Question:
Please tell us about products that you worked on, and about any major challenges that you faced.

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When I entered the company in 1975 I was engaged in inverter development, and at that time thyristors were being replaced by bipolar transistors. Transistors control electric power through switching, and their signals are fast compared to thyristors. Given the oscilloscopes of the day, it was very difficult to capture the subtle or excessive phenomena that would occur such as voltage spikes.

After ten years, IGBT switching power devices were adopted and signal speeds rose by an order of magnitude. It was a time in which inverter technology had grown substantially, the digital oscilloscope became available, and IGBT characteristics could be easily measured. However, observing switching phenomena was quite troublesome because the oscilloscopes still did not offer many calculation and analysis functions. If you look at a zoomed switching waveform, you will notice that when the switch is turned ON, voltage between collector and emitter of the switching devices drops, and current flows. In PWM drives, if we have a calculation function that can calculate the instantaneous power loss of the voltage and current of each waveform, I think we can easily perform efficient circuit design with low switching loss.

Question:
What are currently some of the key issues surrounding motors and inverters?

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In terms of manufacturing, customers will be demanding higher productivity; the keywords will be higher speed, and higher precision. Manufacturing in Japan places importance on the level of production volume that can be reached per unit of time, so items must be positioned very quickly and accurately.

For example with chip mounters, parts are constantly getting smaller and smaller, so the corresponding placement accuracy has to rise equivalently. A generation ago, the position sensing resolution of the encoder on the end of the motor was 13 bits but now 17 bits is standard, and 20 bits is available for applications requiring higher precision. To control the mounter quickly and accurately, the speed at which the data from the sensor is processed and calculated must also be very high. Furthermore, control of the minute torque required for slight movements of the motor demands high-precision control of voltage and current. In other words, smooth control is impossible without increasing the resolution of the output PWM, so precision is everything.

Additionally, there are some tough requirements on the mechanical side as well. For example, positioning must not only be fast, but also have rapid acceleration. If the object under acceleration is rigid this is not a problem, but less rigid objects experience “springy motion,” so to quickly position the object at its destination without any wobbling or wavering requires smooth, fast control technology. To achieve faster motion, the machines must be made lighter.

With industrial inverters, high efficiency and energy savings are especially important. And recently there is demand for support for so-called “new energy” such as wind power and photovoltaic power generation. For energy savings, we are incorporating inverters using high-efficiency IPM (interior permanent magnet) motors into our products. These can be made with decreased loss compared with induction motors, and because they are compact and lightweight, the device onto which the motor is attached also becomes, by extension, smaller, more lightweight, and less energy-consuming. If the efficiency of an induction motor is 90% and that of an IPM motor is 95%, that's a 5% improvement in loss. Loss is associated with the generation of heat so extra thermal design features can be eliminated, which means that the 5% loss improvement actually translates into a 30% reduction in the required volume of the motor. Our Super Energy-Saving Drive VS-686SS5 is acclaimed for its enabling of reductions in total equipment cost and savings of resources and it received the Minister for International Trade and Industry Award for the Promotion of Energy Savings in 1997. I think from now on we will have to continue to think about high efficiency and energy savings.

 

Question:
What kind of new technologies are out there that can provide solutions for the challenges of energy-savings?

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One technology that can provide an energy-saving solution is the matrix converter. A matrix converter utilizes AC to AC direct power conversion technology to convert a three-phase AC power supply directly to an arbitrary voltage and frequency using PWM control. Unlike most inverters that are unidirectional, matrix converters are bi-directional; that is, they can control current in both directions with no energy loss. Also, regenerative operation is possible, so some of the motor's braking energy can be recovered by the power supply. While the output characteristics are the same as those of inverters, matrix converters have the advantage that the input current waveform can be a sinewave. Theoretically no power supply harmonics should be generated, and it has many other improved characteristics such as higher reliability. We have started collaboration with Dr. Koyama at Nagasaki University to research matrix converters. I think in the future this is going to be a technology that will be used widely in many kinds of fields.

Also, if SiC (silicon carbide) can be used for the power devices, the loss in the devices themselves would be extremely small. And since it can be used under high temperatures, I think you could embed the drive circuit inside the motor, shrink the drive device while expanding its capacity, and achieve increased reliability.