Research On Energy Efficiency And Control Of Motor Driving System For Portal Or Overhead Crane

The power plant of mobile mechanism and load’s hoisting mechanism is often three-phase asynchronous motor for the bridge crane and gatry crane. If the crane could be economically running with low energy consumption and high efficiency, the key problem is that the crane’s motor driving system can be effectively controlled with low energy consumption and high efficiency. Motor’s energy efficiency problems are including two aspects of problems. The first is motor’s energy consumption and the second is motor’s working efficiency when the motor is running.Motor’s working efficiency and power factor can directly affect motor driving system’s energy consumption. And load rate is the important parameter that affects motor’s working efficiency and power factor. The relationship of numerical fitting between motor’s efficiency and different motor’s power was found by analyzing motor’s efficiency data. The relationship is accord with exponential change law. The numerical fitting carve has theoretical guiding significance for motor’s may be high efficiently running when the load rate is30-40%. Motor’s power factor may be close to rated power factor when the load rate is more than60%. The motor’s efficiency curve has more wide region of high efficiency comparing with motor’s power factor curve. High running motor’s power factor is not always high. When motor’s load rate is not less than60%, motor’s power factor and working efficiency is all high.In order to effectively judge motor operation’s economy, motor operation’s efficiency and economic load rate must be reasonably determined. There are three running conditions according to the combined efficiency and rated combined efficiency. The first is no-economic operation, the second is basic reasonable operation and the third is economic operation. The calculation methods of integrated power saving rate have mainly power calculation method, combined efficiency calculation method and cumulative energy calculation method. Motor’s combined efficiency will change according to parabola with load torque’s change. Motor’s combined efficiency curve is lower than efficiency curve when line loss caused by reactive power is considered. Motor’s peak efficiency point will deviate toward the direction of load rate’s increase. So the region of economic operation will decrease.One of important demand for motor driving system’s saving energy should be motor’s high effectively running. So motor running’s internal loss must be decreased, especially decrease motor’s internal electric loss. In order to realize container crane’s saving energy operation of optimal voltage regulation aiming at crane’s working characteristics of constant torque operation mode and variable working condition’s load, the direct relationship between electric total loss and stator voltage or load torque is obtained based on the asynchronous motor’s Γ-shape equivalent circuit because the stator’s copper loss and iron loss are regarded as invariable loss that only relates to stator voltage and the rotor’s copper loss is regarded as variable loss that is changed following load torque’s changing. The optimal regulation voltage is obtained through mathematical calculation on the condition that the asynchronous motor be stable running. The electric total loss will be minimum when the stator’s voltage is the optimal regulation voltage. The research and simulation results showed:the electric total loss was commonly influenced by the stator voltage and load torque; the optimal regulation voltage would be changing according to the exponential law with the load torque’s changing; the electric total loss’s error between the exact solution and the approximate solution obtained according to the approximate slip ratio while the asynchronous motor’s stable running was bigger when the stator voltage was less than220V, and the error was nearly zero when the stator voltage was more than220V.Motor’s stator’s voltage and frequency are samely controlled. Motor should have good dynamic performance, including smooth speed regulating, fast starting prompt braking and fast tracking load torque. These measures have important significance for crane’s energy saving. In order to achieve these goals, control crane’s motor driving system to real-time track the abrupt load torque and make the motor stably run with a given rotational speed, the equivalent moment of inertia and equivalent load torque on the rotor of the hoisting mechanism and the motor driving system’s dynamic equation are derived through equivalently calculating, and the synchronous rotating coordinate according to rotor flux linkage oriented is constructed, and the load torque tracking’s vector converter close-loop control system is designed with the slip angle frequency between the synchronous angular velocity and the rotor’s electric angular velocity. The research and engineering example calculation results showed:the close-loop control system’s starting time with no-load was faster0.34s than the open-loop system, and the motor could be stably starting, and the difference of electromagnetic torque’s peak value was148N-m for the open-loop system and the close-loop control system; the electric power that the close-loop control system’s motor consumed was less than the electric power that the open-loop system’s motor consumed, especially the open-loop system’s peak value of electric power was2.5times for the close-loop control system’s peak value on the motor’s starting stage, and the motor’s effect of energy saving was obvious.Vector inverter control’s motor driving system’s based on vector transfer has wide speed adjustable range. Vector inverter control is a stepless speed regulation method and motor’s slip power will be not changed. Vector inverter control that is combine with modern control theory and method can be applied into situation where the requirement of speed control performance should be high, and also has obvious energy-saving effect for crane’s motor driving system. Crane’s motor driving system’s active disturbance rejection controller is designed aiming at motor’s mathematical model’s equivalent structure in MT coordinate system. There are4first-order active disturbance rejection controller. The first can control magnetic flux linkage of flux-linkage equation. The second can control revolving speed of speed equation. The third can control stator current’s excitation component of field current equations. And the forth can control stator current’s torque component of field current equations. The closed-loop system’s motor has good starting dynamic performance. Energy consumption of starting will increase with load torque’s increase for the open-loop system’s motor, and especially when crane’s load torque is full and heavy, load torque’s influence on the energy consumption of starting is obvious. Energy consumption of starting for the closed-loop system’s motor is hardly not changed with load torque’s changing. Motor’s energy saving effect of the closed-loop system is prominent when motor is starting. For the closed-loop system, energy saving rate is88%when motor’s load torque is full, energy saving rate is64%when motor’s load torque is medium, and energy saving rate is55%when motor’s load torque is light.