JP5645622B2 - Isolated operation detection device and isolated operation detection method - Google Patents

Description

  Embodiments described herein relate generally to an isolated operation detection device and an isolated operation detection method.

  An example of the configuration of the prior art is shown in FIG. 8, and the configuration, operation, and conditions will be described. As shown in FIG. 8, in the conventional isolated operation detection device, the DC power of the DC power source 1 made of, for example, a solar cell or a fuel cell is converted into AC power by the inverter bridge 2, and is filtered by a filter composed of a reactor 3 and a capacitor 4. A high frequency component by PWM control is removed and the high frequency component is supplied to the load 9 via the contactor 6.

  On the other hand, the inverter bridge 2 operates in conjunction with the AC power supplied from the AC power system 8 via the circuit breaker 7. The AC voltage supplied to the load 9 is detected by the voltage detector 10, and a signal synchronized with the AC voltage phase is input to the phase shift circuit 23 by the PLL circuit 22, and the sine wave signal Vs is supplied to the current reference circuit 12 through the sine wave circuit 26. Is entered.

The amplifier 11 detects the voltage of the DC power source 1 and inputs the signal V11, which is compared and amplified with the voltage reference V ^* , to the current reference circuit 12. The current reference circuit 12 inputs the product of the signal V11 and the signal Vs to the amplifier 13 as an alternating current reference I ^* . The amplifier 13 controls the alternating current reference I ^* and the inverter output current detected by the current detector 5 to coincide with each other, and the PWM circuit 14 performs PWM control of the inverter bridge 2 via the drive unit 15.

  On the other hand, the AC voltage is detected from the voltage detector 10, the frequency of the AC voltage is detected by the frequency f detection circuit 30, and the output of the sine wave circuit 26 is output by the phase shift circuit 23 via the first function 31 and the addition limit circuit 32. The phase of the signal Vs is shifted to control the inverter reactive power (I × Vsin θ).

Further, the frequency change rate of the AC voltage is detected by the frequency change rate (df / dt) detection circuit 28, and V ₃₁ and V ₂₉ are added by the addition limit circuit 32 through the second function 29.

JP 2010-115094 A

  The islanding operation detection method as described above is called “high-speed slip mode frequency shift”, and its characteristic can detect islanding at high speed in about 100 ms.

However, the 2012 target has been required to achieve the following FRT (Fault Ride Through) (1) and (2) against frequency changes.
(1) In a test simulating stepwise frequency increase at the time of instantaneous voltage decrease, even if 0.8 Hz increase continues for 3 cycles (50 Hz system), it does not malfunction due to excessive frequency and frequency change rate, that is, no independent operation is detected. about.

(2) In a test simulating a frequency drop at the time of recovery from an instantaneous voltage drop, for a significant change in frequency such as a frequency drop at 2 Hz / sec (change from 50 Hz to 47.5 Hz in 1.25 seconds (sweep)) The islanding operation is not detected, and the islanding operation is detected in about 100 msec due to the change in frequency.
That is, there is a need for a highly reliable isolated operation detection device and isolated operation detection method that can detect an isolated operation at high speed without malfunctioning when not operating alone.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an isolated operation detection device and an isolated operation detection having an FRT function without malfunction even when the frequency changes suddenly or changes for a long time. It is to provide a method.

The isolated operation detection device according to the embodiment is an isolated operation detection device for an inverter that converts DC power into AC power and operates in conjunction with an AC power system, and detects voltage output from the inverter, The reactive power or current phase is controlled in a direction in which the frequency of the output voltage detected by the voltage detecting means promotes a change by positive feedback, and a positive value is obtained when the frequency change rate of the frequency exceeds a predetermined value. When the frequency change rate falls below the specified value, the value changes to the negative value, and the reactive power or current phase is controlled in such a direction that the value that changes stepwise facilitates the change by positive feedback. and function means for outputting, integrated value is detected whether islanding detection level above the value obtained by subtracting the dead zone component from a value that changes the stepwise every predetermined time, the independent operation detecting level And abnormality detecting means outputs a signal to stop the inverter when it is above, as well as synchronization with the AC power system and said inverter output voltage phase, controls the predetermined reactive power or current phase by an output of the function unit The reactive power control of the output of the inverter is performed, and when the inverter is disconnected from the AC power system, the reactive power of the inverter is determined based on the frequency of the output voltage of the inverter and the value that changes stepwise. Driving means for driving to change, and for stopping the inverter when receiving a signal for stopping the inverter from the abnormality detecting means.

It is a figure showing roughly the example of 1 composition of the isolated operation detection device concerning a 1st embodiment. It is a figure which shows an example of the characteristic function of the 1st function circuit of the isolated operation detection apparatus shown in FIG. It is a figure which shows an example of the characteristic function of the 2nd function circuit of the isolated operation detection apparatus shown in FIG. It is a figure which shows an example of the output of the addition limit circuit of the isolated operation detection apparatus shown in FIG. It is a figure for demonstrating an example of the operation | movement of a limit circuit at the time of implementing a FRT function in the isolated operation detection apparatus shown in FIG. FIG. 2 is a diagram for explaining an example of operations of an arithmetic circuit and a level detection circuit when performing an FRT function in the isolated operation detection device shown in FIG. 1. It is a figure which shows an example of the frequency change at the time of an alternating current system failing. It is a figure which shows an example of the frequency change at the time of an alternating current system failing. It is a figure for demonstrating an example of the operation | movement of a frequency detection in the isolated operation detection apparatus shown in FIG. It is a figure which shows an example of the simulation result of the frequency change at the time of a single operation. It is a figure which shows an example of the simulation result of the frequency change at the time of a single operation. It is a figure showing roughly the example of 1 composition of the independent operation detection device concerning a 2nd embodiment. It is a figure which shows roughly the example of 1 structure of the conventional isolated operation detection apparatus.

