WorldWater & Solar Technologies, Corp. has developed a series of industrial drives using microprocessor-based variable frequency units. The AquaMax™ variable frequency drives, or VFD, are custom designed to accept 3-phase AC power from grid, diesel or wind and DC solar power, either independently or in combination. This is what makes these drives unique in high power motor controls.

The VFD can be looked at in two separate sections, the first being the power-conditioning unit and the second being a pulse width modulated frequency control. The AquaMax™ Series is available in both 208 volt and 480 volt 3-phase AC grid voltages. The horsepower (Hp) range is from 5 Hp to 600 Hp for 480V applications and from 5 Hp to 125 Hp for 208 volts. (Higher Hp is available upon request.)

The power-conditioning unit can accept both 3-phase AC and DC or solar input power. This provides an advantage over other variable motor drives. When both voltage sources are supplied to the power-conditioning unit, one source"is identified as the primary voltage source and the second voltage as the secondary source. If AC grid voltage is the primary source, motor control is from the AC grid voltage. If solar, or other DC sources, are identified as the primary source, then AC grid voltage becomes the secondary voltage source. With both voltage sources present, loss of one voltage will automatically cause switching to the other source, making for seamless operation with no loss in motor operation.

Solar operation of VFD requires special design considerations. Solar power is not a constant DC voltage and is dependent on varying sun conditions. It is this frequent changing of solar DC voltage that resulted in the patented control system design which WorldWater & Power uses in its AquaMax™ series. This is especially important in countries or areas where grid voltage is unreliable or is not available. The control system constantly monitors solar voltage, which is a function of solar power, and will automatically change motor speed to compensate for power changes. For example, if the motor is operating at 60 Hz, it demands power sufficient to support 60 Hz operation. If the sun is not capable of supporting this operation, the control board reduces the motor frequency to match the solar output power. This function constantly samples the solar voltage and automatically adjusts motor frequency to available solar power.

Important Features for AquaMax™ VFD Operation

1. Frequency: Motor speed acceleration and deceleration is a WorldWater set parameter. Acceleration determines the time it will take the AquaMax™ drive to ramp from 0 Hz to a maximum of 60 Hz and is set for 60 seconds. By controlling the ramp speed, motor inrush currents are held to a minimum. Deceleration allows for control shutdown and is set for 10 seconds.
2. Temperature: The drive heat sink temperature is monitored by a microprocessor unit and will shut down the drive in case of overheating.
3. Overcurrent: This is limited to 150 percent of the drive rated current.
4. AC Overvoltage Trip: The input voltage is set to 120 percent of the AC grid voltage.
5. Phase Fault Detection: Any combination of short-circuit phase currents or phase-to-ground currents will cause the drive to shut down.