What is the difference between soft start and variable frequency start?

1. I think that the principle of soft-start is to use solid-state relays (or triacs), through phase-shift triggering (or zero-crossing triggering),
Motor speed regulation.
The frequency converter starts the motor process is the frequency conversion velocity modulation, in the work movement may carry on the forward rotation speed control, the brake, the reversal speed control, the frequency conversion movement and so on the electric motor work.
2. The frequency conversion is started by changing the frequency. It can be started with load and there will be no inrush current. The soft start is started by reducing the voltage. The starting torque will be affected to a certain extent and there will be a certain inrush current.
3, soft start is a step-down start, but the step-down value can be continuously and smoothly adjusted, with the same step-down start, all at the expense of starting torque. The frequency converter changes the voltage and frequency at the same time and continuously adjusts the speed without reducing the torque.
4. Now that the frequency converter can adjust the speed, it can also save energy. So why are many manufacturers now producing soft starters? What is its development trend?
5. The problem is that the inverter needs energy-saving before the speed is adjusted, and the inverter is more expensive than the soft-start. In the case of non-speed control, the inverter plays the same role as the soft start. Why spend more renminbi for the same thing?
6, soft starter technology is relatively low, easy localization, stable performance, the price is much lower than the inverter! ! Therefore, soft starters still have room for survival in the country.
7. While the price of the inverter is higher than that of the soft starter, the inverter with feedback is higher. Such as: In special occasions, such as when the load rate is less than 1/3, when there is feedback energy, the on-line soft rise cost is extremely low.
High-power frequency conversion, variable frequency or industrial frequency conversion, the first cut-off method is more costly to implement for the inverter. There is a problem of out-of-sync and phase difference.
Soft-running triac modules are much easier to implement.
In the future, the inverter will surely replace the soft start, but the premise is that the cost will drop. Only when IGBTs are manufactured on a large scale in China, is the inverter replacing the soft start.
8. The soft starter is used for high power motors to reduce the impact of high currents on the motor and the power grid at startup. Its working principle is to add the full voltage from 0V to complete the start-up process of the motor in its particular start-up time; the frequency converter is to change the frequency of the output power to achieve the motor speed adjustment, which is generally used in equipment that requires variable speed Of course, it can also realize the normal start-up process of the motor.
Why do we need a soft starter too? Because there is no need for speed change in high-power motor equipment, it is better to reduce the damage to the motor equipment and the power grid in order to start the process (eg high-power fans, pumps, etc.). At the same time, the price of the soft starter with the same power is much less than the frequency converter.
1. What is a soft starter? What is the difference between it and the inverter?

Soft starter is a novel motor control device integrating motor soft start, soft stop, light load energy saving and various protection functions. It is called Soft Starter abroad. Its main component is three antiparallel shunts and its electronic control circuit connected in series between the power supply and the controlled motor.

Different methods are used to control the conduction angle of the three opposite parallel shunts, so that the input voltage of the controlled motor varies according to different requirements, and different functions can be realized.

Soft starters and frequency converters are two completely different applications. Inverter is used for the need for speed control, its output not only changes the voltage but also changes the frequency; soft starter is actually a voltage regulator, when the motor starts, the output only changes the voltage and does not change the frequency. The frequency converter has all the soft starter functions, but its price is much more expensive than the soft starter and the structure is much more complicated.

