JP3518511B2 - Method for detecting isolated operation of distributed power supply - Google Patents

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 source that is interconnected with a power system.

[0002]

2. Description of the Related Art Conventionally, as a distributed power source (distributed power source) that is interconnected with a power system such as a distribution system, an inverter type such as a solar power generation facility and a rotation using a gas turbine generator etc. There is a machine type, but in any distributed power source, measures are taken to prevent islanding in order to protect the grid.

As a measure for preventing the isolated operation, when a transition from the interconnected operation of the distributed power source to the isolated operation occurs due to the system stop, this transition is detected and the distributed power source is disconnected from the system,
This is to prevent electric shock on the system side.

As a method of detecting the transition from the interconnected operation to the isolated operation, there are a passive method of passively detecting from a sudden change in the voltage phase and frequency of the system, and a current and a voltage that cause disturbance in the system. There is an active method that constantly injects the voltage and frequency of the system by injection and actively detects from the degree of this fluctuation, but the passive method is generally excellent in high speed, and the transition to islanding operation can be performed quickly. There is an advantage that can be detected.

As one of the passive method for detecting the isolated operation, there is a voltage phase jump detection method described in, for example, Japanese Patent Laid-Open No. 8-88897, which is a system stoppage. This is a method of detecting the transition from the sudden change in the voltage phase of the system due to the imbalance between the power generation output of the distributed power source and the load when the distributed power source is switched from the interconnected operation to the isolated operation.

That is, when the distributed power source shifts from the interconnected operation to the isolated operation due to the system stop, the load power factor of the system changes from the power factor during the interconnected operation, and this power factor change is regarded as a change of the voltage phase of the system. appear.

Then, for example, at time tx in FIG. 6, when the distributed power source shifts from the interconnected operation to the isolated operation due to the system stop, the phase of the system voltage (voltage phase) shown by the solid line in the figure jumps momentarily. Sudden change.

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 regular one cycle during the independent operation are positive and
Negative half cycles are both N / 2 counts long,
The length becomes N counts, and only one cycle immediately after the time tx suddenly changes to N ′ counts (N ≠ N ′).
Negative half cycle is N "count, N '" count (N ", N'" ≠ N / 2).

Therefore, conventionally, the number of clock pulses between zero cross points of the system voltage is measured to monitor the number of clock pulses in each one cycle, and the count number N → N ′ →
The jump of the system voltage phase is detected from the sudden change of N, and the transition from the interconnected operation of the dispersed power sources to the isolated operation due to the system stop is performed.

[0010]

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

According to the present invention, it is possible to accurately detect a shift from the interconnected operation of a distributed power source to a stand-alone operation due to system stoppage by a voltage phase jump detection method while preventing erroneous detection due to system noise, load fluctuations and the like. It is also an issue to provide a concrete method for its detection.

[0012]

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

Therefore, in the reference cycle, which is a predetermined cycle before the current cycle, it is assumed that the distributed power sources are interconnected and the system is normal, and the system data is converted from sampling data (voltage sampling data) by A / D conversion of the system voltage. The wave voltage component is digitally repeatedly extracted, and 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.

When the system is stopped in the current cycle and the distributed power source shifts from the interconnected operation to the independent operation, a sudden change in the voltage phase occurs in the system and the voltage phase of the extracted component of the current cycle is extracted from the reference cycle. The voltage phase of the component deviates by more than a predetermined value.

Then, based on the comparison of the system fundamental wave voltage components of both cycles, the deviation of the voltage phase of the predetermined value or more is detected a plurality of times (set times), and the system is detected on the condition of the plurality of detections. A sudden change in the voltage phase is detected, and a shift from the interconnected operation to the isolated operation due to the system stop of the distributed power source is detected.

[0016] In this case, erroneous detection due to system noise, load fluctuations, etc. is prevented and the shift to islanding operation is detected under the condition of detecting a plurality of cycles of a large deviation of the phase of the system voltage. There is no erroneous detection that can occur when detecting from a single change in the cycle length associated with a sudden change in voltage phase, and a highly reliable voltage phase jump detection method for isolated operation detection of a distributed power supply can be provided.

