| The large electric wheel dump truck is the main equipment in the open-pit mine transportation in China,which has the characteristics of strong load capacity and high efficiency of transportation,bearing 40% of the world’s coal and 90% of the iron ore transportation.As the driving core of the electric wheel dump truck,it is very important to design a system with low cost,small weight and size,and better display of working ability to meet all kinds of requirements in the process of the dump truck.When the power supply of the traditional electric wheel dump truck is uphill,the diesel engine power is insufficient,the power supply voltage stability performance is low,and the response speed is slow.In this paper,bidirectional dc-dc converter is added in the driving aspect.At the same time,in order to better protect the life of the electric wheel dump truck,the output current ripple is required to be small.The conventional single-phase dc-dc converter has high inductance,high cost,low conversion rate and slow dynamic response.In this paper,three-phase staggered and parallel technology and ripple cancellation principle are adopted to reduce peak-to-peak value and average current value of inductance current flowing through each phase,as well as current stress of switch tube and reduce loss,and also effectively improve dynamic response.Firstly,four kinds of basic converters are analyzed.Switching power devices in bidirectional buck-boost converters are easy to be connected in parallel with other devices,and the current and voltage stress of switching elements and diodes are minimal,and the overall loss is small.This paper presents a three-phase interlaced bidirectional buck-boost converter,analyzes the principles of each mode,and derives the output current ripple expression of dc-dc converter,verifying that interlaced technology can greatly reduce the output ripple value.Secondly,in order to better analyze the dynamic performance of the converter,the Boost mode and Buck mode of bidirectional dc-dc converter are modeled by using the state space method to obtain the transfer function.Since the input and output of bidirectional dc-dc converter need constant voltage and current,this paper adopts voltage and current double closed-loop control to realize the constant voltage charging while the current inner loop limits the current,so as to prevent excessive current from damaging the switching device.Through Matalb simulation of different working modes,the current ripple values of traditional single-phase bidirectional dc-dc converter and three-phase staggered bidirectional dc-dc converter are compared respectively.Finally,the hardware and software of the system are designed and the main functions of the chip are introduced.The experiment platform of a prototype is built and the waveform of the prototype is used to verify the correctness of the theoretical analysis in this paper. |
