A motor controller is a device or group of devices that serves to set in some predetermined way the performance of an electric motor. The motor controller may include manual or automatic means to start and stop the motor, select forward or backward rotation, select and adjust speed, adjust or limit torque, and protect against overload and errors.
There are many types of beginnings:
- Direct On Line (DOL)
- Star delta starter
- Starter auto transformer
Video Motor controller
Apps
Every electric motor must have some sort of controller. The motor controller will have different features and complexities depending on the task to be performed by the motor.
The simplest case is the switch to connect the motor to a power source, such as in small appliances or electrical appliances. Switches can be operated manually or may be relays or contactors connected to some form of sensor to automatically start and stop the motor. The switch may have several positions to select different motor connections. This allows the commencement of low-voltage motors, reversing controls or selecting multiple speeds. Overload and overcurrent protection can be eliminated in very small motor controllers, which depend on the supply circuit to have more protection than current. The small motor may have a built-in overload device to automatically open the circuit on excessive loads. Larger motors have protective overload relays or temperature sensing relays included in the controller and fuse or circuit breakers for overcurrent protection. Automatic motor controllers may also include limit switches or other devices to protect the driven machine.
More complex motor controllers can be used to accurately control the speed and torque of the connected motor (or motor) and can be part of a closed loop control system for precise positioning of the driven engine. For example, numerically controlled lathes accurately position the cutting tool according to the programmed profile and compensate for various disruptive load conditions and forces to maintain the position of the device.
Maps Motor controller
Motor control type
Motor control can be done manually, remotely or automatically operated. They may include only the means to start and stop the motor or they may include other functions.
The electric motor controller can be classified by the type of motor it is to push such as permanent magnet, servo, series, separately vibrant, and alternating current.
The motor controller is connected to a power source such as a battery pack or power supply, and a control circuit in the form of an analog or digital input signal.
Starter motor
Small motors can be started simply by plugging them into an electrical outlet or by using a switch or circuit breaker. Larger motors require a special switching unit called a motor starter or motor contactor. When energized, the direct starter on line (DOL) immediately connects the motor terminal directly to the power supply. Low-voltage starter, star-delta or soft connect the motor to the power supply through the voltage reduction device and increase the applied voltage gradually or in steps. In smaller sizes, the motor starter is a manually operated switch; larger motors, or those requiring remote or automatic control, using magnetic contactors. A very large motor running on a medium voltage supply supply (thousands of volts) can use a power circuit breaker as a switching element.
The direct on channel (DOL) or across line applies full line voltage to the motor terminal, initial location or chamber, usually found in the ELO image. This is the simplest type of starter motor. The DOL starter motor also contains protection devices, and in some cases, condition monitoring. The smaller size of on-line direct activation is manually operated; larger sizes use electromechanical contactors (relays) to replace motor circuits. Direct solid-state on line starters also exist.
Direct on-channel activation can be used if high motor inrush does not cause excessive voltage drop in the supply circuit. The maximum size of the allowed motor on the direct channel starter may be limited by the supply utility for this reason. For example, a utility may require rural customers to use a reduced voltage start for motors larger than 10 kW.
DOL start is sometimes used to start small water pumps, compressors, fans and conveyor belts. In the case of an asynchronous motor, such as a 3-phase squirrel-cage motor, the motor will draw a high start current until its speed rises to full speed. This initial current is usually 6-7 times greater than the full load current. To reduce the inrush, larger motors will have the start of a reduced voltage or variable speed drive to minimize dips voltage to the power supply.
Starting flips can connect the motor for rotation in both directions. Such starters contain two DOL circuits - one for clockwise and the other for counter-clockwise operations, with mechanical and electrical interlocks to prevent simultaneous closure. For a three phase motor, this is achieved by swapping the two-phase connecting cables. Single phase AC motors and direct-current motors require enhancements to reverse rotation.
Reduce the voltage starter
Two or more contactors may be used to provide a reduced starting voltage of the motor. By using autotransformer or series inductance, lower voltages are present in the motor terminals, reducing initial torque and current inrush. When the motor has reached a fraction of its full load speed, the starter switches to full voltage at the motor terminal. Since the autotransformer or series reactor only carries heavy starting motor currents for a few seconds, the device can be much smaller than the equipment rated continuously. The transition between low and full voltage can be based on the elapsed time, or triggered when the current sensor indicates the motor current begins to decrease. The patented autotransformer starter in 1908.
