Optimization of energy consumption in wastewater pumping

Pumppauksessa arvioidaan olevan niin teknisesti kuin taloudellisestikin huomattavia mahdollisuuksia säästää energiaa. Maailmanlaajuisesti pumppaus kuluttaa lähes 22 % sähkö-moottorien energiantarpeesta. Tietyillä teollisuudenaloilla jopa yli 50 % moottorien käyttämästä sähköenergiasta voi kulua pumppaukseen. Jäteveden pumppauksessa pumppujen toiminta perustuu tyypillisesti on-off käyntiin, jolloin pumpun ollessa päällä se käy täydellä teholla. Monissa tapauksissa pumput ovat myös ylimitoitettuja. Yhdessä nämä seikat johtavat kasvaneeseen energian kulutukseen. Työn teoriaosassa esitellään perusteet jätevesihuollosta ja jäteveden käsittelystä sekä pumppaussysteemin pääkomponentit: pumppu, putkisto, moottori ja taajuusmuuttaja. Työn empiirisessä osassa esitellään työn aikana kehitetty laskuri, jonka avulla voidaan arvioida energiansäästöpotentiaalia jäteveden pumppaussysteemeissä. Laskurilla on mandollista laskea energiansäästöpotentiaali käytettäessä pumpun tuoton ohjaustapana pyörimisnopeuden säätöä taajuusmuuttajalla on-off säädön sijasta. Laskuri ilmoittaa optimaalisimmanpumpun pyörimisnopeuden sekä ominaisenergiankulutuksen. Perustuen laskuriin, kolme kunnallista jätevedenpumppaamoa tutkittiin. Myös laboratorio-testitsuoritettiin laskurin simuloimiseksi sekä energiansäästöpotentiaalin arvioimiseksi. Tutkimukset osoittavat, että jätevedenpumppauksessa on huomattavia mandollisuuksia säästää energiaa pumpun pyörimisnopeutta pienentämällä. Geodeettisen nostokorkeuden ollessa pieni, voidaan energiaa säästää jopa 50 % ja pitkällä aikavälillä säästö voi olla merkittävä. Tulokset vahvistavat myös tarpeen jätevedenpumppaussysteemien toiminnan optimoimiseksi.

Converter-flux-based current control of voltage source PWM rectifiers - analysis and implementation

Pulsewidth-modulated (PWM) rectifier technology is increasingly used in industrial applications like variable-speed motor drives, since it offers several desired features such as sinusoidal input currents, controllable power factor, bidirectional power flow and high quality DC output voltage. To achieve these features,however, an effective control system with fast and accurate current and DC voltage responses is required. From various control strategies proposed to meet these control objectives, in most cases the commonly known principle of the synchronous-frame current vector control along with some space-vector PWM scheme have been applied. Recently, however, new control approaches analogous to the well-established direct torque control (DTC) method for electrical machines have also emerged to implement a high-performance PWM rectifier. In this thesis the concepts of classical synchronous-frame current control and DTC-based PWM rectifier control are combined and a new converter-flux-based current control (CFCC) scheme is introduced. To achieve sufficient dynamic performance and to ensure a stable operation, the proposed control system is thoroughly analysed and simple rules for the controller design are suggested. Special attention is paid to the estimationof the converter flux, which is the key element of converter-flux-based control. Discrete-time implementation is also discussed. Line-voltage-sensorless reactive reactive power control methods for the L- and LCL-type line filters are presented. For the L-filter an open-loop control law for the d-axis current referenceis proposed. In the case of the LCL-filter the combined open-loop control and feedback control is proposed. The influence of the erroneous filter parameter estimates on the accuracy of the developed control schemes is also discussed. A newzero vector selection rule for suppressing the zero-sequence current in parallel-connected PWM rectifiers is proposed. With this method a truly standalone and independent control of the converter units is allowed and traditional transformer isolation and synchronised-control-based solutions are avoided. The implementation requires only one additional current sensor. The proposed schemes are evaluated by the simulations and laboratory experiments. A satisfactory performance and good agreement between the theory and practice are demonstrated.

