Active power line conditioner with synchronous transformation control

• US 5,355,025 A
• Filed: 12/14/1993
• Issued: 10/11/1994
• Est. Priority Date: 10/30/1992
• Status: Expired due to Term

• Current Assignee: Electric Power Research Institute Incorporated
• Original Assignee: Electric Power Research Institute Incorporated
• Inventors: Moran, Steven A., Brennen, Michael B.
• Primary Examiner(s): Sterrett, Jeffrey L.
• Application Number:
  US08/167,324
• Time in Patent Office: 301 Days
• Field of Search: 307/105, 318/806, 323/207, 363/39, 363/40, 363/44
• US Class Current: 307/105
• CPC Class Codes: G05F 1/70 Regulating power factor; Regulating reactive current or power
• CPC Class Codes: H02J 3/01 Arrangements for reducing harmonics or ripples
• CPC Class Codes: H02J 3/1814 wherein al least one reactive element is actively controlled by a bridge converter, e.g. unified power flow controllers [UPFC]
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]
• CPC Class Codes: Y02E 40/40 Arrangements for reducing harmonics

Abstract

An improved active power line conditioner is disclosed. The active power line conditioner includes a series inverter coupled to an energy input source, and a parallel inverter coupled to a non-linear load. The non-linear load is powered by a three phase load current which includes fundamental components and harmonic components. An energy storage element is electrically connected between the series inverter and the parallel inverter. The series inverter is controlled by a series filter controller which performs synchronous transformations on the load current to generate a series filter feedforward signal corresponding to the fundamental components of the load current. The series filter feedforward signal is applied to the series inverter to generate sinusoidal input currents for the non-linear load. The parallel inverter is controlled by a parallel filter controller which performs synchronous transformations on the load current or series inverter input voltages to generate a parallel filter signal corresponding to the harmonic ripple components of the load current. The parallel filter signal is applied to the parallel inverter to generate sinusoidal voltages for the non-linear load.

Claims

1. An active power line conditioner comprising:

a series inverter coupled to an energy input source;

a parallel inverter coupled to a load, said load being powered by a three phase load current which includes fundamental components and harmonic components;

an energy storage element electrically connected between said series inverter and said parallel inverter;

series filter controller means, coupled to said series inverter, for generating a series filter feedforward signal corresponding to said fundamental component of said load current, said series filter controller means utilizing a synchronous transformation mechanism for processing said load current to generate said series filter feedforward signal; and

parallel filter controller means, coupled to said parallel inverter, for producing a parallel filter signal corresponding to said harmonic ripple components of said load current, said parallel filter controller means utilizing a synchronous transformation mechanism for processing output voltages from said load to generate said parallel filter signal;

wherein said series filter feedforward signal is applied to said series inverter to generate sinusoidal input currents for said load, and said parallel filter signal is applied to said parallel inverter to generate sinusoidal voltages for said load.

2. The apparatus of claim 1 wherein said synchronous transformation mechanism includes

a 3-to-2 phase transformer which receives said three phase load current and resolves it into a single current vector which rotates at a current vector constant frequency with respect to a stationary reference frame with an i_ds axis and an i_qs axis;

a stationary-to-rotating transformer which receives said current vector and generates a reference frame with an i_d axis and an i_q axis which rotates at said current vector constant frequency, said stationary-to-rotating transformer converting said current vector into I_d and I_q signals, each of which includes a dc component, corresponding to said fundamental components of said load current, and superimposed ac components, corresponding to said load current harmonics; and

a low pass filter for filtering said superimposed ac components of said I_d and I_q signals to generate I_df and I_qf signals corresponding to said fundamental components of said load current.

3. The apparatus of claim 2 further comprising

a rotating-to-stationary transformer to perform the inverse operation of said stationary-to-rotating transformer on said I_df and I_qf signals to generate I_ds '"'"' and I_qs '"'"' signals;

and

a 2-to-3 phase transformer to perform the inverse operation of said 3-to-2 phase transformer on said I_ds '"'"' and I_qs '"'"' signals, thereby generating a three phase fundamental reference signal corresponding to said fundamental components of said load current.

