SOLAR DRIVE SYSTEM AND METHOD FOR TRACKING THE MAXIMUM POWER POINT OF A PHOTOVOLTAIC ARRAY

Abstract

A solar drive system, having: at least one photovoltaic array generating a DC current; at least one inverter electrically connected to the photovoltaic array for inverting the DC current into an AC current; at least one electric motor electrically connected to the inverter for supplying the electric motor with the AC current; and at least one device for determining a present rotational frequency of the electric motor; wherein the inverter is configured to track a maximum power point of the photovoltaic array by performing a Perturb and Observe Maximum Power Point Tracking method and to determine a step direction of the Perturb and Observe Maximum Power Point Tracking method using the determined present rotational frequency of the electric motor.

Claims

1. A solar drive system, comprising: at least one photovoltaic array generating a DC current; at least one inverter electrically connected to the photovoltaic array for inverting the DC current into an AC current; and at least one electric motor electrically connected to the inverter for supplying the electric motor with the AC current; wherein the inverter is configured to track a maximum power point of the photovoltaic array by performing a Perturb and Observe Maximum Power Point Tracking method and to determine a step direction of the Perturb and Observe Maximum Power Point Tracking method using the present rotational frequency of the electric motor.

2. The solar drive system according to claim 1, wherein the inverter is configured to determine the present rotational frequency of the electric motor from the frequency of the AC current of the inverter.

3. The solar drive system according to claim 1, further comprising: at least one device for determining the present rotational frequency of the electric motor and being arranged on the electric motor and electrically connected to the inverter.

4. The solar drive system according to claim 3, wherein the device comprises at least one sensor element for detecting the present rotational frequency of the electric motor and being arranged on the electric motor, the sensor element being connected to the inverter by wire or wireless.

5. The solar drive system according to claim 3, wherein the device is a component of a motor electronic of the electric motor, the motor electronic being connected to the inverter by wire or wireless.

6. A method for tracking the maximum power point of a photovoltaic array driving an electric motor, comprising: performing a Perturb and Observe Maximum Power Point Tracking method; and determining a step direction of the Perturb and Observe Maximum Power Point Tracking method using the determined present rotational frequency of the electric motor.

7. The method according to claim 6, wherein the present rotational frequency of the electric motor is determined from the frequency of an AC current supplied from an inverter to the electric motor.

8. The method according to claim 6, wherein the present rotational frequency of the electric motor is directly measured.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above mentioned attributes and other features and advantages of the invention and the manner of attaining them will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein

[0027] FIG. 1 shows a solar drive system according to an embodiment of the invention,

[0028] FIG. 2 shows a voltage controller of a solar drive system according to a further embodiment of the invention, and

[0029] FIG. 3 shows a method for tracking the maximum power point of a photovoltaic array driving an electric motor according to a further embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0030] FIG. 1 shows a solar drive system 1 according to an embodiment of the invention.

[0031] The solar drive system 1 comprises a photovoltaic array 2 generating a DC current Ipv and a DC voltage Vpv. The solar drive system 1 further comprises an inverter 3 electrically connected to the photovoltaic array 2 for inverting the DC current Ipv into an AC current, and die DC voltage Vpv into an AC voltage. In addition, the solar drive system 1 comprises an electric motor 4 electrically connected to the inverter 3 for supplying the electric motor 4 with the AC current. The electric motor 4 is a pump motor of a pump 5 for pumping a liquid, especially water.

[0032] The inverter 3 is configured to track a maximum power point of the photovoltaic array 2 by performing a Perturb and Observe Maximum Power Point Tracking method and to determine a step direction of the Perturb and Observe Maximum Power Point Tracking method using the present rotational frequency of the electric motor 4. For this, the inverter 3 is further configured to determine the present rotational frequency of the electric motor 4 from the frequency of the AC current of the inverter 3.

[0033] Alternatively, the solar drive system 1 may comprise a device 6 for determining a present rotational frequency of the electric motor 4. The device 6 may be electrically connected to the inverter 3 to supply the determined present rotational frequency to the inverter 3. In most cases the rotational frequency of the electric motor 4 will be assumed to be the inverter 3 AC output frequency, but the external device 6 could alternatively be used.

[0034] The device may comprise at least one sensor element (not shown) for detecting the present rotational frequency of the electric motor 4 and being arranged on the electric motor 4, the sensor element being connected to the inverter 3 by wire or wireless. Alternatively, the device 6 may be a component of a motor electronic (not shown) of the electric motor 4, the motor electronic being connected to the inverter 3 by wire or wireless.

[0035] FIG. 2 shows a voltage controller 7 of a solar drive system (not shown) according to a further embodiment of the invention.

[0036] The voltage controller 7 comprises a differentiator 8 for determining the difference Ve between a setpoint voltage Vsp and the present voltage Vpv generated by the photovoltaic array (not shown). The difference voltage Ve is supplied to a PID 9 of the voltage controller 7. PID 9 generates a control signal Fem supplied to the electric motor (not shown). With the control signal Fem the rotational frequency of the electric motor is adjusted to achieve a requested array voltage setpoint. So, for example, if the voltage Vpv increases above Vsp, the voltage controller 7 will suitably increase the rotational frequency of the electric motor to bring the voltage Vpv back down again. For this, the electric motor power consumption needs to be a monotonic function of rotational frequency of the electric motor.

[0037] FIG. 3 shows a method for tracking the maximum power point of a photovoltaic array driving an electric motor according to a further embodiment of the invention.

[0038] A present rotational frequency of the electric motor is determined continuously or in time intervals and a Perturb and Observe Maximum Power Point Tracking method is performed.

[0039] In method step 10 a perturbation step by varying a load/voltage is made and the present rotational frequency of the electric motor is determined after this perturbation. Then, the determined present rotational frequency is compared with the previously determined present rotational frequency of the electric motor. If the determined present rotational frequency is less than the previously determined present rotational frequency, the step direction is changed in method step 20. If the determined present rotational frequency is greater than the previously determined present rotational frequency, the step direction is not changed and the next perturbation step is made in method step 30 in the last step direction. These method steps are repeated until the determined present rotational frequency equals the previously determined present rotational frequency. Then the present voltage of the photovoltaic array has reached the setpoint voltage. Thus, it is determined a step direction of the Perturb and Observe Maximum Power Point Tracking method using the determined present rotational frequency of the electric motor.

[0040] Although the invention has been explained and described in detail in connection with the preferred embodiments it is noted that the invention is not limited to the disclosed embodiments. A person skilled in the art can derive from these embodiments other variations without leaving the scope of protection of the invention.