Description - DET System I-V Characteristics

Description of direct energy transfer solar array and power converter interaction.

Direct Energy Transfer System I-V Characteristics  D
Figure 1: DET System I-V Characteristics

Ordinate - Current

Abscissa - Voltage

Blue Line - Plot of solar array output impedance. Starts out as a horizontal line (current source) and then gradually curves into a vertical line (voltage source).

Red Line - Plot of input impedance of a switching-mode power supply, a load that gets its power from the solar array. The plot starts out as a resistive straight line showing current increases as voltage increases, then when switching action starts, turns into a constant power hyperbola with current decreasing as power increases.

Point A - Point A labeled where resistive part of regulator input impedance intercepts constant current portion of solar array output impedance. This is a stable but undesired operating point, undesired in that the switching-mode power supply load latches up as a resistive load before switching action starts.

Point B - Point B labeled where constant power hyperbola of regulator input impedance intercepts the constant current portion of the solar array output impedance. A black vertical dotted line is drawn through this point indicating a separatrix in the phase plane.

Point R - Point R is labeled on the solar array output impedance at the inflection point between a constant current source and a constant voltage source. This is the unstable solar array maximum power point that the shunt regulator (not shown on the graph) regulates the solar power system bus voltage.

Point C - Point C is labeled where the solar array and switching-mode power supply load would operated if the solar array shunt regulator failed open. This would be a voltage higher than the desired regulated bus voltage.

Webmaster and editor: Jerrold Foutz,
Original: 09 July 1999, revised July 31, 2003