KR20060037813A - Phase locked loop - Google Patents

Abstract

This invention removes zero-sequence, which is a problem mainly when an unbalance occurs, and can improve the operation characteristics of the PLL algorithm when an unbalance occurs without affecting the fast response at all. The reversed phase component is related to a phase locked loop (PLL) for power conversion equipment, which reduces output instability even by tuning PI controller parameters of an existing PLL.

When the three-phase AC power signals Va, Vb, and Vc are input, an adder for subtracting zero-phase components and a signal Va ', Vb', and Vc 'input from the adder are dq-converted. A dq converter for outputting the voltage signals V _ds and V _qs , a sine wave generator for generating and outputting the sinusoidal signals sin (θ _PLL ) and cos (θ _PLL ) using the PLL output θ _PLL ; A multiplier for multiplying one voltage signal (V _ds , V _qs ) by the sinusoidal signals (sin (θ _PLL ) and cos (θ _PLL )) and a signal inputted from the multiplier, thereby adding a PLL output error (PLLerr). = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )) and the above-described PLL output error (PLLerr = -V _ds sin (θ _PLL ) so that V _qs cosθ = V _ds sinθ). _qs + V cos (θ _PLL)) is zero, new input from the PI control, and a gain adjuster, and wherein a gain adjuster 8 which adjusts the gain of the signal inputted from the PI controller (6) so that the By providing the integration comprises the integrator output.

Phase-locked loop, adder, PI controller, integrator, gain adjuster, PLL, multiplier

Description

Phase locked loop for power conversion equipment

1 is a diagram showing an instantaneous value of a three-phase balanced alternating current (AC) system voltage as a vector.

2 is a diagram illustrating a d-q transformation in a stationary coordinate.

3 is a diagram illustrating a d-q transformation in rotational coordinates.

4 is a view showing that the d-axis is parallel to the system voltage V when V _qs cos θ = V _ds sin θ.

5 is a configuration diagram of a conventional standard phase locked loop (PLL).

6 is a diagram illustrating a conventional standard phase locked loop (PLL) applied to a power conversion facility.

FIG. 7 is a diagram showing a conversion of a three-phase unbalanced alternating current (AC) waveform to an equilibrium component. FIG.

8 is a diagram illustrating a vector configuration of a three-phase unbalanced alternating current (AC) waveform.

9 is a configuration diagram of a phase locked loop (PLL) for power conversion equipment according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

1: d-q converter 2, 4: multiplier

3: adder 5: sign generator

6: PI controller 7: cosine generator

8: gain adjuster 9: integrator

The present invention relates to the field of phase locked loop (PLL), and more specifically, to remove the zero-phase component that is mainly a problem when an unbalance occurs, so that the PLL algorithm does not affect the fast response characteristics at all. The reverse phase component, which can improve the operating characteristics of and can reduce the instability of the output even by tuning the PI controller parameters of the existing PLL, is a phase locked loop (PLL) for power conversion equipment. To provide.

In power conversion facilities such as FACTS (Flexible AC Transmission System) and HVDC (High Voltage Direct Current system), three-phase balanced AC is required because there must be reference information to properly control the firing angle of power converters such as converters. (AC) The synchronization phase information of the power system is needed.

There are basically two directions for this.

The first method is to measure the frequency directly from the synchronous generator. However, in this method, the speed of the synchronizer is fluctuated when an accident occurs in an alternating current (AC) system, so that the frequency input signal may be distorted, resulting in unstable control of the firing angle.

The second method is to measure frequency from alternating current (AC) system waveforms. A phase locked loop (PLL) having an algorithmic configuration as shown in FIG. 5 is used for this method. This will be described in detail with reference to FIGS. 1 to 4 as follows.

1 is a diagram showing an instantaneous value of a three-phase balanced alternating current (AC) system voltage as a vector. The three-phase equilibrium alternating current (AC) system voltage as shown in FIG. 1 can be converted into dq stop coordinates as shown in FIG. 2 using the following equation (1), and the following equation (2) ) Can be converted into dq rotational coordinates as shown in FIG. 3.

In this case, as shown in FIG. 4, if V _qs cos θ = V _ds sin θ, the d-axis can be regarded as parallel to the system voltage V, and thus the system synchronization phase θ can be obtained.

This algorithm is represented by the phase locked loop (PLL) of FIG. 5 is a configuration diagram of a conventional standard phase locked loop (PLL).

