Analysis and Design of Spatial Six-Step Controllers for Permanent Magnet Synchronous Machines

Background: Ankle sprain is a common sports injury. While the effects of static constraints in stabilizing the ankle joint are relatively well understood, those of dynamic constraints are less clear and require further investigation. Purpose: This study was undertaken to evaluate the dynamic stability of the ankle joint during the landing phase of running and stop-jump maneuvers in athletes with and without chronic ankle instability (CAI). Study Design: Controlled laboratory study. Methods: Fifteen athletes with CAI and 15 age-matched athletes without CAI performed running and stop-jump landing tasks. The dynamic ankle joint stiffness, tibialis anterior (TA)/peroneus longus (PL) and TA/gastrocnemius lateralis (GL) co-contraction indices, ankle joint angle, and root-mean-square (RMS) of the TA, PL, and GL electromyographic signals were measured during each task. Results: During running, the CAI group exhibited a greater ankle inversion angle than the control group in the pre-landing phase (P = .012-.042) and a lower dynamic ankle joint stiffness in the post-landing phase (CAI: 0.109 ± 0.039 N·m/deg; control: 0.150 ± 0.068 N·m/deg; P = .048). In the stop-jump landing task, athletes with CAI had a significantly lower TA/PL co-contraction index during the pre-landing phase (CAI: 49.1 ± 19; control: 64.8 ± 16; P = .009). In addition, the CAI group exhibited a greater ankle inversion (P = .049), a lower peak eversion (P = .04), and a smaller RMS of the PL electromyographic signal in the post-landing phase (CAI: 0.73 ± 0.32; control: 0.51 ± 0.22; P = .04). Conclusion: Athletes with CAI had a relatively inverted ankle, reduced muscle co-contraction, and a lower dynamic stiffness in the ankle joint during the landing phase of sports maneuvers and this may jeopardize the stability of the ankle. Clinical Relevance: Sports training or rehabilitation programs should differentiate between the pre-landing and post-landing phases of sports maneuvers, and should educate athletes to land with an appropriate ankle position and muscle recruitment.

Negative stiffness (NS) structures have obvious advantages in attenuating low-frequency vibration. Although most existing NS structures exhibit good damping effects, their stability is poor, limiting their application in complex mechanical systems. To improve their damping and stability, a negative stiffness structure composed of rubber spring and elastic beam (NSS-RB) is proposed. Its elastic properties are studied via numerical modeling. Numerical and experimental results show NSS-RB has high static and low dynamic stiffness, achieving good damping and stability. Applied to a power battery package damping system, NSS-RB outperforms the rubber spring (RS) system in vibration reduction: the low-frequency vibration attenuation rate exceeds 90%, with good ride comfort and no instability.

Aiming to isolate disturbance vibration for heavy machines with low frequency, a novel hydro-pneumatic vibration isolator with high-static and low-dynamic (HSLD) stiffness is proposed, which contains bellows structure as elastic element and pressurized gas and incompressible liquid as working media. Due to that the natural frequency of isolation system with such isolator is close to zero and loading capacity can be adjusted by the gas pressure, the proposed device is termed as pneumatic near-zero frequency (NZF) vibration isolator. To obtain the mathematical model of isolator’s stiffness, the quasi-static derivation based on gas state equation is carried out first. Results prove that the presented isolator possesses ideal high-static and low-dynamic stiffness, which is also verified by the experimental data measured by a quasi-static test. The proportion of gas volume to total volume of gas and liquid media, respectively, in bellows and cylinder chambers are significant physical parameters, which dominate the nonlinearity extent of isolator’s stiffness. Different from most existing isolators, the proposed isolator includes fluidic damping and friction damping. The former is expressed by classic square-velocity-type nonlinear model, and the latter is modeled as Coulomb damping. To obtain dynamic response and vibration isolation transmissibility, the harmonic balance method is applied. A direct current term is added in the trial solution, which reflects the asymmetry of dynamic response. In respect of transmissibility analysis, square-velocity nonlinear damping brings a favorable advantage that it can ensure the fine force transmissibility in both resonance region and effective isolation band. This conclusion holds consistently under base motion excitation. Friction damping cannot give the same conclusion. Further comparison with a linear vibration isolator exhibits that the HSLD stiffness characteristics of the NZF isolator breaks through the trade-off between large loading capacity and small static deformation, and the square nonlinearity of fluid damping is able to overcome the dilemma that weak linear vicious damping is beneficial for isolation performance within the effective isolation frequency band, but cannot suppress resonance amplitude and transmissibility. And the experimental transmissibility is in good agreement with the analytical result. Besides, the influences of excitation variation on isolation performance are estimated theoretically. Due to the hardening stiffness, overload acceleration will cause the increase in linearized natural frequency of NZF isolator system, and thus, isolation effectiveness will be reduced.

