JP2013078207A - Electric power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion system capable of quickly and appropriately determining generation of a momentary voltage drop.SOLUTION: The electric power conversion system, which is connected to a power system, converts DC power into AC power and outputs the AC power to the power system, includes: an angular acceleration information acquisition section that acquires information of an angular acceleration of a system voltage; and a system state determination section that determines generation of a momentary voltage drop on the basis of the angular acceleration.

Description

  The present invention relates to a power conversion device linked to a power system.

  2. Description of the Related Art Conventionally, power converters that are connected to a power system, convert DC power into AC power, and output the power to the power system have been used. For such a power converter, requirements for system stabilization are being studied.

  According to the requirements for system stabilization, for example, the power conversion device is required to continue operation in response to transient power system fluctuations such as instantaneous voltage drop (hereinafter referred to as “instantaneous voltage drop”). . Under such circumstances, in the power conversion device, it is desired that the occurrence of the voltage sag can be determined quickly and accurately in order to enable appropriate response to the voltage sag.

JP 2003-153433 A

  However, for example, in the conventional method of detecting the value of the system voltage and determining the occurrence of the instantaneous drop based on the detection result, it is not easy to determine the occurrence of the instantaneous drop quickly and accurately.

  In view of the above-described problems, an object of the present invention is to provide a power conversion device that makes it easy to quickly and accurately determine the occurrence of a sag.

  A power conversion device according to the present invention is a power conversion device that is connected to a power system, converts DC power to AC power, and outputs the power to the power system, and acquires angular acceleration information of the system voltage. It is set as the structure provided with the acquisition part and the system | strain state determination part which determines generation | occurrence | production of instantaneous drop based on the said angular acceleration.

  According to the power conversion device of the present invention, it is easy to quickly and accurately determine the occurrence of an instantaneous drop.

It is a lineblock diagram of the power converter concerning a 1st embodiment of the present invention. It is explanatory drawing regarding the waveform of a system voltage. It is a flowchart regarding determination of a system state and the operation | movement relevant to this. It is a block diagram of the power converter device which concerns on 2nd Embodiment of this invention. It is a block diagram of the power converter device which concerns on 3rd Embodiment of this invention. It is explanatory drawing regarding the determination conditions of a system state.

  Embodiments of the present invention will be described below by taking each of the first to third embodiments as an example.

1. First Embodiment [Configuration of Power Conversion Device, etc.]
First, the first embodiment will be described. FIG. 1 is a configuration diagram of a power conversion device 1 according to the first embodiment. The power conversion device 1 has a terminal Ta and a terminal Tb, and a DC power source is connected to the terminal Ta (in the present embodiment, the solar cell 2 is taken as an example, but another DC power source may be used). Are connected and used in a form linked to the electric power system 3 via the terminal Tb.

  Note that the solar cell 2 outputs DC power obtained by photoelectric conversion of sunlight to the power conversion device 1. The power conversion device 1 can be connected to the power system 3 in various forms. In the example illustrated in FIG. 1, the power conversion device 1 is connected to the power system 3 via a power line having a coil (L), a resistor (R), and the like, and is between the positive side and the negative side of the power line. A load is connected to.

  The power conversion device 1 includes a capacitor 11, an inverter 12, an interconnection relay 13, an overcurrent prevention circuit 14, a control device 15, and the like. The capacitor 11 is provided mainly for power smoothing, and both ends thereof are connected to the positive electrode side and the negative electrode side of the terminal Ta, respectively.

  The inverter 12 is driven to perform a switching operation according to the gate signal Sg received from the control device 15, converts the DC power input from the terminal Ta side into AC power, and outputs the AC power to the terminal Tb side. The inverter 12 has a configuration in which, for example, a plurality of transistors that are switched ON / OFF by a gate signal Sg are bridge-connected, and a diode is connected in antiparallel to each switching element.

  The interconnection relay 13 is provided on a line connecting the inverter 12 and the terminal Tb, and operates to open when receiving the disconnection signal Sr from the control device 15. When the interconnection relay 13 is opened, the power conversion device 1 is disconnected from the power system 3.

  The overcurrent prevention circuit 14 stops the operation of the power conversion device 1 as an overcurrent prevention function (error stop) when the output current of the power conversion device 1 exceeds a predetermined device protection level, that is, when an overcurrent occurs. ) By operating the overcurrent prevention function, it is possible to protect the device from overcurrent.

