Jan Verveckken

Predictive Direct Torque Control for Flux and Torque Ripple Reduction

In this paper, a prediction scheme is presented to diminish both the torque and flux ripples in a direct torque control (DTC) induction motor drive. In a discrete implementation of the classical DTC scheme, the time delay associated with data processing results in additional torque and flux ripples. This part of the ripples can amount to a significant fraction of the overall ripple if the hysteresis bands are comparable to the maximum torque and flux variations in one sampling interval. This paper presents a prediction scheme with low computational complexity and low parameter sensitivity, both comparable to the standard DTC scheme. The prediction scheme can easily be extended to compensate for multiple time delays when the sampling frequency is raised but the computation time remains unchanged. Experimental results show the diminishing effect of the prediction scheme on the torque and flux ripples.

Direct Power Control of Series Converter of Unified Power-Flow Controller With Three-Level Neutral Point Clamped Converter

A unified power-flow controller (UPFC) can enforce unnatural power flows in a transmission grid, to maximize the power flow while maintaining stability. Theoretically, active and reactive power flow can be controlled without overshoot or cross coupling. This paper develops direct power control, based on instantaneous power theory, to apply the full potential of the power converter. Simulation and experimental results of a full three-phase model with nonideal transformers, series multilevel converter, and load confirm minimal control delay, no overshoot nor cross coupling. A comparison with other controllers demonstrates better response under balanced and unbalanced conditions. Direct power control is a valuable control technique for a UPFC, and the presented controller can be used with any topology of voltage-source converters. In this paper, the direct power control is demonstrated in detail for a third-level neutral point clamped converter.

Direct power control for Universal Power Flow Controller series converter

To maximize the power flow in a transmission grid while maintaining stability, unnatural power flows can be enforced by a Unified Power Flow Controller. Theoretically the control of active and reactive power flow can be without overshoot or cross coupling. Direct power control, based on instantaneous power theory, can apply the full potential of the power converter and achieve better results. Simulation is performed on a full 3 phase model with non-ideal transformers, series multilevel converter and load. Experiments on a 3 phase scaled model with multilevel converter are performed. Simulation results are confirmed by experimental results and demonstrate minimum control delay, no overshoot and no cross coupling. Direct power control is a valuable control technique for a UPFC, and the presented controller can be applied to voltage source converters. In this paper, the Direct Power Control is demonstrated in detail for a 3 level Neutral Point clamped inverter.

Design of inverse controller with cross-coupling suppression for UPFC series converter

The power flow control problem of a transmission line equipped with a Universal Power Flow Controller is investigated. Two controllers for the series converter of a UPFC are proposed. Dynamic or static model inverses are used to linearize control and suppress cross-coupling dynamics. Both controllers realize first order step responses with arbitrary time constant and cross-coupling suppression. Main benefits of these controllers are low controller complexity, minimal required system parameter knowledge and first order system behavior with arbitrary time constant. Controller complexity is no more than two parallel PI controllers for the steady-state inverse controller, or four for the dynamic inverse controller. Cross-coupling suppression performance of both controllers depends only on knowledge of inductance-resistance ratio of transmission line. Simulation results at 1 kHz demonstrate cross-coupling suppression and first order behavior. Control bandwidth allows damping of inter-area oscillations.

Prediction-based ripple reduction in Direct Torque Control of an induction machine

In this paper, a new prediction technique is presented in order to minimize both torque and flux ripple in direct torque control (DTC) of an induction machine. When the classical DTC scheme is implemented on a discrete-time base using a digital controller, the choice of the appropriate voltage vector is based on calculated values of torque and flux corresponding to the previous sampling moment. This time delay causes a large fraction of the overall ripple when the hysteresis bands are small compared to the maximum torque and flux variations during one sampling period. This paper aims to present a predictive scheme to correct for this time delay. The technique is characterized by its computational simplicity since it only makes use of the calculated effects of voltage vectors during the previous sampling intervals. The scheme does not require additional motor parameters and therefore shows the same robustness towards parameter variations as the conventional DTC scheme. The prediction scheme can be extended to compensate for an additional time delay when the sampling frequency is raised but the overall process time remains unchanged. Simulations and experimental results show the effectiveness of the proposed prediction scheme to reduce both torque and flux ripple.

