Analysis and comparison of speed regulation scheme

Analysis and comparison of crane speed regulation schemes

in recent years, the update and development of bridge cranes are mainly marked by improving the service performance of cranes, among which the speed regulation of cranes is the most prominent. The following is an analysis and comparison of several commonly used speed regulation schemes for cranes

1. rotor resistance speed regulation

(1) the cam controller controls the rotor asymmetric resistance. This scheme is mostly used in the main control circuit of 5 ~ 10t general bridge crane. The rotor is connected in series with asymmetric resistance to change the inherent characteristic curve of the motor to achieve the purpose of speed regulation. This scheme has simple structure and low cost, but the speed changes greatly. The intermediate speed plastic clings to the mold surface due to shrinkage and is unstable. Strictly speaking, it cannot be called a speed regulation scheme, which can only improve the starting characteristics of the motor

(2) the master controller controls the motor single-phase and reverse down speed regulation

this scheme is mostly used in the master control circuit of 16 ~ 50t general bridge crane, which is characterized by reversible asymmetric circuit. The rotor of each gear of the rising motor is connected with starting resistance in series; Descending the first gear is reverse braking, which only works when returning to the first gear from the second gear, and the load must be greater than 56% of the rated load; The second gear of descent is single-phase braking, which is mainly used for light load descent; Descending the third gear is regenerative braking. The scheme has simple structure and low cost, but it can't speed up when rising. The mechanical characteristics are very soft, the speed change rate is great, and it can't run for a long time at low speed

2. The self-excited dynamic braking speed regulation

circuit is characterized by a reversible asymmetric circuit, which disconnects the three-phase AC power supply of the motor when it drops, and supplies the initial excitation current to the two-phase stator winding to form an air gap magnetic field. Under the action of the motor's functional load, the motor rotor cuts the air gap magnetic field, generating induced current and braking torque. After rectification, it is sent to the stator winding to increase the exciting current, strengthen the air gap magnetic field and increase the braking torque. When the braking torque is equal to the torque of potential energy load acting on the motor shaft, the rotor current and self-excited current remain unchanged, and the motor operates stably. When the rotor resistance is changed, the motor speed changes, and when the crane rises, it is equivalent to the rotor series resistance starting and speed regulation. The scheme has medium speed and high speed gears when the weight drops, which is energy-saving and reliable. However, the stable low speed due to the accumulation of damage cannot be obtained when rising, and the speed cannot be adjusted under light load, which is inconvenient to operate

3. hydraulic pushrod speed regulation

the rotor of the motor is connected to the pushrod motor stator of the speed regulating electric hydraulic brake through the transformer. Because the voltage and frequency of the motor rotor change with its running speed, when the motor speed increases, the rotor voltage and frequency decrease correspondingly, the thrust of the electric hydraulic brake also decreases, and the braking torque of the f brake increases correspondingly, so that the motor speed decreases. On the contrary, the motor speed decreases, the braking torque decreases, and the motor speed increases. When the load torque, variable braking torque and the dynamic torque generated by the motor are balanced, the motor operates stably, so as to achieve the purpose of speed regulation. In this scheme, high resistance is connected to the rotor of the motor, and stable low speed can be obtained when the system rises and falls. However, it can only obtain a low speed, with soft intermediate speed characteristics, and the mechanical part of the crane must be modified before it can be used

4. eddy current brake speed regulation

the motor is coaxially connected with the eddy current brake. When the motor drops at low speed, the motor is powered off and the eddy current brake is powered on. When the brake is opened and the load drops, the eddy current brake sends out braking torque. When the load torque is balanced with the braking torque of the eddy current brake, the load decreases at a stable low speed. When the intermediate speed of the motor drops, it is in the reverse electric state, and the excitation winding of the eddy current brake is energized. The system obtains the synthetic curve of the artificial characteristics of the motor and the eddy current braking torque. When the load torque is balanced with the above synthetic torque, the medium speed drop} high speed drop of the motor is in the feedback braking state. When rising, the motor operates in the forward electric state, and the speed regulation principle is basically the same as that when falling. This scheme can speed up and down, and the speed regulation ratio can reach 1:lo. Intermediate speed and low speed can be obtained. However, the speed changes greatly, the intermediate speed can not run for a long time, and the circuit is complex, so the mechanical part of the crane must be modified before use

