MEAN WELL Product Manager, Kai Li, Sager Electronics Technical Support Manager for Power, Don Baldwin
Highly flexible, high-wattage AC/DC power supplies that can operate with a choice of three-wire or four-wire three-phase and single-phase input power provide a selection of direct high-voltage current (HVDC) outputs like 115, 230, and 380 volts DC (Vdc) that are variable from 1 to 120 percent of rated voltage, support 7.5 to 28.5 kW loads, and include a choice of thermal design implementations, are essential in a growing array of green energy and Industry 4.0 processes including burn-in systems, energy storage installations, electrolysis, ultraviolet (UV) curing, laser cutting, and other applications. These systems can be deployed in various environments that include different input power availability, require various HVDC outputs, and can benefit from the choice of liquid cooling using cold plates or internal fan cooling. And the power supplies must be low profile with high power densities.
AC/DC power supplies that can provide up to 15 kilowatts (kW) of power in a 2U profile, operate from a range of inputs while providing high power densities with HVDC outputs, and can be adapted for liquid or forced air cooling are exceedingly difficult to design. Fortunately, designers of green energy and Industry 4.0 systems can turn to ready-made power supplies with all those attributes plus programmable output voltages and currents and include parallel operation with active current sharing to support higher power demands.
This article starts with a review of three-wire and four-wire delta (Δ) and wye (Y) three-phase (3φ) and single-phase (1φ) AC power, and presents families of low profile 7.5-kW and 15-kW AC/DC power supplies from MEAN WELL that provide high levels of input power flexibility for green energy and Industry 4.0 applications along with output choices of 115, 230 and 380 Vdc with output voltage and current programmability, ability to be used in parallel for higher power applications, plus a range of monitoring functions and forced air or liquid cooling.
AC power by the numbers
Electronic systems for green energy and Industry 4.0 applications are often installed in locations with existing AC power infrastructure. MEAN WELL’s RST-7K5-HV series (7.5 kW) and RST-15K-HV series (15 kW) AC/DC power supplies are specifically designed to support a range of 3φ and 1φ AC configurations to maximize installation flexibility.
A 3φ AC system can support three times the power of a 1φ system, with only a 50% increase in conductors (from two to three). The conductors between the load and voltage source are called lines. The voltages in a 3φ system are named based on their relationships. The voltage between any pair of power lines is the line voltage. The phase voltage is measured between any line and neutral. For example, in a “208/120” 3φ service, the line voltage is 208 Vac while the phase voltage is 120 Vac.
There are two basic 3φ configurations, Δ and Y. Both can be implemented using three or four wires, denoted as 3φ3W and 3φ4W, respectively. The 4W configurations include neutral connections not found in 3W systems. Typical voltage ranges for 3φ power are 196 to 305 Vac (nominal voltages from 200 to 277 Vac) and 340 to 530 Vac (480 Vac nominal) (Figure 1).
1Φ is also an option
The preferred power sources for MEAN WELL’s RST-7K5-HV and RST-15K-HV families are 3Φ4W Y with a voltage range of 340 to 530 Vac or 3Φ4W Δ power with an input range of 196 to 305 Vac. To ensure maximum installation flexibility, these power supplies can also operate with 1Φ2W, 196 to 305 Vac power (Figure 2). Note that operating with 1Φ2W power may lead to certain characteristics different from the specification sheet, like larger ripple and noise, and designers are encouraged to contact the factory for details.
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Adjustable output voltages & currents
These high-wattage power supplies have full power voltage ranges of 115 to 138 Vdc for 115 Vdc output models, 216 to 260 Vdc for 230 Vdc models, and 334 to 400 Vdc for 380 Vdc models. The output voltages (VO) are adjustable from 1% to 120% of the nominal rating, with the maximum available power based on the rated wattage of the unit. At very low Vo, overshoot and undershoot may exceed the specified values for dynamic load conditions.
A DIP switch on the front panel enables users to select the voltage trimming method between using a potentiometer, on the front panel, or by applying an external control voltage. At higher output voltages, the output current derates linearly with the increased voltage (Figure 3).
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Figure 3: The output voltage of RST-7K5-HV and RST-15K-HV power supplies can be adjusted by applying an external voltage (left) with the output current derated above the nominal rated voltage (right) (Image: MEAN WELL)
Users can also use the DIP switch on the front panel to set a constant current output and an overload protection mode, including:
Default overload protection is between 100% and 107% of rated current.
The RST-7K5-HV and RST-15K-HV HVDC power supply families have monitoring signals, including an over-temperature alarm, DC-OK signal, fan-fail alarm, and an AC fail alarm to speed system integration and support high levels of system reliability. They also feature active current sharing for up to four RST-7K5-HV or two RST-15K-HV for a total of 28.5 kW in both cases. Their wide operating temperature range of -30 to + 70 °C, with linear derating above 45 °C to 40% of full power at 70 °C, makes them well suited for harsh environments. And their outstanding thermal performance supports a high-density 2U high package.
Finally, the 7.5 kW models are available with a choice of fan cooling and liquid cooling over the same operating temperature range. Water cooling can support much higher heat flux and superior thermal transfer than forced air cooling (Figure 4). The water-cooled models can be integrated directly with a preexisting chiller system like those used for laser cutting systems. In one study with a MEAN WELL water-cooled power supply, the temperatures of the power MOSFETs and capacitors were about 6 to 18 °C cooler for a water-cooled installation compared with forced air cooling1. Lower component temperatures directly contribute to higher reliability.
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MEAN WELL’s RST-7K5-HV and RST-15K-HV families of HVDC power supplies can support installations with 1φ or 3φ power. They feature adjustable output voltages and currents and have full monitoring functions to speed system integration and support highly reliable operation. The 7.5 kW models are available with a choice of fan cooling and liquid cooling over the same operating temperature range for optimal thermal performance.