Kenji Nandoh

Stabilizing control method for suppressing oscillations of induction motors driven by PWM inverters

A novel control method that suppresses oscillations generated when an induction motor is driven by PWM (pulse width modulated) inverters is described. The suppression is done by keeping the power direction constant throughout the period of oscillation of the negative current component of the inverter input current. This period is determined only by the frequency of the PWM signals. Because it is not affected by motor parameters, such as the number of poles or motor capacity, the gains of the regulator in the control system do not have to be adjusted, even if this method is applied to various kinds of induction motor drive systems. Experiments have proven that oscillations can be suppressed regardless of the motor type or speed. This stabilizing control is suitable for general-purpose inverters that drive various types of motors. >

Tripless control method for general-purpose inverters

The control method described prevents general-purpose inverters without current regulators from tripping easily, i.e. to be tripless no matter how their load is varied, and enables motors to rotate stably at high frequencies. It uses only current sensors and is a combination of pulse-width-modulated (PWM) control and torque control. The PWM control changes an asynchronized mode to a synchronized mode when the modulation ratio becomes more than one, enabling the carrier wave frequency to be continuously varied with the inverter frequency so that motors can rotate stably over a wide frequency range. The torque control uses a real and reactive component detector, magnetic flux compensator, slip compensator, and current limit controller. Experiments prove that this tripless control can be satisfactorily applied to general-purpose inverters. >

Automatic torque boost control method suitable for PWM inverter with a high switching frequency

A torque control method is described that can generate a motor torque larger than the rated torque over a wide speed range without a current regulator and a speed sensor, even if the induction motor is driven by a pulse-width-modulation (PWM) inverter with a high switching frequency. Control is performed by a magnetic flux compensation control loop. The first control loop suppresses the magnetic flux reduction generated when the load torque and the inverter angular frequency are varied. This reduction is calculated using both inverter angular frequency and slip angular frequency. The current distortion due to the dead time of the PWM signals is suppressed by correcting the signal pulse widths on the basis of errors generated between the PWM reference signals and the inverter output voltage. Experiments confirmed that an induction motor could generate motor torque of more than 150% of the rated torque. The current distortion factor was less than 10% over a wide frequency range. >

Magnetic flux compensating torque control method suitable for general purpose inverters with superaudible switching frequencies

A novel torque control method which is suitable for general-purpose induction motor variable speed devices driven by superaudible frequency PWM (pulse width modulation) inverters is described. In the torque control, the primary magnetic flux reference is compensated, using only current sensors, on the basis of the inverter angular frequency and the slip angular frequency, so that motor torque can be generated according to load torque. The superaudible frequency PWM signals are generated by divisions of duration times of the voltage vectors, determined on the basis of the primary magnetic flux reference. Experiments showed that high-performance torque characteristics suitable for general-purpose inverters could be obtained by this method.<<ETX>>

Microprocessor Control System with I/O Processing Unit LSI for Motor Drive PWM Inverter

In order to increase the performances and decrease the size and cost of control circuits for pulsewidth modulated ( PWM) inverters, a microcomputer control system has been developed. It consists of a microcomputer and an I/O processing unit large-scale integration (LSI) to control a variable-speed motor. The microcomputer performs complicated calculations and analyses of driving conditions. The I/O processing unit LSI detects motor driving states (analog to digital convsrsion and pulse count, etc.), generates PWM pulse outputs, and protects the inverter against overcurrents and power outages. The I/O processing unit LSI functions using the command data from the microcomputer. Conversion and count data can be sent to the microcomputer from the I/O processing unit LSI. For the convenience of interfaces to the microcomputer, all-digital logic circuits are developed for the I/O processing unit LSI. For example, PWM pulse outputs are generated by comparing digital data of a carrier timer and step level of a modulation wave. Undesirable harmonic components can be reduced easily by command data from the microcomputer.