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

When the fixed sampling method is used, the phase difference 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 based on the frequency variation of the system fundamental wave. Is corrected and the phases of the two voltage components are compared, the detection accuracy is significantly improved.

On the other hand, the sampling of the detection voltage of the system is
The sampling frequency may be synchronized with the frequency of the system fundamental wave, and in this case, the highly accurate isolated operation detection of the voltage phase jump method can be performed without performing the correction calculation of the error based on the frequency fluctuation.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a single wire connection showing a distributed power supply 1 and an islanding operation detection device 2 thereof, which is connected to a distribution line 3 as an electric power system through a switch 4 for interconnection / disconnection and the inverter type or The rotating machine type distributed power supply 1 is connected, and when the system is normal, the distributed power supply 1 is connected to the system power supply.

Further, the voltage of the distribution line 3 (system voltage) 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 detector 2, the low pass filter (LPF) 7 for removing the folding error (noise) of digital processing, and the sample and hold circuit (S).
/ H circuit) 8.

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

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

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

On the other hand, the signal of the measured voltage v (t) passed through the low pass filter 7 is also supplied to the frequency measuring circuit 12,
The circuit 12 measures, for example, the system fundamental wave frequency component of the measurement voltage v (t) by filtering 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 by digital filter processing, for example, based on what is called Fourier calculation, Repeating the extraction of the system fundamental wave voltage component (vector amount) at the sample and hold intervals described above, and by the voltage phase detection processing, one cycle, which is a predetermined cycle before the current cycle (latest cycle), is checked for the interconnection operation phase. As the reference cycle, compare the phase of the system fundamental wave voltage component of the current cycle (hereinafter referred to as the current cycle voltage phase) and the phase of the system fundamental wave voltage component of the reference cycle (hereinafter referred to as the reference cycle voltage phase) to determine the current cycle voltage phase Is deviated from the reference cycle voltage phase by more than the set value (settling value), that is, the phase jump 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 target cycle (0th cycle) is "0", and each one cycle before this cycle is sequentially cycled. "-1", "-"
2 ", ...," -6 ", ..., and each cycle after the" 0 "cycle is" +1 "," +2 ",
..., "+5", ..., A system stoppage occurs at time tx of the cycle of "-1", and the phase of the system fundamental wave voltage component changes from the phase at the time of interconnection operation before tx to the time of islanding operation. If the phase suddenly changes, the current cycle is before "-2",
After "-1" to "+3" and "+4", the comparison result of the voltage phase between the current cycle and the reference cycle four cycles before is as follows.

(B) The current cycle is before "-2", the current cycle is before "-2", and the reference cycle is before "-6" (if the current cycle is "-3", the reference cycle is in the figure). However, the comparison result shows no phase change because both cycles have the same phase of the interconnected operation. (B) Current cycle is "-1" to "+3" (i) Current cycle is "-1", reference cycle is "-5"
In this case, a system stoppage occurs in the current cycle, and the voltage phase of the current cycle includes a transient phenomenon, so the phase comparison result (whether or not there is a phase change) becomes indeterminate. (Ii) The current cycle and the reference cycle are "0" and "-".
4 ”,“ +1 ”and“ -3 ”, and“ +2 ”and“ -2 ”, the current cycle is the independent operation phase and the reference cycle is the interconnection operation phase. During this time, the voltage phase of both cycles is Is surely deviated by more than the set value, and the phase comparison result has a phase change more than twice. (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) Since the current cycle is "+4" or later, the current cycle is "+4" or later, the reference cycle is "0" or later, and both cycles have the same phase of the independent operation. Therefore, the phase comparison result is (a). There is no phase change as well.

That is, by comparing the phases of the system fundamental wave voltage components of the current cycle and the reference cycle, while the current cycle becomes a plurality of cycles immediately after the cycle at the system stop time tx, the voltage phase of the current cycle becomes the reference cycle. There are two or more cycles for detecting a phase change with a deviation of a set value or more, for example, 2 ° to 20 ° or more from the voltage phase. In the above example, the cycle difference between the current cycle and the reference cycle was set to 4, but by increasing this value, the number of detection cycles with a phase change can be increased to 3 or more, and more reliable detection can be performed. it can.