  The overcurrent prevention function plays an important role in protecting the device. However, when the overcurrent prevention function is activated and the operation of the power converter 1 is stopped, the power converter 1 is restored. (Restart) takes time. Therefore, from the viewpoint of stably operating the power conversion device 1, it is desirable to avoid a situation where the output current becomes an overcurrent so as not to operate the overcurrent prevention function as much as possible.

  Therefore, the power conversion device 1 limits the output current command value and gate blocks as necessary, so as to avoid the situation where the output current becomes an overcurrent as much as possible. Details of this point will become apparent from the description given later.

  The control device 15 includes a bandpass filter 21, a frequency / phase / amplitude calculation unit 22, a coordinate conversion unit 23, an angular acceleration calculation unit 24, a system state determination unit 25, an isolated operation detection unit 26, a DC voltage control unit 27, and a limiter 28. , An active current control unit 29, a reactive current control unit 30, a coordinate conversion unit 31, a gate signal generation unit 32, and the like.

Further, the control device 15 includes a detection value of the AC voltage between the terminals Tb (AC voltage detection value v _s ), a detection value of the AC current flowing through the terminal Tb (AC current detection value i _s ), and between both ends of the capacitor 11. Each signal of the DC voltage detection value (DC voltage detection value E _d ) at is input. The control device 15 performs AD conversion of these signals at a predetermined sampling frequency (for example, 17.5 kHz), and performs each process on the obtained digital signal.

Bandpass filter 21 is the input signal of the AC voltage detected value v _s is subjected to a filtering process of the high and low pass cutoff for this signal (bandpass), and outputs to the frequency / phase / amplitude calculator 22 . Note the AC voltage detected value v _s has a value corresponding value of the system voltage (the voltage of the power system 3), or to.

Frequency / phase / amplitude calculation unit 22, based on the signal of the AC voltage detected value v _s received from the band-pass filter 21, the frequency of the system voltage (angular velocity) omega, phase theta, and the amplitude V _s is calculated (estimated) The calculation result signal is sent to the subsequent stage. Incidentally frequency / phase / amplitude calculation unit 22, for each period of the AD converter in the control unit 15, the frequency omega, which is phase theta, and is possible to calculate the amplitude V _s.

Of the calculation result signals, the phase θ signal is sent to the coordinate conversion unit 23 and the coordinate conversion unit 31, the frequency ω signal is sent to the angular acceleration calculation unit 24 and the isolated operation detection unit 26, and the amplitude V _s signal is isolated operation. Each is sent to the detector 26. The form of the calculation process performed by the frequency / phase / amplitude calculation unit 22 is not particularly limited. For example, a calculation formula or LUT [Look Up Table] that is appropriately set in advance may be used. good.

Coordinate conversion unit 23 performs coordinate transformation on the alternating current detection value i _s by using the signal of the phase theta, obtaining the active current detection value i _{p (active} ingredient) and reactive current detected value i _{q (reactive} component). The coordinate conversion unit 23, a signal of the active current detected value i _p to the active current controller 29, the reactive current controller 30 a signal of the reactive current detection value i _q, and sends each.

  The angular acceleration calculation unit 24 calculates the angular acceleration dω / dt of the system voltage based on the signal of the frequency ω, and sends a calculation result signal (signal of the angular acceleration dω / dt) to the system state determination unit 25.

  The system state determination unit 25 determines the state (system state) of the electric power system 3 based on the signal of the angular acceleration dω / dt, and uses the system state determination signal Sd representing the determination result as the isolated operation detection unit 26 and the limiter. 28. The system state determination unit 25 sets the system state to “normal”, “single operation”, “instantaneous voltage drop (small phase jump)”, and “instantaneous voltage drop” according to the magnitude of angular acceleration | dω / dt | (Phase jumping large) "is determined.

  More specifically, when the magnitude of angular acceleration | dω / dt | is equal to or smaller than a predetermined threshold A, it is determined as “normal” and is larger than the threshold A and equal to or smaller than the threshold B (a predetermined value larger than the threshold A). If it is, it is determined as “single operation” (a state in which an abnormality to the extent that can induce the single operation of the power converter 1 has occurred).

