Hybrid Modulation Strategy with Voltage Balancing Control for Four-level Neutral-point Clamped Converters

Capacitor voltage imbalance in four-level(4L)neutral-point clamped(NPC)converters is a direct factor hindering their application.In particular,when they are applied in motor drives,space vector pulse-width modulation(SVPWM)is a more popular scheme,but conventional 4L SVPWM cannot achieve the voltage balancing control of DC-link capacitors,is complex to implement,and requires costly computation.A hybrid modulation method with capacitor voltage-balancing control for 4L NPC converters is proposed.The proposed method is achieved using three-level(3L)SVPWM and two-level(2L)carrier-based pulse-width modulation(CPWM)based on the concept of"4L=3L+2L".Thus,it can be easily implemented on a digital chip because the modulation process is nearly identical to that of 3L SVPWM without the more cumbersome 4L SVPWM algorithm.Meanwhile,any proven optimization scheme of 3L SVPWM can be directly applied to the proposed method to further improve performance.Simulation and experimental results for a 4L active NPC converter demonstrate the effectiveness of the proposed method.

Balancing control of unicycle robot by using sliding control

This paper discusses about balancing control of unicycle robot.Unicycle robot consists of pitch which acts like inverted pendulum and roll which acts like reaction wheel pendulum.The robot which does not have actuator located in yaw axis is made to derive the simple dynamics.Lagrange equation is applied to deriving dynamic equations.Obtained dynamic equations are used to design the sliding mode control.State variables of the designed control are pitch angle and roll angle.Sliding mode control has chattering problem,which is eliminated by using the sigmoid function as switching function.Finally the control performance and eliminated chattering problem is verified by simulation.

Capacitor Voltage Imbalance Mechanism and Balancing Control of MMC When Riding Through PTG Fault

Modular multilevel converter (MMC) based fault ride through (FRT) control is a promising solution to deal with the pole-to-ground (PTG) fault in high voltage direct current (HVDC) system. However, when MMC switches to the FRT control, capacitor voltage imbalance between upper and lower arms will occur, resulting in the deterioration of FRT performance. This letter provides a comprehensive analysis for the imbalance issue from the perspective of fundamental frequency circulating current (FFCC). It is found the imbalance during FRT stage will not expand continuously, but converge to a certain value gradually. The specific imbalance degree is closely associated with the amplitude of FFCC. In order to solve the imbalance issue, an open-loop balancing control is proposed. By introducing a fundamental frequency feedforward item to the inherent circulating current control, the proposed method can not only balance the capacitor voltages, but also minimize the amplitude of FFCC, and consequently the power loss of MMC during FRT process can be reduced. Finally, simulation results of PSCAD/ EMTDC verify the validity of theoretical analysis.

Fully Decoupled Branch Energy Balancing Control Method for Modular Multilevel Matrix Converter Based on Sequence Circulating Components

The modular multilevel matrix converter(M3C)is a potential frequency converter for low-frequency AC transmission.However,capacitor voltage control of high-voltage and largecapacity M3C is more difficult,especially for voltage balancing between branches.To solve this problem,this paper defines sequence circulating components and theoretically analyzes the influence mechanism of different sequence circulating components on branch capacitor voltage.A fully decoupled branch energy balancing control method based on four groups of sequence circulating components is proposed.This method can control capacitor voltages of nine branches in horizontal,vertical and diagonal directions.Considering influences of both circulating current and voltage,a cross decoupled control is designed to improve control precision.Simulation results are taken from a low-frequency transmission system based on PSCAD/EMTDC,and effectiveness and precision of the proposed branch energy balancing control method are verified in the case of nonuniform parameters and an unbalanced power system.

Simplified Cluster Voltage Balancing Control Based on Zero-sequence Voltage Injection for Star-connected Cascaded H-bridge STATCOM

The cluster DC voltage balancing control adopting zero-sequence voltage injection is appropriate for the starconnected cascaded H-bridge STATCOM because no zerosequence currents are generated in the three-phase three-wire system.However,as the zero-sequence voltage is expressed in trigonometric form,traditional control methods involve many complicated operations,such as the square-root,trigonometric operations,and inverse tangent operations.To simplify cluster voltage balancing control,this paper converts the zero-sequence voltage to the dq frame in a DC representation by introducing a virtually orthogonal variable,and the DC components of the zero-sequence voltage in the dq frame are regulated linearly by proportional integral regulators,rather than being calculated from uneven active powers in traditional controls.This removes all complicated operations.Finally,this paper presents simulation and experimental results for a 400 V±7.5 kvar star-connected STATCOM,in balanced and unbalanced scenarios,thereby verifying the effectiveness of the proposed control.

