Controllable Degrees Of Freedom Research Articles

Joint antenna selection and beamforming for frequency diverse multiple‐input multiple‐output radar in mainlobe spectrum interferences and signal‐dependent interferences coexistence scenarios

AbstractDue to the controllable degrees of freedom of frequency diverse array in the distance dimension, the frequency diverse multiple‐input multiple‐output (FDA‐MIMO) radar can easily deal with mainlobe interference, which is often difficult to solve in traditional phased arrays. Nevertheless, the performance of FDA‐MIMO radar will suffer from degradation in the scenario where spectrum interferences and signal‐dependent interferences coexist. In order to solve this problem, a novel FDA‐MIMO radar framework via antenna switching is proposed. Based on this framework, an effective method for jointly optimising antenna selection and beamforming against spectrum interferences and signal‐dependent interferences is developed. The resulting optimization problem is nonconvex and NP‐hard owing to the integer constraints caused by antenna selection. By relaxing the integer constraints, the original problem can be transformed into a convex optimization form and an iterative reweighting strategy is used to force the obtained solution to satisfy the integer constraints. Simulation examples show that the proposed algorithm has better performance in output signal‐to‐interference‐plus‐noise ratio (SINR) and beampattern radiation performance than the existing competitive methods.

Simultaneously focusing electromagnetic and acoustic waves by double-physical-fields null medium

A novel double-physical-fields lens that can simultaneously focus acoustic and electromagnetic waves into a given region is designed based on double-physical-fields null medium, which can be realized by metal plates with subwavelength separations/thicknesses and precisely designed lengths. Numerical simulations show the proposed double-physical-fields lens can create exactly the same focusing effect for both electromagnetic and acoustic waves, i.e., the same focal spot size and efficiency at the same focal length. Four typical lens with different output surfaces are studied, which shows different focusing characteristics, e.g., noodle-shaped focal spot, tiny focal spot, and capsule-shaped focal spot. With the help of the designed double-physical-fields lens, an additional degree of freedom for control can be provided by simultaneously focusing acoustic and electromagnetic waves, which may lead to wider range of applications than single-field focusing.

Loss Balance and Transient DC-Bias Suppression Strategies in Three-Level DAB Converters Modulated With Five DoFs

In the three-level (3 L) neutral-point-clamped (NPC) dual-active-bridge (DAB) converter, both sides of the converter can adapt to higher DC bus voltage, and more control degrees of freedom (DoFs) are provided compared to the conventional DAB converter. In the PWM generating technique with 5 DoFs, loss imbalance may develop in inner switches and outer switches because the leading or lagging arm is introduced, affecting system reliability. In addition, the transient DC-bias issue may also arise in the 3L-NPC-DAB converter modulated with 5 DoFs, leading to the transformer saturation. In this paper, two strategies are proposed to suppress the loss imbalance and the transient DC-bias in the current stress and magnetizing branches. It is also general and applicable for SPS, DPS, and TPS modulations. Furthermore, the loss balance strategy and DC-bias suppression strategy are applied in the PWM generation technique simultaneously without additional components. With the proposed solutions, the loss imbalances of inner switches and outer switches are suppressed and DC-bias in the integral of voltages on both sides of the 3L-NPC-DAB converter is abolished. The effectiveness of the proposed strategies is validated by a series of experiments conducted under varying situations.

Generic Dynamically Reconfigurable Battery With Integrated Auxiliary Output and Balancing Capability

Modular multilevel converters (MMC) and cascaded H-bridge (CHB) converters are established concepts in ultra-high-voltage systems. In combination with batteries, these circuits allow dynamically changing the series/parallel configuration of the battery modules, also known as reconfigurable batteries. A large body of research discusses applications of such systems in grid-storage and electromobility with a single load, such as an electric drive. However, most studies neglect the presence of auxiliary loads, which require additional voltage levels and isolation from the high-voltage battery. This paper proposes a decoupling method that can fork a second (galvanically isolated) output off a reconfigurable dc battery without negatively affecting the main output by exploiting the many control degrees of freedom in the modular circuit. The proposed system provides a nonisolated port for the dc link of the motor-drive inverter(s), while generating an additional isolated output at another voltage for auxiliaries. The auxiliary output benefits from the interleaving effect, which increases the operating frequency of the transformer and reduces the filter size. The solution does not require additional active switches for the auxiliary port and can operate with a wide range of voltages. The integrated auxiliary circuit can also balance the modules during idling and charge/discharge cycles. Both simulation and experiments validate the analysis.

