Mechanical Analysis and Performance Optimization for the Lunar Rover’s Vane-Telescopic Walking Wheel

It is well-known that optimizing the wheel system of lunar rovers is essential.However,this is a difficult task due to the complex terrain of the moon and limited resources onboard lunar rovers.In this study,an experimental prototype was set up to analyze the existing mechanical design of a lunar rover and improve its performance.First,a new vane-telescopic walking wheel was proposed for the lunar rover with a positive and negative quadrangle suspension,considering the complex terrain of the moon.Next,the performance was optimized under the limitations of preserving the slope passage and minimizing power consumption.This was achieved via analysis of the wheel force during movement.Finally,the effectiveness of the proposed method was demonstrated by several simulation experiments.The newly designed wheel can protrude on demand and reduce energy consumption;it can be used as a reference for lunar rover development engineering in China.

A Novel Soft Start Method of Super Large Capacity High Voltage Motor

The large current generated by starting directly of super large capacity and high voltage induction motor would have a huge impact on the grid as well as the motor itself.The variation of the power factor and electromagnetic torque during direct start of motors with different capacity and voltage levels are obtained.Aiming at the problem that the secondary impact of auto-transformer starter is too large and the cost of magnetic control starter is too high,the auto-transformer and magnetic control soft start method of super large capacity and high voltage motor is proposed and the basic working principle is analyzed.The calculation formula of cost for magnetic control soft starter and auto-transformer and magnetic control soft starter is deduced,and specific examples are analyzed and compared.It is concluded that the choice of auto-transformer with appropriate tapping ratio can greatly reduce the cost of auto-transformer and magnetic control soft starter compared with the other one.Finally,the simulation and experiment results show that the start method can effectively avoid secondary current impact and constrain the motor starting current to less than 2.5 times the rated current.

Parallel diode-clamped linear converter for withstand test and partial discharge measurement of electric equipment

High-voltage withstand tests are essential for electric equipment like power transformers,electric cable lines,gas insulated switchgears etc.The partial discharge(PD)measurement for such equipment under applied high voltage is also required at the same time.Pulse Width Modulation(PWM)-based variable frequency power supply(VFPS)finds wide applications in the series resonance high-voltage testing circuits.However,the steep rising and falling voltage edges in the PWM process will produce large amount of partial discharge interference in a wide spectrum range,which will confuse the real partial discharge signal of the device and lead to the wrong estimation of the insulation status.This paper proposes a new VFPS based on the highefficiency linear power amplifier without PD interference.The topology and principle of the VFPS are given and discussed.A prototype rated at 232 V/35 A was designed and constructed to verify the feasibility of the proposed VFPS.Physical experiments were carried out on the prototype.

Optimal electromagnetic hybrid negative current compensation method for high-speed railway power supply system

To achieve economical compensation for the huge-capacity negative sequence currents generated by high-speed railway load, an electromagnetic hybrid compensation system(EHCS) and control strategy is proposed.The EHCS is made up of a small-capacity railway static power conditioner(RPC) and a large-capacity magnetic static var compensator(MSVC). Compared with traditional compensation methods, the EHCS makes full use of the SVC’s advantages of economy and reliability and of RPC’s advantages of technical capability and flexibility. Based on the idea of injecting a negative sequence, the compensation principle of the EHCS is analyzed in detail. Then the minimum installation capacity of an EHCS is theoretically deduced. Furthermore, a constraint optimization compensation strategy that meets national standards, which reduces compensation capacity further, is proposed. An experimental platform based on a digital signal processor(DSP) and a programmable logic controller(PLC) is built to verify the analysis. Simulated and experimental results are given to demonstrate the effectiveness and feasibility of the proposed method.

Pareto optimal allocation of fault current limiter based on immune algorithm considering cost and mitigation effect

This paper presents a multi-objective Pareto optimal method for allocation of fault current limiters based on an immune algorithm, which takes into account two objectives of the cost and fault current mitigation effect. A sensitivity factor calculation method based on the rate of fault current mitigation is proposed to reduce the search space and improve the efficiency of the algorithm.In this approach, the objective functions related to the cost and fault current mitigation effect are established. A modified inversion operator based on equal cost is proposed to converge to global optimal solutions more effectively. The proposed algorithm is tested on the IEEE39-bus system, and obtains the Pareto optimal solutions,from which the user can select the most suitable solutions according to the preferences and relative importance of the objective functions. Simulation results are used to verify the proposed method.

Coupled autotransformer and magneticcontrol soft-start method for super-largecapacity high-voltage motors

The large current generated by a direct start of the super-large-capacity high-voltage induction motor would have a huge impact on the power grid as well as the motor itself.Traditional soft starters have the shortcomings of discontinuous adjustment,voltage sags,sudden torque mutation,secondary current impact and high cost.To resolve this issue,the authors propose a novel coupled autotransformer and magnetic-control(CATMC)soft-start method.The structure of the new CATMC soft starter combines the functions of the autotransformer and magnetic control reactor via an innovative electric and magnetic circuit design.In this study,the authors analyse the magnetic circuit structure and working principles of the CATMC soft starter.Then,to validate its principle and performance,the authors conduct a simulation study using ANSYS software and design and test an 18 MW/10 kV CATMC soft starter prototype.The simulation results demonstrate that the CATMC soft starter effectively avoids secondary current impact and constrains the motor starting current to<2.5 times the rated current.The public connection point bus voltage also meets the voltage sag requirement of the IEEE standard and reduces the impact on the power grid.