Hengbing Zhao

Present and future applications of supercapacitors in electric and hybrid vehicles

This paper is concerned with supercapacitors (electrochemical capacitors) and their applications in electric drive vehicles in place of or in combination with batteries. The electric drive vehicles considered are hybrid vehicles. Data are presented for the new carbon/carbon device from Skeleton Technologies showing an energy density of 9 Wh/kg and 95% efficient power capability of 1730 W/kg. Both of these characteristics are significantly better than those of commercially available devices. Test data are also shown for a hybrid supercapacitor from Yunasko that has an energy density greater than 30 Wh/kg and a 95% efficient power capability of 3120 W/kg. This device has the best performance of any supercapacitor device tested at UC Davis to date. Various vehicle applications of supercapacitors have been reviewed in detail. Simulation results are presented for light duty vehicles using supercapacitors in place of lithium batteries in hybrid vehicles. It was found in all cases that the vehicles using the supercapacitors had the same as or better performance than those using batteries and in general were more efficient.

An intelligent solar powered battery buffered EV charging station with solar electricity forecasting and EV charging load projection functions

An intelligent energy management approach for a solar powered EV charging station with energy storage has been studied and demonstrated for a level 2 charger at the University of California-Davis West Village. The approach introduces solar PV electrical energy forecasting and EV charging demand projection to optimize the energy management of the charging station. The percentage of cloud cover is extracted from a weather forecast website for estimating the available PV electrical energy. A linear fit of the historical EV charging load from the same day of the week over the previous six weeks is employed for extracting the charging pattern of the workplace EV charging station. Both simulations and actual operation show that intelligent energy management for a charging station with a buffer battery can reduce impacts of the EV charging system on utility grids in terms of peak power demand and energy exchange, reduce grid system losses, and benefit the charging station owner through the Time-of-Use rate plans.

Ultracapacitors in micro-and mild hybrids with lead-acid batteries: Simulations and laboratory and in-vehicle testing

This paper describes work directed toward the demonstration of ultracapacitors in a 2001 Honda Insight. The general approach used in this project is to replace the NMH battery with ultracapacitor modules maintaining the 12V lead-acid battery to power the accessories. Both the ultracapacitors and the 12V battery will be recharged from the electric motor/generator driven by the engine. The Insight is being modified so that it can operate as a stop-start hybrid with and without power assist and as a mild hybrid using the full power capability of its 10 kW electric motor. In the case of the start-stop hybrid, the modified Insight will use 16V ultracapacitor modules; in the case of the mild hybrid, the vehicle will use 48V modules as part of a 176V electric driveline. The energy storage units have been tested in the laboratory using cycles appropriate for the vehicle tests. The energy storage and maximum power capability of each of the storage units was found to be sufficient to meet the project requirements at high efficiency for the vehicle test cycles. Careful laboratory testing of the vehicle systems is being performed in the laboratory using a Bitrode battery tester, which controls the discharge of the ultracapacitors and the lead-acid battery and provides for their appropriate charge as specified in the control strategy for the system. The Honda Insight has been equipped with a modified on-board diagnostics (OBD) readout unit which plugs into the standard OBD port in the vehicle. The readout displays conventional engine and electric driveline component data. A MIMA (Manual Integrated Motor Assist) kit, which has been installed in the Insight, permits the driver to modify and control manually the operation of the hybrid powertrain via a manual joy stick. A circuit board, which will replace the joystick with a programmed digital signal, is being developed. The operation of the Honda Insight has been simulated using the Advisor program, which has been modified at UC Davis to treat various hybrid drivelines including the micro-HEV and the mild hybrid cases. The simulation results indicate that the fuel economy of the micro-hybrid can be significantly higher than the conventional ICE vehicle, but significantly lower than that of a mild-hybrid using a higher power electric motor and a more extensive energy storage unit (battery or ultracapacitor). The simulations indicate that the fuel economies of the mild-hybrid using the NMH battery or the ultracapacitors are not expected to be much different.

