JP2012016159A - Power conversion device and power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device which converts a DC power to an AC power of an output frequency that is set at present, outputs the AC power, and can set an amount of change at a shorter interval when the change is imparted to the output frequency.SOLUTION: The power conversion device which converts the DC power to the AC power of the output frequency that is set at present and outputs the AC power, comprises a change imparting part which performs a change imparting operation as an operation of imparting the change to the output frequency. The change imparting part divides a change imparting period in which the change should be imparted into a plurality of sections that are shorter than a cycle of the AC power, and sets the amount of the change for each section.

Description

  The present invention relates to a power conversion device that converts DC power to AC power, and a power supply system using the same.

  Conventionally, power conditioners (hereinafter sometimes abbreviated as “power converters”) that supply power generated by a distributed power source (such as a solar power generation system) to an electric power system are widely used. Has been. The power converter can be regarded as one form of a power conversion device that converts DC power into AC power.

  The power converter has a function of converting DC power generated by the distributed power source into AC power having a preset output frequency and outputting the AC power to the power system. In order to match the power output to the power system with the power in the power system, this output frequency is generally set to substantially match the frequency of the power in the power system.

  By the way, when using a power conditioner, it is necessary to pay attention to the occurrence of a single operation state (a state where a single operation is performed). The isolated operation is, for example, that the distributed power supply continues to supply power even though the power system has a power failure. From the viewpoint of safety, etc., isolated operation should be avoided as much as possible, and when an isolated operation state occurs, measures such as promptly disconnecting the distributed power source from the power system are required.

  For this reason, many power converters are provided with means for detecting whether an isolated operation state has occurred (detecting an isolated operation), and when an isolated operation state occurs, the distributed power supply should be disconnected from the power system. It has become. In addition, each patent document discloses one that detects an isolated operation by various methods.

  In addition, as a method of detecting an isolated operation, a passive method or an active method can be given. In the active method, for example, power that is intentionally not matched with the normal power system (given an error) is output to the power system, and whether the power in the power system follows this or not is determined. This is a method of detecting islanding by looking. According to the active method, it is possible to detect an isolated operation even in a state where the isolated operation is not detected by the passive method, for example, in an equilibrium state where the power generation amount of the distributed power source and the load power amount on the power system are balanced. Is possible.

  As one of the active methods, a single operation is detected by giving a change (intentional error) to the output frequency and detecting that the frequency of the power in the power system follows this change. A method (hereinafter referred to as a “frequency change applying method” for convenience). According to the frequency change imparting method, the output frequency is changed when the occurrence of a single operation state is suspected (for example, when an electrical fluctuation that satisfies a certain condition is detected).

  If the frequency of the power in the power system does not follow this change and does not deviate from the normal frequency range, it is determined that no single operation state has occurred. Conversely, if the frequency of the power in the power system follows this change and deviates from the normal frequency range, it is determined that the single operation state has occurred. For example, in the case of a power system of 50 Hz, the normal frequency range is a range of 50 ± 2 Hz (a range that is assumed not to deviate when the power system is normal).

  If the islanding condition does not occur, the effect of the change in the output frequency on the power system is minimal, so the power frequency in the power system does not deviate from the normal frequency range. This frequency follows the change and deviates from the normal frequency range. Therefore, according to the frequency change imparting method, it is possible to detect an isolated operation.

  If the amount of change in the output frequency is too small, the frequency of the power in the power system cannot be deviated from the normal frequency range (purged outside the range) even if an isolated operation state has occurred. Therefore, in the frequency change imparting method, when the single operation state occurs, the amount of change in the output frequency is a certain amount (in order to ensure that the power frequency in the power system deviates from the normal frequency range). For example, it is necessary to set the frequency to about 3.5 Hz at the maximum.

  However, if the output frequency is changed greatly at a stretch, the output frequency changes abruptly before and after the change is applied. For this reason, when no stand-alone operation has occurred, for example, the phase difference between the output power and the power in the power system becomes very large, causing an overcurrent on the distributed power source side and connecting to the power system or power system. There is a risk that the power supply to the load may be greatly disturbed.

  Therefore, when changing the output frequency, consideration is given to gradually changing the amount of change, not the maximum amount of change at once. As a result, it is possible to moderate the change in output frequency and suppress the above-described problems as much as possible.

Japanese Patent No. 3424443 JP 2003-180036 A

  By the way, paying attention to the detection speed of the isolated operation state, conventionally, such a quick detection has not been required. More specifically, detection was required within about 0.5 seconds in the case of the passive method, and within about 1.0 seconds in the case of the active method. Therefore, even when the frequency change applying method described above is applied, it is not necessary to change the output frequency so rapidly, and at intervals of one cycle or more of the output power (for example, according to the zero crossing of the output waveform). It was enough to gradually change the amount of change.

  However, in recent years, there has been a tendency for the number of distributed power sources connected to the power system to increase significantly, and the influence of isolated operation on safety and the like has been increasing. Under such circumstances, it is expected that it will be strongly demanded in the future to provide a function to detect the single operation more quickly and appropriately cope with it in the power conditioner. More specifically, in the future, it is expected that it is desired to detect an isolated operation within about 0.1 second (about 5 cycles in a 50 Hz waveform).

