Low Part Count Research Articles

A Control Design Technology of Isolated Bidirectional LLC Resonant Converter for Energy Storage System in DC Microgrid Applications

This paper presents a new control method for a bidirectional DC–DC LLC resonant topology converter. The proposed converter can be applied to power the conversion between an energy storage system and a DC bus in a DC microgrid or bidirectional power flow conversion between vehicle-to-grid (V2G) behavior and grid-to-vehicle (G2V) behavior. Furthermore, such a converter can be applied to energy storage systems for decentralized renewable energy generation systems, such as solar and wind power. In addition, this converter can be combined with a bidirectional inverter to allow energy storage in the system to improve the safety, stability, and power quality of the microgrid. In the proposed circuit structure, we use a bidirectional DC–DC LLC, which has the advantages of a higher voltage conversion ratio, lower part count, simpler control than similar converters such as DAB, CLLC, and L–LLC converters, and bidirectional power flow and electrical isolation. Specifically, to extend the battery life, it can be employed as a control strategy for discharging the energy stored in the battery (SOC) and reducing the temperature rise generated by the internal solid electrolyte interphase (SEI) when discharging the battery under the variation in distributed energy resource (DER) generation and load demand. To realize the bidirectional power conversion without using any auxiliary inductor and only changing the control strategy, the forward step-down power conversion was based on pulse frequency modulation (PFM) control, and the reverse step-up power conversion was based on pulse width modulation (PWM) control. In this paper, we introduce the bidirectional converter topology and its control strategy for the DC microgrid battery energy storage system. Finally, a 500 W prototype is built to verify the effectiveness of the proposed converter.

Single-Stage Isolated DC/AC Converter With Continuous Dynamic Model and Controller Design

This article proposes an analysis and controller design of a bidirectional bridgeless single-stage DC/AC converter with high frequency-link and low part count. Dual phase-shift control is proposed to control and modulate the AC power and to minimize the Root Mean Square (RMS) of the transformer current. Furthermore, the phase shift angle is chosen to assure wide range of ZVS turn-on of all the switching devices. The proposed controller has a reduced THD at the output AC current without zero-crossing spikes. A continuous-time average model, that well predicts both transient and steady-state relations between the high-frequency AC link and the DC side, is needed to simplify the controller design. Since complex discrete-time models were used in previous literatures, simple and powerful continuous-time tools were not used to design the closed-loop system. In this paper, a novel continuous-time Generalized Average Model (GAM) is proposed. The derived model precisely predicts the high-frequency state variables of the converter, including a simple formula for the transformer current RMS value. The formula is used to minimize the transformer current to reduce the losses. Moreover, the transient analysis and the closed-loop control design are presented. A prototype circuit is tested to verify the performance of the proposed control scheme with the proposed isolated single-stage DC/AC converter.

Modeling of a Zero CO2 and Zero Heat Pollution Compressed Air Engine for the Urban Transport Sector

Zero CO2 and Zero heat pollution compressed air engine for the urban transport sector is an engine design that is powered and lubricated solely by compressed air. In other to guarantee these functionalities for the engine design, its modeling was done following the mechanical engineering design method. This article highlights the creation of a mathematical model of the engine. This work covers the design synthesis and the analysis of the kinematics of the engine. For the design synthesis; FAST, GRAFCET and later one realization of conceptual sketches all deductions from the problem definition. With the sketches considered, the kinematics and dynamic formulations where later on realized. The design chosen highlight’s the external forces to come principally from an isothermal expansion process of the compressed air what is termed the expansion chamber of the engine. The analysis was done on the kinematics of the engine with considerations of some assumptions. This article ends with remarkable results as it concerns the engine’s simplicity and guaranteed high efficiency. These conclusions were drawn from the compact nature of the design, the low part count and the reduced displaceable masses which give little of no conflicting movements in the engine design.