Calculation analysis of energy saving tools for fan and pump applications

This thesis analyses the calculation of FanSave and PumpSave energy saving tools calculation. With these programs energy consumption of variable speed drive control for fans and pumps can be compared to other control methods. With FanSave centrifugal and axial fans can be examined and PumpSave deals with centrifugal pumps. By means of these programs also suitable frequency converter can be chosen from the ABB collection. Programs need as initial values information about the appliances like amount of flow and efficiencies. Operation time is important factor when calculating the annual energy consumption and information about it are the length and profile. Basic theory related to fans and pumps is introduced without more precise instructions for dimensioning. FanSave and PumpSave contain various methods for flow control. These control methods are introduced in the thesis based on their operational principles and suitability. Also squirrel cage motor and frequency converter are introduced because of their close involvement to fans and pumps. Second part of the thesis contains comparison between results of FanSave’s and PumpSave’s calculation and performance curve based calculation. Also laboratory tests were made with centrifugal and axial fan and also with centrifugal pump. With the results from this thesis the calculation of these programs can be adjusted to be more accurate and also some new features can be added.

Supplier Energy Audits in Thermal Power Plants

This master’s thesis handles an operating model for an electric equipment supplier conducted sale oriented energy audit for pumping, fan and other motor applications at power plants. The study goes through the largest factors affecting internal electricity use at a power plant, finds an energy audit –like approach for the basis of information gathering and presents the information needed for conducting the analysis. The model is tested in practice at a kraft recovery boiler of a chemical pulping mill. Targets chosen represent some of the largest electric motor applications in the boiler itself and in its fuel handling. The energy saving potential of the chosen targets is calculated by simulating the energy consumption of the alternatives for controlling the targets, and thereafter combining the information with the volume flow duration curve. Results of the research are somewhat divaricated, as all the information needed is not available in the automation system. Some of the targets could be simulated and their energy saving potential calculated quite easily. At some of the targets chosen the monitoring was not sufficient enough for this and additional measurements would have been needed to base the calculations on. In traditional energy audits, energy efficiency of pump and fan applications is not necessarily examined. This means that there are good possibilities for developing the now presented targeted energy audit procedure basis further.

Life cycle costs in heating, ventilation and air-conditioning systems with drive

Energy consumption and energy efficiency have become an issue. Energy consumption is rising all over the world and because of that, and the climate change, energy is becoming more and more expensive. Buildings are major consumers of energy, and inside the buildings the major consumers are heating, ventilation and air-conditioning systems. They usually run at constant speed without efficient control. In most cases HVAC equipment is also oversized. Traditionally heating, ventilation and air-conditioning systems have been sized to meet conditions that rarely occur. The theory part in this thesis represents the basics of life cycle costs and calculations for the whole life cycle of a system. It also represents HVAC systems, equipment, systems controls and ways to save energy in these systems. The empirical part of this thesis represents life cycle cost calculations for HVAC systems. With these calculations it is possible to compute costs for the whole life cycle for the wanted variables. Life cycle costs make it possible to compare which variable causes most of the costs from the whole life point of view. Life cycle costs were studied through two real life cases which were focused on two different kinds of HVAC systems. In both of these cases the renovations were already made, so that the comparison between the old and the new, now existing system would be easier. The study indicates that energy can be saved in HVAC systems by using variable speed drive as a control method.

Kaksiakselisen välijäähdytyksellä, välipoltolla ja rekuperaattorilla varustetun mikrokaasuturbiinin osakuormahyötysuhteen säilyvyyden optimointi

Työssä pyrittiin etsimään differentiaalievoluutioalgoritmilla kaksiakseliselle, välijäähdytyksellä, välipoltolla ja rekuperaattorilla varustetulle mikrokaasuturbiinille sellaiset kompressorien painesuhteet ja rekuperaattorin rekuperaatioaste, että saavutettaisiin mandollisimman hyvä osakuormahyötysuhteen säilyvyys. Osakuormatehon säätömenetelmäksi oli valittu pyörimisnopeussäädön ja turbiinien sisääntulolämpötilan alentamisen yhdistelmä, jossa generaattorilla varustetun akselin pyörimisnopeus sekä molempien turbiinien sisääntulolämpötilat olivat toisistaan riippumatta vapaasti säädettävissä. Työssä löydettiin optimaalinen säätömenetelmien yhdistelmä, jolla saavutetaan parempi osakuormahyötysuhteen säilyvyys, kuin millään käytetyistä menetelmistä yksinään. Lisäksi havaittiin, ettei optimaalinen säätömenetelmä merkittävästi riipu koneikolle valituista suunnittelupisteen parametreista. Osakuormahyötysuhteen säilyvyyden kannalta optimaalinen koneikko ei merkittävästi poikennut suunnittelupisteen hyötysuhteen kannalta optimaalisesta.

