Jeroen De Maeyer

The Nyquist Criterion: A Useful Tool for the Robust Design of Continuous-Time

In this brief, we introduce a figure of merit for the robustness of continuous-time (CT) ΣΔ modulators. It is based on the Nyquist criterion for the equivalent discrete-time loop filter. We show how CT modulators can be designed by optimizing this figure of merit. This way, we obtain modulators with increased robustness against variations in the noise-transfer-function (NTF) parameters. This is particularly useful for constrained systems, where the system order exceeds the number of design parameters. This situation occurs, for example, due to the effect of the excess loop delay or the finite gain bandwidth of the operational amplifiers. Additionally, it is shown that the optimization is equivalent to the minimization of H∞, which is the maximum out-of-band gain of the NTF. This explains why conventional design strategies that are based on H∞, such as Schreiers approach, provide quite robust modulator designs in the case of unconstrained architectures.

\Sigma\Delta

Generally, one of the key requirements of modern buildings, besides an appropriate heating and ventilation, is to offer and maintain a suitable lighting. In this contribution, a description of a system capturing and re-directing sunlight into open spaces inside the building without affecting the inside temperature (isotherm) is given. The system mainly consists of three principal components: a mirror capturing the light of the sun and reflecting it inside the building via a prism system, a printed circuit board with two photovoltaic sensors for positioning the mirror, and finally, a motor rotating the printed circuit board and mirror. A closed-loop control system to track the movement of the sun is proposed. The results show good tracking behavior.

Modulators

A recently published paper by Rossi et al. [1] deals with an alleged new invention being a combination of Incremental and Cyclic A/D conversion, and makes strong claims about this being a new invention.

An efficient closed loop control system to follow, capture and redirect daylight

The fluctuating behavior of wave energy is a challenge to reach high efficiencies of implemented power take-off (PTO) systems due to the bidirectional movement and high variable loads. The described PTO based on a power sharing transmission (PST) tackles this by converting the bidirectional rotation into a unidirectional rotation of a generator equipped with a flywheel to reduce fluctuation in the output. The generator can then be operated at or close to its optimum efficiency. An auxiliary machine is in charge of the controls. The PST is modeled and implemented in an existing hydrodynamic model of a heaving buoy. A basic control is realised in the simulation resulting in the confirmation of the conversion to a unidirectional rotation and facilitating assessment of the machine efficiencies.