Regenerative power units save energy

03/13/2013


3. Matrix converter

A matrix converter is a direct ac-to-ac power converter that has motoring and regeneration capability. Recent technology advances in power semiconductor and CPU computing power have made commercial products possible. Basic features of the matrix converter are:

- All-in-one, where ac input is directly converted into variable frequency ac output by nine bidirectional switches. So the functions of the sinusoidal regen converter and VFD are combined. This feature enables the motors’ operation in motoring and regeneration modes without an additional VFD.

- No electrolytic capacitor: Matrix converter needs less maintenance because there is no diode rectifier and dc electrolytic capacitor in the main power flow. Generally, an electrolytic capacitor is bulky and has a shorter lifetime than other components.

- Low input current harmonics: Input current control capability makes it possible to reduce input current harmonics significantly. Input current harmonic distortion is in the range of 5% to 10% under full load condition. Neither phase-shifting transformer nor external line reactor is required to reduce harmonic currents, which are usually bulky.

- Compact size: Physical size of matrix converter is smaller than the sinusoidal PWM converter-inverter system, which has motoring and regenerative power capabilities that are the same as the matrix converter. [5-7]

Figure 4 shows regenerative energy flow by the matrix converter. At left is a concept block diagram, and at right is the power circuit schematic. Courtesy: Yaskawa America Inc.

4. Utility cost saving by regeneration power unit

Figure 5 demonstrates the energy costs of operating a 45 kW elevator system with and without a regenerative power unit. Average motoring power consumed per cycle is 8.8 kW while regenerative power is 4.78 kW. If a dynamic braking unit is used to produce braking torque, 11,300 kWh will be converted into heat loss. By installing a regenerative power unit, 54% of power can be saved and annual utility cost savings is $1017 assuming average electricity costs of 9 cents per kWh.

Figure 5 provides an example of regenerative energy and utility cost saving in an elevator application. Courtesy: Yaskawa America Inc.

5. Regeneration power unit selection

All three regeneration power units described have a good energy cost savings capability under regenerative load conditions. The regenerative converter described in section 2 is the best low-cost solution. But if extra advantages such as low input current harmonics and unity power factor are also important, the best solution may differ. The table compares various aspects of three regeneration power units.

Table: Comparison of Regeneration Power Units 

Table compares regeneration capabilities. Courtesy: Yaskawa America Inc.

- Jun Kang is research and application manager, Yaskawa America Inc. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering and Plant Engineering, mhoske(at)cfemedia.com.

Key concepts

Certain applications benefit from regenerative technologies that convert kinetic energy back into electricity instead of dissipating at wasted heat. Select the best regen unit for the application.

Consider this

Have you looked at your processes for regenerative opportunities? After return on investment, it prints money, as they say.

Go Online

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This article is part of the April 2013 CFE Media supplement, Industrial Energy Management. See other articles linked below.


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Paul , MA, United States, 03/22/13 09:26 AM:

Does anyone have some specific information about this technique: cost, pay back, net present value, design and installation time, maintenance costs / stoppages.

Thanks