2. What is the soft start of the motor? Which are the starting methods?

Use a soft starter connected in series between the power supply and the controlled motor to control the conduction angle of its internal thyristor, so that the motor input voltage gradually increases from zero with a preset function, until the end of the start, giving the motor full voltage, that is During soft start, the starting torque of the motor gradually increases during the soft start and the rotational speed gradually increases. Soft start generally has the following starting methods.
(1) Ramp boost soft start. This kind of starting method is the simplest, does not have the electric current closed loop control, only adjusts the thyristor conduction angle, causes it to increase with the time the certain function relation. The disadvantage is that, due to the open-ended flow, during the motor starting process, sometimes a large inrush current is generated to damage the thyristor, which has a large impact on the power grid and is rarely used in practice.
(2) Ramp constant current soft start. This starting method is that the starting current is gradually increased in the initial stage of starting the motor, and the current is kept constant (t1 to t2) when the current reaches a predetermined value until the start is completed. During start-up, the rate of change of the current rise can be adjusted according to the motor load. With a large rate of current rise, the starting torque is large and the starting time is short.
This starting method is the most widely used starting method, and is especially suitable for the starting of fans and pump loads.
(3) Step start. Start up, that is, in the shortest time, the starting current will quickly reach the set value, which is a step start. By adjusting the starting current set value, a quick start effect can be achieved.
(4) Pulse impact start. In the start-up phase, the thyristor is turned on for a short period of time with a large current for a short period of time. The thyristor then rises linearly according to the original set value and is connected to a constant current to start.
This starting method, which is less applied in general loads, is suitable for heavy-duty start-up applications that need to overcome large static friction.

3. What are the differences between soft start and traditional decompression start methods?

The traditional decompression starting methods for cage motors include Yq start, auto decompression start, and reactor start-up. These starting methods all belong to graded decompression starting. There are obvious shortcomings, that is, secondary inrush current occurs during starting. The difference between soft start and traditional decompression start mode is:
(1) No inrush current. When starting the motor, the soft starter gradually increases the conduction angle of the thyristor so that the motor starting current linearly rises from zero to a set value.
(2) constant current start. The soft starter can introduce current closed-loop control to keep the motor in constant current during start-up to ensure a smooth start of the motor.
(3) According to the load situation and the selection of power system relay protection characteristics, it is free to steplessly adjust to the best starting current.

4. What is the soft stop of the motor?

When the motor is stopped, the traditional control method is completed through a momentary power failure. However, there are many applications that do not allow the motor to shut down momentarily. For example, high-rise buildings and building water pump systems, if stopped instantaneously, will have a huge "water hammer" effect, causing damage to pipes and even water pumps. In order to reduce and prevent the "water hammer" effect, a gradual shutdown of the motor is required, that is, a soft stop. The use of a soft starter can satisfy this requirement. In the pumping station, the application of soft stop technology can avoid the damage of the pump station's “hatch” and reduce maintenance costs and maintenance workload.

The soft stop function in the soft starter is that the thyristor gradually decreases the conduction angle from full conduction after the shutdown instruction is obtained, and transitions to a fully-closed process after a certain period of time. The parking time can be adjusted from 0 to 120s according to actual needs.

5. How does soft starter achieve light-load energy saving?

The cage type asynchronous motor is an inductive load and the current in the stator coil winding lags the voltage during operation. If the operating voltage of the motor is constant, when the load is light, the power factor is low, and when the load is heavy, the power factor is high. The soft starter can achieve the purpose of light load and energy saving by reducing the motor terminal voltage, increasing the power factor, and reducing the copper and iron consumption of the motor under light load; when the load is heavy, the motor terminal voltage is increased to ensure the normal operation of the motor. .

6. What are the protection features of the soft starter?

(1) Overload protection function: The soft starter has introduced a current control loop so that it can track and detect the change of the motor current at any time. By increasing the setting of the overload current and the inverse time control mode, an overload protection function is realized. When the motor is overloaded, the thyristor is turned off and an alarm signal is issued.
(2) Phase loss protection function: During operation, the soft starter detects the change of the three-phase line current at any time. Once the current is cut off, a phase loss protection response can be made.
(3) Overheat protection function: The temperature of the thyristor heat sink is detected by the soft starter's internal thermal relay. Once the radiator temperature exceeds the allowable value, the thyristor is automatically shut off and an alarm signal is issued.
(4) Other functions: Through the combination of electronic circuits, various other interlock protections can also be implemented in the system.