Implementable Strategy Research of Brake Energy Recovery Based on Dynamic Programming Algorithm for a Parallel Hydraulic Hybrid Bus

The purpose of this paper is to develop an implementable strategy of brake energy recovery for a parallel hydraulic hybrid bus. Based on brake process analysis, a dynamic programming algorithm of brake energy recovery is established. And then an implementable strategy of brake energy recovery is proposed by the constraint variable trajectories analysis of the dynamic programming algorithm in the typical urban bus cycle. The simulation results indicate the brake energy recovery efficiency of the accumulator can reach 60% in the dynamic programming algorithm. And the hydraulic hybrid system can output braking torque as much as possible.Moreover, the accumulator has almost equal efficiency of brake energy recovery between the implementable strategy and the dynamic programming algorithm. Therefore, the implementable strategy is very effective in improving the efficiency of brake energy recovery.The road tests show the fuel economy of the hydraulic hybrid bus improves by 22.6% compared with the conventional bus.

Indirect measurement technology of new energy vehicles? braking force under dynamic braking conditions

Currently,direct braking-force measurement under dynamic conditions requires a considerable modification to the vehicles and has poor compatibility because there are many types of vehicles.Thus,in this paper,an indirect measurement method of new-energy vehicles,braking force under dynamic braking conditions is proposed.The mechanical wheel and axle model at low/idling/high speeds is established using the piston-pressure formula,force transfer in the brake-wheel cylinder,relative movement between the wheel and the roller,among others.On this basis,the relationship between wheel braking force and roller-linear acceleration is further derived.Our method does not alter existing vehicle structures or sensor types.The standard sealing bolt is temporarily replaced with a hydraulic sensor for coefficient calibration.Afterward,the braking force can be indirectly calculated using the roller-linear velocity data.The method has characteristics of efficiency and high accuracy without refitting vehicles.

An Integrated Reactive Power Control Strategy for Improving Low Voltage Ride-through Capability

Among all renewable energies,wind power is rapidly growing,whereby it has the most participation to supply power.Doubly fed induction generator(DFIG)is the most popular wind turbine,as it can play a very significant role to enhance low voltage ride through(LVRT)capability.Ancillary services such as voltage control and reactive power capability are the main topics in wind power control systems that should be handled profoundly and carefully.The lack of reactive power during fault period can result in instability in generators and/or disconnection of the wind turbine from the power system.The main aims of this study are to illustrate the most effective approaches subject to improve the efficiency,stability,and reliability of wind power plant associated with LVRT capability enhancement.This effectiveness and efficiency are demonstrated by,firstly,comparison between all types of wind turbines,focusing on the ancillary services,after the existing advanced control strategies.According to the literature,there is a consensus that modifying converter-based control topology is the most effective approach to enhance LVRT capability in DFIG-based wind turbine(WT).Therefore,an advanced integrated control strategy is designed by considering the effect of the rotor side converter(RSC)and the grid side converter(GSC).A model of the wind power plant is presented based on the control objectives.MATLAB/Simulink is also used to illustrate the effectiveness of the designed algorithm.

Transient stability enhancement of DC-connected DFIG and its converter system using fault protective device

Transient stability of doubly-fed induction generators(DFIGs)is a major concern in both AC and DC grids,and DFIGs must stay connected for a time during grid faults according to the power grid requirements.For this purpose,this work proposes an overcurrent and overvoltage protective device(OCV-PD)to ensure that DCbased DFIG system can stay connected and operate well during the faults.Compared with a series dynamic braking resistor(SDBR),two aspects are improved.First,a twolevel control strategy and DC inductor circuit are used to ensure that the OCV-PD can limit the current impulse to protect DFIG system during an overcurrent fault.Second,the OCV-PD can protect system from overvoltage fault which a SDBR cannot do.Simulation results verify itsvalidity and feasibility,finding that for overcurrent protection the OCV-PD outperforms a SDBR with an average decreased index of 3.29%,and for overvoltage protection it achieves an average index of 1.02%.