| In the city driving cycles,as the single energy source for electric vehicles,battery needs to be charged and discharged frequently to meet the requirements of automobile acceleration and deceleration,which seriously affects the battery life.The study subject is hybrid power system composed of battery and ultracapacitor in electric vehicles.On the premise of satisfying the power performance and economy of automobile's energy consumption,a new energy management strategy is proposed to achieve the rational allocation of power demand between battery and ultracapacitor.The energy management strategy can avoid battery receiving the transient power to the limit,thus the service life of hybrid power system is prolonged.First,the key problems of hybrid power and the existing energy management strategies are analyzed.Then,the characteristics of key components in the hybrid power system are analyzed,including the battery charging and discharging characteristics,temperature characteristics,transient power characteristics and ultracapacitor charging and discharging characteristics.And the battery model,ultracapacitor model and DC/DC converter model were established in ADVISOR.After analyzing the structure characteristics of different composite power systems,a suitable hybrid power structure was selected.On this basis,under the premise of the quality and price constraints,the parameters of energy sources of hybrid power system were matched to meet the energy and power requirements of target driving cycles.Compared with a single power,the quality of matched hybrid power system is reduced by 31.5%.Then,the basic principle of wavelet transform is analyzed,and the concept of sliding window is put forward to make up for the shortcoming that the wavelet transformation can not deal with the data in real time.Thus the real time wavelet energy management strategy was put forward and a real time wavelet algorithm based on Mallat fast wavelet algorithm was designed through reasonable selection for filtering method,sliding window size,decomposition depth,boundary extension method and so on.Then the principle of fuzzy control is analyzed and the energy management strategy of fuzzy controller is put forward.Under the total power demand,the fuzzy controller was designed.After that,the fuzzy control strategy and the real time wavelet strategy were combined into a new real time wavelet-fuzzy control energy management strategy by changing the quantization factor of fuzzy controller.The ADVISOR2002 software was redeveloped because there was no hybrid power module in it.The simulation models of three strategies including real time wavelet,fuzzy controller and real time wavelet-fuzzy control were developed in ADVISOR.Then the simulation models of three strategies were added to the model base of ADVISOR and respectively proceeded to the simulation.The results show that the management effect of real time wavelet-fuzzy control method is more stable and optimal.Under the precondition of coordinating the state of charge of each energy source,the real time wavelet-fuzzy control method can decompose the total power demand into high and low frequency power signal to every energy source,which makes the battery undertake the slow varying power load and improves significantly the utilization of ultracapacitor.At the same time,the real time wavelet-fuzzy control strategy can better stabilize the bus voltage and the state of charge of the battery.Compared with a single power,the value of the power,current and capacity loss of battery in the hybrid power system with real time wavelet-fuzzy control are obviously reduced,which indicates that the battery is well protected.The hybrid power system can also improve the dynamic performance of the whole vehicle.Finally,a scaled-down hardware-in-the-loop simulation on hybrid power system is conducted to verify the real time wavelet strategy.The experiment results prove the feasibility of the real time wavelet strategy. |
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