Power system with method for adding multiple generator sets

• US 7,656,060 B2
• Filed: 10/31/2007
• Issued: 02/02/2010
• Est. Priority Date: 10/31/2007
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Algrain, Marcelo C.
• Primary Examiner(s): Deberadinis; Robert L.
• Application Number:
  US11/980,344
• Publication Number:
  US 20090108676A1
• Time in Patent Office: 825 Days
• Field of Search: 307/84
• US Class Current: 307/84
• CPC Class Codes: H02J 3/42 with automatic parallel connection when synchronisation is achieved
• CPC Class Codes: H02J 3/466 Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
• CPC Class Codes: H02J 3/48 Controlling the sharing of the in-phase component
• CPC Class Codes: H02J 3/50 Controlling the sharing of the out-of-phase component

Abstract

A method of operating a power system is provided. The power system has a plurality of generator sets and a bus. The method monitors the bus and generator sets disconnected from the bus. The method supplies to a control device information associated with the operating state of each of the generator sets and the bus. The method determines a relative frequency mismatch and a relative phase mismatch between the frequency and phase of the bus and a generator, and generates a frequency speed bias and a phase speed bias for the generator. The method adds the frequency and phase speed biases to form a total speed bias, tunes the total speed bias to make the frequency and phase speed biases combine in a complementary manner, and connects the generator to the bus when the voltage, frequency, and phase of the generator are within a permissible range of the bus.

Claims

1. A method of operating a power system, the power system including a plurality of generator sets and a bus, each generator set including at least a generator and an engine, the method comprising:

monitoring at least one generator set that is disconnected from the bus;

monitoring one of the bus and at least one reference generator set that is connected to the bus;

supplying, to a control device, information associated with the operating state of each of the generator sets and information associated with the bus;

determining a relative frequency mismatch between the frequency of at least one of the bus and the reference generator set and the frequency of the disconnected generator to generate a frequency speed bias for the disconnected generator set;

determining a relative phase mismatch between the phase of at least one of the bus and the reference generator set and the phase of the disconnected generator set to generate a phase speed bias for the disconnected generator set;

adding the frequency speed bias and the phase speed bias to form a total speed bias;

tuning the total speed bias to cause the frequency speed bias and the phase speed bias to combine in a complementary manner; and

connecting the disconnected generator set to the bus when the voltage, frequency, and phase of the disconnected generator set are within a permissible range of the voltage, frequency, and phase of at least one of the bus and the reference generator set.

2. The method of claim 1, wherein determining the relative frequency mismatch between the frequency of at least one of the bus and the reference generator set and the frequency of the disconnected generator set includes comparing the outputs of a first integrator with an input of a fixed value based on whether the disconnected generator set instantaneous voltage is positive, and a second integrator with an input of a fixed value based on whether one of the bus and reference generator set instantaneous voltage is positive, to determine the relative frequency mismatch of the disconnected generator set and one of the bus and reference generator set.

3. The method of claim 1, further including restricting the maximum level of the frequency speed bias.

4. The method of claim 1, wherein determining the relative phase mismatch includes determining whether the phase of the disconnected generator set lags or leads the phase of one of the bus and reference generator set.

5. The method of claim 1, wherein determining the relative phase mismatch between the phase of at least one of the bus and the reference generator set and the phase of the disconnected generator includes applying XOR logic to a logic signal of the disconnected generator voltage waveform and a logic signal of at least one of the bus and the reference generator set voltage waveform.

6. The method of claim 1, further including restricting the maximum level of the phase speed bias.

7. The method of claim 1, further including controlling a plurality of generators with a synchronization and load sharing control including a plurality of control devices, each control device being associated with one of the plurality of generators.

8. The method of claim 1, wherein tuning the total speed bias includes allowing the frequency of the disconnected generator to come within a predetermined amount of the frequency of at least one of the bus and the reference generator set before adding the frequency speed bias and the phase speed bias to form the total speed bias.

9. The method of claim 8, further including connecting the disconnected generator to the bus, after the voltage of the disconnected generator matches the voltage of at least one of the bus and the reference generator set by a predetermined amount.

