JP7083687B2 - Power conversion device and power conversion system method - Google Patents

Description

The present invention generally relates to the control of power conversion, and more particularly to the control of power conversion from RES (Renewable Energy Source) or BESS (Battery Energy Storage System) in the power system.

In recent years, there has been a tendency to increase the amount of power generated by RES in the electric power system. BESS is also drawing attention because RES power generation depends on uncontrollable factors such as weather.

Patent Document 1 discloses a technique relating to control of a microgrid composed of a plurality of microgrid resources, specifically, a control method for independent operation of each microgrid resource in a situation where power generation is possible.

WO2017 / 067585

As a generator in an electric power system, a synchronous generator is generally known. Synchronous generators have inertia and contribute to the stability of the power system.

When RES and BESS are added to the power system, synchronous generators are opened from the power system in order to maintain the balance between supply and demand of electric power. Since both RES and BESS are generally non-inertial generators, the stability of the power system is a concern when RES and BESS are increased in place of synchronous generators.

The power conversion device has a power conversion control unit that controls a power conversion unit that converts DC power from RES or BESS in the power system into AC power. The power conversion control unit detects an accident state including an accident flag indicating whether or not an accident has occurred, based on the AC power as the output of the power conversion unit. Based on the detected accident state, the power conversion control unit receives a control signal to be input to the power conversion unit from among a plurality of operation modes including one or more stabilized operation modes that contribute to the stabilization of the power system. Select the indicated operation mode.

It is expected that the stability of the power system will be maintained even if RES and BESS increase in the power system.

An example of the configuration of the entire system including the power system according to the first embodiment is shown. An example of the configuration of the power conversion device is shown. An example of the configuration of the power conversion unit is shown. An example of the configuration of the detection unit is shown. An example of mode selection processing is shown. An example of the configuration of the designated part is shown. An example of the configuration of the detection unit according to the second embodiment is shown. An example of the mode selection process according to the second embodiment is shown. A part of the mode selection process according to the third embodiment is shown.

Hereinafter, some embodiments of the present invention will be described with reference to the drawings. In the following description, the common code among the reference codes may be used when the same type of elements are not distinguished, and the reference code may be used when the same type of elements are distinguished. For example, when RES is not distinguished, it is called "RES102", and when RES is distinguished, it is called "RES102A" or "RES102B".

FIG. 1 shows an example of the configuration of the entire system including the power system.

The power system includes a power grid 100 and a plurality of generators connected to the power grid 100. Examples of the plurality of generators include synchronous generators 101, RES102 and BESS104. Examples of the RES 102 include a wind power generator (wind turbine) 102A and a solar power generator (solar cell panel) 102B. Some of the synchronous generators 101, RES102 and BESS104 may be omitted.

A power converter 105 (eg 105A and 105B) is interposed between the RES 102 (eg 102A and 102B) and the power grid 100. Further, a power conversion device 105 (105C) is interposed between the BESS 104 and the power grid 100. The power conversion device 105 improves system stability in the event of an accident in the power grid 100.

The power generation of at least RES102 and BESS104 in the power system is controlled or managed by a higher-level control device 106 such as an energy management center. The host controller 106 manages the power grid 100, as indicated by reference numeral 107. For example, the host controller 106 periodically or irregularly acquires power grid information including information indicating the state of the power grid 100. The host control device 106 determines one or more threshold values to be set in each power conversion device 105 based on the acquired power network information, and as shown by reference numeral 108, one or more determined in each power conversion device 105. Set the threshold value of. As will be described later, the operation mode is switched based on the one or more threshold values, and such a threshold value can be specified from the upper control device 106. The upper control device 106 can acquire the power grid information, but the upper control device 106 is based on the power generation amount predicted for at least one of the RES 102 and the BESS 104 based on the acquired power network information (for example, based on the power network information). In order to determine one or more thresholds used by the power conversion device 105, it can be expected that the operation mode of each power conversion device 105 can be maintained in a mode according to the state of the power grid 100. Details of one or more thresholds will be described later. In this embodiment, one or more threshold values are set from the upper control device 106 (furthermore, at least one of the one or more threshold values is updated based on the acquired power grid information. ), At least one of the one or more threshold values may be preset as a fixed value.

FIG. 2 shows the configuration of the power conversion device 105.

The power conversion device 105 has a power conversion control unit (hereinafter, control unit) 202 that controls the power conversion unit 201 in addition to the power conversion unit 201 that converts DC power from RES or BESS in the power system into AC power. .. At least a part of the control unit 202 may be realized by executing one or more computer programs by a processor, or one or more hardware circuits (for example, FPGA (Field-Programmable Gate Array) or ASIC (for example). It may be realized by Application Specific Integrated Circuit)). The following description of each function of the control unit 202 is an example, and a plurality of functions may be combined into one function, or one function may be divided into a plurality of functions.

The power conversion unit 201 is connected to the RES 102 or BESS 104 and the power grid 100. The power conversion unit 201 converts the DC power from the RES 102 or the BESS 104 into AC power according to the control signal from the control unit 202. AC power is supplied to the power grid 100. As described above, the power grid 100 is managed by the host controller 106 as indicated by reference numeral 107.

The control unit 202 specifies an operation mode, a detection unit 203 for detecting an accident state, a determination unit 204 for determining an operation mode, and a power conversion unit for a control signal indicating control contents based on the operation mode. It has a designated unit 205 (transmitted to 201).

The detection unit 203 detects and outputs an accident state including an accident flag indicating whether or not an accident has occurred, based on at least a part of local information which is information about AC power as an output of the power conversion unit 201. The output accident state is input to the determination unit 204.

The determination unit 204 is from a communication unit 206 that receives one or more threshold values from an external device such as the host control device 106 as indicated by reference numeral 108, and one or more threshold values and the detection unit 203 that are received by the communication unit 206. Operation indicated by a control signal input to the power conversion unit 201 from among a plurality of operation modes (multiple operation modes including one or more stabilized operation modes that contribute to the stabilization of the power system) based on the accident state of It has a selection unit 207 for selecting (determining) a mode. The selection unit 207 outputs an operation mode command, which is a control command indicating the selected operation mode.

The designation unit 205 receives the local information and the operation mode command, and generates a control signal in response to the operation mode command. The control signal is a signal indicating the control content determined based on the received local information and the operation mode indicated by the operation mode command. The designation unit 205 transmits the generated control signal to the power conversion unit 201.

According to the control unit 202, even if RES102 and BESS104 increase in the power system, it can contribute to maintaining the stability of the power system.

FIG. 3 shows the configuration of the power conversion unit 201.

The power conversion unit 201 includes a power stage 301, an input voltage transformer 3, an input current transformer 4, an input detection unit 5, an output voltage transformer 6, an output current transformer 7, an output detection unit 8, and a PWM (Pulse). Width Modulation) section 304. The electric power generated by the RES 102 or the BESS 104 goes through the power stage 301, and further goes through the line cable 302 between the power conversion unit 201 and the power grid 100.

The input voltage value and input current value (DC voltage value and DC current value) of the power stage 301 are derived by the input voltage transformer 3 and the input current transformer 4, and these values are obtained by the input detection unit 5 as the input voltage value V. It is converted into a signal representing _dc and a signal representing the input current value I _dc . Similarly, the output voltage value and output current value (AC voltage value and AC current value) of the power stage 301 are derived by the output voltage transformer 6 and the output current transformer 7, and these values are output by the output detection unit 8. It is converted into a signal representing the voltage values V _a , V _b and V _c and a signal representing the output current values I _a , I _b and I _c . Information including V _a , V _b , V _c , I _a , I _b and I _c is output as local information. V _a , V _b and V _c are three-phase voltage values, and I _a , I _b and I _c are three-phase current values.

The control signal generated based on the output local information is input from the designated unit 205 to the PWM unit 304, and the PWM unit 304 generates a pulse for controlling the power stage 301 based on the control signal.

FIG. 4 shows an example of the configuration of the detection unit 203.

The detection unit 203 detects and outputs an accident state composed of FLG _FRT , V _FRT , Δω and ω _pp . FLG _FRT is an accident flag indicating whether or not an accident has occurred. V _FRT is an example of a value related to voltage amplitude (V _mag ), and specifically, is the lowest value of V _mag . Δω and ω _pp are examples of values related to frequency. Δω is the frequency deviation (ω is the frequency). ω _pp is the pp frequency (peak to peak frequency).

