Solar-DC: L2 Powering Residential and Business Sectors

1. Solar-DC: L2Powering Residential and Business Sectors Ashok Jhunjhunwala, ashok@tenet.res.in Prabhjot Kaur IIT Madras

2. L2: DC Powering for Appliances Having seen the case for DC power-lines at homes, let us look at appliances Appliances, Motors and recent trends Use of direct DC power replacing AC power Efficiencies, Availability, Costs

3. Changing trends in Appliances: some Examples • TV • Sizes and shapes • Electronics • Display technology

4. PRESENT TECHNOLOGY- LED TV 40 % less Power consumption 30% Less cost LEDs areDC-powered

5. Lighting The data is from our Lab tests/ estimations from specifications of some brands in market / internet

6. Microwave Oven - Evolution 2000 1947 900 watts 3000 watts

7. What is Common in advancing Appliances? 240 volts AC LED Lights are DC LED TVs are DC Latest Microwaves are DC 3000 volts AC >3000 volts DC Reduced Power consumption Reduced sizes Ease of Use Reduced Cost What drives: Movement from AC to DC Technology - common to all appliances Electronics is anyways DC : Laptops, Mobile Phones, computers, speakers etc.

8. Motored Loads is the next biggest load • Which are the motorizedLoads? • Fans • Air Conditioner • Washing Machine • Water Pumps • Mixers and Grinders • The Energy consumption and Efficiency of these appliances depend largely on the type of motor used

9. Introduction to Motors

10. Principle • Create Magnetic fields which oppose each other • Resultant force makes rotor to turn • Stator is always stationary • Both Stator as well as Rotor could be either permanent Magnet or Electro-magnet • If rotor is an electro-magnet, fed by external DC voltage, it would need brushes • Brushes have maintenance issues and looses • AC at 50 Hz reverses poles in every cycle (50 times per second) • Motors designed to rotate at fixed speed could be simple • Will not require brush

11. 3-phase AC Induction Motor 3-phase AC Motor example Problem of non-smooth torque can be corrected by three phase AC Induction Motor

12. 3 phase AC Induction Motor Source: http://www.mpoweruk.com/motorsac.htm Source: https://en.wikipedia.org/wiki/Induction_motor Working Principle • 3 phase winding circuit on stator (with offset electrical angle of 120 deg) connected to 3 phase AC source: will make rotation smooth • establishes a rotating magnetic field in Rotor (with coil forming closed loop), rotates at synchronous speed • Speed of motor, Motor RPM = (120 X f ) /P, where f = supply frequency (in cycles/sec), P = Number of motor windings pole

13. New Generation Motors: Enabled by Power Electronics • Power Electronics gives us ability to design pulse shape for power signals • Signals with different pulse-widths, switching on and off at different times can create varying Magnetic field • Start with DC power Signals (if AC alone is available, convert first to DC) • Create multiple signals (three or six or whatever) with frequency varying in time

14. BLDC Motor Working Principle Stator windings are supplied with current to produce magnetic field Power Electronics control the currents through the windings Rotor magnetic field created by permanent magnet Opposing magnetic field causes motor to rotate. Highlights Core and Rotor losses are nil so efficiency increased by 10 % Mostly uses powerful Neodymium magnet With speed change, efficiency remains constant Very low power factor Limitation: Dependency on permanent magnet and presently expensive

15. SRM Motor Working Principle • Power applied to stator windings (6 poles) induce rotor magnetic reluctance: creates force that attempts to align the rotor pole with nearest stator pole • Number of stator / rotor poles can be varied: 6/4 SR motor has 6 stator and 4 rotor poles • Electronics used to switch on the windings of successive stator pole in sequence Highlights • No permanent magnets required • Have torque ripple and noise: can be controlled by large number of poles and signal design • China has 90% of rare-earth materials (like Nb) used in permanent magnet • may control prices tomorrow • SR Motors use only steel produced by SAIL

16. New Generation Motors • New Generation Motors have far higher efficiencies • But need DC power to begin with • Also called DC-powered Motors

17. Speed-control for existing AC Motor Appliances • Speed Control of AC Induction Motor enabled by a Variable Frequency Drive (VFD): can be retro-fitted • Huge amount of power saving • Low starting current • Controlled power factor • Applications • Electric Vehicles • Air conditioning systems • Most industrial machinery • Lifts and pumps • Domestic appliances, fans, cooler etc.

18. Variable Frequency Drive AC DC AC RECTIFIER (AC - DC) INVERTER (DC - AC) 50 Hz Power Zero - 50 Hz 50 Hz To Motor VFD Zero - 50 Hz Electrical Energy • A variable frequency drive converts 50 Hz utility power into DC, then converts to a variable voltage, variable frequency output • By switching the inverter device on and off many times per half cycle, a pseudo-sinusoidal current waveform generated at desired frequency • Efficiency can improve at lower speeds

19. Summarizing the Move towards DC appliances • All home / office appliances are shifting to DC technology • Bring in huge efficiencies • Integrates with DC electronics • Becoming Smarter and smaller • These DC appliances need an AC-DC converter if powered by AC • Costs + additional power-loss + point of failure • Strong Case for using DC micro-grid at homes / offices • Easier integration of renewable energy sourcesas all renewables are DC power sources • Easier integration of power-storage

20. Time for Quiz: 1. Which among these appliances run on motor (i) Air conditioner (ii) Fan (iii) TV (iv) Inverter • i & ii • ii &iii • iii & iv • i& iv Ans: a 2. Which motors amongst these have highest energy efficiency? • PMDC motor • Single phase induction motor • BLDC motor • Three phase induction motor Ans. c

21. DC Motors DC motor animation • Stator PM or Electromagnet with DC Power: fixed magnetic field • Rotor is electromagnet with DC power connected through brushes • Initially rotates, as it rotates, brushes change the direction of current, rotates again • Problem: Torque is not uniform and goes to zero when Rotor magnetic field is perpendicular to stator magnetic field + poor efficiency due to brushes

22. AC Motor Single phase Ac Induction motor diagram • AC at 50 Hz reverses poles in every cycle (50 times per second) • So if Stator is given AC, its magnetic field will reverse every 10 msec • Rotor can be permanent Magnet • or Induced magnet (coil loop around magnetic core): Induction Motor • Rotor will rotate at 50 Hz

23. Single phase AC Induction Motor • Highlights • Efficiency 75 – 85 % • Five types of losses: • Core (hysteresis + eddy current ): 25% • Stator (I2R loses): 35% • Rotor (I2R losses ): 25% • Friction: 5% • Stray: 10% • Power factor is very high at reduced loads • Efficiency decreases on decreasing the load & rpm • Additional energy is consumed in inducing a secondary magnetic field • Working Principle • Stator windings supplied with AC current to produce changing magnetic field • Rotor is magnetic material with coil-loop; Secondary magnetic field induced in rotor produces current • Opposing magnetic field causes rotation • But rotation will not be smooth Image courtesy: http://www.learnengineering.org/2013/08/three-phase-induction-motor-working-squirrel-cage.html

24. When Motors drive a fan