Practical Evaluation of Loss Reduction in Isolated Series Resonant Converter with Fixed Frequency Modulation

Nowadays, power converters with reduced cost, compact size and high efficiency are evolving to overcome the emergent challenges of renewable energy integrations. In this context, there is an increased demand for well-designed power converters in renewable energy applications to reduce energy utilization and handle a variety of loads. This paper proposes a center-tapped bridge cascaded series-resonant LC dual active bridge (DAB) converter for DC-DC conversion. The low part count of the proposed converter enables a high-power density design with reduced cost. The proposed converter offers reduced conduction losses as the reverse current is eliminated by adopting current blocking characteristics. Reverse current blocking also enables zero voltage switching (ZVS) and zero current switching (ZCS) over a wide operating range. Therefore, using a simple fixed frequency modulation (FFM) scheme offers a wide operating range compared to a conventional DAB converter. A thorough comparison of the proposed converter and a conventional DAB converter is provided based on conduction losses and switching losses to illustrate the performance improvement. Lastly, the effectiveness of the proposed converter is validated through simulation and experimental results.

Stretchable Optical Waveguide Sensor Capable of Two-Degree-of-Freedom Strain Sensing Mediated by a Semidivided Optical Core

With the rising demand for flexible strain sensors for soft robots, optical sensing solutions have been proven to be electrically safe, stable, and precise. This study presents a highly stretchable optical waveguide sensor that extends existing solutions to two degrees of freedom while maintaining low manufacturing complexity and part count. Through casting in a 3D-printed mold, a polymer waveguide is manufactured, featuring a semidivided core cross section. The light from a near-infrared LED light source is guided to two phototransistors connected to each chamber. The connection between both core chambers makes the power throughput amplitude and ratio at the two outputs dependent on the strain amplitude as well as its location or direction. The proposed waveguide is experimentally compared with single and dual core designs in four different strain modes, to sense elongation, local deformation amplitude and position across length, twisting angle and direction, as well as bending amplitude and direction in a soft finger. While influences of the manual manufacturing process are apparent, the results verify that the presented waveguide sensor can be effectively applied in these four strain scenarios. We also demonstrate that information about superimposed strain states can be obtained from the time signal.

Hybrid Three-Phase Transformer-Based Multilevel Inverter With Reduced Component Count

This paper proposes a novel three-phase transformer-based multilevel inverter (MLI) topology to maximize the output voltage levels for high-power high-voltage applications while reducing component counts as compared to its transformer-based counterparts. The proposed hybrid topology is formed by connecting a three-level T-type module with full H-bridge cells through single-phase transformers. The T-type module is fixed while the full H-bridge cell can be repeated for enlarging the output voltage levels without increasing the voltage stress on switches. Key features of the proposed topology include low part count, capacitor-free, diode-free, voltage boosting, simple control, and modularity. Within the framework, a simple low-frequency pulse width modulation (LFPWM) switching scheme is used to control the output voltage, and the working principle is detailed for seven-, nine-, and N-level operation. The operability and performance of the proposed topology are numerically verified and experimentally validated at different loads. Moreover, its conversion efficiency is experimentally examined. Finally, a comparative study with existing transformer-based MLI circuits is conducted to prove its key merits.

Design of a novel tendon-driven manipulator structure based on monolithic compliant rolling-contact joint for minimally invasive surgery

PurposeCompliant mechanisms are commonly used in the design of manipulator and surgical robotic tools for minimally invasive surgery (MIS) thanks to their compactness, ability of miniaturization and lower part count. However, conventional compliant joint has higher internal stiffness, which limits the bending radius. To overcome this problem, a novel tendon-driven manipulator structure based on monolithic compliant rolling-contact joint (CRCJ) is proposed.MethodsThe proposed rolling-contact mechanism is used to prevent cable slack during actuation, which occurs in conventional compliant joint design. By means of selective laser sintering (SLS) technique, the CRCJ can be fabricated in a monolithic structure, thus granting the CRCJ both the advantages of compliant joints and rolling-contact mechanism. Simulations with nonlinear finite element analysis (FEA) and experiments were conducted to evaluate and compare the mechanical properties of the proposed CRCJ with conventional leaf-type compliant joint including the bending and compliant motion.ResultsExperimental results showed that the CRCJ has lower bending stiffness, higher maximum bending angle (over 180^{circ }) and a higher compliance compared to conventional compliant hinges, which allows a larger workspace and reduces the possibility of tissue injury. Agreement was also found between the nonlinear FEA and experiments regarding the relation between actuation force and bending angle. A primary prototype of a 3-DOF handheld laparoscopic manipulator with a diameter of 7 mm was further developed.ConclusionA dexterous tendon-driven monolithic manipulator structure based on CRCJ for MIS is proposed. A preliminary prototype of a handheld laparoscopic manipulator demonstrates the capability of the CRCJ for steerable medical devices. However, design improvements based on FEA and application-orientated prototypes considering anatomical requirements still show room for improvements.

