490 lines
13 KiB
Text
490 lines
13 KiB
Text
##
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# Procedural model of a Cessna 172S electrical system. Includes a
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# preliminary battery charge/discharge model and realistic ammeter
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# gauge modeling.
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#
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##
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# Initialize internal values
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#
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var battery = nil;
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var alternator = nil;
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var last_time = 0.0;
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var vbus_volts = 0.0;
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var ebus1_volts = 0.0;
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var ebus2_volts = 0.0;
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var ammeter_ave = 0.0;
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##
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# Initialize the electrical system
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#
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init_electrical = func {
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battery = BatteryClass.new();
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alternator = AlternatorClass.new();
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# set initial switch positions
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setprop("/controls/engines/engine[0]/master-bat", 1);
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setprop("/controls/engines/engine[0]/master-alt", 1);
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setprop("/controls/switches/master-avionics", 1);
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setprop("/systems/electrical/outputs/autopilot",0.0);
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# Request that the update function be called next frame
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settimer(update_electrical, 0);
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logprint(3, "Electrical system initialized");
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}
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##
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# Battery model class.
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#
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BatteryClass = {};
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BatteryClass.new = func {
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var obj = { parents : [BatteryClass],
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ideal_volts : 24.0,
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ideal_amps : 30.0,
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amp_hours : 12.75,
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charge_percent : 1.0,
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charge_amps : 7.0 };
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return obj;
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}
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##
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# Passing in positive amps means the battery will be discharged.
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# Negative amps indicates a battery charge.
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#
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BatteryClass.apply_load = func( amps, dt ) {
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var amphrs_used = amps * dt / 3600.0;
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var percent_used = amphrs_used / me.amp_hours;
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var charge_percent = me.charge_percent;
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charge_percent -= percent_used;
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if ( charge_percent < 0.0 ) {
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charge_percent = 0.0;
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} elsif ( charge_percent > 1.0 ) {
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charge_percent = 1.0;
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}
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if ((charge_percent < 0.1)and(me.charge_percent >= 0.1))
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{
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print("Warning: Low battery! Enable alternator or apply external power to recharge battery.");
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}
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me.charge_percent = charge_percent;
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setprop("/systems/electrical/battery-charge-percent", charge_percent);
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# print( "battery percent = ", charge_percent);
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return me.amp_hours * charge_percent;
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}
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##
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# Return output volts based on percent charged. Currently based on a simple
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# polynomial percent charge vs. volts function.
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#
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BatteryClass.get_output_volts = func {
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var x = 1.0 - me.charge_percent;
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var tmp = -(3.0 * x - 1.0);
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var factor = (tmp*tmp*tmp*tmp*tmp + 32) / 32;
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return me.ideal_volts * factor;
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}
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##
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# Return output amps available. This function is totally wrong and should be
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# fixed at some point with a more sensible function based on charge percent.
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# There is probably some physical limits to the number of instantaneous amps
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# a battery can produce (cold cranking amps?)
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#
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BatteryClass.get_output_amps = func {
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var x = 1.0 - me.charge_percent;
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var tmp = -(3.0 * x - 1.0);
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var factor = (tmp*tmp*tmp*tmp*tmp + 32) / 32;
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return me.ideal_amps * factor;
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}
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##
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# Alternator model class.
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#
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AlternatorClass = {};
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AlternatorClass.new = func {
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var obj = { parents : [AlternatorClass],
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rpm_source : "/engines/engine[0]/rpm",
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rpm_threshold : 800.0,
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ideal_volts : 28.0,
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ideal_amps : 60.0 };
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setprop( obj.rpm_source, 0.0 );
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return obj;
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}
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##
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# Computes available amps and returns remaining amps after load is applied
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#
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AlternatorClass.apply_load = func( amps, dt ) {
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# Scale alternator output for rpms < 800. For rpms >= 800
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# give full output. This is just a WAG, and probably not how
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# it really works but I'm keeping things "simple" to start.
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var rpm = getprop( me.rpm_source );
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var factor = rpm / me.rpm_threshold;
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if ( factor > 1.0 ) {
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factor = 1.0;
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}
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# print( "alternator amps = ", me.ideal_amps * factor );
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var available_amps = me.ideal_amps * factor;
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return available_amps - amps;
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}
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##
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# Return output volts based on rpm
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#
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AlternatorClass.get_output_volts = func {
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# scale alternator output for rpms < 800. For rpms >= 800
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# give full output. This is just a WAG, and probably not how
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# it really works but I'm keeping things "simple" to start.
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var rpm = getprop( me.rpm_source );
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var factor = rpm / me.rpm_threshold;
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if ( factor > 1.0 ) {
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factor = 1.0;
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}
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# print( "alternator volts = ", me.ideal_volts * factor );
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return me.ideal_volts * factor;
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}
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##
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# Return output amps available based on rpm.