As shown in FIG. 5, the conventional standard phase locked loop (PLL) has a three-phase alternating current (AC) power signal Va, Vb, or Vc input thereto, and then converts dq to convert the voltage signal V _ds,. Sine generator 5 and cosine generator that generate and output sinusoidal signals sin (θ _PLL ) and cos (θ _PLL ) using dq converter 1 outputting as V _qs ) and PLL output θ _PLL (7), a first multiplier 2 and a second multiplier (2) for multiplying and outputting the voltage signals V _ds and V _qs and the sinusoidal signals sin (θ _PLL ) and cos (θ _PLL ), respectively. 4) and the signals input from the first multiplier 2 and the second multiplier 4 above, and are output as a PLL output error (PLLerr = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )). PI controller of the adder 3 and, V _qs cosθ = V _ds above PLL output error by such that sinθ (PLLerr _ds = -V sin (θ _{PLL) qs} + V cos (θ _PLL)) to be zero ( 6) and the gain of the signal input from the PI controller 6 described above. And a gain regulator 8 for adjusting and an integrator 9 for integrating and outputting the signal input from the gain regulator 8 described above.

The conventional standard phase locked loop (PLL) by the above configuration has the same effect.

When the three-phase AC power signals Va, Vb, and Vc are input, the dq converter 1 converts them to dq and outputs them as voltage signals V _ds and V _qs .

On the other hand, the PLL output (θ _PLL ), which is the output signal of the phase-locked loop (PLL), is fed back to the front end, and becomes sin (θ _PLL ) while passing through the sine generator 5 while the PLL output (θ _PLL ) is fed back. Through cosine generator 7, cos (θ _PLL ) is obtained.

The signals sin (θ _PLL ) and cos (θ _PLL ) are each multiplied by the voltage signal V _ds through the first multiplier 2 to become sin (θ _PLL ), and the second multiplier 4. By multiplying by the voltage signal (V _qs ) and becomes V _qs cos (θ _PLL ).

These values become the PLL output error PLLerr of −V _ds sin (θ _PLL ) + V _qs cos (θ _PLL ) through the adder 3 and are output to the PI controller 6.

In the PI controller 6, the VLL output error (PLLerr = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )) becomes 0 by setting V _qs cosθ = V _ds sinθ so that the PLL output ( [theta] is equal to the input phase [theta] to be synchronized.

As described above, the algorithm of the phase locked loop (PLL) illustrated in FIG. 5 is a simple and very effective method, and thus, power such as a flexible AC transmission system (FACTS) and a high voltage direct current system (HVDC) as shown in FIG. It is applied to conversion equipment as standard.

As described above, in the case of an inverter which is a power control equipment for power control applied to a three-phase balanced AC power system such as FACTS and HVDC, a phase locked loop (PLL) is used to obtain a reference frequency for controlling the firing angle of the inverter. do.

The phase locked loop (PLL) provides basic frequency information for controlling the firing angle of power conversion equipment such as FACTS and HVDC, and thus greatly affects the stability and performance of the power conversion equipment.

Therefore, the PLL has a great influence on the stability and performance of the power conversion equipment. Therefore, the PLL should operate at high speed as well as accurate response characteristics, and provide accurate reference synchronous phase information. Accordingly, a simple configuration of the phase locked loop (PLL) is essential. For this purpose, a lot of researches on the phase locked loop (PLL) have been conducted. As a result, a standard phase locked loop (PLL) algorithm has been developed.

However, in the conventional phase locked loop (PLL), zero-sequence and negative sequence due to the unbalance of the AC system exist in the input signal of the phase locked loop (PLL) algorithm. As a result, when the AC power system is unbalanced or when a distorted system waveform occurs, an instability occurs in the output.

That is, the phase locked loop (PLL) is a general algorithm widely used for the control of power conversion equipment such as FACTS and HVDC, but zero phase component is applied to the input signal of the phase locked loop (PLL) when the unbalanced AC waveform is introduced. Because of the presence of zero-sequence and negative sequence, transient instability occurs.

Therefore, there is a need for a method of effectively eliminating instability without affecting the calculation speed of the phase locked loop (PLL).

To this end, there is a method of removing a zero-sequence and a negative sequence and inputting only a positive sequence to an input terminal of a phase locked loop PLL.

However, this method has a problem in that an additional algorithm for detecting a normal component is required and a time delay element for making a 120 degree phase shift element such as a phase shifter is required.

An object of the present invention is to solve the conventional problems as described above, by eliminating the zero-phase component (Zero-Sequence), which is a problem mainly when an unbalance occurs, without affecting the high-speed response characteristics at all, the PLL algorithm when an unbalance occurs The reverse phase component, which can improve the operating characteristics of and can reduce the instability of the output even by tuning the PI controller parameters of the existing PLL, is a phase locked loop (PLL) for power conversion equipment. To provide.

