Johann Bals

Periodic disturbance rejection of a PMSM with adaptive control algorithms

Permanent magnet synchronous motors (PMSMs) produce a parasitic oscillating torque due to several reasons. This contribution cancels the oscillating torque with adaptive control algorithms. Therefore a mathematical model of the PMSM is necessary. A model with nonlinear dynamics and a Fourier approach for the ripples is used as a mathematical description. Through comparisons between measured data and simulated data it is shown that the model assumptions are valid. The adaptive algorithm is implemented as an add-on controller to the already existing control system which consists of a feedforward part and a basis controller. The challenge is that the closed loop system has a resonant frequency and the algorithm should have the same performance for all frequencies. Experimental results show the performance and convergence of the adaptive algorithm at constant and non constant velocity.

Optimization based steady-state analysis of switched power electronic systems

This paper introduces an optimization based approach towards steady-state analysis of switched power electronic systems. The convergence performance of the optimization is improved by the estimation of the state variables in steady-state. Accurate state variable estimation can be achieved by previously simulating a set of multi-resolution approximations – averaged models of the original topological model using generalized averaging technique. An unified harmonic state space representation for a wide class of power electronic systems is presented to allow automatical generation of the averaged models with selective approximation accuracy. The proposed approach that has been implemented in Dymola is demonstrated by a pulse width modulated buck converter.

A novel Modelica signal analysis tool towards design of more electric aircraft

The development of future more electric aircraft systems is a challenging process: The respective subsystems are highly integrated to achieve an optimum efficiency and performance both at aircraft and at systems level. For master this multi-disciplinary challenge, the use of powerful modeling and simulation technologies such as Modelica in all phases of the system development process is a key success factor. In this paper, a novel Modelica signal analysis tool - Modelica Scope that is suitable for the virtual testing activities in the verification and validation phase is presented. The Modelica Scope tool is implemented in the Modelica language incorporating diverse signal measurement and analysis capabilities and can be easily integrated in all simulation environments supporting Modelica such as Dymola, SimulationX etc. The motivation, design concept as well as implementation and distinct features of the tool are discussed and illustrated.

Multi-level power quality assessment towards virtual testing of more electric aircraft

This paper introduces a multi-level power quality assessment approach towards virtual testing of more electric aircraft. Three levels with increasing accuracies are rough, approximated and exact power quality assessment. The requirement to the accuracy of power quality assessment strongly depends on different analysis jobs. With the multi-level power quality assessment approach, both sufficient accuracy and minimal cost can be ensured. Advanced steady-state analysis approaches for the switched power electronic systems with regard to the exact power quality assessment are introduced. The convergence performance of the applied steady-state analysis approaches is significantly improved by estimation of the state variables at steady-state using a generalized averaging technique. The proposed approach that has been implemented in Dymola is demonstrated by a pulse width modulated buck converter.

Worst Case Braking Trajectories for Robotic Motion Simulators

Motion simulators based on industrial robots can produce high dynamic accelerations and velocities compared to classical hydraulic hexapod systems. In case of emergency stops, large and possibly harmful accelerations can occur. This paper aims to provide an optimization procedure to generate worst case trajectories in order to test for these harmful accelerations, by maximizing the kinetic energy prior the emergency stop. The dynamical and mechanical limits of the robot are considered as constraints of the optimization criterion. An exemplary worst case trajectory is simulated using a braking model and the resulting Head Injury Criterion (HIC) is calculated and compared with older tests, using non-optimized trajectories. A significant higher, yet with the current robot dynamics not harmful HIC value can be generated.

Towards a Model-Based Energy System Design Process

Advanced modeling and simulation techniques are becoming more important in todays industrial design processes and for aircraft energy systems in specific. They enable early and integrated design as well as validation of finalized system and component designs. This paper describes the main methods and tools that can be applied for different phases of the energy design process. For demonstration, the object-oriented modeling language Modelica was chosen, since it enables convenient modeling of multi-physical systems. Based on this standard, common modeling guidelines, a modeling library template, and common interfaces have been provided. A common modeling infrastructure is proposed with considerations on additional libraries needed for local tasks in the energy design process. The developed methods and tools have been tested by means of some predefined use cases, which are performed in cooperation with diverse aircraft industrial partners. Each use case represents a specific modeling, simulation, or design task. This use case approach covers a wide range of the overall energy system design process.

