Piet Vanassche

On the difference between two widely publicized methods for analyzing oscillator phase behavior

This paper describes the similarities and differences between two widely publicized methods for analyzing oscillator phase behavior. The methods were presented in [3] and [6]. It is pointed out that both methods are almost alike. While the one in [3] can be shown to be, mathematically, more exact, the approximate method in [6] is somewhat simpler, facilitating its use for purposes of analysis and design. In this paper, we show that, for stationary input noise sources, both methods produce equal results for the oscillators phase noise behavior. However, when considering injection locking, it is shown that both methods yield different results, with the approximation in [6] being unable to predict the locking behavior. In general, when the input signal causing the oscillator phase perturbations is non-stationary, the exact model produces the correct results while results obtained using approximate model break down.

Symbolic modeling of periodically time-varying systems using harmonic transfer matrices

This paper presents an algorithm for generating symbolic expressions for the harmonic transfer functions of linear periodically time-varying (LPTV) systems, like mixers and PLLs. The harmonic transfer functions characterize the up- and downconversion behavior of the wanted and unwanted signal components. The algorithm, which the authors call Symbolic HTM, is based on the organization of the harmonic transfer functions into a harmonic transfer matrix. This representation allows one to manipulate LPTV systems in a way that is similar to linear time-invariant systems, making it possible to generate symbolic expressions relating the overall harmonic transfer functions to the building block parameters. These expressions can be used as design equations or as parameterized models for use in simulations or synthesis. Comparison of the symbolic models with numerical data shows them to be accurate, even for small numbers of modeling terms.

Optimal Control of Traction Motor Drives Under Electrothermal Constraints

Peak torque and power density requirements for traction motor drives continue to increase, while demands on reliability are getting increasingly stringent as well. With the knowledge that most of the failure mechanisms are related to excessive temperature (cycling), thermal management is a key for increasing performance, without jeopardizing reliability. This paper proposes a control strategy for active thermal management of permanent magnet synchronous motor (PMSM) drives, based on real-time estimation and feedback of switching device and motor temperatures. By regulating the switching frequency and current control limit, critical components can be safeguarded from excessive temperature rise. Furthermore, optimal dq-current control vectors are calculated within the temperature and voltage constraints, to maximize the drives efficiency and speed-torque envelope. Hence, the control strategy enables the drivetrain to operate safely at maximum attainable performance limits. The strategy is experimentally validated on an 11-kW PMSM drive for a number of representative vehicle loads, including a maximum standstill torque test, a maximum acceleration test, and a driving cycle test.

PeopleMover: an example of interdisciplinary project-based education in electrical engineering

In this paper, the authors present an interdisciplinary design project that was introduced into the electrical engineering curriculum as an example of project-based education. Within the project, students design and implement an autonomous rail system intended for people transportation from system specifications down to a fully working system including hardware and software. The educational assets and drawbacks are discussed as well as the practical issues of setting up a large educational project. The current state of the project and an overview of future improvements based on student feedback are highlighted as well.

Behavioral modeling of (coupled) harmonic oscillators

This paper presents a method for constructing behavioral models for harmonic oscillators and sets of coupled harmonic oscillators. These models are useful for system-level simulations and tradeoff analysis. The modeling method allows capturing the steady-state and transient behavior of the target oscillators through a sequence of transformations of the circuit equations. Model extraction is based on ideas of perturbation analysis and averaging. The resulting models are evaluated at a computational cost that is well below that of solving the original circuit equations. Another major advantage of the approach is the explicit separation of the slow- and fast-varying components of the oscillators behavior. This allows using a much larger time step during numerical simulations. The technique is illustrated for both a single harmonic oscillator and a harmonic quadrature oscillator.

Layout and performance of the power electronic converter platform for the VSYNC project

This paper presents the power electronic platform used for the VSYNC project. In this project, inverters are controlled in such a way as to exhibit a virtual rotational inertia towards the grid, in order to limit grid frequency variations in grids containing a high share of inverter-connected DER. First the layout and operation of the platform are described in detail, showing its versatility for research purposes. Next the performance of the platform is illustrated using experimental results obtaining using a grid-connected inverter in a laboratory setup.

PMSM Drive Current and Voltage Limiting as a Constraint Optimal Control Problem

This paper proposes an algorithm for optimal current trajectory control of (interior) permanent magnet synchronous motor (PMSM) drives, considering the motor/inverter current and voltage limitations. In contrast to common voltage feedback flux-weakening strategies, it applies a differential rather than a conventional integral approach to regulate the current vector. Linearized motor equations are used to express torque and voltage amplitude changes relative to the actual operating point as a function of dq-current increments. Optimal dq-current step adjustments are calculated from these approximate voltage/torque increment lines according to machine state feedback. This allows for the constraint optimization problem to be solved in real time. Each iteration, the dq-current setpoint vector is incrementally shifted in an optimal direction, rapidly converging to a solution within the voltage/current limits, which minimizes error on torque request with maximum efficiency. Extensive experimental results on an interior PMSM setup demonstrate the strategys dynamic performance and robustness.

A Generalized Method for Computing Oscillator Phase Noise Spectra

This paper presents a generalized semi-analytic method for computingoscillator phase noise spectra, including the details veryclose to the oscillation frequency. The starting point is a generalrelation between an oscillators output power spectral density andthe characteristics of the input noise processes. For weak inputnoise processes that vary sufficiently fast over time, this relation reducesto an analytic expression. For cases that do not satisfy theseconditions, the relation is, in part, evaluated numerically. This isaccomplished using techniques for exponential data fitting. The resultingmethod is able to compute oscillator phase noise spectra fora wide range of input noise characteristics.

Dynamic DC-link voltage adaptation for thermal management of traction drives

Power density and reliability specifications for motor drives in traction applications are getting increasingly stringent. The main challenge in meeting these conflicting requirements, is managing heat dissipation. A drives peak torque rating is limited by switching device temperatures which must be kept below critical values at all times for the sake of reliability, preferably without major hardware adaptations. In this challenge lies a large potential for advanced control algorithms. This paper proposes a PMSM drive control strategy which combines active thermal management with dynamic DC-link voltage adaptation. The bus voltage level is adjusted to the required PMSM terminal voltage in each operating point. Doing so, switching losses can be reduced at low speed by lowering the bus voltage. At high speed, the voltage level is boosted and field-weakening operation and the associated additional losses are avoided. An 11 kW PMSM drive, with an active front-end controlling the bus voltage, is used as a test setup to mimic a series-hybrid drivetrain. Compared to a fixed DC-link voltage, efficiency maps show a significant inverter loss reduction at low speed. This results in lower switching device temperatures which in turn allows a higher peak torque rating.

Constructing Symbolic Models for the Input/Output Behavior of Periodically Time-Varying Systems Using Harmonic Transfer Matrices

A new technique is presented for generating symbolic expressions for the harmonic transfer functions of linear periodically time-varying (LPTV) systems, like mixers and PLLs. The algorithm, which we call Symbolic HTM, is based on the organisation of the harmonic transfer functions into a harmonic transfer matrix. This representation allows to manipulate LPTV systems in a way that is similar to linear time-invariant (LTI) systems, making it possible to generate symbolic expressions which relate the overall harmonic transfer functions to the characteristics of the building blocks. These expressions can be used as design equations or as parametrized models for use in simulations. The algorithm is illustrated for a downconversion mixer.