JP2002218661A - Sole operation detecting method of distributed power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect shift to a sole operation from system operation of a distributed power supply caused by a system interruption by a voltage phase skip detection system, preventing an erroneous detection due to such as noise and load fluctuation of a system. SOLUTION: A detected voltage of a power system (distribution line) is sampled to perform an A/D conversion, sampled voltage data obtained by the A/D conversion is processed through a digital filter, of a system fundamental wave voltage component from the sampled voltage data is repeated and comparison of the phase of the system fundamental wave voltage component of a current cycle with a phase of the fundamental wave voltage component of a reference cycle is repeated using one cycle prior to a predetermined cycle from the current cycle as a reference cycle of an linked phase. If it is detected two times or more as set times from the comparison that when the phase of the fundamental wave voltage component of the current cycle is deviated from the phase of the system fundamental wave voltage component of the reference cycle by a set value or more, a rapid change of the voltage phase is detected and shift to the sole operation of the distributed power supply 1 is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting an isolated operation of a distributed power supply that is connected to an electric power system.

[0002]

2. Description of the Related Art Conventionally, a distributed power source (distributed power source) that is connected to an electric power system such as a power distribution system or the like is an inverter type such as a photovoltaic power generation facility or a rotary type using a gas turbine generator or the like. Although there is a machine type, any of the distributed power sources is provided with measures to prevent islanding for the purpose of protecting the interconnection.

In order to prevent the islanding operation, when the transition from the interconnection operation of the distributed power supply to the islanding operation due to the system stop occurs, the transition is detected and the distributed power supply is disconnected from the system.
The purpose is to prevent electric shock on the system side.

[0004] As a method of detecting the transition from the interconnected operation to the isolated operation, a passive method of passively detecting a sudden change in the voltage phase or frequency of the system, and a current or voltage that causes disturbance to the system are used. There is an active method in which the voltage and frequency of the system are constantly fluctuated by injection, and active detection is performed based on the degree of this fluctuation.However, the passive method is generally excellent in high-speed operation and makes it possible to quickly shift to islanding operation. There are advantages that can be detected.

As one of the passive type islanding detection methods, there is a voltage phase jump detection type detection method described in, for example, JP-A-8-88979. Is a method of detecting the transition from a sudden change in the voltage phase of the system due to imbalance between the power generation output of the distributed power supply and the load when the distributed power supply shifts from the interconnected operation to the isolated operation.

That is, when the distributed power supply shifts from the interconnected operation to the isolated operation due to the system stoppage, the load power factor of the system changes from the power factor at the time of the interconnected operation, and this change in the power factor is regarded as a change in the voltage phase of the system. appear.

When, for example, at time tx in FIG. 6, the distributed power supply shifts from interconnected operation to isolated operation due to system stoppage, the phase (voltage phase) of the system voltage indicated by a solid line in the figure jumps instantaneously. Change suddenly.

In the case of FIG. 6, when the length between the zero-cross points of the voltage waveform is counted by the number of clock pulses, the normal one cycle during the interconnection operation and the single operation during the independent operation are positive and negative, respectively.
Both negative half cycles are N / 2 counts long,
The length becomes N counts, and only one cycle immediately after time tx suddenly changes to N ′ count (N ≠ N ′).
The negative half cycle is N ″ count, N ″ ″ count (N ″, N ′ ″ ≠ N / 2).

Therefore, conventionally, the number of clock pulses between the zero cross points of the system voltage is measured to monitor the number of clock pulses in each cycle, and the count number N → N ′ →
A jump of the system voltage phase is detected from a sudden change in N to detect a transition from the interconnected operation of the distributed power supply to the isolated operation due to the system stoppage.

[0010]

In the conventional method for detecting the isolated operation of the distributed power supply of the voltage phase jump detection method, when the transition from the interconnection operation of the distributed power supply to the isolated operation due to the system stop occurs, the instantaneous operation is performed. In order to detect the transition to the isolated operation of the distributed power supply based on one detection of the change in the cycle length of the system voltage due to the sudden change of the system voltage phase, for example, the zero cross point of the system voltage may be changed due to system noise or load fluctuation. If it fluctuates, there is a problem that erroneous detection is very easily performed, and highly reliable detection cannot be performed.