In this paper, a novel current control technique is proposed to control both active and reactive power flow from a renewable energy source feeding a microgrid system through a single-phase parallel-connected inverter. The parallel-connected inverter ensures active and reactive power flow from the grid with low-current total harmonic distortion even in the presence of nonlinear load. A p-q theory-based approach is used to find the reference current of the parallel-connected converter to ensure desired operating conditions at the grid terminal. The proposed current controller is simple to implement and gives superior performance over the conventional current controllers, such as rotating frame proportional-integral controller or stationary frame proportional resonant controller. The stability of the proposed controller is ensured by direct Lyapunov method. A new technique based on the spatial repetitive controller is also proposed to improve the performance of the current controller by estimating the grid and other periodic disturbances. Detailed experimental results are presented to show the efficacy of the proposed current control scheme along with the proposed nonlinear controller to control the active and reactive power flow in a single-phase microgrid under different operating conditions.

This paper studies distributed feedback optimization for linear uncertain multiagent systems subject to a class of external disturbances with unknown frequencies. Specifically, the objective is to regulate the outputs of the multiagent system to a common value that minimizes a prescribed global cost function, a sum of local cost functions. A crucial strategy is to develop a distributed optimizer that generates reference signals for the low-level decentralized tracking controllers. For the control synthesis, we use the normal form to derive an internal-model-based control law for the reference tracking and disturbance rejection, and use an adaptive control technique to handle the unknown frequencies of the disturbances. The coupling between the optimizer and the physical control systems is dealt with by a composite Lyapunov function. It is shown that the proposed solution guarantees the boundedness of the closed-loop signals and ensures that the output of each agent converges to the desired minimizer for any initial state. A numerical example demonstrates the effectiveness of the proposed method.

A typical boring bar is a metal cutting tool with large overhang ratio, due to which it is characterized by low dynamic stiffness. Therefore, during cutting process, it is susceptible to cutting instability, known as machine tool chatter. In this paper, the use of an active dynamic absorber to actively control machine tool chatter in a boring bar is studied. An active dynamic absorber is designed such that it can be easily assembled with a commercially available steel boring bar. A piezoelectric pusher is used as the actuator for the active dynamic absorber. The dynamic equations of the boring bar with active dynamic absorber are calculated from experimentally obtained frequency response functions of the system. Optimal control theory is applied to the dynamic equations to calculate state variable feedback parameters. The state variable feedback is implemented using a Digital Signal Processing (DSP) chip. Cutting tests were performed with this setup for different cutting conditions, and for different overhangs of the boring bar. Stable cutting operations were performed using the boring bar with active dynamic absorber, for length to diameter (L/D) ratio upto 9.

Buildings are often constructed on a continuous layer of vibration isolation to reduce vibrations and structure-borne noise. There are many vibration isolation products (rubber mats, textiles, polymer foams), but none fulfils all requirements in terms of load-bearing capacity, performance, and cost. In previous work, we have shown that silica aerogel particle beds display a low resonance frequency and correspondingly high vibration isolation performance. Loose silica aerogel granules are not a practical vibration isolation solution. In order to guide the future development of dedicated vibration isolation products based on aerogels, we determine the vibro-acoustic properties of a variety of existing commercial and R&D stage mesoporous composites, that have been developed for thermal insulation applications. The sample set includes monolithic aerogels (polyurethane), silica aerogel composites (aerogel – fibers, aerogel impregnated foams, aerogel bound with polymer foam), glued fumed silica-fiber boards, and nanoporous polymer foam composite boards. The silica aerogel and fumed silica composites display low resonance frequencies (down to 8 Hz for 40 mm, strongly dependent on composite type) and a low dynamic stiffness and loss factor over a wide range of static loads. The polymer aerogel, nanoporous foam and polymer-bound silica aerogel granule board all display higher resonance frequencies, consistent with their higher static stiffness. Although optimized for thermal insulation rather than vibration isolation, many of the tested silica aerogel and fumed silica composites are competitive with the best vibration isolation products on the market in terms of vibration isolation performance. The diversity of materials tested informs on which approaches, materials, and materials combinations are most promising to target vibration isolation.

A compact X-shaped mechanism based 3-DOF anti-vibration unit with enhanced tunable QZS property

This paper deals with the problem of robust tracking and disturbance rejection for a linear time-invariant system where the uncertainty of the system is represented in a structured form and the output to be controlled may be different from the measurement output. First, the problem is considered in a rather classical setting in that the required property of tracking and disturbance rejection can be attained as long as the resulting closed-loop system remains stable. Conditions for solvability of the problem are given and two algorithms are presented for designing controllers having the robust tracking and disturbance rejection property. Second, the problem of robust output regulation with robust stability is formulated as one of finding a controller such that the resulting closed-loop system satisfies an additional requirement of robust stability and thus the output regulation property can be maintained for all perturbations of uncertain parameters within a prescribed set. A procedure based on a high gain observer approach is proposed to solve this problem.

