JPH09308112A - Single operation detection method for inverter for system interconnection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute the detection of active single operation of an inverter without fail. SOLUTION: In an inverter 2, which is interconnected with the system S where a power factor controller 26 generates an inverter gate reference signal from the difference between an active current command value Ip * and an output current Idi and the voltage Vout at interconnection point and the current is controlled by sine wave PWM control, a reactive current command value Q* which changes in triangular form is generated 32, and a voltage Vout signal is delay by 90 deg. 31, and a reactive current command value IQ* which changes in triangular form is made by multiplying it by the command value Q*, and it is added to a command value Ip * 24. On the other hand, reactive power QDET is detected from the voltage Vout and the current Iout 12, and |QDET-Q*| is compared with the reference value 35, and when it is over the reference value, this outputs an inverter stop signal. At power failure of the system, a breaker 52R2 is turned off and the system interconnection is cut off, so the reactive power control ceases to work, and QDET becomes a fixed value dependent upon load, so |QDET-Q*| changes into triangular wave form, and it gets over the reference value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid interconnection in a system in which a DC power source and a grid are interconnected via an inverter, such as a solar power generation system, when the grid is out of operation and is operated independently. For independent operation detection method of inverter for automobile.

[0002]

2. Description of the Related Art FIG. 6 shows a grid interconnection system of a photovoltaic power generation system. The inverter 2 is a device that converts direct current from the solar cell 1 into alternating current, is connected to the system (commercial power supply) S, and supplies power to the load L.

A state in which a power failure occurs in the system and power is supplied only by the inverter is called islanding. Since this isolated operation state hinders the restoration work of the system, etc., when this isolated operation occurs, this state must be promptly detected to stop the inverter.

When the power required by the load ≈ power supplied to the inverter, the voltage at the interconnection point a hardly changes even if the power fails in the system.
It is difficult to detect the islanding state with overvoltage relays, undervoltage relays, etc. connected to the interconnection point.

Therefore, the frequency and the electric power are constantly changed in small amounts by the control of the inverter, and when the isolated operation occurs, the change in the fluctuation is detected to determine the isolated operation, and the inverter is stopped. This method is called an active islanding detection method.

Table 1 shows a typical method of this active islanding detection method.

[0007]

[Table 1]

[0008]

By the way, in the above-mentioned conventional active independent detection method, the control circuit for detecting and determining the frequency and electric power which are changed by a minute amount becomes complicated, and the size of the printed board becomes large. There was a problem.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to perform active islanding detection simply by adding a simple circuit to the control circuit of the inverter. An object is to provide an independent operation detection method for an inverter for system interconnection that can be performed.

[0010]

According to the present invention, a power factor 1 control section produces an inverter gate reference signal from a difference signal between an active current command value and an output current signal and an interconnection point voltage signal, and sine wave PWM control is performed. A method for detecting an isolated operation of a grid-controlled inverter controlled by current, wherein a means for generating a reactive power command value that changes in a triangular wave shape and a phase of an interconnection point voltage signal are delayed by 90 ° and the reactive power is added to the signal. Means for multiplying the command value to output a reactive current command value that changes in a triangular wave shape, means for adding the reactive current command value that changes in a triangular wave shape to the active current command value, and the triangular wave reactive power command value And an isolated operation determination unit that takes the absolute value of the difference between the connection point reactive power detection value and compares it with a reference value and outputs a stop signal of the inverter when the reference value is exceeded.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 shows a control block diagram of an isolated operation detection type grid interconnection inverter. In FIG. 1, S is a system, L is a load, 1 is a solar cell, 2 is a current-controlled inverter that converts direct current from a solar cell input via a circuit breaker 72B into alternating current having a system frequency, and TR is a filter F. A transformer for boosting the inverter output voltage output via the inverter to the system side voltage, MG and 52R ₁ are connection switches and circuit breakers, 52
R ₂ is a system breaker, CT ₁ is an inverter control current detector that detects the inverter output current, and CT ₂ is a breaker 52R
Current detector for reactive power detection, which detects the system side current of P
T ₁ is a voltage detector for detecting the voltage of the contact point a, 20 (2
1 to 29) are control circuits of the inverter 2, 30 (31 to 3)
5) is an isolated operation detection unit added to the control circuit of the inverter.

