* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Power Systems for Aerospace, Marine and
Power over Ethernet wikipedia , lookup
Electric machine wikipedia , lookup
Ground (electricity) wikipedia , lookup
Solar micro-inverter wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Current source wikipedia , lookup
Audio power wikipedia , lookup
Power factor wikipedia , lookup
Electrical ballast wikipedia , lookup
Induction motor wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Fault tolerance wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Utility frequency wikipedia , lookup
Power MOSFET wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Electric power system wikipedia , lookup
Electrical substation wikipedia , lookup
Opto-isolator wikipedia , lookup
Surge protector wikipedia , lookup
Stray voltage wikipedia , lookup
Stepper motor wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Electrification wikipedia , lookup
Power engineering wikipedia , lookup
Power inverter wikipedia , lookup
Three-phase electric power wikipedia , lookup
History of electric power transmission wikipedia , lookup
Distribution management system wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
Voltage optimisation wikipedia , lookup
Buck converter wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Mains electricity wikipedia , lookup
Power Systems for Aerospace, Marine and Automotive Applications (H64AN1) Power converters The More Electric Aircraft Motivations: Fuel burn/efficiency, reliability, maintainability, availability, dispachability, performance, weight/size, cost Remove hydraulic system: reduce weight, easy maintenance, power on demand Remove pneumatic system: improved efficiency “bleedless” engine Advanced diagnostics and prognostics: increased availability Lower running costs (less maintenance scheduled and unscheduled) Challenges High quality electric motor drives DC link capacitors Power quality and stability Weight/volume (conversion/wiring/power distribution significant) Total non-thrust power more than 1MW Generator Control Unit, GCU: Regulates voltage, Protects generator, Controls & excites generator, Manages main bus contactors APU LSG 2x250kVA RSG 2x225kVA For 2 motors, the options are: 2 single converters powering each motor o 2 DC capacitors, 2 heat sinks - large/heavy system Dual use power converter o Share 1 converter using a switch to operate either motor - large/inefficient due to switch contacts (higher losses) Dual output power converter o Shared DC capacitor, heat sink & current measurement + Individual power semiconductors allows system optimisation for each motor + 1 Hall Effect transducer + shared rectifier circuit means cost/weight/size decreases Future HVDC systems 2x250kVA Power distribution Left Side Generator and RSG connected to engines Auxiliary Power Unit (APU) is a gas turbine generator located at the back of the plane, used to start engine, run ECS without running main engines, and can also act as back up to a failed engine/generator Electrical power distribution system 28V DC loads (small aircraft) 115V AC 3phase loads (current civil standard) 230V AC 3- ±270V DC phase VF (future loads (future military) civil) Aerospace voltages quoted as line to neutral (peak): 230V peak 400V line to line Electro-Mechanical actuator (EMA): Power Motor o Actuator is moved as motor spins converter Reduction + compact gearbox – ball screw can jam (surface unmovable) Electro-Hydrostatic Actuator (EHA) o No direct connection between motor and actuator arm o 3-ph supplypower convertermotorpumphydraulic ram + surface is movable if there is a hydraulics failure (fluid leak) + familiar technology for aircraft component manufacturers Actuator control: Power converter o All controlled surfaces can be Supply Converter output current (300Hz control loop) powered by more than 1 Control Motor speed (30Hz control loop) voltage transducers Ram position (2Hz control loop) power source Feedback o Actuation can be controlled by Actuator/ram position demand hydraulic and/or electrical circuits Primary: critical for flight e.g. ailerons, rudder, elevators. Secondary: useful for comfort and safety but not critical e.g. flaps, slats Ball screw Electrical power systems Model based design