Detecting device and detecting method for detecting output impedance angle of inverter

Abstract

A method for detecting an output impedance angle of an inverter includes controlling an inverter to output a second voltage signal and a current signal based on a first voltage signal; receiving the signals, and calculating and outputting first and second active powers, and first and second reactive powers using the signals; calculating and outputting third and fourth active powers, and third and fourth reactive powers based on the first and second active powers, the first and second reactive powers, and the predetermined impedance angle; determining whether the amplitude is a constant value; if so, determining whether an absolute value of the first differential value of the third and fourth reactive powers is less than a first power reference value; if so, the impedance angle outputted from the inverter is the impedance angle; if not, setting the impedance angle as the predetermined impedance angle plus or minus the compensation angle.

Claims

1. A detecting method for detecting an output impedance angle of an inverter, comprising: (a) providing a first voltage signal, wherein the first voltage signal comprises an amplitude and a power angle, one of the amplitude and the power angle is a variable value, and the other one of the amplitude and the power angle is a constant value; (b) controlling an inverter to output a second voltage signal and a current signal based on the first voltage signal; (c) calculating and outputting a first active power, a second active power, a first reactive power, and a second reactive power based on the second voltage signal and the current signal; (d) setting an impedance angle to be an initial impedance angle; (e) setting a predetermined impedance angle to be the impedance angle; (f) calculating and outputting a third active power, a fourth active power, a third reactive power, and a fourth reactive power based on the first active power, the second active power, the first reactive power, the second reactive power, and the predetermined impedance angle; (g) determining whether the amplitude is a constant value; (h) if it is determined that the amplitude is a constant value, determining whether an absolute value of a first differential value of the third reactive power and the fourth reactive power is less than a first power reference value; (i) if it is determined that the absolute value of the first differential value is less than the first power reference value, setting the output impedance angle of the inverter as the impedance angle; (j) if it is determined that the absolute value of the first differential value is not less than the first power reference value, setting the impedance angle as a sum of the predetermined impedance angle and a compensation angle or as the predetermined impedance angle minus the compensation angle, and repeating step (e) to step (h) until it is determined that the absolute value of the first differential value is less than the first power reference value in step (i); (k) if it is determined the amplitude is not a constant value, determining whether an absolute value of the second differential value of the third active power and the fourth active power is less than a second power reference value; (l) if it is determined that the absolute value of the second differential value is less than the second power reference value, setting the output impedance angle of the inverter as the impedance angle; (m) if it is determined that the absolute value of the second differential value is not less than the second power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle or to the predetermined impedance angle minus the compensation angle, and repeating step (e), step (f), step (g), step (k) until it is determined that the absolute value of the second differential value is less than the second power reference value in step (l).

2. The detecting method of claim 1, wherein the initial impedance angle is set as a maximum value, and wherein if it is determined that the absolute value of the first differential value is not less than the first power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle or to the predetermined impedance angle minus the compensation angle comprises: if it is determined that the absolute value of the first differential value is not less than the first power reference value, setting the impedance angle equal to the predetermined impedance angle minus the compensation angle.

3. The detecting method of claim 1, wherein the initial impedance angle is set as a maximum value, and wherein if it is determined that the absolute value of the second difference is not less than the second power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle or to the predetermined impedance angle minus the compensation angle comprises: if it is determined that the absolute value of the second difference is not less than the second power reference value, setting the impedance angle equal to the predetermined impedance angle minus the compensation angle.

4. The detecting method of claim 1, wherein the initial impedance angle is set as a minimum value, and wherein if it is determined that the absolute value of the first differential value is not less than the first power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle or to the predetermined impedance angle minus the compensation angle comprises: if it is determined that the absolute value of the first differential value is not less than the first power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle.

5. The detecting method of claim 1, wherein the initial impedance angle is set as a minimum value, and wherein if it is determined that the absolute value of the second difference is not less than the second power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle or to the predetermined impedance angle minus the compensation angle comprises: if it is determined that the absolute value of the second difference is not less than the second power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle.

6. The detecting method of claim 1, wherein the first active power and the first reactive power are an active power and a reactive power before value changes, and the second active power and the second reactive power is an active power and a reactive power after value changes.