According to the present invention, it is possible to accurately detect the transition from the interconnection operation of the distributed power supply to the isolated operation due to the system stoppage by the voltage phase jump detection method while preventing erroneous detection due to system noise or load fluctuation. It is also an issue to provide a specific method of the detection.

[0012]

In order to solve the above-mentioned problems, in the method for detecting the isolated operation of a distributed power supply according to the present invention, a detected voltage of a power system is sampled and A / D-converted. The voltage sampling data obtained by the conversion is digitally filtered to extract a system fundamental voltage component, and one cycle before a predetermined cycle before the current cycle is set as a reference cycle of a connection operation phase, and the system fundamental wave voltage component of the current cycle is used as a reference cycle. The phase is repeatedly compared with the phase of the system fundamental voltage component of the reference cycle.Based on this comparison, the phase of the system fundamental voltage component of the current cycle is equal to or greater than the set value from the phase of the system fundamental voltage component of the reference cycle. Shift 2
When the set number of times or more is detected, a sudden change in the voltage phase is detected to detect the shift of the distributed power supply to the isolated operation.

Therefore, in the reference cycle before the current cycle by a predetermined cycle, it is assumed that the distributed power supply is operated in the normal state and the interconnection of the distributed power supply is performed, based on the sampling data (voltage sampling data) obtained by A / D conversion of the system voltage. The wave voltage component is repeatedly extracted digitally, and the phase of each time point of the extracted component of the current cycle is compared with the phase of each time point of the reference cycle.

Then, when a system stoppage occurs in the current cycle and the distributed power supply shifts from the interconnection operation to the isolated operation, a sudden change in the voltage phase occurs in the system, and the voltage phase of the component extracted in the current cycle is extracted from the reference cycle. It deviates from the voltage phase of the component by a predetermined value or more.

[0015] Based on a comparison of the system fundamental voltage components of both cycles, a deviation of the voltage phase of the predetermined value or more is detected a plurality of times (set number of times). A sudden change in the voltage phase is detected, and a transition from the interconnected operation to the isolated operation due to the system stoppage of the distributed power supply is detected.

In this case, under the condition that a plurality of cycles with a large shift in the phase of the system voltage are detected, erroneous detection due to system noise, load fluctuation, and the like is prevented, and the transition to islanding operation is detected. There is no erroneous detection that can occur when detecting from a single change in the cycle length due to a sudden change in voltage phase, and it is possible to provide a highly reliable method for detecting the isolated operation of a distributed power supply using the voltage phase jump detection method.

If the sampling of the detection voltage of the system is performed by a fixed sampling method with the sampling frequency kept constant, detection timing control and the like can be easily performed without using a PLL synchronization circuit or the like.

In the case of performing the above-mentioned fixed sampling method, a phase shift based on the frequency fluctuation of the system fundamental wave between the system fundamental voltage component of the current cycle and the system fundamental voltage component of the reference cycle extracted from the voltage sampling data. Is corrected and the phases of the two voltage components are compared, the detection accuracy is significantly improved.

On the other hand, sampling of the detection voltage of the system is as follows.
This may be performed at a sampling frequency synchronized with the frequency of the system fundamental wave. In this case, highly accurate islanding detection of the voltage phase jump method can be performed without performing the error correction calculation based on the frequency fluctuation.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a single line connection showing a distributed power supply 1 and an isolated operation detection device 2 thereof. The inverter type or the power supply system shown in FIG. The rotating power source 1 is connected, and when the system is normal, the distributed power source 1 is connected to the system power source.

The voltage (system voltage) of the distribution line 3 is measured by the instrument transformer 5 and the analog measured voltage v
The signal of (t) passes through the auxiliary transformer 6 of the detection device 2 and the low-pass filter (LPF) 7 for removing aliasing error (noise) in digital processing, and the sample-and-hold circuit (S)
/ H circuit) 8.

The circuit 8 repeats sampling and holding the signal of the measurement voltage v (t) at the cycle of the pulse based on the sample / hold command pulse given from the arithmetic processing unit (CPU) 9, and sometimes. The hold output of the instantaneous sampling value is supplied to the A / D converter 10.

