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 generate. 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 power system for running an electrically driven device using a power load defining an active load when in operation comprising:
a generator, the generator having a minimum efficient load rating, the generator electrically coupled to the electrically driven device;
a load bank, the load bank electrically coupled to the generator and positioned to provide a passive load on the generator when engaged; and
a controller positioned to engage the load bank and activate the passive load, wherein a process variable for the controller is actual generator power load, and wherein a second process variable for the controller is 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.
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 power system of claim 1 , wherein the load bank is electrically coupled to the generator via an inverter, the inverter being controlled by the controller to increase or decrease an amount of passive load connected to the generator.
4. The power system 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 power system 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 power system 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 power system 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
d
c
2
,
where P d is the power dissipated, N B is the number of load banks, R is a per-phase resistance of the three phase resistive load banks, and M is the duty cycle of the inverter.
8. The power system of claim 1 , wherein the electrically driven device is an electric motor capable of dynamic braking, and the power generated thereby is dissipated by the load bank.
9. The power system of claim 3 , wherein the inverter comprises a chopper.
10. The power system of claim 1 , wherein the controller is a step change controller, a state controller, a proportional controller, a proportional integral controller, a proportional integral derivative controller, a proportional derivative controller, an adaptive controller, or a predictive controller.
11. 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, wherein a process variable for the controller is actual generator power load, and wherein a second process variable for the controller is 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;
calculating a total minimum efficient load of the one or more generators;
calculating a total power demand of the one or more electrically driven devices;
calculating, from the total minimum efficient 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.
12. The method of claim 11 , 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.
13. The method of claim 11 , 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.
14. The method of claim 13 , 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.
15. The method of claim 13 , 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.
16. The method of claim 15 , 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.
17. The method of claim 15 , 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
d
c
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.
18. The method of claim 11 , 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.