Renewable energy site reactive power control

• US 9,728,974 B2
• Filed: 10/10/2013
• Issued: 08/08/2017
• Est. Priority Date: 10/10/2013
• Status: Active Grant

• Current Assignee: TMEIC Corp. Americas
• Original Assignee: Tmeic Corporation (Toshiba Corporation)
• Inventors: Rudolph, Benjamin D., Bixel, Paul S.
• Primary Examiner(s): Tan, Richard
• Application Number:
  US14/050,928
• Publication Number:
  US 20150102674A1
• Time in Patent Office: 1,398 Days
• Field of Search: 307 52
• CPC Class Codes: H02J 3/16 by adjustment of reactive power
• CPC Class Codes: H02J 3/18 Arrangements for adjusting, eliminating or compensating reactive power in networks for adjustment of voltage H02J3/16
• CPC Class Codes: H02J 3/1842 wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02J 3/50 Controlling the sharing of the out-of-phase component
• CPC Class Codes: H02M 1/4233 using a bridge converter comprising active switches
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02E 40/20 Active power filtering [APF]
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

Methods, systems, controller devices, and computer program products for reactive power control at a renewable energy site are provided. Embodiments address dynamic performance problems associated with control loop delay and the changing modes of operation for meeting utility voltage and reactive power constraints. Provided is a method for reactive power control involving: (a) determining a site-wide reactive power command comprised by a sum of a reactive power feedforward or compensation term and an integrator term; and (b) distributing the site-wide reactive power command among inverters. Embodiments can include a reactive power control term based on the sum of a single integrator and reactive power compensation term, an integrator anti-windup mechanism based on the status of individual inverters, a means for decreasing detrimental effects of loop delay during reactive power reference changes, and/or a means of implementing voltage and power factor limits with smooth transfer between reactive power operating regions.

Claims

1. A method for reactive power control for a renewable energy site that comprises one or more inverters, the method comprising:

(a) determining a site-wide reactive power command (Q_COM) comprised by a sum of a reactive power error integrator term (Q_INT) and a reactive power compensation term (Q_COMP) that is a function of a power-factor reference (PF_REF) real power feedback (P_FBK) and a reactive power offset (LRPCoffset); and

(b) distributing the site-wide reactive power command among the one or more inverters.

2. The method of claim 1, wherein the determining of the site-wide reactive power command is based on a power factor control subject to voltage threshold control or is based on a voltage control subject to power factor threshold control.

3. The method of claim 1, wherein the determining of the site-wide reactive power command involves choosing between a power factor control mode and a voltage control mode and is performed using a linear switch block with fixed transition time to transition between the power factor control mode and the voltage control mode.

4. The method of claim 1 further comprising integrator anti-windup based on either an upper limit computed at least partly from maximum feedback power, or windup enabled logic based on a number of saturated inverters.

5. The method of claim 1 further comprising:

providing for LoopDelay compensation by;

comparing a present inverter reactive power feedback signal with a corresponding reactive power reference which was computed LoopDelay seconds previously to determine if an inverter is saturated, and replacing current site reactive power reference gain used to generate site reactive power error with site reactive power reference gain generated LoopDelay seconds previously.

6. A method for reactive power control for a renewable energy site that comprises one or more inverters, the method comprising:

(1) providing data from a renewable energy site chosen from one or more of;

(a) reactive power feedback (Q_FBK);

(b) reactive power upper (Q_UL) and lower (Q_LL) limits;

(c) a voltage reference (SiteVRef);

(d) voltage feedback (V_FBK);

(e) voltage upper (V_UL) and lower (V_LL) limits;

(f) a power factor reference (PF_REF); and

(g) a power feedback (P_FBK); and

(2) calculating at least one source of error as;

(a) a reactive power error (SiteQErr) based in part on Q_FBK and P_FBK;

(b) a gain-multiplied voltage threshold error based in part on V_FBK, V_UL, and V_LL;

(c) voltage error (SiteVErr) based in part on V_FBK and Vref;

(d) a gain-multiplied reactive power threshold error based in part on Q_FBK, Q_UL, and Q_LL;

(3) selecting the source of error to be calculated based in part on choosing between a power factor control mode and a voltage control mode;

(4) inputting the error into an integrator to provide an error integral (Q_INT);

(5) calculating a reactive power compensation term (Q_COMP) based in part on PF_REF and P_FBK;

(6) adding Q_INT to Q_COMP to yield a site-wide reactive power command (Q_COM);

(7) and distributing Q_COM among the one or more individual inverters.

7. The method of claim 6, wherein Q_COMP is a linear function of site real power feedback (P_FBK) and is calculated by adding a reactive power offset (LRPCoffset) to the product of a reactive power gain multiplied by the power feedback (P_FBK).

8. The method of claim 7, wherein the data comprises inverter power feedbacks (Inv.P_FBK) and wherein the distributing of Q_COM to the individual inverters is based on the inverter power feedbacks (Inv.P_FBK) by generating an inverter reactive power command (Inv[x].QCom[k]).

9. The method of claim 6, wherein the SiteQErr is calculated:

(a) based on a reactive power reference (SiteQrefGain) based on;

10. The method of claim 6, wherein the SiteVErr is calculated based on a gain K_IV based on:

SiteVErr=(SiteVRef−

V_fbk)K_IV.

