Shunt Type Charge Controller: Part A
By Jurgen Eckstein 1990

	This type represents a charge controller for a system that includes
a PV-array, a load, and battery storage.  The controller represents a 
shunt type controller.  A multiple step control scheme is implemented.  
If the battery voltage exceeds the gassing voltage specified by the user, 
the current into the battery will be limited to the current corresponding
to the gassing voltage.  Excess energy is shunted through a dissipater.
	A blocking diode is included in the model to prevent the battery 
from being discharged through the cell.  It is assumed that the voltage
drop across the diode is constant throughout the simulation and depends
only on the particular diode.  This value is supplied by the user.  Another
diode is included in the undervoltage protection device.  This way the 
battery can be disconnected from the load (so the battery will not discharge),
while the array can still charge the battery.
	The shunt controller is divided into two components: Part A and B.
Part B contains the undervoltage control and the overvoltage control while 
Part A controls the rest.  Sample input and output are included in the 
source code.

REF:  Detailed Modeling of Photovoltaic System Components (Masters Thesis)
      Solar Energy Laboratory  University of Wisconsin at Madison