When the presence of this phase change is detected twice or more (2 cycles) a set number of times during the number of cycles from the reference cycle to the current cycle (here, 4 cycles), the memory circuit 11 is detected. Based on the memory of RAM,
Detects abrupt changes (jumps) in the voltage phase of the system fundamental wave voltage component due to system shutdown, and detects the transition to islanding.

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

In this case, the transition from the interconnected operation of the distributed power source 1 to the isolated operation is performed on condition that the voltage jump due to the system stoppage of the system fundamental wave voltage component of the distribution line 3 is detected twice or more times. Since the system noise is detected, it is possible to prevent erroneous detection due to load fluctuations and significantly improve the reliability of detection of the shift to islanding operation. It is possible to prevent islanding.

Next, the specific arithmetic processing of the arithmetic processing unit 9 will be described. First, the rated angular frequency of the system fundamental wave of the distribution line 3 is ω ₀ = 2π · f ₀ , (f ₀ is 60 Hz or 5
0Hz system fundamental frequency), 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 can be obtained by the Fourier transform of the following equations 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 of one cycle of the system fundamental wave), the cos component Vc and sin component Vs of one cycle are given by
As shown in.

[0037]

[Equation 3]

[0038]

[Equation 4]

Then, assuming that the reference cycle is one cycle n cycles before the current cycle, the voltage Vi in the equations (3) and (4) is sampled at the sampling points of each one cycle of each mark of the system voltage in FIG. Voltage V _{0 to} V _2k-1 , ..., V _2kn
˜V _{2k (n + 1) −1} , and at time t ₀ , the latest sampling voltage V ₀ of the current cycle with i = ₀ is obtained, and time −
When (2π / ω ₀ ) · n, the first sampling voltage V _2kn of the reference cycle of i = _2kn is obtained.

Further, the cos component Vc, s of the current cycle
Assuming that the in component Vs is Vc ₀ and Vs ₀ , Vc ₀ and Vs ₀ are the cos and sin components of the voltage fundamental wave obtained from the sampling voltages V _{0 to} V _2K-1 of the current cycle in FIG. 3, and n cycles Cos component Vc, s of the previous reference cycle
If the in component Vs is Vcn, Vsn, Vcn, Vs
n is the sampling voltage V _{2kn to} V of the reference cycle in FIG.
The cos component of the voltage fundamental wave obtained from _{2k (n + 1) -1} , s
It is an in component.

Then, the arithmetic processing section 9 determines whether the current cycle is 2
Cos component V of k sampling voltages V _{0 to} V _{2k- 1}
c ₀ , sin component Vs ₀ and cos component Vcn of _2k sampling voltages V _{2kn to} V _{2k (n + 1) −1} of the reference cycle,
The extraction of the sin component Vsn is repeated.

Further, the cos of the extracted reference cycle
Based on the vectors of the component Vcn and the sin component Vsn, the phase of the vector of the cos component Vc ₀ and the sin component Vs ₀ of the current cycle deviates in the advance direction or the delay direction by the set value or more, and the shaded area in FIG. It detects whether or not it becomes a vector.

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

Then, the cos component Vc _{0 of} the current cycle,
Whether or not the vector of the sin component Vs _{0 is} the vector in the shaded area in FIG. 4 can be detected by whether or not the following formula 5 or formula 6 is established, and if so, the vector of both components Vc ₀ and Vs ₀ Is located in the shaded area in FIG. In addition, <,> in both equations represent inner products.