Experiments With a Rotor-Hybrid Gas Bearing System Undergoing Maneuver Loads From Its Base Support

Abstract Gas bearings enable microturbomachinery (MTM) with a large power to weight ratio, low part count, and nearly frictionless motion, thus resulting in systems operating over extended maintenance intervals and with improved fuel efficiency. Envisioned oil-free vehicle transportation systems implementing gas bearings range from small size gas turbines, to unmanned aerial vehicles, to turbochargers (TC), and more to come. In these vehicles, base or support transient displacements transmit forces exciting the rotor-bearing system; hence, the need to characterize system integrity under stringent operating conditions. This paper reports experiments demonstrating the ability of a hybrid gas bearing-rotor system to withstand maneuver actions that suddenly remove the ground support. The test rig consists of a rigid motor-rotor, supported on tilting pad hybrid gas bearings supplied with pressurized air. The rotor is housed in a thick steel casing that is attached to a rigid base plate. The whole test rig hangs from a crane; two steel cables connect to one side of the base and a nylon webbing attaches to the other side of the base. The other end of the webbing ties to a release mechanism, which when released, frees one side of the rig base. Suddenly, the whole test rig rotates and displaces downward while the tensions in the taut cables rapidly increase and pull the test rig as it swings back and forth. The crane support enables two release maneuvers: one turns the rig ∼90 deg and the other flips it 180 deg, both events occurring while the rotor spins at 70 krpm (surface speed 105 m/s). The measured rotor displacements relative to the casing demonstrate a momentary increase in motion amplitude, up to ∼1.15 mm since the bearings also displace, along with a maximum casing deceleration of ∼7 g when the cables stop the rig fall. The measurements show the rotor response is free of subsynchronous whirl frequencies that could evidence a rotor dynamic instability. Very low frequency motions denote the swing frequency of the hanging rig and jerk motions from the crane lifting and bouncing when the rig is at its lowest vertical position. In one instance, power to the motor unexpectedly interrupted and the rotor underwent an unplanned shaft speed coastdown. In spite of the large displacements recorded, the rotor survived both events; it continues to operate to this day. The experiments demonstrate that the hybrid gas bearing system could withstand large amplitude rotor excursions. The measurements provide a novel method for testing gas bearings, as the induced excitations are multidirectional, while the test rig encounters a short period of free falling, followed by a quick deceleration with large forces. A simple kinetics model of the test rig drop produces peak decelerations similar in magnitude to those measured.

A Lean Satellite Electrical Power System with Direct Energy Transfer and Bus Voltage Regulation Based on a Bi-Directional Buck Converter

The lean satellite approach requires aggressive measures for cutting development time and resource utilization; therefore, the power system should be simple, with a low part count, high reliability, and good electrical performance. The fully-regulated bus direct energy transfer (FRDET) architecture is considered the most common solution for big satellites; however, it is rarely used in lean satellite designs because of its complexity and the lack of commercial off-the-shelf solutions. Based on this, a new implementation of the FRDET architecture was proposed, prototyped, and evaluated. The system was based on a bidirectional converter that charges and discharges the battery while maintaining the bus voltage regulation. The system was evaluated by comparing it with the prevailing architectures in the field, in terms of efficiency and average harvested solar power per orbit. The proposed system was superior in both aspects which made it more suitable for its application in lean satellite designs.