In the control circuit 20, 21 is a voltage control amplifier for amplifying the deviation between the DC voltage command value V _DC * of the inverter and the DC voltage detection value V _DC by PI operation amplification, and 23 is from the output of the voltage control amplifier 21 and PT _1. The multiplier 24 multiplies the continuous contact voltage of _{No. 1} and outputs the active current command I _P * having the same phase as the _{continuous contact} voltage V _out, and 24 is the reactive current command I _P * from the independent operation detection unit 30. Adder for adding _Q *, 2
5 is a subtracter for subtracting the current I _det from CT ₁ from the added effective and reactive current commands, and 26 is the rated effective of the inverter in response to the continuous contact voltage V _out from PT ₁ and the current command from the subtracter 25. A power factor control unit that outputs a gate reference signal for adjusting the power factor to 1 when outputting electric power, 27 is a triangular wave generator for PWM, 28 is a gate reference signal from the power factor control unit and a triangular wave generator 27 A comparator for comparing the triangular wave and outputting a PWM control signal, and 29 is a gate logic circuit for outputting the PWM control signal to the gate of the inverter 2.

In the islanding operation detection unit 30, 31 is PT
_The phase shifter that delays the phase of the interconnection point detection voltage V _out from ₁ by 90 °, 32 is a triangular wave generating unit that changes and outputs the reactive power command value Q * in a triangular waveform, and 33 is 90 ° from the phase shifter 31.
Delay voltage and reactive power command value Q * from the triangular wave generator 32
And a multiplier 34 for outputting the reactive current command value _IQ * to the adder 24, and 34 is the voltage V _out from PT ₁ and CT ₂
From the current I _out2 from the reactive power detector, 35 detects the detected reactive power Q _DET from the triangular wave generator 32.
Absolute value of the difference of the reactive power command Q * from | _QDET- Q * |
Is obtained, and the absolute value is compared with a judgment standard, and when it exceeds the judgment standard, an independent operation judging unit outputs an inverter stop signal.

Next, the operation of this system will be described. The islanding operation detection unit 30 delays the interconnection point detection voltage V _out by 90 ° with the phase shifter 31 and multiplies this by the reactive power command value Q * (FIG. 2A) that changes in a triangular wave form from the triangular wave generator. A multiplier 33 multiplies it and outputs it as a reactive current command value I _Q * to the adder 24 of the control circuit 20 of the inverter to add it to the active power command value I _P *. Then, only the reactive current command value I _Q * changes while the active current command value I _P * remains constant.

The inverter 2 is controlled on the basis of the active current command I _P * and the reactive current command I _Q *, but when the system side circuit breaker 52R ₂ is OFF and is not connected to the system S, the reactive power is Since the control does not work, a reactive current depending on the load L flows. Further, when the circuit breaker 52R ₂ is ON and is connected to the system S, the reactive power control operates, so that the reactive current based on the reactive current command _IQ * and the reactive current depending on the load L flow.

As described above, when the inverter 2 is connected to the grid S, the reactive power control works, so that the reactive power that changes in a triangular wave shape is output from the inverter like the reactive power command value Q *. . Then, when the inverter is connected to the grid, the reactive power detection value detected by the reactive power detection unit 34 changes in a triangular wave shape (the first half of FIG. 2B).

When the system S fails, the circuit breaker 52R ₂ becomes OF
Since it becomes F, the reactive power control of the inverter 2 does not work as described above. Therefore, when a system power failure occurs, there is no reactive power that changes in a triangular wave due to the reactive current command _IQ *, and there is only a certain reactive power that depends on the load L.
The reactive power detection value Q _DET detected by the reactive power detection unit 34 becomes a constant value (the latter half of FIG. 2B).

