Integrated control system and method for controlling mode, synchronization, power factor, and utility outage ride-through for micropower generation systems

• US 20010048290A1
• Filed: 07/03/2001
• Published: 12/06/2001
• Est. Priority Date: 08/26/1998
• Status: Active Grant

• Current Assignee: Perfect Galaxy International Limited
• Original Assignee: Thomas C. Matty, Thomas C. Underwood, William B. Hall
• Inventors: Matty, Thomas C., Hall, William B., Underwood, Thomas C.
• Granted Patent: US 6,380,719 B2
• Time in Patent Office: Days
• US Class Current: 322/20
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/40 Synchronising a generator for connection to a network or to another generator

Abstract

An integrated system for comprehensive control of an electric power generation system utilizes state machine control having particularly defined control states and permitted control state transitions. In this way, accurate, dependable and safe control of the electric power generation system is provided. Several of these control states may be utilized in conjunction with a utility outage ride-through technique that compensates for a utility outage by predictably controlling the system to bring the system off-line and to bring the system back on-line when the utility returns. Furthermore, a line synchronization technique synchronizes the generated power with the power on the grid when coming back on-line. The line synchronization technique limits the rate of synchronization to permit undesired transient voltages. The line synchronization technique operates in either a stand-alone mode wherein the line frequency is synthesized or in a connected mode which sensed the grid frequency and synchronizes the generated power to this senses grid frequency. The system also includes power factor control via the line synchronization technique or via an alternative power factor control technique. The result is an integrated system providing a high degree of control for an electric power generation system.

Claims

1. A state machine having a plurality of control states for electric power transformation in a device having a full wave rectifier connected to a generator, a DC bus connected to the output of the full wave rectifier, an inverter connected to the DC bus, an inductor unit connected to the output of the inverter, a first contactor unit selectively connecting and disconnecting the inductor unit to and from a grid, and a precharge circuit connected to the DC bus;

the state machine comprising;

an initialization state for initializing the state machine;

a first neutral state for idling the state machine while monitoring commands and system parameters;

a pre-charge state for enabling and monitoring the precharge circuit to pre-charge the DC bus to a pre-charge DC voltage;

a second neutral state for disabling the pre-charge circuit and closing the first contactor;

an engine start state for verifying DC link voltage, sending a speed command to the start inverter unit, enabling the start inverter, updating the speed command being sent to the start inverter unit, and determining successful engine start;

a power on-line state for enabling a current mode in said inverter and controlling the inverter to deliver power at a level determined by a power level command;

a power off-line state for opening the first contactor, switching the inverter to a voltage mode, and setting the power level command to a nominal power level;

a shutdown state for disabling the inverter, opening the first contactor after waiting for a cool-down time period, and reinitializing the state machine,

a state controller for controlling the following permitted transitions between said control states;

said initialization state →

said first neutral state ←

→

said pre-charge state →

said second neutral state ←

→

said start engine state ←

→

said power on-line state →

said power off-line state →

said shutdown state.

2. The state machine according to

claim 1

, further comprising:

a third neutral state for receiving a command including the power level command and a shutdown command;

said state controller permitting the following additional state transitions;

said start engine state →

said third neutral state ←

→

said power on-line state.

3. The state machine according to

claim 1

, said state controller permitting the following additional state transitions:

neutral state →

pre-charge state upon receiving a pre-charge start command;

precharge state →

neutral state when a pre-charge rate at which said pre-charge circuit charges the DC bus is not within tolerance values or when the DC bus voltage does not achieve the pre-charge DC voltage.

4. The state machine according to

claim 1

, said state controller permitting the following additional state transitions:

pre-charge state →

start engine state upon successfully achieving the precharge DC voltage on the DC bus and receipt of a start engine command.

5. The state machine according to

claim 1

, said state controller permitting the following additional state transitions:

start engine state →

third neutral state upon receiving a zero power level command,

third neutral state →

power on-line state upon successful engine start and receiving a nonzero power level command,

power on-line state →

power off-line state upon receipt of an off-line command or upon a failed diagnostic test or a grid outage,

power off-line →

third neutral state upon successful diagnostic tests for a predetermined time period,

third neutral state →

shutdown upon receiving a shutdown command,

shutdown state →

said first neutral state upon receiving restart command, and

said second neutral →

shutdown state upon a fault condition or shutdown command.