10. A power system, comprising:

a bus;

a plurality of generator sets operable to supply electricity to an electric power load, at least one of which is a reference generator set connected to the bus;

a generator set including at least a generator and an engine;

a frequency speed bias circuit, configured to input a voltage waveform from the generator set, input a voltage waveform from one of the bus and the reference generator set, generate a relative frequency mismatch, and output a frequency speed bias from a first PID controller;

a phase speed bias circuit, configured to input a voltage waveform from the generator set, input a voltage waveform from one of the bus and the reference generator set, generate a signal proportional to a phase error between the generator set and one of the bus and the reference generator set, and output a phase speed bias from a second PID controller;

a total speed bias circuit, configured to add the frequency speed bias and the phase speed bias to form a total speed bias and tune the total speed bias to make the frequency speed bias and the phase speed bias combine in a complementary manner; and

a generator breaker configured to connect the generator to the bus when the voltage, frequency, and phase of the generator are within a permissible range of the voltage, frequency, and phase of one of the bus and the reference generator set.

11. The power system of claim 10, wherein the frequency speed bias circuit includes a first integrator and a second integrator, the input to the first integrator being a fixed value based on whether the generator set instantaneous voltage is positive and the input to the second integrator being a fixed value based on whether one of the bus and the reference generator set instantaneous voltage is positive, whereby the difference between the first integrator and the second integrator outputs, just before reset of the first integrator and second integrator, determines the relative frequency mismatch of the generator and one of the bus and the reference generator set.

12. The power system of claim 10, further including a signal limiter that restricts the amount of instantaneous change the frequency speed bias can apply to the speed of an engine of the generator.

13. The power system of claim 10, wherein the phase speed bias circuit is configured to apply XOR logic to a logic signal of the generator voltage waveform and a logic signal of one of the bus and the reference generator set voltage waveform.

14. The power system of claim 13, wherein the phase speed bias circuit includes both an XOR output immediately after a leading edge occurrence of the logic signal of one of the bus and the reference generator set voltage waveform, and a logic signal of one of the bus and the reference generator set voltage waveform output detector, using an AND logic function block to compare the results to determine if the phase of the generator lags or leads the phase of one of the bus and the reference generator set.

15. The power system of claim 10, further including a signal limiter that restricts the amount of instantaneous change the phase speed bias can apply to the speed of an engine of the generator.

16. The power system of claim 10, wherein the power system includes a synchronization and load sharing control with a plurality of control devices, each control device being associated with one or more of the plurality of generators and each control device configured to control one or more generators.

17. The power system of claim 10, wherein the total speed bias circuit includes allowing the frequency of the generator to come within a predetermined amount of the frequency of one of the bus and the reference generator set before starting to account for the phase speed bias in the total speed bias and a signal limiter to restrict the amount of instantaneous change the total speed bias can apply to the speed of an engine of the generator.

18. The power system of claim 17, further including the voltage of the generator to match the voltage of one of the bus and the reference generator set by a predetermined amount before connecting the generator set to the bus.

19. A power system, comprising:

a bus;

a plurality of generator sets operable to supply electricity to an electric power load at least one of which is a reference generator set connected to the bus;

a disconnected generator set including at least a generator and an engine;

a synchronization and load sharing control, comprising;

a frequency speed bias circuit, including a bandpass filter, a hard limiter, an integrator which resets on leading edge, a hold block, a summer, and a first PID controller, the frequency speed bias circuit outputting a frequency speed bias;

a phase speed bias circuit, including a bandpass filter, a hard limiter, an integrator which resets on leading edge, a first logic function block, a hold block, a leading edge detector, a second logic function block, and a second PID controller, the phase speed bias circuit outputting a phase speed bias;

a total speed bias circuit, including a summer and a limiter, the total speed bias circuit outputting a total speed bias; and

a generator breaker to connect the disconnected generator set to the bus when the voltage, frequency, and phase of the disconnected generator set are within a permissible range of the voltage, frequency, and phase of one of the bus and the reference generator set.

20. The power system of claim 19, wherein the synchronization and load sharing control has a plurality of frequency speed bias circuits, phase speed bias circuits, and total speed bias circuits.