[0045]

[Equation 5] <(Vcn + jVsn) · e ^{j (90 ° + θ)} , (Vc ₀
+ JVs ₀ )> ≧ 0

[0046]

[Equation 6] <(Vc ₀ + jVs ₀ ) · e ^{−j (90 ° + θ)} , (Vc ₀
+ JVs ₀ )> ≧ 0

In the above calculation, the inner product calculation section is expanded and P
= Vcn · Vc ₀ + Vsn · Vs ₀ , Q = Vcn · Vs ₀
As −Vsn · Vc ₀ , this is the same as the determination based on whether or not the following _equation 7 or 8 is established, and the arithmetic processing unit 9 makes a cos component Vc ₀ ,
It is detected that the sin component Vs ₀ is a vector in the shaded area in FIG. 4, and it is detected that there is a phase change.

[0048]

[Equation 7] P · sin θ−Q · cos θ ≦ 0

[0049]

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

When the presence of the phase change is detected the set number of times, the shift to the isolated operation is detected.

By the way, it is easy to carry out the A / D conversion of the A / D converter 10 by a fixed sampling method in which the sampling frequency is made constant based on a clock pulse having a constant frequency. When the system frequency of the electric wire 3 fluctuates, the 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, ω = ω ₀ (1+) where ω is an angular frequency including the frequency fluctuation of the input signal v (t).
Δ), (Δ is the amount of frequency fluctuation), and when the absolute value (amplitude) of the input signal v (t) is 1, then v
(T) = sin (ω · t + θ), (θ is an initial value).

Then, when this input signal v (t) is Fourier-transformed 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,
The reference cycle n cycles before the current cycle is − (n + 1) regardless of whether the frequency of the input signal v (t) fluctuates.
· (2π / ω ₀ ) -− n · (2π / ω ₀ ), where c
The os component Cn and the sin component Sn are expressed by the following equations 11 and 1
It can be obtained from the formula of 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 the gain variation and the phase variation based on the frequency variation of the system.
3, expressed by the equation (14).

Δ in the equation is Δ = (ω-ω ₀ ) / ω ₀ =
It is a frequency variation amount of (f−f ₀ ) / f ₀ , and is {2 / (2+
Δ)} · {sin (Δπ) / Δπ}, {2 (1 + Δ) /
(2 + Δ)} · {sin (Δπ) / Δπ} is the gain fluctuation, and (2n + 1) Δπ is the phase fluctuation.

[0061]

[Equation 13]

[0062]

[Equation 14]

In the two equations (13) and (14), if the frequency fluctuation amount Δ of the system voltage is 0, Δ → 0, {sin
Since (Δπ) / Δπ} → 1 is satisfied, Cn = cos
θ, Sn = sin θ, and both components Cn, Sn without error
Is extracted.

However, in the case of the fixed frequency sampling method, when the frequency fluctuation amount Δ is not 0, the equations 13 and 1 are given.
As is clear from the equation 2 of 4, the amplitudes and phases of the components Cn and Sn deviate from each other, and particularly the fluctuation of the phase is greatly influenced by the cycle number n.

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

Therefore, in the case of the fixed frequency sampling method, the arithmetic processing section 9 calculates the component Cn, which is based on the frequency variation Δ.
The error between Sn, C ₀ and S ₀ is corrected by the calculation described below.

First, in the two equations (13) and (14), assuming that the frequency variation Δ is practically | 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]

Also, the components C ₀ and S ₀ of the current cycle with 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), the cos components C ₀ and Cn have a gain of 1 / third compared to the sin components S ₀ and Sn in both the current cycle and the reference cycle.
(1 + Δ) small, the components Cn and Sn of the reference cycle apparently have a phase delay of 2nΔπ compared with the components C ₀ and S ₀ of the current cycle.

Then, in order to detect the transition from the phase change between the current cycle and the reference cycle to the islanding operation, basically only the phase shift of the voltage components of both cycles based on the frequency fluctuation of the system should 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 this gain accurately by including the terms of sin (Δπ) / Δπ in the equations (13) and (14), and multiply the cos components C ₀ and Cn by (1 + Δ) to obtain sin. It suffices to equalize the components S ₀ , Sn.

Therefore, 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 the phases of the components Cn and Sn of the reference cycle are 2nΔπ.
, The component C ₀ of the current cycle and the reference cycle,
The phase shifts of S ₀ , Cn, and Sn are corrected, and the frequency fluctuation of the system in the case of the fixed sampling method is corrected.

