Tamás Kovácsházy

Iterative fuzzy model inversion

Nowadays model based techniques play very important role in solving measurement and control problems. Recently for representing nonlinear systems fuzzy models became very popular. For evaluating measurement data and for controller design also the inverse models are of considerable interest. In this paper a technique to perform fuzzy model inversion is introduced. The method is based on solving a nonlinear equation derived from the multiple-input single-output (MISO) forward fuzzy model simple by interchanging the role of the output and one of the inputs. The utilization of the inverse model can be either a direct compensation of some measurement nonlinearities or a controller mechanism for nonlinear plants. For discrete-time inputs the proposed technique provides good performance if the iterative inversion is fast enough compared to system variations, i.e. the iteration is convergent within the sampling period applied. The proposed method can be considered also as a simple nonlinear state observer, which reconstructs the selected input of the forward fuzzy model from its output using an appropriate strategy and a copy of the fuzzy model itself. It is also shown that using this observer concept completely inverted models can also be derived.

Genetic algorithms in fuzzy model inversion

Recently model-based techniques became very popular and widely used in solving measurement and control problems. For measurement data evaluation and for controller design also the inverse models are of considerable interest. The inverse models can be utilized either as a direct compensation of some measurement nonlinearity, or as a controller mechanism for nonlinear plants. In this paper an improved technique for fuzzy model inversion is introduced. Multiple-input single-output (MISO) forward fuzzy models are considered, where inversion is performed simply by interchanging the role of the output and one of the inputs. The proposed method is based on a simple nonlinear state observer, which reconstructs the selected input of a system, represented by a forward fuzzy model, from its output and the remaining inputs using an appropriate prediction-correction type control strategy and a copy of the fuzzy model itself. The overall performance of the suggested technique is highly influenced by the nature of the nonlinearity and the actual prediction-correction mechanism applied. The novelty of this paper is the introduction of genetic algorithms to control the iterative model inversion.

Transients in reconfigurable control loops

In this paper transient management techniques are investigated in a scenario where the reconfiguration or replacement of a forward-loop controller is required due to changes in the environment or in the plant. Such a change in the closed control loop may have undesirable transient effects, which may degrade the performance of the controlled system. Since the transient cancellation and reduction schemes used in open-loop systems can not be used here, new solutions are proposed for run-time transient handling.

Transient reduction in control loops in case of joint plant-controller reconfiguration

In control systems undesirable transients may occur when either the controller or the plant is reconfigured during the operation. This paper gives a new solution for the transient reduction problem in simple feedback control loops to maintain the smooth steady-state behavior even if both the plant and the controller are changed simultaneously. The transients are reduced in least-squares sense by using an anti-transient signal.

Transients in reconfigurable digital signal processing systems

To solve measurement and control problems, the processing of input data is performed typically by model-based digital signal processing (DSP) systems, which contain a representation of our knowledge about the nature and the actual circumstances of the problem at hand. If the nature or the actual circumstances change, the corresponding model should also be changed. Similarly, if the amount of knowledge about the problem increases due to measurements, an improved model can be suggested which provides better performance. As a consequence, the real-time adaptation or reconfiguration of the DSP system to be applied can hardly be avoided. The transients caused by these adaptations/reconfigurations is investigated. It is shown that for feedback systems, i.e., for infinite impulse response (IIR) filters, these transients are strongly structure-dependent and that the so-called orthogonal filter structures also provide good performance in this respect.

Parameter Estimation in Linear Electromagnetic Devices

The parameters of electrical machines can change considerably during operation due to thermal effects. Therefore, the corresponding models and the estimates of parameters can be subject to a significant bias and uncertainty, which degrade the performance of the system. In this paper, a method is developed to estimate the resistance of the coil of a linear electromagnetic actuator, i.e., of a single-coil linear solenoid. In the electrical model of the solenoid actuator, the inductance depends on the current. The inductance is identified from the transient waveform of the current (step response), and an estimate of the resistance is provided by extrapolating to the steady state of the current. Thus, the resistance can be estimated before the system reaches the steady state. The presented method is generalized to pulsewidth-modulation (PWM) drive conditions by considering the average of the current of the coil in the successive PWM cycles. This improves the suppression of measurement noise. The developed approach is demonstrated through numerical and experimental analyses.

Performance evaluation of PTPd, a IEEE 1588 implementation, on the x86 Linux platform for typical application scenarios

The paper introduces the results of performance evaluation of IEEE 1588 Clock Synchronization technology implementation on the x86 (Intel) Linux platform. First, the typical application scenarios of IEEE 1588 in modern distributed measurement systems are listed, and based on that test systems are derived for testing with different configurations. These test systems are 1) a full software implementation in which no hardware elements support IEEE 1588, 2) a partial IEEE 1588 aware system in which end nodes synchronizing clocks support hardware time stamping but network elements do not, and 3) a full IEEE 1588 aware solution in which both end nodes and network elements support the standard. The hardware assisted PTP implementation utilized for evaluation has been developed by the authors of the paper, and available from http://home.mit.bme.hu/~khazy/ptpd/. The hardware assisted implementation is based on the Linux operating kernel infrastructure specifically developed for high precision network time keeping available from the kernel version of 2.6.30, and uses Network Interface Cards with IEEE 1588 hardware time stamping available on the market. The initial results show that clock accuracy (master-slave clock difference) less than one microsecond is achievable with using a full IEEE 1588 implementation even in the case of high network traffic and slave node (a node that synchronizes its clock to a master clock) load in standard Linux. The paper also details how the implementation of the clock servo realized by fixed point arithmetic computations (quantization) effect the achievable clock accuracy and proposes enhancements to the current solution.

SNMP-based approach to scalable smart transducer networks

Nowadays on the embedded systems market there is a remarkable shift from the industry field buses to the Ethernet and internet (TCP/IP) communication technologies. The work presented in this paper aims to introduce an approach to develop TCP/IP based smart sensor and actuator networks, which are scalable, both in physical size and in the number of sensors and actuators. This approach uses the SNMP (Simple Network Management Protocol) internet technology and the IEEE 1451 Standard for Smart Transducer Interface for Sensors and Actuators.

Model-based fault-adaptive control of complex dynamic systems

Complex control applications require capabilities for accommodating faults in the controlled plant. Fault accommoda- tion involves the detection and isolation of faults, and then taking appropriate control actions to mitigate the fault effects and main- tain control. This requires the integration of fault diagnostics with control in a feedback loop. This paper discusses a generic frame- work for building fault-adaptive control systems using a model- based approach, with special emphasis on the modeling schemes that describe different aspects of the system at different levels of abstraction and granularity. The concepts are illustrated by a fault adaptive notional fuel system control example.

Transient reduction in reconfigurable control systems utilizing structure dependence

Reconfigurable control systems are promising alternatives to efficiently control complex time-variant and/or non-linear systems, such as vehicles, gas turbines, etc., which might require a certain level of fault-operational behaviour, as well. Reconfigurable control systems are designed to be able to change the controller at run-time to react to failures, compensate the time-variant and/or nonlinear nature of plant, or accommodate changes in the control objectives. However, these changes in the plant and/or in the controller may cause an intolerable transient. Management of these reconfiguration transients is an open issue. The dependence of the structure of the plant and the controller is identified as a key factor determining the reconfiguration transients. In this paper, some of the possibilities of reducing these transients are investigated. The results are demonstrated on a plant with two modes (operational and failure) controlled by properly designed PID controllers.