  Hereinafter, an isolated operation detection device and an isolated operation detection method according to an embodiment will be described with reference to the drawings.

  The inverter isolated operation detection device according to the present embodiment synchronizes the voltage phase of the output power of the AC power system and the inverter, controls the output current to a predetermined current phase, and controls the reactive power of the output of the inverter. Further, when the inverter is disconnected from the AC power system, the inverter is driven so that the reactive power of the inverter changes based on the frequency of the output voltage of the inverter.

  Furthermore, the characteristic curve of reactive power with respect to the frequency is moved so that the reactive power becomes almost zero following the normal frequency change (steady state) sufficiently, and the frequency is positively fed back to the fast frequency change (abnormal state). To control the direction to promote the change.

  The isolated operation detection device according to the present embodiment is an isolated operation detection protection device for an inverter that converts DC power output from a DC power source, such as a solar cell or a fuel cell, into AC power and operates in conjunction with an AC system. And detecting the voltage phase, frequency, and frequency change rate on the output side of the inverter, obtaining a reference phase from the detected voltage phase, and generating an AC current reference having a phase corresponding to the reference phase. Controls the output current and corrects the reference phase θ according to the frequency and the value that changes stepwise according to the frequency change rate, thereby detecting that the inverter is disconnected from the AC system and speeding up the protection operation To do.

  In addition, the acquired reference phase is corrected to advance or delay according to the increase or decrease of the inverter frequency, and the polarity and magnitude of the value that changes stepwise according to the frequency change rate. Protection is performed by detecting an excessive calculation result using a value that changes stepwise according to the rate of change.

  That is, in the isolated operation detection device according to the present embodiment, when the AC side of the inverter is disconnected from the AC power system, the frequency of the AC power source and the frequency change rate slightly increase or decrease. An increase or decrease in the frequency and the frequency change rate is detected, and when the frequency is increased and the frequency change rate is positive, the current phase of the inverter is advanced and positive feedback is applied in the direction of further increasing the frequency. An increase or decrease in the frequency and the frequency change rate is detected, and when the frequency decreases or the frequency change rate is negative, the current phase of the inverter is delayed and positive feedback is applied in the direction of further decreasing the frequency.

  As described above, the voltage, frequency, and frequency change rate of the AC power supply are detected by rapidly breaking the balance between the inverter output and the power consumption at the load, and stepped according to the frequency value and the frequency change rate. When the value that changes to exceeds a predetermined value, the isolated operation is detected at an early stage and the operation of the inverter is stopped.

FIG. 1 schematically shows a configuration example of an isolated operation detection apparatus according to the first embodiment.
The isolated operation detection apparatus according to the present embodiment includes a DC power source 1 including, for example, a solar cell or a fuel cell, and an inverter bridge 2 that converts DC power output from the DC power source 1 into AC power. 2 isolated operation is detected. The AC power output from the inverter bridge 2 is removed of high frequency components by PWM control by a filter including a reactor 3 and a capacitor 4, and supplied to a load 9 via a contactor 6.

The isolated operation detection device according to the present embodiment includes a voltage detector 10 that detects an AC voltage that is output from the AC power system 8 and the inverter bridge 2 and supplied to the load 9, and an output voltage that is detected by the voltage detector 10. The reactive power Q or the current phase θ is controlled in a direction in which the frequency (f) is promoted by positive feedback, and the frequency (f) changes stepwise according to the frequency change rate (df / dt) of the frequency (f). A function means for controlling and outputting the reactive power Q or the current phase θ in a direction in which the value promotes the change by positive feedback, and detecting whether or not the value based on the step-change value is equal to or higher than the isolated operation detection level K; The abnormality detection means for outputting a signal for stopping the inverter bridge 2 when the islanding operation detection level K is equal to or higher, and the voltage phases of the outputs of the AC power supply system 8 and the inverter bridge 2 When the inverter bridge 2 is disconnected from the AC power system 8 by synchronizing and controlling the reactive power of the inverter bridge 2 by controlling the reactive power Q or the current phase θ by the output of the function means, the inverter bridge 2 Is driven so that the reactive power Q of the inverter bridge 2 changes based on the frequency (f) of the output voltage and the value that changes stepwise, and the inverter receives the signal for stopping the inverter bridge 2 from the abnormality detecting means. Driving means for stopping the bridge 2.
The AC voltage detected by the voltage detector 10 is supplied to the voltage relay 17, the frequency relay 18, and the frequency detection circuit 30 of the abnormality detection means.

  The driving means includes an amplifier 11, a current reference circuit 12, an amplifier 13, a PWM circuit 14, a driving unit 15, a PLL circuit 22, a phase shift circuit 23, and a sine wave circuit 26, and uses an output from the addition limit circuit 32. The output power of the inverter bridge 2 is controlled, and the inverter bridge 2 is stopped when an abnormality is notified from the abnormality detection circuit 19 of the abnormality detection means.

  The inverter bridge 2 is operated in conjunction with AC power supplied from the AC power system 8 via the circuit breaker 7. The AC voltage supplied to the load 9 is detected by the voltage detector 10 and supplied to the PLL circuit 22. The PLL circuit 22 inputs a signal V 22 synchronized with the AC voltage phase to the phase shift circuit 23, and a sine wave signal Vs is inputted to the current reference circuit 12 through the sine wave circuit 26.

The amplifier 11 detects the voltage of the DC power source 1, compares it with the voltage reference V ^*, and inputs a signal V 11 obtained by amplifying the difference to the current reference circuit 12. The current reference circuit 12 inputs the product of the signal V11 and the signal Vs to the amplifier 13 as an alternating current reference I ^* . The amplifier 13 controls the AC current reference I ^* and the output current of the inverter bridge 2 detected by the current detector 5 to coincide with each other, and the PWM circuit 14 performs PWM control of the inverter bridge 2 via the drive unit 15.

  The abnormality detection means includes a voltage relay 17 that detects an abnormality in the AC voltage supplied to the load 9, a frequency relay 18 that detects a frequency abnormality from the AC voltage supplied to the load 9, and a value output from the limit circuit 36. An arithmetic circuit 37 that integrates a value obtained by subtracting a reset amount A, which will be described later, from an absolute value of the above, and an integrated value (a value based on a value that changes in a stepped manner) output from the arithmetic circuit 37 is compared with the isolated operation detection level K. The level detection circuit 38 that detects an abnormality by the above, and the abnormality detection circuit 19 that outputs a signal notifying the abnormality when the abnormality is detected by the voltage relay 17, the frequency relay 18, and the level detection circuit 38.

  When an abnormality is detected by the abnormality detection means, the abnormality detection circuit 19 is supplied with a signal for notifying the drive unit 15 of the abnormality, and the drive unit 15 stops the inverter drive and opens the contactor 6 to complete the operation. The inverter bridge 2 is opened from the grid connection.

  The function means includes a frequency detection circuit 30 that detects the frequency of the AC voltage output from the AC power system 8 and the inverter bridge 2, and a frequency change rate detection circuit that detects the frequency change rate of the frequency detected by the frequency detection circuit 30. 28, a limit circuit 36 that outputs a value that rises or falls in a step-like manner as described later according to the value of the frequency change rate detected by the frequency change rate detection circuit 28, and the reactive power Q or current phase angle with respect to the frequency Depending on the characteristic function of θ, the reactive power Q or current phase angle θ is calculated and output so that the reactive power flows when the frequency change is positive and the delayed reactive power flows when the frequency change is negative. Characteristic function of reactive power Q or current phase angle θ with respect to the first function circuit 31 to be output and the step-like value output from the limit circuit 36 Therefore, the reactive power Q or the current phase angle θ is calculated so that the reactive power flows forward when the value changing stepwise is positive, and the reactive power flows when the value changing stepwise is negative. And a second limit circuit 32 for adding the output of the first function circuit 31 and the output of the second function circuit 29 to each other.

  In FIG. 1, the frequency detection circuit 30 detects the frequency (f) of power supplied to the load 9 from the AC voltage detected by the voltage detector 10 and transmits it to the first function circuit 31 and the frequency change rate detection circuit 28. To do.

  FIG. 5 is a diagram for explaining an example of the frequency detection operation in the frequency detection circuit 30. The frequency detection circuit 30 detects the zero cross signal of the AC power supply voltage, detects the frequency (f) with the next rise from the rise of the zero cross signal as one cycle, and takes one cycle from the fall of the zero cross signal to the next fall. For example, when the AC power supply is 50 Hz, the frequency (f) is detected every 10 ms. When the frequency (f) is detected by the frequency detection circuit 30 in this way, one cycle is performed from the rise of the zero cross to the next rise, for example, when the AC power supply is 50 Hz, rather than detecting the frequency every 20 ms. Can be detected at high speed.

The first function circuit 31 inputs the output V ₃₁ (reactive power or current phase θ) calculated by the characteristic function from the received frequency (f) to the addition limit circuit 32.

  FIG. 2A shows an example of the relationship between the frequency (f) and the reactive power (or current phase θ) of the inverter bridge 2 in the vicinity of the reference frequency f0. As shown in FIG. 2A, in the vicinity of the reference (rated) frequency f0, the inverter bridge 2 has a characteristic that the reactive power (or current phase θ) increases in the advance direction as the inverter output frequency (f) increases.

The frequency change rate detection circuit 28 detects the frequency change rate (df / dt) of the frequency (f) output from the frequency detection circuit 30 and transmits it to the limit circuit 36. In FIG. 1, when the positive or negative frequency change rate df / dt diverges as shown in FIG. 3A, the limit circuit 36 has an absolute value according to the magnitude of the input frequency change rate (df / dt). A value that changes stepwise from a small value to a large value is output. That is, the limit circuit 36 changes stepwise so that the frequency change rate changes to a positive value when the frequency change rate exceeds a predetermined value, and changes to a negative value when the frequency change rate becomes a predetermined value or less. Specifically, the limit circuit 36 outputs a value when the frequency change rate (df / dt) exceeds a predetermined value when the frequency change rate (df / dt) is positive (absolute frequency change rate). When the value is increased), the output is changed to the positive value, and when the frequency change rate (df / dt) is equal to or less than the predetermined value (when the absolute value of the frequency change rate is reduced), the negative side The output is changed to the value of.

  Further, the limit circuit 36, when the frequency change rate (df / dt) is negative, when the frequency change rate (df / dt) becomes less than a predetermined value (when the absolute value of the frequency change rate becomes large). The output is changed to a negative value, and the output is changed to a positive value when the frequency change rate (df / dt) exceeds a predetermined value (when the absolute value of the frequency change rate becomes small).

  FIG. 3A shows an example in which the frequency change rate (df / dt) diverges and the output of the limit circuit 36 changes stepwise to the positive side or the negative side. This is because the frequency (f) changes so as to diverge by positive feedback.

  6A and 6B are examples of simulation results obtained by the isolated operation detection device according to the present embodiment when the inverter bridge 2 is operated independently. In this example, it is a simulation when the inverter bridge 2 becomes an independent operation at the time of 0.00 s. In the case shown in FIG. 6A, after the inverter bridge 2 is in an independent operation, the frequency (f) changes while the frequency change rate (df / dt) is gradually increased by the positive feedback action. In the case shown in FIG. 6B, after the inverter bridge 2 is in a single operation, the frequency (f) changes while the frequency change rate (df / dt) gradually increases in the negative direction due to the positive feedback action. .

  FIG. 4A shows an example of a stepwise frequency increase when the instantaneous voltage decreases. FIG. 4B shows an example of the frequency drop when the instantaneous voltage drops. As shown in FIGS. 6A and 6B, the frequency (f) changes while the frequency change rate (df / dt) increases (or decreases) as shown in FIGS. 6A and 6B. At the time of failure of 8, the change of the frequency change rate (df / dt) at the time of failure shown in FIGS. 4A and 4B becomes almost constant, and the difference between these is clear. By utilizing this difference, in this embodiment, the absolute value of the value that changes stepwise according to the frequency change rate (df / dt) output from the limit circuit 36 during the single operation gradually increases. While distinguishing between failure of the AC power system 8 and isolated operation, the output of the limit circuit 36 is used as the input of the second function circuit 29.

In the following description, the absolute value of the output value at which the frequency change rate (df / dt) has passed through the limit circuit 36 is defined as a limit value as follows.

The arithmetic circuit 37 calculates the limit value every 10 ms, subtracts the dead zone from the reset amount A (limit value−A), integrates the result every 10 ms,

Is calculated. This result is input to the level detection circuit 38,

    As a result, the level detection circuit 38 compares the detected value with the isolated operation detection level K, and the isolated operation is detected when the detected value exceeds the isolated operation detection level K. When the level detection circuit 38 detects an isolated operation, the level detection circuit 38 notifies the abnormality detection circuit 19 to that effect, and the abnormality detection circuit 19 stops the inverter bridge 2 and at the same time opens the contactor 6 to disconnect the inverter bridge 2 from the system. Open.

  The reason why the output value of the limit circuit 36 is input to the second function circuit 29 with polarity is to prevent the reactive power from changing suddenly when it is not an independent operation due to a large frequency change rate (df / dt). In addition, even if the output of the frequency change rate detection circuit 28 is directly input to the second function circuit 29, the reactive power fluctuation may increase, but the action at the time of detecting the isolated operation is the same (the reactive power changes suddenly). Then, the voltage changes suddenly, which is not preferable. However, it is possible to detect an isolated operation at high speed even with this method).

  That is, the output of the frequency change rate detection circuit 28 may be used as the input of the second function circuit 29. In this case, the function means includes a frequency detection circuit 30 that detects the frequency (f) from the voltage detected by the voltage detector 10, and the reactive power Q advances when the frequency (f) detected by the frequency detection circuit 30 increases. The first function circuit 31 that controls the reactive power Q to increase in the delay direction when the frequency (f) decreases and the frequency change rate (df) from the frequency (f) detected by the frequency detection circuit 30. / Dt), and when the frequency change rate (df / dt) detected by the frequency change rate detection circuit 28 is positive, the reactive power Q is shifted in the advance direction and the frequency change rate. When (df / dt) is negative, the second function circuit 29 controls the reactive power Q to shift in the delay direction, and the sum of the output of the first function circuit 31 and the output of the second function circuit 29 It comprises an adding limit circuit 32 for controlling the reactive power Q of the inverter bridge 2, a.

  FIG. 3B (a) shows, as an example, the value of (limit value−0.02) when the output value of the limit circuit 36 changes stepwise as shown in FIG. 3A. FIG. 3B (b) shows, as an example, a value of Σ (limit value−0.02) when the output value of the limit circuit 36 changes stepwise as shown in FIG. 3A. At this time, if the level K is 0.5, Σ (limit value−0.02) becomes 0.895 after 50 ms, and the isolated operation detection device according to the present embodiment detects the isolated operation in the shortest 50 ms. be able to.

  In addition, when the output of the limit circuit 36 changes as shown in FIG. 3, the isolated operation can be detected in the shortest time when the value of the isolated operation detection level K is 0.465 or more and 0.895 or less. The isolated operation detection level K is set according to how the step-like value output from the limit circuit 36 changes.

  Further, the FRT regulations require that the isolated operation not be detected even when the frequency changes suddenly as shown in FIG. 4A. However, as shown in FIG. 3B (b), Σ (limit value−0 The value of .02) becomes 0.095 after 20 ms, but is much smaller than 0.5, and it is clear that even if the frequency changes suddenly, it is not erroneously detected.

  Furthermore, as shown in FIG. 4B, the frequency changes for a long time at a frequency change rate (df / dt) of 0.04 Hz / 20 ms (0.02 Hz / 10 ms when sampling every 10 ms) (when 50 Hz). In this case, since the value of limit value −0.02 shown in FIG. 3B (a) is zero (limit value −0.02 = 0), Σ (limit value −0. 02) = 0 <0.5, and even in this case, the erroneous detection of the isolated operation is not performed.

The output of the limit circuit 36 is also input to the second function circuit 29. The output of the limit circuit 36 is input to the second function circuit 29, after being inputted to the characteristic function of the second function circuit 29, is added to the output V ₃₁ of the first function circuit 31 in addition limit 32, the inverter current phase To change the reactive power and shift the frequency by applying positive feedback to the frequency.

The second function circuit 29 inputs the output V ₂₉ (reactive power or current phase θ) calculated by the characteristic function from the value obtained by limiting the received frequency change rate (df / dt) by the limit circuit 36 to the addition limit circuit 32. .

  FIG. 2B shows an example of the relationship between the value input from the limit circuit 36 and the reactive power (or current phase θ) of the inverter bridge 2. As shown in FIG. 2B, the inverter bridge 2 has a characteristic that the reactive power (or current phase θ) increases in the advance direction as the value input from the limit circuit 36 increases.

Adding the limit circuit 32 receives an output _{V 29} and an output _{V 31,} by adding the output _{V 29} and an output _{V 31} for outputting an output _{V 29} that limit the maximum value to the phase shift circuit 23. FIG. 2C shows an example of the output V ₃₂ of the addition limit circuit 32. As shown in FIG. 2C, the output V ₃₂ has a large slope near the rated frequency f0 so as to promote changes in the frequency and the frequency change rate. Phase shift circuit 23 shifts the phase of the output signal Vs of a sine wave circuit 26 to control the output reactive power of the inverter bridge 2 (I × Vsinθ) by the reference phase obtained from the output V _32.

  As described above, the isolated operation detection device according to the present embodiment operates with the characteristics of the slip mode frequency shift, and as shown in FIG. 2C, the current phase advances as the frequency (f) increases near the rated frequency f0. The phase of the output signal Vs of the sine wave circuit 26 is shifted so that the advance reactive power increases.

  That is, in the isolated operation detection device according to the present embodiment, when the AC side of the inverter is disconnected from the AC power system, the frequency (f) and the frequency change rate (df / dt) of the AC power source slightly increase or decrease.

  When an increase or decrease in the frequency (f) and the frequency change rate (df / dt) is detected and the frequency (f) is increased and the frequency change rate (df / dt) is positive, the current phase of the inverter bridge 2 is detected. The positive feedback is applied in the direction in which the frequency (f) further increases.

  When an increase or decrease in the frequency (f) and the frequency change rate (df / dt) is detected, and the frequency (f) decreases or the frequency change rate (df / dt) is negative, the current phase of the inverter bridge 2 is changed. The positive feedback is applied in the direction in which the frequency (f) further decreases with a delay.

  As described above, by rapidly breaking the balance between the output of the inverter and the load, the frequency change rate (df / dt) of the AC power supply is input to the arithmetic circuit 37 via the limit circuit 36, and the frequency is calculated by the arithmetic circuit 37. The integral value of the limit value of the rate of change (df / dt) is calculated, and the integral value is judged by the level detection circuit 38, and at the same time, the high speed islanding detection with the FRT tolerance is performed. When the system becomes abnormal voltage or abnormal frequency by the voltage relay 17 or the frequency relay 18, the inverter is gated off due to the system abnormality, and at the same time, the contactor 6 is opened to open the inverter from the system.

  That is, according to the present embodiment, it is possible to provide an isolated operation detection device and an isolated operation detection method having an FRT function without malfunction even when the frequency changes suddenly or changes for a long time.

  Next, an isolated operation detection device and an isolated operation detection method according to the second embodiment will be described with reference to the drawings. Note that, in the following description, the same components as those in the isolated operation detection device and the isolated operation detection method according to the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

FIG. 7 shows a configuration example of the isolated operation detection apparatus according to the second embodiment.
In the isolated operation detection device according to the present embodiment, the inverter bridge 2 has three phases and the power source (AC power system) 8 has three phases, so that the active power P and the reactive power Q of the inverter output are generally detected by the PQ detection circuit. 35, and the amplifier 13a compares and amplifies the active power reference P ^* to V13a, compares the output Q ^* and Q of the reactive power reference circuit 33 to V13b, and converts the outputs of V13a and V13b to three-phase conversion. The three-phase inverter bridge 2 is driven as a PWM signal through the circuit 34, the reactive power Q of the three-phase inverter is controlled to control the reactive power at the time of independent operation, and the inverter frequency is shifted at high speed by a positive feedback action. Is configured to do.

  FIG. 7 shows a configuration example of the isolated operation detection device according to the present embodiment. The inverter bridge 2 of the inverter independent operation detection device according to the present embodiment is a three-phase bridge inverter. Reactors 3a, 3b, and 3c are connected to the AC side of inverter bridge 2, and reactors 3a, 3b, and 3c are delta-connected to filter capacitors 4a, 4b, and 4c, respectively. The current detectors 5a and 5b are connected in two phases and measure the output current of the inverter bridge.

  In the present embodiment, the driving means includes an amplifier 11, an amplifier 13a, an amplifier 13b, a PWM circuit 14, a reactive power reference circuit 33, a three-phase conversion circuit 34, a PQ detection circuit 35, and a driving unit 15, and includes an addition limit circuit. The active power P and reactive power Q of the output power of the inverter bridge 2 are controlled using 32 outputs, and the inverter bridge 2 is stopped when an abnormality is notified from the abnormality detection unit.

The PQ detection circuit 35 calculates active power P and reactive power Q from the output current of the inverter bridge 2 and the voltage supplied to the load 9. Amplifier 11 outputs the detected voltage reference V ^* and comparative amplified active power reference P ^* the voltage of the DC power source 1 to the amplifier 13a. The amplifier 13 a inputs a signal V 13 a obtained by amplifying the active power reference P ^* and the active power P output from the amplifier 11 to the three-phase conversion circuit 34.

The output V ₃₂ of the addition limit circuit 32 is input to the reactive power reference circuit 33. Reactive power reference circuit 33 outputs to the amplifier 13b reactive power reference Q ^* based on the output _{V 32.} The amplifier 13b amplifies an error between the reactive power reference Q ^* and the reactive power Q of the inverter bridge 2 detected by the PQ detection circuit 35, and outputs the amplified signal as a signal V13b. The signal V13b is input to the three-phase conversion circuit 34, the output of the three-phase conversion circuit 34 that converts the signal V13b into a signal corresponding to the three-phase inverter is input to the PWM circuit 14, and the PWM circuit 14 passes through the drive unit 15. A method of controlling the output current of the inverter bridge 2 and controlling the active power and the reactive power is performed in the three-phase inverter.

  As described above, in the case of the single phase shown in FIG. 1, the reactive power was changed by changing the current phase to detect the single operation of the inverter bridge 2 at a high speed. However, in the case of the three phases shown in FIG. By directly controlling the electric power, the single operation of the inverter bridge 2 is detected at high speed.

  As shown in FIG. 7, except for the above-described configuration, the isolated operation detecting apparatus according to the first embodiment of the present invention shown in FIG. That is, according to the isolated operation detection device and the isolated operation detection method according to the present embodiment, the balance between the output of the inverter and the load is rapidly increased as in the isolated operation detection device and the isolated operation detection method according to the first embodiment. By breaking, the frequency change rate (df / dt) of the AC power supply is input to the arithmetic circuit 37 via the limit circuit 36, and the arithmetic circuit 37 calculates the integral value of the limit value of the frequency change rate (df / dt). When the integrated value is determined by the level detection circuit 38 and becomes equal to or higher than a certain value, high-speed islanding operation with FRT tolerance is detected, and at the same time, the voltage relay 17 and the frequency relay 18 are connected to the abnormal voltage and abnormal frequency. When this happens, the gate of the inverter is shut off due to a system abnormality, and at the same time, the contactor 6 is opened to open the inverter from the system.

  That is, according to the present embodiment, it is possible to provide an isolated operation detection device and an isolated operation detection method having an FRT function without malfunction even when the frequency changes suddenly or changes for a long time.

  In FIG. 1 and FIG. 7, the frequency (f) is detected and input to the addition limit circuit 32 via the first function circuit 31, but the movement of the frequency (f) is used instead of the frequency (f). The difference between the past and the present of the average (fm) is calculated, the moving average difference value Δfm (past moving average fm−current moving average fm) is calculated, and the moving average difference value Δf is input to the first function circuit 31. The action is the same even if you enter it.

  In this case, the function unit detects the frequency (f) from the voltage detected by the voltage detector 10, and detects the frequency moving average (fm) from the detected frequency (f). A moving average detection circuit (not shown) that outputs a difference Δfm between the frequency moving average and the current frequency moving average, and when the output of the moving average detection circuit rises, the reactive power increases and the output of the moving average detection circuit increases. The first function circuit 31 that controls the reactive power to increase in the direction of delay when it falls, and the frequency change rate detection circuit 28 that detects the frequency change rate (df / dt) from the frequency (f) detected by the frequency detection circuit 30. The limit circuit 36 that limits the frequency change rate (df / dt) detected by the wave number change rate detection circuit 28 to change in a stepped manner, and the output of the limit circuit 36 is , The second function circuit 29 that controls the reactive power to shift in the advance direction, and controls the reactive power to shift in the delay direction when the output of the limit circuit 36 is negative, and the output of the first function circuit 31 and the second And an addition limit circuit 32 for controlling the reactive power of the inverter based on the sum of the outputs of the two-function circuit 29. The first function circuit 31 outputs a reactive power or current phase value so that a change in the moving average difference value Δfm is promoted by positive feedback.

In addition, it cannot be overemphasized that the calculation demonstrated in the said 1st Embodiment and 2nd Embodiment can be processed via a microcomputer.
As described above, according to the first embodiment and the second embodiment, the frequency change rate (df / dt) is set in a pattern that limits the frequency change rate (df / dt) with respect to a stepwise frequency change. Limited.

This is the result of calculating the output of the limit circuit 36 by the calculation circuit 37.