Kenttätietojen hyödyntäminen taajuusmuuttajan luotettavuuden suunnittelussa

Taajuusmuuttaja on yhä yleisempi laite perinteisten oikosulkumoottoreiden nopeuden säädössä, niin teollisuudessa kuin muilla käyttökohteissa. Ensimmäiset laitetyypit olivat mekaanisesti suurikokoisia ja vaativat laitteen tekniseltä tuelta ja kunnossapidolta hyvää teknistä perehtyneisyyttä laitteisiin. Teknologian kehittymisen myötä laitteiden teho/kokosuhde on pienentynyt ja tarjolla on useita eri sovelluskohteisiin suoraan soveltuvia taajuusmuuttajia varustettuna helppokäyttöisillä ja kaupallisilla käyttöliittymillä. Laitteen elinkaaren aikainen luotettavuusjohtaminen edellyttää valmistajalta varsinaisen laitesuunnittelun lisäksi tarkoituksenmukaisia testausmenetelmiä ja kokemusperäistä luotettavuustietoa myös asennetusta laitekannasta. Työssä on käyty taajuusmuuttajan suunnittelun kannalta läpi luotettavuuden käsitteistö sekä yleisimpiä luotettavuusmenetelmiä. Luotettavuusnäkökohtia verrataan asennetusta laitekannasta saatuihin kokemuksiin laitteen valmistajan ja tuotetuen kannalta. Työssä on esitetty luokittelun perusteita ja menetelmät, miten käytön aikana voidaan arvioida laitteen teknistä tilaa sekä huomioida se kunnossapidon suunnittelussa. Johtopäätöksenä huomataan, että asennuspaikka ja käyttösovellus määrittävät taajuusmuuttajan käytettävyyden. Kenttätietoja voidaan hyödyntää paikallisen kunnossapidon kannalta kunnossapidon ja investointien suunnittelussa. Toisaalta valmistajan tuotekehitys saa asennetuista laitteista kokemuksia seuraavan sukupolven tyypin suunnittelun perustaksi. Tekniikan voimakkaan kehittymisen seurauksena uusien taajuusmuuttajatyyppien valmistus kestää yhä lyhyemmän ajanjakson, jolloin asennetusta laitekannasta saatu kenttäkokemus on arvokasta tietoa laitevalmistajalle. Yhteenvetona valmistajan laiterekistereitä voidaan kehittää siten, että niihin on tallennettavissa laitekartoitusten perusteella kerättyä informaatiota, jota niin valmistajan myynti, tuotetuki kuin laitesuunnittelu voi omassa toiminnassaan hyödyntää.

Pumppukäyttöjen energiankulutuksen määrittäminen prosessimittauksia käyttäen

Pumppukäytöt vastaavat noin neljännestä Euroopan alueen sähkömoottoreissa kuluvasta energiasta. Energian hinnan nousun vuoksi energian säästäminen ja energiatehokkuus ovat nousseet tärkeään asemaan paljon energiaa kuluttavassa teollisuudessa. Pumppukäyttöjen hyötysuhteen parantaminen on noussut olennaiseen osaan paperi- ja kartonkiteollisuuden energiatehokkuustarkasteluissa. Tässä työssä tarkastellaan kartonkikoneen pumppukäyttöjen toiminnan energiatehokkuutta moottorin virtamittausten perusteella. Analyysi perustuu moottorin akselitehon määrittämiseen ja sen perusteella tehtävään pumpun toimintapisteen laskentaan. Työssä esitellään käytetyt estimointimenetelmät ja niillä saadut tulokset kartonkikoneen pumppukäytöille. Lisäksi työssä arvioidaan kolmen yksittäisen pumppukäytön energiankulutuksen säästöpotentiaalia. Työssä käytettyä menetelmää voidaan käyttää sekä vakio- että vaihtonopeuspumppukäyttöjen toiminnan ja hyötysuhteen analysointiin.