Enhancing the Ride-Through Capability of DC-Link Voltage in NPC Multilevel Unified Power-Flow Controllers

Multilevel converters are attractive for unified power-flow controller (UPFC) applications, due to their high-voltage and power capability. Among multilevel topologies, the three-level neutral-point-clamped (NPC) converter allows back-to-back connection as the UPFC shunt and series converters. Besides the pulsewidth-modulated (PWM) multilevel control schemes, UPFCs require constant dc-link voltage and balanced voltages in the NPC multilevel dc capacitors. This paper proposes three main contributions to increase the dc-link voltage steadiness of multilevel UPFCs under line faults: 1) decoupled active and reactive linear power controllers; 2) real-time PWM generation; and 3) double balancing of dc capacitor voltages. A case study using part of the Portuguese transmission network is presented. The results show the effectiveness of the real-time PWM generation and dc-link capacitor voltages balancing included in NPC series and shunt converters to keep the dc-link voltage steadiness under line faults, overall enhancing the UPFC ride-through capability.

Optimal analytic LCL filter design for grid-connected voltage-source converter

Grid connected converters produce current harmonics, which need to be mitigated towards the grid. Passive output filters are the standard solution. Considering the growing count of low-power energy sources, the cost of output filters as well as the energy losses in them must be taken into account during the design phase. Existing design methods for these output filters are tedious in use; optimality of the filter design is not guaranteed, adapting the methods for other objectives is difficult. In this paper, an analytic design method for converter output filters is proposed, functional for filters of any order, and demonstrated for filters of 3rd order. It is optimized for minimal total material and energy loss cost over the lifetime. Based on the converter, grid, expected lifetime and use, cost of energy and material, and grid harmonic standards, this method calculates the optimal filter components; it outperforms other methods in optimal cost and energy efficiency. This method is readily usable, fully analytic and adaptable to other conditions, prerequisites or optimality objectives.

Development of an open-source smart energy house for K-12 education

Energy consumption in buildings represents about one-third of the world-wide energy consumption. Consumers often are not fully aware of energy-conserving measures they could take. Intelligent control of the heating and lighting systems in buildings is one way to increase energy-efficiency. Children and young adults influence domestic energy consumption, by using appliances such as TV and lighting. Often, they are not aware of the costs incurred. The goal of this research is to develop a educational platform for energy efficiency education aimed towards the full age range of K-12 education. A scaled model of a house is used, to explain the energy flows in the residential setting, well-known by the target audience. A model house is designed, with actual loads, using an Arduino Uno electronics platform as an interface to a PC. A reference program in the integrated development environment S4A allows visualizing the energy consumption in a simple manner. The children control a number of scaled household appliances interactively. A survey with the first 25 children (aged 10-12) suggests higher awareness of energy consumption.

Comparison of three-level torque hysteresis controllers for direct torque control

In this paper, a comparison is made between different implementations of the three-level torque comparator for a Direct Torque Control (DTC) based induction motor drive. The DTC scheme controls stator flux and torque by means of hysteresis comparators, respectively a two-level control structure for the stator flux and a three-level comparator for the electromagnetic torque. The standard three-level hysteresis controller has a DC offset torque error. In this paper, an additive implementation is investigated in order to remove this DC offset error. The operational principles of the different implementations are compared based on continuous and discrete simulation results, which demonstrate the additional advantages of the additive structure in a discrete implementation of the control scheme.

Developing engineering-oriented educational workshops within a student branch

The development of two educational workshops, one on energy efficiency and one on human-machine interfaces, is detailed and discussed. Attraction to engineering is not created as much as lost at early ages through current education methods. Through positive, hands-on experiences with engineering in K-12 education, this trend can be turned. IEEE student branches have as part of their mission the education and creation of quality educational resources for the public. After searching in vain for suitable inexpensive material, the IEEE student branch Leuven decided to design and create two workshops on engineering topics for an audience of 10-12 year olds. Handling this as a repeatable project, the student branch found partners to create a low budget project for the attendees. Using the skillset of the specific partners and organizers optimally on the subtasks, a successful repeatable cooperation is realized. This paper discusses the environment in which the project is realized, the steps to it, and how it (indirectly) benefits the organizing student branch.