6. The state machine according to

claim 1

,

the device further including, an emergency stop input,

said state machine controller opening the first contactor unit and switching the control state to said shutdown state upon receipt of an emergency stop signal from the emergency stop input.

7. The state machine according to

claim 1

,

said pre-charge state and said start engine state respectively returning to said first and second neutral states upon failure of a pre-charge cycle and a start engine cycle.

8. The state machine according to

claim 2

,

said power on-line state returning to said third neutral step when the power level command indicates zero requested power.

9. The state machine according to

claim 1

,

wherein said initialization, pre-charge, power on-line, power off-line, and/or shutdown states perform diagnostic tests on the device,

said state controller controlling state transitions based on results of the diagnostic tests.

10. The state machine according to

claim 1

, the device further including an engine for driving said generator, an engine control unit connected to said engine, and a start inverter connected to the DC bus and to said generator, said engine control unit controlling said engine ignition and fuel for the engine, said engine start state controlling said start inverter to drive the generator as a motor to thereby spin the engine and permit starting thereof, said engine start state also sending an engine start command to the engine control unit.

11. The state machine according to

claim 10

,

wherein said initialization, pre-charge, power on-line, power off-line, and/or shutdown states monitor the engine,

said state controller controlling state transitions based on results of the diagnostic tests.

12. The state machine according to

claim 1

,

said pre-charge state also diagnosing the inverter,

said state controller controlling state transitions based on results of the diagnostic tests.

13. The state machine according to

claim 1

,

said engine start state determining successful engine start by monitoring current drawn from the DC bus by the start inverter and engine speed wherein if the current drawn falls below a current limit value and an engine speed exceeds a speed limit then engine start is successful.

14. A method of controlling real and reactive power developed by a main inverter in an electrical power generation control device, comprising the steps of:

sampling the three-phase currents output from said inverter,

transforming the sampled three-phase current data to two-phase current data,

transforming the two-phase current data to a rotating reference frame,

controlling an output voltage according to a comparison result between a DC reference signal having a real and a reactive reference signal component,

transforming the output voltage to a stationary reference frame,

transforming the stationary reference frame output voltage to a three-phase reference signal, and

controlling said inverter based on the three-phase reference signal,

wherein the DC reference signal designates the real and reactive power output by the controlled inverter.

15. The method according to

claim 14

, further comprising the step of:

connecting the electrical power generation control device to a grid,

determining the value of the DC reference signal according to utility power factor request data supplied by a utility feeding the grid.

16. The method according to

claim 14

, further comprising the step of:

determining the value of the DC reference signal according to a power factor command received from an operator interface.

17. The method according to

claim 14

,

said output voltage controlling step utilizing a proportional and integral control method.

18. The method according to

claim 14

,

said inverter control step generating a PWM control signal based on the three-phase reference signal to control the inverter output.

19. An apparatus for synchronizing a line frequency of power output from an inverter with a grid frequency, comprising:

a grid frequency sensor connected to the grid and outputting a grid frequency signal indicative of the grid frequency;

an A/D converter sampling the grid frequency signal from said grid frequency signal generator;

a signal processor controlling said A/D converter to perform A/D conversion of the grid frequency signal at a reference frequency;

a clock connected to said digital signal processor for establishing the reference frequency and sending the reference frequency to said digital signal processor;

a first counter for storing a frequency count, said first counter updating the frequency count value according to the reference frequency;

an edge detector for detecting a rising or falling edge of the digitally converted grid frequency;

a second counter for storing a synchronization value, said second counter adding a count value to the synchronization value according to the reference frequency;

a correct frequency range detector detecting whether the frequency count is within a frequency range;

a frequency range error corrector for setting the count value to a predetermined count value when said correct frequency range detector detects that the frequency count is outside the frequency range;

a count value calculator for calculating the count value by dividing 360°

by the frequency count when said edge detector detects the rising or falling edge;

a frequency count resetter for resetting the frequency count value to zero when said edge detector detects the rising or falling edge and said count value calculator completes the calculation of the count value;

a synchronization detector detecting synchronization when the synchronization value is substantially zero or 360°

; and

a synchronization value adjuster for adjusting the synchronization value by an error value.

20. The apparatus according to

claim 19

, further comprising:

an iterator for iterating the functions performed by the apparatus until said synchronization detector detects correct synchronization.

21. The apparatus according to

claim 19

,

said synchronization value adjuster calculating the error value based on the synchronization value,

an error limiter limiting the error value to a predetermined range of error values thereby preventing large phase shift jumps.

