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Power control PID parameters of speed limiter

News by ninechip | On 2018-11-12 16:11
In normal operation of large turbo generator sets, DEH side power open loop and DCS side power closed loop control mode are generally used. In this control mode, the proportion of PID parameters in power control will affect the oscillation frequency of the system. When the proportion coefficient is too large, the power system will enter the negative damping region, which is easy to induce low-frequency oscillation.
   Low frequency oscillation still occurs in a 300MW circulating fluidized bed unit under normal steam distribution function when coordinated control and the speed governing system is put into operation. After that, the proportional coefficient KP of power control PID parameters is changed from 3 to 0.3, and the input limit of PID deviation is increased, no low frequency oscillation occurs again. Similar scenarios are not uncommon, especially in the case of power grid failures and poor linearity of steam turbine regulation, the unit power is prone to large mutations, at this time if the power control PID regulation is too large, it is easy to cause repeated fluctuations in the regulation system, thus causing low-frequency oscillation of the system.
   When the deviation between the main steam pressure and the set value exceeds the dead zone, the main steam pressure is "pulled back" by limiting the unit power. The main steam pressure adjustment loop of some units is operated by setting the main steam pressure deviation adjustment coefficient and by power control PID. If the regulation is too strong, it will also induce low-frequency oscillation. Now we will need a speed governing system.
   In fact, because the proportional coefficient of the power control PID parameters is similar to the magnification of the speed governing system, most of the low-frequency oscillations caused by the power control PID parameters are the result of the combined action of the two, especially in the case of poor linearity of turbine regulation, small local unequal rate of turbine speed, and power control PI. In the case of strong D regulation, the power sloshing of the unit is almost inevitable, and the low-frequency oscillation of the power system will be caused when the continuous operation is carried out.
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