7. The detecting method of claim 1, wherein if it is determined that the absolute value of the first differential value is not less than the first power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle or to the predetermined impedance angle minus the compensation angle comprises: if it is determined that the absolute value of the first differential value is not less than the first power reference value, calculating a first variance of the power angle, and determining whether a product of the first differential value and the first variance is larger than zero; if it is determined that the product of the first differential value and the first variance is larger than zero, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle; if it is determined that the product of the first differential value and the first variance is not larger than zero, setting the impedance angle equal to the predetermined impedance angle minus the compensation angle.

8. The detecting method of claim 7, wherein if it is determined that the product of the first differential value and the first variance is larger than zero, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle comprises: if it is determined that the product of the first differential value and the first variance is larger than zero, setting a minimum value of the impedance angle as the predetermined impedance angle; obtaining an angle difference by subtracting the predetermined impedance angle from a maximum value of the impedance angle; and obtaining the compensation angle by dividing the angle difference by two; wherein if it is determined that the product of the first differential value and the first variance is not larger than zero, setting the impedance angle equal to the predetermined impedance angle minus the compensation angle comprises: if it is determined that the product of the first differential value and the first variance is not larger than zero, setting the maximum value of the impedance angle as the predetermined impedance angle; obtaining the angle difference by subtracting the minimum value of the impedance angle from the predetermined impedance angle; and obtaining the compensation angle by dividing the angle difference by two.

9. The detecting method of claim 1, wherein if it is determined that the absolute value of the second difference is not less than the second power reference value, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle or to the predetermined impedance angle minus the compensation angle comprises: if it is determined that the absolute value of the second difference is not less than the second power reference value, calculating a second variance of the amplitude, and determining whether a product of the second difference and the second variance is larger than zero; if it is determined that the product of the second difference and the second variance is larger than zero, setting the impedance angle equal to the predetermined impedance angle minus the compensation angle; if it is determined that the product of the second difference and the second variance is not larger than zero, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle.

10. The detecting method of claim 9, wherein if it is determined that the product of the second difference and the second variance is larger than zero, setting the impedance angle equal to the predetermined impedance angle minus the compensation angle comprises: if it is determined that the product of the second difference and the second variance is larger than zero, setting a maximum value of the impedance angle as the predetermined impedance angle; obtaining an angle difference by subtracting a minimum value of the impedance angle from the predetermined impedance angle; and obtaining the compensation angle by dividing the angle difference by two; wherein if it is determined that the product of the second difference and the second variance is not larger than zero, setting the impedance angle equal to the sum of the predetermined impedance angle and the compensation angle comprises: if it is determined that the product of the second difference and the second variance is not larger than zero, setting the minimum value of the impedance angle as the predetermined impedance angle; obtaining the angle difference by subtracting the predetermined impedance angle from the maximum value of the impedance angle; and obtaining the compensation angle by dividing the angle difference by two.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows:

(2) FIG. 1 is a schematic diagram of a detecting device for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(3) FIG. 2A is a flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(4) FIG. 2B is a portion of the flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter as shown in FIG. 2A according to embodiments of the present disclosure.

(5) FIG. 2C is a portion of the flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter as shown in FIG. 2A according to embodiments of the present disclosure.

(6) FIG. 3 is a flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(7) FIG. 4 is a flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(8) FIG. 5A is an operation diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(9) FIG. 5B is an operation diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(10) FIG. 5C is an operation diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(11) FIG. 6A is an operation diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(12) FIG. 6B is an operation diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(13) FIG. 6C is an operation diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure.

(14) In accordance with common practice, the various described features/elements are not drawn to scale but instead are drawn to best illustrate specific features/elements relevant to the present disclosure. Also, wherever possible, like or the same reference numerals are used in the drawings and the description to refer to the same or like parts.

DETAILED DESCRIPTION

(15) The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

(16) Unless otherwise defined herein, scientific and technical terminologies employed in the present disclosure shall have the meanings that are commonly understood and used by one of ordinary skill in the art. Unless otherwise required by context, it will be understood that singular terms shall include plural forms of the same and plural terms shall include singular forms of the same.

(17) For automatically detecting output impedance angles of inverters simply and accurately so as to enable efficient control of inverters, the present disclosure provides a detecting device and a detecting method for detecting an output impedance angle of an inverter, which will be described below.