A Hybrid Nine-Level, 1- Grid Connected Multilevel Inverter With Low Switch Count and Innovative Voltage Regulation Techniques Across Auxiliary Capacitor

A 1-φ hybrid nine-level inverter (H9LI) topology has been proposed in this paper. The proposed H9LI topology uses a simple phase disposition pulsewidth modulation strategy to generate nine-voltage levels in the output. The main advantage of this topology is that it has a low switch count (ten switches) compared to the existing nine-level inverter topologies. To regulate the voltage across auxiliary capacitor, two innovative control techniques are proposed, which are integrated with the inverter modulation technique itself. Hence, it does not require any extra voltage balancing circuits to maintain the voltage across the auxiliary capacitor and input dc capacitors. A major advantage of these control techniques is that they eliminate the sensing of the coupled inductor current. Another significant advantage of H9LI is that loss distribution among all the power switches is more uniform compared to existing nine-level inverters. Due to low part count and absence of extra voltage balancing circuits, the H9LI achieves higher efficiency (η ≍ 94.5%) and lower cost. Furthermore, the requirement of filter size reduces due to the presence of coupled inductor in H9LI. The proposed 1-φ grid connected H9LI is verified through MATLAB/Simulink simulations and validated through experiments on a laboratory prototype of 400-VA rating.

Analysis of Carrier-Based PWM Patterns for a Three-Phase Five-Level Bidirectional Buck$+$Boost-Type Rectifier

This paper analyzes three different carrier-based modulation patterns applied to a three-phase high-power-factor-corrected (PFC) five-level buck+boost-type converter acting as an interface between dc distribution systems and an ac grid. The modulation is analyzed employing the space vectors theory so that the achievable performance is demonstrated. The main advantage of the analyzed modulation strategy is its simplicity, which makes it suitable for digital signal controller (DSC) implementations. This seems straightforward for voltage source converters, but is a challenge for current-multilevel converters that typically employ field-programmable gate array devices to achieve better harmonic distortion performance. This is due to modern power electronics DSCs being typically designed for other converter topologies. The power converter is constructed with two phase-shift-modulated six-switch buck-type PFC converters, paralleled by interphase transformers, and an inverting circuit. The system features: bidirectional current carrying capability; relatively low parts count; high utilization of the semiconductors; and low current and voltage ripple at its terminals. The principle of operation, detailed description, analysis of the modulation strategy, and dimensioning equations for three different power circuit realizations are described in this paper assuming the analyzed modulation patterns. The feasibility of the presented converter is demonstrated by means of a constructed hardware prototype.

Non‐isolated multiple‐input boost converter for energy harvesting

In this Letter, a new dual/multiple-input non-isolated boost converter is proposed. It provides a positive boosted output voltage without any additional transformer. It is suitable to interface sources of different current–voltage characteristics to a common load, with a simple topology and a low part count. The topology and the behaviour are similar to the single-input boost converter; hence, the control strategy can be accomplished easily. It can be used in low-voltage energy harvesting applications to collect energy from multiple sources. Simulations and experimental results are presented to demonstrate the effectiveness of the proposed topology.

Development of an inductor incorporated onto a carbon fiber MAV structural component

Insect-sized flapping wing micro air vehicles (MAVs) are beginning to take flight but have many technical hurdles to overcome. One of the greatest challenges of MAV design is attaining lightweight microelectronic components of optimal size and shape. In this paper an inductor for incorporation onto a carbon fiber MAV body component is modeled using a multiphysics and lumped parameter approach. A magnetostatic simulation using finite elements provides insight into the magnetic flux density distribution of the inductor. Simulation allows the inductor to be adapted to various shapes and sizes. Lumped values are generated based upon desired values for a MAV inductor. Microelectromechanical systems (MEMS) processes are used to fabricate the inductor directly on a MAV carbon fiber body (e.g. fuselage) component. Fabrication is prototyped on a semiconductor wafer. The inductor (a major contributor to the MAV weight budget) forms the basis for a lightweight, voltage transformer. By transferring the copper conductors to a structural component, the circuitry becomes part of the vehicle structure. This type of MEMS fabrication allows for optimal sizing, weight reduction, a lower part count and much higher levels of integration. These parameters are critical for operational MAV applications.

