Estimating forest plant area index (PAI) with the simultaneous separation of overstory vegetation (OV) and understory vegetation (UV) is essential to study forest carbon and water cycles. Measuring PAI of OV and UV using conventional field surveys within forests is challenging, particularly for subtropical regions of China, where terrain slope can exceed 10°. The effective PAI (PAIe) instead of PAI for UV is usually measured by the conventional method of subtracting PAIe of OV from total PAIe. We find PAIe obtained using this strategy is underestimated by 25%–85%. Thus, we propose an approach to estimate PAIe and PAI of both OV and UV on sloped terrain by using single-station (SS) terrestrial laser scanner (TLS) data. Results are verified by comparing them with multistation (MS) TLS data acquired coincidentally. Then we analyze the effects of horizontal range and slope correction on PAI estimated from SS TLS data. The results show that the correlation between SS and MS PAI (PAIe) is strong, with$R^{2}$of 0.88 (0.81) and 0.52 (0.75) (${p}~\lt 0.01$) for OV and UV, respectively. We recommend imposing a horizontal 20-m radius range for data acquired from SS TLS for PAI estimations. The difference between PAI estimations with and without a slope correction can be neglected. These results demonstrate that SS TLS data can serve as a means for PAI estimations of both OV and UV, which should help facilitate large-scale estimation in the subtropical forests of China.

In order to improve the effective transfer range and then enhance the interoperability of magnetic coupling wireless power transfer (MC-WPT) systems, an electromagnetically induced transparency (EIT)-like MC-WPT system is proposed in this paper, which can maintain a reasonable level of power and efficiency over a wide range of transfer distance. Firstly, the circuit model of the tri-coil MC-WPT system is presented along with several key concepts, including EIT mechanism and eigen parameters. Then the energy efficiency characteristic of the system in eigen state is investigated, based on which the energy efficiency improvement principle and corresponding parameter design condition of the EIT-like mechanism are derived. Finally, practical systems are designed, simulated and measured to show the accuracy and effectiveness of the proposed method. The simulation and experimental results show that, with the proposed method, the effective transfer range that takes into account both output power and transfer efficiency is greatly improved. The method is particularly suitable for the design of electric vehicle charging piles, based on which the effective charging of vehicles with different chassis heights on a charging pile can be achieved.

A design methodology for making magnetic coupling wireless power transfer (MC-WPT) systems resonate at given frequencies is proposed in this paper. Proposing such a method not only can improve the energy efficiency against frequency splitting, but also can satisfy the requirement of frequency standards and then promote its industrial application. The method is based on eigenvalues configuration and comprehensively considers all electric parameters. The quantitative relationship between the performance indexes and electric parameters is derived, based on which the expected electric parameters can be quickly and accurately determined. The design theory and design flow are provided, and practical systems are designed, simulated and measured to show the effectiveness of the proposed method. The results show that the proposed method can: 1) eliminate frequency splitting to make MC-WPT systems resonate at a given frequency; 2) utilize frequency splitting to make MC-WPT systems resonate at two given frequencies.

Reliable communication is of great significance for the intelligentization of DC microgrids. A new signal and power composite modulation (SPCM) method is proposed to achieve Power Line Communication (PLC) for Photovoltaic panels and Switched Reluctance Generator (SRG) based DC microgrids using Current Chopping Control (CCC) method. By tuning the reference value of chopping current, voltage ripples with different frequencies can be brought out on the power bus for transmitting data. At the receiver side, Fast Fourier Transform (FFT) method is employed for analyzing the voltage ripples to demodulate the carrier frequency and extract the transmitted data. The simulation results are presented for verifying the feasibility of the proposed SPCM strategy.

In this paper, the Pulse Train (PT) control strategy is tentatively applied to the Parallel-connected Buck Converters (PBC) with current-sharing ability. However, in Continuous Conduction Mode, undesirable low-frequency voltage oscillation will be brought about by the PT control. Therefore, the Capacitor-Current-Feedback based PT (CCF-PT) control is newly proposed to eliminate the low-frequency voltage oscillation. The experimental results indicate that, the proposed CCF-PT control method can successfully achieve effective suppression of low-frequency oscillation by properly configuring the capacitor current feedback coefficient.

With the rapid intelligentzation of smart grid, power converters with higher performances and lower cost are necessarily required. Pulse Train (PT) controlled power converters have the advantages of fast response and simple structure, but are also suffered from undesired low frequency oscillation as operated in continuous conduction mode (CCM). In this paper, a PT controlled buck converter with dual output interfaces is newly proposed by introducing the coupled inductors. By adjusting the coupling coefficient and the second side voltage of the coupled inductor, the low-frequency oscillation of output voltage could be effectively suppressed. Experimental results are presented to validate the practicability of this new PT controlled converter.

Power converter characterized with high controllability and has been widely popularized in smart grid. A novel three-level voltage source converter structured by H-Bridge for AC-DC-AC conversion is presented in this paper. The operation principle and control strategies of the proposed converter are investigated. A new simplified PWM strategy with redundant switching combination processor is adopted to control and balance the capacitors. Furthermore, the output performance of the proposed converter is evaluated by experimental results.