Drive speed-adjustable
An adjustable speed (ASD) or variable speed drive (VSD) is a combination of interconnected equipment that provides driving and adjusts the operating speed of a load mechanic. The electrically adjustable speed driver consists of an electric motor and a speed controller or power converter plus enhancements and equipment. In general use, the term "drive" is often applied only to the controller. Most modern ASD and VSD can also implement soft start motors.
Intelligent controller
An Smart Motor Controller (IMC) uses a microprocessor to control the power of electronic devices used for motor control. IMC monitors the load on the motor and adjusts the motor torque to the motor load. This is done by reducing the voltage to the AC terminals and at the same time decreasing the current and kvar. This can provide a measure of increased energy efficiency for motors that run under light load for most of the time, resulting in less heat, noise, and vibration generated by the motor.
Overload relay
The starter will contain a protective device for the motor. This will minimally include a thermal overload relay. Thermal overload is designed to open the initial circuit and thus cut power to the motor if the motor draws too much current from the supply for a long time. Excess relays have normally closed contacts that are open due to the heat generated by the excess currents flowing through the circuit. Thermal overload has a small heater that increases the temperature when the current motor is running up.
There are two types of thermal overload relays. In one type, the bi-metal strip near the heater turns when the heating temperature rises up mechanically causing the device to run and open the circuit, cutting power to the motor if it becomes overloaded. The thermal overload will accommodate the high high initial current of a motor while accurately protect it from overcurrent current. The heating and action coil of the bi-metal strip introduces a time delay which gives the motor time to start and settle into the normal running current without excessive heat tripping. Thermal overload can be manually or automatically reset depending on their application and has an adjuster that allows them to be accurately set to the current running motor.
The second type of thermal overload relay uses eutectic alloys, such as solder, to maintain spring contact. When too much current passes through the heating element for too long, the alloy melts and the spring releases contact, opens the control circuit and turns off the motor. Since the eutectic alloy elements are not adjustable, they are resistant to casual interference but require the change of heating coil elements to fit the motor rated current.
Digital digital overload relays containing microprocessors can also be used, especially for high-value motors. This device modeled the heating of the motor windings by monitoring the motor current. They can also include measurement and communication functions.
Loss of voltage protection
A starter using a magnetic contactor typically obtains a power supply for the contactor coil from the same source as the motor supply. Additional contacts from the contactor are used to maintain the contactor coils that are energized after the start command for the motor is removed. If a loss of supply voltage occurs for a moment, the contactor will open and not close again until a new start command is given. this prevents restarting the motor after power failure. This connection also provides small level protection against low power supply voltage and phase loss. However, since the contactor coil will hold the closed circuit with as little as 80% of the normal voltage applied to the coil, this is not the primary means of protecting the motor from low-voltage operation.
Servo controller
The servo controller is a broad category of motor control. Common features are:
- precise closed-loop position control
- fast acceleration rate
- precise speed control Servo motors can be made of several types of motors, the most common are:
- brush DC motor
- brushless DC motor
- Servo AC motor
The servo controller uses position feedback to close the control loop. This is usually implemented with encoders, resolvers, and Hall effect sensors to directly measure the rotor position.
Other position feedback methods measure the rear EMF in the undriven coil to infer the rotor position, or detect the resulting Kick-Back traction voltage whenever the power of the coil is switched off instantaneously. This is therefore often called the "uncensored" control method.
The servo can be controlled using pulse-width modulation (PWM). How long the pulse remains high (usually between 1 and 2 milliseconds) determines where the motor will try to position itself. Other control methods are pulses and direction.
Stepper motor controller
A stepper, or stepping, motor is the number of poles that are synchronous, uneven, high, polyphase motors. The controls are usually, but not exclusively, done open loop, ie the position of the rotor is assumed to follow a controlled rotating field. Therefore, the exact position with steppers is simpler and cheaper than closed-loop control.
Modern stepper controllers drive motors with much higher voltages than motors that are labeled voltage, and limit the current through the cut. The usual setting is to have a position controller, known as indexer , sending step pulses and direction to a separate higher-voltage driving circuit responsible for commutation and current turnover.
References
- "Dallas Personal Robotics Group". Short H-Bridge Operation Theory . Archived from the original on January 12, 2013 . Retrieved July 7, 2005 .
- Links to manufacturers, associations, and other resources.
See also
- Motor control center (MCC)
Source of the article : Wikipedia
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