Commonly used terms for frequency converters (II)

Number of motor poles

In an induction motor, the stator is used to generate a magnetic field inside the motor, which magnetizes its rotor and causes the shaft to rotate. Coils are wound around a symmetrical core and arranged in sequence around the inner diameter of the stator. When current is passed through the coils, electromagnets are generated. In a single-phase motor, each of these electromagnets is matched with another electromagnet that is 180° out of phase and of opposite polarity, thus generating a magnetic field. In a three-phase AC motor, three such electromagnets constitute one motor pole. The number of poles of a motor is one of the factors that determine the torque per hp and speed per Hz of the motor.

Single-phase power

 A typical 230-V AC single-phase electrical system that uses two live wires and a neutral wire to transmit power. This system is mainly used in applications that do not require three-phase power or in remote areas where the cost of transmitting three-phase power is too high.

Three-phase power

Mainly used in commercial and industrial facilities, three-phase electrical systems use a neutral point or ground and three live wires, each transmitting one AC phase. Each phase is a sine wave that is 120 degrees, or one-third of the cycle, out of phase. Each phase peaks at a different time, making the total power look like continuous DC power.

Control board

The control board is a printed circuit board (PCB) that is the main component used to interface between external devices and operators and the inverter. As the brain of the inverter, the PCB accepts real-world instructions, such as "run" or "accelerate", and performs the target function. The control PCB is usually connected to the main circuit of the inverter through the gate driver board.

Copy keyboard

A inverter keyboard that can store programming into the non-volatile RAM of the keyboard itself. These stored parameters can usually be loaded into another inverter that requires the same programming.

AC permanent magnet motor

The permanent magnet motor is a synchronous AC motor. There are two main types of AC permanent magnet motors, including surface mount and internal mount. Unlike ordinary induction motors, there is no slip between the stator and rotor during normal operation of the permanent magnet motor. There is no I2R loss in the rotor, so the rated efficiency of the PM motor is higher than that of the induction motor. High energy savings and smaller size make permanent magnet motors a useful alternative to induction motors, although not all VFDs can operate permanent magnet motors.

V/F Mode

Also known as V/Hz mode, this is a simple method of controlling an AC induction motor via a VFD. A ratio is determined based on the base voltage and motor base frequency ratings. This ratio produces a linear pattern that the VFD follows to produce the rated motor torque. The ratio of voltage to frequency is the level of flux in the machine, which in turn determines the amount of torque the machine produces at a given operating point.

Open-loop vector

A complex but effective method of motor control that allows VFDs to achieve the best characteristics of DC drive control (precise torque control over a wide speed range) without the brush maintenance and high initial cost of DC motors. For optimal performance, the position or deviation of the motor rotor must be accurately estimated. In open-loop vector control, the rotor position must be calculated by other means due to the lack of actual shaft position feedback. However, the slight loss in motor performance is offset by the cost savings of eliminating the feedback device, VFD input, and associated wiring compared to closed-loop vector operation.

Closed-Loop Vector

A complex but highly effective motor control method that allows a VFD to achieve the control benefits of a DC drive without the physical limitations of a DC motor. Feedback devices such as encoders or resolvers provide the necessary motor slip information to close the loop between the VFD output frequency and the actual motor shaft speed.

RS-485

A serial network standard that defines the electrical and physical characteristics of transmitting and receiving information in an industrial environment. A key feature of RS-485 is that it is a multi-point connection scheme that allows many devices to communicate over long distances using only two or four wires and a shield.

Ethernet

A hardware and message transmission specification that defines a network device or node. It consists of the first two layers of the OSI model: the physical layer (cables, RJ45 connectors) and the data link layer (i.e., defines how messages are transmitted from one device to another).

Protocol

A set of rules that define how messages are created for use in fieldbus networks. These rules detail how communications between devices (such as VFDs) are constructed and delivered. Different protocols cannot usually be mixed in a single network without the use of a gateway device. Common examples of protocols include Ethernet/IP, DeviceNet, Profibus, Profinet, Modbus RTU, and Modbus TCP/IP.