Energy Conversion Circuit Research Articles

Active Equalization of Lithium Battery Pack with Adaptive Control based on DC Energy Conversion Circuit

Background:: How to solve the inconsistency of battery pack is a key point to ensure reliable operation of electric vehicles. Battery equalization is an effective measure to address the inconsistency. Passive equalization method has poor efficiency and thermal management problems. Average voltage equalization method is only suitable for situations where there is a significant voltage difference between batteries. The SOC-based equalization method is relatively difficult and may inevitably lead to the accumulation of errors during the process. Objective:: In order to avoid the disadvantages of traditional control methods, a new control method is proposed to improve the accuracy and self-adaptation of active equalization, which is easy to be realized without online calculation. Methods:: Cascaded bidirectional Buck-boost circuit is adopted as the novel equalization topology. Based on fuzzy PID theory, an adaptive digital-analog hybrid control strategy based on fuzzy PID is proposed in this paper. Parameter design of the fuzzy PID controller is carried out. A battery equalization system based on cascaded bidirectional Buck-boost circuit is designed and developed. Experimental verification is conducted on relevant hardware platforms. Results:: An adaptive digital-analog hybrid control strategy based on fuzzy PID is proposed. Compared to passive equalization, this proposed method provides high efficiency. Regarding traditional voltage control, the method improves control reliability and flexibility. Compared to the average voltage equalization method, the approach needs less convergence time. Moreover, the control method is much easier to realize than the SOC-based equalization method. Conclusion:: By using the presented adaptive control based on DC energy conversion circuit, the degree of self-adaptation of the equalization process has been obtained as higher and the inconsistency as smaller.

Dual Frequency Energy Harvesting System Based on Planar Inverted F-shaped Antenna

<p>With the expansion of Internet of things (IoT) scale and the extension of its application fields, node energy acquisition has become one of the constraints on the development and application of IoT technology. Wireless energy acquisition is faced with the challenge of how to enhance power conversion efficiency under low input power in the broadband range. This study aimed to improve the capability of energy collection and transmission in wireless communication, an efficient dual-frequency energy harvesting system was proposed, moreover a novel dual-frequency planar inverted-f antenna (PIFA) and its energy conversion circuit for Radio frequency (RF) energy harvesting were designed by studying the characteristics of ambient RF energy and antenna. The developed antenna is designed and manufactured for GSM 900mhz or DCS 1.8 GHz to harvest the ambient energy provided by nearby devices. It is proved that the new dual-frequency antenna still has high efficiency when the input power is less than -20 dbm, and can maximize the receiving energy. The system works with an energy conversion and storage module to convert weak signals into required voltages, the simulation and test results show that the maximum conversion efficiency of the prototype is about 65% at 920MHZ and 1.8GHz at -20 dBm input power.</p> <p> </p>

Time-sharing orbit jump and energy harvesting in nonlinear piezoelectric energy harvesters using a synchronous switch circuit

Nonlinearity has enabled energy harvesting to advance toward higher power output and broader bandwidth in monostable, bistable, and multistable systems. However, operating in the preferable high-energy orbit (HEO) rather than the low-energy orbit (LEO) for making such advancement has restricted their applications. Based on a monostable nonlinear system, this paper proposes a self-contained solution for time-sharing orbit jump and energy harvesting. The joint dynamics of an electromechanical assembly consisting of a nonlinear energy harvester and a switched-mode piezoelectric interface circuit for high-capability energy harvesting is studied. The proposed solution is carried out by utilizing a cutting-edge switched-mode bidirectional energy conversion circuit (BECC), which enables time-sharing dual functions of energy harvesting and vibration exciting. A theoretical model is established based on impedance analysis and multiple time scales method to analyze the stability, frequency response, and phase evolution of the autonomous and nonautonomous nonlinear energy harvesting systems. In particular, the detailed dynamics for the orbit jumps with the vibration exciting mode of BECC are studied. Experiments are performed to validate the full-hysteresis-range orbit jumps with the monostable nonlinear energy harvester. The harvested power after orbit jumps yields a nine-fold increase, compensating for the energy consumption under vibration exciting mode quickly. The proposed solution also refrains the system from extra mechanical or electrical energy sources for orbit jumps, which leads to the first self-contained solution for simultaneous energy harvesting and orbit jump in nonlinear piezoelectric energy harvesting. This work enhances the practical utility of nonlinear energy harvesting technologies toward engineering applications.