4. The apparatus of claim 3 further comprising means for adding a link restoration signal to said three phase fundamental reference signal, said link restoration signal providing a sinusoidal current reference to compensate for energy depleted from said energy storage element.

5. The apparatus of claim 3 wherein said three phase fundamental reference signal is applied to a series current processor where a series input current is subtracted from said three phase fundamental reference signal to generate a series filter error signal.

6. The apparatus of claim 5 wherein said series filter error signal is applied to a pulse-width modulator which generates drive signals for said series filter inverter.

7. The apparatus of claim 2 further comprising means for adding a fundamental regulating current to said I_df and I_qf signals.

8. The apparatus of claim 1 further including an energy storage controller for generating a link restoration signal, said energy storage controller multiplying a voltage error signal by instantaneous output voltage reference signals.

9. The apparatus of claim 8 wherein said voltage error signal is generated by subtracting an energy storage element voltage from an energy storage element reference voltage.

10. The apparatus of claim 8 wherein said instantaneous output voltage reference signals are established by a rotating-to-stationary transformer and a 2-to-3 phase transformer which operate on first and second output voltage reference signals.

11. The apparatus of claim 1 wherein said synchronous transformation mechanism includes

a 3-to-2 phase transformer which receives a three phase output voltage from said non-linear load and resolves it into a single voltage vector which rotates at a voltage vector constant frequency with respect to a stationary reference frame with a v_ds axis and a v_qs axis;

and

a stationary-to-rotating transformer which receives said voltage vector and generates a reference frame with a v_d axis and a v_q axis which rotates at said voltage vector constant frequency, said stationary-to-rotating transformer converting said voltage vector into v_d and v_q signals, each of which includes a dc component, corresponding to said fundamental components of said load voltage, and a superimposed ac component, corresponding to load harmonics present in said output voltage.

12. The apparatus of claim 11 further comprising

a rotating-to-stationary transformer to perform the inverse operation of said stationary-to-rotating transformer on said v_d and v_q signals to generate V_ds '"'"' and V_qs '"'"' signals;

and

a 2-to-3 phase transformer to perform the inverse operation of said 3-to-2 phase transformer on said v_d and v_q signals, thereby generating a three phase fundamental parallel reference signal corresponding to said fundamental components of said load current.

13. The apparatus of claim 12 further comprising a first mixer for adding said three phase fundamental parallel reference signal with feedback signals corresponding to said load current.

14. The apparatus of claim 13 further comprising a second mixer for adding said three phase fundamental parallel reference signal with a link restoration signal which compensates for energy depleted from said energy storage element.

15. The apparatus of claim 14 further comprising a third mixer for adding said three phase fundamental parallel reference signal with the inverse of a parallel inverter feedback signal to generate a parallel filter error signal.

16. The apparatus of claim 15 wherein said parallel filter error signal is applied to a pulse-width modulator which generates drive signals for said parallel filter inverter.

17. The apparatus of claim 1 wherein said synchronous transformation mechanism includes

a 3-to-2 phase transformer which receives said three phase load current and resolves it into a single current vector which rotates at a current vector constant frequency with respect to a stationary reference frame with an i_ds axis and an i_qs axis;

a stationary-to-rotating transformer which receives said current vector and generates a reference frame with an i_d axis and an i_q axis which rotates at said current vector constant frequency, said stationary-to-rotating transformer converting said current vector into I_d and I_q signals, each of which includes a dc component, corresponding to said fundamental components of said load current, and a superimposed ac component, corresponding to said load current harmonics; and

a low pass filter for filtering said superimposed ac components of said I_d and I_q signals to generate I_df and I_qf signals corresponding to said fundamental components of said load current.