Lane-changing control for hybrid electric vehicles with dedicated hybrid transmission based on robust model predictive control

Car-following and lane-changing are extremely important for vehicles. The traditional adaptive cruise control (ACC) strategy has various drawbacks due to the complicated driving conditions. A new control strategy of robust model predictive control (RMPC) for car-following and lane-changing is proposed based on a new type of hybrid electric vehicle (HEV) with dedicated hybrid transmission (DHT-HEV). The control model includes a vehicle model, a following and lane-changing model and an RMPC controller. The vehicle model integrates the DHT-HEV and dynamic models with a longitudinal dynamic model, seven degrees of freedom (DOF) vehicle dynamic model and three DOF control model. The following and lane-changing model is described as car-following and lane-changing models of two-quintic function. The RMPC controller is used to balance the control of vehicle longitudinal and lateral dynamics with the lateral acceleration disturbance. Simulation results demonstrate that the RMPC controller can track the reference trajectory during two lane-changing process when the test scenarios of different accelerations are set compared with the conventional ACC control. Different Np (predictive horizon) and Nc (control horizon) are also analysed to improve the solving performance of RMPC. Results indicate that the solving performance of the system is optimal when Np = 30 and Nc = 1. Furthermore, different weight coefficient matrixes ( Q and R) are taken into the consideration by coordinating the car-following performance and lateral stability. Accordingly, the controllers of RMPC-LC, RMPC-ACC and RMPC-LA are set, demonstrating that the control of RMPC-LA best balances two aspects and is always within a safe car-following distance. Meanwhile, the hardware in the loop (HIL) is utilised to verify the effectiveness of the proposed RMPC control strategy, which comprises model compilation, the establishment connection between the D2P ECU and the simulator and control input.

Attitude constraint-based recovery for under-actuated AUVs under vertical plane control during the capture stage

The landed docking method is one of the most widely used underwater recovery methods because it imposes fewer restrictions on AUV configuration and applies to a wide range of applications. During the capture stage, the AUV and the recovery device are in close proximity, and if the attitude of the AUV fluctuates significantly, a collision may occur and cause damage. Existing studies for the common underactuated AUV do not effectively constrain the non-directly controlled degrees of freedom, posing a significant safety risk to the underwater recovery in the capture stage. To address this issue, a vertical plane control strategy that considers the safety interval of non-direct controlled degrees of freedom is proposed to keep the attitude angle within the safety interval during the docking process. To begin, the non-directly controlled AUV's pitching motion is analyzed and simplified to demonstrate that it has input-to-state stability during the capture stage, and an estimate of its uniform ultimate bound is provided so that the motion boundary can be estimated. Then, based on the backstepping method, a thrust-gain-constrained vertical surface control strategy is proposed: for the directly controlled heaving motion and rolling motion, precise control is achieved through a reasonable configuration of control parameters; for the non-directly controlled pitching motion, the thrust-constrained gain is calculated through the ultimate bound so that the force applied to the pitch degrees of freedom of the thruster is constrained and the purpose of indirect control is achieved. Using this strategy, the pitch motion is guaranteed to be inside the safe interval, resulting in accurate, safe, and quick recovery control during the capture stage.

Control of Two-Degree-of-Freedom Inertial Appendages of a Small-Scale Jumping Robot for Enhanced Terrestrial and Aerial Maneuverability

Small-scale jumping robots are promising for rugged terrain locomotion due to their strong ability to overcome obstacles. Appendages are widely adopted by them to improve maneuverability and thus better adapt to real-world applications. However, existing appendages of small-scale jumping robots have limited operational modes or control degrees of freedom (DOFs), constraining their functionality. Here, we present a maneuvering mechanism with two-DOF inertial appendages to improve the maneuverability of jumping robots. It allows the robot to function diversely in different phases by changing the operation behavior. The terrestrial maneuverability is endowed by advanced appendage–ground interactions. By smoothly driving the appendages to control two-DOF body attitude before triggering the jump, the robot allows the omnidirectional jumping trajectory modulation. By controlling the rhythmic disengagement and contact between the appendages and the flat substrate, the crawling locomotion mode is achieved. In the aerial maneuver, the robot redirects its angular momentum to stabilize its two-DOF body attitude through rapid appendage manipulation. Such multifunctional appendages provide a versatile solution for jumping robots to improve maneuverability.

