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

• US 6,316,918 B1
• Filed: 03/27/2000
• Issued: 11/13/2001
• Est. Priority Date: 08/26/1998
• Status: Expired due to Term

• Current Assignee: Perfect Galaxy International Limited
• Original Assignee: Satcon Technology Corporation
• Inventors: Hall, William B., Matty, Thomas C., Underwood, Thomas C.
• Primary Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US09/535,541
• Time in Patent Office: 596 Days
• Field of Search: 307/85, 307/86, 307/87, 290/1.R, 290/40.B, 322/7, 322/8, 322/20, 322/29
• 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. 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.

2. The apparatus according to claim 1, further comprising:

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

3. The apparatus according to claim 1,

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.

4. The apparatus according to claim 2, 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.

5. The apparatus according to claim 4, further comprising;

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

6. The apparatus according to claim 5,

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.

7. 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.

8. The method according to claim 7, further comprising the step of:

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

9. The method according to claim 7,

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.

10. The method according to claim 8, 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.

11. The method according to claim 8, further comprising the step of:

inputting a power factor phase shift value, and

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