electrical systems simulation o Validate/verify requirements o Model faults and analyse stability/transients o Use distributed computing for faster results of complex (behavioural) models Diagnostics: what the malfunction is and the cause Prognostics: prediction of failure of device/system Power failure sequence: Main generators (duplex and quadplex systems) Large users of power: Environmental Control System (for cabin heating/cooling, pressurisation during flight), WIPS (Wing Ice Protection System), actuation o Pneumatic (WPS, ECS, engine start) o Hydraulic (slats, flaps, landing gear) o Electrical (galleys/lights, avionics) Generator Control Unit (GCU) works like a voltage regulator DC (GRbusIloads) vs. AC (GbusAC-AC converterloads) + Distributed energy storage + Variable frequency systems + Fewer conductors required - Power stages more complex (internal energy storage often required – less efficient) - Rectifier in critical path to all loads + Only 1 power conversion stage - Circuit breakers much bigger + Circuit breakers small & cheap o AC power generation is conventionally sourced by constant frequency generators fed by a Constant Speed Drive Constant speed shaft Variable speed 3-phase (CSD) which produces a fixed output CSD Generator engine 400Hz, 115V of 400z + allows generators to operate in parallel - expensive to purchase & maintain (due to patents) o Variable Speed/Constant Frequency generation: - not yet proven technology, power Variable speed 3-phase VF Power Generator engine 400Hz, converter converter is key failure point 115V o Variable Frequency generation: + generator directly connected to power Variable speed 3-phase bus (simple & reliable) Generator engine 320-900Hz, 230V or 115V + cheaper - requires motor drives (IM’s performance decrease & weight increase) fuel and hydraulic pumps heavier and less reliable Ground Power Supply: Rectification techniques: 3 or 6 phase o 6-pulse diode Aircraft 400Hz 50Hz Output PWM controlled Transformer Rectifier power filter inverter bridge (5 leg) bridge rectifier mains (400Hz) 6-pulse Provides isolation Attenuates sw. Controls output + simple circuit diode bridge (& voltage gain) frequency components voltage waveform - large 5th and 7th harmonics o Autotransformer (ATRU) and 12-pulse rectifier + cancellation of 5th and 7th harmonics - requires inter-phase reactors Actuators: + no reactive power + fewer wires + no AC losses + no frequency effects (like skin effect) - safety issues - AC supply from generators needs rectification (heavy transformers) failure → failure APU start & batteries → Ram Air Turbine deployed & batteries o Multiple sources of power required: To ensure fault tolerant systems To reach required failure levels for flight Protection features: o I2t protects wires from thermal overloads Simple process I2R o Arc Fault Protection (AFP), Delta Current (ΔC), Ground Fault Interruption (GFI), Differential Protection (DP) Electrical load management systems Electro-mechanical relay and electro-thermal circuit breaker + Well understood technology + Air gap isolation + High tolerance to over voltages + High temperature relay performance + Low on state resistance - Lots of wiring Contactors and relays - Requires electronics to provide protection - Slow on/off times - Lack of control - Slow improving technology Solid State Power Controller (SSPC) + Switch DC currents + Fast (µs) + No arcing + Can detect faults other than short circuits + Facilitates more efficient power distribution technologies + Improved diagnostics and prognostics + Technology improvements expected + Cost coming down The More Electric Car Hybrids Petrol is very good for energy storage, batteries have poor kW/kg Series hybrid Battery Series o + urban driving (stop/start) Power hybrid Motor converter Parallel hybrid Engine Gen o + can be driven by engine or battery or both Power o + regenerative braking Battery converter Motor/ Series-parallel hybrid Parallel generator hybrid Engine o Combination of both using mechanical power splitter Hybrid terms in common use: o Full hybrid: vehicle can drive with just batteries, engine or both – requires large and expensive lithium ion batteries o Mild hybrid: engine used for primary power, motor used for start, acceleration