Comparison of Hysteresis Based PWM Schemes ΔΣ-PWM and Direct Torque Control

This paper presents the differences and similarities of ΔΣ-PWM as a hysteresis-based PWM scheme with direct torque control (DTC) using simulation models. The variable switching frequency caused by the hysteresis element is examined with regard to its instantaneous values. The comparison is based on an equal maximum switching frequency as a design criterion. With this first assumption, the variation of the instantaneous switching frequency is higher when using DTC because of the temporary prioritization of one inverter leg. Besides the lower variation, ΔΣ-PWM shows a higher average switching frequency. Because the switching frequency is related to the torque ripple, the usage of ΔΣ-PWM results in a smaller torque ripple. Due to the dependence of torque ripple on switching frequency, a second comparison is carried out based on the same average switching frequency. In this comparison the ΔΣ-PWM shows higher torque ripple than DTC.

Design and Control of a Variable Geometry Hybrid Wheel-Leg

Conventional wheeled platforms provide sufficient locomotion on smooth surfaces but are limited when contending with obstacles such as stairs, steep inclines, or rugged terrain. Legged robots, which are better suited in traversing such obstacles, require an increased number of actuators, and thereby expend more energy. This paper describes the Adaptive Wheel-Leg, AWL, that provides mobile robots with the benefits of both wheels and legs. AWL is a two degree-of-freedom, hybrid wheel-leg topology with instantaneous switching between modes. AWL provides two modes: 1) a single actuator rolling mode for smooth surfaces, and 2) a walking mode for rugged terrain. This paper presents the mechanism’s design and control methods. An experimental model and a simulation of an AWL equipped hexapod are also discussed.

Passive Discrete Variable Stiffness Joint (pDVSJ-II): Modeling, Design, Characterization, and Testing Toward Passive Haptic Interface

In this paper, the modeling, design, and characterization of the passive discrete variable stiffness joint (pDVSJ-II) are presented. The pDVSJ-II is an extended proof of concept of a passive revolute joint with discretely controlled variable stiffness. The key motivation behind this design is the need for instantaneous switching between stiffness levels when applied for remote exploration applications where stiffness mapping is required, in addition for the need of low-energy consumption. The novelty of this work lies in the topology used to alter the stiffness of the variable stiffness joint. Altering the stiffness is achieved by selecting the effective length of an elastic cord with hook's springs. This is realized through the novel design of the cord grounding unit (CGU), which is responsible for creating a new grounding point, thus changing the effective length and the involved springs. The main features of CGU are the fast response and the low-energy consumption. Two different levels of stiffness (low, high) can be discretely selected besides the zero stiffness. The proposed physical-based model matched the experimental results of the pDVSJ-II in terms of discrete stiffness variation curves, and the stiffness dependency on the behavior of the springs. Two psychophysiological tests were conducted to validate the capabilities to simulate different levels of stiffness on human user and the results showed high relative accuracy. Furthermore, a qualitative experiment in a teleoperation scenario is presented as a case study to demonstrate the effectiveness of the proposed haptic interface.

A solution for SRM starting hesitation: from FE analysis to bench validation

Purpose – The starting hesitation of a switched reluctance motor (SRM) is an issue which must be considered in the early motor design. It is mostly handled as a control concern. The starting procedure of a SRM using a single Hall-effect position sensor is analysed in this paper. This low cost position measurement solution requires a specific control strategy. That has been developed for a three-phase 6/4 SRM. The paper aims to discuss these issues. Design/methodology/approach – The starting procedure begins with a rotor alignment step intending to bring the rotor to a known position. Afterward, only one phase is supplied on a periodic basis, to drive the rotor in the desired direction and accelerate up to a predefined speed threshold. Thus, the proposed procedure drastically simplifies the control strategy and permits a low cost sensor based control. 2D finite elements simulations are performed to analyse the starting performances in terms of response time and power efficiency. Both electrical and mechanical transients are considered in the simulation model thanks to simplifying assumption which consists in applying a time averaged voltages instead of instantaneous switching. Finally, the entire starting procedure with a one phase supply procedure is tested experimentally. Findings – A starting procedure of a three-phase SRM is implemented. The control effectiveness is validated by complementary FE calculations and measurements. Originality/value – The starting hesitation issue of a three-phase SRM is solved with an easy control strategy. During the acceleration phase, only one phase is self-controlled.

Design of Dual-Power Supply Automatic Switching Device without Disturbance

The dual power supply system is widely used in our daily life. When power instantaneously switched between the main power and the stand-by power supply, the voltage fluctuations had the varying degree influence on machines. Based on the principle of correlation coefficient of two waveforms and instantaneous reactive power theory, the dual-power supply automatic and instantaneous switching device without disturbance is provided in this paper. The equipment could identify and isolate the broken-down power source in 5ms. At the same time, power supply keeps continuous meeting the requirements of power quality without voltage drop.

High-Accuracy Programmable Timing Generator with Wide-Range Tuning Capability

In this paper, a high-accuracy programmable timing generator with wide-range tuning capability is proposed. With the aid of dual delay-locked loop (DLL), both of the coarse- and fine-tuning mechanisms are operated in precise closed-loop scheme to lessen the effects of the ambient variations. The timing generator can provide sub-gate resolution and instantaneous switching capability. The circuit is implemented and simulated in TSMC 0.18 μm 1P6M technology. The test chip area occupies 1.9 mm2. The reference clock cycle can be divided into 128 bins by interpolation to obtain 14 ps resolution with the clock rate at 550 MHz. The INL and DNL are within −0.21~+0.78 and −0.27~+0.43 LSB, respectively.