Impedance Modeling and Stability Analysis of Energy Controlled Modular Multilevel Converter

In recent years, the modular multilevel converter (MMC) has been widely used in high-voltage dc (HVDC) transmission, which, however, brings about various stability issues, such as sub- -synchronous oscillation (SSO). To deal with these stability issues, many active and passive damping methods have been proposed. In fact, the MMC itself has more control degrees of freedom compared to the two-level voltage-source converter (VSC), such as internal energy, circulating current, etc., which can be exploited to improve the system stability. Based on the idea, the internal energy of MMC is utilized to suppress the SSOs in this paper. The frequency-coupling impedance model of MMC with energy controller is first developed based on the harmonic state-space (HSS) method by considering the internal dynamics and all control links, which is verified by frequency scanning result in simulation. The stability analysis of the energy controlled MMC-HVDC for wind farm integration is conducted and a modified energy control structure of MMC is also proposed to further improve the stability of the interconnected system.

Towards ideal focusing of diffused light via optical wavefront shaping

Controllable optical propagation, such as forming diffraction-limited optical focusing, beyond the diffusion limit in biological tissue or tissue-like scattering media, has been desired for long yet considered challenging. In the past two decades, optical wavefront shaping (WFS) has been proposed and has progressed, demonstrating its remarkable potential. That said, inherent tradeoffs still exist among optimization speed, control degree of freedom, and energy gain, which has hindered wide applications of the technology. Most recently, an analogue optical phase conjugation system was developed, equipped with stimulated emission light amplification that effectively achieves the least tradeoff ever, yielding high-gain and high-speed performance of optical focusing through dynamic thick media.

Network Interface Program for Actuator Controllers for Pseudo-Dynamic Hybrid Simulation

ABSTRACT A network interface program for controllers (NICON) for pseudo-dynamic hybrid simulations is presented. The program is implemented as an independent program residing between the simulation model and an actuator controller with various functions necessary for hybrid simulations, such as communication, coordinate transformation, error compensation. These functions are generalized to allow for a generic configuration of actuator setup theoretically with any number of control points and control degrees of freedom. Application examples of NICON to hybrid simulations of civil infrastructures subjected to earthquakes or fire are presented.

Generation, Topological Charge, and Orbital Angular Momentum of Off-Axis Double Vortex Beams

Compared with the on-axis vortex beam and the off-axis single vortex beam, the off-axis double vortex beam has more control degrees of freedom and brings rich physical properties. In this work, we investigate theoretically and experimentally the generation, topological charge (TC), and orbital angular momentum (OAM) of off-axis double vortex beams. It is demonstrated that the tilted lens method can detect not only the magnitudes and signs of two TCs of the off-axis double vortex beam but also the spatial distribution of the TCs. Moreover, the average OAM value of the off-axis double vortex beam decreases nonlinearly as the off-axis distance increases, although its TC is independent of the off-axis distance of phase singularities. The results indicate that the average OAM of the off-axis double vortex beam can be easily controlled by changing the relative position of two-phase singularities, thereby realizing the applications of multi-degrees of freedom particle manipulation, optical communication, and material processing.

Vibration Suppression of a Specific Harmonic Component by Teeth Flux Density Control Using Multi-Phase MATRIX Motor

In recent years, progress in power semiconductor switching devices has created more additional advantages that can be realized using multi-phase inverter-fed motors. The authors propose a MATRIX motor to realize electric motors with higher functionalities than conventional electric motors. Since the MATRIX motor is driven by H-bride inverters connected with each phase winding, it has a high degree of freedom in control. Moreover, these inverters can change their connections to different phase coils to realize a wide operating range. The voltage equation of each mode can be expressed using the transformation matrix when the winding connection is changed. Therefore, we call the proposed motor MATRIX motor. In addition, since motors are being applied to various applications that operate within proximity of people, further quietness of the motor is required. In this paper, we propose a method to suppress vibration caused by a specific harmonic order radial direction electromagnetic force via teeth flux density control using the MATRIX motor. The specific order radial force and vibration are suppressed by utilizing two features of the MATRIX motor. One is a high degree of freedom of current control owing to multi-phase drive and the other is local flux density observation. The effectiveness of the proposed method was clarified using experimental results.