Optimal control design for switched reluctance machines with right-sized modeling

Compared to the traditional electric machines, switched reluctance machines (SRM) exhibit significant improvement on production, robustness and efficiency. However, some inherent drawbacks of those kinds of machines such as noise and high torque ripple at low speed have to be well managed. Moreover, improved performance such as higher energy density, better dynamic response are to be expected. To solve these challenging issues, dedicated control strategies usually provide more efficient ways, in contrast to other methods like mechanical re-design. Accurate and right-sized mathematical models are crucial for the controller synthesis using iteration based multi-objective optimization approach. Due to the strong nonlinear characteristics of SRMs, deriving the right-sized models of a SRM is really a challenging work. In this paper, the analytical representation of SRM magnetic characteristics with adjustable complexity are derived and used for multi-objective optimization based controller synthesis. Furthermore, inverse modeling technique is applied to achieve the exact mapping between commanded current and torque for the close-loop current control, which can significantly improve the system performance relating to torque ripple, control accuracy, etc. The simulation results of a 22KW 16/12, 4 phase SRM is presented to illustrate the proposed design approaches.

Wavelet library for Modelica

Wavelet analysis is being widely used in different fields for signal processing to increase efficiency and flexibility. A wavelet library has been a standard component in many simulation programs. However, wavelet analysis has not yet been included in Modelica as a standard component. To fill this blank, a comprehensive wavelet library has been developed for Modelica. This library includes fifteen commonly used wavelet families. It can carry out continuous transform, forward and inverse discrete transforms, and multi-level decomposition and reconstruction in one-dimensional space. In addition, special application tools for multi-resolution analysis and wavelet denoising are provided. Moreover, some examples are given to provide the users a quick start point to build up their own algorithms. This library was programmed and tested according to the Modelica language specification 3.2 under the Dymola platform version 2013. The test results prove the functionalities of the library.

Modelling and Use of an Aircraft Electrical Network Simulation for Harmonics Consideration in Generator Design

In upcoming and future airplanes, more nonlinear electrical loads and loads behaving nonlinearly will be connected to the power distribution network. This induces advanced demands on the network to keep the power quality. The generator design also has to face the new demands and constraints. Trade offs between performance, weight, and latterly power quality have to be made and design choices have to be backed up by qualitative and quantitative measures. In a prior study a design tool chain was elaborated for an externally excited synchronous generator. In the first part of this paper this study is concluded. An outlook is given on the generator size demanded in relation to the portion of nonlinear loads in the network, in case the industrial standards are kept unchanged. The power quality criteria can be gained by time-domain simulation. This simulation can be computationally extensive, especially in case of a large ramp up time to the operating point. Therefore in the second part of this paper an approach for advanced initialization using equivalent models in frequency domain is given. Both frequency and time domain models were embedded component wise using the modelling language Modelica. Thus, simulation based studies can be performed within a single graphical and object-oriented modelling and simulation suite. A novel rectifier model in time-domain is presented, which has benefits for the harmonic initialization.

Gearbox Ripple Rejection of Robots Using Observer and Adaptive Control Theory

Abstract Robots are often run with permanent magnet synchronous motors (PMSM) with a high ratio gearbox. Both parts can produce parasitic oscillations (ripples), which let the robot shake at tool center point. The gearbox ripple problem is more complicated to be solved with control theory because only motor side sensors should be used. Due to the internal model principle gearbox side information is necessary to solve the problem. The first algorithm uses an observer to get gearbox side information where the second algorithm uses a gearbox side rate sensor. The algorithms are tested with a nonlinear SISO problem and with a nonlinear MIMO system. In both cases the ripples are canceled with an adaptive controller which estimates the phase and magnitude of the ripple. This adaptive controller is designed separately and is added to the existing basis controller. The algorithms are tested in simulation and on a testbed, which is an industrial application.