The converter 10 A / D converts the momentary hold output of the sample-and-hold circuit 8 based on the A / D conversion command pulse given from the arithmetic processing unit 9 and converts the measured voltage v (t). The signal is converted into voltage sampling data at intervals of, for example, 30 electrical degrees.

Then, these voltage sampling data are written in the RAM of the memory circuit 11 connected to the arithmetic processing unit 9, and the latest fixed amount (for n cycles) is stored in this RAM.
Is held.

On the other hand, the signal of the measurement voltage v (t) passed through the low-pass filter 7 is also supplied to the frequency measurement circuit 12,
The circuit 12 measures the component of the system fundamental frequency of the measurement voltage v (t) by filtering, for example, and supplies the measurement result to the arithmetic processing unit 9.

Next, the arithmetic processing unit 9 executes various processing programs such as digital filter processing and voltage phase detection processing held in the ROM of the memory circuit 11, and executes digital filter processing based on a so-called Fourier operation, for example. The extraction of the system fundamental wave voltage component (vector quantity) is repeated at the sample and hold intervals, and one cycle before the current cycle (the latest cycle) by a predetermined cycle is determined by the voltage phase detection processing. A reference cycle, a phase of a system fundamental voltage component of the current cycle (hereinafter referred to as a current cycle voltage phase) is compared with a phase of a system fundamental voltage component of the reference cycle (hereinafter referred to as a reference cycle voltage phase), and a current cycle voltage phase is obtained. Whether the phase shifts from the reference cycle voltage phase by more than the set value (set value), that is, the jump of the phase Detecting the presence or absence of, accumulates hold the detection result to the RAM of the memory circuit 11.

When the reference cycle is one cycle, for example, four cycles before the current cycle, as shown in FIG. 2, the cycle of interest (0th cycle) is set to "0", and each cycle before this cycle is cycled in order. "-1", "-
2 ”,...,“ −6 ”,..., And one cycle after the cycle of“ 0 ”is“ +1 ”,“ +2 ”,
, “+5”,..., And a system stop occurs at time tx of the “−1” cycle, and the phase of the system fundamental wave voltage component is changed from the phase of the interconnected operation before tx during the isolated operation. If the phase suddenly changes, the current cycle is before "-2",
Since the current cycle is "-1" to "+3" or "+4" or later, the comparison result of the voltage phase between the current cycle and the reference cycle four cycles before is as follows.

(A) Current cycle is before "-2" Current cycle is before "-2" and reference cycle is before "-6" (if current cycle is "-3", the reference cycle is , But the cycle is "-7"), but since both cycles have the same phase of the interconnection operation, the comparison result shows no phase change. (B) Current cycle is "-1" to "+3" (i) Current cycle is "-1" and reference cycle is "-5"
In this case, the system stops in the current cycle, and the voltage phase of the current cycle includes a transient phenomenon, so that the phase comparison result (whether or not there is a phase change) is uncertain. (Ii) When the current cycle and the reference cycle are “0” and “−”
4 "," +1 "and" -3 ", and" +2 "and" -2 ", the current cycle is the isolated operation phase and the reference cycle is the interconnected operation phase. Deviates more than the set value, and the phase comparison result has a phase change twice or more. (Iii) The current cycle is “+3” and the reference cycle is “−
When it becomes "1", a system stop occurs in the reference cycle,
Since the phase of the reference cycle includes a transient phenomenon, the phase comparison result becomes uncertain as in (i). (C) After the current cycle is "+4" After the current cycle is "+4", the reference cycle is a cycle after "0", and both cycles have the same phase of the isolated operation. There is no phase change as in the case of.

That is, by comparing the phase of the system fundamental wave voltage component between the current cycle and the reference cycle, while the current cycle is a plurality of cycles immediately after the cycle at the system stop time tx, the voltage phase of the current cycle is changed to the reference cycle. , Two or more cycles are detected to detect the presence of a phase change with a deviation of at least the set value, for example, 2 ° to 20 ° or more. In the above example, the cycle difference between the current cycle and the reference cycle is set to 4. However, by increasing this value, the number of cycles for detecting the presence of a phase change can be increased to 3 or more. it can.