18. The apparatus of claim 17 further comprising

a rotating-to-stationary transformer to perform the inverse operation of said stationary-to-rotating transformer on said I_df and I_qf signals to generate I_df-s and I_qf-s signals;

and

a 2-to-3 phase transformer to perform the inverse operation of said 3-to-2 phase transformer on said I_df-s and I_qf-s signals, thereby generating a three phase fundamental reference signal corresponding to said fundamental components of said load current.

19. The apparatus of claim 18 further comprising

a mixer for subtracting said three phase fundamental reference signal from instantaneous load current signals to generate a load harmonic error signal.

20. The apparatus of claim 19 wherein said load harmonic error signal is applied to a pulse-width modulator which generates drive signals for said parallel filter inverter.

21. The apparatus of claim 1 further including a vector phase-locked loop comprising:

a 3-to-2 phase transformer for continuously producing an instantaneous vector sum for first and second serial inverter input voltage signals;

a phase detector, coupled to said 3-to-2 phase transformer, for sequentially establishing, from said first and second serial inverter input voltage signals, a plurality of relative phase values Θ

between said voltage signals;

a timing mechanism for selecting one of said relative phase values Θ

to form a selected phase value; and

means for defining a sin Θ and

a cos Θ

value corresponding to said selected phase value.

22. The apparatus of claim 1 wherein said parallel filter controller means generates an intermediate parallel filter signal corresponding to said fundamental components of said load current, said intermediate parallel filter signal being subtracted from an instantaneous fundamental load current signal to generate said parallel filter signal corresponding to said harmonic ripple components of said load current.

23. A power filter circuit comprising:

a phase-locked loop for establishing first and second relative phase error signals for two voltage reference signals;

a parallel inverter coupled to a load, said load being powered by a single phase load current which includes a fundamental component and harmonic components;

a parallel filter controller, coupled to said parallel inverter and said phase-locked loop, said parallel filter controller including;

means for multiplying said first and second relative phase error signals with said load current to generate a real current signal and a reactive current signal, said real and reactive current signals each including a dc component and an ac component;

first and second low pass filters, coupled to said multiplying means, for respectively filtering said real and reactive current signals to yield first and second dc signals corresponding to said dc components of said real and reactive current signals;

first and second multipliers for multiplying said first and second dc signals with said load current signals to respectively produce an instantaneous fundamental load active current signal and an instantaneous load reactive current signal;

an adder for adding said instantaneous fundamental load active current signal with said instantaneous load reactive current to generate an instantaneous fundamental load current;

a subtractor for subtracting said instantaneous fundamental load current from said load current to generate a load harmonic ripple component signal;

wherein said load harmonic ripple component signal is applied to said parallel filter to generate sinusoidal voltages for said load.

24. The apparatus of claim 23 wherein said phase-locked loop includes:

a 3-to-2 phase transformer for continuously producing an instantaneous vector sum for said voltage reference signals;

a phase detector, coupled to said 3to-2 phase transformer, for sequentially establishing, from said voltage reference signals, a plurality of relative phase values Θ

between said voltage reference signals;

a timing mechanism for selecting one of said relative phase values Θ

to form a selected phase value;

means for defining a sin Θ and

a cos Θ

value corresponding to said selected phase value, said sin Θ

value corresponding to said first relative phase error signal and said cos Θ

value corresponding to said second relative phase error signal.

25. A method of operating an active power line conditioner which provides a three phase load current, which includes fundamental components and harmonic components, to a load, said active power line conditioner being of the type which includes a series inverter coupled to a parallel inverter through an energy storage link, said method comprising the steps of:

generating a series filter feedforward signal corresponding to fundamental components of said load current by executing a synchronous transformation on said load current;

applying said series filter feedforward signal to said series inverter to generate sinusoidal input currents for said load;

producing a parallel filter signal corresponding to said harmonic ripple components of said load current by performing a synchronous transformation on output voltages from said load; and

feeding said parallel filter signal to said parallel inverter to generate sinusoidal voltages for said load.