Induction Motor Drive Energy Efficiency - Simulation and Analysis

A coupled system simulator, based on analytical circuit equations and a finite element method (FEM) model of the motor has been developed and it is used to analyse a frequency-converterfed industrial squirrel-cage induction motor. Two control systems that emulate the behaviour of commercial direct-torque-controlled (DTC) and vector-controlled industrial frequency converters have been studied, implemented in the simulation software and verified by extensive laboratory tests. Numerous factors that affect the operation of a variable speed drive (VSD) and its energy efficiency have been investigated, and their significance in the simulation of the VSD results has been studied. The dependency of the frequency converter, induction motor and system losses on the switching frequency is investigated by simulations and measurements at different speeds for both the vector control and the DTC. Intensive laboratory measurements have been carried out to verify the simulation results.

Energiankulutuksen vähentäminen jäähdytyspiirin pumppausprosessissa

Pumppujen oikean mitoituksen lisäksi niiden tuoton säätämisellä on merkitystä pumppausprosessin energiankulutukseen. Työssä tarkastellaan pyörimisnopeussäädön ja virtauksen kuristamisen eroja pumppauksen tilavuusvirran säätämisessä erityisesti energiatehokkuuden kannalta. Työn kokeellisessa osiossa tarkastellaan erään jäähdytyspiirin pumppujen hyötysuhteita ja lasketaan mahdollinen energiansäästöpotentiaali, mikäli pumppujen säätäminen olisi toteutettu pyörimisnopeussäädöllä.

Monitoring of centrifugal pump operation by a frequency converter

Centrifugal pumps are widely used in industrial and municipal applications, and they are an important end-use application of electric energy. However, in many cases centrifugal pumps operate with a significantly lower energy efficiency than they actually could, which typically has an increasing effect on the pump energy consumption and the resulting energy costs. Typical reasons for this are the incorrect dimensioning of the pumping system components and inefficiency of the applied pump control method. Besides the increase in energy costs, an inefficient operation may increase the risk of a pump failure and thereby the maintenance costs. In the worst case, a pump failure may lead to a process shutdown accruing additional costs. Nowadays, centrifugal pumps are often controlled by adjusting their rotational speed, which affects the resulting flow rate and output pressure of the pumped fluid. Typically, the speed control is realised with a frequency converter that allows the control of the rotational speed of an induction motor. Since a frequency converter can estimate the motor rotational speed and shaft torque without external measurement sensors on the motor shaft, it also allows the development and use of sensorless methods for the estimation of the pump operation. Still today, the monitoring of pump operation is based on additional measurements and visual check-ups, which may not be applicable to determine the energy efficiency of the pump operation. This doctoral thesis concentrates on the methods that allow the use of a frequency converter as a monitoring and analysis device for a centrifugal pump. Firstly, the determination of energy-efficiency- and reliability-based limits for the recommendable operating region of a variable-speed-driven centrifugal pump is discussed with a case study for the laboratory pumping system. Then, three model-based estimation methods for the pump operating location are studied, and their accuracy is determined by laboratory tests. In addition, a novel method to detect the occurrence of cavitation or flow recirculation in a centrifugal pump by a frequency converter is introduced. Its sensitivity compared with known cavitation detection methods is evaluated, and its applicability is verified by laboratory measurements for three different pumps and by using two different frequency converters. The main focus of this thesis is on the radial flow end-suction centrifugal pumps, but the studied methods can also be feasible with mixed and axial flow centrifugal pumps, if allowed by their characteristics.