Open-Circuit Fault-Tolerant Vector Control for Five-Phase SPMSM Based on Five-Phase Six-Leg Inverter

Five-phase permanent-magnet synchronous motor (PMSM) has the ability of fault-tolerant operation, which is beneficial for high reliability occasions. A fault-tolerant current vector control strategy based on five-phase six-leg inverter is proposed for open-circuit fault in this article. It deals with single-, double-, and triple-phase fault conditions. First, the overall control scheme is established based on the mathematical model of five-phase surface-mounted PMSM. To release more control degrees of freedom, the constraint for the sum of fault-tolerant phase currents is removed, and the control variates method is used to calculate the optimal fault-tolerant currents. Furthermore, to achieve the current tracking, the corresponding reduced-order current transformation matrices are derived, and the corresponding main power topology, the five-phase six-leg voltage source inverter (VSI), is established. The unbalanced operation of the topology is investigated, the equivalence to the full-bridge VSI is proved, and the voltage utilization and voltage unbalance of five phase half-bridge, full-bridge, and six-leg inverter are compared. Then, the corresponding carrier-based PWM control strategy based on zero-sequence injection has been proposed, which is equivalent with the three-dimensional space vector PWM algorithm and is computationally efficient. The experimental results confirm the effectiveness of the proposed fault-tolerant control strategy.

Analysis and robust control of system with uncertainty and disturbance using equivalent-input-disturbance approach

This paper addresses the control problem of an uncertain system suffering from an exogenous disturbance. A new degree of control freedom is developed to handle the problem based on the equivalent-input-disturbance (EID) approach. The effect of the disturbance and uncertainties is equivalent to that of a fictitious disturbance on the control input channel, which is called an EID. A state observer and an improved EID (IEID) estimator are devised to produce an estimate that is used to compensate for the disturbance and uncertainties in a control law. A second-order low-pass filter is employed in the estimator to provide a way to solve a tradeoff between disturbance rejection and noise suppression. The slope of the Bode magnitude curve at high frequencies is two times larger for the IEID estimator than for a conventional one. This makes the IEID estimator less sensitive to measurement noise and more practical. Sufficient analyses reveal the mechanism of disturbance rejection, uncertainty attenuation, and noise suppression of an IEID-based control system. A theorem is derived to guarantee system stability and a procedure is presented for system design. Simulations and experiments of the position control of a magnetic levitation system are carried out to show the validity of the presented method.

A Study and Implementation of Inductive Power Transfer System Using Hybrid Control Strategy for CC-CV Battery Charging

In this paper, a hybrid control strategy is studied and implemented on an Inductive Power Transfer (IPT) system to simultaneously realize zero-voltage switching (ZVS) and constant current (CC) and constant voltage (CV) battery charging. A steady-state analysis of pulse frequency modulation was conducted, based on the characteristic of voltage gain versus switching frequency, and CC and CV charging modes were promised. The ZVS of the inverter was obtained by satisfying the minimum requirement of full discharge of the junction capacitor on the MOSFETs using a commutation current during the dead-time interval. Two control degrees of freedom are needed to realize the two control targets. This hybrid control strategy adopts a self-oscillating (SO) control to achieve ZVS and phase shift (PS) control and a constant output for the series–series (SS)-compensated IPT system. To validate the hybrid control strategy, a 1.6 kW prototype with 360–440 V input voltage and 250–400 V output voltage was built and the experimental results show that the peak efficiency can reach 96.1%. Compared with the conventional variable frequency (VF) control, the hybrid control method proves that an additional control variable can fulfill the control target in a more flexible manner, which makes the switching frequency close to the resonant frequency during the charging process, minimizing the reactive current in the resonant tank and improving system efficiency.

Design of a Compact Planar Magnetic Levitation System with Wrench–Current Decoupling Enhancement

Magnetic levitation technology has promising applications in modern manufacturing, especially for fine-motion stage and long-range omnidirectional planar motors. This paper presents the development of a compact planar maglev prototype with the potential to achieve both applications to increase flexibility for the manufacturing system. The planar stator is designed by using optimized square coils arranged in the zigzag configuration, which provides a better uniform magnetic flux density compared with another configuration. The stator is a compact and portable module with built-in current amplifier units. The single-disc magnet mover is deployed with five controllable degrees of freedom. The cross-coupling effect is decoupled by a precomputed Lorentz force based wrench—current transformation matrix stored in the lookup table. A 2-D linear interpolation is implemented to enhance decoupling effectiveness which is offered via discrete lookup data. Experiments with motion-tracking cameras and a basic controller demonstrate the results of fine step motion of 10 and 20 µm and rotation steps of 0.5 and 1.0 mrad. The potential for multidirectional material handling is represented by a total horizontal translation range of 20 mm by 20 mm with a maximum air gap of 26 mm and a total rotation range of 20 degrees for both roll and pitch.

