Solar aided coal-fired power generation system participating in primary frequency regulation and control method thereof

A solar aided coal-fired power generation system participating in primary frequency regulation, comprising:

• a boiler (1), a steam turbine (2) connected to an outlet of the boiler (1), a high-pressure heater (3) connected to a high-pressure cylinder extraction port of the steam turbine (2), a deaerator (4) connected to a medium-pressure cylinder extraction port of the steam turbine (2), a low-pressure heater (5) connected to a low-pressure cylinder extraction port of the steam turbine (2), and a condenser (6) connected to a low-pressure cylinder exhaust port of the steam turbine (2);
• the solar aided coal-fired power generation system further comprises a high-pressure feedwater bypass regulation system and a low-pressure condensate bypass regulation system to enable two primary frequency regulation schemes consisting of a high-pressure feedwater bypass regulation scheme and a low-pressure condensate bypass regulation scheme:
• 1) in the scheme, feedwater at an outlet of the deaerator (4) is boosted by a feedwater pump (8) and divided into two paths, wherein one path passes through the high-pressure heater (3) and a feedwater valve (7) before entering the boiler (1), and the other path passes through a feedwater bypass valve (11) before entering a high-pressure bypass heat exchanger (12) to merge into the boiler (1);
• meanwhile, a heat exchange working fluid of the high-pressure bypass heat exchanger (12) is boosted by a high-pressure bypass pump (13) before entering a first solar collector (14) to absorb solar energy collected, and then enters the high-pressure bypass heat exchanger (12) to transfer heat to the feedwater;
• during the primary frequency regulation process, output power of the steam turbine (2) is rapidly changed by adjusting the feedwater bypass valve (11), thereby meeting requirements of the primary frequency regulation;
• 2) in the low-pressure condensate bypass regulation scheme, condensate at an outlet of the condenser (6) is boosted by a condensate pump (10) and divided into two paths, wherein one path passes through the low-pressure heater (5) and a deaerator inlet valve (9) before entering the deaerator (4), and the other path passes through a condensate bypass valve (15) before entering a low-pressure bypass heat exchanger (16) to merge into the deaerator (4);
• meanwhile, a heat exchange working fluid of the low-pressure bypass heat exchanger (16) is boosted by a low-pressure bypass pump (17) before entering a second solar collector (18) to absorb the solar energy collected, and then enters the low-pressure bypass heat exchanger (16) to transfer heat to the condensate;
• during the primary frequency regulation process, the output power of the steam turbine (2) is rapidly changed by adjusting the condensate bypass valve (15), thereby meeting requirements of the primary frequency regulation;
• wherein a method for controlling the solar aided coal-fired power generation system participating in primary frequency regulation comprises formulating a primary frequency regulation control logic and a heater outlet temperature control logic according to operating characteristics of the solar aided coal-fired power generation system, which comprises specific steps of:
• 1) formulating the primary frequency regulation control logic:
• according to an operating status of a power grid, obtaining a maximum frequency adjustment Δfmax when the primary frequency regulation is needed, and then converting into a required maximum power adjustment ΔPmax with a speed droop δ of a generation unit, which is:
• ΔPmax=f1(Δfmax)=Δfmax/δ
• according to an actual operating status of the solar aided coal-fired power generation system, determining a maximum power adjustment ΔPLPH,max of the low-pressure condensate bypass regulation scheme, and comparing with the required maximum power adjustment ΔPmax, wherein if ΔPmax>ΔPLPH,max, the high-pressure feedwater bypass regulation scheme is selected for the primary frequency regulation;
• if ΔPmax≤ΔPLPH,max, the low-pressure condensate bypass regulation scheme is selected for the primary frequency regulation;
• after determining a regulation scheme for the primary frequency regulation, obtaining a real-time frequency value fpv according to the operating state of the power grid, and comparing with a stable frequency value fsp required by the power grid, so as to calculate a frequency deviation Δf, setting parameters of the frequency deviation in a speed governor to obtain a power adjustment ΔP, wherein the parameters comprise a frequency modulation deadband and a speed droop:
