Studies for the application of an adaptative controller to hydroturbine generators

This paper describes some studies made towards the automatization of hydroturbine generators with microcomputers. The overall design will include an automata controlling the starting-up and shutting-down procedure as well as an self-tuning regulator for the speed control. A self-tuning regulator based on the classical pole-assignment-method is studied. The algorithm uses a fast procedure for solving the polynomial equation implicit to selfturner regulator. This procedure is very simple from a computational point of view as only applications of elementary transformations on a 2 x 2 polynomial matrix are needed.The algorithm has been programmed on a Digital PDP 1103 computer and applied to some test problems

Sampling-time harmonic control for cascaded H-bridge converters with thermal control

Cascaded H-bridge converter (CHB) is a multilevel topology that is a well-suited solution for multiple applications such as flexible ac transmission systems or motor drives. This paper is focused on a CHB where the cells present an aging mismatch. This can be caused by the maintenance operation which forces the replacement of some damaged cells of the converter with new or repaired ones. In this paper, a new improved approach of the active thermal control (ATC) of the CHB using discontinuous pulsewidth modulation (PWM) (D-PWM) is presented. The D-PWM technique is used to reduce the power losses of one cell reducing its average temperature in order to increase its remaining lifetime. However, the combination of D-PWM with traditional phase-shifted PWM (PS-PWM) introduces high harmonic distortion in the output voltage of the CHB converter at twice the carrier frequency. A detailed harmonic distortion analysis of the CHB output voltage when the D-PWM based ATC is active is presented. From this analysis, a modification of the traditional PS-PWM is derived to eliminate the harmonic distortion at twice the carrier frequency. Experimental results show how the ATC using D-PWM is achieved whereas the harmonic distortion around twice the carrier frequency is eliminated. © 1982-2012 IEEE

Model predictive control for single-phase NPC converters based on optimal switching sequences

In this paper, a model predictive control (MPC) based on optimal switching sequences (OSSs) for a singlephase grid-connected full-bridge neutral-point-clampled (NPC) power converter is presented. The predictive control algorithm is formulated in terms of OSSs, which was originally proposed to govern three-phase power converters. In this work, the OSS concept is extended to control singlephase power converters. The proposed MPC algorithm belongs to the continuous control set MPC (CCS-MPC) and is able to provide fixed switching frequency while handling system constraints. The proposed algorithm has been experimentally tested in an NPC power converter prototype. Experimental results show the desired fixed switching behavior in the steady state condition and the intrinsic fast dynamic provided by MPC during transients. Furthermore, the test outcomes demonstrate the robustness of the proposed controller under large system parameter deviations.Ministerio Español de Economía y Competitividad ENE2013-45948-RConsejería de Innovación Ciencia y Empresa (Junta de Andalucia) P11-TIC-7070ju

Common-mode voltage mitigation of dual three-phase voltage source inverters in a motor drive application

Electric variable speed drives (VSDs) based on two VSDs connected to a multiphase machine are an attractive solution to replace high-power mechanic and hydraulic systems in many sectors of industry and transportation because they present high performance with reduced cost, volume and weight. Among the causes which affect the reliability of dual VSDs, the common-mode current flowing through the machine bearing is an important issue. This paper faces the mitigation of the common-mode current by reducing the common-mode voltage (CMV) generated by the operation of a dual VSD. The CMV reduction is carried out without introducing any extra device and/or passive filtering method. This CMV reduction is performed by applying a specific phase-displacement between the modulation strategies of each single inverter drive. The proposed technique has been evaluated in a down scaled experimental setup in order to test its effectivenes

A Very High Resolution Stacked Multilevel Inverter Topology for Adjustable Speed Drives

This paper proposes a novel 49-level stacked inverter topology for drives. The 49 levels are achieved by stacking three 17-level inverters. Each of the 17-level inverter is developed by cascading a flying capacitor (FC) inverter with three capacitor-fed H-bridges. The device count can be reduced by making the FC and the three cascaded H-bridges common to the dc link in each phase using selector switches in between them. The selector switches need to operate at fundamental frequency only. Also, the devices need to block very low voltages. Hence, MOSFETs can be used. This topology requires three dc sources, each of Vdc/6 only, which can be replaced with stacked batteries for electric vehicle applications. The reduction in the dc voltage requirement is achieved by using a normal symmetric six-phase induction motor with parallel connection of the opposite phase windings. All the floating capacitors in the topology can be balanced irrespective of any modulation index or load power factor. Due to the high number of voltage levels, nearest level control can be used instead of pulse width modulation, which reduces the switching losses. The dv/dt during the inverter operation is also less. Detailed experimental results at different speeds of operation and during transients ensure that the novel topology can be a viable option for high-power adjustable speed drives

Extended Linear Modulation Operation of a Common-Mode-Voltage-Eliminated Cascaded Multilevel Inverter With a Single DC Supply

Zero-common-mode-voltage (CMV) operation of multilevel inverters results in reduced dc-bus utilization and reduced linear modulation range. In this paper, a method to increase the linear modulation range for zero-CMV operation without increasing the dc-bus voltage using a cascaded multilevel inverter with a single dc supply is presented. Using this method, the peak fundamental output voltage can be increased from 0.499 to 0.637 Vdc with zero CMV inside the linear modulation range. Also, various pulse width modulation (PWM) switching sequences are analyzed in this paper, and the PWM sequence that gives minimum current ripple is used for the zero-CMV operation of the inverter. The inverter topology with single dc supply is realized by cascading a two-level inverter with two floating-capacitor-fed full-bridge modules. Simulation and experimental results for steady-state and dynamic operating conditions are presented to validate the proposed method

Multilevel Dodecagonal Space Vector Generation Using Stacked Inverter Cells for IM drives

This paper proposes a new induction motor drive scheme to generate a dense multilevel dodecagonal space vector structure, by stacking two 3-level flying capacitors and cascading two H-bridges. The proposed scheme combines the benefits of both multilevel as well as dodecagonal voltage space vector structure. All the capacitors in the stacked inverters are balanced using switching state redundancies within a sampling period. The H-bridges act as a harmonics filter and provide only reactive power, irrespective of load power factor and the capacitors are naturally balanced. The stacked inverter operates in quasi square wave mode throughout the modulation range and results in less switching losses. Both the simulation and experimental results are included in the paper to support the effectiveness of the proposed scheme

Stacked Multilevel Inverter fed Six Phase Induction Motor with Reduced DC Link and Lower Voltage Devices

This paper proposes a novel configuration of six phase IM to drive from a three phase stacked multilevel inverter. Apart from greater fault tolerance compared to three phase, a six phase machine enables the use of low voltage devices for the inverter. Also the inverter used here is a three phase nine level stacked inverter which itself uses low voltage devices. Thus MOSFETs can be used for the inverter. The nine level inverter is formed by stacking 2 five level inverters each of which is developed by cascading an FC and a capacitor fed H-bridge. The inverter can be stacked further to obtain still higher number of voltage levels. This enables the use of batteries at the front end and still lower voltage devices which will significanly improve the efficiency. Hence this will find applications in electric vehicles because of the direct battery drive. Experiment is conducted on a 15 KW six phase IM by reconfiguring it as a three phase machine and driven by the three phase nine level stacked inverter using V/f control scheme. Detailed experimental results are provided to validate the concept