(18) FIG. 1 is a schematic diagram of a detecting device for detecting an output impedance angle of an inverter according to embodiments of the present disclosure. As shown in the figure, the detecting device 100 for detecting an output impedance angle of an inverter comprises a voltage signal setting unit 110, a digital control unit 120, an active power/reactive power (PQ) calculation unit 130, a rotation changing unit 140, and an impedance angle detection unit 150.

(19) In this embodiment, the voltage signal setting unit 110 is configured to output a first voltage signal, and the first voltage signal comprises an amplitude U.sub.c and an power angle . In one embodiment, an output side of an inverter 900 is coupled to a grid. The power angle can be a phase difference between the first voltage signal and a voltage of the grid, but is not limited thereto. One of the amplitude U.sub.c and the power angle is a variable value, and the other one of the amplitude U.sub.c and the power angle is a constant value. The digital control unit 120 is configured to control the inverter 900 to output a second voltage signal u.sub.0 and a current signal i.sub.0 based on the first voltage signal. The PQ calculation unit 130 is configured to calculate and output a first active power P.sub.1, a second active power P.sub.2, a first reactive power Q.sub.1 and a second reactive power Q.sub.2 based on the second voltage signal u.sub.0 and the current signal i.sub.0. The rotation changing unit 140 is configured to calculate and output a third active power P.sub.1, a fourth active power P.sub.2, a third reactive power Q.sub.1 and a fourth reactive power Q.sub.2 based on the first active power P.sub.1, the second active power P.sub.2, the first reactive power Q.sub.1, the second reactive power Q.sub.2 and a predetermined impedance angle {circumflex over ()}. The impedance angle detection unit 150 is configured to calculate the output impedance angle based on the third active power P.sub.1, the fourth active power P.sub.2, the third reactive power Q.sub.1, the fourth reactive power Q.sub.2 and the first voltage signal.

(20) For facilitating understanding of steps for detecting an output impedance angle of an inverter of the detecting device 100, reference is now made to FIG. 2A, which is a flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure. As shown in the figure, in step 210, an impedance angle is set to be an initial impedance angle .sub.0. In step 220, a set predetermined impedance angle {circumflex over ()} is set to be an impedance angle . In step 230, the voltage signal setting unit 110 is used to output the first voltage signal, and the first voltage signal comprises the amplitude U.sub.c and the power angle . In step 240, the impedance angle detection unit 150 is used to determine whether a value of the amplitude U.sub.c is a constant value. If it is determined that the value of the amplitude U.sub.c is a constant value, step 251 is performed to calculate a variance of the power angle . For example, if the power angle changes from .sub.1 to .sub.2, the variance =.sub.2.sub.1.

(21) Subsequently, steps 252253 can be performed in advance, or performed after step 251. In step 252, the PQ calculation unit 130 is used to calculate the first active power P.sub.1, the second active power P.sub.2, the first reactive power Q.sub.1 and the second reactive power Q.sub.2 based on the second voltage signal u.sub.0 and the current signal i.sub.0. The first active power P.sub.1 and the first reactive power Q.sub.1 are calculation values when the power angle is .sub.1. The second active power P.sub.2 and the second reactive power Q.sub.2 are calculation values when the power angle is .sub.2. In step 253, the rotation changing unit 140 is used to calculate the third reactive power Q.sub.1 and the fourth reactive power Q.sub.2, and calculate a first differential value Q of the reactive power Q (Q=Q.sub.2Q.sub.1) based on the first active power P.sub.1, the second active power P.sub.2, the first reactive power Q.sub.1, the second reactive power Q.sub.2 and the predetermined impedance angle {circumflex over ()}. The third reactive power Q.sub.1 is a calculation value of the first active power P.sub.1, the first reactive power Q.sub.1 and the predetermined impedance angle {circumflex over ()}. The fourth reactive power Q.sub.2 is a calculation value of the second active power P.sub.2, the second reactive power Q.sub.2 and the predetermined impedance angle {circumflex over ()}.

(22) In addition, in step 254, the impedance angle detection unit 150 is used to determine whether an absolute value of the first differential value Q of the third reactive power Q.sub.1 and the fourth reactive power Q.sub.2 is less than the first power reference value Q.sub.c. If it is determined that the absolute value of the first differential value Q is less than the first power reference value Q.sub.c, the impedance angle is the output impedance angle of the inverter (step 270). If it is determined that the absolute value of the first differential value Q is not less than the first power reference value Q.sub.c, a direction of Q is further determined, that is, step 255 is performed. In one embodiment, approximately 5% of the inverter rated power is regarded as the first power reference value Q.sub.c. If a value of the first power reference value Q.sub.c is smaller, a higher accuracy of the detection result is achieved.