  Therefore, when applying the frequency change applying method, it is necessary to give a change of a certain magnitude to the output frequency in a very short time. As a result, the change in the output frequency cannot be made sufficiently gradual simply by changing the amount of change at intervals of one cycle or more of the output power. Therefore, a measure for making the change in the output frequency more gradual is highly desired. One example of this measure is to gradually increase the amount of change at shorter intervals.

  Further, when the frequency change imparting technique is used to place an emphasis on detecting an isolated operation very quickly, it is necessary to set the amount of change in the output frequency to a certain level within a very short time. In consideration of such various situations, it is desirable that the amount of change in the output frequency is set at a shorter interval in the power conditioner.

  The power conversion device according to the present invention is a power conversion device that converts DC power into output power that is AC power of an output frequency that is currently set, and outputs the change. And the change applying unit is configured to divide the change applying period in which the change should be given into a plurality of sections shorter than the period of the output power, and to set the amount of change for each section. .

  According to this configuration, the amount of change in the output frequency is set at shorter intervals. Therefore, for example, when a predetermined amount of change is applied to the output frequency within the same period, the amount of change (change amount) is gradually changed step by step in comparison with a case where the amount of change (change amount) is gradually changed at intervals of one cycle or more of AC power. The amount of change can be changed.

  In addition, the power conversion device configured as described above, which is connected to an electric power system, sets an output frequency according to the frequency of electric power in the electric power system, and outputs the output electric power to the electric power system. An isolated operation determining unit that determines whether or not the frequency of the electric power in the power system follows the change in a situation where the change is given to the output frequency. Based on this, it may be configured to determine whether or not an isolated operation state has occurred. In this case, it is also possible to determine whether or not the change has been followed for each section described above.

  According to this configuration, it is possible to detect the occurrence of the single operation state by employing the frequency change applying method described above. For example, it is possible to detect the occurrence of the isolated operation state within one cycle of the output power.

  Further, in the above configuration, the change applying unit may be configured to increase the amount of the change step by step for each section until it is determined whether or not the frequency of the power in the power system follows the change. Good.

  Further, in the above configuration, the change providing unit increases the change amount step by step for each section until the change amount reaches a predetermined maximum amount during the change applying period. After reaching the maximum amount, the amount of the change may be decreased step by step for each section.

  According to this configuration, when giving a predetermined maximum amount of change to the output frequency, it is possible to realize this while making the change to the output frequency as gentle as possible.

  Further, in the above configuration, the change imparting unit performs an imparting operation for giving the change to the output frequency every time the occurrence of a single operation state is suspected, and the single operation determination unit includes: It is good also as a structure which discriminate | determines the presence or absence of generation | occurrence | production of a single operation state, whenever the said provision operation | movement is performed.

  In the above configuration, the voltage command waveform is calculated and the inverter circuit is controlled so that the target voltage waveform to be output is the voltage command waveform. The power conversion device configured as described above, wherein the change imparting unit gives the change by changing a frequency in the voltage command waveform, and the single operation determination unit includes the voltage command waveform and the voltage command waveform. Further, it may be configured to determine whether or not the frequency of the power in the power system follows the change based on the detected difference from the voltage waveform in the power system.

  In the above configuration, the voltage command waveform is calculated and the inverter circuit is controlled so that the target voltage waveform to be output is the voltage command waveform. An output power converter having the above-described configuration, which determines a current command waveform that is a target of a waveform of an output current, wherein the voltage command waveform includes the detected voltage waveform in the power system, and It is calculated by combining the waveform corresponding to the voltage drop when the current of the current command waveform flows from the inverter circuit to the power system, and the change applying unit changes the frequency in the current command waveform. The single operation determination unit is configured to provide a difference between the current command waveform and the detected voltage waveform in the power system. Based on, it may be configured to frequency of the power in the power system it is determined whether or not to follow the change.

  Further, in the above-described configuration, each of the plurality of sections may be a section divided for each constant phase angle of less than 2π in the output power. According to this configuration, the output power waveform can be made smoother than when the width of each section is not a constant phase angle.

  A power supply system according to the present invention includes the power conversion device according to the above configuration and a DC power source that generates the DC power, and converts the DC power into AC power and supplies the AC power to the power system. And According to this configuration, it is possible to enjoy the advantages of the power conversion device according to the above configuration.

  As described above, according to the power conversion device of the present invention, the amount of change in the output frequency is set at shorter intervals. Therefore, for example, when giving a predetermined amount of change to the output frequency within the same period, the amount of change is changed little by little as compared with the case where the amount of change is gradually changed at intervals of one cycle or more of AC power. Is possible. Moreover, according to the electric power supply system which concerns on this invention, it becomes possible to enjoy the advantage of the power converter device which concerns on this invention.

It is a lineblock diagram (state linked to an electric power system) of a power conditioner concerning an embodiment of the present invention. It is a flowchart of a connection state control operation. It is a flowchart of an isolated operation discrimination operation. It is explanatory drawing which shows the content of the change provision pattern. It is a graph which shows the waveform of the output voltage when a change is given to the output frequency. It is explanatory drawing regarding the waveform of an output voltage. It is explanatory drawing regarding the condition of the change of an output frequency. It is a block diagram of the power condition control apparatus which concerns on this embodiment. It is a flowchart of the independent operation discrimination | determination operation | movement of another form. It is explanatory drawing regarding provision of the change to an output frequency.

