Fuyuan Yang

Dynamic Programming Algorithm for minimizing operating cost of a PEM fuel cell vehicle

A PEM (Proton Exchange Membrane) fuel cell city bus utilizes a PEM fuel cell engine as the primary source, and a li-ion battery system as the auxiliary power source. By optimizing the power split strategy and recycling braking energy, this kind of power-train has advantages of zero emission and high energy efficiency. However, the cost of hydrogen gas is far more expensive than that of the electric energy. How to split the power between the two power sources so as to minimize the operating cost, as well as guarantee the vehicle dynamic performance, becomes an important topic. This paper proposes a Dynamic Programming Algorithm (DPA) to solve the minimizing problem. Some details of the DPA are discussed, e.g. the principles of selecting parameters for the algorithm. The effectiveness of the algorithm is verified by comparing simulating results of different algorithms. Results show that, 1) by using the DPA algorithm, we can find the optimal control strategy in an objective way. 2) The constraints of vehicle dynamic performance on the optimal problem have great influences on the optimal results. 3) To predict the power requirement in the near future is very important to achieve an optimal real-time strategy.

Equivalent Consumption Minimization Strategies of Series Hybrid City Buses

With ever growing concerns on energy crisis and environmental issues, alternative clean and energy efficient vehicles are favoured for public applications. Internal combustion engine(ICE)-powered series hybrid buses and fuel cell (FC) hybrid buses, respectively as a near-term and long-term strategy, have a very promising application prospect. The series hybrid vehicle utilizes an ICE/FC as the main power source and a battery/ultra capacity (UC) as the auxiliary power source. The main power source supplies the average vehicle power, and the auxiliary power source functions during accelerating and decelerating. Because the battery/UC fulfills the transient power demand fluctuations, the ICE/FC can work steadly. Thus, the durability of the fuel cell stack could be improved compared with a pure FC-powered bus in the FC series hybrid bus. And the PM and NOx can be greatly lowered in the ICE series hybrid bus compared with a traditional city bus. Besides, the ability of the energy storage source to recover braking energy enhances the fuel economy greatly. The hybrid configuration raises the question of energy management strategy, which chooses the power split between the two. The strategy is developed to achieve system-level objectives, e.g. fuel economy, low emission and battery charge-sustaining, while satisfying system constraints. Energy management strategies in the recent literature can be generally categorized into two types: rule-based strategies and optimal strategies. A rule based strategy can be easily implemented for the real-time applications based on heuristics (N.Jalil, N.A.Kheir & M.Salman, 1997). Such a strategy could be further improved by extracting optimal rules from optimal algorithms (S.Aoyagi, Y.Hasegawa & T.Yonekura, 2001). Optimal strategies differ from each other in the time range. Fuel consumption in a single control cycle is minimized in an instantaneous optimal strategy (G.Paganelli, S.Delprat & T.M.Guerra, 2002). And a global optimal strategy minimises it over a whole determined driving cycle using determined dynamic programming method (DDP) (Chan Chiao Lin et al., 2003), or over a undetermined driving cycle using stochastic dynamic programming method (SDP) (Andreas Schell et al., 2005). Other strategies minimize fuel consumption over an adaptive time span, which could be adjusted on the basis of vehicular speed, pedal 7

SOC Detection of Diesel Engines Based on Online Estimation of Motored Pressure

In this paper, a diesel SOC (Start of Combustion) online detection method is developed in a diesel engine equipped with serial produced in-cylinder pressure signal sensors. Motored pressure trace is estimated in real time and the difference between the measured actual cylinder pressure and the estimated motored pressure is calculated. SOC is defined as the separation point of the two different pressure traces. In order to realize accurate motored pressure estimation, a thermodynamic analysis of the motored process of engines is done and a new concept “equivalent adiabatic exponent” is proposed. The pressure difference 0.2 MPa is taken as the criteria of combustion start. The SOC detection algorithm is executed in a MCU based electronic control unit. Engine tests are done in steady states as well as dynamic states.Copyright

Transient control of low-temperature premixed combustion using ISG motor dynamic torque compensation

The use of low-temperature premixed combustion can significantly reduce NOx and soot emission of diesel engines. However, due to application of high EGR rate, the combustion process is sensitive to the variation of the intake fresh air amount. In engine transient operating conditions, the reduction of oxygen concentration of the fuel-air mixture will lead to deterioration of soot emission and the thermal efficiency. Limiting the transient air-fuel ratio by reducing the fuel injection amount is a feasible solution to eliminate the soot emission peak. However it will result in insufficient power output of the engine. In order to solve this problem, an ISG motor, which has the advantage of fast torque response, is integrated on the diesel engine. An in-cylinder pressure based engine torque on-board estimation method is designed and verified. Through calculating the difference between the desired engine torque and the actual engine output torque, a strategy using ISG motor dynamic torque compensation to improve transient power performance is designed. Experiments with different transient control strategies are carried out. The result shows that, by using air-fuel ratio limitation and ISG motor dynamic torque compensation in transient operation conditions of low-temperature premixed combustion, the soot emission can be reduced substantially, while the engine keeps good power performance.