Present and Future Applications of Supercapacitors in Electric and Hybrid Vehicles

This paper is concerned with supercapacitors (electrochemical capacitors) and their applications in electric drive vehicles in place of or in combination with batteries. The electric drive vehicles considered are hybrid vehicles and fuel cell vehicles. The first section of the paper presents recent test data for advanced proto-type devices. The data for the new carbon/carbon device from Skeleton Technologies showed an energy density of 9 Wh/kg and 95% efficient power capability of 1730 W/kg. Both of these characteristics are significantly better than those of commercially available devices. Test data are shown for a hybrid supercapacitor from Vunasko that has an energy density greater than 30 Wh/kg and a 95% efficient power capability of 3120 W/kg. This device has the best performance of any supercapacitor device tested at TIC Davis to date. Various vehicle applications of supercapacitors have been reviewed in detail. Simulation results are presented for light duty vehicles using supercapacitors in place of lithium batteries in hybrid and fuel cell vehicles. It was found in all cases that the vehicles using the supercapacitors had the same as or better performance than those using batteries and in general were more efficient. The cost of supercapacitors compared to lithium batteries was discussed briefly. It was shown that when one recognizes that the energy stored in the capacitors is less than 1/10 that in the batteries for hybrid applications, the price of supercapacitors needs to decrease to about .5.1 cent Farad for capacitors to be cost competitive with high power batteries at

A Comparison of Zero-Emission Highway Trucking Technologies

500-700/kWh. In addition, there is a good possibility that the life of the capacitors would be equal to that of the hybrid vehicles.

Evaluation of a PV Powered EV Charging Station and Its Buffer Battery

Author(s): Zhao, Hengbing, PhD; Wang, Qian; Fulton, Lewis, PhD; Jaller, Miguel, PhD; Burke, Andrew, PhD | Abstract: Zero-emission long-haul trucking technologies are being developed that can play a critical role in achieving California’s climate change goals and virtually eliminate air pollution from these vehicles. Hydrogen fuel-cell electric, catenary electric and dynamic inductive charging technologies are being demonstrated in small scale projects worldwide. In this study, these three zero-emission truck technologies were reviewed in detail and vehicle and infrastructure challenges and costs for each of the technologies assessed. In the near- to mid-term, electrifying the entire California state highway system or deploying large hydrogen stations at many statewide truck stops would require very large capital costs, on the order of billions of dollars, even though, at least initially, there will likely be relatively few zero-emission long-haul trucks in use. Considering technology readiness, energy efficiency, and capital cost, the most feasible approach for the zero-emission technologies for long-haul trucks may be to deploy local or regional catenary systems. Dynamic inductive charge systems could be introduced, though with perhaps more disruption as roadways are prepared for this service. Hydrogen fuel cell trucks will benefit from some scalability but will require large hydrogen refueling stations along highways. The initial “up-front” investment in infrastructure for hydrogen trucks appears somewhat lower than for the other two options but the cost of providing hydrogen to vehicles will be high, especially if provided using electrolysis. In the longer-term, all three of the technologies could become economically competitive with diesel trucking, though this depends on many factors and uncertainties.

Optimization of Fuel Cell System Operating Conditions for Fuel Cell Vehicles

This research analyses the operation of a solar PV powered electric vehicle charging station with energy storage that has been developed and demonstrated at the University of California – Davis, West Village, the largest planned zero-energy consumption community in the U.S. The intelligent energy management approach introduces solar PV electrical energy forecasting and EV charging demand projection to optimize the state of charge (SOC) of the buffer battery. The charging station has been operated continuously and routinely used by several EV users for a year. The actual operation shows that a workplace charging station equipped with a buffer battery and with intelligent energy management can lower and reduce the station’s peak power demand and reduce the energy exchange with the utility grid by a factor of 2. The battery recharging power demand was shifted away from the on-peak time periods to the off-peak time periods, which will benefit the charging station owner from less energy use during peak periods when time-of-use rates are higher. The standard cell voltage deviation of the 220 cells was calculated to analyse the battery cell consistency during the resting, charging, and discharging periods. The analysis shows that the 220 50Ah cells show excellent voltage consistency with voltage deviation of less than 0.005 V within the battery SOC of 20-80%. The voltage deviation doubles when the battery SOC reaches 90%. The comparison of cell voltage deviation at the beginning and after one year operation indicates that the battery shows perfect cell voltage consistency and there is no obvious consistency deterioration during the battery resting, charging and discharging periods.