and regenerative braking o Soft hybrid: similar to mild hybrid but motor not used for acceleration 12V vs. 42V + Optimised technology + More efficient for higher power systems + Proven systems/reliability + Reduced mass and volume (motors) - Relative short - Potential safety issues (electrocution, customer perception) term cost - Cost of change (development, retraining…) Initial systems will have a hybrid of 12V/42V using DC-DC converter Peak powers of systems usually much more than average power Wheels Wheels High Voltage design and testing Marine power systems Modern systems have a mixture of gas turbine and diesel generators to supply HV bus and LV bus o + reduced fuel consumption o + faster response + better manoeuvrability o + reduction in volume o + less propulsion noise + less vibration o – increased investment costs o – bigger variety of components o – cost of service skills and maintenance engineers Voltages from 11kV (for 20MW) to 440V 60Hz (common for American low power devices) Inverters LV: VSI IGBT Cycloconverter Multi-level VSI CSI :HV Switching devices Motor waveforms Control VSI IGBTs + Very high switching frequencies + Low switching losses - Low voltages - Relatively low current - Expensive for power level - High conduction losses PWM waveform + Good motor voltage and current waveforms + Smooth torque reduces motor losses, noise in propeller signature and vibration - Poor input harmonics + PWM control is conventional technology + Can achieve very high performance with vector control + Faster torque response than CSI or cycloconverter Cycloconverter CSI Thyristors + Cheap for power level + High voltage and current ratings + Low on state losses - Poor supply power factor at low speeds - Harmonic rich supply current Switches parts of Quasi-square supply voltage into wave motor motor current + Better current - Pulsations in waveforms than CSI current/torque + High torque - Spikes in - Motor frequency < supply voltage 1/3 supply frequency (due to high slow speed di/dt) - Supply PF lag - May need - Speed dependant PWM at low harmonics speeds - Big converter (each + Relatively phase must be simple control isolated) + Thyristor - Requires 2 bridges inverter very per phase for bisimple directional current - Performance limited by slow switching of thyristors Current Source Inverter (CSI) o Rectifier feeds large inductor, inverter directs DC current into phases of synchronous AC machine 2 bridges (for bidirectional current) Cycloconverter: Supply Load o Direct AC-AC converter that switches Transformer parts of input voltage for isolation Voltage Source Inverter (VSI) o 3-ph supply rectifier DC link IGBT inverter Induction Motor Multilevel VSI o Connect lower voltage IGBTs in series (in a 2-level inverter) or use diode clamped inverter: o + Better output voltage than 2-level VSI o Use 3-level/5-level/7-level… inverters to produce better output voltages and reduce device voltage balancing o T45 uses VSI drive for Advanced Induction Motor (AIM) which has 3 channels x 5 Hbridges (= 15 phases/windings in total) + Fault tolerant + Efficient at low speeds/loads Podded systems Motor and propeller are outside main ship body, power converter is still in the ship o Saves space in the ship o Greater manoeuvrability (since pod can rotate ±180°) Definitions: Tracking: progressive formation of a conducting path o occurs at any voltage Partial discharge: electrical discharge which does not completely bridge gap o Reduces life of insulation, fast nanosecond current pulses - EMC issues Disruptive discharge: completely bridges gap Cable o Can permanently damage insulation Partial discharge Conductor Void Corona Types: Ground Air o Voids within cable insulation: Ground o Corona discharge around a conductor’s sharp point: Surface Air o Surface discharge between 2 conductors: discharge Ground o Partial discharge between wire and plane Paschen’s law defines minimum voltage at which breakdown occurs in an insulator with uniform field (327V in air) making modifications for temperature and operating frequency Breakdown occurs when accelerated electrons create additional electrons (ionisation) upon impact with insulator molecules and is self-sustaining o Acceleration, a = qE/m the higher the velocity, the