Novel High Step-Up DC–DC Converter With an Active Coupled-Inductor Network for a Sustainable Energy System

In this letter, a novel high step-up dc–dc converter with an active coupled-inductor network is presented for a sustainable energy system. The proposed converter contains two coupled inductors which can be integrated into one magnetic core and two switches. The primary sides of coupled inductors are charged in parallel by the input source, and both the coupled inductors are discharged in series with the input source to achieve the high step-up voltage gain with appropriate duty ratio, respectively. In addition, the passive lossless clamped circuit not only recycles leakage energies of the coupled inductor to improve efficiency but also alleviates large voltage spike to limit the voltage stresses of the main switches. The reverse-recovery problem of the output diode is also alleviated by the leakage inductor and the lower part count is needed; therefore, the power conversion efficiency can be further upgraded. This letter shows the key waveforms of the proposed converter and the detailed derivation of the steady-state operation principle. The voltage conversion ratio, the effect of the leakage inductance and the parasitic parameters on the voltage gain are discussed. The voltage stress and current stress on the power devices are illustrated and the comparisons between the proposed converter and other converters are given. Finally, a prototype circuit rated 200-W output power is implemented in the laboratory, and the experimental results show the satisfactory agreement with the theoretical analysis.

Forced Coefficients for a Short Length, Open Ends Squeeze Film Damper With End Grooves: Experiments and Predictions

Squeeze film dampers (SFDs) are effective to ameliorate shaft vibration amplitudes and to suppress instabilities in rotor–bearing systems. Compact aero jet engines implement ultra-short length SFDs (L/D ≤ 0.2) to satisfy stringent weight and space demands with low parts count. This paper describes a test campaign to identify the dynamic forced response of an open ends SFD (L = 25.4 mm and D = 125.7 mm), single film land, and oil fed through three holes (120 deg apart), operating with similar conditions as in an aircraft engine. Two journals make for two SFD films with clearances cA = 0.129 mm and cB = 0.254 mm (small and large). The total oil-wetted length equals Ltot = 36.8 mm that includes deep end grooves, width and depth = 2.5 × 3.8 mm, for installation of end seals. In the current experiments, the end seals are not in place. A hydraulic static loader pulls the bearing cartridge (BC) to a preset static eccentricity (eS), and two electromagnetic shakers excite the BC with single frequency loads to create circular orbits, centered and off-centered, over a prescribed frequency range ω = 10–100 Hz. The whirl amplitudes range from r = 0.05cA–0.6cA and r = 0.15cB–0.75cB while the static eccentricity increases to eS = 0.5cA and eS = 0.75cB, respectively. Comparisons of force coefficients between the two identical dampers with differing clearances show that the small clearance damper (cA) provides ∼4 times more damping and ∼1.8 times the inertia coefficients than the damper with large clearance (cB). The test results demonstrate damping scales with ∼1/c3 and inertia with ∼1/c, as theory also showed. Analysis of the measured film land pressures evidence that the deep end grooves contribute to the generation of dynamic pressures enhancing the dynamic forced response of the test SFDs. A thin film flow model with an effective groove depth delivers predictions that closely match the test damping and inertia coefficients. Other predictions, based on the short length bearing model, use an effective length Leff ∼ 1.17L to deliver damping coefficients 15% larger than the experimental results; however, inertia coefficients are ½ of the identified magnitudes. The experiments and analysis complement earlier experimental work conducted with centrally grooved SFDs.