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#
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AlternatorClass.get_output_amps = func {
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# scale alternator output for rpms < 800. For rpms >= 800
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# give full output. This is just a WAG, and probably not how
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# it really works but I'm keeping things "simple" to start.
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var rpm = getprop( me.rpm_source );
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var factor = rpm / me.rpm_threshold;
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if ( factor > 1.0 ) {
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factor = 1.0;
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}
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# print( "alternator amps = ", ideal_amps * factor );
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return me.ideal_amps * factor;
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}
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##
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# This is the main electrical system update function.
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#
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update_electrical = func {
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var time = getprop("/sim/time/elapsed-sec");
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var dt = time - last_time;
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last_time = time;
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update_virtual_bus( dt );
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# Request that the update function be called again next frame
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settimer(update_electrical, 0);
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}
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##
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# Model the system of relays and connections that join the battery,
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# alternator, starter, master/alt switches, external power supply.
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#
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update_virtual_bus = func( dt ) {
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var serviceable = getprop("/systems/electrical/serviceable");
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var external_volts = 0.0;
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var load = 0.0;
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var battery_volts = 0.0;
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var alternator_volts = 0.0;
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if ( serviceable ) {
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battery_volts = battery.get_output_volts();
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alternator_volts = alternator.get_output_volts();
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}
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# switch state
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var master_bat = getprop("/controls/engines/engine[0]/master-bat");
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var master_alt = getprop("/controls/engines/engine[0]/master-alt");
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if (getprop("/controls/electric/external-power"))
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{
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external_volts = 28;
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}
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# determine power source
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var bus_volts = 0.0;
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var power_source = nil;
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if ( master_bat ) {
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bus_volts = battery_volts;
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power_source = "battery";
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}
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if ( master_alt and (alternator_volts > bus_volts) ) {
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bus_volts = alternator_volts;
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power_source = "alternator";
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}
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if ( external_volts > bus_volts ) {
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bus_volts = external_volts;
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power_source = "external";
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}
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# print( "virtual bus volts = ", bus_volts );
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# starter motor
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var starter_switch = getprop("controls/switches/starter");
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var starter_volts = 0.0;
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if ( starter_switch ) {
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starter_volts = bus_volts;
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load += 12;
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}
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setprop("systems/electrical/outputs/starter[0]", starter_volts);
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if (starter_volts > 12) {
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setprop("controls/engines/engine[0]/starter",1);
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setprop("controls/engines/engine[0]/magnetos",3);
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} else {
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setprop("controls/engines/engine[0]/starter",0);
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}
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# bus network (1. these must be called in the right order, 2. the
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# bus routine itself determins where it draws power from.)
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load += electrical_bus_1();
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load += electrical_bus_2();
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load += cross_feed_bus();
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load += avionics_bus_1();
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load += avionics_bus_2();
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# system loads and ammeter gauge
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var ammeter = 0.0;
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if ( bus_volts > 1.0 ) {
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# ammeter gauge
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if ( power_source == "battery" ) {
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ammeter = -load;
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} else {
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ammeter = battery.charge_amps;
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}
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}
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# print( "ammeter = ", ammeter );
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# charge/discharge the battery
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if ( power_source == "battery" ) {
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battery.apply_load( load, dt );
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} elsif ( bus_volts > battery_volts ) {
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battery.apply_load( -battery.charge_amps, dt );
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}
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# filter ammeter needle pos
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ammeter_ave = 0.8 * ammeter_ave + 0.2 * ammeter;
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# outputs
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setprop("/systems/electrical/amps", ammeter_ave);
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setprop("/systems/electrical/volts", bus_volts);
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if (bus_volts > 12)
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vbus_volts = bus_volts;
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else
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vbus_volts = 0.0;
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return load;
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}
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electrical_bus_1 = func() {
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# we are fed from the "virtual" bus
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var bus_volts = vbus_volts;
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var load = 0.0;
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# Cabin Lights Power
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if ( getprop("/controls/circuit-breakers/cabin-lights-pwr") ) {
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setprop("/systems/electrical/outputs/cabin-lights", bus_volts);
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load += bus_volts / 57;
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} else {
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setprop("/systems/electrical/outputs/cabin-lights", 0.0);
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}
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# Instrument Power
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setprop("/systems/electrical/outputs/instr-ignition-switch", bus_volts);
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# Fuel Pump Power
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if ( getprop("/controls/engines/engine[0]/fuel-pump") ) {
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setprop("/systems/electrical/outputs/fuel-pump", bus_volts);
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load += bus_volts / 28;
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} else {
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setprop("/systems/electrical/outputs/fuel-pump", 0.0);
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}