However, the value of | Q _DET -Q * | changes in a triangular wave when a system power failure occurs (FIG. 2 (c)), and when the value exceeds a predetermined isolated operation determination reference value Q _S , it becomes independent. The operation determination unit 35 outputs an inverter stop signal to stop the inverter 2 (FIG. 2 (d)).

As described above, the connection contact voltage is delayed by 90 °, and the product of this and the reactive power command value in a triangular wave is multiplied by the reactive current command to control the grid interconnection inverter.
When reactive power at the interconnection point is detected and when | reactive power command value-reactive power detection value |> reference value, it is judged as an isolated operation state and the inverter is stopped, so active independent operation detection is ensured. Can be executed.

Embodiment 2 In this embodiment, in the circuit of FIG. 1, the independent operation determination unit 35 is provided with the following determination reference setting unit, and | Q _DET -Q
The value of * | was compared with the judgment reference value from this setting section.

That is, the reactive power detecting section 34 for the period T of the triangular wave of one cycle of the reactive power command value Q * from the triangular wave generator 32.
The reactive power detection value Q _{DET from} is integrated to obtain the bias component Q _B (Fig. 3 (a)), the bias component Q _B is subtracted from the reactive power detection value Q _DET for the next triangular wave one cycle, and that value is operated independently. A judgment criterion setting unit for outputting the judgment criterion value Q _S (FIG. 3B) is provided, and when | Q _DET −Q * | is compared with this judgment criterion value Q _S and an inverter stop signal is output when the criterion value is exceeded. I tried to output it.

Since the inverter 2 in FIG. 1 is controlled by the power factor control circuit 26 so that the power factor becomes 1.0 at the rated output, the bias component at this time becomes almost zero. Further, when the output of the inverter 2 is 0, the bias component becomes maximum and its value is determined by the capacitance of the capacitor C of the filter F. Therefore, the bias component Q _B has a linear relationship with the inverter output.

Therefore, by detecting the output of the inverter and calculating the bias component by calculation, subtracting this bias component from the reactive power detection value, and using this value as the criterion for the independent operation determination, the reactive power is detected when the system is normal. Since the command value Q * and the detected value Q _{DET of the above} are almost the same, the range of the value of | Q * -Q _DET | It will also be affected.

Embodiment 3 In this embodiment, the islanding operation detection unit 30 in the circuit of FIG. 1 is modified as shown in FIG.

In FIG. 4, reference numeral 36 is an active power detector for detecting the active power P _DET at the interconnection point from the interconnection point detection voltage V _out from PT ₁ and PT ₂ (FIG. 1) and the current I _out2 , and 37 is A correction value calculation unit for calculating the isolated operation determination correction value Q _H from the active power P _{DET according} to the graph of FIG. 5, and 38 is an isolated operation determination unit.

The islanding operation determination unit 38 is a triangular wave generation unit 32.
Calculating means for calculating the value of | Q * −Q _DET + Q _H | from the reactive power command Q * from the reactive power command Q *, the reactive power Q _DET from the reactive power detection unit 34, and the correction value Q _H from the correction value calculation unit 37. The absolute value thus obtained is compared with a reference value Q _S for independent operation determination, and when it exceeds the reference value, it is composed of a comparison means for outputting an inverter stop signal. In FIG. 4, 31 and 32
Are phase shifters and multipliers used in the same manner as in FIG.

Since the power factor control unit 26 of FIG. 1 is adjusted so that the power factor becomes 1 when the inverter 2 outputs the rated active power, the power factor = 1 when the active power≈0. However, the reactive power Q _{O corresponding} to the reactive current I _C flowing from the system to the capacitor C of the filter F is generated at the system interconnection point a.