Is compared with the isolated operation detection level K, and the isolated operation is detected when the integrated value is equal to or higher than the isolated operation detection level K, thereby realizing high-speed isolated operation with FRT tolerance. Furthermore, for long-term changes over 1.25 seconds of the frequency change rate df / dt (0.04 Hz / 20 ms, or 0.02 Hz / 10 ms),

    When the reset amount A is 0.04 Hz / 20 ms (0.02 / 10 ms when sampling every 10 ms), it is detected as an independent operation, and further, the rise time from the rise of the zero cross point of the power supply voltage By performing 10 ms sampling detection by measuring and controlling the time from falling to falling, it is possible to detect higher-speed isolated operation. The reset amount A is preferably about 2 Hz / s (in the case of 50 Hz, 0.04 Hz / 20 ms, and in the case of sampling every 10 ms, 0.02 / 10 ms). The reset amount A is set, for example, so as not to feel a frequency drop at the time of recovery from an instantaneous voltage drop. In order to perform FRT for a failure whose frequency change rate changes at 0.04 Hz / 20 ms, resetting 0.04 makes it insensitive. The reset amount A is changed according to the specification of the FRT.

  In addition, the input of the second function 29 in FIGS. 1 and 7 may cause the reactive power to change suddenly even if the output of the frequency change rate detection circuit 28 is directly input, but the single operation is performed while satisfying the FRT regulations. Needless to say, this is done at high speed.

  In addition, the frequency detection is slightly slower than the isolated operation detection every 20 ms, but almost satisfactory performance is achieved.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

V ^* : Voltage reference, I ^* : AC current reference, A: Reset amount, V ₃₁ , V ₂₉ , V ₃₂ ... Output, P: Active power, Q: Reactive power, P ^* : Active power reference, Q ^* : Invalid Power reference, Δf ... Moving average difference value of frequency, K ... Single operation detection level, 1 ... DC power supply, 2 ... Inverter bridge, 3-phase inverter bridge, 3, 3a, 3b, 3c ... Reactor, 4, 4a, 4b, 4c ... capacitor 5, 5a, 5b, 5c ... current detector, 6 ... contactor (relay), 7 ... breaker, 8 ... AC power system, 9 ... load, 10 ... voltage detector (voltage detection means), 11 , 13, 13a, 13b ... amplifier, 12 ... current reference circuit, 14 ... PWM circuit, 15 ... drive unit, 17 ... voltage relay, 18 ... frequency relay, 19 ... abnormality detection circuit, 22 ... PLL circuit, 23 ... phase shift Circuit, 26 ... Sine wave circuit, 28 ... frequency change rate detection circuit, 29 ... second function circuit, 30 ... frequency detection circuit, 31 ... first function circuit, 32 ... addition limit circuit, 33 ... reactive power reference circuit, 34 ... three phase Conversion circuit, 35 ... PQ detection circuit, 36 ... limit circuit, 37 ... arithmetic circuit, 38 ... level detection circuit.

Claims (11)