ZVS–ZCS High Step-Up/Step-Down Isolated Bidirectional DC–DC Converter for DC Microgrid

A soft-switched isolated bidirectional dc–dc converter is proposed for distributed generation systems. Dual coupled inductor based flyback energy conversion circuit achieves high voltage step-up/down ratio and high efficiency at lowered duty cycle and, attributes the galvanic isolation. Active switch based capacitor multiplier cell appreciably reduces voltage stresses on low-voltage (LV) and high-voltage (HV) stage MOSFETs, thereby allowing low voltage rating devices(small <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>ds</i>(ON)</sub> ). Active-voltage-clamping type circuit extensively suppresses the voltage spikes across LV-switches caused by leakage inductance. Indeed, this clamp circuitry is formed without any additional switches/diodes, thus reduces clamp device count. By availing of quasi–resonance, thus without needing the HV stage snubber, switching voltage spikes are substantially alleviated. Further, this clamp along with quasi–resonance achieves zero-voltage (ZVS) and zero-current (ZCS) switching, over wide load range, for all switches in both step-up and step-down operations. Reduced voltage stresses, minimized clamp device count, diminished conduction losses and bidirectional soft-switching performance collectively enhances the efficiency. A 600 –W laboratory built set-up working at 75 kHz verifies the viability of the design concept. Measured peak efficiencies in boost and buck stages are 96.65% and 96.58%, respectively.

On the positive and negative damping effect of piezoelectric structure using switched-mode bidirectional energy conversion circuit

The introduction of a switched-mode bidirectional energy conversion circuit (BECC) facilitates the development of piezoelectric devices toward integrated and energy-efficient multi-functional designs. These new designs realize the organic combinations of two or more functions among energy harvesting (EH), vibration excitation (VE), and dynamic sensing. Yet, the structural effect after applying the BECC was not comprehensively investigated and strictly quantified. This letter analyzes the electromechanical joint dynamics of a piezoelectric structure using the BECC, which was developed after the synchronized triple bias-flip (S3BF) technique, under different EH and VE operation modes. It shows that the EH modes electrically induce an extra positive damping effect, while the VE modes induce a negative one. A lumped model and impedance analysis are used to evaluate the electrically induced damping and the energy conversion efficiency by the BECC. The closed-form expression of the vibration displacement under different operation modes is derived. Experiments are carried out under different operation modes and frequencies. The theoretical and experimental results show good agreement. They validate the damping tuning capability of BECC in either positive or negative damping directions. This switched-mode interface circuit offers a promising solution for building an adaptive dynamic control of piezoelectric structures with high energy efficiency.

Fabrication, structural and piezoelectric force microscopy analyses of nanorod ZnO-PVDF thin films

Piezoelectric nanogenerators are composite nanostructure films with a capability of the mechanical-to-electrical energy conversion for potential applications in self-sustained, low-powered electronic devices. In this work, Zinc Oxide (ZnO) nanorods served as piezoelectric materials and they were grown by two steps: (1) Spray Pyrolysis and (2) Hydrothermal Method on copper foils. Afterwards, poly (vinylidene difluoride) (PVDF) was spin-coated on ZnO nanorods with a spinning speed of 500 rpm. After spin-coating, the PVDF films were either air-cooled or heated at 100 °C for 10 min. Piezoelectric Force Microscopy (PFM) was performed to investigate the piezoelectric and ferroelectric behaviour of PVDF and the increment of piezoelectric response by adding ZnO nanorods to PVDF. Then, the ZnO film, pristine PVDF film and ZnO-PVDF were assembled with Al foil on top to construct nanogenerators for comparison. Lastly, the measurement of electric output voltage was carried out using energy conversion circuit.