• ΔP=f2 (Δf)
• superimposing an adjustment output Δμ, which is obtained by the power adjustment ΔP in a PID controller, on a control valve corresponding to the high-pressure feedwater bypass regulation scheme or the low-pressure condensate bypass regulation scheme, so as to generate a latest valve opening μnew:
• μnew=μold+Δμ
• wherein μold is an initial valve opening;
• finally, applying an optimal scheme to the primary frequency regulation to form a closed-loop optimization control logic;
• and
• 2) formulating an outlet water temperature control logic for the high-pressure heater and the low-pressure heater:
• for the primary frequency regulation with the high-pressure feedwater bypass regulation scheme, formulating the outlet water temperature control logic as:
• first, using a temperature sensor to obtain a temperature Tf,pv when the feedwater enters the boiler (1), and comparing the temperature Tf,pv with a preset temperature Tf,sp for the feedwater to enter the boiler (1), so as to obtain a temperature deviation ΔT1;
• using the temperature sensor to obtain a temperature Ts,pv when a working fluid of the first solar collector (14) enters the high-pressure bypass heat exchanger (12), and comparing the temperature Ts,pv with a preset temperature Ts,sp for the working fluid of the first solar collector (14) to enter the high-pressure bypass heat exchanger (12), so as to obtain a temperature deviation ΔT2;
• accumulating the two temperature deviations to obtain a total temperature deviation ΔTh:
• ΔTh=ΔT1+ΔT2;
• calculating the total temperature deviation ΔTh in the PID controller to obtain a direct control command ΔΨh for the high-pressure bypass pump (13):
• ΔΨh=f (ΔTh);
• meanwhile, due to long solar collector piping and large thermal inertia, processing a primary frequency regulation fast command with feedforward correction for temperature control of each section;
• and using a control command Δμh for the feedwater bypass valve (11), which is obtained in the primary frequency regulation control logic of the high-pressure feedwater bypass regulation scheme, to generate a feedforward signal command Δφh for the high-pressure bypass pump (13) through a function generator:
• Δφh=f (Δμh)
• finally, superimposing the direct control command ΔΨh and the feedforward signal command Δφh on the high-pressure bypass pump (13) to generate a latest speed command σh,new thereof:
• σh,new=σh,old+ΔΨh+Δφh
• wherein:
• σh,old is an initial speed of the high-pressure bypass pump (13);
• for the primary frequency regulation with the low-pressure condensate bypass regulation scheme, formulating the outlet water temperature control logic as:
• first, using the temperature sensor to obtain a temperature Tc,pv when the condensate enters the deaerator (4), and comparing the temperature Tc,pv with a preset temperature Tc,sp for the condensate to enter the deaerator (4), so as to obtain a temperature deviation ΔT3;
• using the temperature sensor to obtain a temperature To,pv when a working fluid of the second solar collector (18) enters the low-pressure bypass heat exchanger (16), and comparing the temperature To,pv with a preset temperature To,sp for the working fluid of the second solar collector (18) to enter the low-pressure bypass heat exchanger (16), so as to obtain a temperature deviation ΔT4;
• accumulating the two temperature deviations to obtain a total temperature deviation ΔTd:
• ΔTd=ΔT3+ΔT4;
• calculating the total temperature deviation ΔTd in the PID controller to obtain a direct control command ΔΨd for the low-pressure bypass pump (17):
• ΔΨd=f (ΔTd);
• meanwhile, due to long solar collector piping and large thermal inertia, processing a primary frequency regulation fast command with feedforward correction for temperature control of each section;
• and using a control command Δμd for the condensate bypass valve (15), which is obtained in the primary frequency regulation control logic of the low-pressure condensate bypass regulation scheme, to generate a feedforward signal command Δφd for the low-pressure bypass pump (17) through the function generator:
• Δφd=f (Δμd)
• finally, superimposing the direct control command ΔΨd and the feedforward signal command Δφd on the low-pressure bypass pump (17) to generate a latest speed command σd,new thereof:
• σd,new=σd,old+ΔΨd+Δφd
• wherein:
• σd,old is an initial speed of the low-pressure bypass pump (17).