Generator load control
A power system for an electrical system with highly fluctuating loads is powered by one or more power sources that are slow to react to load changes. The power sources are connected to electrical equipment used on the drill rig which provide active load to the generators. One or more load banks may be positioned to provide passive load to the generators to maintain generally constant generator load, while allowing for instant access to power as active load increases. Generators may be run at 100% capacity, a maximum efficient capacity, or at a high enough level to allow for a sufficiently rapid increase in power output. At least one parameter of a drilling operation may be utilized to anticipate load demand changes.
1. A method for controlling a load bank comprising:
providing a power system for running one or more electrically driven devices using a power load defining an active load when in operation, the power system including:
one or more generators, each generator having a minimum efficient load rating, each generator electrically coupled to the electrically driven device;
the load bank, the load bank electrically coupled to the generator and positioned to provide a power load defining a passive load on the generator when engaged; and
a controller positioned to engage the load bank and activate the passive load;
calculating a total minimum generator load of the one or more generators by multiplying the minimum efficient load rating by the number of generators;
calculating a total power demand of the one or more electrically driven devices;
calculating, from the total minimum generator load and the total power demand, a load bank power demand; and
engaging the load bank with the controller to provide passive load to the generators generally equal to the load bank power demand.
2. The power system of claim 1 , wherein the load bank is adapted to provide one or more of a resistive, inductive, liquid, wind resistance, regenerative, inertial, or capacitive load or to provide load to charge a battery or to run a motor/generator set.
3. The method of claim 1 , wherein the load bank is electrically coupled to the generator via an inverter, the inverter being controlled by the controller to selectively connect and disconnect the load bank from the generator.
4. The method of claim 3 , wherein the inverter is coupled to a variable frequency drive, the variable frequency drive having a DC link, so that the load bank draws power from the DC link.
5. The method of claim 3 , wherein the inverter is driven by a PWM signal sent by the controller, and the passive load is determined by the duty cycle of the inverter.
6. The method of claim 5 , wherein the duty cycle of the PWM signal proportionally controls the passive load of the load bank from 0-100% of the load capability of the load bank.
7. The method of claim 5 , wherein the load bank further comprises one or more three phase resistive load banks, and the duty cycle is calculated according to:
M
=
P
d
·
R
3
·
N
B
·
V
dc
2
,
where P d is the power dissipated as passive load, N B is the number of load banks, R is the per-phase resistance of the three phase load banks, and M is the duty cycle of the inverter.
8. The method of claim 1 , wherein the output power of the one or more generators is controllable by the controller, and the method further comprises:
controlling the power output of the one or more generators based on the total power demand.
9. The method of claim 1 , wherein a process variable for the controller is actual generator load.
10. The method of claim 9 , comprising an additional variable for the controller selected from the group consisting of depth of wellbore, hook load, pump pressure, pump rate, length of drill string, weight on bit, increase or change in current, increase or change in power, and number of engines online, or any changes or requested changes thereto.