  When an abnormality (disturbance) occurs in the electric power system 3, the magnitude | dω / dt | of the angular acceleration tends to increase more than usual due to the influence. Further, as the degree of abnormality is higher, the magnitude of angular acceleration | dω / dt | tends to be larger. The above-described threshold A has a “normal” system state in which the abnormality that induces the single operation of the power conversion device 1 does not occur, and the abnormality that can induce the single operation of the power conversion device 1 occurs. It is appropriately set based on a preliminary survey or the like so that the determination of the system state of “single operation” can be performed satisfactorily.

  When the magnitude of angular acceleration | dω / dt | is greater than threshold value B and equal to or less than threshold value C (predetermined value greater than threshold value B), “instantaneous drop occurrence (small phase jump)” Among these, it is determined that the degree of phase jump is relatively small. Note that the instantaneous drop refers to, for example, a case where the remaining voltage is 20% or less and the duration is 1 second or less. However, the conditions such as the voltage drop amount and the duration time in the case of the instantaneous drop are not limited to this content, and may be other conditions.

  When the magnitude of the angular acceleration | dω / dt | is particularly large, there is a possibility that an instantaneous drop due to lightning strikes has occurred, not an abnormality in the system state that can induce an independent operation of the power converter 1. Expected to be high. The above-described threshold value B is based on a preliminary survey or the like so that the determination of the system state of “single operation” and the system state of “instantaneous voltage drop occurrence (small phase jump)” in which a voltage sag has occurred is satisfactorily performed. Are set appropriately.

  When the magnitude of the angular acceleration | dω / dt | is larger than the threshold value C, “instantaneous drop occurrence (phase jumping large)” (a state in which the degree of phase jumping is relatively large in a state where the instantaneous drop occurs) It is determined. The “instantaneous drop occurrence (phase jump large)” state corresponds to, for example, a case where the degree of phase jump exceeds a certain threshold value (for example, any value in the range of 30 to 90 deg) in the positive or negative direction. As an example, the system state when the system voltage has a waveform shifted by 180 degrees as shown in FIG. 2 corresponds to “instantaneous drop occurrence (large phase jump)”. In the state where a sag has occurred and the degree of phase jump does not exceed the threshold value, “spot sag occurrence (small phase jump)” corresponds.

  Further, when the system state determination unit 25 determines that the system state is “instantaneous drop occurrence (large phase jump)”, the system state determination unit 25 sends the gate block signal Sb to the gate signal generation unit 32 in order to stop the operation of the inverter 12. It is like that. As will be described later, the gate block signal Sb is a signal for blocking the transmission of the gate signal Sg (gate block).

Isolated operation detection unit 26, by passive detection method based on the signal of the signal and the amplitude V _s of the frequency omega, detects the occurrence of the islanding operation of the power conversion apparatus 1. In addition, the specific method in which the isolated operation detection part 26 detects an isolated operation is not specifically limited, A various method is employable.

  The isolated operation detection unit 26 receives the system state determination signal Sd indicating the state of “independent operation” from the system state determination unit 25, and detects the occurrence of the isolated operation by the passive detection method. The disconnection signal Sr is sent to 13. In this way, the isolated operation detection unit 26 causes the power system 3 to be disconnected in accordance with the detection result of the occurrence of the isolated operation. However, when the islanding operation detection unit 26 receives the system state determination signal Sd indicating the state of “instantaneous drop occurrence (small phase jump)”, the islanding operation detection unit 26 sends the disconnection signal Sr regardless of the detection result of the occurrence of the islanding operation. It is set not to.

The DC voltage control unit 27 receives a signal of the DC voltage detection value E _{d and} a signal of a command value (DC voltage command value E _d *) for the DC voltage detection value E _d . The DC voltage command value E _d * is a value that is appropriately set in advance. Then, the DC voltage control unit 27 generates a signal for causing the difference between these values to approach zero as a signal of an effective current command value i _p * (command value for the effective current detection value i _p ), and sends it to the limiter 28. Send it out.

