MOVE 2014 DC Distribution for Electric Vehicle Development Prof. Eric Cheng The HK PolyU

Contents AC vs DC Power Distribution Lightings Energy storage Motors Solar The distribution V to G

AC Distribution AC power distribution is commonly used, and mature. Supporting Devices such as UPS, DVR, APF are well developed Ease with ac voltage conversion Transformer techniques have been used for good voltage and current conversion under various load conditions with High efficiency All associated protections have been developed: Voltage Transformation Circuit Breaker Protection Established Voltage Stability techniques

AC distribution with 220V and 50Hz (Existing system)

Why DC distribution Most of the electrical parts and systems are based on DC: lighting, heating, air-conditioning, elevator, escalator, entertainment appliances and industrial drives. They may accept or use AC but internally have embedded with an AC-DC converter to obtain the necessary DC. The DC distribution system is an alternative method for delivering power. The method has been proven to have advantages over the conventional AC distribution/transmission in terms of energy saving, operation and cost.

DC Distribution Versus AC Distribution Higher efficiency Suitable for today technology Easy to connect to renewable energy storage Work with electric vehicle for additional energy storage Higher efficiency for distribution Easy for different DC sources connected together.

Examples of DC The computer units are derived by low voltage DC such as 3-20V. The motor drive inverter also has a DC link supplied by AC-DC rectifier of around V. Most of the electronic lighting is now embedded with an electronic ballast which is also with a DC link of several hundred volts. The recent popular LED lighting is also a DC based system. Battery is also a DC System Solar Panel is DC source

Why not DC before Power Electronics has developed rapidly in last 2 decades for power conversion It allows the higher performance DC-DC power conversion The use of DC is now confirmed with the extensively use of –Energy storage –Inverter controlled motors –Renewable energy source

Examples of DC for Vehicles (transportation) ABB Onboard DC Grid use1000Vwith 20% saving in fuel efficiency improvement. DC Distribution has been in aircraft: F22 Raptor and Lockheed- Martin JSF X-35A/B/C Source : ABB Communications. c1257b ef.aspx

DC operation to apparatus and units in general

DC components development for Electric Vehicles Charger Battery Active suspension Integrated motor drive In-wheel motor Central computer Actuators

DC Distribution Improves power to computer Efficiency DC used for Computer units High efficiency for DC-DC power conversion for high speed computer Improved reliability using DC battery energy storage and capacitors

Smart DC City and V to G Vehicle provides DC energy storage Direct DC connection EV is a huge energy storage in city

LED lighting system DC based LED designed for front, rear & signal lights DC-DC power driver Thermal design Low loss Spectrum control

Power E.Research Center Energy Storage The energy storage devices are DC –DC battery –Fuel cell –Super-capacitor –Battery from Electric Vehicle or Hybrid vehicle

Battery Management Systems Why: –Balancing –Safety –Condition Monitoring State of charge SoC State of health SoH

17 Power circuit of active cell balancing

Energy storage / Battery management System Our solution: Very low loss balance Active balancing to reduce loss and improve response State of charge (SoC) and State of Health (SoH) estimation Suitable for renewable energy system and EV Integration of battery and super-capacitor Supercapacitor management Battery management Active balancing

Motor are DC driven Most motors such as DC, switched- reluctance, Induction, are driven with an inverter. Using DC will reduce the AC-DC sub-circuit

In-wheel SR Motor Technologies and Features : Based on switched-reluctance machines High efficiency High low speed torque Simple design and high performance 1 st SR in-wheel machines in the world Why our drive better: Fault tolerance Low cost – 20% <Induction Motors Low weight - 20% <Induction Motors Direct drive High power regenerative braking Extend to Anti-lock Braking System (ABS) Extend to Skid steering (EST) Specifications: DC Input:240V Power: 5kW Range: 50Nm Speed: rpm

In-wheel Electric Vehicle Fault tolerance No permanent magnets (no rare earth materials) Simple structure High speed High torque Future motors All classical problems have been solved

Wireless Power Transfer Allow DC power conversion to transfer through partition, glass or wall. Use the same technology for wireless charger High frequency resonant switching, magnetic resonant, near field analysis Power E.Research Center

Power System in Truck Solar Power Control System with MPPT Solar Photovoltaic Modules Battery Air Conditioner Control Unit A/C Power On Electrical Engineering Department, The Hong Kong Polytechnic University Solar Vehicles Vehicle Electronics

Example of development for Engineering Vehicles

Example of Development for Hong Kong Electric Lorry and Smart

Example of development

Safety Proposed Low voltage DC 20V –For control and power –Lower than extraneous safety voltage in different standards –SELV BS EN –ELV IEC (60V) –Lower than Zone 0 SELLV of Code of Practice Electrical Wiring of EMSD(30V)

Switching Install power breaker with zero-current switching: –Develop zero-current switching such as quasi- resonant, extended resonance and resonant transition. Residual current device: For unbalance current. MCCB/MCB for DC

The DC Smart Home

DC vehicle and distribution are important DC system to enhance new energy development in the all equipment. A set of new standards for DC system will be made, that is equivalent to its AC counter parts. The standards and the patent developed for the project is a wealth for the R&D. All the other parties have to follow our standards and patent for DC systems. More importantly, the system will provide good saving in materials and energy. It will make the system stable and more reliable and increase life time. The system is compatible with other renewable energy source and energy storage (All DC based). Power electronics is a driving technology for DC operation in EV

Problems encountered in DC distribution Switching: Requires soft-switching to turn on and off DC current. DC power conversion still need high frequency power in the intermediate stage DC safety: Electrostatic, electrolysis, electromigration EMC study for DC system

Conclusion EV is a micro grid of DC DC interfacing to DC grid is the future power conversion