I. Overview

As we all know, three-phase AC asynchronous motors are widely used in various industries due to their low cost, high reliability and easy maintenance. However, it has great shortcomings when it is started directly: First, its starting current is as high as 5-7 times the rated current, which requires a large margin in the power grid and reduces the service life of electrical control equipment. Increasing maintenance costs, even affecting the normal operation of other electrical equipment; secondly, the starting torque can reach twice the normal torque, which will impact the load, increase the friction of the transmission components and additional maintenance. Because of the above reasons, a three-phase asynchronous motor step-down starting device appeared.

The traditional reduced voltage starting has the following methods:

1, a reactor is connected in series in the stator circuit of the motor to make a part of the voltage drop on the reactor;

2, star-delta conversion step-down starting (Y -△). The motor is connected in a star shape when starting, and after starting, it becomes a delta connection through a converter;

3, start the compensator start (autotransformer start).

Traditional starting equipment is bulky, costly, and has a complex structure. It is difficult to control the torque of the motor that matches the load, which means that it is difficult to obtain a suitable starting current and starting torque; and it will generate a high current spike at the moment of switching. , The resulting mechanical vibration will damage the motor rotor, shaft connector, intermediate gear and load.

Therefore, there is a need for a starting device that can overcome the disadvantages of traditional starting. The Jabil brand new generation digital intelligent motor control module developed and produced by Yinhe Company not only completely overcomes the shortcomings of traditional starting, but also makes further improvements and enhancements to various starting methods, and also adds many other functions, such as: Energy-saving operation, overcurrent protection, overheating protection, phase loss protection, etc.

This kind of module adopts digital tube display and button control. The whole starting process is automatically completed by the single-chip computer according to the preset setting, so the operation is extremely convenient.

The user adjusts the parameter settings by pressing the buttons, and can choose different starting methods according to the actual situation, and can easily control the starting current to obtain the motor torque matching the load.

2. Module internal structure and electrical principle

The internal structure of the module is shown in Figure 1. It can be seen from the figure that the main circuit of the module, the phase control circuit and the single-chip microcomputer are jointly packaged in the same housing, and multiple current and voltage sensors are built in at the same time. Connect the module and the control box with connectors to realize the setting and display of various functions.

figure 1

The main circuit is 6 glass passivated square thyristor chips, which are pasted on the DBC (Ceramic Copper Clad Laminate) through integrated welding technology and welded together with the thermally conductive copper plate. When the module is used, the thermal conductive copper plate and the heat sink are in close contact with the thermal conductive silicone grease. This structure makes the module have high insulation performance and heat dissipation performance.

Figure 2 is a block diagram of the electrical principle of the module. The phase shift circuit part is the JP-SSY01 digital phase shift integrated circuit independently developed by Yinhe. The circuit is SOP28 packaged, 5V single power supply, fully digital processing mode, with high phase shift accuracy and symmetry. Add a 0-10V level signal to the control terminal to control the phase shift angle.

The synchronous transformer outputs the synchronous signal to the phase-shifting circuit, one of which is additionally distributed to the single-chip microcomputer as the reference for the single-chip to collect voltage and current signals. In this way, the calculation error caused by the change of the alternating current frequency is overcome, and the calculation accuracy is improved.

There are two types of sensors: voltage sensors and current sensors. Hall elements are used in both sensors, which have the characteristics of small size, fast response, and high linearity. They can be conveniently placed inside the module through an integrated design with the module structure. The two kinds of sensors transfer the voltage analog quantity and the current analog quantity to the 12-bit high-speed A/D converter, and through the A/D conversion, the corresponding digital quantity is transferred to the single-chip microcomputer for processing.

The display and control part uses a serial port to communicate with the single-chip microcomputer. This communication method greatly reduces the connection between this part and the module. 5 digital tube display and 8 button control make the display and control intuitive and convenient.

3. Main functions

The intelligent motor control module can mainly complete the following functions:

1, voltage ramp start

2, current limit start

3, voltage sudden jump function

4, soft parking

5. Energy-saving operation

6, overcurrent, overheating, phase loss protection

are introduced as follows:

1, voltage ramp start

As shown in Figure 3, the system first adds a voltage Us to the motor, and then the voltage rises linearly from Us to the maximum voltage Umax. At this time, the voltage applied to the motor terminals is equal to the grid input voltage. Us is set by the user, and the voltage that can be selected by the user is 80-300 V. Ts is set by the user and can be selected from 1-90 seconds. In actual use, the user selects the appropriate parameters according to the actual situation, such as the size of the motor power, the size of the load, etc., to achieve the best starting effect.

This starting method is characterized by a stable starting, which can reduce the impact of the starting current on the power grid, and at the same time greatly reduce the mechanical vibration caused by the starting torque to the load.

2, current limit start

As shown in Figure 4, this starting mode is set by the user a current value Ik, during the entire starting process, the actual current does not exceed the set value Ik. Ik is set by the user according to the actual load.

