En términos generales, puede decirse que existen tres tipos básicos de variadores de velocidad: mecánicos, hidráulicos y eléctrico-electrónicos. Dentro de cada tipo pueden encontrarse más subtipos, que se detallarán a continuación. Cabe aclarar que los variadores más antiguos fueron los mecánicos, que se emplearon originalmente para controlar la velocidad de las ruedas hidráulicas de molinos, así como la velocidad de las máquinas de vapor.

Los variadores de velocidad mecánicos e hidráulicos generalmente son conocidos como transmisiones cuando se emplean en vehículos, equipo agroindustrial o algunos otros tipos de maquinaria.

Mechanical variators

Schematic 3D animation of operation.

Electric-electronic drives

There are four categories of electric-electronic speed variators:

Los variadores eléctrico-electrónicos incluyen tanto el controlador como el motor eléctrico, sin embargo es práctica común emplear el término variador únicamente al controlador eléctrico.

Los primeros variadores de esta categoría emplearon la tecnología de los tubos de vacío. Con los años después se han ido incorporando dispositivos de estado sólido, lo cual ha reducido significativamente el volumen y costo, mejorando la eficiencia y confiabilidad de los dispositivos.

Drives for DC motors

These drives allow you to control the speed of series, shunt, compound and permanent magnet DC motors "Magnet (physics)"). Variable speed drives are devices that allow the speed of an electrically controlled motor to be varied.

In the case of any of the above machines, the following expression is true:

where.

Solving for the mechanical speed, we obtain:

Then, from () it can be seen that the mechanical speed of a DC motor is directly proportional to the terminal voltage (VT) and inversely proportional to the magnetic flux (FM), which in turn depends on the field current (IF). Taking advantage of this situation is that this type of drive can control the speed of a DC motor: by controlling its terminal voltage, or by manipulating the value of the field current.

Eddy current drives

An eddy current drive consists of a fixed speed motor and an eddy current clutch. The clutch contains a fixed speed rotor (coupled to the motor) and a variable speed rotor, separated by a small air gap. It also has a field coil, whose current can be regulated, which produces a magnetic field that will determine the mechanical torque transmitted from the input rotor to the output rotor. In this way, the greater the intensity of the magnetic field, the greater the torque and speed transmitted, and the lower the magnetic field, the lower the torque and speed in the output rotor. The control of the output speed of this type of drives is generally carried out through a closed loop, using the feedback element as a feedback element.

Operational slip drives

This type of inverter is only applied to wound rotor induction motors. In any induction motor, the mechanical speed (nM) can be determined by the following expression:.

Where s is the slip of the motor, whose value ranges between 0 and 1. Thus, the greater the slip, the lower the mechanical speed of the motor. Slip can be increased by increasing the resistance of the rotor winding or by reducing the voltage across the rotor winding. In this way, speed control can be achieved in wound rotor induction motors. However, this type of drive is less efficient than others, which is why it currently has very little application.

Drives for AC motors

Variable frequency drives (AFD, Adjustable Frequency Drive; or VFD Variable Frequency Drive) allow you to control the speed of both induction motors (squirrel cage asynchronous or wound rotor motors) and synchronous motors by adjusting the power supply frequency to the motor.

where:.

As can be seen in the expressions () and (), the frequency and speed are directly proportional, in such a way that by increasing the frequency supplied to the motor, the speed of the shaft will increase, and by reducing the value of the frequency the speed of the shaft will decrease. This is why this type of inverter manipulates the power supply frequency to the motor in order to control the speed of the machine.

These drives maintain the Voltage/Frequency ratio (V/Hz) constant between the minimum and maximum values ​​of the operating frequency, in order to avoid magnetic saturation of the motor core and also because operating the motor at a constant voltage above a given frequency (reducing the V/Hz ratio) decreases the motor torque and its ability to provide constant output power.

En términos generales, puede decirse que existen tres tipos básicos de variadores de velocidad: mecánicos, hidráulicos y eléctrico-electrónicos. Dentro de cada tipo pueden encontrarse más subtipos, que se detallarán a continuación. Cabe aclarar que los variadores más antiguos fueron los mecánicos, que se emplearon originalmente para controlar la velocidad de las ruedas hidráulicas de molinos, así como la velocidad de las máquinas de vapor.

Los variadores de velocidad mecánicos e hidráulicos generalmente son conocidos como transmisiones cuando se emplean en vehículos, equipo agroindustrial o algunos otros tipos de maquinaria.

Mechanical variators

Schematic 3D animation of operation.

Electric-electronic drives

There are four categories of electric-electronic speed variators:

Los variadores eléctrico-electrónicos incluyen tanto el controlador como el motor eléctrico, sin embargo es práctica común emplear el término variador únicamente al controlador eléctrico.

Los primeros variadores de esta categoría emplearon la tecnología de los tubos de vacío. Con los años después se han ido incorporando dispositivos de estado sólido, lo cual ha reducido significativamente el volumen y costo, mejorando la eficiencia y confiabilidad de los dispositivos.

Drives for DC motors

These drives allow you to control the speed of series, shunt, compound and permanent magnet DC motors "Magnet (physics)"). Variable speed drives are devices that allow the speed of an electrically controlled motor to be varied.

In the case of any of the above machines, the following expression is true:

where.

Solving for the mechanical speed, we obtain:

Then, from () it can be seen that the mechanical speed of a DC motor is directly proportional to the terminal voltage (VT) and inversely proportional to the magnetic flux (FM), which in turn depends on the field current (IF). Taking advantage of this situation is that this type of drive can control the speed of a DC motor: by controlling its terminal voltage, or by manipulating the value of the field current.

Eddy current drives

An eddy current drive consists of a fixed speed motor and an eddy current clutch. The clutch contains a fixed speed rotor (coupled to the motor) and a variable speed rotor, separated by a small air gap. It also has a field coil, whose current can be regulated, which produces a magnetic field that will determine the mechanical torque transmitted from the input rotor to the output rotor. In this way, the greater the intensity of the magnetic field, the greater the torque and speed transmitted, and the lower the magnetic field, the lower the torque and speed in the output rotor. The control of the output speed of this type of drives is generally carried out through a closed loop, using the feedback element as a feedback element.

Operational slip drives

This type of inverter is only applied to wound rotor induction motors. In any induction motor, the mechanical speed (nM) can be determined by the following expression:.

Where s is the slip of the motor, whose value ranges between 0 and 1. Thus, the greater the slip, the lower the mechanical speed of the motor. Slip can be increased by increasing the resistance of the rotor winding or by reducing the voltage across the rotor winding. In this way, speed control can be achieved in wound rotor induction motors. However, this type of drive is less efficient than others, which is why it currently has very little application.

Drives for AC motors

Variable frequency drives (AFD, Adjustable Frequency Drive; or VFD Variable Frequency Drive) allow you to control the speed of both induction motors (squirrel cage asynchronous or wound rotor motors) and synchronous motors by adjusting the power supply frequency to the motor.

where:.

As can be seen in the expressions () and (), the frequency and speed are directly proportional, in such a way that by increasing the frequency supplied to the motor, the speed of the shaft will increase, and by reducing the value of the frequency the speed of the shaft will decrease. This is why this type of inverter manipulates the power supply frequency to the motor in order to control the speed of the machine.

These drives maintain the Voltage/Frequency ratio (V/Hz) constant between the minimum and maximum values ​​of the operating frequency, in order to avoid magnetic saturation of the motor core and also because operating the motor at a constant voltage above a given frequency (reducing the V/Hz ratio) decreases the motor torque and its ability to provide constant output power.