Comprehensive predictive control of neutral-point voltage balancing for back-to-back three-level NPC converters

A comprehensive predictive strategy was proposed for the neutral-point balancing control of back-to-back three-level converters. The phase currents at both sides and the DC-link capacitor voltages were measured for the prediction of the neutral-point current. A quality function was found to balance the neutral-point, and a metabolic on-times distribution factor was used as a predicator to minimize the quality function at each switching state. Simulation results show that the proposed method produces smaller ripples in tested signals compared with the established one, namely, 9.15% less in a total harmonic distortion(THD) of line-to-line voltage, 1.08% less in the THD of phase current, and 0.9 V less in the ripple of the neutral-point voltage. The obtained experimental results show that the main harmonics of the line-to-line voltage and the phase current in the proposed method are improved by 10 d B and 6 d B, respectively, and the ripple of neutral-point voltage is halved compared to the established one.

ADAPTIVE CONTROLLER AND ITS APPLICATION IN FORCE SYSTEM OF ASYMMETRIC CYLINDER CONTROLLED BY SYMMETRIC VALVE

Partial pressure, system vibration and asymmetric system dynamic performance exit in asymmetric cylinder controller by symmetric valve hydraulic system. To solve this problem in the force control system, model reference adaptive controller is designed using equilibrium point stability theory and output error equation polynomial. The reference model is selected in such a way that it meets the system dynamic performance. Hardware configuration of asymmetric cylinder controlled by asymmetric valve hydraulic system is replaced by intelligent control algorithm, thus the cost is lowered and easy to application. Simulation results demonstrate that the proposed adaptive control sheme has good adaptive ability and well solves asymmetric dynamic performance problem. The designed adaptive controller is fairly robust to load disturbance and system parameter variation.

Postural control deficits identify lingering post-concussion neurological deficits

Concussion,or mild traumatic brain injury,incidence rates have reached epidemic levels and impaired postural control is a cardinal symptom.The purpose of this review is to provide an overview of the linear and non-linear assessments of post-concussion postural control.The current acute evaluation for concussion utilizes the subjective balance error scoring system(BESS) to assess postural control.While the sensitivity of the overall test battery is high,the sensitivity of the BESS is unacceptably low and,with repeat administration,is unable to accurately identify recovery.Sophisticated measures of postural control,utilizing traditional linear assessments,have identified impairments in postural control well beyond BESS recovery.Both assessments of quiet stance and gait have identified lingering impairments for at least 1 month post-concussion.Recently,the application of non-linear metrics to concussion recovery have begun to receive limited attention with the most commonly utilized metric being approximate entropy(Ap En).Ap En,most commonly in the medial-lateral plane,has successfully identified impaired postural control in the acute post-concussion timeframe even when linear assessments of instrumented measures are equivalent to healthy pre-injury values;unfortunately these studies have not gone beyond the acute phase of recovery.One study has identified lingering deficits in postural control,utilizing Shannon and Renyi entropy metrics,which persist at least through clinical recovery and return to participation.Finally,limited evidence from two studies suggest that individuals with a previous history of a single concussion,even months or years prior,may display altered Ap En metrics.Overall,non-linear metrics provide a fertile area for future study to further the understanding of postural control impairments acutely post-concussion and address the current challenge of sensitive identification of recovery.

Optimal Control Strategy for Buck Converter Under Successive Load Current Change

A new control algorithm is presented for digitally controlled dc-dc converters to achieve a fast response under a successive load-change.Under the steady-state condition,the tight voltage regulation is processed by the conventional digital PID compensator.If the load disturbance is significant,the controller switches to an optimal control scheme.With the integration of the capacitor current,the proposed algorithm predicts the optimal switch over time based on the charge balance control,and the minimal voltage derivation and recovery time are thus achieved when the load current has a successive load-change.The method for calculating the optimal switch over time is described,and the implementation of the proposed algorithm with a digital controller is treated in detail.Furthermore,the simulation and experiment results are provided to validate the effectiveness of the approaches.

Balance recovery control for biped robot based on reaction null space method

A biped walking robot should be able to keep balance even in the presence of disturbing forces. This paper presents a step strategy concept of biped walking robot that is stabilized by using reaction null space method. The called ＂step strategy＂ can be modeled by means of the reaction null space method that introduced earlier to tackle dynamic interaction problems of free-floating robots, or moving base robots in general. 6-DOF biped robot model simulations are used to confirm the validity.