Current limiting starting can make the large inertia load be started and accelerated with the minimum current, and can be used to set the current upper limit to meet the use of grid capacity in limited occasions. This starting method is particularly suitable for constant torque loads.

3, voltage sudden jump function

In practical applications, many loads have great static friction; in the voltage ramp starting mode, the voltage gradually rises from small to large. If the voltage ramp is used directly for starting, the applied voltage is too small to overcome the static friction of the load during the period of starting, and the motor will not move, causing damage to the motor due to heat. The voltage jump function solves this problem. Before the motor starts, the module first outputs a voltage Ut for a period of time Tt to overcome the static friction force. After the motor rotates, it starts in the original setting mode, thus better protecting the motor. For loads that don't need this function, just set Tt to 0 in the settings. Ut can be adjusted, the range is 0-380V, Tt can be adjusted, the range is 0-10 seconds (Figure 5).

4, soft parking

As shown in Figure 6, after pressing the stop button, the output voltage of the module immediately drops to Up1, then gradually drops, after the time Tp, drops to Up2, and then immediately drops to 0. Up1 can be adjusted, the range is 100-380V; Up2 can be adjusted, the range is 0-300V; the range of Tp adjustment is 0-90 seconds.

This kind of soft parking can greatly reduce the impact of liquid in pipeline equipment.

5. Energy-saving operation

For large friction loads, due to the large starting current required, a larger power motor is required, and the operating load torque required by the normal load is much smaller than the rated torque of the motor, which causes the motor to run at light load. For intermittent loads, the working time to maintain a large current occupies a small part of the entire cycle, resulting in waste of light load reactive power loss and greatly reducing the operating power factor. The intelligent motor control module detects the voltage and current, determines the size of the load added to the motor, and automatically adjusts the output voltage according to the size of the load, so that the motor can work in the best efficiency work area to achieve the purpose of energy saving.

6, protection function

There are three protection functions: overcurrent protection, overheat protection, and phase loss protection.

If one of the above three failures occurs during startup or operation, the module will automatically power off, and the digital tube on the control box will flash to display the cause of the failure. After the failure is eliminated, press the reset button to restore normal.

In the above protection, the overcurrent protection value is adjustable.

4. Experimental situation and practical application introduction

We have actually measured and recorded an intelligent motor control module in use.

The load used is a 18.5KW fan, and the actual measured voltage is about 390V.

To make a comparison, first remove the module and start directly.

After closing the air switch, the voltage immediately rises to 390V, and the current rapidly rises to 150A. It lasts for a period of time and then gradually decreases, and finally stabilizes at about 30A. At the same time, the sound of strong mechanical vibration generated by the fan due to the impact of large current can be clearly heard.

Then connect the intelligent motor control module, set the current limit mode to start, the current limit value is 90A, and turn on the energy-saving operation.

Press the "Start" button, and it can be observed that the current rise speed is obviously slower, gradually rising to 90A, and after holding for 2-3 seconds, it gradually decreases to 30A. The voltage rises slowly from 0V to 390V. The starting time is 6 seconds. During the whole starting process, the motor starts smoothly, and no mechanical shock is heard.

After 15 seconds, the voltage gradually drops to 355V, the current does not change, and stable operation begins.

Digital intelligent motor control modules have been widely used in various production fields and other occasions, and are introduced as follows:

1, reduce the motor starting current (generally when the AC motor is started directly, the impulse current is 5-7 times the rated current);

2. Avoid instantaneous voltage drop on the power supply line when the motor starts, which may cause malfunction of equipment and meters;

3, to prevent the moment impact when starting, causing mechanical shaft breakage or waste;

4, the motor can be started more frequently (soft starter generally allows 10 times/hour, so that the motor will not overheat);

5. It can prevent water hammer effect on pump loads and prevent pipeline rupture;

6. ​​For some process applications (such as yarn dyeing machinery), it can prevent quality problems caused by uneven dyeing due to too fast starting;

7. For some fragile container grouting production lines, it can prevent container damage;

8. The starting current needs to be controlled to reduce the impact on the machine, and it can also be adapted to the occasions of lower capacity power supply transformers (such as injection molding machines);

9. It can reduce the grid adaptation capacity and save the cost of capacity expansion;

10. It is necessary to adjust the starting characteristics conveniently.

It can be seen from the above that the digital intelligent motor control module integrates motor starting, energy-saving operation, and protection. The outstanding features are small size, strong functions, easy installation, simple operation, maintenance-free, and high reliability. It is an ideal replacement product for traditional starting equipment.

references:

1, "Semiconductor Inverting Technology" (2nd Edition) Shanghai Machinery Technical College Mo Zhengkang Chief Editor

2, "Computer Control Technology and Application" Xiangtan Institute of Mechanical and Electrical Technology, Harbin Institute of Technology Weihai Branch

Liu Guorong, Liang Jingkai Editor-in-Chief

3, "Intelligent Motor Control Module Instruction Manual" (version 2) Zibo Linzi Yinhe High-Tech Development Co., Ltd.