When this phase change is detected twice (two cycles) or more during the number of cycles from the reference cycle to the current cycle (here, during four cycles), the memory circuit 11 Based on the memory in RAM,
A sudden change (jump) of the voltage phase of the system fundamental wave voltage component due to system stoppage is detected, and a transition to islanding operation is detected.

Further, upon detecting the shift to the islanding operation, the input / output interface circuit 13 outputs a contact and display signal for the islanding operation to the outside, and the switch 4 is immediately opened by the contact signal to immediately open the distributed power source. 1 is disconnected from the distribution line 3 and the operation of the distributed power supply 1 is stopped.

In this case, the transition from the interconnection operation of the distributed power source 1 to the isolated operation is performed on condition that the voltage jump caused by the system stop of the system fundamental wave voltage component of the distribution line 3 is detected two or more times. Because of this, system noise can prevent erroneous detection due to load fluctuations, significantly improve the reliability of detection of transition to islanding operation, and provide a highly reliable voltage phase jump detection type distributed power supply. The prevention of islanding can be realized.

Next, a specific calculation process of the calculation processing section 9 will be described. First, the rated angular frequency of the system fundamental wave of the distribution line 3 is expressed as ω ₀ = 2π · f ₀ , where f ₀ is 60 Hz or 5 Hz.
0 Hz system fundamental frequency), the input signal v (t)
The cosine component (cos component) Vc and the sine component (sin component) Vs of the system fundamental wave voltage component included in the equation (1) can be obtained by the following Fourier transform of Expressions 1 and 2.

[0034]

(Equation 1)

[0035]

(Equation 2)

Then, in the case of a discrete value system of digital processing,
Assuming that the sampling frequency is 2k · f ₀ (2k is the number of samplings in one cycle of the system fundamental wave), the cos component Vc and sin component Vs in one cycle are expressed by the following _equations ( ₃₎ and (4).
It becomes as shown by.

[0037]

(Equation 3)

[0038]

(Equation 4)

Assuming that the reference cycle is one cycle which is n cycles before the current cycle, the voltage Vi in the equations (3) and (4) is the sampling of the system voltage at each sampling point in each cycle marked by the symbol in FIG. voltage _{V 0 ~V 2k-1, ...} , V 2kn
ＶV _{2k (n + 1) −1} , and at time t ₀ , the latest sampling voltage V ₀ of the current cycle at i = ₀ is obtained, and
When (2π / ω ₀ ) · n, the sampling voltage V _2kn becomes the first sampling voltage in the reference cycle of i = 2kn.

Further, the cos component Vc, s of the current cycle
Assuming that the in components Vs are Vc ₀ and Vs ₀ , Vc ₀ and Vs ₀ are the cos component and the sin component of the voltage fundamental wave obtained from the sampling voltages V _{0 to} V _{2K -1} of the current cycle in FIG. Cos component Vc, s of previous reference cycle
Assuming that the in component Vs is Vcn, Vsn, Vcn, Vs
n is the sampling voltage V _{2kn to} V in the reference cycle of FIG.
Cos component of voltage fundamental wave obtained from _{2k (n + 1) -1} , s
In component.

Then, the arithmetic processing section 9 executes the second cycle of the current cycle.
k number of sampling voltage _{V 0} ~V 2k- ₁ of cos component V
c ₀ , sin component Vs _0, and cos components Vcn of _2k sampling voltages V _{2kn to} V _{2k (n + 1) −1 in} the reference cycle,
The extraction of the sin component Vsn is repeated.

Further, the cos of the extracted reference cycle is
With reference to the vector of the component Vcn and the vector of the sin component Vsn, the phase of the vector of the cos component Vc ₀ and the vector of the sin component Vs _{0 in} the current cycle is shifted more than the set value in the leading direction or the lagging direction. Detect if it is a vector.

