TVE15056

Examensarbete 30 hp Juni 2015

Wireless control and measurement system for a hydropower generator with brushless exciter Fredrik Evestedt

Masterprogram i förnybar elgenerering Master Programme in Renewable Electricity Production

Abstract Wireless control and measurement system for a hydropower generator with brushless exciter Fredrik Evestedt

Teknisk- naturvetenskaplig fakultet UTH-enheten Besöksadress: Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0 Postadress: Box 536 751 21 Uppsala Telefon: 018 – 471 30 03 Telefax: 018 – 471 30 00 Hemsida: http://www.teknat.uu.se/student

Hydropower has been around for more than a century and is considered a mature technology, but with recent advancements in power electronics and simulation capability new exciting ways to increase efficiency and reliability is possible. At Uppsala University a brushless exciter has been constructed for the experimental test rig, SVANTE. Power electronics are mounted on the shaft for control of the generator's excitation current. In addition a wireless control and measurement system is needed to provide the desired switching patterns to the power electronics and to evaluate performance of the system. In this thesis a shaft mounted embedded system for control and measurement is constructed as well as magnetic field sensors with measurement range up to 700mT. The computational power comes from a National Instruments sbRIO-9606. The system has 14 individual totem pole power electronics driving channels, 48 analog input channels for current signals and it communicates wirelessly through a bluetooth connection. The system is tested and works satisfactory but has not been mounted on the rotating side of the generator due to delays in the manufacturing.

Handledare: José Perez Ämnesgranskare: Urban Lundin Examinator: Juan de Santiago TVE15056

Sammanfattning Vattenkraft har det senaste ˚ arhundradet varit och ¨ar fortfarande en av Sveriges fr¨amsta k¨ allor till elektrisk energi. Tekniken som vattenkraft bygger p˚ a ¨ar mogen och drifts¨aker, men med den senaste tidens utveckling inom kraftelektronik och simuleringsverktyg ¨oppnas nya m¨ojligheter att ¨oka effektivitet, styrbarhet och drifts¨ akerhet. P˚ a Uppsala Universitet finns en experimentgenerator, SVANTE, d¨ar nya tekniker kan utv¨arderas. P˚ a generatorns axel har en borstl¨ os matare monterats och f¨or att kunna k¨ora denna kr¨avs kraftelektronik f¨or att kontrollera exciteringsstr¨ommen till rotorn. Kraftelektroniken beh¨over i sin tur regleras samt att olika storheter s˚ asom sp¨anning, str¨om och magnetf¨alt beh¨over m¨atas. Detta examensarbete handlar om konstruktionen av ett inbyggt system f¨or att tr˚ adl¨ost h¨amta in m¨atdata fr˚ an sensorer samt styra kraftelektronik som sitter monterat p˚ a axeln i ett vattenkraftverk. Detta implementeras i programvaran LabVIEW fr˚ an National Instruments p˚ a en sbRIO-9606. Ut¨over detta konstrueras kretskort f¨ or m¨atning av magnetf¨alt upp till 700mT. Det konstruerade systemet fungerar tillfredsst¨allande och testas genom att en v¨axelriktare samt en DC-DC omvandlare styrs fr˚ an systemet. Magnetf¨altsensorerna fungerar bra ¨over hela m¨atomr˚ adet med bra linj¨ aritet och m¨ atnoggrannhet. Allt som allt har fyra kretskort designats och utv¨arderats dessutom har LabVIEW-kod skrivits.