When the limiter 28 receives the system state determination signal Sd representing the “instantaneous drop occurrence (small phase jump)” state from the system state determination unit 25, the limiter 28 receives the signal of the effective current command value i _p * Filter processing for limiting the size is performed, and the filtered signal is output to the active current control unit 29. On the other hand, when the system state determination signal Sd indicating the state of “instantaneous drop occurrence (small phase jump)” has not been received, the limiter 28 directly uses the input signal of the effective current command value i _p * as it is. Output to.

The filtering process performed by the limiter 28 is such that the magnitude of the active current command value i _p * does not exceed a predetermined limit value Lim (when the limit value Lim exceeds the limit value Lim, for example, the same value as the limit value Lim). The process is corrected so that

Active current control unit 29, the signal of the active current detection value i _p from the coordinate converter 23 is input, active current command value i _{p *} of the signal is input from the limiter 28. Then, the effective current control unit 29 generates a signal for causing the difference between these values to approach zero as a signal of the effective voltage command value v _p * (command value for the effective voltage detection value v _p ), and the coordinate conversion unit To 31.

The reactive current control unit 30 receives a signal of the reactive current detection value i _{q and} a signal of a command value (reactive current command value i _q *) for the reactive current detection value i _q . The reactive current command value i _q * is a value set appropriately in advance. Then, the reactive current control unit 30 generates a signal that causes the difference between these values to approach zero as a signal of the reactive voltage command value v _q * (command value for the reactive voltage detected value v _q ), and the coordinate conversion unit To 31.

The coordinate conversion unit 31 performs coordinate conversion on the effective voltage command value v _p * (effective component) and the reactive voltage command value i _q * (invalid component) using the signal of the phase θ to obtain the AC voltage command value v _s *. Ask. The coordinate conversion unit 31 sends a signal of the AC voltage command value v _s * to the gate signal generation unit 32.

The gate signal generation unit 32 generates a pulse signal having a duty ratio corresponding to the AC voltage command value v _s * as the gate signal Sg and sends it to the inverter 12. In this way, the gate signal generation unit 32 performs PWM [Pulse Width Modulation] control of the inverter 12.

  Further, when receiving the gate block signal Sb, the gate signal generation unit 32 fixes the gate signal Sg at, for example, a low level. Thereby, when the gate block signal Sb is transmitted from the system state determination unit 25, the gate block is performed. That is, the drive of the inverter 12 is stopped and the output of the inverter 12 is shut off. When the sending of the gate block signal Sb is released, the gate block is released, and the gate signal generation unit 32 resumes sending the gate signal Sg for driving the inverter 12.

[Operation of power converter, etc.]
As a basic operation, the power conversion device 1 performs an operation of converting DC power received from the solar cell 2 into AC power by the inverter 12 and outputting the AC power to the power system 3.

Further, as described above, the control device 15 exchanges AC based on various detection values (v _s , i _s , E _d ), preset command values (E _d *, i _q *), and the like. The inverter 12 is controlled by calculating the voltage command value v _s * and generating the gate signal Sg. The AC voltage command value v _s * corresponds to the operation amount of the inverter 12.

The control device 15 calculates the AC voltage command value v _s * so that the output of the power conversion device 1 matches the power state of the power system 3. The active current command value i _p * obtained in the process of calculating the AC voltage command value v _s * corresponds to the command value (output current command value) of the current output by the power conversion device 1. The conversion of power by the inverter 12 is performed so that the value of the current output to the power system 3 becomes a value corresponding to the output current command value.

  Further, the control device 15 determines the system state based on the angular acceleration dω / dt of the system voltage, and controls the operation of the power conversion device 1 according to the determination result. Here, determination of the system state and the flow of operations related thereto will be described below with reference to the flowchart of FIG.

  When the angular acceleration calculation unit 24 calculates the angular acceleration dω / dt of the system voltage (step S11), the system state determination unit 25 sets the magnitude | dω / dt | of the angular acceleration as a threshold (threshold A to threshold C). ) To determine the system state (steps S12 to S14).

  When the magnitude | dω / dt | of the angular acceleration is larger than the threshold A (third threshold) (Y in step S12) and not more than the threshold B (first threshold) (N in step S13), the system state is It is determined as “single operation”. When the determination is made as described above, the operation mode of the control device 15 is set to the “independent operation compatible mode” (step S15).