One of the main problems of electrohydraulic drives is relatively low dynamic load stiffness due to compressibility of oil. Sudden load variations can cause significant deviations of the position of the drive and, consequently, a reduced precision of the controlled process. This has led to a partial substitution of electrohydraulic drives by electromechanical drives in a low power range recently. One of the approaches to increase dynamic stiffness of a cylinder is to raise valve dynamics. Thus, the system can react to a control deviation and provide the cylinder with a compensating flow faster. The objective of this paper is to show the development of a stiff cylinder drive using a new high-response servovalve the hybrid valve. In contrast to a conventional servovalve with an unmovable sleeve, the idea of the hybrid valve is to actuate both the spool and the sleeve simultaneously in opposite directions. Using a piezo-actuator as sleeve drive provides the hybrid valve with very high dynamics in the range of small valve opening, which should be sufficient to increase the disturbance rejection of the cylinder. The performance of the valve prototype and of the cylinder will be shown, and application fields will be discussed in this work.

The rheological properties of magnetorheological elastomers are influenced by magnetically sensitive fillers and the elastomer matrix. The ability to respond to an external magnetic field is imparted by the fillers, while the load-bearing capability is determined by the matrix type. In this paper, the effect of matrix material on the properties of magnetorhological elastomer is explored experimentally. Carbonyl iron particle content is varied by 0%, 15% and 25% by volume to produce magnetorheological elastomer samples using natural rubber, silicone rubber and nitrile butadiene rubber matrices. Forced transmissibility test approach was employed to evaluate the field induced variations in the dynamic stiffness and loss factor of magnetorheological elastomers. The dynamic stiffness of nitrile butadiene rubber is the highest, while that of silicone rubber is the lowest. Addition of carbonyl iron particles significantly improves stiffness, although these gains depend on the properties of unfilled matrix. The addition of 25% by volume of carbonyl iron particle increased the dynamic stiffness of a silicone rubber matrix based magnetorheological elastomer by 67.78%, while the similar change in magnetorheological elastomer with nitrile butadiene rubber matrix was 38.58%. The field dependent response of magnetorheological elastomers is governed by the matrix and ferromagnetic filler concentration. These qualities are higher in magnetorheological elastomer with a low initial dynamic stiffness matrix and lower in magnetorheological elastomers with a stiffer matrix.

This paper proposed a new neural network algorithm with fuzzy iterative learning controller and applied to a certain turbofan engine rotor speed control system. A dynamic neural network was used to identify the plant on-line. The control signal was then calculated iteratively according to the responses of a reference model and the output of identified plant. A fuzzy logic block with four very simple rules was added to the loop to improve the overall loop properties. Experimental results demonstrate the proposed control strategy provides better disturbance rejection and transient properties than those achieved by conventional mechanical-hydraulic controller(MHC) and analogue engine electronic controller(AEEC). At the same time, it can improve transitional quality in control system, and meet the demands of high performance and high control accuracy in turbofan engine

In this paper, an improved predictive functional control (PFC) scheme for permanent magnet synchronous motor (PMSM) control system is proposed, on account of the standard PFC method cannot provides a satisfying disturbance rejection performance in the case of strong disturbances. The PFC-based method is first introduced in the control design of speed loop, since the good tracking and robustness properties of the PFC heavily depend on the accuracy of the internal model of the plant. However, in orthodox design of prediction model based control method, disturbances are not considered in the prediction model as well as the control design. A minimumorder observer (MOO) is introduced to estimate the disturbances, which structure is simple and can be realized at a low computational load. This paper adopted the MOO to observe the load torque, and the observations are then fed back into PFC model to rebuild it when considering the influence of perturbation. Therefore, an improved PFC strategy with torque compensation, called the PFC+MOO method, is presented. The validity of the proposed method was tested via simulation and experiments. Excellent results were obtained with respect to the speed trajectory tracking, stability, and disturbance rejection.

In direct adaptive inverse control (DAIC), parameters of the controller are estimated directly in the feed-forward loop. In this paper, we propose a closed loop direct adaptive inverse control (CDAIC) scheme which improves tracking, error convergence, and disturbance rejection properties of DAIC. CDAIC is applicable to stable or stabilized, minimum or nonminimum phase linear plants. CDAIC and DAIC are compared using computer simulations for disturbance free and disturbed discrete type nonminimum phase linear plants. CDAIC shows better results compared to DAIC in terms of mean square tracking error and disturbance rejection.

The tuning of PID controllers can essentially be posed as the problem of selecting open-loop zeros such as to obtain a desired system response. In this paper, the general case wherein stable open-loop system zeros can be cancelled is considered, allowing more freedom in placing open-loop zeros, as opposed to just two zeros in the case of a PID controller. Subsequently, optimal open-loop zeros are computed such as to minimize the deviation from a desired reference impulse response, while maintaining the relative degree and the type of the reference system, thus giving the controlled system desired input tracking and disturbance rejection properties. Further, due to the inverse compensation of the plant zeros, the controller is in general causal when the relative degree of the plant and the reference system are similar.