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Contents 1 Introduction 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Project description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Theory 2.1 Excitation systems . . . . . . . . . . . . . . . . . . . . 2.2 Power electronics . . . . . . . . . . . . . . . . . . . . . 2.3 Bluetooth . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Serial peripheral interface . . . . . . . . . . . . . . . . 2.5 Aliasing and anti-aliasing filters . . . . . . . . . . . . . 2.6 Successive approximation analog to digital converters . 2.7 The Hall effect . . . . . . . . . . . . . . . . . . . . . . 2.8 Current measurement techniques . . . . . . . . . . . . 2.8.1 Resistive current sensing . . . . . . . . . . . . . 2.8.2 Current transformer . . . . . . . . . . . . . . . 2.8.3 Hall effect based current measurement . . . . . 2.9 Voltage measurement techniques . . . . . . . . . . . . 2.9.1 Resistive divider . . . . . . . . . . . . . . . . . 2.9.2 Hall effect based voltage measurement . . . . . 2.10 LabVIEW . . . . . . . . . . . . . . . . . . . . . . . . . 3 Method 3.1 System overview . . . . . . . . . . . . . . . 3.2 Single Board RIO, sbRIO-9606 . . . . . . . 3.3 General purpose inverter controller, NI 9683 3.4 Rotor main board . . . . . . . . . . . . . . 3.4.1 Power supply . . . . . . . . . . . . . 3.4.2 RN41XV, bluetooth module . . . . . 3.4.3 ADC input signal conditioning . . . 3.4.4 AD7490, analog to digital converter 3.4.5 Relay control . . . . . . . . . . . . . 3.5 Current measurement . . . . . . . . . . . . 3.6 Voltage measurement . . . . . . . . . . . . . 3.7 Magnetic field measurement . . . . . . . . . 3.8 Serial communication in LabVIEW . . . . . 3.9 SPI in LabVIEW . . . . . . . . . . . . . . . 4 Results 4.1 Magnetic field sensor . . . . . . . . 4.2 Rotor main board . . . . . . . . . 4.3 The finished main unit . . . . . . . 4.4 Rotor distribution boards . . . . . 4.4.1 Distribution board for rotor 4.4.2 Distribution board for rotor

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5 Conclusions

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Bibliography

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Appendices

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Appendix A LabVIEW code

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Appendix B Schematics and Layouts

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Introduction

The first modern hydropower plant in Sweden was constructed at the end of the ninetieth century, it was situated in the river Viskan and could produce 2.2kW. An extremely small generator by today’s standards but it was the start of an enormous exploitation of the Swedish rivers. Today, the total installed power is 16.15GW and in 2013, hydropower supplied 60.8TWh of energy to the Swedish grid. This corresponds to 41% of the total energy consumption [1]. The majority of today’s big hydropower plants were built in the 1950s and 1960s as a result of the construction of a 400kV transmission line from Harspr˚ anget to Hallsberg. The power plants are getting old so refurbishment and upgrades are required to keep up with today’s standards. In this process new technologies can be implemented to potentially increase reliability, controllability and efficiency.

1.1

Background

At the Division of Electricity, Uppsala University, an 185kVA experimental generator called SVANTE is available. Specifications of the machine can be seen in Tab. 1 [2]. Table 1: Main specifications of SVANTE. Frequency Number of pole pairs Speed Slots per pole and phase Number of stator slots Stator inner diameter Stator length Air gap length Power of driving motor Rotor weight Stator weight

50Hz 6 500rpm 3 108 725mm 303mm 8.3mm 75kW 900kg 700kg

At the moment upgrades are done to facilitate new research projects, below is a list of the new additions. • New shaft lathed to fit the new additions. • A six-phase brushless exciter. • Permanent magnet thrust bearing. • Electromagnetic thrust actuator. • Power electronics for active control of the exciter and rotor currents. • Sensor and control electronics.

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A CAD-drawing of the experimental rig with the new components installed can be seen in Fig. 1.

Figure 1: CAD-drawing of SVANTE with the new shaft [3].

1.2

Project description

With the installation of a brushless exciter on the shaft, there is a need for a way to rectify and control the excitation current in the main generator. An embedded control and measurement system mounted on the shaft is needed for for this purpose, the system shall communicate wirelessly to a main control unit and be able to drive power electronics devices. The project is separated into two parts with two thesis workers cooperating. This thesis will be 4

about the construction of the control and measurement systems while the other part is about the power electronics and the related control scheme. A specification of requirements is presented below. • Simultaneous sampling of currents and voltages relevant to the control of the active rectifier and the buck converters. • Enough processing power to implement space vector modulation. • Accurate measurement of magnetic field up to 700mT on the rotor poles. • Magnetic field measurements of 28 positions on the shaft. • Wireless communication to the system. • LabVIEW-programmable hardware The thesis describing the power electronics can be found here [4].

