Maximum power point motor control
View Patent ↗A method and apparatus are implemented in software to control motor speed as a function of available power in a DC source-inverter-AC motor system, i.e. to perform maximum power tracking of motor speed. An inverter or motor drive converts DC power from a DC source, such as a solar panel, to AC power, to power the motor. The inverter or motor drive is controlled by software, implemented either by programmable features built directly into the inverter or drive or by a separate programmable device connected to the inverter or drive, to track motor power as a function of source power. The software-controlled inverter or drive sets motor speed as a function of source power by sensing only a single parameter, the DC source voltage. The software-controlled inverter or drive samples the source voltage at preset intervals, and changes the frequency of the AC output of the inverter or drive to match or track the available power so that the motor operates at or near its optimum for any source voltage.
1. Apparatus for converting DC power from a DC source to AC power to drive an AC motor, comprising:
a software-controlled inverter which produces an AC output from a DC input;
wherein the software-controlled inverter carries out an algorithm for varying the AC output frequency in response to changes in the DC voltage from the DC source so that the speed of an AC motor driven by the inverter tracks the maximum power available from the DC source;
wherein the algorithm comprises a series of instructions for sequentially:
sampling the DC source voltage at a preset sampling interval,
comparing the present sampled value of the DC voltage to the prior sampled value,
determining whether a change of AC frequency is required based on the comparison of the present to the prior sampled DC voltages,
producing a control signal if a change in AC frequency is required,
changing the AC frequency in response to the control signal, and
continuously repeating the series of instructions.
2. The apparatus of claim 1 wherein the software-controlled inverter is internally programmable with the algorithm and produces internal control signals to change the AC output frequency of the inverter.
3. The apparatus of claim 1 wherein the software-controlled inverter comprises an inverter and a separate controller connected to the inverter which is programmable with the algorithm and produces control signals that are input into the inverter to change the AC output frequency of the inverter.
4. The apparatus of claim 1 wherein a change in AC frequency is required when the present value of the sampled DC voltage exceeds the prior value by a preset amount.
5. A system comprising:
a DC source;
a software-controlled inverter connected to the DC source to produce an AC output from a DC input;
an AC motor connected to the AC output from the inverter;
wherein the software-controlled inverter carries out an algorithm for varying the AC output frequency in response to changes in the DC voltage from the DC source so that the speed of the AC motor tracks the maximum power available from the DC source;
wherein the algorithm comprises a series of instructions for sequentially:
sampling the DC source voltage at a preset sampling interval,
comparing the present sampled value of the DC voltage to the prior sampled value,
determining whether a change of AC frequency is required based on the comparison of the present to the prior sampled DC voltages,
producing a control signal if a change in AC frequency is required,
changing the AC frequency in response to the control signal, and
continuously repeating the series of instructions.
6. The system of claim 5 wherein the DC source is a solar array.
7. The system of claim 6 further comprising a water pump driven by the AC motor.
8. The system of claim 5 wherein the software-controlled inverter is internally programmable with the algorithm and produces internal control signals to change the AC output frequency of the inverter.
9. The system of claim 5 wherein the software-controlled inverter comprises an inverter and a separate controller connected to the inverter which is programmable with the algorithm and produces control signals that are input into the inverter to change the AC output frequency of the inverter.
10. The system of claim 5 wherein a change in AC frequency is required when the present value of the sampled DC voltage exceeds the prior value by a preset amount.
11. The system of claim 5 wherein the DC source is a solar array.
12. The system of claim 11 further comprising a water pump driven by the AC motor.
13. A method for powering an AC motor from a DC source comprising:
obtaining DC power from a DC source;
converting the DC power to AC power;
powering the AC motor with the AC power;
varying the AC frequency in response to changes in the DC voltage from the DC source so that the speed of the AC motor tracks the maximum power available from the DC source;
wherein the AC frequency is varied by carrying out an algorithm in a software-controlled inverter;
wherein the algorithm comprises a series of instructions for sequentially:
sampling the DC source voltage at a preset sampling interval,
comparing the present sampled value of the DC voltage to the prior sampled value,
determining whether a change of AC frequency is required based on the comparison of the present to the prior sampled DC voltages,
producing a control signal if a change in AC frequency is required,
changing the AC frequency in response to the control signal, and
continuously repeating the series of instructions.
14. The method of claim 13 wherein the DC power is obtained from a solar array.
15. The method of claim 14 further comprising driving a water pump with the AC motor.
16. The method of claim 13 wherein a change in AC frequency is required when the present value of the sampled DC voltage exceeds the prior value by a preset amount.