Soft start and frequency converter
Soft starter is actually a kind of motor soft start, soft stop, light load energy saving and multiple protection functions
Inverter, it is mainly used in places where speed is required, and its output not only changes the voltage but also changes the frequency at the same time;
The soft starter is used where the voltage is reduced to start and stop, and the motor speed is unchanged at this time; but the frequency converter is mainly used to adjust the motor control device. It is mainly a three-phase parallel thyristor and its electronic control circuit connected in series between the power supply and the controlled motor. By controlling the conduction angle of the three-phase parallel thyristor, the input voltage of the controlled motor can be changed according to different requirements to realize various functions.
In fact, it is a voltage regulator. When the motor is started, the output only changes the voltage, not the frequency. The inverter manufacturers emphasize that the inverter has all the soft starter functions, but its price is more expensive than the soft starter, and the structure is more complicated.
The inverter manufacturer believes that the biggest difference between the two is that the inverter can be arbitrarily set for operation.
The frequency of running, but the soft starter only plays the role of soft start and stop.
Definition and function of soft starter
The soft starter is connected in series between the power supply and the controlled motor, and the internal thyristor is controlled by a microcomputer to trigger the conduction angle to achieve AC voltage regulation, so that the motor input voltage gradually rises from zero with a preset function relationship, until the end of the start. The full voltage of the motor is soft start. In the process of soft start, the starting torque and speed of the motor gradually increase, until the thyristor is fully turned on, and the motor works on the mechanical characteristics of the rated voltage to achieve a smooth start and reduce the starting current. . Avoid starting an overcurrent trip. When the motor reaches the rated number of revolutions, the start-up process ends, and the rated voltage is provided for the normal operation of the motor.
Machine control device, called Soft Starter abroad. The soft starter uses a three-phase parallel thyristor as a voltage regulator, and connects it to the power source. The soft starter (soft starter) is a novel motor that integrates motor soft start, soft stop, light load energy saving and multiple protection functions. Between the stators. Such a circuit is a three-phase fully controlled bridge rectifier circuit. When using the soft starter to start the motor, the output voltage of the thyristor gradually increases, and the motor gradually accelerates until the thyristor is fully turned on. The motor works on the mechanical characteristics of the rated voltage to achieve smooth starting, reduce the starting current, and avoid starting over-current tripping. When the motor reaches the rated number of revolutions, the start-up process ends, and the soft start.
The thyristor automatically replaces the completed thyristor with a bypass contactor to provide rated voltage for the normal operation of the motor to reduce the heat loss of the thyristor, prolong the service life of the soft starter, improve its working efficiency, and prevent the power grid from harmonic pollution. . The soft starter also provides a soft stop function. The soft stop is the opposite of the soft start process. The voltage gradually decreases and the number of revolutions gradually drops to zero to avoid the torque impact caused by the free stop.
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The main function
Overload protection function: The soft starter introduces a current control loop, so it can track and detect changes in the motor current at any time. By increasing the setting of overload current and inverse time control mode, the overload protection function is realized. When the motor is overloaded, the thyristor is turned off and an alarm signal is issued.
Phase loss protection function: When working, the soft starter detects the changes of the three-phase line current at any time. Once the current is cut off, it can make a phase loss protection response.
Overheating protection function: The temperature of the thyristor radiator is detected by the internal thermal relay of the soft starter. Once the radiator temperature exceeds the allowable value, the thyristor will be automatically turned off and an alarm signal will be issued.
Measuring circuit parameter function: When the motor is working, the detector in the soft starter always monitors the running state of the motor, and sends the monitored parameters to the CPU for processing, and the CPU analyzes, stores, and displays the monitored parameters. Therefore, the motor soft starter also has the function of measuring loop parameters.
Other functions: through the combination of electronic circuits, other interlocking protections can also be realized in the system.
Inverter definition and function
A converter that converts alternating current with a fixed voltage and frequency into alternating current with a variable voltage and frequency is called a frequency converter. Reduce the impact load caused when the motor starts, control the speed of the motor, lengthen the start time, smooth the current, and achieve the purpose of soft start.
At the same time, the efficiency of the power grid and the electric motor can be improved. In fact, the frequency converter is mainly used in energy saving, through adjustment, change the output voltage, current, frequency. Generally, the frequency converter is used for the motor for speed regulation.
Working principle of frequency converter
The frequency converter is the equipment that transforms the industrial frequency power supply (50Hz or 60Hz) into the AC power supply of various frequencies to realize the variable-speed operation of the motor. Among them, the control circuit completes the control of the main circuit, the rectifier circuit converts alternating current into direct current, the DC intermediate circuit smoothes and filters the output of the rectifier circuit, and the inverter circuit reverses the direct current into alternating current (and the core control circuit realizes: AC- Orthogonal process). The frequency conversion technology was born in response to the need for stepless speed regulation of AC motors.