Design considerations for an engine-integral reciprocating natural gas compressor

Abstract Conventionally, compressed natural gas (CNG) vehicles are refueled using a high-cost, centralized, and sparse network of CNG fueling stations that has primarily been developed for the use of fleet customers. An engine-integral reciprocating natural gas (NG) compressor has the capability to disrupt the incumbent CNG market by enabling the use of NG for personal transportation, fueled at home, from the preexisting low-pressure NG infrastructure, at low parts count, using conventional components, and therefore at low incremental costs. The principal objective of this paper is therefore to describe and analyze the dynamic and thermal design considerations for an automotive engine-integral reciprocating NG compressor. The purpose of this compressor is to pressurize storage tanks in NG vehicles from a low-pressure NG source by using one of the engine cylinders as a multi-stage reciprocating compressor. The engine-integral compressor is developed by making changes to a 5.9 l displacement diesel-cycle automotive engine. In this novel design and implementation, a small tank and its requisite valving are added to the engine as an intermediate gas storage system to enable a single compressor cylinder to perform two-stage compression. The resulting maximum pressure in the storage tank is 250 MPa, equivalent to the storage and delivery pressure of conventional CNG delivery systems. Dynamic simulation results show that the high cylinder pressures required for the compression process create reaction torques on the crankshaft, but do not generate abnormal rotational speed oscillations. Thermal simulation results show that the temperature of the storage tank and engine increases over the safety temperature of the natural gas storage system unless an active thermal management system is developed to cool the NG before it is admitted to the storage tanks.

Quasi‐resonant LED driver with capacitive isolation

A low part count, efficient quasi-resonant light-emitting diode driver is proposed. The proposed driver relies on a capacitive safety isolation barrier, which eliminates the need for a bulky isolation transformer; thus, the footprint area can be reduced. Operation frequencies of 100–350 kHz further contribute to miniaturisation of the proposed driver. The feasibility of the proposed topology is verified by simulation and experimental results.

A Novel High step-up converter with a quasi active switched-inductor structure for renewable energy systems

A novel high step-up dc–dc converter with a quasi-active switched-inductor structure for a renewable energy system is presented in this paper. The proposed converter is composed of two coupled inductors which can be integrated into one magnetic core, two capacitors, two active switches, and three diodes. The primary sides of coupled inductors are charged in parallel by the input source, and the secondary sides of coupled inductors are discharged in series with the input source and two capacitors to achieve high step-up voltage gain with an appropriate duty ratio. The two sets of diode–capacitor circuits not only help to lift the voltage conversion gain but also alleviate voltage spike affected by the leakage inductance to limit the voltage stress across the power switch effectively. Therefore, the two low on-state resistance switches can be adopted to reduce conduction loss. Furthermore, the two diodes have no reverse-recovery problem due to turn off naturally, the reverse-recovery problem of the output diode is also alleviated by the leakage inductor and lower part count is needed; therefore, the power conversion efficiency can be further improved. The operating principles and steady-state analyses are discussed in detail; then, the performance of the proposed converter is compared with existing converters. Finally, a prototype is established in the laboratory, and the experimental results are given to verify the correctness of the analysis.

A Novel Switched-Coupled-Inductor DC–DC Step-Up Converter and Its Derivatives

This paper presents a novel dc-dc converter configuration, which successfully integrates two technologies, including a switched capacitor and a switched coupled inductor, into one converter. By adopting a coupled inductor to charge a switched capacitor, the voltage gain can be effectively increased, and the turns ratio of the coupled inductor can be also reduced. Not only lower conduction losses but also higher power conversion efficiency is benefited from a lower part count and lower turns ratios. The proposed converter is simply composed of six components, which can be further derived to varied converters for different purposes, such as a bidirectional converter. The operating principle and steady-state analysis are discussed in this paper. A 250-W laboratory hardware prototype is completed and verified. The voltage gain is up to 11. The highest efficiency is 97.2%, and the full-load efficiency is kept at 93.6%.

High efficiency, 100mJ per pulse, Nd:YAG oscillator optimized for space-based earth and planetary remote sensing

We report on a newly solid state laser transmitter, designed and packaged for Earth and planetary space-based remote sensing applications for high efficiency, low part count, high pulse energy scalability/stability, and long life. Finally, we have completed a long term operational test which surpassed 2 Billion pulses with no measured decay in pulse energy.