  In the “independent operation mode”, the system state determination signal Sd indicating “independent operation” is input to the independent operation detection unit 26. Thereby, the isolated operation detection part 26 will output the disconnection signal Sr, if an isolated operation is detected by a passive detection system. As a result, the power conversion device 1 can be disconnected from the power system 3 to eliminate the isolated operation.

  The isolated operation detection unit 26 receives the system state determination signal Sd indicating “independent operation” (that is, the magnitude of angular acceleration | dω / dt | exceeds the threshold A and is equal to or less than the threshold B). It may be determined that an isolated operation has occurred, and the disconnection signal Sr may be output. In this case, when the grid state is determined as “single operation”, the disconnection signal Sr is immediately output, and the power conversion apparatus 1 is disconnected from the power system 3.

  When the magnitude of the angular acceleration | dω / dt | is greater than the threshold B (Y in step S13) and equal to or less than the threshold C (second threshold) (N in step S14), (Small phase jump) ”. When the determination is made in this way, the operation mode of the control device 15 is the “first instantaneous low response mode” (step S16).

In the “first instantaneous voltage reduction mode”, the limiter 28 receives an output current command value (effective current command value i) by inputting the system state determination signal Sd indicating “instantaneous voltage drop (small phase jump)” to the limiter 28. _p *) is subjected to filter processing for limiting the size thereof. As a result, when it is determined that an instantaneous drop has occurred, the output current command value is limited so as not to exceed the limit value Lim, and the magnitude of the output current of the power converter 1 is suppressed. As a result, the operation of the overcurrent prevention function by the overcurrent prevention circuit 14 can be avoided as much as possible.

  In addition, when the system state determination signal Sd representing “instantaneous drop occurrence (small phase jump)” is input to the isolated operation detection unit 26, the isolated operation detection unit 26 detects the occurrence of isolated operation by the passive detection method. Regardless of the result, the disconnection signal Sr is not output. As a result, it is possible to avoid unnecessary disconnection due to the occurrence of the instantaneous drop. As described above, when it is determined that an instantaneous drop has occurred, the isolated operation detection unit 26 prohibits disengagement (so that disengagement is not performed) regardless of the detection result of the occurrence of isolated operation.

  If the magnitude | dω / dt | of the angular acceleration is larger than the threshold value C (Y in step S14), the system state is determined as “instantaneous drop occurrence (large phase jump)”. When the determination is made in this way, the operation mode of the control device 15 is the “second instantaneous voltage reduction mode” (step S17).

  In the “second instantaneous voltage reduction mode”, the system state determination unit 25 sends the gate block signal Sb, whereby the gate block is performed in the inverter 12. As a result, the output current of the power conversion device 1 is suppressed, and it is possible to avoid the operation of the overcurrent prevention function by the overcurrent prevention circuit 14 as much as possible.

  In the case of “instantaneous voltage drop (large phase jump)”, the degree of abnormality in the power system 3 is higher than in the case of “flash voltage occurrence (small phase jump)”. Abnormalities tend to be large. Therefore, in the “second instantaneous low response mode”, the output current becomes almost zero by executing the gate block, and the output current can be suppressed more strongly than in the “first instantaneous low response mode”. ing.

  The isolated operation detection unit 26 also receives the system disconnection signal Sr regardless of the detection of the isolated operation by the passive detection method even when the system state determination signal Sd representing “instantaneous drop occurrence (large phase jump)” is input. May be set not to output. As a result, even in the “second instantaneous voltage reduction mode”, it is possible to avoid unnecessary disconnection due to the occurrence of an instantaneous voltage drop.

  When the magnitude of angular acceleration | dω / dt | is equal to or less than the threshold value A (N in step S12), the system state is determined to be “normal”. When the determination is made in this way, the operation mode of the control device 15 is the “normal mode” (step S18).

  In the “normal mode”, the control device 15 performs a normal operation without limiting the output current command value or sending the gate block signal Sb. It should be noted that when the mode is shifted from the “first instantaneous voltage reduction mode” to the “normal mode”, the limitation on the output current command value that has been performed so far is cancelled. That is, when the output current command value is limited and the magnitude of angular acceleration | dω / dt | becomes equal to or less than the threshold value A, the limitation on the output current command value is released.

