Hitachi’s PHM Motor Control Strategy Increases Motor/Inverter Efficiency By Up To 3%
16 August 2010
by Jack Rosebro
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| Above: conventional pulse-width modulated (PWM) motor control. Below: Hitachi’s pulse harmonic modulated (PHM) motor control. Click to enlarge. |
Hitachi has announced the development of a high-speed motor control strategy which improves overall motor and inverter efficiency by as much as 3%, while reducing inverter cooling requirements by as much as 40%.
Conventional motor control strategies utilize pulse width modulation (PWM) of switched direct current to produce voltage signals that drive an alternating current. However, the switching required to produce such signals reduces available peak voltage and produces heat which much be transported away from the switching devices. Alternate switching strategies are typically employed at higher motor speeds to minimize such losses.
Hitachi has developed Pulse Harmonic Modulation (PHM), a drive strategy which reduces switching by as much as 80%, leading to reduced heat losses at the inverter.
The harmonic content of the waveform has been minimized, and the waveform has been refined to minimize copper losses as well as iron losses. At higher speeds, motor output can be as much as 10% higher using pulse harmonic modulation.
However, significant copper losses remain at speeds below 60 km/h (37 mph), and Hitachi envisions a two-part motor control strategy that would utilize PWM at lower speeds and switch to PHM at higher speeds. Although pulse harmonic modulation was developed for 50-100 kW motors, it can be adapted to larger motors, as well.
Hitachi forecasts that the market for hybrid, plug-in hybrid, and electric vehicles will expand to 13 million units by 2020, with demand for hybrid construction machinery and hybrid-electric locomotives increasing by the same year to 12,000 units and 2,000 units, respectively.
The company is presently supplying electric motors to US-based manufacturers of hybrid and plug-in hybrid vehicles, and expects to see its PHM strategy adopted in production vehicles within the next two to three years.
Hitachi will present details of the technology at the 2010 Annual Conference of IEE of Japan, Industry Applications Society later this month.
Resources
Hitachi motor strategy (Japanese)
The battery to wheel efficiency will soon reach over 90% and could even be higher when 2 or 3 technologies are combined. Excess heat could be used to keep the cab warm in winter time.
Posted by: HarveyD | 16 August 2010 at 07:24 AM
"The battery to wheel efficiency will soon reach over 90%"
Its already at 92.5% if you dont count the losses at the wheel bearings, half shaft universals, differential and gear reducer..sheez that right there is probably over 10%. Maybe its time for in-wheel motors.
Posted by: Herm | 16 August 2010 at 07:53 AM
Yes, higher efficiency in-wheel motors + higher efficiency inverters, controllers etc could reach something as high as 95% to 96% (battery to wheels) before 2020.
Posted by: HarveyD | 16 August 2010 at 08:34 AM
If you going to track efficiency, you need to add in the power required to cool the motors and controllers. That don't come free.
Posted by: The Kid | 16 August 2010 at 12:26 PM
Air friction is the largest inefficiency of operating most motor vehicles on motorways. But this is rarely mentioned. ..HG..
Posted by: Henry Gibson | 17 November 2010 at 10:48 PM