Abstract-Low voltage distribution feeders are designed for unidirectional energy supply from transformer to consumer. However, the implementation of small-scale PV production units on local utilities may result in bidirectional energy flows. The simultaneous power injection at sunny moments may cause a serious voltage rise along the feeder. These overvoltages may not only damage critical loads but also switches PV inverters off causing loss of green energy at the most productive moments. This paper presents a method to limit the voltage rise by introducing small battery buffers at local production sites. A smart inverter decides whether the PV energy is injected in the grid or buffered in the batteries. The relation between battery buffer size and overvoltage reduction is presented for a typical Belgian residential distribution feeder. The influence of the buffer along the feeder is calculated by working with synthetic load profiles and solar irradiation data.

Stepping motors are often used for low-power open-loop positioning. In conventional stepping motor drives, a step rate or speed is imposed. To avoid step loss in open-loop, most stepping motors are driven at maximum current resulting in a poor energy efficiency. However, when position feedback is available, the drive current can be optimised. A position sensor adds costs and complexity to the system. Therefore, rotor position estimators are developed, often referred to as sensorless controllers. A drawback in some of these methods is the requirement of information on the mechanical load which is usually not available or varies over time. In this study, an alternative estimator is proposed, based on the load angle between the current excitation vector and the instantaneous rotor flux position. This load angle reflects the capability of the system to follow the speed setpoint and gives an indication of the robustness to torque disturbances. Therefore the load angle estimation is interesting to provide feedback to a controller which adapts the drive current. Here, an estimator is proposed solely based on electrical motor parameters and electrical measurements. The algorithm, based on a sliding discrete Fourier transformation, is applicable with the typical full-, half-and micro-stepping drive algorithms. Finally, measurement results validate the estimation algorithm.

Abstract-The standard squirrel-cage induction machine has nearly reached its maximum efficiency. In order to further increase the energy efficiency of electrical machines, the use of permanent magnets in combination with the robust design and the line start capability of the induction machine is extensively investigated. Many experimental designs have been suggested in literature, but recently, these line-start permanent-magnet machines (LSPMMs) have become off-the-shelf products available in a power range up to 7.5 kW. The permanent magnet flux density is a function of the operating temperature. Consequently, the temperature will affect almost every electrical quantity of the machine, including current, torque, and efficiency. In this paper, the efficiency of an off-the-shelf 4-kW three-phase LSPMM is evaluated as a function of the temperature by both finite-element modeling and by practical measurements. In order to obtain stator, rotor, and permanent magnet temperatures, lumped thermal modeling is used.

Abstract. The number of installed distributed generation (DG) in residential areas rapidly increases, specifically in the form of photovoltaics (PV), causing some undesired side effects such as voltage rise. Overvoltage can damage critical loads, but is also disadvantageous for the owner because inverters switch off in case of overvoltage, resulting in output loss. Voltage limits are investigated through calculation and simulation of the voltage profile in a typical low voltage (LV) grid by using load data. Insolation data is used for the particular case of PV. This paper presents practical guidelines for the maximum power acceptance in a residential distribution network and the estimation of PV production loss due to overvoltage.

The rapidly growing amount of distributed generation in low voltage distribution grids issues some undesired side effects. Simultaneous power injection may cause a serious voltage rise along the feeder. These overvoltages may not only damage critical loads but also switch off PV inverters causing loss of green energy at the most productive moments. This paper discusses the origin and different possibilities to limit this induced voltage rise. The option of introducing local energy buffering is further elaborated. The relation between buffer size and overvoltage reduction is presented for a typical Belgian residential distribution feeder. The influence of buffers along the feeder is calculated by working with synthetic load profiles and solar irradiation data