Greener processing of SrFe12O19 ceramic permanent magnets by two-step sintering

With an annual production amounting to 800 kilotons, ferrite magnets constitute the largest family of permanent magnets in volume, a demand that will only increase as a consequence of the rare-earth crisis. With the global goal of building a climate-resilient future, strategies towards a greener manufacturing of ferrite magnets are of great interest. A new ceramic processing route for obtaining dense Sr-ferrite sintered magnets is presented here. Instead of the usual sintering process employed nowadays in ferrite magnet manufacturing that demands long dwell times, a shorter two-step sintering is designed to densify the ferrite ceramics. As a result of these processes, dense SrFe₁₂O₁₉ ceramic magnets with properties comparable to state-of-the-art ferrite magnets are obtained. In particular, the SrFe₁₂O₁₉ magnet containing 0.2% PVA and 0.6% wt SiO₂ reaches a coercivity of 164 kA/m along with a 93% relative density. A reduction of 31% in energy consumption is achieved in the thermal treatment with respect to conventional sintering, which could lead to energy savings for the industry of the order of 7.10⁹ kWh per year.     

A magnetic MEMS actuator using a permanent magnet and magnetic fluid enclosed in a cavity sandwiched by polymer diaphragms

A magnetic microelectromechanical systems (MEMS) actuator using a small permanent neodymium-magnet surrounded by magnetic fluid (MF) was developed and characterized. The magnet is enclosed in a cavity sandwiched by two identical thin PET-sheet diaphragms and is able to move smoothly due to the MF. The diaphragms deflect when an external magnetic force is applied to the magnet. This structure was adopted to prevent the diaphragms from being stiffened by attaching or fabricating a magnetic layer on the diaphragm surface and to secure the necessary volume of magnetic material. The magnets are 2–4 mm in diameter and the cavity is 5 mm in diameter and 1 mm in depth. The diaphragms are 20 μm in thickness. Experiments showed the displacement amplitude generated at the diaphragm center was in the range of 10–50 μm for attractive and repulsive magnetic force when magnetic flux density of 4–30 mT was applied. The response was within about 1 s. The deflection profile of the diaphragms can also be varied by changing the magnet position.     

Data-driven soft sensor of downhole pressure for a gas-lift oil well

Downhole pressure is a key variable in the operation of gas-lift oil wells. However, maintaining and replacing downhole sensors is a challenging task. In this context, we design and implement a data-driven soft sensor to estimate online the downhole pressure based on other (seabed and platform) available measurements. Such application is based on a two-step procedure. In the first step, discrete-time black-box and gray-box NARX models are identified offline and independently using historical data. Both polynomial and neural models are obtained. In the second step, recursive predictions of these multiple models are combined with current measured data (of variables other than the downhole pressure) by means of an interacting bank of unscented Kalman filters. In doing so, a closed-loop model prediction is performed. Three issues are investigated in this paper concerning: (i) the usage of a filter bank rather than a single filter approach, (ii) the availability of seabed variables as inputs of the models compared to the case where only platform variables are available, and (iii) the employment of gray-box models in the filters. Experimental results along 7 months of tests indicate that such closed-loop scheme improves estimation accuracy and robustness compared to the free-run model prediction or to the use of a single unscented Kalman filter. The method employed in this paper can also be applied to other soft sensing applications in industry.     

A passivity-based controller under low sampling for speed control of PMSM

Controller performances are strongly limited by the switching frequency of the converter and the computational capacity of the target board. Therefore, in such a context the design of controllers that provide good performances under possible large sampling period length is necessary. To tackle these limitations, a digital design is described for speed control of permanent magnet synchronous machines. It is based on the interconnection and the damping assignment passivity-based control (IDA-PBC) techniques extensions to the sampled-data context.     

Model based reduced-order observers for a class of mechatronic systems with mitigation of disturbances effects using the Attractive Ellipsoid Method

State-estimation of mechatronic systems is essential because, in addition to position and velocity, there are electric and magnetic signals that must be measured, and can lead to sophisticated and expensive instrumentation systems. This paper addresses the problem of state-estimation for underactuated mechanical systems whose active joints are driven by permanent magnet dc-motors. Luenberger-type structures are designed, where the measured state variables and the dynamic model are used to construct the unavailable ones, in presence of uncertainties and disturbances as inputs. To avoid the peaking phenomenon is one of the main challenges on state observation for nonlinear systems. Underactuated mechatronic systems are not immune to this problem, which is exacerbated when external disturbances are taken into account. The major purpose here is to use a robust reduced observer to estimate the unmeasured state variables. The Attractive Ellipsoid Method provides reliable estimation of unmeasured state signals because it reduces the influence of external disturbances on the estimate error signals. This ensures that the estimated signals converge to an invariant set of minimal size around the real ones. The first design is based on the quasi-linear representation that meets the observability condition. The second considers the entire nonlinear model, which necessitates the availability of the entire position vector. The major findings are demonstrated experimentally on a non-traditional mechatronic system: the linear double pendulum system whose last joint is constrained by two linear springs. This shows a significant improvement of the estimation response, concerning robust techniques based on the linear approximation, towards its application in designing an adaptive observer to provide state and parameters estimation simultaneously, which is essential in robust and adaptive control systems.     