higher the probability of ionising collisions o Mean free path: electron’s average distance between collisions High gas density low mean free path o Townsend breakdown: electron avalanche positive ions accelerate to the cathode secondary electrons new avalanche o Higher temperature lower gas density higher mean free path o In non-uniform fields, partial discharge is determined by how sharp the electrode is, breakdown is mainly determined by gap size Gap clearance = Pam/Pa o 1 mbar = 100 Pa o Vpk = √2 x Vrms o Every 25° above room temperature adds 0.1mm clearance o Critical frequency = 200/d (kHz) where d is gap distance (mm) Slow moving positive ions distort the electric field decrease breakdown voltage by 20% Above critical frequency, add 20% clearance Dielectric analysis of solid insulation can predict the partial discharge inception voltage 𝑡𝜀 The percentage of the system voltage through an air gap = 𝑟 Insulation o εr is the relative permittivity of the cable insulator 𝑉 o 𝑉𝑠𝑎𝑓𝑒 = 𝑏𝑟𝑒𝑎𝑘𝑑𝑜𝑤𝑛 𝑜𝑓 𝑎𝑖𝑟 𝑔𝑎𝑝 % 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑖𝑛 𝑎𝑖𝑟 𝑔𝑎𝑝 𝑑+𝑡𝜀𝑟 Insulation +V Cable d Electric field distribution in steady state DC system Air t defined by resistivity varies significantly with 0V Ground temperature o Discharge recharges much slower in DC system In an aircraft, as conductor size increases insulation decreases (due to size/weight constraints) voltage rating decreases o A higher voltage rating does not necessarily compensate for a decrease in current rating PD Corona/voids/surface PD testing: amplitude PD Test PD AC o Optical, RF/EMI, acoustic object LCR 270° Phase 0 o Electrical: 90° o Results: PD detector Tracking Voltage to allow tracking based on voltage required to evaporate a contaminant o Boiling point, θliquid is lower at lower pressure (higher altitudes) o 𝑉 2 𝑤ℎ 𝜌(𝜃𝑙𝑖𝑞𝑢𝑖𝑑 )𝑑 = 𝜃𝑙𝑖𝑞𝑢𝑖𝑑 −𝜗𝑎𝑚𝑏𝑖𝑒𝑛𝑡 𝑇 o To prevent tracking: Make sure system cannot be polluted (keep clean/dry) Use coating to restrict flow between electrodes User interface (steering wheel) Electric Power Steering Modernisation of power steering: o (Currently) electrically assisted hydraulic electric With power system steer-by-wire (no mechanical feedback motor connection) Encoder Challenges/requirements: o High power density Microprocessor o High efficiency (controller) o High reliability (10ppm failure rate) o Silent operation Power Power converter converter o Ultra low torque ripple o Very high safety integrity OS motor/ NS motor/ o 12V supply actuator actuator Types: o Pinion drive o Rack drive: motor placed on rack o Column drive: motor near steering wheel Diagram of main steer-by-wire system: Microprocessor controller uses shunt resistor in return path (high reliability due to low component count) and vector control Power considerations: o Peak power ≈ 1.2kW, 60-80A o Battery harness (important) ≈ 10-20mΩ, 1-2V drop Torque ripple components: o Fundamental ripple o Harmonics due to manufacturing deviations o Harmonics due to errors n current measurements Solution: introduce cancellation harmonics in software Safety and reliability o Failure Mode and Effects Analysis (FMEA) o Fault Tree Analysis o Diagnostics o Eliminate failure modes by design Voltage boost system: HV bus DC-DC 3-phase 12V Battery EMC filter Motor converter inverter o By using HV, it: Motor position + eliminates supply Supercapacitor and current Controller fluctuations at input of drive + reduces current rating T + increases performance + decreased torque ripple 28V 12V + cost/size of motor decreases Speed + torque-speed envelope is extended: o By interleaving, the following are achieved: + low input and DC capacitor current ripple + low device current ratings + possible redundancy + separation of heat generating components + smaller capacitor, thus improved transient response - more complex control - increased component count Future o New motor designs o Moving EPS technology to other automotive applications (e.g. clutch, braking…) + reduces development costs o Sensorless control + lower component count lower cost + higher reliability - low speed - more complex control - audible noise (from carrier signal injection) - additional sensor needed for di/dt techniques (for short periods of energy boost) Reliability calculations