In FIG. 4, the cos component Vcn and the sin component Vsn of the reference cycle n cycles before are the vector α of the phase 0 °, and the cos component Vc ₀ and the sin component of the current cycle are The vector β of Vs ₀ has a phase set value θ (for example, 2 ° ≦
θ ≦ 20 °) or more, and is located in the shaded region.

Then, the cos components Vc ₀ ,
Whether or not the vector of the sine component Vs _{0 is} the vector of the hatched portion in FIG. 4 can be detected based on whether the following Expression 5 or Expression 6 is satisfied, and if it is satisfied, the vector of both components Vc ₀ and Vs ₀ Are located in the hatched portions in FIG. Note that <and> in both equations indicate inner products.

[0045]

## EQU5 ## <(Vcn + jVsn)) ej ^{(90 ° + θ)} , (Vc ₀
+ JVs ₀ )> ≧ 0

[0046]

<(Vc ₀ + jVs ₀ ) · e ^{−j (90 ° + θ)} , (Vc ₀
+ JVs ₀ )> ≧ 0

The above operation is performed by expanding the inner product operation unit and calculating P
= Vcn · Vc ₀ + Vsn · Vs ₀ , Q = Vcn · Vs ₀
-Vsn · Vc ₀ is the same as determining whether or not the following Expression 7 or 8 holds. The arithmetic processing unit 9 determines the cos components Vc ₀ ,
It is detected that the sin component Vs ₀ is a vector in the shaded area in FIG. 4 and the presence of a phase change is detected.

[0048]

[Mathematical formula 7] P · sin θ−Q · cos θ ≦ 0

[0049]

[Equation 8] P · sin θ + Q · cos θ ≦ 0

When the phase change is detected for the set number of times, the shift to the islanding operation is detected.

The A / D conversion of the A / D converter 10 can be easily performed by a fixed sampling method in which the sampling frequency is fixed on the basis of a clock pulse or the like having a constant frequency. When the system frequency of the electric wire 3 fluctuates, the aforementioned cos components Vc ₀ , Vcn,
The sin components Vs ₀ and Vsn include gain (amplitude) fluctuation and phase fluctuation based on this fluctuation.

That is, assuming that the angular frequency of the input signal v (t) including the frequency fluctuation is ω, ω = ω ₀ (1+
Δ) and (Δ is the amount of frequency variation). At this time, if the absolute value (amplitude) of the input signal v (t) is 1, v
(T) = sin (ω · t + θ), where (θ is an initial value).

Then, when this input signal v (t) is subjected to Fourier transform at a constant angular frequency ω ₀ , the cos component C and sin component S extracted by the Fourier transform are expressed by the following equations (9) and (10). As shown.

[0054]

(Equation 9)

[0055]

(Equation 10)

Further, if the fixed sampling method is used,
Regardless of whether or not the frequency of the input signal v (t) fluctuates, the reference cycle n cycles before the current cycle is − (n + 1)
(2π / ω ₀ ) to −n · (2π / ω ₀ ), and c
The os component Cn and the sin component Sn are represented by the following equations (11) and (1).
It is obtained from the equation (2).

[0057]

[Equation 11]

[0058]

(Equation 12)

When the Fourier transform (integration) of the equations (11) and (12) is performed, the components Cn and Sn include gain fluctuation and phase fluctuation based on the frequency fluctuation of the system.
3, expressed by Equation 14.

Note that Δ in the equation is Δ = (ω−ω ₀ ) / ω ₀ =
(F−f ₀ ) / f _{0 is} a frequency variation amount, and Δ2 / (2+
Δ)｝ · {sin (Δπ) / Δπ}, {2 (1 + Δ) /
(2 + Δ)｝ · {sin (Δπ) / Δπ} is a gain variation, and (2n + 1) Δπ is a phase variation.

[0061]

(Equation 13)

[0062]

[Equation 14]

In the equations (13) and (14), if the frequency variation Δ of the system voltage is 0, Δ → 0, ｛sin
Since (Δπ) / Δπ｝ → 1, Cn = cos
θ, Sn = sin θ, and both components Cn, Sn
Is extracted.

However, in the case of the fixed frequency sampling method, when the frequency variation Δ is not 0, Equations 13 and 1
As is clear from the two equations (4), the amplitudes and phases of the components Cn and Sn are shifted, and the fluctuation of the phase is greatly affected by the cycle number n.

