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Dedicated vector control

01 May 2023

LEVERAGING THE design of the BLH motor for precision control, Oriental Motor has introduced the BLH2D driver implementing dedicated vector control for speed tracking and low noise operation for use with the BLH series.

The BLH2D driver offers high speed stability with variable load factor and low noise. It is available for analogue setting, digital setting and RS-485 communication.

The analogue BLH2D driver has an analogue setting with a potentiometer or external DC voltage for setting the speed. Current, I/O and motor feed lines are compatible with the earlier BLH model. The braking and stopping movement can be configured as free-running or, optionally, recuperating mode.

The digital version has the option to set desired driving profiles using the MEXE02 parameterisation software via a PC’s USB port. Functions available include speed, torque limitation, acceleration and deceleration time. To enhance ease-of-use, Oriental Motor has added inputs and outputs and stepless speed control with PWM (pulse width modulation) input. With this model, analogue speed adjustment is still possible.

The third BLH2D version has RS-485 communication and is primarily intended for applications where the status of the drive is to be constantly monitored or the commissioning effort is to be kept low. It can be used to upgrade systems and replace an existing BLH model.

Digital control as vector control

The BLH2D driver regulates the phase currents through vector control in the motor control system. This makes it possible to implement an energy recovery and torque limitation function. Changing the motor drive system from conventional block commutation to sinus commutation results in three-phase variables become a two-dimensional coordinate system which is highly efficient and also enables the motor current to be controlled depending on the rotor position. An interpolation function detects the exact rotor position, using standard Hall sensors to enable the BLH2D driver to operate the motor in all four quadrants for controlled braking.

Key benefits include improved speed regulation during deceleration and improved speed stability during load changes. The BLH2D driver also has a torque limiting function and a load factor display function to monitor the torque generated. The calculated load factor can be displayed and checked using the status monitor function of the MEXE02 parameterisation software. If irregularities are detected, predictive maintenance can be initiated.

Regenerative energy during braking

To avoid overvoltage, the BLH2D driver uses active feedback voltage suppression control, where regenerative energy is immediately fed back to the motor when needed without it having to be converted into heat via a resistor.

Regenerative power can also be used for charging batteries, feeding energy directly back into the power supply. The hardware design incorporates a FET to interrupt the power supply as needed.

Deceleration process options

Braking can be through using regenerative power without feeding energy back into the power supply, or without, whereby energy is freewheeling and not fed back to the power supply. A third option is to use regenerative power fed back to a power supply, for example a battery.

The first braking method is suitable, for example, for belt drives in conjunction with a switched-mode power supply. Operation with frequent recuperation however, can lead to a sharp increase in motor temperature.

The second deceleration process controls the braking torque so that no regenerative energy is generated and the deceleration process is unregulated. This method does not increase the driver’s internal and is compatible with the original BLH motor and is ideal if no braking torque is to be generated during stopping.

The third selectable deceleration method, is suitable for downward travel of a driverless transport vehicle, for example, maintaining the set speed and using a suitable power supply without increasing the supply or internal voltages.

Inrush current protection

The new BLH2D driver includes a FET in the inrush current suppression circuit. The delay capacitor between gate and source is gradually charged to control the voltage applied to the electrolytic capacitor with a fixed time constant.

Sinus commutation has also reduced noise in the BLH2D driver. It has a smoother current waveform than the original, with reduced rotational and surface vibrations. A tracking analysis of the motor surface vibration showed a significantly lower audible level in 20 Hz to 20 kHz frequency range compared to the earlier generation driver, resulting in lower noise development.

Other notable enhancements for the BLH2D driver include an increase in the limited operating range. For the 30W motor, the torque could be increased by 15%, and by 20% for the 50W motor.