A Hybrid Energy Storage System for a Coaxial Power-Split Hybrid Powertrain

A hybrid energy storage system (HESS) consisting of batteries and supercapacitors can be used to reduce battery stress and recover braking energy efficiently. In this paper, the performance of a novel coaxial power-split hybrid transit bus with an HESS is studied. The coaxial power-split hybrid powertrain consists of a diesel engine, a generator, a clutch, and a motor, whose axles are arranged in a line. A mathematical model of the coaxial power-split hybrid powertrain with an HESS is established and the parameters are configured using experimental data. Subsequently, to estimate the system performance, a program is designed based on Matlab and Advisor. A rule-based control strategy is designed and finely tuned for the coaxial power-split hybrid powertrain. Then, using the Chinese Transit Bus City Driving Cycle (CTBCDC), the system characteristics and energy efficiencies of the designed coaxial power-split hybrid powertrain with an HESS are analysed. The results indicate that the proposed coaxial power-split hybrid powertrain with an HESS can fulfil the drivability requirement of transit bus and enhance the energy efficiency significantly compared with a conventional powertrain bus as well as reduce the battery stress simultaneously. Using an HESS is a good solution for the coaxial power-split hybrid transit bus.

Active Voltage Control enhances overall operating efficiency of traction motor in electric bus

Bus voltage affects the characteristic curve of traction motor, as well as high-efficiency region. This paper discusses if it is possible to improve the motor efficiency by AVC (Active Voltage Control), and if so, to what extent. Based on China Bus Urban Cycle, an 8-meter electric bus is studied via simulation in Matlab/Simulink. And the AVC controller is designed to determine the most efficient bus voltage in every time slot. The comparison of instantaneous motor efficiency is made between AVC and 624V. The results indicate that AVC has potential to enhance overall operating efficiency of traction motor in electric bus: 2.8% improvement of driving efficiency and 0.79% of regenerating efficiency can be achieved.

A Research on Engine Phase and Speed Estimation Method Based on Cylinder Pressure Sensor

Cylinder pressure based combustion state control is a direction that has drawn much attention in the field of internal combustion engine control, especially in the field of diesel HCCI (Homogeneous Charge Compression Ignition) research. In-cylinder pressure sensors have the potential to diagnose or even replace many traditional sensors, including camshaft and crankshaft sensors. This paper did research on engine synchronization method based on in-cylinder pressure signal. The research was based on a 4-cylinder high pressure common rail diesel engine equipped with 4 PSG (Pressure Sensor Glow Plug) type piezo-resistance cylinder pressure sensors, intended for HCCI research. Through theoretical analysis and experimental proof, methods and models for cylinder identification, engine phase estimation and engine speed estimation are given and further verified by experiments. Results show that cylinder pressure sensor could be used to identify cylinder instead of cam shaft sensor. The models for engine phase and speed estimation have been proved to have precision of 3° crank angle and 4.6rpm, respectively. The precision of engine phase and speed estimation provides a possibility for the engine to run if the crankshaft sensor fails, but more researches have to be carried out with respect to crankshaft sensor replacement.Copyright

Optimal Battery Discharging Strategy for a Range Extended Fuel Cell City Bus

This paper proposes an optimal energy management strategy for a range extended fuel cell city bus, which is powered by a Proton Exchange Membrane (PEM) fuel cell system and a Li-ion battery system. Targeting at minimizing the daily operating cost, the strategy is deduced based on the dynamic programming (DP) algorithm for a global optimized problem. The strategy is compared with several other strategies in simulating model, e.g. Charge Depleting and Charge Sustaining (CDCS) and two-stage linear blended strategies. The operating cost with the linear blended strategy is the lower than other two-stage linear blended strategies. The operating cost with the CDCS strategy is 1.3 % less than that of the linear blended strategy. The operating cost with the DP strategy is 10 % less than that of the linear blended strategy. The hydrogen cost occupies more than 95 % of the entire operating cost. To minimize the hydrogen consumption is the key to reduce the operating cost. With the DP strategy, the efficiency of fuel cell system is 58.7 %, compared to an average level of 53 % with other strategies. The battery efficiency influent the daily operating cost slightly. In order to apply the optimal strategy into a vehicle, the optimal State of Charge (SOC) trajectory curve is fitted with a nonlinear exponential formula. An iterative algorithm based on this formula is deduced, and can be applied to an embedded digital control unit.

Dynamic control for low cost auxiliary power unit of electric bus

A lower cost Auxiliary Power Unit(APU) of series hybrid bus based on diesel engine, permanent magnet synchronous motor and uncontrolled rectifier is presented in this paper. On the basis of a built system model, and according to static data, an APU power closed-loop controller which is consisted of forward-control circuit and PID feedback-control structure is developed. The simulation results show that, better dynamic characteristics of power output for the lower cost auxiliary power unit of hybrid bus is realized, with the forward and PID control method, and to a certain extent, meanwhile the stability of engine speed is guaranteed.