A Dual-Transformer-Based Hybrid Dual Active Bridge Converter for Plug-in Electric Vehicle Charging to Cope With Wide Load Voltages

A dual-transformer-based hybrid dual active bridge (DAB) converter for plug-in electric vehicle charging to cope with wide load voltages is introduced in this article. The control degrees of freedom are extended by splitting the leg and transformer of the conventional DAB converter (CDABC) in two parts. Based on the numerical analysis, the full-domain four-variable closed-form optimal trajectories targeting at the minimum root mean square value of the leakage inductor current is attainted, and the unified-segmental control strategy is proposed to handle the working modes shifting without the current inrush. As a result, the conduction losses and switching losses can be significantly reduced in boost mode compared to CDABC. The discussed converter and control strategy are verified by a 1.0-kW prototype.

High-gain and high-speed wavefront shaping through scattering media.

Wavefront shaping (WFS) is emerging as a promising tool for controlling and focusing light in complex scattering media. The shaping system's speed, the energy gain of the corrected wavefronts, and the control degrees of freedom (DOF) are the most important metrics for WFS, especially for highly scattering and dynamic samples. Despite recent advances, current methods suffer from trade-offs that limit satisfactory performance to only one or two of these metrics. Here, we report a WFS technique that simultaneously achieves high speed, high energy gain, and high control DOF. By combining photorefractive crystal-based analog optical phase conjugation (AOPC) and stimulated emission light amplification, our technique achieves an energy gain approaching unity, more than three orders of magnitude larger than conventional AOPC. The response time of ~10 μs with about 106 control modes corresponds to an average mode time of about 0.01 ns/mode, which is more than 50 times lower than some of the fastest WFS systems to date. We anticipate that this technique will be instrumental in overcoming the optical diffusion limit in photonics and translate WFS techniques to real-world applications.

Simulation of yolk-shell nanostructures optical properties

A yolk-shell structure is a double-layer hollow nanostructure, which is composed of a shell, a cavity, and a core. The yolk-shell structures have fascinating properties because of their attractive localized surface plasmon resonance (LSPR) feature, which arouses considerable interest in both optically active nanostructures and practical applications. Compared with the single metal nanostructure, a yolk shell has a more controlled degree of freedom, superior optical properties, and potential applications in photocatalysis and solar cell. However, the preparation of yolk shells often requires multiple steps, making it difficult to control the geometric parameters accurately, which leads to uncontrollability of the experimental results. Therefore, it is necessary to study how the size and composition of a yolk shell affect LSPR properties to further guide and optimize the experimental process. Based on the discrete dipole approximation (DDA) method, the absorption spectra, near-field enhancement, and sensing properties of yolk-shell nanoparticles were analyzed. By adjusting the diameters of cavities, cores, shells, and the materials of the shells, we study the influence of yolk-shell structures on the LSPR properties. In detail, the thicknesses of the shells are set from 5 to 20 nm, the diameters of the cavities being set from 50 to 70 nm and the diameters of the yolks are set from 20 to 40 nm. The materials of the shells are set to be dielectric TiO2 and metallic Au, and both of them have Au cores. It is found that Au@Au yolk shells with large cavities or thick shells have better absorption efficiency, but Au @ TiO2 yolk shells are just the opposite. For near-field intensity, Au@Au yolk shells are higher than Au @ TiO2. A yolk-shell structure with larger cavity has smaller full width at half maximum. These results can effectively guide the design of yolk-shell structures for sensing and optoelectronic applications based on LSPR.

Dynamic Operability Analysis for Process Design and Control of Modular Natural Gas Utilization Systems.

Process modularization is an alternative process design and construction framework, in which modular units are independent and replaceable blocks of a process system. While modular plants have higher efficiency and are safer to construct than conventional stick-built plants (Roy, S. Chem. Eng. Prog. 2017, 113, 28-31), they are significantly more challenging to operate because of the loss in the control degrees of freedom that comes with process integration and intensification (Bishop, B. A.; Lima, F. V. Processes 2021, 9, 2165). To address this challenge, in this work, operability analyses are performed to consider the design and operation of modular units. Initially, a steady-state operability analysis is employed to find a set of feasible modular designs that are able to operate considering different modular plant conditions. A dynamic operability analysis is then applied to the feasible designs to identify the operable designs that are capable of rejecting the operational disturbances. Lastly, a closed-loop control measure is introduced to compare the performances of the different operable designs. The proposed approach is implemented in a modular membrane reactor to find a set of operable designs considering different natural gas wells, and the respective closed-loop nonlinear model predictive control performance of these units is evaluated.