  The embodiment of the present invention will be described below with reference to a power conditioner (power conditioner) linked to an AC power system.

  FIG. 1 shows a configuration diagram of the power conditioner of the present embodiment (a state connected to a power system). As shown in the figure, the power conditioner 1 has terminals T1 and T2, a DC power supply 2 is connected to the terminal T1, and an existing power system is connected to the terminal T2. The DC power source 2 is, for example, a solar power generation system, and generates DC power. The DC power source 2 corresponds to one of distributed power sources as viewed from the power system.

  The power system is formed by connecting a system power source 3 and a system circuit breaker 4 used to interrupt the power system to power wiring. Note that the power system in this embodiment transmits a commercial power supply of 50 Hz (normal frequency range is 50 ± 2 Hz). A load 5 (such as various electric devices) that receives power supply from the power system is also connected to the power system. In addition, the power system can be considered similarly even if it is in another form (for example, one that transmits a 60 Hz commercial power source).

[About the configuration of the power conditioner]
Next, the configuration of the power conditioner 1 will be described. As shown in FIG. 1, the power conditioner 1 includes a diode 11, a capacitor 12, an inverter circuit 14, an inductor 15, a capacitor 16, a current detection circuit 17, a voltage detection circuit 18, an interconnection relay 19, a power condition control device 20, and the like. Yes.

  The power sent from the DC power supply 2 is adjusted in state by each element (11, 12) and delivered to the inverter circuit 14. The inverter circuit 14 converts the received power into alternating current and sends it to the subsequent stage side. The inverter circuit 14 operates in accordance with the gate signal Sg received from the power control device 20.

  The waveform of the electric power sent from the inverter circuit 14 is adjusted by the inductor 15 and the capacitor 16, and is output to the power system via the interconnection relay 19. Hereinafter, the power (or voltage or current) output from the power conditioner 1 to the power system is referred to as “output power” (or “output voltage” or “output current”) for convenience. The frequency of output power (AC power) is referred to as “output frequency”.

  The connection relay 19 is switched between open and closed according to the relay switching signal Sr received from the power condition control device 20. Normally, the interconnection relay 19 is closed, and the power conditioner 1 and the DC power supply 2 are linked to the power system. However, when the linkage relay 19 is opened, the linkage is released.

  The current detection circuit 17 is a circuit that continuously detects the value of the current flowing through the terminal T2. Information on the current value detected by the current detection circuit 17 is transmitted to the power controller 20 as a current detection signal Id.

  The voltage detection circuit 18 is a circuit that continuously detects a voltage value between both poles of the terminal T2. Information on the voltage value detected by the voltage detection circuit 18 is transmitted to the power controller 20 as a voltage detection signal Vd.

  Hereinafter, power (or voltage, current) in the power system is referred to as “system power” (or “system voltage”, “system current”) for convenience. The frequency of the system power (AC power) is referred to as “system frequency”. The power conditioner control device 20 can continuously detect the system power, the system voltage, and the system current by continuously receiving the current detection signal Id and the voltage detection signal Vd.

  The power control device 20 is a device that controls the power control 1 so as to execute various kinds of arithmetic processing based on the received current detection signal Id and voltage detection signal Vd and to perform appropriate operations. The power condition control device 20 sends the gate signal Sg to control the inverter circuit 14 and sends the relay switching signal Sr to control the interconnection relay 19.

  Here, the output power or the like needs to comply with a predetermined interconnection rule. That is, it is necessary that the distortion factor, power factor, and the like of the harmonic voltage related to the output of the power converter 1 fall within a specified range, and that the waveform of the output current be a sine wave. Also, the output power must be matched with the grid power so that the power status of the grid is not disturbed (that is, the AC frequency, phase, voltage amplitude, etc. are substantially matched). It is said.

  The power condition control device 20 calculates a voltage command waveform based on the current detection signal Id and the voltage detection signal Vd so that such a condition is normally satisfied. Then, the power controller 20 generates and sends a gate signal Sg based on the voltage command waveform, and controls the inverter circuit 14 by a PWM [Pulse Width Modulation] method. That is, the power controller 20 controls the inverter circuit 14 so that the target voltage waveform to be output is the voltage command waveform. Thereby, the power conditioner 1 outputs a voltage having a waveform that substantially matches the voltage waveform in the power system to the power system. In this way, the power conditioner 1 outputs the output power adjusted to match the system power to the power system. Various methods are already known for calculating the voltage command waveform so that the output power matches the system power.

  Focusing on the AC frequency, the power controller 20 detects the system frequency based on at least one of the current detection signal Id and the voltage detection signal Vd. Then, the power control device 20 calculates a voltage command waveform in consideration of the detection result and a voltage drop due to current flow, and controls the inverter circuit 14 according to the calculation result. As a result, in normal times, the output frequency is indirectly set so as to coincide with the detected system frequency.

[About connected state control operation]
By the way, when the isolated operation state occurs, it is necessary to quickly release the connection to the power system in the power conditioner 1. Therefore, the power condition control device 20 controls the connection state between the power conditioner 1 and the power system appropriately in accordance with whether or not the single operation state has occurred in parallel with the control of the inverter circuit 14 as described above. Then, the interconnection state control operation is executed. Hereinafter, this interconnection state control operation will be described in more detail with reference to the flowchart shown in FIG.

