HICONICS HIVERT-Y (T) VF Vector Control Frequency Converters

The HIVERT-Y(T) VF series is a vector-controlled frequency converter for an asynchronous or synchronous electric motor that not only generates harmonic phase currents but also provides control of the rotor magnetic flux.

Main elements of the HIVERT-Y(T) VF series

Starting cabinet

When the motor power exceeds 1800 kW, the starter cabinet effectively suppresses the transformer supply surge current and prevents the automatic overvoltage protection from starting, and the built-in resistor limits the current and partially absorbs electrical energy.

Transformer

The isolation transformer is a dry-type transformer with forced air cooling. It is equipped with a temperature controller, a real-time control and monitoring system, and a winding temperature monitoring system. When the temperature of the transformer winding exceeds the permissible value, the system sends a fault signal and opens the lower fan of the transformer.

Power elements

When the adaptive power of the VFD motor is less than 1800 kW, the power elements increase the buffer process, which is used to limit the pre-charging current of the power elements and protect the input side of the IGBT. As a result, the HIVERT-Y(T) VF series products have 100% rated power. The power cell uses the IGBT to perform synchronous rectification: the synchronous rectifier controller detects the amplitude and phase of the input voltage in real time. It controls the voltage generated from the IGBT on the rectifier side and the phase difference of the input voltage of the power cells. The magnitude and direction of the electric power is determined by the voltage of the power cell.

Control system

A control or monitoring system consists of a controller, an interface board and a human-machine interface (HMI).

Principle of operation of frequency converters of the HIVERT-Y(T) VF series

The basic principle of vector control is to separately control the magnetizing current of the motor and the quadrature current, which is proportional to the mechanical torque on the shaft. Although the rotation of the rotor is driven by a rotating magnetic field, in a real system the rotor rotates at a slower speed than the rotational speed of the magnetic field. The difference in these speeds is called slip. The slip can be expressed as a frequency ratio, but the slip frequency is more commonly used for description. The rotor is induced by an alternating current, creating a magnetic field in it, which generates the driving torque. The slip gives the motor the ability to regulate the rotation speed to some extent. As the load on the motor increases, the rotor speed decreases. This causes an increase in the slip frequency, which in turn increases the flux and drive torque in the rotor.

The HIVERT-Y(T) VF series closed-loop high-voltage frequency converter uses a motor-mounted encoder or analog sensor to provide a positive indication of the shaft position to the microprocessor. The position and speed of the motor rotor, torque and power output are monitored in real time by the digital encoder. It sends digital pulses to the VFD processor, which reads them and uses the information to control the motor torque. The sensors of the HIVERT-Y(T) VF series produce 1024 pulses per revolution, which provides more precise control and reduces the likelihood of static error.

How vector control works

All internal motor signals from the input wires are sinusoidal. Such signals are difficult to process programmatically, especially when PID algorithms (PID = proportional, integral, derivative) are used to control the current. However, when calculating the reference point, the signals inside the motor can be mathematically processed. The Clarke transform and Park transform are used to calculate the movement of currents from a stationary reference plane to a rotating plane.

The Clarke transformation equation: Iα = Ia Iβ = 0.577 (Ia + 2Ib)

Next, the Park transform is used to switch to a two-axis rotational coordinate system coaxial to the motor rotation.

Park’s transformation equation: Id = Iα cosΘ + Iβ sinΘ Iq = -Iα cosΘ + Iβ sinΘ, where Θ is the angle of rotation.

When using vector control for three-phase synchronous and induction motors, the plane of rotation is always oriented according to the rotor, and the angle is calculated based on its position using a sensor. The rotor winding resistance and inductance are used to calculate the current display parameters. These values determine the time constant that adapts the motor slip to the correct value during transient current fluctuations.

Areas of application of the HIVERT-Y(T) VF series

The frequency inverters of this series are used in a wide variety of applications and industries. They are used in the energy sector in forced-draft ventilation systems or in slurry pumps. They are used in the mining industry in pumps and dust collectors, and in metallurgy in compressor and blast furnace blowers. This is not a complete list of applications for the HIVERT-Y(T) VF series.

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