Working Principle of Automatic Control System of Diesel Generator Set

At present, with the continuous growth of enterprise business, the daily energy consumption of the data center is also showing a trend of simultaneous growth. Once the mains power failure occurs, a single diesel generator can not meet the data center backup power demand at all, so it often needs more power. Units are running in parallel. In order to improve the economic efficiency and system reliability of the power system operation, this requires that the system control logic not only requires the unit itself to have good performance, but also requires each unit to reasonably bear the active and reactive loads in the downstream system. These requirements are collectively reflected In the speed regulation system of the prime mover and the voltage regulation system of the synchronous generator.

1. Droop control.

In order to ensure the stability of parallel operation of diesel generator sets, droop control is often adopted, that is, P/f droop control and Q/V droop control are used to obtain stable frequency and voltage. This control method affects the active power output by each unit. Separate control with reactive power, without the need for communication and coordination between units, to achieve peer-to-peer control between units, and to ensure the balance of supply and demand and frequency stability of the diesel generator set parallel system.

The droop control adopts voltage and current dual-loop control. The current inner loop has a fast dynamic response speed, which is used to improve the power quality of the generator set. The voltage outer loop controller has a slower dynamic response speed, which can control the output voltage of the system and generate an inner loop reference. Signal. First, use the measurement module to collect the voltage and current of the load point, calculate the instantaneous active and reactive power of the generator set, and then pass the low-pass filter LPF to obtain the corresponding average power; assuming the rated frequency is running, the generator set's output active power P, F, U are the frequency and rated voltage amplitude of the power system respectively. The output frequency and voltage amplitude commands are obtained through the droop link, and then the reference voltage is generated through the voltage synthesis link. Then, the reference voltage will be used as the voltage and current dual link Controller input.

2. Speed regulation (active power-frequency control) system.

Taking the rated power fN of the synchronous generator as the reference value, when the active power of the downstream load increases to Pred, the output frequency of the synchronous generator droops to the new stable value of fref, and the slope of section AB is the static adjustment of the synchronous generator. Difference coefficient mp, Δf=fref-fN, ΔP=PN-Pred. When diesel generator sets are running in parallel, each generator dynamically adjusts its frequency and power until all load requirements are met. If the capacity of each generating unit is the same, the static adjustment coefficient is also the same, and the output power is naturally the same; if the unit capacity is different, the static adjustment coefficient of the unit with a larger single unit capacity is larger, and the unit will naturally bear more downstream loads.

3. Voltage regulation (reactive power-voltage control) system.

In the same way, the slope of the CD section is called the reactive power-voltage droop control coefficient nq of the synchronous generator, which reflects the relationship between the reactive power increment of the generating set and the terminal voltage deviation, and ΔU=Uref-UN, ΔQ=QN-Qred . According to the control block diagram of the excitation power unit of the synchronous generator, the reference voltage is obtained through the calculation of the measurement link and the difference adjustment link, and then compared with the generator terminal voltage (the voltage regulator is PI control), so that the generator terminal voltage is always Quickly follow the voltage command.

If you want to know more about diesel generators, please contact Dingbo Power by email dingbo@dieselgeneratortech.com.