Although multi current-valley control can be used to eliminate the low-frequency oscillation for pulse train controlled DC/DC converters operated in continuous conduction mode (CCM), the number of preset current-valley values are necessarily increased, which will increase the complexity of the controller. Meanwhile, the output voltage ripple is uncontrollable and varies with the changes of the load. Thus a sliding current-valley based PT (SCV-PT) control method is proposed in this paper. The approximate discrete-time models of SCV-PT is derived and used for theoretical analysis. The simulation and experimental results are present to prove the feasibility and practicability of SCV-PT control method.

In order to improve the DC-bus voltage control performance and suppress the transient fluctuation of DC-bus voltage, a nonlinear disturbance observer (NDO) based DC-bus controller is proposed in this paper. The feed-forward compensation of active power disturbance is achieved by the proposed controller to reject the influence of parameter variations and the mismatched disturbance from the output terminals. The active power disturbance of feed-forward compensation can be effectively estimated by the NDO without requirement of measuring the load and sources power, which will reduce the hardware cost and also increase the reliabilities of DC microgird. The feed-forward compensation gain is designed by taking convergence rate of the observer and the influence of compensation gain on the stability of DC microgrid into account. Simulations are carried out to verify the performance of the proposed control method in consideration of different disturbances.

The main purpose of this paper is to explore the spontaneous synchronization of two Chua's circuits based on coupled memristors with cubic nonlinearity. An analog circuit is designed to simulate the magnetic flux controlled memristor with coupling effects and then applied to implement the coupled Chua's circuit. Simulation is carried out to numerically exhibit the strange attractors and spontaneous synchronization caused by increasing the coupling strength.

High voltage gain DC-DC converters as used in photovoltaic, fuel cells and other low-voltage distributed generation system have played a significant role in the large-scale promotion of new energy generation. A high step-up integrated DC-DC converter based on one active switch is proposed in this paper by making use of advantages of the quadratic Boost converter (QBC) and the voltage multiplying modular (VMM). Firstly, VMM was embedded into QBC, and this two modules share the same input DC source and the active switch. And then the output terminals of these two modules were connected in series sharing the same output diode and filter capacitor. The above combination constitutes the newly proposed integrated converter. One attractive performance of this converter is the gain can be not only controlled by the duty ratio but also the turn ratio of the coupled inductor in VMM. In addition, the low voltage stress across the switch can be achieved since the switch is not directly clamped at the high output voltage, which is conducive for optimizing the energy transmission efficiency. The zero input current ripples can be achieved by reasonably configuring the values of the fully coupled inductor as well as the auxiliary inductor. The operation principles and the steady state performances of the proposed converter are verified by the experimental prototype.

This paper explores the dynamic behavior of dual flux coupled memristor circuits in order to further ascertain fundamental theory of memristor circuits. Different cases of flux coupling are mathematically modelled where two memristors are connected in both series and parallel, with consideration given to the polarity of each device. The dynamic behavior is characterized based on the constitutive relations, with a variation of memductance represented in terms of flux, charge, voltage and current. The agreement between theoretical and simulation analyses affirm the memristor closure theorem with coupled memristor circuits behaving as a different type of memristor with higher complexity.

Tremendous efforts have been put into dissecting the inherent characteristics and potential applications of Memcapacitor (MC), which possesses unique abilities of storing both information and energy [1]. Recently, coupling is disclosed as the third relation beyond series and parallel connections of memristive circuits in [2], of which the mechanical dynamic coupling of MCs is taken into account for illustration purpose. Coupled MCs could provide us more opportunities for developing new electronic devices with unique functions. However, very few works currently focus on the practical implementation of coupled MC emulators and its possible application in electronic circuits. In this letter, a practical emulator of coupled MC is newly proposed and then used for structuring Relaxation Oscillators (ROs), of which the period and duty cycle of output oscillating signal can be purposefully controlled in virtue of the coupling action.

The main purpose of this paper is to explore the oscillating characteristics of an astable multivibrator based on memristor and 555 timer. An analog circuit is utilized to simulate magnetic flux controlled memristor and then applied to implement the astable multivibrator. The voltage across the memristor emulator is analytically calculated. Simulation is carried out to confirm the theoretical analysis. The agreement between simulation and analytical calculation validates the feasibility of using memritor to achieve astable multivibrator.

The memcapacitor has the potential to be the most useful new component of recent years due to its functional and dynamic similarities to the memristor but with much lower power requirements. Although research interest is growing, there are very few memcapacitor based circuits. Here a memcapacitor based chaotic circuit is described with a novel method to emulate a charge controlled memcapacitor.

The main purpose of this paper is to design a circuit possessing meminductive property by making use of a new floating memristive emulator. A concise analog circuit is proposed to simulate a flux controlled memristor and this analog memristive emulator is then used to design a meminductive circuit. To confirm the design effectiveness, PSpice is hence introduced and all the simulated waveforms provide conclusive evidences to validate the correctness of this new memristor emulator and meminductive circuit.

After the successful solid state implementation of memristors, a lot of attention has been drawn to the study of memristor based chaotic circuits. In this paper, a Twin-T notch filter feedback controller is designed and employed to control the chaotic behavior in a memristor based chaotic circuit. Both simulation and experiment results validate the proposed control method.