Kenichi Iimori

New current-controlled PWM rectifier-voltage source inverter without DC link components

The voltage-source inverters are normally equipped with an electrolytic capacitor in their DC link, the electrolytic capacitor has several disadvantages such as increasing size, limiting converter life and reliability. Therefore several approaches for removing the DC link capacitor have been studied. This paper proposes a new voltage source inverter without DC link components, whose rectifiers are controlled by suitable current feedback to adjust near-sinusoidal AC source current waveforms at unity power factor. The calculated characteristics are described for a 0.75 kW induction motor driven by this inverter.

A study of dead-time of PWM rectifier of voltage- source inverter without DC link components and its operating characteristics of induction motor

A voltage-source inverter without dc-link components is an ac-to-ac converter having dual bridges of a pulsewidth-modulated (PWM) rectifier and a PWM inverter that can be controlled independently. While conventional matrix converters have disadvantages, such as a complicated commutation scheme and necessity of a large-sized clamp circuit, commutation, and protection of our inverter can be implemented easily. In order to control the PWM rectifier and the PWM inverter independently, snubber circuits for the PWM rectifier are required to assure the path of load current during dead time. In this paper, analytical method of a snubber circuit and operating characteristics of a snubber circuit are described when a 0.75-kW induction motor is driven by our inverter.

Approaches to suppressing shaft voltage in brushless DC motor driven by PWM inverter

This paper describes the shaft voltage reduction achieved by the brushless DC motor for air conditioning driven by the voltage source inverter. First, the simplified equivalent circuit of the concentrated winding brushless DC motor is derived based on the common mode equivalent circuit where stray capacitance is taken into account. Then, the electrostatic capacity distributions between winding and stator core, winding and magnet, stator core and magnet, and magnet capacitance are measured, and the shaft voltage is calculated with the simplified equivalent circuit. Finally, the bridge type equivalent circuit is derived, and it is confirmed with calculation and experiment that the shaft voltage can be suppressed when the inside and outside of the rotor core are insulated with resin (hereinafter, the insulated rotor).

Zero-switching-loss PWM rectifier of converter without DC link components for induction motor drive

A new commutation strategy for the PWM rectifier section of the converter without DC link components is described. The advantages of the system are the zero-switching-loss and the snubberless circuit of the PWM rectifier section. During the zero voltage vector period of the inverter section, the load current does not flow in the PWM rectifier section. So, if each switching operation of the PWM rectifier section are done in the zero voltage vector period, zero current commutation can be possible. The proposed strategy is verified by computer simulation and experimental test on an induction motor drive.

Suppressing Bearing Voltage in an Inverter-Fed Ungrounded Brushless DC Motor

This paper describes the bearing voltage reduction achieved by the brushless dc motor for air conditioning driven by the voltage source inverter. First, the simplified equivalent circuit of the brushless dc motor is derived based on the common-mode equivalent circuit where stray capacitance is taken into account. Then, the electrostatic capacity distributions between a winding and a stator core, a winding and a magnet, a stator core and a magnet, and magnet capacitance are measured, and the bearing voltage is calculated with the simplified equivalent circuit. It is confirmed with the experiment that the bearing voltage can be suppressed when the inside and outside of the rotor core are insulated with resin (hereafter, the insulated rotor) and that the electrostatic capacity of the rotor is made smaller. Finally, a bridge-type equivalent circuit is derived in an air conditioning fan motor where the frame is not grounded, an insulated rotor is actually designed, and the bearing voltage is measured.

Comparison of configurations of voltage boosters in PWM inverter with voltage boosters with regenerating circuit augmented by electric double-layer capacitor

In an interior permanent magnet (IPM) motor drive system, which has a regenerating circuit augmented by electric double-layer capacitor (EDLC), two types of configurations of voltage boosters, battery and EDLC are investigated and compared. For one of the configurations, the battery and the EDLC are connected in series and the set of battery and EDLC is connected to the dc link of an inverter through a bidirectional voltage booster. In addition, the EDLC is also connected to the dc link through the other bidirectional voltage booster (configuration I). For the other of the configurations, the battery is connected to the dc link through a bidirectional voltage booster and the EDLC is connected to the dc link through the other bidirectional voltage booster, independently (configuration II). For both configurations, stability and electrical characteristics are investigated for various situation of dc link voltage and output power by simulation. Finally, the results show advantages of the connection I.

Suppressing of common mode voltage on ac motor with changing ground point of DC link in PWM inverter

With the increased application of adjustable-speed drive of ac motor, there has been a growing number of failures such as electromagnetic interference(EMI) caused by common mode current, and bearing current. Especially, bearing current leads to motor bearing material erosion and early mechanical failure. To reduce the bearing current, there are two methods, one is reduce the common mode voltage, and another one is reduce the motor shaft voltage itself. This paper describes the approaches to suppress the Common mode voltage on ac motor with changing the ground point of DC link in PWM inverter.

A study of digital filter for rotor speed detection with slot harmonic current for induction motor

In rotor speed detection with slot harmonic component of the motor current of induction motors, the cutoff frequencies of filters for extracting slot harmonic component should be changed in accordance with the rotor speed. In this paper, we introduce DSP based band pass filter (infinite impulse response filter) to change the cutoff frequencies of the filter and investigate the static and dynamic characteristics of the filter. Moreover, we investigate the range of the cutoff frequencies which can estimate speed correctly. Finally, we demonstrate speed sensorless operation with the introduced band pass filter.