Assuming that the cos component and the sin component of the current cycle of n = 0 are C ₀ and S ₀ , these components C ₀ and S ₀ are also apparent from the equations (13) and (14). The influence of the frequency variation Δ is included.

Therefore, in the case of the fixed frequency sampling method, the arithmetic processing unit 9 determines the components Cn,
The errors of Sn, C ₀ , and S ₀ are corrected by the calculation described below.

First, in Equations (13) and (14), assuming that the frequency variation Δ is a practical | Δ | ≦ 5%, | Δ |
= 5%, | sin (Δπ) /Δπ|=0.9
96, which can be regarded as | sin (Δπ) / Δπ | ≒ 1.

Therefore, the components Cn and Sn of the reference cycle n cycles before are represented by the following two equations (15) and (16).

[0069]

(Equation 15)

[0070]

(Equation 16)

The components C ₀ and S ₀ of the current cycle when n = ₀
Is expressed by the following two equations (17) and (18).

[0072]

[Equation 17]

[0073]

(Equation 18)

As is clear from the equations (15) to (18), in both the current cycle and the reference cycle, the gain of the cos components C ₀ and Cn is 1 / compared to the gain of the sin components S ₀ and Sn.
(1 + Δ) is small, and the components Cn and Sn of the reference cycle have an apparent phase delay of 2nΔπ as compared with the components C ₀ and S ₀ of the current cycle.

Then, in order to detect the shift to the isolated operation from the phase change between the current cycle and the reference cycle, basically, only the phase shift of the voltage components of both cycles based on the frequency fluctuation of the system needs to be corrected. However, in this embodiment, the gain is also corrected in order to further improve the detection accuracy.

It is not necessary to correct the gain accurately including the term of sin (Δπ) / Δπ in the equations (13) and (14), and multiplies the cos components C ₀ and Cn by (1 + Δ) to obtain a sin. It is sufficient to make them equal to the components S ₀ , Sn.

Then, the arithmetic processing unit 9 multiplies the component Cn of the reference cycle and the component C _{0 of the} current cycle by (1 + Δ) and sets the phase of the components Cn and Sn of the reference cycle to 2nΔπ.
Only the current cycle and the components of the reference cycle C ₀ ,
The phase shift of S ₀ , Cn, and Sn is corrected, and a correction is made for the frequency fluctuation of the system in the case of the fixed sampling method.

First, when the gain is corrected, the components Vc ₀ and Vs _{0 of} the current cycle and the components Vcn and Vsn of the reference cycle are obtained.
Are the components Vc ₀ ′, Vs ₀ ′, Vcn ′, and Vsn ′ shown by the following _equations 19, 20, 21, and 22 after the correction.

[0079]

Vc ₀ ′ = (1 + Δ) · Vc ₀

[0080]

Vs ₀ ′ = Vs ₀

[0081]

Vcn ′ = (1 + Δ) · Vcn

[0082]

Vsn '= Vsn

Next, when phase correction is performed, the inner product operation determination of Equations 5 and 6 is as shown in the following Equations 23 and 24.

[0084]

<２３ (Vcn ′ + jVsn ′) · e ^{j2n Δπ} · e
^{j (90 ° + θ)} ｝, (Vc ₀ '+ jVs ₀ ')> ≧ 0

[0085]

<２４ (Vcn ′ + jVsn ′) · e ^{j2n Δπ} · e
^{−j (90 ° + θ)} ｝, (Vc ₀ '+ jVs ₀ ')> ≧ 0

Further, by expanding the inner product calculation units of Expressions 23 and 24, P = Vcn ′ · Vc ₀ ′ + Vsn ′ · Vs ₀ ′,
Assuming that Q = Vcn ′ · Vs ₀ ′ −Vsn ′ · Vc ₀ ′, the equation for calculating the phase change detection is as shown in the following equations 25 and 26.

[0087]

(25) P · sin (θ + 2nΔπ) −Q · cos
(Θ + 2nΔπ) ≦ 0

[0088]

(26) P · sin (θ−2nΔπ) + Q · cos
θ−2nΔπ) ≦ 0

In the case of the fixed sampling method, the arithmetic processing section 9 operates specifically as shown in the flowchart of FIG.

