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Hitachi

Power Electronics

Best Fits for High Torque Application

Robust speed sensor-less vector control technology prevents over current conditions and operates machines in a safe and continuous mode when the impact load reaches 200%.
HIVECTOL-HVI is capable of driving a heavy starting load (200% torque) and can not only match but excel in performance compared to a DC motor. HIVECTOL-HVI best fits mixers and extruders for rubber and plastic industries.

For high torque applications such as rubber mixers, extruders, and agitators, Hitachi uses a method that controls the output voltage by adjusting current flux component using measurement of overload current. Smooth torque control in the operating speed range and and high torque at the startup is achieved by sensor-less vector control by using calculated required current for torque and excitation for the given load.
A sensor-less vector control scheme needs no speed feedback device (speed sensor) and it improves system reliability and maintainability.

Lower Parts Count Enhances Reliability

In order to reduce inrush current when the main power is turned on, a pre-charging circuit is required to charge DC capacitors. Hitachi uses its patented external pre-charging circuit and pre-charging is done by a separate power supply.
The other method is to use a pre-charging circuit with each Cell Inverter.
Comparing between the two pre-charging methods, the external pre-charging method is very simple and reduces the parts count.

Patented Pre-Charging method

Pre-charging circuit charges the DC capacitor before the input medium voltage breaker is turned on. This is done in order to prevent the inrush current when the medium voltage main power supply turns on.
HIVECTOL-HVI uses a separate LV power source for pre-charging. This power supply is switched on for about 20 seconds, during which capacitors in the inverter cells charge. Once capacitor charging is completed, the LV supply is disconnected and the medium voltage breaker for main supply is turned on. Compared to a pre-charging circuit that uses a thyristor switch and a resistor in each cell unit, the arrangement of separated pre-charging circuit is simple and easy to maintain. This design leads to high reliability in inverter operation.
Separated pre-charging circuit method has been patented by Hitachi Ltd (Patent No.3,535,477).

Instantaneous Voltage Drop Measure

Automatic Restart upon Instantaneous Power Failure
After input power recovery, the automatic restart function maintains continuous operation in the case of instantaneous power failure. The coasting motor can be reaccelerated to the reference speed automatically.