Data-Enabled Modeling and Analysis of Multistage Manufacturing Systems with Quality Rework Loops

In a multistage serial production line, multiple inspection stations and repair processes are typically involved to ensure high product quality. Quality rework is the activity to repair or repeat the work on the defect parts during manufacturing processes. The rework process after each inspection can add cost and cycle time to the normal process and impose negative impact on the throughput. This paper studies real-time performance of multistage serial manufacturing systems with quality rework loops and machine random failures. A production line with multiple quality rework loops is first unify by segmenting it into a set of serially connected quality rework loops. An event-based data-enabled mathematical model is developed to evaluate real-time production rate of each machine for such a system. In addition, the system properties are analyzed and permanent production loss due to quality rework loops and random machine failures are identified respectively. The permanent production loss attribution to each disruption event and machine can be used as real-time performance indicators to diagnose production system inefficiency. The mathematical model and system performance identification methodology are studied analytically and validated through numerical case studies.     

PMSM比例谐振自抗扰电流谐波抑制方法

基于扩展状态观测器的永磁同步电机转子位置和速度估算中,由于死区效应、电气元件误差、逆变器非线性因素会产生大量的电流谐波,影响位置和速度估计精度。本文提出一种基于比例谐振与自抗扰控制的PR-ADRC电流环控制策略,可以有效抑制dq坐标系下6次电流谐波,从而降低静止坐标系下5、7次谐波含量。基于MATLAB和HiGale平台对提出方法进行仿真和实验验证,结果表明改进后的电流环降低了三相电流谐波,估算反电动势波形良好,转子位置和速度估算误差降低,无位置传感器控制系统控制精度得到提高。     

基于FOPID+ADRC的永磁同步电机低速控制

永磁同步电机(permanent magnet synchronous motor,PMSM)是一个非线性、多变量、强耦合系统,具有不确定的外部干扰。为了提高其低速运行时的控制精度,采用一种改进自抗扰控制(active disturbance rejection control,ADRC)对其进行控制。首先通过插值法构建一个新的非线性函数来代替ADRC中原有的最优控制函数,使其在原点处更平滑和连续。并将此函数应用于扩张观测器(extended state observer,ESO),最后将非线性误差反馈率(nonlinear state error feedback,NLSEF)用分阶数比例积分微分(fractional-order proportion integration differentiation,FOPID)代替以提高其动态性能。经SIMULINK仿真结果表明,该控制算法在PMSM低速控制中比传统ADRC具有更快的响应速度和更好的抗干扰能力。     

基于开关序列的永磁同步电机模型预测磁链控制

为了消除传统的模型预测转矩控制(Model predictive torque control,MPTC)算法中的权重因子,减小计算量并提高稳态控制精度,本文提出了一种基于开关序列的永磁同步电机模型预测磁链控制(Model predictive flux control- switching sequence,MPFC-SS)算法。首先,通过分析电磁转矩和磁链的关系,将对转矩和定子磁链幅值的控制等效转换为对d、q轴磁链的控制,避免了权重因子的设计;其次,采用定子磁链无差拍预测控制计算所需的参考电压矢量,并根据其所在扇区选择对应开关序列;然后,基于磁链无差拍预测控制原则,计算开关序列中基本矢量的最优作用时间,有效减小电流谐波和转矩脉动,实现定子磁链的准确跟踪。最后,对传统MPTC和所提算法进行了实验对比研究,结果表明：所提算法具有计算量小、电磁转矩脉动小、电流谐波含量低等优点。     

A New Full‐Order Sliding Mode Observer Based Rotor Speed and Stator Resistance Estimation for Sensorless Vector Controlled Pmsm Drives

Sensorless control of a permanent magnetsynchronous motor (PMSM) at low speed remains a challenging task. In this paper, a sensorless vector control of PMSM using a new structure of a sliding mode observer (SMO) is proposed. To remove the mechanical sensors, a full‐order (FO‐SMO) is built to estimate the rotor position and speed of PMSM drives. The FO‐SMO, which replaces a sign function by a sigmoid function, can reduce the chattering phenomenon. In order to overcome time delay, we cancel the low pass filter. This sensorless speed control shows great sensitivity to stator resistance and system noise. To improve the robustness of sensorless vector control, a full‐order SMO technique has been used for stator resistance estimation. A novel stator resistance estimator is incorporated into the sensorless drive to compensate for the effects of stator resistance variation. The validity of the proposed FO‐SMO with a 1.1 kw low‐speed PMSM sensorless vector control is demonstrated by experiments. In this paper, experimental results for FO‐SMO, back‐EMF SMO and MRAS techniques were obtained with fixed point DSP‐based (TMS320F240).