VVVF elevators

     In 1982,Mitsubishi Electric successfully developed a special frequency converter for elevators by using GTR module and 16-bit microprocessor,and took the lead in introducing fully computerized AC VVVF elevators in the world.Driven by AC motors and controlled through vector transformation and PWM,VVVF elevators have their operational performances reaching or surpassing those of nearly all previous elevators adopting various AC and DC drive systems,and a lot of energy is saved in addition.At the beginning of the nineties,with the appearance of more advanced IGBT and further development of computer technology and LSI,Mitsubishi Elevator has timely applied up-to-date technology and elements to VVVF elevators,thus achieving high performance and reliability in digitized and miniaturized products and keeping its VVVF elevators in the leading position in the world.At present,Mitsubishi Elevator VVVF is fully applied to elevators,hydraulic elevators,escalators and moving walks,covering elevators with a speed range of 0.45m/s 12.5m/s.

   For any elevator speed,Mitsubishi VVVF 
drive systems using PWM and vector transformation can accurately adjust the motor rpm in accordance with the optimal speed curve.The frequency conversion system designed specifically for elevator systems integrates IGBT module or IPM module,high-speed CPU and LSI.Its accurate computing capacity,quick response capability and excellent disturbance resistance make it possible for speed variations at start,travel and stop to fully adapt to the psychological feeling of the human body and for the passengers to enjoy comfortable and stable up and down travels.Furthermore,elevators adopting Mitsubishi VVVF can save nearly 50% energy,when compared with conventional AC voltage variable speed-regulated elevators,in addition to reduced capacity of power supply equipment.
 Ⅰ  Description of Mitsubishi speed curve:

A. Start:The digital linear weighing device weighs accurately the load in the car.The car isstarted after a torque is applied accurately according to the measured weight,so as to avoid start impact due to the car load.
B.  Acceleration/deceleration:The drive system conducts accurate computation,responds quickly and effectively suppresses disturbance so as to achieve a perfect actual speed curve to ensure good travel comfort.
C.  Stop:Accurate control and zero speed stop avoid braking and stopping impact.
Ⅱ   Description of ordinary elevator curve:
A.  Start:Switch-type weighing device and non-linear switching output can not accurately measure the load in the car.When released,the brake can not make effective compensation for unbalanced load,so that start impact is likely to happen.
B.  Acceleration/deceleration:relatively slow response,poor resistance to disturbance,many burrs on the actual speed curve,low travel comfort.
C.  Stop:low control accuracy,no zero-speed stop,impact with braking/stopping.
     Applying VVVF for elevator drive to the door operator system,Mitsubishi has designed a special VVVF-driven intelligent door operator system.Dual closed loop control for speed and current is applied for effective control of the speed and torque for door opening/closing.

    Door weight (heavy stainless steel door or light painted steel door,for example) on each floor is memorized in an intelligent way,and based on that,the door opening/closing torque is regulated automatically to realize quick,smooth and quiet door opening/closing.In the meanwhile,flexible current measurement and torque control enable quick inspection and reverse opening in case of door closing being blocked (by hand of the passenger for instance),thus reducing impact upon the blocking object,improving passenger safety,and avoiding possible damage of the door system by heavy blocking objects.