Research and Analysis on Technical Improvement of Steam Electro-hydraulic Control System

Technical improvement of coordinated control system

1. Commissioning of the coordinated control system before the improvement. Before May 1998, the Huaneng Shantou Power Plant’s boiler coordinated control system had restored the original design configuration loop and completed the automatic test work to verify the system design function, but at that time CCS The automatic input is less than 85%, and the main adjustment systems such as steam temperature, water supply, negative pressure, and water level of the deaerator are not ideal and do not fully meet the regulatory requirements. The load change test of the turbine-boiler coordinated control system can only pass the small load, slow and small disturbance test (disturbance range 5MW, change rate 5MW/min), and the unit coordinated control cannot be put into operation at all.

2. Technical improvement of load command feedforward loop

2.1 The improved principle The original design unit coordination is in CCBF, CCTF, TF2 mode, and the feedforward of the boiler fuel quantity is only LDC load command. When the unit is put into CCBF, CCTF coordination mode, the pure time delay of pulverizing and boiler combustion is long. , The fuel quantity, steam temperature, and steam pressure fluctuate greatly when the load changes, and it cannot be adjusted normally when the load changes greatly.

The technical improvement plan of the load command feedforward loop: (1) Increase the amount of fuel plus inertia-unit power negative deviation feedforward to partly reverse the excessive fluctuation of the fuel quantity; (2) Increase the power frequency negative deviation feedforward to improve Reduce the excessive disturbance to the boiler thermal load of the unit due to the sudden change of the power of the grid frequency fluctuation. Field tests have proved that the dynamic adjustment performance under the improved CCBF and CCTF coordination mode is significantly improved.

2.2 Parameter adjustment test after feedforward loop modification

The specific considerations are as follows:

(1) When setting K3, avoid possible oscillation of the fuel closed loop circuit. The current actual setting is 0.16.

(2) The setting of K2 frequency response coefficient is related to K3, and the furnace side PID proportional coefficient in the two modes of CCBF and CCTF should be taken into consideration. Since the tracking loop is working, when the fuel quantity-unit power is unbalanced, the feedforward dynamic part is completed by K2 and K3, and K2* should be less than 0.75. The inertia link Ti value is related to the thermal inertia of the boiler, and the specific test should be passed. Find the best value. The current actual setting is K2=0.65, K3=0.16, Ti=240s.

(3) The setting of K1 also considers the BF1 working condition. Because the feedforward goes /N0 under the BF1 working condition, the LDC feedforward actually becomes the unit power, and the current setting is 0.72.

(4) Simplified calculation of feedforward ratio after the feedforward loop is improved. At the beginning of the dynamic process of LDC unit load command changes, power and fuel increase at the same time, and the feedforward ratio of the furnace master control is [email protected]=0.87, that is, the fuel and air volume required at the beginning of the dynamic process, 87% is completed by feedforward , The remaining 13% and the overshoot part are completed by the regulator. When the power changes caused by the cycle change, the feedforward ratio [email protected]=0.754, that is, the fuel volume and air volume required at the beginning of the dynamic process, 75% is completed by the feedforward, and the remaining 25% and overshoot are completed by the regulator . The feedforward ratio of the fuel quantity of the two variable load conditions accounts for most of the total fuel demand, and a small part is completed by the differential and proportional tracking adjustment of the regulator, which effectively improves the dynamic performance of the system adjustment.

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