In the present invention, a phase-locked loop (PLL) is used because the zero phase component is removed as an input signal of a phase-locked loop (PLL) algorithm for an unbalanced AC waveform generated when a failure occurs such as a 1-wire or 2-wire ground fault in an AC power system. The performance is improved without affecting the computation speed of the algorithm.

As a means for achieving the above object, the configuration of the present invention includes an adder for subtracting zero-phase components, respectively, when three-phase AC power signals Va, Vb, and Vc are input, and inputted from the adder. The dq converter converts the signals Va ', Vb', and Vc 'and outputs them as voltage signals V _ds and V _qs , and the sinusoidal signals sin (θ _PLL ) and cos using the PLL output θ _PLL . a multiplier for outputting multiplied by (θ _PLL)) to the sine wave generator for generating and outputting the voltage signal (V _ds, V _qs) and the above-described sinusoidal signal _{(sin (θ PLL), cos} (θ PLL)) , respectively and And an adder which adds a signal input from the multiplier and outputs it as a PLL output error (PLLerr = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )), so that V _qs cosθ = V _ds sinθ. a PLL output error (PLLerr _ds = -V sin (θ _{PLL) qs} + V cos (θ _PLL)) and the PI controller to zero, adjusting the gain of the signal inputted from the PI controller (6) May comprise an integrator for integrating and outputting the signal input from the gain regulator, wherein a gain adjuster (8).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings in order to describe in detail enough to enable those skilled in the art to easily carry out the present invention. . Other objects, features, and operational advantages, including the object, operation, and effect of the present invention will become more apparent from the description of the preferred embodiment.

For reference, the embodiments disclosed herein are only presented by selecting the most preferred embodiment in order to help those skilled in the art from the various possible examples, the technical spirit of the present invention is not necessarily limited or limited only by this embodiment Rather, various changes, additions, and changes are possible within the scope without departing from the spirit of the present invention, as well as other equivalent embodiments.

9 is a configuration diagram of a phase locked loop (PLL) for power conversion equipment according to an embodiment of the present invention. As shown in Fig. 9, the configuration of the phase-lock loop for power conversion equipment according to one embodiment of the present invention is that each of the zero-phase components when the three-phase AC power signals Va, Vb, and Vc are input. Adder 11, 12, 13 for subtracting and dq-convert the signals Va ', Vb', Vc 'input from the adders 11, 12, 13, and the voltage signals V _ds , V _qs. Sine generator 5 and cosine generator 7 for generating and outputting sinusoidal signals sin (θ _PLL ) and cos (θ _PLL ) using dq converter 1 to be outputted as) and PLL output θ _PLL . ) And a first multiplier 2 and a second multiplier 4 for multiplying and outputting the voltage signals V _ds and V _qs and the sinusoidal signals sin (θ _PLL ) and cos (θ _PLL ), respectively. And an adder which adds the signals input from the first multiplier 2 and the second multiplier 4 and outputs them as a PLL output error (PLLerr = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )). (3) and the above-described PLL output such that V _qs cos θ = V _ds sin θ Adjusting the gain of the signal input from the PI controller 6 and the PI controller 6 so that the output error (PLLerr = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )) becomes 0. And a gain regulator 8 and an integrator 9 for integrating and outputting the signal input from the gain regulator 8 described above.

The operation of the phase-locked loop (PLL) for power conversion equipment according to the embodiment of the present invention by the above configuration is as follows.

The present invention is a phase locked loop (PLL) algorithm, which is a synchronous phase measurement method for an AC system used for control of a power conversion facility connected to an AC power system such as a flexible AC transmission system (FACTS) and a high voltage direct current system (HVDC). It is about improving.

In the case of phase-locked loop (PLL), a synchronous phase detection algorithm used as standard in power systems, zero-sequence and negative sequence exist in the PLL input signal when an AC system unbalance occurs. This results in transient instability. Among the above-described zero-phase components and inverse phase components, the main instability is zero-phase components.

This instability is gradually solved by the PI controller of the phase locked loop (PLL). However, if the zero-phase component is removed from the input signal in advance, the instability is greatly reduced and the response characteristic of the PLL is greatly improved.

The elimination of the zero-phase component described above only requires subtracting Vabc = (Va + Vb + Vc) / 3 from each input Va, Vb, Vc, so that additional elements in the phase locked loop PLL, in particular phase shifts, No time delay is needed. This makes it very simple to improve the performance of an effective phase locked loop (PLL).

The theoretical basis of the present invention will be described in more detail as follows.

As shown in FIG. 7, the three-phase AC unbalanced waveform is interpreted as a three-phase equilibrium vector component of the normal components (V _b1 , V _c1 ), the reverse phase components (V _b2 , V _c2 ), and the zero phase component (V _b0 ). can do.