Since the reactive power Q _{O for} this capacitor is generated irrespective of the reactive power command for islanding detection, at this time, | Q * −Q _DET | ≧ Q _O. Therefore, when the reactive power Q _O is larger than the isolated operation determination reference value, the isolated operation detection unit 30 in FIG. 1 may erroneously determine the isolated operation state.

However, the islanding operation detection unit 30 'shown in FIG.
Since | Q * -Q _DET + Q _H | is compared with the reference value Q _S for independent operation determination, the active power output from the inverter is 0 to 0.
In any range of 100%, the error judgment of the islanding operation detection by Q _O is eliminated.

[0030]

Since the present invention is configured as described above, the following effects can be obtained.

(1) The active islanding detection of the inverter can be surely executed.

(2) Since the conventional inverter only needs to add the islanding operation detecting section having a simple circuit configuration to the control circuit of the inverter for controlling the power factor at the rated active power output to be 1, the size of the printed board is increased. There is no need to do it, and at a low cost.

[Brief description of drawings]

FIG. 1 is a control block diagram showing an example of an islanding operation detection method according to the present invention.

FIG. 2 is a time chart showing an islanding detection characteristic.

FIG. 3 is an explanatory diagram of an islanding operation determination standard.

FIG. 4 is a block diagram showing another example of the islanding operation detection unit.

FIG. 5 is a graph for calculating an isolated operation determination correction value.

FIG. 6 is a system interconnection system configuration diagram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solar cell 2 ... Inverter 20 ... Inverter control circuit 24 ... Active / reactive current command value adder 26 ... Power factor control unit 30 ... Single operation detection unit 31 ... -90 degree phaser 32 ... Triangular wave reactive power Triangle wave generator 33 that generates a command 33 ... Multiplier 34 ... Reactive power detection unit 35 ... Individual operation determination unit _IP * ... Active current command value _IQ * ... Reactive current command value Q * ... Reactive power command value _QDET ... Invalid power detection value Q _S ... isolated operation determination reference value Q _H ... isolated operation determination correction value Q _O ... filter capacitor component reactive power

Claims (3)

[Claims] 1. A grid interconnection inverter for producing an inverter gate reference signal by a power factor controller from a difference signal between an active current command value and an output current signal and an interconnection point voltage signal, and performing current control by sine wave PWM control. In the isolated operation detection method, a means for generating a reactive power command value that changes in a triangular wave shape and a phase of the interconnection point voltage signal are delayed by 90 ° and the signal is multiplied by the reactive power command value to form a triangular wave shape. A means for outputting a varying reactive current command value, a means for adding the reactive current command value varying in a triangular wave shape to the active current command value, and the triangular wave reactive power command value and the interconnection point reactive power value An islanding operation detection method for a grid-connected inverter, comprising: an islanding operation determination means that takes an absolute value of the difference and outputs a stop signal of the inverter when the value exceeds a reference value when the difference is exceeded. 2. The inverter for grid interconnection according to claim 1, wherein the reactive power detection value is integrated to obtain a bias component, and the bias component is subtracted from the reactive power detection value to obtain an islanding operation determination standard. Independent operation detection method. 3. A single grid-connected inverter that controls the current by the sine-wave PWM control by creating an inverter gate reference signal by the power factor controller from the difference signal between the active current value and the output current signal and the interconnection point voltage signal. An operation detection method, a means for generating a reactive power command value that changes in a triangular waveform, and a phase of the interconnection point voltage signal delayed by 90 °, and the signal is multiplied by the reactive power command value to change in a triangular waveform. Means for outputting the reactive current command value, the means for adding the reactive current command value that changes in a triangular waveform to the active current command value, and the correction value calculation for obtaining the isolated operation determination correction value from the interconnection active power value. Means, absolute value calculation means for subtracting the connection point reactive power detection value from the reactive power command value, adding the isolated operation determination correction value, and obtaining the absolute value thereof, and comparing this absolute value with the independent operation reference value to obtain a reference value. The value Islanding detection method of system interconnection inverter, characterized by having a single operation determination means for outputting an inverter stop new signal If there example.