First, when the gain correction is performed, the components Vc ₀ and Vs _{0 of} the current cycle and the components Vcn and Vsn of the reference cycle.
Becomes components Vc ₀ ′, Vs ₀ ′, Vcn ′, and Vsn ′ indicated by the following _equations 19, 20, 21, and 22 after correction.

[0079]

[Formula 19] Vc ₀ '= (1 + Δ) · Vc ₀

[0080]

## EQU20 ## Vs ₀ '= Vs ₀

[0081]

(21) Vcn ′ = (1 + Δ) · Vcn

[0082]

(22) Vsn '= Vsn

Next, when the phase is corrected, the inner product calculation judgments of the equations 5 and 6 are as shown in the following equations 23 and 24.

[0084]

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

[0085]

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

[0086] In addition, the number 23, to expand the inner product calculation unit number 24, P = Vcn '· Vc 0' + Vsn '· Vs 0',
Assuming that Q = Vcn ′ · Vs ₀ ′ −Vsn ′ · Vc ₀ ′, the operation determination formula for phase change detection is as shown in the following equations 25 and 26.

[0087]

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

[0088]

[Equation 26] P · sin (θ−2nΔπ) + Q · cos
θ-2nΔπ) ≦ 0

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

First, in step Z _1, the hold output of the current (latest) sampling value is converted into voltage sampling data by the A / D converter 10 using the fixed sampling method.
The data is converted, and the data is written into the memory circuit 11 by the arithmetic processing unit 9 to be accumulated and held.

Next, in step Z ₂ , the arithmetic processing unit 9 reads the current measurement result of the frequency measuring circuit 12, writes it in the memory circuit 11 to store and store it, and stores the latest result stored in the memory circuit 11. A predetermined number of measurement results are averaged to remove a sudden change in frequency and the like to grasp the current system fundamental wave frequency f.

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

In step Z ₄ , the frequency variation Δ is calculated from Δ = (f−f ₀ / f ₀ ), (f: current system fundamental frequency, f ₀ : reference system fundamental frequency). To do.

Then, in step Z ₅ , the correction calculations of the equations 19 to 22 are performed to obtain the components Vc ₀ , Vs ₀ , Vcn, V
Let sn be the components Vc ₀ ′, Vs ₀ ′, Vcn ′, Vsn ′ To P = Vcn ′ · Vc ₀ ′ in step Z ₆
+ Vsn ′ · Vs ₀ ′, Q = Vcn ′ · Vs ₀ ′ −Vs
Calculate n ′ · Vc ₀ ′.

Further, in step Z ₇ , the phase change detection operation of the equations (25) and (26) is performed. If the results of both equations are positive (> 0), the operation processing unit is performed in step Z _8. The detection timer 9 is reset, the process returns to step Z ₁ via step Z ₉ , and the process is repeated from step Z ₁ .

On the other hand, at step Z ₇ , the calculation result of the equation of the equation 25 or the equation of the equation 26 becomes ≦ 0, and when the phase fluctuation is detected, the process shifts from the step Z ₇ to the step Z ₁₀ .
The detection timer is started, the process returns to step Z ₁ through step Z ₉ , and the process is repeated from step Z ₁ .

When the voltage phase jumps due to the stoppage of the system, the process returns from step Z ₇ through steps Z ₁₀ and Z ₉ to step Z ₁ repeatedly, and when this repetition reaches the set number of times. , The detection timer times out, and the process shifts from step Z ₉ to step Z ₁₁ to detect the shift to the isolated operation, and the contact _and display signals are output.

Therefore, the fixed sampling method makes it possible to reliably transfer the distributed power source 1 to the independent operation without being affected by the system noise, load fluctuation, and the like, and without being affected by the 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 method with high property.

By the way, when the so-called synchronous sampling method is adopted instead of the fixed sampling method, for example, a PLL synchronizing circuit which operates in synchronization with the frequency of the system fundamental wave based on the measurement result of the frequency measuring circuit 12 is used as the detecting device 2. The A / D converter 10 may perform A / D conversion at a sampling frequency synchronized with the frequency of the system fundamental wave based on the clock pulse synchronized with the frequency of the system fundamental wave of the PLL synchronization circuit.