First, in step Z ₁ , the A / D converter 10 converts the hold output of the current (latest) sampling value into the voltage sampling data by the fixed sampling method.
The data is converted, and the data is written into the memory circuit 11 by the arithmetic processing unit 9 and accumulated and held.

Next, in step Z ₂ , the arithmetic processing section 9 reads the current measurement result of the frequency measurement circuit 12, writes it in the memory circuit 11 and stores it, and also stores the latest measurement result stored in the memory circuit 11. A predetermined number of measurement results are averaged, abrupt changes in frequency are removed, and the current system fundamental frequency f is grasped.

[0092] Further, the memory circuit 1 in step Z ₃
From 2, 2k voltage sampling data of each of the current cycle and the reference cycle are read out, and the cos component Vc = Vc of the system fundamental wave voltage of the current cycle is obtained from the calculation of the equations (3) and (4).
c ₀ , sin component Vs = Vs _0, and cos component Vc = Vcn, sin component Vs =
Calculate Vsn.

[0093] Further, the step Z _4, a frequency variation Δ, Δ = (f-f 0 / f 0), (f: current line fundamental frequency, f _0: line fundamental frequency of the reference) calculated from I do.

[0094] Then, in Step Z _5, component Vc ₀ performs correction calculation of number 19 to number 22, Vs _0, Vcn, V
sn is represented by components Vc ₀ ′, Vs ₀ ′, Vcn ′, Vsn ′ It is corrected to, the step _{Z 6, P = Vcn '·} Vc 0'
_{+ Vsn '· Vs 0',} Q = Vcn '· Vs 0' -Vs
Calculate n ′ · Vc ₀ ′.

[0095] Further, the step Z _7, number 25, performs calculation of number 26 wherein the phase change detection, when the both operation result of both equations is positive (> 0), the arithmetic processing unit by Step Z ₈ reset the 9 detection timer, the process returns to step Z ₁ via the step Z _9, repeat the process from step Z _1.

On the other hand, in step Z ₇ , the calculation result of the equation (25) or the equation (26) becomes ≦ 0, and when a phase change is detected, the process proceeds from step Z ₇ to step Z ₁₀ .
Start the detection timer, the process returns to step Z ₁ through Step Z _9, repeat the process from step Z _1.

[0097] When the jump of the voltage phase by the system stop occurs is repeated to return to Step Z ₁ Step Z ₇ through Step Z _10, Z _9, this repeated reaches the set number of times , the detection timer times up, the process proceeds from step Z ₉ to step Z ₁₁ detects the shift to the islanding _contact, outputs a display signal.

Therefore, by the fixed sampling method, the shift of the distributed power supply 1 to the isolated operation can be reliably performed without being affected by system noise, load fluctuation, and the like, and without being affected by system frequency fluctuation. The distributed power supply 1 can be quickly disconnected from the system of the distribution line 3 by detecting the voltage phase jump system having high reliability.

In the case where a so-called synchronous sampling method is employed instead of the fixed sampling method, for example, a PLL synchronizing circuit operating in synchronization with the frequency of the system fundamental wave based on the measurement result of the frequency measuring circuit 12 is provided by the detecting device 2. The A / D conversion of the A / D converter 10 may be performed at a sampling frequency synchronized with the frequency of the system fundamental wave based on a clock pulse synchronized with the frequency of the system fundamental wave of the PLL synchronization circuit.

In the case of this synchronous sampling method, the correction of the fluctuation of the system fundamental wave frequency can be omitted, and there is an advantage that the calculation load of the calculation processing unit 9 is reduced.

The interval (the number of cycles) between the current cycle and the reference cycle is not limited to the above-described embodiment, but may be appropriately set according to the state of the system.