Power quality Motor current harmonics T ripple and motor overheating Supply voltage harmonics may cause malfunction of equipment Supply current harmonics due to rectifiers voltage harmonics due to supply/cable/transformer impedance o – thermal overloads in cables/transformers o – extra transmission losses Transformer o – can cause interference to secondary side Input reactor Rectifier telecommunication systems PF correction M o – false tripping of circuit breakers capacitor bank (improves operation at low speed) Example harmonic current source: o Severe voltage distortion by PF correction capacitor interacting with supply impedance o PF correction capacitor is low impedance at high frequency thus will draw harmonic currents which can get quite big Harmonics occur at frequencies given by 6k±1 (k=1,2,3…) 𝑇𝐻𝐷 = 2 √∑∞ 𝑛=2 𝐼𝑛 𝐼𝑓 where If is the fundamental magnitude Mitigate harmonics by: Adding supply or DC link inductance o + makes output current continuous o + passive approach o - DC voltage decreases (voltage drop across L) Multi-pulse techniques: connect “n” 6-pulse bridge rectifiers in series/parallel supplied from seperate 3-phase supplies phase shifted by 60°/n o + results in cancellation of odd k harmonics (when n=2) Supply o - requires extra transformers and bridge 2 bridges (30° Transformer rectifiers phase shift) o Harmonic orders still present are 6nk±1 Add passive (shunt) filters with low impedance connected in parallel to harmonic source o + most harmonic current flows into filter instead of source o - can introduce resonance in supply o - can be large/bulky o Single tuned notch filter (LC circuit) most common 1 o Where the harmonic filter impedance, 𝑍ℎ = 𝑋𝐿 + 𝑋𝐶 = 𝑗𝜔𝐿𝑓 + = Load 𝑗𝜔𝐶𝑓 𝑗𝜔𝐿𝑓 (1 − 𝜔𝑠 = √ 𝐿 1 𝜔2 𝐿𝑓 𝐶𝑓 ) thus a zero impedance (series resonance) at frequency, 1 𝑓 𝐶𝑓 However, there is parallel resonance (high impedance) due to supply impedance just below notch frequency, 𝜔𝑝 = √(𝐿 1 𝑠 +𝐿𝑓 )𝐶𝑓 so must make sure this isn’t near any significant harmonics, though generators don’t tend to generate even harmonics 𝑉2 Reactive power, 𝑄 = 𝐿𝐿 (VAr) [x transformer %] 𝑋 Rated IC = reactive power per phase (Q/3) / phase voltage (415/√3) Current drawn due to supply distortion, Ish = phase voltage distortion / filter impedance at harmonic frequency Current drawn at hth harmonic due to load = Ilh Worst case for total harmonic current when Ish and Ilh in phase (thus sum) + efficient way to reduce harmonic distortion + can connect several different filters for different frequencies - complex to design, need to take into account change in resonant frequency, voltage distortion harmonic currents from other loads, no limit on harmonic current o Add Active Shunt Filter (ASF): a power converter (controlled current source) connected in parallel to harmonic source that inject cancellation harmonics at point of common coupling + 1 filter can compensate for many frequencies (wideband harmonic mitigation) If+Ih If Non-linear + reactive power compensation load -Ih - requires very fast current control loops Shunt filter - expensive o Use a sinusoidal (PWM) rectifier: that acts as a controlled voltage source + has switching harmonics that can be easily reduced with a passive filter - very expensive Reliability: uses MTBF and λ and is determined by individual components in system. Optimised in actuation and ECS systems. o Mean Time Before Failure, MTBF = 1/λ (hours) where λ is failure rate λ of individual components are split into sections/levels λ sum for next level and multiply in same level with duplex systems o MTBF method used because aircraft operators would like to predict time to failure for preventative maintenance and reduced operating costs. But it does not take into account: Power system protection Reason for failure Must distinguish between transients and faults to prevent false trips Build quality Transients (voltage swells) caused by sudden removal of a large load Actual operating environment generator control cannot act quickly enough control causes change in system The impact of a failure on other components voltage (and frequency) Availability: how likely a component will work. Optimised with duplication of onidentical components for redundancy at expense of reliability e.g. fuel pumps