Patent Application
20150021982
1. Field
The disclosed concept relates generally to direct current electrical generating systems, and in particular, to photovoltaic systems.
2. Background Information
It is known to provide circuit breakers or fuses at a combiner box to electrically disconnect an entire string of photovoltaic (PV) modules in a PV system. However, even if the string of PV modules is electrically disconnected at the combiner box, the PV modules will continue to generate power if they are illuminated. When the wiring in the string or PV module is compromised, this can create a fire hazard as well as a shock hazard to firefighters or service personnel.
There is room fir improvement in direct current electrical generating systems.
These needs and others are met by aspects of the disclosed concept which provide a system including a plurality of direct current electrical generating modules electrically connected to a power line, each direct current electrical generating module including an electromechanical switch structured to interrupt power flowing through the power line.
In accordance with aspects of the disclosed concept, a system comprises: a power line; a control line; a plurality of direct current electrical generating modules, each of the direct current electrical generating modules being electrically connected to the power line and the control line and including an electromechanical switch structured to interrupt power flowing through the power line; and a control module electrically connected to the control line and structured to electrically control the electromechanical switch of each of the direct current electrical generating modules via the control line.
In accordance with other aspects of the disclosed concept, a system comprises: a power line; a power line control transmitter electrically connected to the power line and structured to transmit a control signal through the power line; and a plurality of direct current electrical generating modules, each of the direct current electrical generating modules being electrically connected to the power line and including an electromechanical switch structured to interrupt power flowing through the power line and a power line control receiver structured to receive the control signal transmitted through the power line and to control operation of the electromechanical switch based on the received control signal.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.
As employed herein, the term “number” shall mean one or an integer greater than one (Le., a plurality).
As employed herein, the term “string” shall mean a series electrical circuit connection of a plurality of electrical generating modules.
As employed herein, the term “combiner box” shall mean a box, an enclosure or another suitable structure where one or both ends of a plurality of strings can be fused and/or protected. A combiner box electrically combines in parallel direct current from a plurality of strings.
As employed herein, the term “direct current electrical generating module” (DC EGM) shall mean a photovoltaic (PV) electrical generating module, a battery or a fuel cell.
As employed herein, the term “power line” shall mean a number of power conductors that electrically connect DC EGMs on a string in series between a positive bus and a negative bus located at the feed end of the string.
As employed herein, the term “control line” shall mean a number of conductors that electrically connect DC EGMs on a string to a control module located at the feed end of the string.
As employed herein, the term “feed forward fault” shall mean a fault defined by a non-zero forward current and a corresponding voltage that is significantly lower than Voc (e.g., without limitation, a voltage less than about 20% of open circuit voltage) or Vmpp (voltage at the maximum power point). For example, a feed forward fault can indicate an external short toward the feed (inverter) end of a string.
The disclosed concept is described in association with protection for PV circuits, although the disclosed concept is applicable to a wide range of DC applications, including for example and without limitation, relatively higher DC voltage circuits, such as wind power, hybrid vehicles, electric vehicles, marine systems and aircraft.
Referring to
Power system 20 further includes an inverter 32 electrically connected to the positive and negative busses 26,28. The inverter 32 converts direct current power received from the positive and negative busses 26,28 to alternating current power. A sub-array shutdown switch 34 is electrically connected between the inverter 32 and the positive bus 26. The sub-array shutdown switch 34 can be opened to interrupt current flowing between the inverter 32 and the positive bus 26. While this configuration is suitable for, for example and without limitation, a negatively grounded PV array, it should be appreciated that other configurations may be employed without departing from the scope of the disclosed concept. In one example embodiment, the sub-array shutdown switch 34 may be electrically connected between the inverter 32 and the negative bus 28. This configuration is suitable for, for example and without limitation, a positively grounded PV array. In another example embodiment, one sub-array shutdown switch 34 may be electrically connected between the positive bus 26 and the inverter 32 and another sub-array shutdown switch 34 may be electrically connected between the negative bus 28 and the inverter 32. This configuration is suitable for, for example and without limitation, an ungrounded PV array.
A number of conductors 36 forma control line that is electrically connected to each of the DC EGMs 22. The control line is also electrically connected to a control module 38 located at the feed end of the string 21. The control module 38 is structured to electrically control electromechanical switches 40 (
The control module 38 is structured to receive an input signal INPUT and to control the electromechanical switches 40 based on the received input signal INPUT.
The input signal INPUT may be provided to the control module 38 by, for example and without limitation, an arc-fault detector and a sub-array shutdown switch. Turning briefly to
Referring back to
Referring to
In some example embodiments of the disclosed concept, the electromechanical switches 40 are normally open and prevent current from flowing through the power line when no current is flowing through the control line. The electromechanical switches 40 then close and allow current to flow through the power line when a sufficient current flows through the control line. However, it is also contemplated that the electromechanical switches 40 can be normally closed when no current flows through the control line and then open when a sufficient current flows through the control line.
The electromechanical switches 40 may employ a relatively greater current to transition from an open position to a closed position than a current employed to maintain the electromechanical switches 40 in the closed position. In order to reduce the amount of power used to electrically control the electromechanical switches 40, the control module 38 may provide a first current on the control line to transition the electromechanical switches 40 from an open position to a closed position, and then provide a lesser second current to maintain the electromechanical switches 40 in the closed position.
The solar cells 42 are structured to harvest solar energy and convert it to direct current electrical power. The junction box 44 electrically couples the solar cells 42 to the power line such that the direct current electrical power from the solar cells 42 is provided to the power line.
While the electromechanical switch 40 and the junction box 44 are shown as separate components in
Referring to
Turning to
EGMs 122 included in power system 120 of
Referring now to
The switching circuit 146 is electrically connected to the control line and the power supply circuit 144. The switching circuit 146 is structured to permit current to flow through the power supply circuit 144 to the electromechanical switch 140 or to prevent current from flowing through the power supply circuit 144 to the electromechanical switch 140 based on a voltage on the control line. Thus, opening and closing of the electromechanical switch 140′ is electrically controlled via the control line.
The DC EGM 122 shown in
Referring now to
Turning to
The PLC receiver 242 is further structured to allow the encoded control signal to pass through it and continue on the power line to subsequent DC EGMs 222. Thus, when the electromechanical switch 240 is open, the encoded control signal can bypass the electromechanical switch 240 by passing through the PLC receiver 242. To this extent, the PLC receiver 242 may include a high pass filter structured to block direct current power from passing through it, but allow the encoded control signal to pass through it.
By employing the PLC transmitter 224 and the PLC receivers 242, power system 220 of
The power system 20′ of
The power system 20″ of
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