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2 2.1

Theory Excitation systems

Excitation systems can be classified into three categories based on the power source for the excitation. DC excitation systems DC generators are used as power source and provide the current to the rotor through slip rings. They were used in early hydropower systems but got superseded by AC exciters in the mid 1960s. AC excitation systems A second generator is used as power source, generally the generator is on the same shaft as the main generator. The AC output is then rectified and fed into the rotor windings. The rectification can either be stationary with current being fed through slip rings to the rotor, or it can be rotating and no slip rings is needed. Static excitation systems Static excitation systems supply the excitation current through slip rings and take their power directly from the main generator [6].

2.2

Power electronics

Power electronics is defined as the application of solid-state electronics to the control and conversion of electric power. It is based primarily on switching power semiconductor devices to generate a desired voltage or current [7].

2.3

Bluetooth

Bluetooth is a wireless technology for exchanging data, invented by Ericsson in 1994. It uses the 2.4GHz ISM band with gaussian frequency shift keying (GFSK) as modulation scheme. In GFSK the frequency of the carrier is shifted to carry the modulation, a binary 1 is represented by a positive deviation in frequency while a binary 0 is represented by a negative frequency deviation. Communication is based on a master-slave principle. One master device can control 7 slaves in a piconet, see Fig. 2.

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Figure 2: Bluetooth master-slave architecture with one master and four slaves. Bluetooth uses frequency hopping techniques to avoid interference. A transmission changes channel within the 2.4GHz ISM band 1600 times per second in a random pattern, this makes it more immune to interference. Version 2.1 + enhanced data rate (EDR) supports a bit rate of 3Mbps and utilizes phase shift keying (PSK) as well as GFSK as modulation schemes. Through the use of the protocol RFCOMM a wireless asynchronous serial port can be established between two devices, a useful feature for sending data between devices. In Tab. 2 the different classes of bluetooth devices are listed. It is sorted based on the transmit power, class 1 is mainly for industrial applications while class 2 is the standard for mobile phones and similar items. Table 2: Bluetooth classes and their corresponding transmit power and range. Class 1 2 3

Transmit power (dBm) 20 4 0

Range (m) 100 10 0.1

To start a bluetooth communication between devices a procedure known as pairing must take place. The process of pairing is as follows. 1. The devices look for other devices in range. 2. The user requests to pair with a specific device. 3. The device prompts for a passkey which is then compared with the other device. 4. If the keys are the same the connection is established. This is only done once, afterwards the devices are paired until a user deletes the pair [8, 9].

2.4

Serial peripheral interface

Serial peripheral interface is a serial data transfer protocol developed by Motorola. It is used for communication between devices in full-duplex mode. Generally a bus has one master and an arbitrary amount of slaves connected to the same data lines. The following lines are available. SCLK - Clock for the bus, controlled by the master. 7

MOSI - Master Out Slave In, output from master to slave. MISO - Master In Slave Out, output from slave to master. SS - Slave Select, used to select which peripheral that is allowed to use the bus. In Fig. 3 a block diagram of a typical SPI connection with two slaves is shown. SCLK MOSI MISO SS1 SS2 Master

SCLK MOSI MISO SS1 Slave 1 SCLK MOSI MISO SS2 Slave 2

Figure 3: Block diagram of a SPI bus with one master and two slaves. Since SPI is full duplex, data is exchanged simultaneously from and to the master. This is accomplished by using a circular buffer consisting of one shift register in the master and one in the slave, see Fig. 4, data exchange is done by shifting the bits between these two registers [10]. MASTER A0 A1 A2 A3 A4 A5 A6 A7

SLAVE MOSI

B0 B1 B2 B3 B4 B5 B6 B7

MISO Figure 4: Circular buffer between master and slave. In Fig. 5 the timing diagram for a transfer of one byte is shown. The communication starts by pulling SS low and the first bit is outputted from the master and the slave on MOSI and MISO. On the rising edge of the SCLK the bit on MISO is read by the master while the bit on MOSI is read by the slave. At the falling edge of SCLK a new bit is outputted on MISO and MOSI respectively and the process repeats until all bits are sent and SS is pulled high.

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Figure 5: Timing diagram for one byte transfer.

2.5

Aliasing and anti-aliasing filters

In sampled measurement systems the aliasing effect has to be considered. The Nyquist sampling theorem says that if you have a signal that is band limited to a bandwidth of fo then you can collect all information in that signal as long as your sample rate is higher than 2 ∗ fo , see Eq. (1). fo