An independent operation detection device for an inverter that converts DC power into AC power and operates in conjunction with an AC power system,
Voltage detecting means for detecting the output voltage of the inverter;
The reactive power or current phase is controlled in a direction in which the frequency of the output voltage detected by the voltage detecting means promotes a change by positive feedback, and a positive value is obtained when the frequency change rate of the frequency exceeds a predetermined value. When the frequency change rate falls below the specified value, the value changes to the negative value, and the reactive power or current phase is controlled in such a direction that the value that changes stepwise facilitates the change by positive feedback. Function means to output;
A signal for detecting whether or not a value obtained by subtracting a dead zone from a value that changes in a stepwise manner at a predetermined time is equal to or higher than an isolated operation detection level, and that stops the inverter when the detected value is equal to or higher than the isolated operation detection level. An abnormality detection means for outputting
The inverter is synchronized with the voltage phase of the AC power supply system and the inverter output, and a predetermined reactive power or current phase is controlled by the output of the function means to perform reactive power control of the output of the inverter. When it is disconnected from the inverter, the inverter is driven so that the reactive power of the inverter changes based on the frequency of the output voltage of the inverter and the value that changes stepwise, and a signal for stopping the inverter is received from the abnormality detection means And a drive means for stopping the inverter when the inverter is operated.   The drive means constitutes a loop that controls the active power and reactive power of the inverter, and when the inverter is disconnected from the AC power system, the frequency of the inverter output voltage and a value that changes stepwise. The inverter independent operation detection device according to claim 1, further comprising means for controlling the reactive power of the inverter based on the frequency so as to control the frequency of the output voltage of the inverter or the frequency change rate in a direction that promotes a change by positive feedback.   The drive means performs output current control of the inverter so that the current of the inverter matches a current reference phase, and when the inverter is disconnected from the AC power system, the frequency of the output voltage of the inverter and the 2. The device according to claim 1, further comprising means for changing the phase of the current reference of the inverter based on the step-change value and controlling the frequency of the output voltage or the frequency change rate to promote the change by a positive feedback action. Driving detection device.   The function means includes a frequency detection circuit that detects a frequency from the voltage detected by the voltage detection means, and when the frequency detected by the frequency detection circuit increases, the reactive power increases in a forward direction and the frequency is increased. A first function circuit that controls the reactive power to increase in the delay direction when it falls, a frequency change rate detection circuit that detects a frequency change rate from the frequency detected by the frequency detection circuit, and the frequency change rate detection A limit circuit that outputs a value that changes in a step-like manner according to the value of the frequency change rate detected by the circuit, and when the output of the limit circuit is positive, the reactive power is shifted in the advance direction and the limit circuit A second function circuit that controls the reactive power to shift in a delay direction when the output of the first function circuit is negative, the output of the first function circuit, and the The sum of the output of the 2 function circuit, independent operation detecting apparatus of the inverter according to claim 2 or claim 3, wherein and an addition limit circuit for controlling the reactive power of the inverter.   The limit circuit is stepped so that when the frequency change rate exceeds a predetermined value, the limit circuit changes to a positive value, and when the frequency change rate becomes a predetermined value or less, it changes to a negative value. The isolated operation detection device for an inverter according to claim 4, wherein a value that changes to 1 is output.   The abnormality detecting means integrates a value obtained by subtracting the reset amount from the absolute value of the step-change value and outputs an integrated value, and determines whether the integrated value is equal to or higher than the isolated operation detection level. The inverter independent operation detection device according to claim 1, further comprising: a level detection circuit that detects an abnormality and an abnormality detection circuit that stops the inverter when an abnormality is detected by the level detection circuit.   The inverter independent operation detection device according to claim 6, wherein the reset amount is a value that makes insensitive frequency reduction at the time of recovery from instantaneous voltage drop.   The frequency detection circuit detects a zero-cross signal of the voltage detected by the voltage detection means, and measures a time from the rising edge of the zero-crossing signal to the next falling edge and a time period from the falling edge to the next rising edge. The inverter independent operation detection device according to claim 4, comprising means. An independent operation detection device for an inverter that converts DC power into AC power and operates in conjunction with an AC power system,
Voltage detecting means for detecting the output voltage of the inverter;
The reactive power or current phase is controlled in a direction in which the difference between the past frequency moving average and the current frequency moving average of the frequency of the output voltage detected by the voltage detecting means is facilitated by positive feedback, and the frequency When the frequency change rate exceeds a predetermined value, it changes to a positive value, and when the frequency change rate falls below a predetermined value, it changes to a negative value. Function means for controlling and outputting reactive power or current phase in the direction of promoting change,
A signal for detecting whether or not a value obtained by subtracting a dead zone from a value that changes in a stepwise manner at a predetermined time is equal to or higher than an isolated operation detection level, and that stops the inverter when the detected value is equal to or higher than the isolated operation detection level. An abnormality detection means for outputting
The inverter is synchronized with the voltage phase of the AC power supply system and the inverter output, and is controlled to a predetermined reactive power or current phase by the output of the function means to perform reactive power control of the output of the inverter. The inverter is driven so that the reactive power of the inverter changes based on the difference between the past frequency moving average and the current frequency moving average and the value that changes stepwise, from the abnormality detecting means. An inverter independent operation detection device comprising: drive means for stopping the inverter when receiving a signal for stopping the inverter. An independent operation detection device for an inverter that converts DC power into AC power and operates in conjunction with an AC power system,
Voltage detecting means for detecting the output voltage of the inverter;
The reactive power or current phase is controlled in a direction in which the frequency of the output voltage detected by the voltage detecting means promotes a change by positive feedback, and a positive value is obtained when the frequency change rate of the frequency exceeds a predetermined value. When the frequency change rate falls below the specified value, the value changes to the negative value, and the reactive power or current phase is controlled in such a direction that the value that changes stepwise facilitates the change by positive feedback. Function means to output;
A signal for detecting whether or not a value obtained by subtracting a dead zone from a value that changes in a stepwise manner at a predetermined time is equal to or higher than an isolated operation detection level, and that stops the inverter when the detected value is equal to or higher than the isolated operation detection level. An abnormality detection means for outputting
The inverter is synchronized with the voltage phase of the AC power supply system and the inverter output, and a predetermined reactive power or current phase is controlled by the output of the function means to perform reactive power control of the output of the inverter. When the inverter is decoupled from the inverter, the inverter is driven so that the reactive power of the inverter changes based on the frequency of the output voltage and the frequency change rate, and when the signal for stopping the inverter is received from the abnormality detecting means. An independent operation detection device for an inverter, comprising: drive means for stopping the inverter. A single operation detection method for detecting single operation of an inverter that converts DC power into AC power and operates in conjunction with an AC power system,
Detecting the output voltage of the inverter;
The reactive power or current phase is controlled in a direction in which the frequency of the detected output voltage is promoted by positive feedback, and when the frequency change rate of the frequency exceeds a predetermined value, the frequency is changed to a positive value. When the rate of change is less than or equal to a predetermined value, it changes to a negative value, and the reactive power or current phase is controlled in a direction in which the value that changes in a step-like manner promotes the change by positive feedback,
Determining that the value obtained by subtracting the dead zone from the value that changes in the step shape every predetermined time is abnormal when the value is equal to or higher than the isolated operation detection level,
Synchronize with the voltage phase of the AC power supply system and the inverter output, and control the reactive power of the inverter output by controlling to a predetermined reactive power or current phase, when the inverter is disconnected from the AC power system, Independent operation of the inverter that drives the reactive power of the inverter to change based on the frequency of the output voltage of the inverter and the value that changes stepwise, and stops the inverter when it is determined to be abnormal Detection method.

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