  Further, when the mode is shifted from the “second instantaneous voltage reduction mode” to the “normal mode”, the transmission of the gate block signal Sb which has been performed so far is stopped, and the gate block is released. That is, when the magnitude of the angular acceleration | dω / dt | becomes equal to or less than the threshold A when the sending of the gate signal Sg is stopped, the blocking of sending the gate signal Sg is released. When the “normal mode” is thus set, the system state is considered to have returned to the normal state, and the operation mode of the control device 15 is restored to the normal mode.

  The series of operations described above (steps S11 to S18) are repeated for each AD conversion cycle in the control device 15 or a cycle according to this, except when the power conversion device 1 is disconnected from the power system 3 or the like. . Therefore, the control device 15 can determine the system state in a very short cycle and can perform an operation adapted to the determination result.

  Further, the conditions for the isolated operation detection unit 26 to output the disconnection signal Sr are not limited to the above-described form. For example, the isolated operation detection unit 26 basically outputs the disconnection signal Sr when the isolated operation is detected by the passive detection method, and when it is determined that the instantaneous drop occurs exceptionally, The disengagement signal Sr may not be output regardless of the detection result. As a result, it is possible to avoid unnecessary disconnection due to the occurrence of the instantaneous drop.

2. Second Embodiment Next, a second embodiment will be described. The second embodiment is basically the same as the first embodiment except that the limit value Lim is determined according to the voltage drop amount of the power system 3. In the following description, emphasis is placed on the description of parts different from the first embodiment, and description of parts equivalent to the first embodiment may be omitted.

  FIG. 4 is a configuration diagram of a power conversion device 1a according to the second embodiment. The control device 15 included in the power conversion device 1a is provided with a limit value determination unit 35.

The limit value determination unit 35 receives the system state determination signal Sd from the system state determination unit 25 and the signal of the amplitude V _s of the system voltage from the frequency / phase / amplitude calculation unit 22. Then, the limit value determination unit 35 determines the limit value Lim based on the signal of the amplitude V _s when receiving the system state determination signal Sd of “instantaneous drop occurrence (small phase jump)”, and the determined limit value The Lim signal is sent to the limiter 28.

More specifically, the limit value determination unit 35 recognizes the voltage drop amount of the power system 3 based on the signal of the amplitude V _s , and the limit value Lim becomes a stricter value (smaller as the voltage drop amount increases). Value). In determining the limit value Lim, for example, an appropriately set calculation formula or LUT may be used. As described above, the limit value determining unit 35 determines the limit value Lim in accordance with the voltage drop amount of the power system 3 when it is determined that the instantaneous drop has occurred.

Further, when the limiter 28 receives the signal of the limit value Lim from the limit value determination unit 35, the limiter 28 performs a filter process for limiting the magnitude of the input signal of the effective current command value i _p * to perform the filter process. The completed signal is output to the active current control unit 29. On the other hand, when the limit value Lim signal is not received, the limiter 28 outputs the input signal of the effective current command value i _p * to the effective current control unit 29 as it is. As in the case of the first embodiment, the filtering process performed by the limiter 28 is a process that prevents the effective current command value i _p * from exceeding the limit value Lim.

When the voltage drop amount of the power system 3 is large, it is assumed that the degree of abnormality such as the system voltage is high and the operation of the power conversion device 1 is likely to become unstable. Therefore, in order to avoid the operation of the overcurrent prevention function by the overcurrent prevention circuit 14 as much as possible, the magnitude of the effective current command value i _p * needs to be more sufficiently limited as the voltage drop amount of the power system 3 is larger. . According to the power conversion device 1a of the second embodiment, it is possible to appropriately set the limit value Lim in accordance with such a purpose.

3. Third Embodiment Next, a third embodiment will be described. The third embodiment is basically the same as the second embodiment except for a system state determination method and the like. In the following description, emphasis is placed on the description of parts different from the second embodiment, and description of parts equivalent to the second embodiment may be omitted.

FIG. 5 is a configuration diagram of a power conversion device 1b according to the third embodiment. The system state determination unit 25 included in the power conversion device 1b receives the signal of the angular acceleration dω / dt of the system voltage, and the frequency / phase / amplitude θ and the amplitude of the system voltage from the frequency / phase / amplitude calculation unit 22. each signal V _s is adapted to be input.