  The power controller 20 continuously monitors whether or not an electrical fluctuation exceeding a reference level has occurred in the power system based on the current detection signal Id or the voltage detection signal Vd at normal times (step S1). ). The “electrical fluctuation” here corresponds to, for example, one or more of voltage drop, frequency change rate change, phase jump, and harmonic voltage change.

  As a cause of the occurrence of the isolated operation state, for example, the interruption of the electric power system due to the influence of lightning can be considered. And when such a power system interruption occurs, the above-described electrical fluctuation occurs at least temporarily. For this reason, when the electrical fluctuation exceeds a certain level, the occurrence of an isolated operation state is suspected. The above-mentioned “reference level” is set to a level at which the occurrence of an isolated operation state is suspected.

  However, even if the isolated operation state does not occur, the electrical fluctuation may exceed the reference level for some reason. That is, when an electrical fluctuation exceeding the reference level is detected, it is considered that the isolated operation state is not generated although the occurrence of the isolated operation state is suspected.

  Therefore, when an electrical fluctuation exceeding the reference level is detected (Y in step S1), the power controller 20 executes a predetermined isolated operation determination operation to determine whether an isolated operation state has occurred. (Step S2). The isolated operation determination operation is an operation for accurately determining whether or not an isolated operation state has occurred in a short time, and the specific contents will be described again.

  When it is determined that the isolated operation state has occurred by executing the isolated operation determination operation (Y in step S3), the power conditioner 20 sends a relay switching signal Sr for opening the connected relay 19 to the connected relay 19. The transmission relay 19 is controlled to open. As a result, the interconnection of the power conditioner 1 to the power system is released, and the independent operation is stopped (step S4).

  On the other hand, when it is determined that the isolated operation state has not occurred by executing the isolated operation determination operation (N in step S3), it is not necessary to release the connection of the power conditioner 1 to the power system. Therefore, the power conditioner 20 does not open the interconnection relay 19 and returns to the operation of step S1. By executing the above-described series of linked state control operations, the power conditioner device 20 accurately determines whether or not an isolated operation state has occurred in a short time, and performs appropriate measures according to the determination result. It has become.

[Independent operation discrimination operation]
The isolated operation determination operation (step S2) is an operation for determining whether or not an isolated operation state has occurred using the frequency change applying method described above. The specific contents of the isolated operation determination operation will be described below with reference to the flowchart shown in FIG.

  Along with the start of the independent operation determination operation, the power control device 20 starts to apply a change (applying operation) to the output frequency according to the change applying pattern (step S12). As described above, the output frequency is set so as to coincide with the system frequency in the normal time, but at the time of executing the isolated operation discriminating operation, the change according to the change imparting pattern is used to detect the isolated operation. It is given as an intentional error.

  Here, the “change imparting pattern” is information registered in the power control device 20 in advance, and indicates how to change the output frequency (how to change the amount of change). Specifically, the change imparting pattern is set to the contents shown in FIG.

  In FIG. 4, for example, in “third section”, the phase angle of the output power is “4π / 8 to 6π / 8” when the start time of the independent operation determination operation is used as a reference (phase angle is 0). Refers to a period. Further, according to FIG. 4, the change amount of the output frequency in the “third section” is “1.0 (Hz)”.

  As shown in FIG. 4, according to the change imparting pattern, the amount of change for two periods (0 to 32π / 8) of the output power is determined. The first half of the period is divided every 2π / 8 phase angle (constant phase angle). In other words, as shown in FIG. 4, it is divided into sections from the first section to the eighth section. In the first to eighth sections, the amount of change is set to gradually increase by 0.5 Hz each time the section is updated.

  On the other hand, the latter half of one cycle is also divided for each phase angle of 2π / 8. In other words, as shown in FIG. 4, it is divided into sections from the ninth section to the sixteenth section. From the ninth section to the sixteenth section, the amount of change is set to gradually decrease by 0.5 Hz each time the section is updated.

  The graph shown in FIG. 5 represents an example of the output power waveform (the output voltage and output current waveforms also have the same tendency) when the output frequency is changed according to the change applying pattern. In the graph, the horizontal axis indicates time t and the vertical axis indicates power y. The waveform shown in FIG. 5 is a waveform when the phase is 0, the output frequency is 50 Hz, and the amplitude is Wo at the start of applying the change.

The power y in the i-th section in the waveform shown in FIG. 5 is approximately expressed by the following equation (1).
y = Wo × sin {2πfi (t−ti) + φi} (1)
Here, fi is the output frequency in the i-th section, ti is the time at the start of the i-th section (= at the end of the i-1 section), and φi is the start time of the i-th section (= i-1 section). The phase at the end of ().

That is, the waveform shown in FIG.
A portion where the phase angle is 0 to 2π / 8 in the waveform of y = Wo × sin (2π × 50 × t) (see the first stage in FIG. 6),
a portion where the phase angle in the waveform of y = Wo × sin (2π × 50.5 × t) is 2π / 8 to 4π / 8 (see the second stage in FIG. 6);
a portion where the phase angle in the waveform of y = Wo × sin (2π × 51 × t) is 4π / 8 to 6π / 8 (see the third stage in FIG. 6);
...
The portion where the phase angle in the waveform of y = Wo × sin (2π × 50 × t) is 30π / 8 to 32π / 8 (see the fourth stage in FIG. 6)
These portions can also be viewed as waveforms formed by connecting them so that the phase angles match.