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# Landing Light Power
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if ( getprop("/controls/lighting/landing-lights") ) {
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setprop("/systems/electrical/outputs/landing-lights", bus_volts);
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load += bus_volts / 5;
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} else {
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setprop("/systems/electrical/outputs/landing-lights", 0.0 );
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}
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# Beacon Power
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if ( getprop("/controls/lighting/beacon" ) ) {
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setprop("/systems/electrical/outputs/beacon", bus_volts);
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load += bus_volts / 28;
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} else {
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setprop("/systems/electrical/outputs/beacon", 0.0);
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}
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# Flaps Power
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setprop("/systems/electrical/outputs/flaps", bus_volts);
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# register bus voltage
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ebus1_volts = bus_volts;
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# return cumulative load
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return load;
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}
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electrical_bus_2 = func() {
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# we are fed from the "virtual" bus
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var bus_volts = vbus_volts;
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var load = 0.0;
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# Nav Lights Power
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if ( getprop("/controls/lighting/nav-lights" ) ) {
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setprop("/systems/electrical/outputs/nav-lights", bus_volts);
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load += bus_volts / 14;
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} else {
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setprop("/systems/electrical/outputs/nav-lights", 0.0);
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}
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# Instrument Lights Power
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setprop("/systems/electrical/outputs/instrument-lights", bus_volts);
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# Strobe Lights Power
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if ( getprop("/controls/lighting/strobe" ) ) {
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setprop("/systems/electrical/outputs/strobe", bus_volts);
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load += bus_volts / 14;
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} else {
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setprop("/systems/electrical/outputs/strobe", 0.0);
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}
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# Taxi Lights Power
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if ( getprop("/controls/lighting/taxi-light" ) ) {
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setprop("/systems/electrical/outputs/taxi-light", bus_volts);
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load += bus_volts / 10;
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} else {
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setprop("/systems/electrical/outputs/taxi-light", 0.0);
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}
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# Pitot Heat Power
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if ( getprop("/controls/anti-ice/pitot-heat" ) ) {
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setprop("/systems/electrical/outputs/pitot-heat", bus_volts);
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load += bus_volts / 28;
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} else {
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setprop("/systems/electrical/outputs/pitot-heat", 0.0);
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}
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# register bus voltage
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ebus2_volts = bus_volts;
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# return cumulative load
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return load;
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}
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cross_feed_bus = func() {
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# we are fed from either of the electrical bus 1 or 2
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var bus_volts = ebus2_volts;
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if ( ebus1_volts > ebus2_volts ) {
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bus_volts = ebus1_volts;
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}
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var load = 0.0;
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setprop("/systems/electrical/outputs/annunciators", bus_volts);
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# return cumulative load
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return load;
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}
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avionics_bus_1 = func() {
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var bus_volts = 0.0;
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var load = 0.0;
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# we are fed from the electrical bus 1
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var master_av = getprop("/controls/switches/master-avionics");
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if ( master_av ) {
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bus_volts = ebus1_volts;
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}
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load += bus_volts / 20.0;
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# Turn Coordinator Power
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setprop("/systems/electrical/outputs/turn-coordinator", bus_volts);
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# Directional Gyro Power
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setprop("/systems/electrical/outputs/DG", bus_volts);
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# Avionics Fan Power
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setprop("/systems/electrical/outputs/avionics-fan", bus_volts);
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# GPS Power
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setprop("/systems/electrical/outputs/gps", bus_volts);
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# HSI Power
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setprop("/systems/electrical/outputs/hsi", bus_volts);
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# NavCom 1 Power
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setprop("/systems/electrical/outputs/nav[0]", bus_volts);
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# DME Power
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setprop("/systems/electrical/outputs/dme", bus_volts);
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# Audio Panel 1 Power
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setprop("/systems/electrical/outputs/audio-panel[0]", bus_volts);
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# Com 1 Power
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setprop("systems/electrical/outputs/comm[0]", bus_volts);
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# return cumulative load
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return load;
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}
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avionics_bus_2 = func() {
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var master_av = getprop("/controls/switches/master-avionics");
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# we are fed from the electrical bus 2
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var bus_volts = 0.0;
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if ( master_av ) {
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bus_volts = ebus2_volts;
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}
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var load = bus_volts / 20.0;
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# NavCom 2 Power
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setprop("/systems/electrical/outputs/nav[1]", bus_volts);
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# Audio Panel 2 Power
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setprop("/systems/electrical/outputs/audio-panel[1]", bus_volts);
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# Com 2 Power
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setprop("systems/electrical/outputs/comm[1]", bus_volts);
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# Transponder Power
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setprop("/systems/electrical/outputs/transponder", bus_volts);
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# Autopilot Power
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setprop("/systems/electrical/outputs/autopilot", bus_volts);
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# ADF Power
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setprop("/systems/electrical/outputs/adf", bus_volts);
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# return cumulative load
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return load;
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}
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# Setup a timer based call to initialized the electrical system as
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# soon as possible.
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settimer(init_electrical, 0);
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