Bionic autonomous learning control of a two-wheeled self-balancing flexible robot

This paper presents an OCPA （operant conditioning probabilistic automaton） bionic autonomous learning system based on Skinner＇s operant conditioning theory for solving the balance control problem of a two-wheeled flexible robot. The OCPA learning system consists of two stages： in the first stage, an operant action is selected stochastically from a set of operant actions and then used as the input of the control system; in the second stage, the learning system gathers the orientation information of the system and uses it for optimization until achieves control target. At the same time, the size of the operant action set can be automatically reduced during the learning process for avoiding little probability event. Theory analysis is made for the designed OCPA learning system in the paper, which theoretically proves the convergence of operant conditioning learning mechanism in OCPA learning system, namely the operant action entropy will converge to minimum with the learning process. And then OCPA learning system is applied to posture balanced control of two-wheeled flexible self-balanced robots. Robot does not have posutre balanced skill in initial state and the selecting probability of each operant in operant sets is equal. With the learning proceeding, the selected probabilities of optimal operant gradually tend to one and the operant action entropy gradually tends to minimum, and so robot gradually learned the posture balanced skill.

Control System of Two-Wheel Self-Balancing Vehicle

This study mainly concerns a motion model and the main control algorithm of two-wheel self-balancing vehicle models.Details of the critical parameters fetching and output value of two-wheel self-balancing vehicle models are introduced,including those concerning balance control,speed control and direction control.An improved cascade coupling control scheme is proposed for two-wheel vehicles,based on a proportional-integral-derivative(PID)control algorithm.Moreover,a thorough comparison between a classic control system and the improved system is provided,and all aspects thereof are analyzed.It is determined that the control performance of the two-wheel self-balancing vehicle system based on the PID control algorithm is reliable,enabling the vehicle body to maintain balance while moving smoothly along a road at a fast average speed with better practical per-formance.

The intervention effect of virtual reality technology on patients recovering from traumatic brain injury: a meta analysis

Objective:To systematically evaluate the intervention effect of virtual reality technology on patients recovering from traumatic brain injury.Methods:The computer retrieved CNKI,VIP,Wan Fang,Embase,The Cochrane Library and PubMed database,and collected randomized controlled trials of virtual reality technology combined with routine rehabilitation training and simple routine rehabilitation training on patients recovering from traumatic brain injury.The retrieval period was from the establishment of the database to July 2019.Two researchers independently screened the literature,extracted the data and evaluated the risk of bias in the included studies.RevMan 5.3 software was used for analysis.Results:A total of 7 articles were included.Meta-analysis results showed that virtual reality technology could significantly improve balance function(mean difference(MD)=3.72,95%confidence interval(CI)(2.61,4.83),P<0.001),daily living ability(MD=11.87,95%CI(10.42,13.32),P<0.001),and exercise ability(MD=3.83,95%CI(2.30,5.36),P<0.001).In the aspect of posture control ability,the trajectory motion length,trajectory velocity and peripheral area were improved(standardised mean difference(SMD)=0.80,95%CI(1.19,0.41),P<0.0001),(SMD=0.95,95%CI(1.45,0.45),P=0.0002),(SMD=0.69,95%CI(1.11,0.26),P=0.001).Conclusion:Virtual reality technology can significantly improve the balance function,daily living ability,motor function and postural control ability of patients recovering from cerebral trauma.Limited by the quantity and quality of the included studies,the above conclusions need to be verified by more high-quality studies.

Stability Analysis of DC-DC Converters with Energy Balance Control

With variation of parameters,DC-DC converters may change from a stable state to an unstable state,which severely degrades the performances of the converter system.In this article,by establishing the state-space average model,the stability and bifurcation of a boost and a buck-boost converter with energy balance control(EBC)is studied,respectively.Then the stability boundary and stable parameter domains are accurately predicted.The obtained stability region provides a parameter regulating range for converter design.Furthermore,compared with the one-cycle control(OCC)method,the EBC possesses an extended stable parameter domain,while avoiding unstable behaviors such as Hopf bifurcation,Quasi-periodic Oscillation even chaos,etc.The theoretic analysis is well validated through simulation and experiment.

Overview on Submodule Topologies,Modeling,Modulation,Control Schemes,Fault Diagnosis,and Tolerant Control Strategies of Modular Multilevel Converters

In the present scenario,modular multilevel converters(MMCs)are considered to be one of the most promising and effective topologies in the family of high-power converters because of their modular design and good scalability;MMCs are extensively used in high-voltage and high-power applications.Based on their unique advantages,MMCs have attracted increasing attention from academic circles over the past years.Several studies have focused on different aspects of MMCs,including submodule topologies,modeling schemes,modulation strategies,control schemes for voltage balancing and circulating currents,fault diagnoses,and fault-tolerant control strategies.To summarize the current research status of MMCs,all the aforementioned research issues with representative research approaches,results and characteristics are systematically overviewed.In the final section,the current research status of MMCs and their future trends are emphasized.

