News Releases 2021Meiden masters the medium-voltage high-frequency inverter
Smooth, efficient new multilevel fixed pulse pattern technology developed

Meidensha Corporation (Meiden) has developed a “multilevel fixed pulse pattern method,” a unique control technology for medium-voltage, high-frequency inverters used to drive motors.

Inverters used to control industrial motors are increasingly gaining larger capacities and higher frequencies as their applications expand. However, they also have problems to contend with, such as lower efficiency due to switching loss and the impact on the operational environment due to, for example, electromagnetic noise in the vicinity.

The new technology has the advantages of improving the efficiency of large-capacity motors, realizing higher frequencies and reducing vibration and noise to facilitate smooth operation.

Research for developing the new technology started in April 2018. Five patents have been obtained so far, with a further six applications currently filed.

Motors for large-capacity fans and pumps used in various infrastructural facilities have their rotation speeds controlled by medium-voltage inverters. Blades used in fans and pumps can be reduced in size by increasing their rotation speeds. In conventional systems, the speeds are increased via gears. If higher speed in motors is possible, the gears used to increase speed are no longer needed and motors themselves can be made smaller, thus saving resources, increasing efficiency, and reducing environmental impact.

This demand for higher-speed motors has led to the demand for higher-frequency inverters.

Medium-voltage inverters are conventionally controlled by the triangular wave comparison pulse width modulation (PWM) control method *1. However, when the output frequencies of such inverters are high, the conventional PWM method suffers the disadvantages of increasing harmonics (waveform distortion), causing motor vibrations and noise, and reducing efficiency.

To solve these problems, the present technology is applied to multilevel inverters that can output multiple voltage levels, enabling control with an optimum pulse pattern with low distortion and high efficiency.

In a test example using the new technology as an add-on to an existing medium-voltage, high-frequency inverter to operate a large-capacity motor, efficiency was improved throughout the actual operation range. Energy saving can be improved by 0.33 percentage points at the rated output and 0.9 percentage points under very effective conditions (both are reference values).



Test evaluation items

Improvement from conventional method

Switching frequency

Reduced by 42.5%

Efficiency

Improved by 0.33 percentage points
at the rated output
(0.9 percentage points at maximum)

Current harmonic

Reduced by 41.2%



■ Features of the multilevel fixed pulse pattern method *2 *3 

- High efficiency
Since an output waveform is controlled with a minimum necessary number of switching times according to a voltage level, the switching loss of an inverter can be reduced more than that by the conventional PWM method which generates unnecessary switching operation.

- Smooth operation
Since a pulse pattern that reduces harmonics is derived and applied in advance, a low-distortion target waveform can be obtained, enabling reduction of a motor’s harmonic loss, vibrations, and noise.

- Stable operation at high frequency
Even when it operates at high speed and frequency, a motor outputs fixed pulse patterns in symmetrical sine waveforms, enabling more stable control than the conventional PWM system, which tends to generate asymmetrical pulse patterns.

- Low impact on insulation of motor windings
Since voltage is changed by one level at a regular interval (consecutive two-level changes are prohibited), instantaneous large voltage (surge voltage) applied to motor windings can be reduced, reducing insulation deterioration of the windings.

- Add-on possible
The control function of the present technology can be added without the need to replace the hardware of an existing inverter.


Meiden will continue creating power electronics products and technologies which contribute to further energy conservation, size reduction, and environmental friendliness in social and industrial infrastructure systems.


*1. The triangular wave comparison pulse width modulation (PWM) control method is one of the existing power control methods. It compares the magnitude of a command voltage and a carrier wave (triangular wave) to modulate into on/off pulses, and then controls semiconductor switches of inverters based on such pulses to obtain an output equivalent to a desired voltage command value.

*2. R. Ogawa, M. Takiguchi and Y. Tadano, “Multilevel Fixed Pulse Pattern Control for Medium-Voltage High-Frequency Inverter,” 2020 23rd International Conference on Electrical Machines and Systems (ICEMS), 2020, pp. 2089-2094, DOI: 10.23919/ICEMS50442.2020.9291237

*3. R. Ogawa, M. Takiguchi and Y. Tadano: “Basic Study Of Pulse Modulation Method For Medium-Voltage, High-Frequency Inverters,” Meiden Jiho No. 367, 2020, No.2, pp.12-19
https://www.meidensha.co.jp/rd/rd_02/rd_02_02/rd_02_02_10/rd_02_02_05_01/__icsFiles/afieldfile/2021/06/14/Review_182_02_web_210607_1.pdf


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