(23) In step 255, the impedance angle detection unit 150 is used to determine whether a product of the first differential value Q and the variance is larger than zero. If it is determined that the product of the first differential value Q and the variance is larger than zero, this indicates that the direction of the first differential value Q and the direction of the variance are the same. At this time, step 256 is performed, in which the impedance angle is set equal to a sum of a predetermined impedance angle {circumflex over ()} and the compensation angle .sub.0, after which the routine returns back to step 220 to perform the foregoing steps again until it is determined that the absolute value of the first differential value Q is less than the first power reference value Q.sub.c in step 254, which indicates that the impedance angle is the output impedance angle of the inverter. If it is determined that the absolute value of the first differential value Q is not less than the first power reference value Q.sub.c, this indicates that the direction of the first differential value Q and the direction of the variance are different from each other. At this time, step 257 is performed, in which the impedance angle is set equal to the predetermined impedance angle {circumflex over ()} minus the compensation angle .sub.0, after which the routine returns back to step 220 to perform the foregoing steps again until it is determined that the absolute value of the first differential value Q is less than the first power reference value Qc in step 254, which indicates that the impedance angle is the output impedance angle of the inverter. In one embodiment, the compensation angle .sub.0 can be set to be 5. If a value of the compensation angle .sub.0 is smaller, a higher accuracy of the detection result is achieved.

(24) On the other hand, in step 240, if it is determined that the amplitude U.sub.c is not a constant value, step 261 is performed to calculate the variance U.sub.c of the amplitude U.sub.c. For example, if the amplitude U.sub.c changes from U.sub.1 to U.sub.2, the value of the power angle is a constant value, and the variance U.sub.c=U.sub.2U.sub.1.

(25) Moreover, steps 262263 can be performed in advance, or performed after step 261. In step 262, the PQ calculation unit 130 is used to calculate the first active power P.sub.1, the second active power P.sub.2, the first reactive power Q.sub.1 and the second reactive power Q.sub.2 based on the second voltage signal u.sub.0 and the current signal i.sub.0. The first active power P.sub.1 and the first reactive power Q.sub.1 are calculation values when the amplitude is U.sub.1. The second active power P.sub.2 and the second reactive power Q.sub.2 are calculation values when the amplitude is U.sub.2. In step 263, the rotation changing unit 140 is used to calculate the third active power P.sub.1 and the fourth active power P.sub.2, and calculate a second difference P of the active power P to be P=P.sub.2P.sub.1 based on the first active power P.sub.1, the second active power P.sub.2, the first reactive power Q.sub.1, the second reactive power Q.sub.2 and a predetermined impedance angle {circumflex over ()}. The third active power P.sub.1 is a calculation value of the first active power P.sub.1, the first reactive power Q.sub.1 and the predetermined impedance angle {circumflex over ()}. The fourth active power P.sub.2 is a calculation value of the second active power P.sub.2, the second reactive power Q.sub.2 and the predetermined impedance angle {circumflex over ()}.

(26) Subsequently, in step 264, the impedance angle detection unit 150 is used to determine whether an absolute value of the second difference P of the third active power P.sub.1 and the fourth active power P.sub.2 is less than a second power reference value P.sub.c. If it is determined that the absolute value of the second difference P is less than the second power reference value P.sub.c, the impedance angle is the output impedance angle of the inverter (step 270). If it is determined that the absolute value of the second difference P is not less than the second power reference value P.sub.c, a direction of P is further determined, that is, step 265 is performed. In one embodiment, approximately 5% of the inverter rated power is regarded as the second power reference value P.sub.c. If a value of the second power reference value P.sub.c is smaller, a higher accuracy of the detection result is achieved.

