June 30th, 2014 
   Aegis Energy Services provides turnkey installation of modular combined heat and power systems. Each cogeneration module includes a natural gas-fueled Chevrolet 8.1 L engine, induction generator, microprocessor control panel, protective switchgear, and heat recovery equipment. Each module is enclosed in a sound attenuated cover and can be installed indoors or outdoors. They feature an EDG6000 (Digital, Multiple PID, SmartVu, Environmentally Sealed, & Tamper Resistant) or ESD5111 (Analog, Isochronous, Variable, & Droop) controller along with an ATB552T2F14 55 mm throttle body due to the strict performance and reliability requirements needed in the application. The ATB552T2F14 features a position feedback sensor used by the air-fuel ratio system to determine the actual throttle position for precise control. Each module is also equipped with an MSP6723 for speed reference.
    Generally, black smoke is an indication that the fuel air mixture is too rich and not all of the fuel is combusting. This can be a result of a cold engine, a dirty or blocked air cleaner system, the fuel injection timing being off, poor quality fuel, or an over-fueled engine. To prevent black smoke, begin by ensuring that you are using good quality fuel and keeping the fuel system clean. GAC also offers a number of products to reduce black smoke. Any GAC governor with adjustable starting fuel can control black smoke at engine startup by adjusting the “starting fuel” adjustment fuel setpoint. Adjusting the “starting fuel” setpoint to decrease the amount of fuel supplied to the engine at startup will therefor reduce black smoke emission. These controllers also have a speed ramping adjustment to allow a gradual increase in engine speed and therefor a smooth response and less black smoke.

     Integral windup (aka reset windup) occurs when the actuator has reached full current (saturation) but the PID (Proportional, Integral, Derivative) controller is still trying to force more current to the actuator in order to bring the engine speed back to the desired level during rapid load changes or startup. The controller integral term accumulates significant error (commanded vs. actual) during the rise (windup) as it continues to command beyond the limit of the actuator. When the engine speed returns to normal and the actuator current reduces, the integrator term will shrink based on the PID settings, however, since it grew for a period of time during the transition, it takes much longer to get back to the desired output creating a large overshoot during the process.  


Windup is more prevalent on gaseous systems because the throttle body response is typically very nonlinear; i.e. the first few degrees of throttle body opening results in much higher engine output than the last few degrees of opening. This implies that during startup, the controller is typically calling for much more throttle body opening than it needs when paired with a regular PID controller.

GAC's Governors Featuring Anti-Windup 

GAC controllers equipped with anti-windup PIDs work to minimize overshoot associated with windup by disabling the integral response when the actuator reaches saturation.  When the engine speed demand returns back to normal, there is no windup, and therefore minimal overshoot.  Some overshoot will remain when the integral response re-enables, during the move to a new set point, but far less than the overshoot occurring without anti-windup.  This feature is found standard in the products below and are thus highly recommended for gaseous applications: