JP5893057B2 - Isolated operation detection device and isolated operation detection method - Google Patents

Description

  The present invention relates to an isolated operation detection device and an isolated operation detection method for a distributed power supply including an inverter linked to a system power supply.

  A distributed power source such as a solar cell or a fuel cell includes a power conditioner that converts a frequency and a voltage into AC power so as to be compatible with the power system in order to be used in conjunction with system power.

  The power conditioner includes a DC / DC converter that adjusts a DC voltage generated by a distributed power source to a predetermined DC voltage value, an inverter that converts DC power output from the DC / DC converter into AC power, An LC filter that removes high-frequency components from the output is provided.

  A ground fault or short-circuit accident occurs in the distribution line where the distributed power source is connected to the grid, or power transmission from the substation to the distribution line has stopped due to a planned power failure, etc. In this case, it is necessary to reliably disconnect the distributed power source from the distribution line in order to prevent the influence on the operation of the division switch and to ensure the safety of the work of the distribution line.

  The isolated operation detection method includes a passive method and an active method, and one or both of them are adopted for the power conditioner.

  Passive method is a method to detect sudden changes in voltage phase and frequency due to power generation output and load imbalance at the time of transition to isolated operation, voltage phase jump detection method to detect sudden change in voltage phase, transformer saturation phenomenon There is a third harmonic voltage distortion rapid increase detection method for detecting the accompanying third harmonic.

  The active method is a method that constantly changes the voltage and frequency by the control system of the power conditioner and the resistance added to the outside, and detects the change that becomes noticeable when shifting to independent operation. There are a slip mode frequency shift method for detecting frequency anomalies by applying positive feedback according to the above, a reactive power fluctuation method for giving a periodic reactive power fluctuation to an output and detecting a frequency fluctuation generated after shifting to an independent operation.

  In Patent Document 1, when the frequency suddenly changes due to an instantaneous drop in the system power supply or the like, it is possible to avoid the occurrence of a false detection (hereinafter referred to as “unnecessary detection”) that is in an isolated operation state, and to An independent operation detection device for an inverter is disclosed that aims to provide a (Fault Ride Through) function, that is, an operation detection device having an operation continuation performance during a system disturbance.

  The isolated operation detection device controls reactive power in a direction in which the frequency of the output voltage of the inverter promotes a change by positive feedback, and a value that changes stepwise according to the frequency change rate promotes a change by positive feedback. A function means for controlling reactive power in the direction, an abnormality detection means for judging an abnormality when a value based on a step-change value is equal to or higher than the isolated operation detection level, an AC power supply system, and The inverter reactive power is synchronized with the voltage phase of the inverter output and controlled to a predetermined reactive power by the output of the function means, and when the inverter is disconnected from the AC power system, the inverter reactive power is based on the frequency and the value that changes stepwise. Driving means for stopping the inverter when an abnormality is detected.

  Further, Patent Document 2 describes that the reactive power injected from each distributed power source to the power system when many units are connected is prevented from being canceled, and even if the reactive power and the load reactive power are balanced, the balanced state is maintained. An isolated operation detection device is disclosed which aims to make it possible to reliably detect an isolated operation by breaking the system.

  The isolated operation detection device is configured to additionally inject additional injection reactive power of a predetermined phase when the already injected reactive power balances with the load reactive power for a certain period, and after the additional reactive power injection for a certain period of time. After a short period of time, the phase of the already injected reactive power is determined based on the sign of the system frequency deviation, and the phase of the already injected reactive power from the sign of the system frequency deviation at the time of determination is a predetermined phase of the additional injected reactive power When the phase is in reverse phase, the additional injection reactive power of the phase corresponding to the sign of the system frequency deviation is injected again for a certain period, and the phase of the already injected reactive power from the sign of the system frequency deviation at the time of determination is added. When it is in phase with the predetermined phase of injection reactive power, the injection of additional injection reactive power is continued in the same phase for the remaining period after the injection of additional injection reactive power until a certain period of time elapses. It is configured.

  Patent Document 3 discloses an isolated operation detection device that can more reliably detect an isolated operation of a power source even when the influence of active fluctuations applied to the output power of a grid-connected inverter does not appear in the system cycle. Is disclosed.

  The islanding operation detection device includes a system cycle measuring unit that measures a system cycle of the system power supply every predetermined period, and an average for each predetermined cycle based on the system cycle measured by the system cycle measuring unit. An average system cycle calculation unit for calculating a system cycle, a plurality of the latest average system cycles calculated by the average system cycle calculation unit, and a deviation from each past average system cycle by a predetermined cycle, respectively. And a determination unit that determines that the power source is in an independent operation state when each of the calculated deviations exceeds a preset threshold value.

  Patent Document 4 discloses that even if the harmonic distortion voltage occurs due to a factor other than the single operation, the single operation can be accurately and quickly determined, and whether the change value of the harmonic distortion voltage has exceeded a threshold value. This is a method for determining whether or not a distributed power source is in an isolated operation state based on whether or not the above determination is made more than once and the number of determinations is changed according to changes in the system cycle. In addition, a method is disclosed in which it is determined whether or not the vehicle is operating alone by changing the threshold value to a plurality of values.

  Further, Non-Patent Document 1 discloses a frequency feedback system with step injection standardized as a standard active isolated operation detection system of a power conditioner for photovoltaic power generation. The frequency feedback method with step injection injects a preset reactive power in a direction to increase the deviation according to the deviation of the system frequency, and the frequency deviation is small and the harmonic voltage or the fundamental voltage is predetermined. This is a method of injecting a certain amount of reactive power for a predetermined time in the direction of decreasing the frequency when the variation condition is satisfied.

JP 2012-120285 A JP 2011-55678 A JP 2010-148201 A JP 2008-35619 A

Japan Electrical Manufacturers' Association JEM1498 issued on August 27, 2012

  The isolated operation detection device disclosed in Patent Document 1 is configured to inject reactive power in a direction that promotes the deviation when the frequency of the output voltage of the inverter fluctuates, in order to improve the responsiveness at that time However, there is a problem in that the apparatus configuration for unnecessary detection is complicated because it has a plurality of function means having different characteristics so as to further increase the amount of reactive power injected in accordance with the frequency change rate.

  Similarly, in Patent Documents 2, 3, and 4, in order to avoid unnecessary detection and to realize operation continuity performance (FRT) during system disturbance, a dedicated control block and control algorithm for unnecessary detection are constructed. There was a problem that control had to be complicated.

  Furthermore, even in the frequency feedback method with step injection defined in Non-Patent Document 1, a clear control circuit for ensuring sufficient responsiveness at the time of frequency feedback control in which reactive energy is injected according to the deviation of the system frequency is presented. However, in order to detect the isolated operation state within 0.2 seconds indicated by the standard, the reactive power injection amount is set according to the value of the frequency change rate as disclosed in Patent Document 1. The problem that the circuit etc. which raises becomes necessary and control becomes complicated is inherent.

  In view of the above-described problems, the object of the present invention is to support a multi-unit interconnection while having an FRT function even when a system frequency suddenly changes, a system voltage phase suddenly changes, or even when those changes continue for a long time. An independent operation detection device and an isolated operation detection method are provided.

In order to achieve the above-mentioned object, the first characteristic configuration of the isolated operation detection device according to the present invention is a distributed type having an inverter linked to a system power supply as described in claim 1 of the claims. A power source isolated operation detection device that measures a system frequency based on a zero cross timing of a system voltage (e _uw ), and a frequency obtained based on the system frequency measured by the system frequency measurement unit generating a reactive power injection amount calculating unit for calculating a reactive power injection quantity in accordance with the deviation, a reference system voltage signal synchronized with the phase angle (theta _uw) of the system voltage (e _uw) is input system voltage (e _uw) the first and the PLL processing unit, the second PLL processing for generating a reference reverse flow current signal synchronized with the phase angle (theta _sp) of reverse flow current _{(i sp)} are reverse flow current is input _{(i sp)} to With the door, and a feedback signal generator for generating a feedback signal based on the phase difference between the two signals (θ _uw -θ _sp), reactive current corresponding to the reactive power injected amount calculated by the reactive power injected amount calculating section Based on the command value and the feedback signal generated by the feedback signal generation unit, the reactive current control that feedback-controls the output current command value for the inverter so that the reactive power of the reactive power injection amount is injected from the inverter. And an inverter control unit that controls the inverter so that the output current value of the inverter becomes the output current command value, and the amount of electricity of the system power source when the reactive power of the reactive power injection amount is injected And an isolated operation detecting unit that detects whether or not the vehicle is in an isolated operation state.

When the system frequency is measured from the zero cross timing of the system voltage (e _uw ) by the system frequency measurement unit and a time-series frequency deviation occurs based on the system frequency, the reactive power injection amount calculation unit invalidates the frequency according to the frequency deviation The power injection amount is calculated. In the feedback signal generation unit, the reference system voltage signal synchronized with the phase angle (θ _uw ) of the system voltage (e _uw ) generated by the first PLL processing unit and the inverse generated by the second PLL processing unit A feedback signal is generated based on the phase difference (θ _uw −θ _sp ) with the reference reverse flow current signal synchronized with the phase angle (θ _sp ) of the tidal current (i _sp ).

  The reactive current control unit generates a reactive current command value corresponding to the reactive power injection amount and a feedback signal generated by the feedback signal generation unit so that the reactive power of the reactive power injection amount is appropriately injected from the inverter. Based on the feedback control of the output current command value of the inverter, the inverter control unit controls the inverter so that the output current value of the inverter becomes the output current command value. Then, the isolated operation detection unit is in the isolated operation state based on the amount of electricity of the system power source when the reactive power of the reactive power injection amount is injected, for example, the system frequency, the system voltage, the total harmonic distortion, etc. To detect.

  In this way, the reactive current control unit feedback-controls the output current command value of the inverter, so that reactive power of the reactive power injection amount that is the target value is accurately and promptly injected into the system power supply. As a result, reactive power injection Therefore, it is possible to quickly detect whether or not the vehicle is in an isolated operation state without detecting unnecessary, without using a complicated algorithm for detecting unnecessary.

  In the second feature configuration, as described in claim 2, in addition to the first feature configuration described above, the gain of the first PLL processing unit is larger than the gain of the second PLL processing unit. The point is set to the value.

The gain of the first PLL processing unit for obtaining the reference system voltage signal synchronized with the phase angle θ _uw of the system voltage (e _uw ) is the reference synchronized with the phase angle (θ _sp ) of the reverse flow current (i _sp ). Since it is set to a value larger than the gain of the second PLL processing unit for obtaining the reverse flow current signal, the system voltage (e _{uw) in} which the voltage, phase, etc. fluctuate transiently due to the disturbance generated on the system power supply side ) Can be obtained with higher sensitivity than the reference reverse current signal. Based on such a phase difference (θ _uw −θ _sp ), the reactive current control unit appropriately feedback-controls the output current command value of the inverter.

  The third feature configuration is the operation calculated by the first PLL processing unit in addition to the first or second feature configuration described above, as described in claim 3. When both the frequency and the system frequency measured by the system frequency measuring unit change in one direction at a plurality of continuous system periods, the system is determined to be in an isolated operation state.

  When reactive power is injected into the system power supply and the phase of the system power supply changes suddenly for some reason, even if the system frequency changes at that time, the system frequency does not change before and after that. Thus, when the power transmission from the system power supply stops and the single operation state is entered, the frequency subsequently fluctuates in the same direction. Therefore, a tendency that both the operating frequency calculated by the first PLL processing unit and the system frequency measured by the system frequency measuring unit using the zero cross signal change in one direction at a plurality of continuous system periods. By determining that the system is in an isolated operation state, it is possible to reliably avoid unnecessary detection of a sudden phase change (FRT) caused by a sudden phase change or a sudden drop in the system power supply.

Further, by using both the operation frequency and the system frequency, it is possible to avoid erroneous detection when a pulse-like pulse width occurs near the zero point of the system voltage _euw .

  In the fourth feature configuration, in addition to any one of the first to third feature configurations described above, the islanding operation detection unit is calculated by the first PLL processing unit. It is detected whether or not it is in a single operation state based on at least the current value of both the operating frequency and the system frequency measured by the system frequency measuring unit, the value before 1 system cycle, and the value before 2 system cycles It is in the point comprised as follows.

  Similar to the third characteristic configuration described above, when the phase of the system power supply changes suddenly, the system frequency does not fluctuate before and after that point of time, but when it becomes an independent operation state thereafter The frequency varies in the same direction. Therefore, by checking the behavior of the system frequency at least at three consecutive system cycles, it is possible to accurately detect whether or not the system frequency is changed due to a sudden phase change of the system power supply.

In the fifth feature configuration, as described in claim 5, in addition to the first or second feature configuration described above, the _islanding operation detection unit may detect a harmonic voltage fluctuation rate of the system voltage (e _uw ). Is in a point that it is detected that it is in a single operation state when the state exceeds a predetermined ratio and the state continues for a predetermined time.

  In the situation where reactive power is injected into the system power supply, even if the harmonic voltage of the system power supply fluctuates due to some reason, the harmonic voltage does not fluctuate significantly in the system cycle before and after that. When the power supply is stopped and the single operation state is entered, the harmonic voltage greatly fluctuates in subsequent continuous cycles. Therefore, when the harmonic voltage fluctuation rate of the system voltage exceeds a predetermined ratio continues for a predetermined time, it is possible to avoid unnecessary detection by detecting that the system is in an isolated operation state.

The sixth feature configuration is the operation calculated by the first PLL processing unit in addition to the first or second feature configuration described above, as described in claim 6. Based on the current value of both the frequency and the system frequency measured by the system frequency measurement unit, the value before one system cycle, and the value before two system cycles, when both change in one direction with a plurality of continuous system cycles It is a case where it is determined, and when the harmonic voltage fluctuation rate of the system voltage (e _uw ) exceeds a predetermined ratio and the state continues for a predetermined time, it is configured to detect that it is a single operation state. is there.

  By combining the fourth and fifth feature configurations described above, the system frequency behavior is checked at least in three consecutive system cycles, and the state where the harmonic voltage fluctuation rate of the system voltage exceeds a predetermined ratio continues for a predetermined time. By checking whether or not to do so, it becomes possible to more reliably avoid the unnecessary detection and to properly detect the single operation state.

  In the seventh feature configuration, as described in claim 7, in addition to any of the first to sixth feature configurations described above, the reactive power injection amount calculation unit may respond to a frequency deviation at a certain point in time. A frequency-corresponding reactive power injection amount calculation unit for calculating the reactive power injection amount from the frequency deviation / reactive power injection amount characteristic table in which the reactive power injection amount is determined so that the frequency deviation thereafter gradually increases, and a frequency at a certain time A step reactive power injection amount calculation unit that calculates a constant amount of reactive power injection in a constant direction when the fundamental wave voltage and / or the harmonic voltage fluctuates without variation in deviation. is there.

  Even when distributed power supplies are connected to multiple power supplies, reactive power with the same tendency is injected from each distributed power source by the step reactive power injection amount calculation unit. In addition to avoiding inconvenient situations that cancel out reactive power, it is possible to avoid unnecessary detection without providing a separate complicated detection algorithm, and to ensure that it is in an isolated operation state. It becomes possible to detect whether or not.

The first characteristic configuration of the islanding operation detection method according to the present invention is a islanding operation detection method for a distributed power source including an inverter linked to the system power source, as described in claim 8, wherein the system voltage e _uw A system frequency measurement step for measuring a system frequency based on zero cross timing of the system, and a reactive power injection amount calculation for calculating a reactive power injection amount according to a frequency deviation obtained based on the system frequency measured in the system frequency measurement step A step, a first PLL processing step in which a system voltage e _uw is input and a reference system voltage signal is generated in synchronization with a phase angle (θ _uw ) of the system voltage e _uw , and a reverse flow current i _sp is input and a reverse flow current and a second PLL processing step of generating a reference reverse flow current signal synchronized with a phase angle theta _sp of i _sp, phase difference between the two signals (θ _uw -θ _sp A feedback signal generation step for generating a feedback signal based on the reactive power injection amount calculated in the reactive power injection amount calculation step and a feedback signal generated in the feedback signal generation step. Based on the reactive current control step for feedback control of the output current command value for the inverter so that the reactive power of the reactive power injection amount is injected from the inverter, the output current value of the inverter to the output current command value An inverter control step for controlling the inverter so as to be, and an isolated operation detection step for detecting whether or not the system is in an isolated operation state based on the amount of electricity of the system power supply when the reactive power of the reactive power injection amount is injected It is in the point equipped with.

  In the second feature configuration, as described in claim 9, in addition to the first feature configuration described above, the gain of the first PLL processing step is larger than the gain of the second PLL processing step. It is in the point set to.

The third feature configuration is the operation calculated in the first PLL processing step in addition to the first or second feature configuration described above, as described in claim 10. It is a case where it is determined that both fluctuate in the same tendency based on the current value of both the frequency and the system frequency measured in the system frequency measurement step, based on the value before the one system cycle and the value before the two system cycles, When the harmonic voltage fluctuation rate of the system voltage e _uw exceeds a predetermined ratio and the state continues for a predetermined time, it is detected that it is in a single operation state.

  As described above, according to the present invention, even when the system frequency suddenly changes, the system voltage phase suddenly changes, or even when those changes continue for a long time, the FRT function is provided and the single operation that can cope with the multi-unit interconnection is possible. A detection device and an isolated operation detection method can be provided.

Circuit block diagram of a distributed power source to which an isolated operation detection device according to the present invention is applied Functional block diagram of an isolated operation detection device according to the present invention Operation explanatory diagram of system frequency measurement unit (A) is explanatory drawing of the frequency deviation and reactive power injection amount characteristic table used in a frequency corresponding reactive power injection amount calculation part, (b) is operation | movement explanatory drawing of a step reactive power injection amount calculation part. (A) is an explanatory diagram at the time of a momentary drop and a sudden phase change, and (b) is a characteristic explanatory diagram of the operating frequency f _PLL and the system frequency f _grid at the time of single operation. (A) is a sequence diagram of the operation frequency _{f PLL} and the power system frequency _{f grid,} (b) the sequence diagram of the harmonic effective voltage THD _v Explanatory diagram of algorithm to detect islanding state Flow chart for detecting the isolated operation state Explanatory diagram of experimental results

Hereinafter, an isolated operation detection device and an isolated operation detection method according to the present invention will be described with reference to the drawings.
FIG. 1 shows a solar battery power generation apparatus 100 that is an example of a distributed power source. The solar battery power generation apparatus 100 is configured to include a solar battery panel SP and a power conditioner PC to which the solar battery panel SP is connected, and is connected to the system power supply e _grid via the interconnection relay _Sgrid . Note that the present invention is not limited to the solar cell panel SP as the power generator connected to the power conditioner PC, and can also be applied when other power generators such as fuel cells are connected.

The power conditioner PC includes a DC / DC converter 1 that boosts a DC voltage generated by the solar panel SP to a predetermined DC link voltage V _dc , and an AC having a predetermined frequency and voltage value so as to be connected to the system power supply. An inverter 3 for converting to a voltage, and an LC filter 4 that includes an inductor L _inv and a capacitor C _inv and removes harmonic components are provided.

The switches S1, S2, S3, and S4 provided in the inverter 3 are turned on / off by PWM control so as to adapt the frequency and voltage to be linked to the system power by the control block including the isolated operation detection device 10, and the LC filter The harmonic component is removed from the output by 4 and output as sinusoidal AC power. In the figure, symbol C _dc is an electrolytic capacitor for stabilizing the DC link voltage, i _inv is the output current of the inverter, L _grid is the system impedance, e _uw is the u-w line voltage, and i _sp is the reverse power flow. current, _{Z L} denotes an AC load.

  FIG. 2 shows a functional block configuration of the isolated operation detection device 10 configured with a microcomputer, a memory, a peripheral circuit, and the like. In the present embodiment, the isolated operation detection device 10 is configured to correspond to the frequency feedback method with step injection and to execute an intended isolated operation detection method based on a control program including an unnecessary detection avoidance algorithm according to the present invention. Has been.

  The isolated operation detection apparatus 10 includes a system frequency measurement unit 11, reactive power injection amount calculation units 20 and 21, a first PLL processing unit 12, a second PLL processing unit 13, a feedback signal generation unit 14, The reactive current control unit 15, the active power generation unit 18, the reactive power generation unit 16, the inverter control unit 19, the isolated operation detection unit 24, and the like are provided.

The system frequency measuring unit 11 is a block that measures the system frequency f _grid based on the zero cross timing of the system voltage e _uw , and includes a voltage dividing circuit that divides the AC voltage and a binarization circuit that binarizes the divided signal. Including a zero-cross detection circuit.

As shown in FIG. 3 (a), a system voltage waveform obtained by resistance-dividing the system voltage e _uw (indicated by a broken line in the figure) is binarized by a binarization circuit with a voltage value of zero as a threshold value. By doing so, a square wave (indicated by a solid line in the figure) having a duty ratio of 50% corresponding to the system frequency is obtained. Counting the time difference between the intermediate value of the falling edge and rising edge of the square wave and the intermediate value of the next falling edge and rising edge with a sampling frequency of 2.5 MHz (accuracy of 0.4 μs.) Thus, the system frequency f _grid corresponding to the system voltage e _uw is measured. The sampling frequency is an example, and is not limited to this value.

  The reactive power injection amount calculation unit includes a frequency-corresponding reactive power injection amount calculation unit 20 and a step reactive power injection amount calculation unit 21.

The frequency corresponding reactive power injection amount calculation unit 20 is a block that calculates the reactive power injection amount according to the frequency deviation Δf _grid obtained based on the system frequency f _grid measured by the system frequency measurement unit 11. The reactive power injection amount K _fvar is calculated from a frequency deviation / reactive power injection amount characteristic table in which the reactive power injection amount is determined so that the subsequent frequency deviation gradually increases according to Δf _grid .

As shown in FIG. 3 (c), the system frequency _fgrid is updated every cycle, and 5 ms. The latest 40 ms. The moving average is calculated and stored in the storage unit. As shown in FIG. 3B, 200 ms. Previous 80ms. 40ms from the moving average of the minute. The frequency deviation Δf _grid is calculated by subtracting the moving average between them.

FIG. 4A shows frequency deviation / reactive power characteristics. The frequency-corresponding reactive power injection amount calculation unit 20 calculates the reactive power injection amount K _fvar based on the frequency deviation / reactive power characteristic, and the reactive power injection calculated within a half cycle of the system frequency f _grid from the calculation of the frequency deviation Δf _grid. The amount K _fvar is injected.

In the frequency deviation / reactive power characteristic, a reactive power injection amount K _fvar having different _slopes is defined in a low-sensitive band region where the frequency deviation Δf _grid is within ± 0.01 Hz and a high-sensitive band region on both outer sides thereof. In any case, the reactive power injection amount K _fvar in the direction of increasing the frequency deviation is defined, and the slope of the second-stage gain in the high-sensitive area is higher than the inclination of the first-stage gain in the low-sensitive area where the frequency deviation Δf _grid is. It is set to be large. The maximum value is ± 0.25 p. u. (Per unit). In addition, the frequency deviation / reactive power characteristic is an example, and is not limited to this characteristic.

The step reactive power injection amount calculation unit 21 injects a constant amount of reactive power in a constant direction in the current phase when there is no change in the frequency deviation Δf _grid at a certain time and the fundamental voltage E _uw and / or the harmonic voltage THD _v changes. _This is a block for calculating the quantity K _fstep . In this specification, the “state in which there is no fluctuation in the frequency deviation” is used as a concept including a state in which the fluctuation is small, that is, a state in the above-described low-sensitive band region.

As shown in FIG. 4B, the step reactive power injection amount calculation unit 21 determines that the harmonic voltage fluctuation satisfies all of the following conditional expressions when the frequency deviation Δf _grid is in the low sensitivity band region. Within a half cycle, the upper limit is 0.1 p. u. The reactive power is injected in the direction of delaying the current phase when viewed from the power conditioner PC, that is, in the direction of decreasing the frequency.

THD _v (z) -THD _avr > 2V
THD _v (z-1) -THD _avr > 2V
THD _v (z-2) -THD _avr > −0.5 V
│THD _v (z-3) -THD _avr (z) │ <0.5V
│THD _v (z-4) -THD _avr (z) │ <0.5V
│THD _v (z-5) -THD _avr (z) │ <0.5V

As shown in the following formula 1, in this embodiment, the total harmonic voltage effective value from the second order to the seventh order is adopted as a preferable aspect as the harmonic voltage effective value THD _v. May be included. In the following description, it is simply expressed as a harmonic voltage. Further, T _{ADC in Equation} 1 is the sampling time of the A / D converter, and n is the harmonic order.
[Equation 1]

Further, when the step reactive power injection amount calculating unit 21 determines that the fundamental voltage fluctuation satisfies all the following conditional expressions when the frequency deviation Δf _grid is in the low-sensitive band region, the step reactive power injection amount calculating unit 21 The upper limit is 0.1 p. u. The reactive power is injected in the direction of delaying the current phase when viewed from the power conditioner PC, that is, in the direction of decreasing the frequency.

E _u.rms (z) −E _uw.rms.avr (z)> 2.5V
E _u.rms (z-1) −E _u.rms.avr (z)> 2.5V
E _uw.rms (z-2) −E _uw.rms.avr (z)> − 0.5V
│E _u.rms (z-3) -E _uw.rms.avr (z) | <0.5V
│E _u.rms (z-4) -E _uw.rms.avr (z) | <0.5V
│E _u.rms (z-5) -E _uw.rms.avr (z) | <0.5V

First PLL processing section 12 is a block for generating a reference system voltage signal synchronized with the phase angle theta _uw of the system voltage e _uw is input system voltage e _uw, the second PLL unit 13 backward flow current i _This is a block for generating a reference reverse flow current signal synchronized with the phase angle θ _sp of the reverse flow current i _{sp when sp} is input.

  In the present embodiment, the gain G1 of the first PLL processing unit 12 is set to a larger value than the gain G2 of the second PLL processing unit 13. Specifically, G2 = 0.5G1 is set, and it is preferable that at least G2 ≦ 0.5G1.

The feedback signal generation unit 14 includes the first PLL processing unit 12 and the second PLL processing unit 13 described above, calculates the phase difference (θ _uw −θ _sp ) of both signals, and determines the feedback signal based on the value. This is a block to be generated.

The reactive current control unit 15 includes a reactive current command value I ^* _q corresponding to the reactive power injection amounts K _fvar and K _fstep calculated by the reactive power injection amount calculating units 20 and 21 and a feedback signal generated by the feedback signal generating unit 14. This block performs feedback control of the output current command value i ^* _inv for the inverter 3 so that reactive power corresponding to the reactive power injection amount is injected from the inverter 3 to the system power supply based on _Iq . That is, the reactive current control unit 15 performs PID calculation so that the feedback signal I _q converges to the reactive current command value I ^* _q , and outputs the calculated value to the reactive power generation unit 16 as a command value.

As shown in Equation 2, the reactive current command value I ^* _q is obtained by changing the fundamental wave active power 2Puw to the amplitude value E _{uw, max.} It is a value _obtained by multiplying the value divided by ₁ by the reactive power injection amounts K _fvar and K _fstep .
[Equation 2]

The active power generator 18 is a block that generates an active power component by multiplying the bias DC voltage output from the DC voltage controller 17 by a sine wave having a phase angle θ _uw corresponding to the system power supply. The bias DC voltage is input from the DC voltage control unit 17 that adjusts and outputs the DC link voltage V _dc input from the DC / DC converter 1 to the DC voltage command value V ^* _dc , and the phase angle θ corresponding to the system power supply. The sine wave of _uw is input from the first PLL processing unit 12.

The reactive power generation unit 16 multiplies the command value feedback-controlled by the reactive current control unit 15 and the sine wave of the phase angle θ _uw corresponding to the system power supply input from the first PLL processing unit 12 to react with the reactive power. It is a block that generates components.

Outputs from the active power generation unit 18 and the reactive power generation unit 16 are added by an adder to generate a current command value i ^* _inv for the inverter 3, and the current command value i ^* _inv is input to the inverter control unit 19. .

The inverter control unit 19 to which the output current value i _inv of the inverter 3 is input as a feedback value performs feedback control using, for example, PID calculation so that the output current value of the inverter 3 becomes the current command value i ^* _inv. A control value for 3, here a duty ratio D, is generated. The duty ratio D generated by the inverter control unit 19 is input to the PWM control unit 22, and control signals for the switches S 1, S 2, S 3 and S 4 are generated by the PWM control unit 22, and the inverter 3 is connected via the buffer circuit 23. Are output to the switches S1, S2, S3 and S4.

The isolated operation detection unit 24 determines whether or not the system is in the isolated operation state based on the amount of electricity of the system power source when the reactive power injection amount is injected, for example, the system frequency, the system voltage, the total harmonic distortion, etc. This is the block to detect. The isolated operation detection unit 24 includes an operation frequency f _PLL corresponding to the system voltage e _uw obtained by the first PLL processing unit 12, a system frequency f _grid measured by the system frequency measurement unit 11, and a fundamental voltage Amplitude value E _{uw, max. 1} and the harmonic voltage effective value THD _v are input.

The operation of the isolated operation detection unit 24 will be described in detail. In general, when the system voltage e _uw is normal (202 ± 10V), if the system frequency _fgrid changes suddenly, it can be correctly detected that it is in a single operation state. A phenomenon that the voltage drops momentarily occurred
1389315476440_2
In some cases, a decrease in input voltage and a phase shift occur.

FIG. 5A shows an example of a waveform at the time of a sag. A voltage drop occurs when the system voltage e _uw is at a phase angle of 90 °, and at the moment when the phase angle is shifted by a maximum of + 41 °, the system frequency _fgrid (z-4) and the operating frequency _fPLL (z-4) decrease in frequency. It is expressed. Due to the large fluctuation of the frequency, there is a possibility that unnecessary detection may be made if the vehicle is in an isolated operation state.

However, when the phase suddenly changes due to a momentary drop or the like, the system frequency _fgrid fluctuates instantaneously at the time of sudden change, but is stable before and after that, whereas it fluctuates at the time of independent operation. Tends to increase.

That is, as shown in FIG. 5B, the isolated operation detection unit 24 has both the operation frequency f _PLL calculated by the first PLL processing unit 12 and the system frequency f _grid measured by the system frequency measurement unit 11. It suffices if it is configured to determine that it is in a single operation state when it changes in one direction at a plurality of consecutive system cycles, and it becomes possible to accurately detect the single operation state while avoiding unnecessary detection.

As shown in FIG. 5B, both values may gradually increase, and conversely, both values may gradually decrease. On the other hand, when the phase changes suddenly as shown in FIG. 5A, the operating frequency f _PLL calculated by the first PLL processing unit 12 and the system frequency f _grid measured by the system frequency measuring unit 11 are used. Both of them rise or fall temporarily only in the cycle at the time of sudden change, and then return to the steady state, so by detecting the tendency, unnecessary detection can be avoided and the isolated operation state can be detected accurately and quickly.

It is further preferable that the isolated operation detection unit 24 is configured to detect that the system is in the isolated operation when the harmonic voltage fluctuation rate of the system voltage e _uw exceeds a predetermined ratio and the state continues for a predetermined time.

  In the situation where reactive power is injected into the system power supply, even if the harmonic voltage of the system power supply fluctuates due to some reason, the harmonic voltage does not fluctuate significantly in the system cycle before and after that. When the power supply is stopped and the single operation state is entered, the harmonic voltage greatly fluctuates in subsequent continuous cycles. Therefore, when the harmonic voltage fluctuation rate of the system voltage exceeds a predetermined ratio continues for a predetermined time, it is possible to avoid unnecessary detection by detecting that the system is in an isolated operation state.

Specifically, in this embodiment, the isolated operation detection unit 24 is based on the current values of both the system frequency e _uw and the system frequency f _PLL , based on the values before the one system cycle and the values before the two system cycles. When it is determined that it changes in one direction in a plurality of system cycles, and when the harmonic voltage fluctuation rate ΔTHD of the system voltage e _uw exceeds a predetermined ratio and the state continues for a predetermined time, it is detected as an isolated operation state However, when either one is not satisfied, it is determined to be in a normal state in order to avoid unnecessary detection.

Specifically, as shown in Equation 3 below, the current value (z), the previous value (z−1), and the two of the average values of the operating frequency f _PLL and the system frequency f _grid 32 cycles before If the product Δf _var (total frequency fluctuation value) of the deviation from the previous value (z−2) is equal to or greater than a predetermined threshold value f _cst , it is determined that it is in an isolated operation, and if it is less than the threshold value f _cst , it is determined to be normal. be able to.

Here, the threshold value f _cst is preferably set to a value in the range of 4 to 9% of the fundamental frequency. For example, if the system frequency is 50 Hz, f _cst is set to a range of 2.0 to 4.5. It is preferable.
[Equation 3]

In this embodiment, as shown in FIG. _6A , the average value of the operating frequency f _PLL and the system frequency f _grid before 32 cycles is used as the average value of each system frequency of the previous 32 cycles based on the previous 32 cycles. Although the average value is adopted, the number of cycles for obtaining the average value need not be limited to 32 and can be set as appropriate.

In addition, as shown in FIG. 6B, the harmonic voltage fluctuation rate ΔTHD is an average value of the harmonic voltage effective value THD _v 32 cycles before, and each harmonic voltage of the previous 32 cycles based on 32 cycles before. The average value of the effective value THD _v is adopted, and is calculated by the following equation (4). Similarly, the number of cycles for obtaining the average value need not be limited to 32 and can be set as appropriate.
[Equation 4]

FIGS. 7 and 8 show an example of a procedure executed by the isolated operation detection unit 24 for avoiding unnecessary detection based on the total frequency fluctuation value Δf _var , the harmonic voltage fluctuation rate ΔTHD, and the fluctuation rate counter. ing.

When the total frequency fluctuation value | Δf _var | is equal to or greater than the threshold 0.3f _cst , the harmonic voltage fluctuation rate ΔTHD is checked. If the harmonic voltage fluctuation rate ΔTHD is equal to or greater than x%, the initial value is set to zero. If the harmonic voltage fluctuation rate ΔTHD is less than 0.5x%, the fluctuation rate counter is reset, and if the harmonic voltage fluctuation rate ΔTHD is less than x% and greater than 0.5x% The process of maintaining the value of the rate counter is repeated every system cycle.

As a result, when the value of the fluctuation rate counter becomes y or more, it is determined that the operation is independent and the inverter 3 is stopped, and the interconnection relay _Sgrid is disconnected and disconnected. When the total frequency fluctuation value | Δf _var | becomes equal to or greater than the threshold value f _cst , the inverter 3 is immediately stopped regardless of the value of the fluctuation rate counter, the inverter 3 is stopped, and the interconnection relay S _grid is disconnected and disconnected. . In the present embodiment, x = 20% and y = 3 can be exemplified as preferable values, but specific values may be set to appropriate values based on experiments or the like as appropriate.

When the total frequency fluctuation value | Δf _var | is less than the threshold value 0.3f _cst , the fluctuation rate counter is simply reset to the initial value. Such processing ensures that unnecessary detection caused by fluctuations in the total frequency fluctuation value | Δf _var | within the threshold value 0.3f _cst is reliably avoided.

The isolated operation detection apparatus 10 described above executes the isolated operation detection method according to the present invention.
That is, the system frequency measurement step of measuring the system frequency based on the zero cross timing of the system voltage e _uw is executed by the system frequency measurement unit 11, and the system measured by the reactive power injection amount calculation units 20 and 21 in the system frequency measurement step A reactive power injection amount calculating step for calculating the reactive power injection amount according to the frequency deviation obtained based on the frequency is executed.

The first PLL processing step of generating a reference system voltage signal synchronized with the phase angle (theta _uw) of the first PLL unit 12 in the system voltage _{e uw} is the input system voltage _{e uw} is performed, the second The second PLL processing step is executed in which the reverse flow current i _sp is input to the PLL processing unit 13 to generate a reference reverse flow current signal synchronized with the phase angle θ _sp of the reverse flow current i _sp , and the feedback signal generation unit 14 Then, a feedback signal generation step for generating a feedback signal based on the phase difference (θ _uw −θ _sp ) between the two signals is executed.

  Further, the reactive current control unit 15 outputs the reactive power from the inverter based on the reactive current command value corresponding to the reactive power injection amount calculated in the reactive power injection amount calculating step and the feedback signal generated in the feedback signal generating step. A reactive current control step for performing feedback control of the output current command value of the inverter is executed so that the injection amount of reactive power is injected, and the inverter control unit 19 causes the inverter so that the output current value of the inverter becomes the output current command value. The inverter control step for controlling the power is executed, and the single operation detection unit 24 detects whether or not it is in the single operation state based on the amount of electricity of the system power source when the reactive power of the reactive power injection amount is injected. An operation detection step is executed.

  Thus, since the reactive current control unit 15 feedback-controls the output current command value of the inverter 3, the reactive power of the reactive power injection amount that is the target value is accurately and promptly injected into the system power supply. As a result, good responsiveness to reactive power injection can be ensured, and even if a complicated algorithm for unnecessary detection is not incorporated in the isolated operation detection unit 24, it is quickly detected that it is in an isolated operation state without unnecessary detection. Can be detected.

As shown in the experimental results described later, the determination threshold values of the total frequency fluctuation value | Δf _var | and the harmonic voltage fluctuation rate ΔTHD used for the determination by the above algorithm are configured to be variable depending on the load condition. Preferably it is. For this purpose, a function block for detecting a load condition is provided, and a determination threshold adjustment for adjusting a determination threshold for the total frequency fluctuation value | Δf _var | and the harmonic voltage fluctuation rate ΔTHD based on the load condition detected by the function block It is preferable to provide the part.

Further, the gain of the first PLL processing unit 12 for obtaining the reference system voltage signal synchronized with the phase angle θ _uw of the system voltage e _uw is the reference reverse current _flowing in synchronization with the phase angle θ _sp of the reverse power current i _sp. Since it is set to a value larger than the gain of the second PLL processing unit 13 for obtaining a signal, the system voltage e _uw whose voltage, phase, etc. fluctuate transiently due to disturbance generated on the system power supply side is appropriately set. The reflected reference system voltage signal can be obtained with higher sensitivity than the reference reverse flow current signal.

Based on such a phase difference (θ _uw −θ _sp ), the reactive current control unit appropriately performs feedback control of the output current command value of the inverter. and if the amount K _fvar is injected, so that good response characteristics even when the variation is reactive power injected amount K _fvar at the boundary of the low sensitivity band region and high sensitivity zones is obtained.

In the above-described embodiment, the isolated operation detection unit has the current value of both the operation frequency calculated by the first PLL processing unit and the system frequency measured by the system frequency measurement unit, the value before one system cycle, and two systems. Based on the value before the cycle, it is determined that both change in one direction in a plurality of continuous system cycles, and the harmonic voltage fluctuation rate of the system voltage e _uw exceeds a predetermined ratio, and the state continues for a predetermined time. In this case, the example of avoiding unnecessary detection by detecting that it is in an isolated operation state has been described, but unnecessary detection is possible even if it is configured to detect that it is in an isolated operation state based on one of both judgment criteria. Can be avoided.

  In the above-described embodiment, the mode in which the frequency feedback method with step injection is incorporated in the isolated operation detection device according to the present invention has been described. However, the isolated operation detection device according to the present invention includes at least the above-described system frequency measurement unit and reactive power. The injection amount calculation unit, the first PLL processing unit, the second PLL processing unit, the feedback signal generation unit, the reactive current control unit, the inverter control unit, and the isolated operation detection unit may be provided. , Slip mode frequency shift method and reactive power fluctuation method other than frequency feedback method with step injection may be incorporated, avoid unnecessary detection not only active method but also passive method Will be able to.

  Each of the above-described embodiments is merely an example of an isolated operation detection apparatus and an isolated operation detection method according to the present invention, and specific configurations (hardware and software), various numerical values, and the like of each component block are described in the present invention. Needless to say, it is possible to change and design appropriately within a range in which the effects of the above can be achieved.

Below, the experimental results of the multi-unit interconnection test will be described.
Using three power conditioners with an active power of 5.5 kW, load at 3 points of P = + 10 (+ 10% load), Q = 0, P = 0, Q = 0 and P = −10, Q = 0 An experiment was conducted under the condition of single operation. In the experiment, the threshold f _cst of the total frequency fluctuation value | Δf _var | was set to 3.6 Hz, the threshold value x of the harmonic voltage fluctuation rate ΔTHD was set to 20, and the threshold value y of the fluctuation rate counter was set to 3.

FIG. 9A shows the THD [%], the harmonic voltage fluctuation rate ΔTHD, and the frequency when the single operation is performed under the load conditions of P = + 10 and Q = 0. FIG. 9B shows the harmonic voltage THD _V [%], the harmonic voltage fluctuation rate ΔTHD, and the frequency when the single operation is performed under the load conditions of P = 0 and Q = 0. FIG. 9C shows the THD [%], the harmonic voltage fluctuation rate ΔTHD, and the frequency when the single operation is performed under the load conditions of P = −10 and Q = 0.

  As shown in FIG. 9 (a), under the load condition of P = + 10, Q = 0, it becomes an independent operation state from the fourth cycle, and thereafter, the harmonic voltage fluctuation rate ΔTHD becomes 20 times or more in three consecutive cycles, In the fourth cycle (at the 7th cycle) after the occurrence of the isolated operation, it was determined as the isolated operation state, and the operation was stopped. As shown in FIG. 9C, the same tendency was confirmed even under the load condition of P = −10 and Q = 0.

  However, as shown in FIG. 9C, under the load conditions of P = 0 and Q = 0, the change in the frequency of the system voltage is faster than the harmonic voltage fluctuation rate ΔTHD, and the element that determines the isolated operation state is the frequency. I found out.

  From this, it was confirmed that the isolated operation state can be detected more quickly and appropriately by changing the threshold shown in FIG. 8 for determining the isolated operation state according to the load condition.

1: DC / DC converter 3: Inverter 4: LC filter 10: Isolated operation detection device 11: System frequency measurement unit 12: First PLL processing unit 13: Second PLL processing unit 14: Feedback signal generation unit 15: Invalid Current control unit 16: reactive power generation unit 18: active power generation unit 18
20, 21: Reactive power injection amount calculation unit 24: Isolated operation detection unit 100: Distributed power source (solar cell power generator)
PC: Power conditioner SP: Solar cell panels S1, S2, S3, S4: Switch elements provided in the inverter bridge

Claims (10)

An isolated operation detection device for a distributed power source having an inverter connected to a system power source,
A system frequency measurement unit that measures the system frequency based on the zero-cross timing of the system voltage (e _uw );
A reactive power injection amount calculating unit that calculates a reactive power injection amount according to a frequency deviation obtained based on a system frequency measured by the system frequency measuring unit;
A first PLL processing unit for generating a reference system voltage signal synchronized with the phase angle (theta _uw) of the system voltage _{(e uw)} is input system voltage _{(e uw),} reverse flow current _{(i sp)} is input And a second PLL processing unit that generates a reference reverse flow current signal synchronized with the phase angle (θ _sp ) of the reverse flow current (i _sp ), and based on the phase difference (θ _uw −θ _sp ) of both signals A feedback signal generator for generating a feedback signal;
Based on the reactive current command value corresponding to the reactive power injection amount calculated by the reactive power injection amount calculation unit and the feedback signal generated by the feedback signal generation unit, the reactive power of the reactive power injection amount from the inverter Reactive current control unit that feedback-controls the output current command value for the inverter so that is injected,
An inverter control unit for controlling the inverter so that the output current value of the inverter becomes the output current command value;
An isolated operation detection unit that detects whether or not the system is in an isolated operation state based on the amount of electricity of the system power supply when the reactive power of the reactive power injection amount is injected,
An isolated operation detection device.   The isolated operation detection device according to claim 1, wherein the gain of the first PLL processing unit is set to a value larger than the gain of the second PLL processing unit.   The isolated operation detection unit is configured when both the operation frequency calculated by the first PLL processing unit and the system frequency measured by the system frequency measurement unit change in one direction at a plurality of continuous system cycles. The isolated operation detection device according to claim 1, wherein the isolated operation detection device is configured to determine an isolated operation state.   The isolated operation detection unit includes at least a current value of both the operation frequency calculated by the first PLL processing unit and the system frequency measured by the system frequency measurement unit, a value before one system cycle, and two system cycles before The isolated operation detection device according to any one of claims 1 to 3, wherein the isolated operation detection device is configured to detect whether or not the vehicle is in an isolated operation state based on the value of. The said independent operation detection part is comprised so that it may detect that it is an independent operation state, when the harmonic voltage fluctuation rate of system voltage ( _euw ) exceeds a predetermined ratio, and the state continues for the predetermined time. The isolated operation detection device according to 1 or 2. The islanding operation detection unit includes a current value of both the operation frequency calculated by the first PLL processing unit and the system frequency measured by the system frequency measurement unit, a value before one system cycle, and a value before two system cycles. Based on the value, when it is determined that both change in one direction in a plurality of continuous system cycles, the harmonic voltage fluctuation rate of the system voltage (e _uw ) exceeds a predetermined ratio, and the state continues for a predetermined time The isolated operation detection device according to claim 1, wherein the isolated operation detection device is configured to detect that it is in an isolated operation state.   The reactive power injection amount calculation unit calculates a reactive power injection amount from a frequency deviation / reactive power injection amount characteristic table in which a reactive power injection amount is determined so that a subsequent frequency deviation gradually increases according to a frequency deviation at a certain time. Reactive power injection amount calculation unit for frequency to be calculated and a constant amount of reactive power injection in a constant direction when the fundamental voltage and / or harmonic voltage fluctuates without fluctuation at a certain time. An isolated operation detecting device according to any one of claims 1 to 6, further comprising: a step reactive power injection amount calculating unit. A method for detecting an isolated operation of a distributed power source including an inverter connected to a system power source,
A system frequency measurement step for measuring the system frequency based on the zero cross timing of the system voltage (e _uw );
A reactive power injection amount calculating step for calculating a reactive power injection amount according to a frequency deviation obtained based on the system frequency measured in the system frequency measuring step;
A first PLL processing step of generating a reference system voltage signal synchronized with the phase angle (theta _uw) of the system voltage _{(e uw)} is input system voltage _{(e uw),} reverse flow current _{(i sp)} is input And a second PLL processing step for generating a reference reverse flow current signal synchronized with the phase angle (θ _sp ) of the reverse flow current (i _sp ), and based on the phase difference (θ _uw −θ _sp ) of both signals A feedback signal generation step for generating a feedback signal;
Based on the reactive current command value corresponding to the reactive power injection amount calculated in the reactive power injection amount calculation step and the feedback signal generated in the feedback signal generation step, the reactive power of the reactive power injection amount from the inverter Reactive current control step for feedback control of the output current command value for the inverter so that is injected,
An inverter control step of controlling the inverter so that the output current value of the inverter becomes the output current command value;
An isolated operation detection step for detecting whether or not the system is in an isolated operation state based on the amount of electricity of the system power supply when the reactive power of the reactive power injection amount is injected,
An isolated operation detection method.   The islanding operation detection method according to claim 8, wherein the gain of the first PLL processing step is set to a value larger than the gain of the second PLL processing step. The isolated operation detection step includes a current value of both the operation frequency calculated in the first PLL processing step and the system frequency measured in the system frequency measurement step, a value before one system cycle, and two system cycles before If the harmonic voltage fluctuation rate of the system voltage e _uw exceeds a predetermined ratio and the state continues for a predetermined time, it is determined that both are in the single operation state. The islanding operation detection method according to claim 8 or 9 , wherein the islanding operation is detected.