  At the start of the independent operation determination operation, the power controller 20 executes necessary calculation processing based on the state of the output power and the change imparting pattern at that time, and first determines a waveform as shown in FIG. deep. Then, the power controller 20 sends out the gate signal Sg so that the output power matches the waveform. Thereby, the provision of the change to the output frequency according to the change provision pattern is realized.

  As is clear from FIG. 4, the change imparting pattern is set so as to change the output frequency by 3.5 Hz at the maximum during one cycle of the output voltage. This 3.5 Hz (maximum amount of change) is set as a value that sufficiently deviates the output frequency, which is about 50 Hz before the change is applied, from the normal frequency range (50 ± 2 Hz) in the power system. ing.

  Then, the power controller 20 changes the output frequency in accordance with the change applying pattern, determines whether the detected system frequency has deviated from the normal frequency range (step S13), and waits for determination after starting to apply the change. It is monitored whether time has passed (step S14). The determination standby time is set to, for example, one cycle of output power (corresponding to a phase angle of 0 to 16π / 8) as a time longer than the time until the maximum amount of change is given to the output frequency.

  When the output frequency is changed here, the system frequency is as follows. When the islanding state is generated, the state of the system power is dominated by the state of the output power. Therefore, the system frequency follows the change of the output frequency, and when the output frequency deviates from the normal frequency range in the power system, the system frequency deviates from the normal frequency range accordingly.

  On the other hand, when the single operation state does not occur, the state of the system power is strongly influenced by the system power supply 3 and the like, and is hardly affected by the state of the output power. Therefore, the system frequency does not follow the change of the output frequency, and even if the output frequency deviates from the normal frequency range in the power system, the system frequency does not deviate from the normal frequency range.

  Therefore, when detecting that the system frequency has deviated from the normal frequency range of the power system (Y in Step S13), the power control device 20 determines that an isolated operation state has occurred (Step S15), The operation discrimination operation is terminated. On the other hand, when the determination standby time has elapsed since the start of the application of the change without the system frequency deviating from the normal frequency range (Y in step S14), the power controller 20 is in the single operation state. Is determined not to occur (step S16), and the current isolated operation determination operation is terminated.

  As described above, the power condition control device 20 changes the output frequency up to 3.5 Hz in a short time of one cycle of output power (generally 20 ms). Therefore, the power condition control device 20 can determine whether or not an isolated operation state has occurred in this short time.

  Here, a graph showing how the output frequency changes when a change of 3.5 Hz is given to the output frequency within one cycle of the output power is shown in FIG. In the graph, the horizontal axis represents the phase angle of the output power, and the vertical axis represents the output frequency.

  Assuming that the interval of changing the amount of change in the output frequency is one period, as shown by the dotted line in FIG. 7, in order to give a change of 3.5 Hz within one period, a large change for 3.5 Hz It is necessary to give at once. The same applies when this interval is longer than one cycle. As described above, when the output frequency changes suddenly before and after the change is applied, for example, the phase difference between the output power and the system power becomes very large when the isolated operation state does not occur. As a result, an overcurrent is generated on the DC power supply 2 side, and there is a risk that a large disturbance will occur in the power supply to the power system and the load 5.

  However, according to the power conditioner 1 of the present embodiment, as shown by a solid line in FIG. 7, the amount of change gradually increases or decreases by 0.5 Hz, and the change in the output frequency becomes relatively gradual. Yes. As described above, in the case of the present embodiment, the amount of change given to the output frequency is changed stepwise at intervals shorter than one cycle of the output power, and the change of the output frequency may be made gradual. It is possible.

  Further, as described above, the width of each section from the first to the sixteenth is a constant phase angle (2π / 8). Therefore, according to the power conditioner 1, it is possible to smooth the waveform of the output power as compared with the case where the width of each section is not a constant phase angle.

[Specific configuration of power control device]
The power condition control device 20 is configured to perform the above-described operation, but the specific form thereof is not particularly limited. For example, the configuration may be such that each necessary process is realized mainly by software processing, or may be mainly realized by hardware processing. The configuration of the power controller 20 in this embodiment is assumed to be the configuration shown in FIG. 8 as an example. The configuration will be described below.

  As shown in FIG. 8, the power controller 20 includes a central processing circuit 21, a current amplitude setting circuit 22, a multiplier 23, a subtractor 24, a controller 25, an adder 26, a triangular wave generation circuit 27, a PWM comparator 28, a voltage amplitude. A calculation circuit 29 and a multiplier 30 are provided.

  The central processing circuit 21 receives the voltage detection signal Vd from the voltage detection circuit 18, and is a circuit that executes various processes according to the signal. The central processing circuit 21 outputs a frequency signal whose amplitude is adjusted (the amplitude is a unit amount). The central processing circuit 21 also has a function of outputting a relay switching signal Sr to the interconnection relay 19.

  The current amplitude setting circuit 22 is a circuit for setting the amplitude of the output current. The current amplitude setting circuit 22 records the amplitude of a standard output current (a value determined to match the power system), and outputs an amplitude signal set to this amplitude.

  The multiplier 23 receives the frequency signal output from the central processing circuit 21 and the amplitude signal output from the current amplitude setting circuit 22 and outputs a signal obtained by multiplying them (output current command). Note that the output current command signal represents a current command waveform that is a target of the waveform of the current output from the power conditioner 1 at normal times. The subtractor 24 receives the current detection signal Id from the current detection circuit 17 and outputs the difference between the output current target value signal and the current detection signal Id. The controller 25 receives the output of the subtracter 24 and outputs a signal representing a voltage corresponding to the output current. This signal output from the controller 25 normally represents a waveform corresponding to a voltage drop when a current command waveform current flows from the inverter circuit 14 to the power system.

  The voltage amplitude calculation circuit 29 receives the voltage detection signal Vd, and calculates the amplitude of the voltage waveform in the power system based on the signal. Then, the voltage amplitude calculation circuit 29 outputs an amplitude signal set to the calculated amplitude. The multiplier 30 receives the frequency signal output from the central processing circuit 21 and the amplitude signal output from the voltage amplitude calculation circuit 29, and outputs a signal generated by multiplying them. This signal output from the multiplier 30 normally represents a voltage waveform in the power system.

  The adder 26 receives the output of the controller 25 and the output of the multiplier 30 and outputs a signal obtained by adding them (inverter operation amount). The waveform represented by the output signal of the adder 26, that is, the waveform obtained by combining the outputs of the controller 25 and the multiplier 30, is the voltage command waveform described above.

  In the PWM comparator 28, the output of the adder 26 is input to the non-inverting input terminal, and the reference triangular wave signal generated by the triangular wave generating circuit 27 is input to the inverting input terminal. The PWM comparator 28 outputs a signal corresponding to these comparison results to the inverter circuit 14 as a gate signal Sg.

  The power control device 20 having such a configuration operates as shown below. The central processing circuit 21 continuously receives the voltage detection signal Vd and detects the system frequency. The central processing circuit 21 generates a frequency signal so as to coincide with the detected system frequency, and outputs the frequency signal to the multiplier 23.

  A series of circuits from the multiplier 22 to the PWM comparator 28 generates a gate signal Sg for PWM control of the inverter circuit 14 by reflecting the frequency signal, the current detection signal Id, and the voltage detection signal Vd. The gate signal Sg is adjusted such that the output power matches the system power in terms of frequency and voltage amplitude.

  Further, the above-described interconnected state control operation (steps S1 to S4) is executed mainly by the central processing circuit 21. That is, the central processing circuit 21 monitors whether the electrical fluctuation exceeding the reference level has occurred by monitoring the voltage detection signal Vd (step S1).

  When an electrical fluctuation exceeding the reference level is detected (Y in step S1), the central processing circuit 21 performs an isolated operation determination operation (steps S12 to S16). At this time, the central processing circuit 21 changes the frequency of the current command waveform and the voltage command waveform and changes the output frequency indirectly by changing the frequency of the frequency signal as the operation of step S12. When it is further determined that an isolated operation state has occurred (Y in step S3), the central processing circuit 21 sends the relay switching signal Sr to the interconnection relay 19 so that the interconnection of the power conditioner 1 to the power system is released. (Step S4).

[Modifications]
As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The present invention can be implemented with various modifications without departing from the gist thereof. In addition, as a modification with respect to this embodiment, the following are mentioned, for example.

  The “change imparting pattern” according to the present embodiment has the contents as shown in FIG. 4, but the contents can be variously modified according to the specifications and usage of the power conditioner 1. For example, the width of each section (in this embodiment, each phase of 2π / 8 in AC power), the sign of the numerical value of change (+ −), its maximum value (3.5 Hz in this embodiment), etc. It can be set as the value of.

  Further, in the present embodiment, each section is a section divided for each constant phase angle, but other forms may be used. For example, each section may be a section that is divided for each phase angle that is not constant (all or part of the section changes), or may be a section that is divided for each time that is not constant or constant.

  Further, in the present embodiment, in order to detect the occurrence of the isolated operation state, it is directly monitored whether the system frequency has deviated from the normal frequency range of the power system (see step S13). However, as a method for detecting the occurrence of the isolated operation state, another method may be adopted. For example, when the power controller 20 has the configuration shown in FIG. 8, the voltage command waveform (or current command waveform) described above and the voltage waveform in the detected power system (that is, the waveform represented by the voltage detection signal Vd) and A method that focuses on the difference between the two may also be employed. The flow of the isolated operation determination operation employing such a method will be described below with reference to the flowchart shown in FIG.

  The central processing circuit 21 starts giving a change to the output frequency according to the change giving pattern (step S22). The application of the change is indirectly realized by changing the frequency of the current signal waveform or the voltage command waveform by changing the frequency of the frequency signal. The purpose of the operation in step S22 is the same as that in step S12 described above.

  Then, the central processing circuit 21, while giving the change, whether the difference between the voltage command waveform (or current command waveform) and the detected voltage waveform in the power system exceeds a predetermined threshold (step S23), and the change It is monitored whether the determination waiting time has elapsed since the start of the grant (step S24). The determination standby time is set, for example, within one cycle of output power (for example, a phase angle of 6π / 8) as the time until the maximum amount of change is given to the output frequency.

