Smooth start of the induction motor: an example of a frequency converter for an induction motor
The well-known method of starting the engine according to the scheme "star-triangle", which you can assemble with your own hands. The circuit has many disadvantages and has an extremely adverse effect on the "life" of the windings. As you know, this is affected by overheating of the windings from high starting current. Used 2 relay for switching from star to triangle, a controller is also used to start the relay data. From the experience of operating automated lines in production, we can say, that motors very often fail from direct connection to the network. Therefore it is necessary to use schemes of smooth start.
However, new devices for smooth starting of induction motors of frequency drive can work with one circuit of windings of the type "star" and change the speed of rotation frequency. Advantages: ??the user had to deal with the same induction motor, operating on the relay circuit of direct start of the electric motor and after replacement of the relay on the Yaskawa A1000 frequency drive. After replacement, the engine runs smoothly and smoothly, mechanical faults are detected instantly and the drive gives an error. No motor overheating. The launch became smooth with uniform acceleration.
Drive parameters for soft start setting
Implemented in this device 3 possible control modes. You need to choose the appropriate method for adjusting the soft start.
Frequency control for induction motors, common applications with variable speed, especially useful for starting several electric motors from one device and when replacing the drive, when the parameters are unknown.
Frequency control with feedback on the speed of the pulse generator, for general purpose applications, which do not require high dynamic characteristics, but require high accuracy in speed. This mode should be used if the parameters of the motor circuit are unknown and auto-tuning cannot be performed.
Vector control with open circuit. Common applications with variable speed. Applications require control with high accuracy and high speed.
Vector control with a closed loop. For general variable speed applications, requiring high speed control accuracy up to zero, rapid torque increase or precise torque control. Engine speed feedback required.
The drive can operate in two modes: normal and severe. In normal mode, the device can withstand overload on 120% for 60 seconds, it is used in applications, where the torque increases with increasing speed (these are fans and pumps). In heavy start mode, the device can withstand overload up to 150% for 60 seconds, it is used in applications, where there are high loads, where the torque is constant (these are extrusion presses, conveyors, cranes and others).
The drive settings have soft start settings, there are four sets of engine acceleration and deceleration periods, which can be specified in the parameters. If necessary, S-curves can be activated, for a smoother start and end of deceleration acceleration.
Ways to configure the device
Also in the parameters of the device there is a possibility to choose a way to prevent a stop during overclocking. (In this article, we consider general information about the possibilities of frequency drive, You can get more detailed information about the parameters from the user manual). The first way is general. Acceleration stops when the setpoint current is exceeded. The second way is intellectual. Acceleration for the minimum possible time without exceeding the level of prevention of engine stop during acceleration.
The device has a choice of how to prevent the engine from stopping during braking:
- The first way is general. Braking stops, as soon as the DC bus voltage exceeds the stop prevention level.
- The second way is intellectual. Maximum fast braking without overvoltage failures.
- The third way is to prevent the engine from stopping with a braking resistor. Preventing the engine from stopping during braking is included in coordination with dynamic braking.
- The fourth way - braking when working with the violation. Inhibition occurs as the flux density of the magnetic field of the motor increases.
- The fifth way is to slow down when working with a violation 2. The braking speed is regulated according to the DC bus voltage. The sixth method - slows down the regulation of the braking speed in accordance with the output current and voltage of the DC bus.
Automatic setting of the induction motor is used to set the required device parameters. Ways to configure the engine: the first is the stationary setting for the phase-to-phase resistance; the second is a rotary auto tuning for frequency control (necessary for the operation of energy saving functions, speed estimation and speed search); the third is inertial tuning (rotational adjustment must be performed before inertial adjustment); fourth - setting the ASR gain (before adjusting with your own hands you need to perform a rotary auto-tuning).
Ways to prevent engine shutdown
Choosing how to prevent the engine from stopping during braking.
- Prevent the engine from stopping with a braking resistor. Preventing the motor from stopping during braking is included in coordination with dynamic braking.
- Braking when working with a violation. Inhibition occurs as the flux density of the motor magnetic field increases.
- Braking when working with a violation 2. The braking speed is regulated according to the DC bus voltage. Included. Slows down the regulation of the braking speed in accordance with the output current and voltage of the DC bus.
Choose how to prevent stopping while working:
- The first is that braking time is off. The drive operates at the specified frequency. Excessive loads can cause loss of speed.
- The second is the braking time. Braking time is used, set by parameter C1-02, along with measures to prevent the engine from stopping. 2: Braking time 2. Braking time is used, set by parameter C1-04, along with measures to prevent stopping.
The level of prevention of an engine stop during operation is also established, level 100% equal to the rated current of the drive.
A number of engine parameters, set manually
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The rated power of the motor is indicated in the plate.
- Rated voltage, indicated in the plate.
- The rated current is indicated in the plate.
- Base frequency. Sets the nominal frequency, specified in his plate.
- The number of poles of the engine. Specifies the number of poles, indicated on its plate.
- Speed constant. Sets the nominal speed, indicated on the plate.
- The number of pulses per revolution of the pulse generator. Specifies the number of pulses per revolution for the pulse generator used (pulse generator or encoder).
- Idle current (stationary auto tuning). Sets the idle current. After setting the power of parameter T1-02 and the rated current of parameter T1-04, this parameter will automatically display the no-load current for a standard 4-pole Yaskawa motor.. Input no-load current, as stated in the test report.
- Nominal engine slip (stationary auto tuning). Sets the nominal slip. When set to the T1-02 motor power device, this parameter will automatically display the slip for a standard Yaskawa 4-pole motor.. Introduces sliding, as stated in the engine test report.
- Engine losses in steel. Specifies the losses in steel to determine the energy saving factor. This value is set by parameter set E2-10 (engine loss in steel) at cyclic change of power. When parameter T1-02 is changed, the default value appears, corresponding to the input power.