11. The method of claim 6 comprising choosing the power factor control mode and wherein when Q_FBK is within Q_UL and Q_LL, the source of error is calculated as SiteVErr, or wherein when Q_FBK exceeds Q_UL or Q_LL, the source of the error is calculated as the gain-multiplied reactive power threshold error which is a reactive power threshold error multiplied by gain K_IQ.

12. The method of claim 6 comprising choosing the voltage control mode and wherein when V_FBK is within V_UL and V_LL, the source of the error is calculated as SiteQErr, or wherein when V_FBK exceeds V_UL and V_LL, the source of the error is calculated as the gain-multiplied voltage threshold error which is a voltage threshold error multiplied by gain K_IV.

13. The method of claim 6, wherein loop delay compensation is implemented by comparing a present inverter reactive power feedback signal with a corresponding reactive power reference which was computed LoopDelay seconds previously to determine if an inverter is saturated and replacing current site reactive power reference gain used to generate the site reactive power error with site reactive power reference gain generated LoopDelay seconds previously.

14. The method of claim 6, further comprising performing loop delay compensation, wherein (a) SiteQRefGain[k] is offset by a LoopDelay term D such that SiteQRefGain[k] is replaced by SiteQRefGain[k−

D], or wherein (b) Inv[x].QCom[k] is offset by a LoopDelay term D such that Inv[x].QCom[k] is replaced by Inv[x].QCom[k−

D].

15. The method of claim 6 comprising integrator anti-windup based on either an upper limit computed at least partly from the maximum feedback power, or windup enabled logic based on a number of saturated inverters.

16. The method of claim 6, wherein the choosing between a power factor control mode and a voltage control mode is performed using a linear switch block with fixed transition time to transition between the power factor control and voltage modes.

17. The method of claim 16, wherein the linear switch block is operably configured to transition an error in and out of threshold modes at a steady slew rate by incrementing a variable, switch, by a parameter, QSlewInc, while the threshold limit input is 1 and decrementing switch by QSlewInc while the threshold limit input is 0 such that output of the linear switch block is given by:

out=in1*switch+in0*(1−

switch)

wherein switch is limited to between 0 and 1.

18. The method of claim 6, wherein the data includes a reactive power output (Inv[x].Q_FBK) and a new integrator value (Q_ERR) is calculated and a counter (NumQFree) increments by one for each inverter with Inv[x].Q_FBK substantially equal to Inv[x].QCom[k], such that Q_ERR continues to be incremented when an absolute value of the new integrator value is less than a previous integrator value, or NumQFree is greater than zero.

19. A system of reactive power control for a renewable energy site comprising:

one or more inverters; and

a reactive power controller in operable communication with at least one of the one or more inverters and operably configured to generate a site-wide reactive power command (Q_COM) by;

(1) providing data from a renewable energy site chosen from one or more of;

(a) reactive power feedback (Q_FBK);

(b) reactive power upper (Q_UL) and lower (Q_LL) limits;

(c) a voltage reference (SiteVRef);

(d) voltage feedback (V_FBK);

(e) voltage upper (V_UL) and lower (V_LL) limits;

(f) a power factor reference (PF_REF); and

(g) a power feedback (P_FBK); and

(2) calculating at least one source of error as;

(a) a reactive power error (SiteQErr) based in part on Q_FBK and P_FBK;

(b) a gain-multiplied voltage threshold error based in part on V_FBK, V_UL, and V_LL;

(c) voltage error (SiteVErr) based in part on V_FBK and Vref;

(d) a gain-multiplied reactive power threshold error based in part on Q_FBK, Q_UL, and Q_LL;

(3) selecting the source of error to be calculated based in part on choosing between a power factor control mode and a voltage control mode;

(4) inputting the error into an integrator to provide an error integral (Q_INT);

(5) calculating a reactive power compensation term (Q_COMP) based in part on PF_REF and P_FBK; and

(6) adding Q_INT to Q_COMP to yield a site-wide reactive power command (Q_COM).

20. The system of claim 19, wherein the reactive power controller is operably configured to distribute the site-wide reactive power command (Q_COM) among one or more inverters which are enabled at the site.

21. The system of claim 20, wherein the data comprises inverter power feedbacks (Inv.P_FBK) and wherein the reactive power controller is operably configured to distribute Q_COM among individual inverters based on the inverter power feedbacks (Inv.P_FBK) by generating an inverter reactive power command (Inv[x].QCom[k]).

22. A method for reactive power control for a renewable energy site that comprises one or more inverters, the method comprising:

(a) determining a site-wide reactive power command comprised by a sum of a reactive power feedforward or compensation term and an integrator term; and

(b) distributing the site-wide reactive power command among the one or more inverters;

wherein the determining of the site-wide reactive power command involves choosing between a power factor control mode and a voltage control mode and is performed using a linear switch block with fixed transition time to transition between the power factor control mode and the voltage control mode; and

further comprising integrator anti-windup based on either an upper limit computed at least partly from maximum feedback power, or windup enabled logic based on a number of saturated inverters.

23. The method of claim 22 further comprising:

providing for LoopDelay compensation by;

comparing a present inverter reactive power feedback signal with a corresponding reactive power reference which was computed LoopDelay seconds previously to determine if an inverter is saturated, and replacing current site reactive power reference gain used to generate site reactive power error with site reactive power reference gain generated LoopDelay seconds previously.