[0102]

The present invention has the following effects. At the time of the reference cycle that is a predetermined cycle before the current cycle, it is assumed that the distributed power supply 1 is operated in a grid-connected state and the grid-based fundamental wave voltage component is determined based on sampling data (voltage sampling data) obtained by A / D conversion of the grid voltage. Is repeatedly extracted digitally, the phase at each time point of the extracted component of the current cycle is compared with the phase at each time point of the reference cycle, and a system stoppage occurs, and the distributed power supply 1 shifts from interconnected operation to isolated operation. In some cases, a deviation of the phase of the system fundamental wave voltage component of both cycles by a predetermined value or more is detected a plurality of times (set number of times), and on the condition of the detection of the plurality of times, a sudden change in the voltage phase of the system is detected. It is possible to detect a shift from the interconnection operation to the islanding operation due to the one system stop.

Therefore, on condition that a large shift of the phase of the system voltage is detected a plurality of times (a plurality of cycles), erroneous detection due to system noise or load fluctuation is prevented, and the distributed power source 1 is stopped by the system stoppage in the voltage phase jump detection system. Is a reliable voltage phase jump detection method, which can detect the transition to islanding operation and eliminates the erroneous detection that can occur when detecting from a single change in the cycle length due to the conventional sudden change in system voltage phase. Can be provided.

The sampling of the detection voltage of the system can be performed by a fixed sampling method with a constant sampling frequency. In this case, there is an advantage that detection timing control and the like can be easily performed without using a PLL synchronization circuit or the like. is there.

When the above-mentioned fixed sampling method is used, the phase shift based on the frequency fluctuation of the system fundamental wave between the system fundamental wave voltage component of the current cycle and the system fundamental wave voltage component of the reference cycle extracted from the voltage sampling data. When the phase of the two voltage components is compared with each other, the detection accuracy is remarkably improved, and the isolated operation of the voltage phase jump detection method with extremely high reliability can be performed by the fixed sampling method.

Further, the sampling of the detection voltage of the system may be performed at a sampling frequency synchronized with the frequency of the system fundamental wave. In this case, without performing the error correction calculation based on the frequency fluctuation, the reliability can be improved. Of the voltage phase jump detection method with high voltage can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the islanding operation detection of FIG. 1;

FIG. 3 is an explanatory diagram of a voltage phase comparison of an arithmetic processing unit in FIG. 1;

FIG. 4 is an explanatory diagram of a determination of a phase shift by an arithmetic processing unit in FIG. 1;

FIG. 5 is a flowchart for explaining the operation of the arithmetic processing unit in FIG. 1;

FIG. 6 is a waveform diagram for explaining detection of an isolated operation in a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 distributed power supply 2 islanding operation detection device 3 distribution line 8 sample and hold circuit 9 arithmetic processing unit 10 A / D converter

Claims (4)

[Claims] 1. A distributed power supply of a voltage phase jump detection system, which detects a transition from the interconnected operation to an isolated operation due to a system stop of a distributed power supply connected to an electric power system from a sudden change in a voltage phase of the system. In the islanding operation detection method, the detected voltage of the system is sampled and A / D converted, and voltage sampling data obtained by the A / D conversion is digitally filtered to extract a system fundamental wave voltage component. One cycle earlier than the predetermined cycle is set as a reference cycle of the interconnection operation phase, and the phase of the system fundamental voltage component of the current cycle and the phase of the system fundamental voltage component of the reference cycle are repeatedly compared. Based on the deviation of the phase of the system fundamental voltage component of the current cycle from the phase of the system fundamental voltage component of the reference cycle by a set value or more, Isolated operation detecting method of distributed power supply, characterized in that when more than the set number of times the detection times, detects the shift to the isolated operation by detecting an abrupt change of the voltage phase. 2. Sampling of a detection voltage of a power system,
2. A method according to claim 1, wherein the sampling frequency is fixed and the fixed sampling method is used. 3. A phase shift between the system fundamental voltage component of the current cycle extracted from the voltage sampling data and the system fundamental voltage component of the reference cycle based on the frequency fluctuation of the system fundamental wave is corrected. 3. The method according to claim 2, wherein the phases are compared. 4. Sampling of a detection voltage of a power system,
2. The method for detecting the isolated operation of a distributed power supply according to claim 1, wherein the method is performed at a sampling frequency synchronized with a frequency of a system fundamental wave.