26. The method of claim 25 further comprising the step of:

generating a link restoration signal by multiplying a voltage error signal by instantaneous output voltage reference signals.

27. The method of claim 26 wherein said voltage error signal is generated by subtracting an energy storage element voltage from an energy storage element reference voltage.

28. The method of claim 25 wherein said generating step includes the steps of:

resolving said three phase load current into a single current vector which rotates at a current vector constant frequency with respect to a stationary reference frame with an i_ds axis and an i_qs axis;

generating from said current vector a reference frame with an i_d axis and an i_q axis which rotates at said current vector constant frequency, said stationary-to-rotating transformer converting said current vector into I_d and I_q signals, each of which includes a dc component, corresponding to said fundamental components of said load current, and superimposed ac components, corresponding to said load current harmonics; and

low pass filtering said superimposed ac components of said I_d and I_q signals to generate I_df and I_qf signals corresponding to said fundamental components of said load current.

29. The method of claim 28 further comprising the steps of

performing the inverse operation of said resolving step on said I_df and I_qf signals to generate I_ds '"'"' and I_qs '"'"' signals;

and

executing the inverse operation of said generating step on said I_ds '"'"' and I_qs '"'"' signals, thereby generating a three phase fundamental reference signal corresponding to said fundamental components of said load current.

30. The method of claim 29 further including the step of applying said three phase fundamental reference signal to a series current processor where a series input current is subtracted from said three phase fundamental reference signal to generate a series filter error signal.

31. The method of claim 30 further comprising the step of applying said series filter error signal to a pulse-width modulator which generates drive signals for said series filter inverter.

32. The method of claim 31 further comprising the step of adding a fundamental regulating current to said I_df and I_qf signals.

33. The method of claim 32 further comprising the step of adding a link restoration signal to said three phase fundamental reference signal, said link restoration signal providing a sinusoidal current reference to compensate for energy depleted from said energy storage link.

34. The method of claim 25 wherein said producing step includes the steps of:

receiving a three phase output voltage from said load and resolving it into a single voltage vector which rotates at a voltage vector constant frequency with respect to a stationary reference frame with a V_ds axis and a V_qs axis; and

generating a reference frame with a V_d axis and a V_q axis which rotates at said voltage vector constant frequency, said generating step converting said voltage vector into V_d and V_q signals, each of which includes a dc component corresponding to said fundamental components of said load voltage, and a superimposed ac component, corresponding to load harmonics present in said output voltage.

35. The method of claim 34 further comprising the steps of:

performing the inverse operation of said receiving step on said V_d and V_q signals to generate V_ds and V_qs signals; and

executing the inverse operation of said generating step on said V_d and V_q signals, thereby generating a three phase fundamental parallel reference signal corresponding to said fundamental components of said load current.

36. The method of claim 35 further comprising the step of:

adding said three phase fundamental parallel reference signal to feedback signals corresponding to said load current.

37. The method of claim 36 further comprising the step of:

adding said three phase fundamental parallel reference signal to a link restoration signal which compensates for energy depleted from said energy storage element.

38. The method of claim 37 further comprising the step of:

adding said three phase fundamental parallel reference signal to the inverse of a parallel inverter feedback signal to generate a parallel filter error signal.

39. The method of claim 38 further comprising the step of:

applying said parallel filter error signal to a pulse-width modulator which generates drive signals for said parallel filter inverter.

40. The method of claim 25 further comprising the steps of:

continuously producing an instantaneous vector sum for first and second serial inverter input voltage signals;

sequentially establishing from said first and second serial inverter input voltage signals a plurality of relative phase values e between said voltage signals;

selecting one of said relative phase values Θ

to form a selected phase value; and

defining a sin Θ and

a cos Θ

value corresponding to said selected phase value.