Therefore, as shown in Fig. 8, the waveforms Va, Vb, and Vc due to the unbalance can be represented by a vector sum of the normal part, the inverse part, and the zero phase part as shown in Equation (3) below.

Va = V _a1 + V _a2 + V _a0 , Vb = V _b1 + V _b2 + V _b0 , Vc = V _c1 + V _c2 + V _c0 (3)

Therefore, the zero-phase component _Vabc0 can be removed from the unbalanced waveforms Va, Vb, and Vc simply by subtracting V _0abc = (Va + Vb + Vc) / 3 from the unbalanced waveforms Va, Vb, and Vc. .

The configuration of the present invention for this purpose is shown in FIG. 7, wherein the zero-phase component ((Va + Vb + Vc) / 3) of the input signals Va, Vb, and Vc of the conventional PLL is shown in FIG. By subtracting the respective signals Va ', Vb', and Vc ', which do not include the zero-phase component, are introduced into the dq converter 1.

When the signals Va ', Vb', and Vc 'which do not include the zero-phase component are input, the dq converter 1 converts them to dq and outputs them as voltage signals V _ds and V _qs .

On the other hand, the PLL output (θ _PLL ), which is the output signal of the phase-locked loop (PLL), is fed back to the front end, and becomes sin (θ _PLL ) while passing through the sine generator 5 while the PLL output (θ _PLL ) is fed back. Through cosine generator 7, cos (θ _PLL ) is obtained.

The signals sin (θ _PLL ) and cos (θ _PLL ) are each multiplied by the voltage signal V _ds through the first multiplier 2 to become sin (θ _PLL ), and the second multiplier 4. By multiplying by the voltage signal (V _qs ) and becomes V _qs cos (θ _PLL ).

These values become the PLL output error PLLerr of −V _ds sin (θ _PLL ) + V _qs cos (θ _PLL ) through the adder 3 and are output to the PI controller 6.

In the PI controller 6, the VLL output error (PLLerr = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )) becomes 0 by setting V _qs cosθ = V _ds sinθ so that the PLL output ( [theta] is equal to the input phase [theta] to be synchronized.

Accordingly, the response characteristics and performance of the phase locked loop PLL are greatly improved and improved by subtracting out the zero-phase component ((Va + Vb + Vc) / 3) which is the most problematic when AC unbalance occurs.

Another unstable factor, the negative sequence, does not appear to be a major factor in the unbalanced phenomenon because it does not appear large when an unbalanced phenomenon occurs, and it is adequately responded by appropriate selection of the PI controller parameter of the algorithm of the phase locked loop (PLL). can do.

As described above, PLL is an algorithm that measures the fundamental frequency necessary for the firing angle control of power conversion facilities such as FACTS and HVDC. If there is an error in the output of the phase locked loop (PLL) algorithm, the firing angle control of the power conversion equipment cannot be precisely influenced, which greatly affects the stability and performance of the overall power conversion equipment. Therefore, the PLL algorithm is very important because it must have a simple and fast response. The present invention effectively reduces the high-speed response characteristics of the conventional phase locked loop (PLL) algorithm and effectively eliminates the additional delay (time delay). Can improve the response characteristics.

As described in the above embodiments, the present invention improves the operation characteristics of the PLL algorithm when an unbalance occurs without removing the zero-sequence which is a problem mainly when an unbalance occurs. Inverse phase components, which may be a factor of instability, have an effect of reducing output instability even by tuning PI controller parameters of an existing PLL.

Claims (2)

An adder for subtracting zero-phase components, respectively, when three-phase AC power signals Va, Vb, and Vc are input; A dq converter for converting the signals Va ', Vb', Vc 'input from the adder to dq and outputting them as voltage signals V _ds and V _qs ; A sinusoidal wave generator for generating and outputting sinusoidal signals sin (θ _PLL ) and cos (θ _PLL ) using a PLL output (θ _PLL ), A multiplier for multiplying and outputting the voltage signals V _ds and V _qs and the sinusoidal signals sin (θ _PLL ) and cos (θ _PLL ), respectively; An adder which adds a signal input from the multiplier and outputs it as a PLL output error (PLLerr = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )), A PI controller such that the above-described PLL output error (PLLerr = -V _ds sin (θ _PLL ) + V _qs cos (θ _PLL )) becomes 0 such that V _qs cosθ = V _ds sinθ, And a gain adjuster for adjusting the gain of the signal input from the PI controller 6 and an integrator for integrating and outputting the signal input from the gain adjuster 8. Synchronous loop. The method of claim 1, And (Va + Vb + Vc) / 3) is subtracted as the zero-phase component described above.

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