Patent Application
20210184468
The present invention relates generally to photovoltaic (PV) array systems. In particular, the present invention relates to a bypass module for enhancing the PV array DC-AC ratio capability within a PV array system.
A PV array system is typically connected to an input of an electric power system to convert and transmit power to the electric power system. It includes PV arrays, a combiner box connected thereto and a PV inverter to convert the power from DC to AC power for the electric power system (e.g., a utility grid). In order to maximize power of the PV array system, it is common for the system to be designed with higher power-rated PV arrays than the power rating of the PV inverter. During operation, the system covers different environmental conditions, some resulting in a higher output power capability of the PV arrays which includes a higher voltage and current capability than the PV inverter is able to operate. Cold weather causes an increase of the PV open-circuit voltage, and high irradiance (e.g., >full sun) causes an increase of the PV short-circuit current. These factors combined can result in a PV array with a much higher power capability than that of the PV inverter.
During operation it is desirable to operate the PV inverter at a power level that maximizes the AC power supplied to utility grid. Therefore, it is desirable to have the highest possible DC-to-AC ratio which increases the chance of a PV inverter tripping or being damaged. Thus, enhancement of the PV array DC-AC ratio in a PV array system without causing problems within the PV inverter is desired.
According to one embodiment, a bypass module is employed in a string at one or more of the PV panels to bypass the respective PV panel when the PV voltage is above an acceptable voltage range to avoid tripping or damaging a PV inverter of a PV array system.
Embodiments of the present invention provides a control system for a PV array system including a plurality of PV panels. The control system includes a bypass module having a first switch device and a second switch device disposed at at least one PV panel connected with others of the plurality of PV panels along a string, and configured to perform a switching operation when PV voltage of at least one PV panel is outside of an acceptable voltage range of the PV array system, and e bypass module short-circuits the PV panel when excess voltage at the PV panel is detected. The control system also including a control module configured to monitor and control operation of the bypass module.
Other embodiments of the present invention include a bypass method for performing a bypass operation at at least one of the PV panels of the PV array system.
The foregoing has broadly outlined some of the aspects and features of various embodiments, which should be construed to be merely illustrative of various potential applications of the disclosure. Other beneficial results can be obtained by applying the disclosed information in a different manner or by combining various aspects of the disclosed embodiments. Accordingly, other aspects and a more comprehensive understanding may be obtained by referring to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings, in addition to the scope defined by the claims.
The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the disclosure. Given the following enabling description of the drawings, the novel aspects of the present disclosure should become evident to a person of ordinary skill in the art. This detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of embodiments of the invention.
As required, detailed embodiments are disclosed herein. It must be understood that the disclosed embodiments are merely exemplary of various and alternative forms. As used herein, the word “exemplary” is used expansively to refer to embodiments that serve as illustrations, specimens, models, or patterns. The Figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components.
In other instances, well-known components, apparatuses, materials, or methods that are known to those having ordinary skill in the art have not been described in detail in order to avoid obscuring the present disclosure. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art.
As noted above, the embodiments provide a bypass module that can be implemented in connection with one or more PV panels within a string to be connected with a combiner box (as depicted in
Details regarding the bypass module 250 will be discussed below with reference to
As shown in
When the total PV voltage across the string 200, or the PV panel 20 OC voltage drops to a sufficient level, then switch 260 can be re-closed and switch 262 can be opened.
A control module 300 as shown in
Operation of the bypass module as controlled by the control module 300 will be described below with reference to
At operation 415, the switch 310 is switched on and the string current travels through the PV panel 210 and out of the positive terminal 200b of the string 200. At operation 420, the voltage sensor 318 measures voltage directly across the PV panel 210 which ranges from approximately 30-40 volts (V). The filter device 320 removes any transient signals. Then at operation 425, the comparator 326 detects that the PV voltage is high (Vhigh) and switch 312 is immediately switched on and switch 310 is delayed by timer device 314 for approximately a few seconds. As a result, at operation 430, the switches 310 and 312 together short-circuit PV panel 210. The voltage at the positive terminal 200b is immediately reduced by one PV panel (e.g., in this case by the short-circuit of PV panel 210). The current of string 200 is reduced since the voltage is lower with the excess short-circuit current from the PV panel 210 flowing down in switch 312. At operation 435, after the short delay switch 310 opens and the current (Iphoto) of the PV panel 210 has no external path so voltage increases and flows in diode 162. The PV panel 210 now is an open circuit with a higher voltage and the current of the string 200 now flows up switch 312. At operation 440, once sufficient sun and time (several minutes) occurs, the PV panels 210 warm up the comparator 328 detects an acceptable voltage (V_OK) and latch is set at the logic device 330. At operation 445, the switch 310 is immediately switched on and switch 312 is delayed by timer device 316 by a few seconds. The PV panel 210 is again short-circuited, and at operation 450, after the short delay the switch 312 is switched off and the PV voltage of the string 200 returns to its normal conditions.
From four (4) to five (5) seconds, the sun comes out, thereby causing the MPPT power to increase to approximately 14 kilowatts (kW) which is considered excess power. From five (5) to six (6) seconds, the converter reacts to curtail the power to near 8 kilowatts (kW) increasing the voltage to approximately 850 volts (V) but decreasing the current. From six (6) to seven (7) seconds, the bypass module operates and the switch 312 shown in
The bypass module of the embodiments of the present invention provides several advantages. Some of the advantages include enhancement of the PV array system DC to AC ratio capacity, and lowering of arc fault energy and manufacturing costs.
This written description uses examples to disclose the invention including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or apparatuses and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