A Bidirectional Energy Conversion Circuit Toward Multifunctional Piezoelectric Energy Harvesting and Vibration Excitation Purposes

Piezoelectric transducers provide a bidirectional channel for converting energy from mechanical form to electrical or in the opposite direction. Various applications were developed with either of these two energy-flow processes. For example, energy harvesters take advantage of the energy flow from mechanical to electrical domains, while vibration exciters utilize that from electrical to mechanical domains. However, few designs have integrated the bidirectional energy-flow processes in a single device in the past. Such an integration is beneficial to some multifunctional applications. The key obstacle of integrated bidirectional design results from the interface circuit design, rather than the transducer. This article makes a breakthrough by proposing a bidirectional energy conversion circuit (BECC) solution for the time-sharing energy harvesting and vibration exciting purpose. It is realized by developing a new control strategy on the synchronized triple bias-flip (S3BF) piezoelectric interface circuit, which was formerly used for energy harvesting enhancement. The control logic for energy harvesting and vibration exciting modes are discussed in detail. The time-sharing multi-functional ability is validated in experiments. It is the first time to realize a compact and integrated self-excitable energy harvester by using a single interface circuit. Experiments are carried out for validating the feasibility of the BECC toward future versatile engineering designs.

Power Source Based on Electric Field Energy Harvesting for Monitoring Devices of High-Voltage Transmission Line

This article proposes a power source based on alternating electric field energy harvesting, which can be used for the condition monitoring devices for a high-voltage (HV) transmission line. The energy-harvesting ability of online and offline harvesters depending on different sizes and installation positions is studied herein through a finite-element simulation. The power source uses a novel energy conversion circuit with a cascaded ladder-type topology that can multiply the power when increasing the number of cascaded stages. We set up an HV experiment platform to test the performances of the energy harvester and the power source. The energy-harvesting ability of the harvester approaches the simulation results. The tested power source with four cascaded stages demonstrates a harvesting ability of 620 μW/μA, making it superior to the reported solutions in previous studies. The proposed circuit shows the latent capability of realizing a higher power density.

Autonomous Wireless Sensor Node with Thermal Energy Harvesting for Temperature Monitoring of Industrial Devices

The feasibility of using thermal energy harvesting to power a wireless sensor node for temperature monitoring of industrial devices is explored and evaluated in this paper. The thermal energy harvesting equipment and energy conversion circuit have been designed and fabricated. A series of experiments with various sleep periods for the sensor node are undertaken. The experimental results show that the thermal energy harvesting equipment and energy conversion circuit are able to power a commercial wireless node when the sleep period of the node is more than 16s, equating to a duty cycle of 5.4%. The results also indicate that the wireless sensor network based on the proposed autonomous wireless sensor node can monitor the industrial device temperature successfully.

Adaptive Rectifier Driven by Power Intake Predictors for Wind Energy Harvesting Sensor Networks

This paper presents a power management technique for improving the efficiency of harvesting energy from air-flows in wireless sensor networks (WSNs) applications. The proposed architecture consists of a two-stage energy conversion circuit: an ac-dc converter followed by a dc-dc buck-boost regulator with maximum power point tracking capability. The key feature of the proposed solution is the adaptive hybrid voltage rectifier, which exploits both passive and active topologies combined with power prediction algorithms. The adaptive converter significantly outperforms other solutions, increasing the efficiency between 10% and 30% with respect to the only passive and the only active topologies. To assess the performance of this approach in a real-life scenario, air-flow data have been collected by deploying WSN nodes interfaced with a wind microturbine in an underground tunnel of the Metro B1 line in Rome. It is shown that, using the adaptive ac-dc converter combined with power prediction algorithms, nodes deployed in the tunnel can harvest up to 22% more energy with respect to previous methods. Finally, it is shown that using power management techniques optimized for the specific scenario, the overall system overhead, in terms of average number of sampling performed per day by a node, is reduced of up to 93%.