| In 1821,electric motors were invented by Faraday,which was nearly half a century earlier than the invention of internal combustion engines.Electricity,known as a type of high-quality energy source,is used by electric motors based on electromechanical energy conversion,which gives electric motors advantages over internal combustion engines in structural complexity,stability,operating range,efficiency,response speed,NVH,maintenance cost,etc.But electric motors cannot replace the position of internal combustion engines as the main power sources of road vehicles yet due to the inherent defects of the batteries,which act as the energy storage device in battery electric vehicles.The defects of batteries include low energy density,high cost of manufacture,short service life,low charging rate,etc.,which make battery electric vehicles fail to compete with fuel vehicles in driving range,convenience,usage cost,etc.The electric driven vehicles equipped with dual power source are born to solve this problem,which significantly amends the shortcomings of battery electric vehicles such as “range anxiety” while retaining the advantages of electric motor drive.As a novel configuration,the dual inverter open-end winding(OEW)motor drive system is especially suitable for the dual power electric driven vehicles.Compared to the traditional single inverter motor drive system with a DC/DC converter,the dual inverter OEW motor drive system has more precise current regulation,more control degrees,better fault-tolerant capability,lower and variable DC bus voltages,and is capable of different inverter and power source combination.Furthermore,it is capable of managing the power flow between the two power sources through the motor windings via the cooperative control of the dual inverter.Based on the points above,the dual inverter OEW motor drive system has remarkable configuration advantages and application prospects on dual power electric driven vehicles.However,the existing control methods have not paid enough attention to the inverter switching loss,and cannot maximize the power sharing range between power sources.In addition,the existing methods are not able to coordinate the requirements between the system efficiency and the power management capability according to the vehicle working condition.Therefore,to apply the dual inverter OEW motor drive system to dual power electric driven vehicles,it also requires targeted design and optimization on the power and dynamic performance,energy efficiency,and power allocation capability,etc.for vehicle operation.There are also existing problems in the cooperative control of the dual inverter,such as the high inverter loss,the strict constraint of the power allocation range caused by motor operating points,and the harsh demands for operating condition of the dual power source,etc.In order to meet the requirements of driving condition and energy management of dual power electric driven vehicles,this research has adopted the dual isolated two-level voltage source inverter(VSI),and the interior permanent magnet synchronous motor(IPMSM).Base on the rotor flux oriented vector control scheme,with the optimization objectives of the control accuracy and the response speed of electromagnetic torque,the operating range of the motor,the system efficiency,and the power allocation range,from bottom to top,this research has focused on the mathematical model of the OEW-PMSM drive system,voltage vector modulation,voltage vector distribution of the dual inverter,control of the electromagnetic torque and the stator current vector,combinations of the dual power source,and the energy management successively.The corresponding control schemes and methods have been raised.Several dynamic simulations and bench tests of the OEW-PMSM drive system,as well as the energy management simulation of the dual power electric driven vehicle have also been implemented.During the research,the following main innovative points have been created:1.A combination and switching strategy of the dual inverter modulation patterns has been proposed based on the sufficient analysis of current ripple characteristics of various modulation patterns under dual SVPWM control scheme,which sufficiently excavated the superiority of the dual inverter configuration.By optimizing the synthesizing pattern and duty cycle of zero vectors,the switching number of inverter bridge arms during a single switching period is reduced,while the ripple of current and electromagnetic torque is lowered significantly.2.A voltage vector distribution strategy has been proposed based on the feasible region of dual inverter’s voltage vector modulation.Under the dual SVPWM scheme,the boundary calculation of the feasible region and the relations between voltage vector distribution and power allocation of the dual inverter have been derived.By specific combinations of particular voltage vectors,such as basic vectors,saturated vectors,specific angle vectors,etc.,the feasible region of voltage vector distribution can be fully utilized,and the capacity of power allocation has been excavated sufficiently.The inverter switching frequency as well as the inverter loss is lowered while the power allocation command is executed accurately.3.A control strategy of electromagnetic torque based on the optimization theory and the Fibonacci search has been proposed.Starting from the initial feasible points provided by Minimum Voltage Vector Amplitude(MVVA)algorithm,the results of SEO algorithm,P1 MAX algorithm and P1 MIN algorithm can be acquired by the optimization methods,which obtain the optimal efficiency of the drive system,the upper and lower limit of the power allocation,respectively.Then the Fibonacci search among the results from the above three algorithms is implemented to obtain the approximate optimal solution of the drive system efficiency under the constraints of motor operating point and power allocation command,whose tightly controlled computational burden and high stability makes it possible to be executed onboard of the vehicle in real time.The proposed Fibonacci based control strategy reconciles the demands of the system efficiency and the power allocation range between two power sources.4.The combination principle of the two power sources has been raised.A power allocation strategy based on common scheme has been proposed.By the employment of the power allocation emphasis factor,the weighted degree of the ideal output power of the two power sources can be regulated quantitatively.This power allocation strategy is capable of the energy management of different power source combinations.The SOC of the auxiliary power source can be regulated steadily while the energy conversion efficiency as well as the power output condition of the main power source is well maintained,which makes the drive system capable of longstanding stable operation.The results of the research indicate that,based on the original architecture of PMSM’s vector control,by employing the voltage vector distribution module with power allocation function,and optimizing the modulation pattern along with the voltage vector combinations,the superiority of dual inverter’s multilevel operation can be embodied.The switching loss of the dual inverter is lowered to the level of single inverter while the power allocation command is precisely executed,the current and torque ripple is also reduced.By the optimization of the electromagnetic torque control,the system efficiency and the power allocation range can be well balanced based on the maximization of the motor operating range,which obtains high efficiency and the capability of wide-range power management at the same time.By matching the power sources properly and managing the energy flow strictly,the power sources can maintain a high efficiency in favorable operating conditions,which endows electric driven vehicles the capability of long-range stable travel. |
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