Abstract:
A boiler-steam turbine plant control system for transferring between boiler-follow, turbine-follow, and coordinated operating modes, without any change in the output of the turbine or the firing rate of the boiler, is disclosed. A feedforward load demand signal controls both the turbine and boiler in parallel. In the turbine-follow mode, a feedback loop trims the feedforward signal to the turbine only. In the boiler-follow mode, a feedback loop trims the feedforward signal to the boiler only. In the coordinated mode, feedback loops trim the feedforward signal to both the turbine and boiler. In response to initiating a transfer to either the boiler or turbine-follow mode, the load demand signals which are controlling the boiler and turbine are held at their pre-transfer value; and the feedforward signal is modified to equal the pre-transfer value of the trimmed feedforward signal. A signal, which is equal in value to the pre-transfer value of the feedforward signal less the value of the trimmed feedforward signal is generated in the output of the feedback loop which is to be placed in service as a result of the transfer. To transfer to the coordinated mode, the feedforward signal is modified to equal a signal representative of the actual power output of the plant. The turbine feedback loop generates a signal representative of the pre-transfer turbine demand signal less the modified feedforward signal. The boiler feedback loop generates a signal representative of the pre-transfer boiler demand signal less the modified feedforward signal.