Noboru Azusawa

A Microprocessor-Controlled Fast-Response Speed Regulator with Dual Mode Current Loop for DCM Drives

A new control method is described in which a microprocessor is used to regulate the speed of a dc motor driven by antiparallel-connected three-phase dual thyristor converters. A distinct feature of this speed regulating system is that speed response is improved by using a fast-response current controller for the internal loop. A fast-response current controller is obtained by employing a nonlinear compensation subloop and a proportional plus integral compensation subloop. The nonlinear compensation subloop is used to linearize the nonlinear load characteristics of the thyristor converter, which are encountered under discontinuous conduction states of current. The proportional plus integral compensation subloop reduces the deviation of detected current from the current reference. With these two current-control subloops a fast motor speed response is achieved under discontinuous as well as continuous conduction states; hence the steady-state accuracy of speed is improved. A speed regulator using a microprocessor was trial manufactured and tested with a 20-kW dc motor. It was found that an extremely fast controlled current response can be obtained even with a relatively long sampling period. Further, normal action was confirmed in four-quadrant operation.

Neutral-point-clamped inverter with parallel driving of IGBTs for industrial applications

This paper describes the design and construction of a neutral point clamped (NPC) inverter and power converter, with outputs of 0.8, 1.6, and 3.2 MVA, which use IGBTs. The inverter and converter are suitable for industrial drive applications, such as rolling mills, water pumps, etc., and they are composed of multi-inverter units in parallel. Each inverter unit is composed of four pairs of parallel IGBTs connected in series. In order to achieve current balance among the parallel connected IGBTs, low inductance laminated bus bars are designed by using an electro-magnetic simulator, and switching waveforms of IGBTs are evaluated by the circuit simulator SPICE using power device models. A variable capacitance snubber circuit is also presented for the NPC inverter to reduce both switching voltage swing and power consumption.