(27) In step 265, the impedance angle detection unit 150 is used to determine whether a product of the second difference P and the variance U.sub.c is larger than zero. If the product of the second difference P and the variance U.sub.c is larger than zero, this indicates that the direction of the second difference P and the direction of the variance U.sub.c are the same. At this time, step 266 is performed, in which the impedance angle is set equal to a predetermined impedance angle {circumflex over ()} minus the compensation angle .sub.0, after which the routine returns back to step 220 to perform the foregoing steps again until it is determined that the absolute value of the second difference P is less than the second power reference value P.sub.c in step 264, which indicates that the impedance angle is the output impedance angle of the inverter. If the product of the second difference P and the variance U.sub.c is not larger than zero, this indicates that the direction of the second difference P and the direction of the variance U.sub.c are different from each other. At this time, step 267 is performed, in which the impedance angle is set equal to the sum of the predetermined impedance angle {circumflex over ()} and the compensation angle .sub.0, after which the routine returns back to step 220 to perform the foregoing steps again until it is determined that the absolute value of the second difference P is less than the second power reference value P.sub.c in step 264, which indicates that the impedance angle is the output impedance angle of the inverter.

(28) In another embodiment, the detecting device 100 and the detecting method 200 for detecting an output impedance angle of an inverter can also employ binary search, which will be described below. It is noted that the maximum value and the minimum value of the impedance angle are .sub.2 and .sub.1, respectively. For example, the maximum value .sub.2 of the impedance angle can be 90, and the minimum value .sub.1 of the impedance angle is 0. For facilitating understanding of the binary search, reference is now made to FIG. 2B, which is a portion of the flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter as shown in FIG. 2A according to embodiments of the present disclosure. It is noted that FIG. 2B only depicts step 255 in FIG. 2A for introducing another embodiment of step 255, and therefore, FIG. 2B does not illustrate all steps of the detecting method 200 for detecting an output impedance angle of an inverter. In step 255, if it is determined that the product of the first differential value Q and variance is larger than zero, step 256A is performed, in which the minimum value .sub.1 of the impedance angle is set equal to the predetermined impedance angle {circumflex over ()} an angle difference is obtained by subtracting the predetermined impedance angle {circumflex over ()} from the maximum value .sub.2 of the impedance angle, and the compensation angle .sub.0 is obtained by dividing the angle difference by two. In addition, in step 255, if it is determined that the product of the first differential value Q and the variance is not larger than zero, step 257A is performed, in which the maximum value .sub.2 of the impedance angle is set equal to the predetermined impedance angle {circumflex over ()}, an angle difference is obtained by subtracting the minimum value .sub.1 of the impedance angle from the predetermined impedance angle {circumflex over ()}, and the compensation angle .sub.0 is obtained by dividing the angle difference by two.

(29) The binary search procedure will be further described in accordance with yet another embodiment. For facilitating understanding of the binary search, reference is now made to FIG. 2C, which is a portion of the flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter as shown in FIG. 2A according to embodiments of the present disclosure. It is noted that FIG. 2C only depicts step 265 in FIG. 2A for introducing another embodiment of step 265, and therefore, FIG. 2C does not illustrate all steps of the detecting method 200 for detecting an output impedance angle of an inverter. In step 265, if it is determined that the product of the second difference P and the variance U.sub.c is larger than zero, step 266A is performed, in which the maximum value .sub.2 of the impedance angle is set equal to the predetermined impedance angle {circumflex over ()}, an angle difference is obtained by subtracting the minimum value .sub.1 of the impedance angle from the predetermined impedance angle {circumflex over ()}, and the compensation angle .sub.0 is obtained by dividing the angle difference by two. In addition, in step 265, if it is determined that the product of the second difference P and the variance U.sub.c is not larger than zero, step 267A is performed, in which the minimum value .sub.1 of the impedance angle is set equal to the predetermined impedance angle 9, an angle difference is obtained by subtracting the predetermined impedance angle {circumflex over ()} from the maximum value .sub.2 of the impedance angle, and the compensation angle .sub.0 is obtained by dividing the angle difference by two.

(30) FIG. 3 is a flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure. The difference between a detecting method 200A for detecting an output impedance angle of an inverter in FIG. 3 and the detecting method 200 for detecting an output impedance angle of an inverter in FIG. 2 is the steps 210, 254, 264. In step 210, the initial impedance angle .sub.0 is set to be 90, and the impedance angle is also set to be 90. Hence, in step 220, the predetermined impedance angle {circumflex over ()} is set to be the impedance angle . In this situation, referring to step 254, if it is determined that the absolute value of the first differential value Q is not less than the first power reference value Q.sub.c the impedance angle is set equal to the predetermined impedance angle {circumflex over ()} minus the compensation angle .sub.0. In addition, referring to step 264, if it is determined that the absolute value of the second difference P is not less than the second power reference value P.sub.c, the impedance angle is set equal to the predetermined impedance angle {circumflex over ()} minus the compensation angle .sub.0. It is noted that other steps in the detecting method 200A for detecting an output impedance angle of an inverter in FIG. 3 are the same as steps in the detecting method 200 for detecting an output impedance angle of an inverter in FIG. 2, and a detailed description regarding such other steps in FIG. 3 will be omitted herein for the sake of brevity.

