Active bypass diode circuit and solar power module with arc flash mitigation feature

#This application claims priority from U.S. Provisional Patent Application No. 61/617,335, filed on 29 Mar. 2012.

#The invention relates generally to the field of photovoltaic (PV) solar power systems, and more specifically to circuits for protecting bypass diodes from overheating under partial shading conditions, and protecting human personnel from arc flash hazards.

#FIG. 1 is a high level block diagram of a conventional PV solar power system 10 including a plurality of PV segments 11 connected in series. Each PV segment 11 comprises a plurality of PV cells that are serially connected between a positive terminal 12 and a negative terminal 13. For example, a typical PV segment includes twenty four PV cells, and produces about 12V between 12 and 13 in full sunlight. So a typical string of twenty four to fifty one serially-connected PV segments 11 produces an output voltage (VSTRING) in the range of 288V to 612V. An inverter 15 converts VSTRING from dc to ac and has an output 16 for coupling to the electric power grid. There is also usually a disconnect switch 17 for shutting down the system 10.

#The accompanying drawings illustrate the invention. In such drawings:

#FIG. 1 is a high level block diagram of a conventional photovoltaic solar power system;

#FIG. 2 is a high level block diagram of a conventional active bypass diode circuit;

#FIG. 3 is a high level block diagram of an active bypass circuit 30 with arc flash mitigation capability, comprising: a bypass diode 21; a switch 22; a control circuit 31; a detection circuit 32; a power management circuit 39; a power supply circuit 38; and a capacitor 26.

#FIG. 4 shows example waveforms to help explain how the active bypass circuit 30 mitigates an arc flash. In FIG. 4 all voltage waveforms are referenced to the most negative node 13. Initially, the PV segment 11 is unshaded, and produces an output voltage (top waveform in FIG. 4) of about 12V. The power supply 38 utilizes this voltage to charge the capacitor 26, and supply power to at least the control circuit 31 and the power management circuit 39.

#At t=t0 the PV string is broken by disconnecting or cutting a cable. This triggers an arc flash, and in response the detection circuit 32 sets it's output 33 high. The power management circuit 39 receives the detection signal 33 and in response sets it's override output 36 high, causing the control circuit 31 to close the switch 22.