Multiple motor operation using solar power
A solar powered system controls multiple motors directly from a single solar power source with a single variable frequency drive (VFD). A control system selectively connects and disconnects individual motors as solar power varies so that the available power can be used effectively and some of the motors can be kept operating rather than shutting down the entire system. The control system includes a detection circuit for detecting the solar array voltage, and a selection circuit for providing shutoff control signals to individual motors based on the solar array voltage and preselected motor shutoff priority criteria.
1 . A control system for operating a motor array from a solar array, comprising:
a sensing circuit for sensing the solar array voltage;
a selection circuit connected from the sensing circuit to the motor array, the selection circuit providing shutoff control signals to individual motors in the motor array based on changes in the solar array voltage and preselected motor shutoff priority criteria.
2 . The control system of claim 1 wherein the sensing circuit comprises a resistor network.
3 . The control system of claim 2 wherein the resistor network comprises a plurality of resistors in series, each resistor producing a voltage drop proportional to the solar array voltage.
4 . The control system of claim 1 wherein the selection circuit comprises a plurality of comparators, each comparator having one input connected to the sensing circuit for receiving a signal based on the solar array voltage and a second input connected to a reference voltage determined by the preselected motor shutoff priority criteria, the output of each comparator being connected to an associated motor.
5 . The control system of claim 3 wherein the selection circuit comprises a plurality of comparators, each comparator having one input connected to an associated voltage drop in the resistor network and a second input connected to a reference voltage determined by the preselected motor shutoff priority criteria, the output of each comparator being connected to an associated motor.
6 . Apparatus comprising:
a solar array for producing DC power;
a variable frequency drive (VFD) connected to the solar array for converting the DC power to AC power;
a motor array comprising a plurality of individual motors connected to the VFD;
a control system according to claim 1 connected between the solar array and the individual motors of the motor array for selectively shutting off individual motors as the solar voltage changes according to the preselected motor shutoff priority criteria.
7 . The apparatus of claim 6 wherein the sensing circuit comprises a resistor network.
8 . The apparatus of claim 7 wherein the resistor network comprises a plurality of resistors in series, each resistor producing a voltage drop proportional to the solar array voltage.
9 . The apparatus of claim 6 wherein the selection circuit comprises a plurality of comparators, each comparator having one input connected to the sensing circuit for receiving a signal based on the solar array voltage and a second input connected to a reference voltage determined by the preselected motor shutoff priority criteria, the output of each comparator being connected to an associated motor.
10 . The apparatus of claim 8 wherein the selection circuit comprises a plurality of comparators, each comparator having one input connected to an associated voltage drop in the resistor network and a second input connected to a reference voltage determined by the preselected motor shutoff priority criteria, the output of each comparator being connected to an associated motor.
11 . A method for controlling the individual motors of a motor array operated from a solar array, comprising:
sensing the solar array voltage;
selecting individual motors to shut off based on changes in the solar array voltage and preselected motor shutoff priority criteria.
12 . The method of claim 11 wherein selecting individual motors to shut off is performed by comparing a sensed voltage proportional to the array voltage to a reference voltage.
13 . The method of claim 12 wherein the reference voltage is determined to shut off an individual motor when the solar voltage reaches a preselected level.
14 . The method of claim 11 further comprising shutting off enough individual motors so that available solar power is sufficient to operate the remaining motors.