  Here, when the system frequency does not follow the change in the output frequency (that is, when the single operation state does not occur), the voltage command waveform (or current command waveform) and the deviation (deviation) of the detected voltage waveform in the power system. And the difference between these waveforms also increases. On the other hand, when the system frequency follows the change of the output frequency (that is, when an isolated operation state occurs), such a waveform shift does not increase and the difference between these waveforms does not increase.

  Therefore, when the central processing circuit 21 detects that the difference between the voltage command waveform (or current command waveform) and the detected voltage waveform in the power system exceeds a predetermined threshold (Y in step S23), the single operation is performed. It is determined that no state has occurred (step S25), and the current isolated operation determination operation is terminated.

  On the other hand, when the determination waiting time has elapsed since the start of the application of the change without the difference exceeding the threshold value (Y in step S24), the central processing circuit 21 indicates that the single operation state has occurred. It discriminate | determines (step S26) and complete | finishes this single operation discrimination | determination operation | movement. In addition, the threshold value here indicates that when the single operation state occurs, the single operation state is such that the difference between the voltage command waveform (or current command waveform) and the detected voltage waveform in the power system does not exceed the threshold value. When it does not occur, the value is set appropriately in advance so as to exceed the threshold value.

  In addition, as mentioned above, the voltage command waveform and the current command waveform can be cited as the waveform to be compared with the voltage waveform in the electric power system, but the deviation (deviation) of the waveform becomes clearer (so that the detection of the isolated operation state can be performed). It is more preferable to adopt the current command waveform in terms of easier). In the isolated operation determination operation (steps S22 to S26) described here, the system frequency follows the change in the output frequency based on the difference between the voltage command waveform (or current command waveform) and the detected voltage waveform in the power system. It has come to detect that.

  As described above, the isolated operation determination operation (steps S22 to S26) also utilizes the fact that the system frequency follows the change in the output frequency when the isolated operation state occurs and does not follow when the isolated operation state does not occur. Thus, the isolated operation is detected. This point is the same as the isolated operation determination operation (steps S12 to S16) described above.

  In addition, in the “change imparting pattern” according to the present embodiment, the change amount is set to increase and decrease regularly (that is, the first half gradually increases and the second half gradually decreases). However, it may be set so that this increase / decrease is irregular.

  In this way, when the isolated operation state has not occurred, the waveform indicating the difference between the output power and the system power has a shape that is largely biased to the negative side or the positive side. In addition, when a single operation state occurs, the waveform does not have such a biased shape. Using this difference, it is possible to determine whether or not an isolated operation state has occurred.

  As for the amount of change in frequency, the amount of change may be increased stepwise for each section until it is determined whether or not the system frequency follows the change given to the output frequency. In this case, after it is determined that it has followed, the amount of change may be increased or decreased, or may be maintained as it is. In increasing or decreasing the amount of change, the speed (increase / decrease) of increasing or decreasing the amount of change may be changed.

  For example, a case is assumed in which the amount of change is increased by 0.6 Hz for each section and it is determined that the change has been followed in the fourth section. In this case, the “increase pattern” shown in FIG. 10 (the amount of change increases after the fifth section), the “continuation pattern” (the amount of change is maintained as it is after the fifth section), and the “decrease pattern” (the first pattern). Any of the following may be realized: the amount of change decreases after the fifth section).

  Further, in this embodiment, when the detected system frequency deviates from the normal frequency range of the power system, it is immediately determined that an isolated operation state has occurred (see steps S13 and S15). Moreover, you may make it discriminate | determine that the isolated operation state generate | occur | produced when the state which deviated continued for a fixed period (for example, about 1 to several cycles). In this way, the time required for the determination is slightly longer, but the accuracy of the determination can be further improved (more carefully determined).

  In the present embodiment, when it is determined that the single operation state has occurred, the connection to the power system is immediately released (the connection relay 19 is opened) (see steps S3 and S4). Instead of this, after a certain time (for example, about 0.1 second) has elapsed since it was determined that the single operation state has occurred, the connection to the power system may be released.

  In addition, when it is determined that the isolated operation state has occurred, the connection to the power system may be released, and a notification signal for notifying the occurrence of the isolated operation state may be output. Furthermore, when it is determined that an isolated operation state has occurred, the power output to the power system may be reduced by, for example, attenuating the amplitude of the current output from the power conditioner 1 to the power system. .

[Others]
As described above, the power conditioner 1 (power conversion device) according to the present embodiment converts the DC power generated by the DC power source 2 into output power (AC power of the currently set output frequency). In addition, a function unit (change imparting unit) that changes the output frequency is provided.

  The change imparting unit divides the change imparting period (two output power cycles) in which the change should be given into a plurality of sections (sections having a width of 2π / 8 phase angle) shorter than the output power period. The amount of change is changed (set) for each section. More specifically, until the amount of change reaches the maximum amount (3.5 Hz), the amount of change is increased step by step (in increments of 0.5 Hz), and the amount of change is maximized. After reaching a large amount, the amount of change is decreased stepwise (by 0.5 Hz) for each section.