(31) FIG. 4 is a flow diagram illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure. The difference between a detecting method 200B for detecting an output impedance angle of an inverter in FIG. 4 and the detecting method 200 for detecting an output impedance angle of an inverter in FIG. 2 is the steps 210, 254, 264. In step 210, the initial impedance angle .sub.0 is set to be 0, and the impedance angle is also set to be 0. Hence, in step 220, the predetermined impedance angle {circumflex over ()} is set to be the impedance angle . In this situation, referring to step 254, if it is determined that the absolute value of the first differential value Q is not less than the first power reference value Q.sub.c, the impedance angle is set equal to a sum of the predetermined impedance angle {circumflex over ()} and the compensation angle .sub.0. In addition, referring to step 264, if it is determined that the absolute value of the second difference P is not less than the second power reference value P.sub.c, the impedance angle is set equal to a sum of the predetermined impedance angle {circumflex over ()} and the compensation angle .sub.0. It is noted that other steps in the detecting method 200B for detecting an output impedance angle of an inverter in FIG. 4 are the same as steps in the detecting method 200 for detecting an output impedance angle of an inverter in FIG. 2, and a detailed description regarding such other steps in FIG. 4 will be omitted herein for the sake of brevity.

(32) FIGS. 5A5C are operation diagrams illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure. First of all, a first voltage signal U.sub.c=U.sub.1 is input, and the power angle changes from .sub.1 to .sub.2. If it is detected that Q*>0 and |Q|Qc, as shown in FIG. 5A, the impedance angle is set as ={circumflex over ()}+.sub.0 and the routine returns to step 220 until |Q|<Qc. As shown in FIG. 5B, the detection is completed, the impedance angle is 60, and the output impedance angle of the inverter is the impedance angle . In addition, if it is detected that Q*<0 and |Q|Qc, as shown in FIG. 5C, the impedance angle is set as ={circumflex over ()}.sub.0 and the routine returns to step 220 until |Q|<Qc. As shown in FIG. 5B, the detection is completed, the impedance angle is 60, and the output impedance angle of the inverter is the impedance angle .

(33) FIGS. 6A6C are operation diagrams illustrating the process steps of a detecting method for detecting an output impedance angle of an inverter according to embodiments of the present disclosure. First of all, a first voltage signal U.sub.c changes from U.sub.1 to U.sub.2, and the value of the power angle is a constant value. If it is detected that P*Uc>0 and |P|P.sub.c, as shown in FIG. 6A, the impedance angle is set as ={circumflex over ()}.sub.0 and the routine returns to step 220 until |P|<Pc. As shown in FIG. 6B, the detection is completed, the impedance angle is 60, and the output impedance angle of the inverter is the impedance angle . In addition, if it is detected that P*Uc<0 and |P|P.sub.c, as shown in FIG. 6C, the impedance angle is set as ={circumflex over ()}+.sub.0 and the routine returns to step 220 until |P|<P.sub.c. As shown in FIG. 6B, the detection is completed, the impedance angle is 60, and the output impedance angle of the inverter is the impedance angle .

(34) As may be appreciated by persons having ordinary skill in the art, the steps of the detecting method for detecting an output impedance angle of an inverter are named according to the function they perform, and such naming is provided to facilitate the understanding of the present disclosure but not to limit the steps. Combining the steps into a single step or dividing any one of the steps into multiple steps, or switching any step so as to be a part of another step falls within the scope of the embodiments of the present disclosure.

(35) In view of the above embodiments of the present disclosure, it is apparent that the application of the present disclosure has a number of advantages. Embodiments of the present disclosure provide a detecting device and a detecting method for detecting an output impedance angle of an inverter so as to detect an output impedance angle of the inverter simply and precisely, and ultimately enable efficient control of the inverter.

(36) Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.

(37) It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.