Control Method of Three-level Neutral-point-clamped Inverter Based on Voltage Vector Diagram Partition

A new modulation approach was presented for the control of neutral-point （NP） voltage variation in the three-level NP-clamped voltage source inverter, and the average NP current model was established based on vector diagram partition. Thus, theory base was built for balancing control of NP potential. Theoretical analysis and experimental results indicate that the proposed method for NP balancing control vector synthe- sizing concept based can make the average NP current zero, and do not influence NP potential within every sample period. The effectiveness of proposed research approach was verified by simulative and experimental results.

A hybridized electromagnetic-triboelectric nanogenerator designed for scavenging biomechanical energy in human balance control

For human beings of different ages and physical abilities, the inherent balance control system is ubiquitous and active to prevent falling, especially in motion states. A hybridized electromagnetic-triboelectric nanogenerator (HETNG) is prepared to harvest biomechanical energy during human balance control processes and achieve significant monitoring functions. The HETNG is composed of a symmetrical pendulum structure and a cylinder magnet rolling inside. Four coils are divided into two groups which form into two electromagnetic generators (EMGs). Besides, two spatial electrodes attached to the inner wall constitute a freestanding mode triboelectric nanogenerator (TENG). With a rectification circuit, the HETNG presents a high output power with a peak value of 0.55 W at a load of 160 Ω. Along with human balance control processes during walking, the HETNG can harvest biomechanical energy at different positions on the trunk. Moreover, the HETNG applied in artificial limb has been preliminarily simulated with the positions on thigh and foot, for monitoring the actions of squat and stand up, and lifting the leg up and down. For the elder that walks slowly with a walking aid, the HETNG equipped on the walking aid can help to record the motions of forwarding and unexpected falling, which is useful for calling for help. This work shows the potential of biomechanical energy-driven HETNG for powering portable electronics and monitoring human motions, also shows significant concerns to people lacked action capability or disabled.

Planning and Control for Passive Dynamics Based Walking of 3D Biped Robots

Efficient walking is one of the main goals of research on biped robots. Passive Dynamics Based Walking （PDBW） has been proven to be an efficient pattern in numerous previous approaches to 2D biped walking. The goal of this study is to develop feasible method for the application of PDBW to 3D robots. First a hybrid control method is presented, where a previously proposed two-point-foot walking pattern is employed to generate a PDBW gait in the sagittal plane and, in the frontal plane, a systematic balance control algorithm is applied including online planning of the landing point of the swing leg and feedback control of the stance foot. Then a multi-space planning structure is proposed to implement the proposed method on a 13-link 3D robot. Related kinematics and planning details of the robot are presented. Furthermore, a simulation of the 13-link biped robot verifies that stable and highly efficient walking can be achieved by the proposed control method. In addition, a number of features of the biped walking, including the transient powers and torques of the joints are explored.

Measurement, modelling, and closed-loop control of crystal shape distribution： Literature review and future perspectives

Crystal morphology is known to be of great importance to the end-use properties of crystal products, and to affect down-stream processing such as filtration and drying. However, it has been previously regarded as too challenging to achieve automatic closed-loop control. Previous work has focused on controlling the crystal size distribution, where the size of a crystal is often defined as the diameter of a sphere that has the same volume as the crystal. This paper reviews the new advances in morphological population balance models for modelling and simulating the crystal shape distribution （CShD）, measuring and estimating crystal facet growth kinetics, and two- and three-dimensional imaging for on-line characterisation of the crystal morphology and CShD. A framework is presented that integrates the various components to achieve the ultimate objective of model-based closed-loop control of the CShD. The knowledge gaps and challenges that require further research are also identified.

Capacity Configuration of Energy Storage Systems for Echelon Utilization Based on Accelerated Life Test in Microgrids

Retired power battery construction energy storage systems(ESSs)for echelon utilization can not only extend the remaining capacity value of the battery,and decrease environmental pollution,but also reduce the initial cost of energy storage systems.In this paper,an ESS constructed of retired power batteries for echelon utilization in microgrids(MGs)is considered.Firstly,considering the influence of different discharge depths on the battery life cycle,the correlation equation between the state of charge(SOC)and the state of health(SOH)is established.Secondly,the accelerated life test method,based on the inverse power law coefficient equation,is proposed,and it is used to evaluate the reliability of the ESS.Finally,according to the SOC characteristics,the dynamic security margin of the ESS is established.The life cycle cost,supply-demand balance and ESS balanced control are comprehensively considered,and the location and capacity of energy storage in MGs are determined.It is simulated using the IEEE-RTS 24 node system;the results show that the investment cost of the ESS is reduced and the operational life is prolonged.