22. The apparatus according to

claim 20

, further comprising:

a pulse width modulation signal generator for generating pulse width modulation signals based on the synchronization value and sending the pulse width modulation signals to the inverter,

wherein the output of the inverter is controlled by the pulse width modulation signals.

23. The apparatus according to

claim 22

, further comprising;

a power factor adjuster for adding a power factor phase shift value to the synchronization value.

24. The apparatus according to

claim 23

,

said grid frequency sensor including:

a transformer connected to the grid,

a low pass filter connected to said transformer, and

an optical isolator connected to said low pass filter, said optical isolator outputting a uni-polar square wave having a frequency equal to the grid frequency,

said A/D converter sampling the uni-polar square wave from said optical isolator, and

said digital signal processor controlling said A/D converter to initiate A/D conversion of the uni-polar square wave at a reference frequency.

25. A method for synchronizing a line frequency of power output from an inverter with a grid frequency, comprising:

detecting a grid frequency signal;

sampling the grid frequency signal;

controlling said sampling step to sample the grid frequency signal at a reference frequency;

establishing the reference frequency;

storing a frequency count value in a first counter,

updating the frequency count value stored in the first counter according to the reference frequency;

an edge detecting step for detecting a rising or falling edge of the sampled grid frequency;

storing a synchronization value in a second counter,

adding a count value to the synchronization value according to the reference frequency;

detecting whether the frequency count is within a frequency range;

a frequency range error correcting step for setting the count value to a predetermined count value when said detecting step detects that the frequency count is outside the frequency range;

calculating the count value by dividing 360°

by the frequency count when said edge detecting step detects the rising or falling edge;

resetting the frequency count value to zero when said edge detecting step detects the rising or falling edge and said calculating step completes the calculation of the count value;

detecting synchronization when the synchronization value is substantially zero or 360°

; and

adjusting the synchronization value by an error value.

26. The method according to

claim 25

, further comprising the step of:

iterating the functions performed by the method steps until said synchronization detecting step detects correct synchronization.

27. The method according to

claim 25

,

said adjusting step calculating the error value based on the synchronization value,

an error limiting step limiting the error value to a predetermined range of error values thereby preventing large phase shift jumps.

28. The method according to

claim 26

, further comprising the step of:

generating pulse width modulation signals based on the synchronization value, controlling the output of the inverter with the pulse width modulation signals.

29. The method according to

claim 26

, further comprising the step of:

inputting a power factor phase shift value, and

adding the power factor phase shift value to the synchronization value.

30. A method of controlling a device having a full wave rectifier connected to a generator, a DC bus connected to the output of the full wave rectifier, an inverter connected to the DC bus, an inductor unit connected to the output of the inverter, and a first contactor unit selectively connecting and disconnecting the inductor unit to and from a grid, the method comprising the steps of:

commanding the inverter to perform online voltage control;

detecting a fault condition indicating a fault in the device or the grid

opening the first contactor;

clearing a time counter;

setting a mode to an offline mode; and

commanding the inverter to perform offline voltage control;

said opening, clearing, setting and commanding offline voltage control steps being performed when said detecting step detects the fault condition or continues to detect the fault condition.

31. The method according to

claim 30

, further comprising the steps of:

determining the mode when said detecting step detects no fault condition; and

incrementing the time counter when said mode determining step determines that the mode is the offline mode.

32. The method according to

claim 31

, further comprising the steps of:

checking the time counter for expiration thereof;

disabling the inverter;

closing the contactor; and

setting the mode to the online mode,

wherein said disabling, closing and setting the online mode steps are performed when said checking step determines that the time counter has expired.

33. The method according to

claim 32

, further comprising the steps of:

determining the mode when said detecting step continues to detect no fault condition;

commanding the inverter to perform online current control; and

enabling the inverter,

said commanding online current control step and said enabling step being performed when said mode determination step determines that the mode is the online mode.

34. The method according to

claim 33

, further comprising the step of:

iterating the method.

35. The method according to

claim 30

,

wherein the fault condition includes a fault in the device, loss of phase in the grid, loss of utility authorization, grid voltage out of range, or loss of synchronization between the device and the grid.

36. The method according to

claim 30

,

inputting an offline command,

wherein upon receipt of the offline command said detecting step detects the fault condition.

37. The method according to

claim 30

, wherein the predetermined time period is approximately 30 seconds.