Evaluation of energy efficiency and best available techniques in pumping processes

The potential for enhancing the energy efficiency of industrial pumping processes is estimated to be in some cases up to 50 %. One way to define further this potential is to implement techniques in accordance to definition of best available techniques in pumping applications. These techniques are divided into three main categories: Design, control method & maintenance and distribution system. In the theory part of this thesis first the definition of best available techniques (BAT) and its applicability on pumping processes is issued. Next, the theory around pumping with different pump types is handled, the main stress being in centrifugal pumps. Other components needed in a pumping process are dealt by presenting different control methods, use of an electric motor, variable speed drive and the distribution system. Last part of the theory is about industrial pumping processes from water distribution, sewage water and power plant applications, some of which are used further on in the empirical part as example cases. For the empirical part of this study four case studies on typical pumping processes from older Master’s these were selected. Firstly the original results were analyzed by studying the distribution of energy consumption between different system components and using the definition of BAT in pumping, possible ways to improve energy efficiency were evaluated. The goal in this study was that by the achieved results it would be possible to identify the characteristic energy consumption of these and similar pumping processes. Through this data it would then be easier to focus energy efficiency actions where they might be the most applicable, both technically and economically.

Servo drive in hoist application

The objective of this master thesis is to test according to hoisting requirements, a servo drive system and compare its performance with the performance of a drive equipped with a vector controlled frequency converter. Both systems utilize closed-loop vector control based on PCL program control. In order to compare the results of tests both systems were connected to the same motor driving a variable speed electrical chain hoist. Tests were based on requirements to both systems. As requirements of tests zero speed operation, operation in field weakening, positioning accuracy and smoothness of motion are taken into consideration. Both systems demonstrate quite similar performance and meet the requirements. Servo drive system demonstrates a high positioning accuracy and dynamic performance. Frequency converter is not able to provide the same positioning accuracy and dynamic performance as servo drive.

Active inverter output filtering methods

Frequency converters are widely used in the industry to enable better controllability and efficiency of variable speed AC motor drives. Despite these advantages, certain challenges concerning the inverter and motor interfacing have been present for decades. As insulated gate bipolar transistors entered the market, the inverter output voltage transition rate significantly increased compared with their predecessors. Inverters operate based on pulse width modulation of the output voltage, and the steep voltage edge fed by the inverter produces a motor terminal overvoltage. The overvoltage causes extra stress to the motor insulation, which may lead to a prematuremotor failure. The overvoltage is not generated by the inverter alone, but also by the sum effect of the motor cable length and the impedance mismatch between the cable and the motor. Many solutions have been shown to limit the overvoltage, and the mainstream products focus on passive filters. This doctoral thesis studies an alternative methodology for motor overvoltage reduction. The focus is on minimization of the passive filter dimensions, physical and electrical, or better yet, on operation without any filter. This is achieved by additional inverter control and modulation. The studied methods are implemented on different inverter topologies, varying in nominal voltage and current.For two-level inverters, the studied method is termed active du/dt. It consists of a small output LC filter, which is controlled by an independent modulator. The overvoltage is limited by a reduced voltage transition rate. For multilevel inverters, an overvoltage mitigation method operating without a passive filter, called edge modulation, is implemented. The method uses the capability of the inverter to produce two switching operations in the same direction to cancel the oscillating voltages of opposite phases. For parallel inverters, two methods are studied. They are both intended for two-level inverters, but the first uses individual motor cables from each inverter while the other topology applies output inductors. The overvoltage is reduced by interleaving the switching operations to produce a similar oscillation accumulation as with the edge modulation. The implementation of these methods is discussed in detail, and the necessary modifications to the control system of the inverter are presented. Each method is experimentally verified by operating industrial frequency converters with the modified control. All the methods are found feasible, and they provide sufficient overvoltage protection. The limitations and challenges brought about by the methods are discussed.

Automatic system identification and optimization of centrifugal pump operation

Centrifugal pumps are a notable end-consumer of electrical energy. Typical application of a centrifugal pump is the filling or emptying of a reservoir tank, where the pump is often operated at a constant speed until the process is completed. Installing a frequency converter to control the motor substitutes the traditional fixed-speed pumping system, allows the optimization of rotational speed profile for the pumping tasks and enables the estimation of rotational speed and shaft torque of an induction motor without any additional measurements from the motor shaft. Utilization of variable-speed operation provides the possibility to decrease the overall energy consumption of the pumping task. The static head of the pumping process may change during the pumping task. In such systems, the minimum rotational speed changes during reservoir filling or emptying, and the minimum energy consumption can’t be achieved with a fixed rotational speed. This thesis presents embedded algorithms to automatically identify, optimize and monitor pumping processes between supply and destination reservoirs, and evaluates the changing static head –based optimization method.