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

The interval (the number of cycles) between the current cycle and the reference cycle is not limited to the one described above, and it goes without saying that it may be set appropriately according to the state of the system.

[0102]

The present invention has the following effects. In the reference cycle that is a predetermined cycle before the current cycle, it is assumed that the distributed power supply 1 is operating normally and the distributed power supply 1 is interconnected, and the sampling data (voltage sampling data) by A / D conversion of the system voltage is used to determine the system fundamental voltage component. Is repeatedly digitally extracted, and 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. A system stoppage occurs and the distributed power source 1 shifts from the interconnected operation to the isolated operation. At this time, a deviation of the phase of the voltage component of the system fundamental wave in both cycles is detected multiple times (set number of times), and if the multiple times are detected, a sudden change in the voltage phase of the system is detected and the distributed power supply is detected. It is possible to detect the shift from the interconnected operation to the isolated operation due to the system stop of No. 1.

Therefore, on condition that a large deviation of the phase of the system voltage is detected a plurality of times (a plurality of cycles), erroneous detection due to system noise and load fluctuation is prevented, and the distributed power source 1 by the system stoppage by the voltage phase jump detection method. It is possible to detect the shift to independent operation of the system, and there is no erroneous detection that can occur when detecting from a single change in the cycle length due to a sudden phase change in the system voltage, and a highly reliable voltage phase jump detection method. Can be provided.

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 can be easily performed without using a PLL synchronizing circuit or the like. is there.

When the fixed sampling method is used, the phase difference 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 based on the frequency variation of the system fundamental wave. When the phases of the two voltage components are corrected by comparing the above, the detection accuracy is significantly improved, and the fixed sampling method makes it possible to perform islanding operation detection of the voltage phase jump detection method with extremely high reliability.

Furthermore, the detection voltage of the system may be sampled at a sampling frequency synchronized with the frequency of the system fundamental wave. In this case, the reliability is calculated without performing the error correction calculation based on the frequency fluctuation. It is possible to perform islanding operation detection with a high voltage phase jump detection method.

[Brief description of drawings]

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

2 is a waveform diagram for explaining islanding detection in FIG. 1. FIG.

FIG. 3 is an explanatory diagram of voltage phase comparison of the arithmetic processing unit of FIG.

FIG. 4 is an explanatory diagram of determination of a phase shift of the arithmetic processing unit of FIG.

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

FIG. 6 is a waveform diagram for explaining islanding detection in a conventional example.

[Explanation of symbols]

1 distributed power supply 2 islanding operation detector 3 distribution lines 8 sample and hold circuit 9 Arithmetic processing section 10 A / D converter

Claims (4)

(57) [Claims] 1. A distributed power source of a voltage phase jump detection system, which detects a transition from the interconnected operation to the independent operation due to a system stoppage of a distributed power source that is interconnected to an electric power system from a sudden change in the voltage phase of the system. In the islanding detection method, the detected voltage of the system is sampled and A / D converted, and the voltage sampling data obtained by the A / D conversion is digitally filtered to extract the system fundamental wave voltage component. The phase of the grid fundamental wave voltage component of the current cycle and the phase of the grid fundamental wave voltage component of the reference cycle are repeatedly compared by using one cycle before the predetermined cycle as a reference cycle of the interconnection operation phase, and Based on the deviation of the phase of the system fundamental wave voltage component of the current cycle from the phase of the system fundamental wave 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 the detection voltage of the power system,
The method for detecting isolated operation of a distributed power supply according to claim 1, wherein the sampling frequency is fixed and a fixed sampling method is used. 3. A 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 is corrected, The method for detecting isolated operation of a distributed power source according to claim 2, wherein the phases are compared. 4. Sampling of the detected voltage of the power system,
The method for detecting isolated operation of a distributed power source according to claim 1, wherein the sampling frequency is synchronized with the frequency of the system fundamental wave.