5. voltage regulation and speed regulation of thyristor stator

each phase of the three-phase power supply of the motor is connected in series with a group of anti parallel thyristors, and the speed regulation is realized by changing the conduction angle of the thyristor and controlling the stator voltage of the motor. The speed regulation range of this scheme can reach 1:10, the speed change rate is less than 5, and the speed can be adjusted up and down, which has a certain development prospect. However, the scheme is complex and difficult to debug

6. variable frequency speed regulation

variable frequency speed regulation is an ideal speed regulation scheme in AC speed regulation, but it is rarely used on cranes, mainly because of the large starting torque of cranes; When the crane descends, the motor is in the energy feedback braking state; It is caused by the higher price of frequency converter. With the progress of science and technology, large-scale integrated circuit technology, microcomputer technology, PWM technology, vector transformation technology and energy feedback technology have been successfully applied to frequency converters, making the application of frequency converters in cranes tend to be mature

(1) working principle

when starting, the contactor km is powered on, the frequency converter is powered on, the signal indicator DM is on, and the R, s frequency conversion control power supply is wired separately from the main circuit, so that when the protection circuit acts, the abnormal output signal of the frequency converter is maintained, which is convenient for maintenance and fault analysis. When the SA master controller turns to the first gear up, K3 and K5 are engaged, and the forward rotation signal STF and low-speed signal RL of the frequency converter are connected with the common terminal SD. At this time, the variable frequency has the starting frequency output, but the motor does not rotate. Because the brake is not opened, the hook slipping due to insufficient starting torque can be avoided. K1 is disconnected for zero position protection and abnormal output protection (inverter B and C contacts are abnormal output contacts). When the output frequency reaches the set value of brake release frequency 3Hz, and international chemical giants such as BASF, Huntsman and Bayer maintain brake release have increased their efforts to expand the Chinese market. After the current detection time reaches the set value of 0.3s, the frequency converter will output a signal through the run terminal to request to open the brake, that is, the run and Se terminals are connected, and the K8 power on contact is closed. K9 suction table, brake motor M2 is powered on. At the same time, stop terminal and SD are connected to self-protection. After the brake motor is powered on, the brake time is 0.3s, and the frequency converter drives the motor to start rotating at a starting frequency of 3Hz. During the acceleration time of the frequency converter, the frequency continuously changes to the set value, so it can be seen that the change of crane lifting speed is also continuous. As SA switches from low gear to high gear, K5, K6 and K7 are combined into seven different states to input the frequency converter, so that it can output seven different frequencies to obtain seven different lifting speeds. When SA stops, it returns to zero through each gear, and the output frequency of the frequency converter decreases continuously within the deceleration time. When the output frequency is equal to the brake closing frequency of the neck converter (6Hz), the mechanical brake receives the closing signal through the run terminal. Run and Se are open, K8 and K9 are powered off, stop terminal is disconnected from SD, and the brake begins to close. The frequency converter stops output after 0.5s, and M1 motor stops rotating

(2) performance characteristics

variable frequency speed regulation adopts magnetic flux vector control technology or large torque lifting technology, which can solve the problems of large starting torque, large torque output and strong load change at low speed; The setting of acceleration and deceleration time can solve the impact of crane starting and braking, so that the speed of the crane changes continuously and runs smoothly; The frequency arrival signal or frequency detection signal is used to control the opening and closing of the brake. The brake is opened only when the output torque of the motor is greater than the load torque, which solves the problem of hook slipping. The regenerative energy of the motor running in the fourth quadrant is converted into 50Hz AC feedback electricity by using the power feedback technology to protect the frequency converter from breakdown; The main control circuit shall be separated and reliably grounded to avoid the deflection of strong current to the weak signal of the frequency converter

variable frequency speed regulation is one of the most ideal schemes for crane speed regulation. The speed regulation ratio can reach more than 1:10, which can realize stepless speed regulation. The mechanical characteristics of each gear speed are very hard, the heavy load low-speed start and operation are stable and reliable, and the setting of acceleration and deceleration time makes the starting and braking speed of each gear quite stable. It has high control accuracy, and is designed with fault display, analysis and parameter monitoring functions, which is easy to use and maintain, and easy to realize automatic control and remote control. (end)