Then, the system state determination unit 25 performs system state determination (including determination of occurrence of instantaneous drop) based on the frequency ω, the phase θ, and the amplitude V _s in addition to the angular acceleration dω / dt. It has become. It should be noted that various forms can be adopted as to what procedure the system state determination unit 25 determines the system state based on such information. Specific examples of the system state determination procedure include the following first to third examples.

In the first example, the system state is determined using each determination condition shown in FIG. Each determination condition shown in FIG. 6 is for each item of the system state (“normal”, “single operation”, “instantaneous drop occurrence (phase jumping small)”, “instantaneous drop occurrence (phase jumping large)”). Determination conditions for parameters (magnitude of angular acceleration | dω / dt |, frequency ω, phase θ, amplitude V _s ) are set.

According to the first example, for example, the magnitude of angular acceleration | dω / dt | is equal to or less than the threshold value A, the frequency ω does not change beyond the reference value, the phase θ does not jump, and the amplitude V _s is normal. Is 100%, the system state is determined to be “normal”.

Also, the magnitude of angular acceleration | dω / dt | is greater than threshold A and less than or equal to threshold B, there is a change in frequency ω that exceeds the reference value, the jump of phase θ is in the range of 0 to X, and amplitude V _s is If it is 0%, the system state is determined as “single operation”.

In addition, the magnitude of angular acceleration | dω / dt | is greater than threshold value B and less than or equal to threshold value C, frequency ω has a change exceeding a reference value, phase θ jump is in the range of X to Y, and amplitude V _s is If it is 0 to 100%, it is determined that the grid state is “instantaneous drop occurrence (small phase jump)”.

The magnitude of the angular acceleration | dω / dt | is greater than the threshold value C, there is a change exceeding the reference value in the frequency omega, jump of the phase θ is in the range of Y～180deg, the amplitude _{V s} is 0 to 100% If there is, the system state is determined to be “instantaneous drop occurrence (large phase jump)”. In the above, X and Y are values set in advance so as to satisfy 0 <X <Y <180 deg. For example, X is any value in the range of 10 to 30 deg, and Y is any value in the range of 30 to 90 deg.

When there is no item that satisfies the determination conditions for all parameters, the system state may be determined as an item that satisfies the determination conditions for the most parameters. In this case, for example, if the magnitude of angular acceleration | dω / dt | is equal to or less than the threshold value A, the frequency ω does not change beyond the reference value, the phase θ does not jump, and the amplitude V _s is less than 100%, The system state is determined as “normal” that satisfies the determination conditions of three parameters (the magnitude of angular acceleration | dω / dt |, frequency ω, and phase θ).

In the second example, the frequency omega, phase theta, and for each of the amplitude V _s, the predetermined sag determination condition is set. In a situation where all of the frequency ω, the phase θ, and the amplitude V _s satisfy the sag determination condition, if the magnitude of the angular velocity | dω / dt | If it is determined that “occurrence (small phase jump)” and the magnitude of angular velocity | dω / dt | exceeds the threshold value C, it is determined that “instantaneous drop occurs (large phase jump)”.

In the third example, the magnitude of the angular velocity | dω / dt |, the frequency omega, phase theta, and arithmetic mean in consideration of weighting of amplitude V _s is calculated, the system state is determined based on the calculation result So that

Note the system condition determination unit 25, in addition to the angular acceleration d [omega / dt, the frequency omega, phase theta, and not all of amplitude V _s, on the basis of any one or two of these, the system condition You may come to judge. According to the power conversion device 1b of the third embodiment, it is possible to more accurately determine the grid state by not only based on the angular acceleration dω / dt but also based on other information related to the grid voltage.

4). Others As described above, the power conversion device according to the present embodiment is connected to the power system 3, converts DC power to AC power, and outputs the AC power to the power system 3. An angular acceleration information acquisition unit (frequency / phase / amplitude calculation unit 22, angular acceleration calculation unit 24, etc.) that obtains dω / dt information, and a system state determination unit that determines the occurrence of an instantaneous drop based on the angular acceleration dω / dt (System state determination unit 25 and the like). In the present embodiment, the case where the system state is determined as “instantaneous drop occurrence (small phase jump)” or “instantaneous drop occurrence (large phase jump)” corresponds to when the occurrence of an instantaneous drop is determined.

  As described above, since the power conversion device according to the present embodiment determines the occurrence of the instantaneous drop based on the angular acceleration dω / dt, it is easy to determine the occurrence of the instantaneous drop quickly and accurately.

  For example, in the method of detecting the frequency and phase from the zero cross timing of the system voltage and determining the occurrence of the voltage sag based on the detection result, it is possible to detect the voltage sag generated during the half cycle of the system voltage waveform. There is a problem that it is difficult and the timing for determining the occurrence of an instantaneous drop tends to be delayed. However, according to the power conversion device according to the present embodiment, it is possible to acquire information on the angular acceleration dω / dt at an interval shorter than a half cycle of the system voltage waveform and determine the occurrence of the instantaneous drop. Such problems are less likely to occur.

  The configuration of the present invention can be variously modified in addition to the above embodiment without departing from the spirit of the invention. That is, the above-described embodiment is an example in all respects, and should be considered not restrictive. The technical scope of the present invention is shown not by the above description of the embodiment but by the scope of the claims, and is understood to include all modifications within the meaning and scope equivalent to the scope of the claims. Should.

DESCRIPTION OF SYMBOLS 1, 1a, 1b Power converter 2 Solar cell 3 Electric power system 11 Capacitor 12 Inverter 13 Interconnection relay 14 Overcurrent prevention circuit 15 Control apparatus 21 Band pass filter 22 Frequency / phase / amplitude calculation part 23 Coordinate conversion part 24 Angular acceleration calculation Unit 25 system state determination unit 26 isolated operation detection unit 27 DC voltage control unit 28 limiter 29 active current control unit 30 reactive current control unit 31 coordinate conversion unit 32 gate signal generation unit 35 limit value determination unit

Claims (10)

A power conversion device that is connected to a power system, converts DC power to AC power, and outputs the power to the power system,
An angular acceleration information acquisition unit for obtaining information on the angular acceleration of the system voltage;
A system state determination unit for determining occurrence of a sag based on the angular acceleration;
The power converter provided with.   The power conversion device according to claim 1, further comprising an operation control unit that controls an operation of the conversion based on a determination result of the system state determination unit. The power conversion device according to claim 2, wherein the conversion is performed such that a value of a current output to the power system becomes a value corresponding to an output current command value.
The operation controller is
A power converter that limits the output current command value so as not to exceed a predetermined limit value when it is determined that an instantaneous drop has occurred. The operation controller is
The power conversion device according to claim 3, wherein the limit value is determined according to a voltage drop amount of the power system. The system state determination unit
The power conversion device according to any one of claims 2 to 4, wherein when the magnitude of the angular acceleration exceeds a preset first threshold, it is determined that an instantaneous drop has occurred. The power conversion device according to claim 5, further comprising: an inverter that is driven according to a gate signal, wherein the conversion is performed using the inverter.
The operation controller is
When the magnitude of the angular acceleration exceeds the first threshold and does not exceed the second threshold set larger than the first threshold, the output current command value is limited so as not to exceed the limit value. ,
A power conversion device that blocks transmission of the gate signal to the inverter when the magnitude of the angular acceleration exceeds a second threshold. The power conversion device according to claim 6, further comprising an isolated operation detection unit that detects the occurrence of isolated operation.
When the magnitude of the angular acceleration exceeds the third threshold set smaller than the first threshold and does not exceed the first threshold, when the occurrence of isolated operation is detected, disconnection from the power system is performed. Power conversion device to be performed. The operation controller is
When limiting the output current command value, when the magnitude of the angular acceleration is equal to or less than a third threshold, the limitation on the output current command value is canceled,
The power conversion device according to claim 7, wherein when the angular acceleration becomes equal to or smaller than a third threshold while the transmission of the gate signal is interrupted, the interruption of the transmission of the gate signal is canceled. The power conversion device according to any one of claims 1 to 6, wherein occurrence of an isolated operation is detected, and disconnection from the power system is performed according to a result of the detection.
A power conversion device that prohibits the disconnection when it is determined that an instantaneous drop has occurred. The system state determination unit
The electric power according to any one of claims 1 to 4, wherein the occurrence of a sag is determined based on at least one detection result of the frequency, phase, and amplitude of the system voltage in addition to the angular acceleration of the system voltage. Conversion device.

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