  Therefore, according to the power conditioner 1, when the maximum amount of change is given to the output frequency, this can be realized while making the change given to the output frequency as gentle as possible. That is, it is possible to make the change given to the output frequency more gradual by changing the change amount little by little in comparison with the case where the change amount is gradually changed at intervals of one cycle or more of the output power. It has become. In addition, it is easy to quickly detect a change in less than one cycle of AC power, and the amount of change can be quickly changed according to the change.

  Note that the power conversion device provided with such a change imparting unit is not only a power converter as described above, but also, for example, a motor that is driven to rotate by AC power (frequency (output frequency) of AC power). It is also possible to use this for determining the rotation speed. In this way, it is possible to suppress the energy loss due to uneven rotation and vibration as much as possible by making the change in the output frequency moderate.

  More specifically, the power conditioner 1 is connected to the power system, sets the output frequency so as to substantially match the frequency of the power in the power system, and outputs the output power to the power system. In addition, a function unit (single operation determination unit) that determines whether or not an isolated operation state has occurred is also provided.

  The change imparting unit gives a change as an intentional error to the output frequency, and the isolated operation determination unit changes the frequency of the power in the power system under a situation where the change is given to the output frequency. It is determined whether or not an isolated operation state has occurred by detecting that the vehicle has been followed.

  In addition, the change imparting unit performs an imparting operation for changing the output frequency every time the occurrence of the isolated operation state is suspected by detecting the electrical fluctuation exceeding the reference level. (See step S1), the isolated operation determination unit determines whether or not an isolated operation state has occurred each time this giving operation is performed. When this electrical fluctuation is a system frequency fluctuation, it can be said that the power conditioner 1 can quickly recognize the change in the frequency and rapidly increase the change by performing the applying operation.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The embodiments of the present invention can be variously modified without departing from the gist of the present invention. In the above description, “power” is mainly used as an index representing the electrical quantity, but it can be read as “voltage” or “current” as long as there is no contradiction.

  The present invention can be used for a power conditioner connected to an electric power system.

1 Power conditioner (power converter)
2 DC power supply (distributed power supply)
3 system power supply 4 system circuit breaker 5 load 11 diode 12 capacitor 14 inverter circuit 15 inductor 16 capacitor 17 current detection circuit 18 voltage detection circuit 19 interconnection relay 20 power condition control device 21 central processing circuit 22 current amplitude setting circuit 23 multiplier 24 subtraction Unit 25 Controller 26 Adder 27 Triangle wave generation circuit 28 PWM comparator 29 Voltage amplitude calculation circuit 30 Multiplier

Claims (9)

A power conversion device that converts DC power into output power that is AC power at the currently set output frequency, and outputs the output power,
A change providing unit for changing the output frequency;
The change imparting unit
The change giving period to which the change should be given is divided into a plurality of sections shorter than the cycle of the output power,
An amount of the change is set for each section. The power conversion device according to claim 1, wherein the power conversion device is connected to an electric power system, sets the output frequency according to a frequency of electric power in the electric power system, and outputs the output electric power to the electric power system.
An independent operation determination unit that determines whether or not an isolated operation state has occurred,
The islanding determination unit
Under the circumstances where the change is given to the output frequency, it is determined whether or not a single operation state has occurred based on whether or not the frequency of the power in the power system follows the change. Conversion device. The change imparting unit
The power converter according to claim 2, wherein the amount of the change is increased stepwise for each section until it is determined whether or not the frequency of power in the power system follows the change. . The change imparting unit
In the change granting period, until the amount of change reaches a predetermined maximum amount, the amount of change is increased step by step for each section,
3. The power conversion device according to claim 2, wherein after the amount of the change reaches the maximum amount, the amount of the change is decreased step by step for each of the sections. The change imparting unit
Every time the occurrence of a single operation state is suspected, a giving operation for giving the change to the output frequency is performed,
The islanding determination unit
The power converter according to any one of claims 2 to 4, wherein the presence / absence of a single operation state is determined each time the application operation is performed. The voltage command waveform is calculated, and the inverter circuit is controlled so that the target voltage waveform to be output is the voltage command waveform, thereby outputting a voltage having a waveform that substantially matches the voltage waveform in the power system. The power conversion device according to claim 5,
The change imparting unit
By giving the change by changing the frequency in the voltage command waveform,
The islanding determination unit
A power conversion device that determines whether or not the frequency of power in the power system follows the change based on a difference between the voltage command waveform and the detected voltage waveform in the power system. The voltage command waveform is calculated, and the inverter circuit is controlled so that the target voltage waveform to be output is the voltage command waveform, thereby outputting a voltage having a waveform that substantially matches the voltage waveform in the power system. The power conversion device according to claim 5,
Determines the current command waveform that is the target of the current waveform to be output.
The voltage command waveform is
The detected voltage waveform in the power system and the waveform corresponding to the voltage drop when the current command waveform current flows from the inverter circuit to the power system are calculated together,
The change imparting unit
By giving the change by changing the frequency in the current command waveform,
The islanding determination unit
A power conversion device that determines whether or not the frequency of power in the power system follows the change based on a difference between the current command waveform and the detected voltage waveform in the power system. Each of the plurality of sections is
The power conversion device according to any one of claims 2 to 7, wherein the power conversion device is a section that is divided for each constant phase angle of less than 2π in the output power. A power conversion device according to any one of claims 2 to 8,
A DC power source for generating the DC power,
The power supply system, wherein the DC power is converted into AC power and supplied to the power system.

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