DC-DC converter with multi-cell diode-capacitor/inductor network

Abstract: Multi-cell diode-capacitor/inductor based boost derived DC-DC converter provides a simple solution for high step-up voltage regulation in solar and fuel cell generation. However, many passive components increase the order of system model and complexity. Transient modeling analysis reveals that time constant of each component in diode-capacitor/inductor network is much smaller than that of other circuit if the directly charging and discharge processes between capacitor through diode is fast enough. The voltage/current relationship of each capacitor/inductor in multi-cell network is fixed. Multi-cell diode-capacitor/inductor network can be seemed as multi-stage DC transformer. Based on the unique feature, this paper proposes the reduced-order modeling approach for high step-up DC-DC converter with multi-cell diode-capacitor/inductor network. Finally, simulation and experiments verify the correctness and effectiveness of new modeling approach. The unified reduced-order model contributes to better understanding of circuit characteristic and simplification of controller parameters design.

Seven-switch five-level active neutral-point clamped converter and optimal modulation strategy

Abstract: The five-level active-neutral-point-clamped (ANPC) converters are newly hybrid topologies which have the advantages of traditional neutral-point-clamped (NPC) and flying-capacitor (FC) multilevel converters A novel seven-switch five-level ANPC (7S-5L-ANPC) inverter topology is proposed, which reduces the number of active semiconductor switches over traditional 5L-ANPC inverter topologies It is capable of operating under any power factor conditions The special modulation strategy for 7S-5L-ANPC is proposed and simulation shows only reactive current is flowing through the seventh switch Thus, low current rating switch can be selected for the seventh switch The proposed 7S-5L-ANPC inverter is very suitable for unity and high power factor applications such as photovoltaic (PV) application A 1KW single-phase inverter prototype is built to verify the validity and flexibility of the proposed topology and modulation

Lower Limb-Driven Energy Harvester: Modeling, Design, and Performance Evaluation

Abstract: Biomechanical energy harvesters have shown that useable amounts of electricity can be generated from daily movement. Where access to an electrical power grid is limited, biomechanical energy harvesters are a viable alternative to accommodate energy requirements for portable electronics. In this paper, we present the detailed design and dynamic model of a lower-limb driven energy harvester that predicts the device output and the load on the user. Comparing with previous harvester models, the novelty of the proposed model is that it accounts for energy required for useful electricity generation, stored inertial energy, and both mechanical and electrical losses within the device. The model was validated with the lower-limb driven energy harvester in 12 unique configurations with a combination of 4 different motor and 3 different electrical resistance combinations (2.5$\Omega$, 6$\Omega$, and 11$\Omega$). Human experimentation shows that the device can generate between 3.7-12.0$W$ with an efficiency between 36.7-56.2$\%$. The model was able to predict the harvester output peak voltage within 5.6$\pm$1.4$\%$ error and the peak force it exerts on the user within 6.2$\pm$2.6$\%$ error over a range of parameter values. The model will help to identify configurations to achieve a high harvester efficiency and provides a better understanding of how parameters affect both the timing and magnitude of the load felt by the user.

Current ripple sensing controller for a single-stage led driver

Abstract: A current-ripple-based control strategy for an AC-DC converter with a series ripple cancellation converter (RCC). Embodiments provide series ripple cancellation by sensing the load current information, and significantly simplify the control circuitry. In addition, the embodiments allow input voltage of the series RCC to tightly track its output voltage peak value with no extra control circuit, thus minimizing the RCC component voltage stress as well as the RCC loss. Embodiments are suitable for driving an LED load, where they eliminate LED light flicker caused by the power factor correction (PFC) stage, and significantly reduce its output capacitance.

Editorial Special Issue on Green Power Supplies

Abstract: A traditional field for power Electronics, Power supply technology is still the key application area that covers computing, telecommunication, server, data center, industry, automobile, electric vehicles (EVs), medical, appliance, solar inverters, and so on. Recent advances have made power supplies greener than before, as they become more energy efficient, cost effective, and environment friendly. Recent development in silicon power device and in wide bandgap devices has improved power density and conversion efficiency. These emerging devices, together with improvements in topologies, cooling, and passive components, are shrinking the size. Magnetic material, passive component design, and integration have contributed to miniaturization with improved manufacturability. Digital control, with low-cost DSP and other control ICs, has advanced the overall performance significantly.

Auxiliary circuit for micro-electromechanical system relay circuit

Abstract: A switching system includes a MEMS switching circuit having a MEMS switch and a driver circuit. An auxiliary circuit is coupled in parallel with the MEMS switching circuit, the auxiliary circuit comprising first and second connections that connect the auxiliary circuit to the MEMS switching circuit on opposing sides of the MEMS switch, first and second solid state switches connected in parallel, and a resonant circuit connected between the first and second solid state switches. A control circuit controls selective switching of a load current towards the MEMS switching circuit and the auxiliary circuit by selectively activating the first and second solid state switches and the resonant circuit so as to limit a voltage across the MEMS switch by diverting at least a portion of the load current away from the MEMS switch to flow to the auxiliary circuit prior to the MEMS switch changing state.

Five-level topology unit and five-level inverter

Abstract: A five-level topology unit, and a five-level inverter. The five-level topology unit circuit comprises an inverter module and a floating capacitor (C s), said inverter module capable of providing five levels of power. The five-level topology unit circuit and the five-level inverter can, given equivalent working conditions and without being provided with additional booster circuits, output an alternating current equivalent to that of a full bridge inverter.

Half-bridge inverter unit and inverter

Abstract: A half-bridge inverter unit and an inverter. The half-bridge inverter unit comprises an inverter control module and an inductor (L1), wherein the inverter control module can provide different connection states in response to different operation modes, thereby enabling a corresponding half-bridge inverter unit to operate in a buck mode or a boost mode, so as to satisfy the requirements of a wide input voltage range. By means of the characteristic of the positive and negative half-cycle symmetry of a grid voltage, the problem of neutral-point voltage balance of two series capacitors in parallel connection with a direct-current power source is solved. The half-bridge inverter unit adopts a single-stage structure, and has a low power consumption, low costs, high efficiency and high stability.