The detection unit 203 has a plurality of blocks 401 to 413. Some blocks 401 and 407 to 412 are included in the SRF-PLL (Synchronous Reference Frame Phase Locked Loop) 400.

The processing performed by the detection unit 203 is, for example, as follows.

The three-phase voltage values (V _a , V _b , and V _c ), which are an example of a part of the local information, are input to the detection unit 203. The block 401 converts the input Va, V _b , and V _c into a fixed reference coordinate system (V _α , V _{β )} by park conversion.

Blocks 402 and 402 calculate V _mag based on V _α and V _β . Block 404 (comparator) compares the calculated _Vmag with a predetermined value (eg 0.9 [pu]).

When the V _mag becomes lower than a predetermined value (for example, 0.9), the block 404 changes the value of the FLG _FRT from "0" (a value meaning that no accident has occurred) to "1" (an accident has occurred). Change to a value that means). Whether or not FLG _FRT = 1 may be determined in place of or in addition to V _mag according to the relationship between ω (for example, Δω) and a predetermined threshold value. When an accident occurs, it affects V _mag and ω (for example, Δω). Therefore, the presence or absence of an accident based on the relationship between the value of at least one of V _mag and ω (for example, Δω) and the threshold value of the value. It is valid to determine. Block 405 gets the lowest value of V _mag . When the delay signal of the FLG _FRT is changed from “0” to “1” by the block 413, the block 406 (S / H (Sample and Hold)) samples and holds the lowest value of the V _mag . At the same time, the voltage frequency (ω) and phase angle (Θ) are derived from the SRF-PLL400. Block 411 detects the frequency deviation (Δω) from the nominal value by comparing the nominal value (ω _n ) with the average frequency obtained by the block 410. Further, the block 412 detects and outputs ω _pp . As a result, the accident state composed of FLG _FRT , V _FRT , Δω and ω _pp is output. The output accident state is input to the determination unit 204. According to the accident state output when V _mag is lower than a predetermined value (for example, 0.9) (that is, while an accident is occurring), when FLG _FRT = 1 and FLG _FRT = 1. V _FRT (minimum value of V _mag ), Δω, ω _pp can be obtained. In the SRF-PLL400, the block 407 converts the fixed reference coordinate system (V _α and V _β ) into the rotating coordinate system (V _d and V _q ) based on the feedback Θ. Block 408 (proportional integrator) calculates ω from V _q . ω is input to the block 411 that outputs Δω via the block 410 (LPF (Low Pass Filter)), and is compared with ω _n . Further, ω is input to the block 412, and the block 412 outputs ω _pp . Further, ω is input to the block 409, and the block 409 calculates Θ (phase angle) based on ω. The calculated Θ is fed back to the block 407.

FIG. 5 shows an example of the mode selection process performed by the determination unit 204.

The accident status (FLG _FRT , V _FRT , Δω and ω _pp ) output from the detection unit 203 is input to the selection unit 207. V _FRT is an example of an amplitude value which is a value indicating an amplitude. Δω and ω _pp are examples of frequency change values which are values indicating the amount of frequency change.

Further, one or more threshold values used in the mode selection process are input to the selection unit 207 from the host control device 106 through the communication unit 206. The input of the accident state and the input of one or more threshold values may be at the same timing or at different timings. One or more thresholds may be held by the selection unit 207. An example of one or more thresholds is the _VFRT threshold _VTH , the Δω threshold _ΔωTH , and the _ωpp threshold _ωppTH .

The selection unit 207 performs a mode selection process. The outline of the mode selection process is as follows. That is, one or more stabilized operation modes include an FRT (Fault Ride Through) mode and a VSG (Virtual Synchronous Generator) mode. In addition to the FRT mode and the VSG mode, the plurality of operation modes include a normal mode which is a normal operation mode when an accident has not occurred. In the mode selection process, the selection unit 207 selects the FRT mode when FLG _FRT = 1. In the same process, the selection unit 207 controls whether or not to select the VSG mode based on the V _FRT . In the same process, the selection unit 207 controls whether or not to deselect the VSG mode (exit from the VSG mode) based on at least one of Δω and ω _pp . The stability of the power system depends on the presence or absence of inertia, the distance from the power converter 105 to the position where the accident occurred, and the state after the accident is resolved (after the FLG _FRT changes from "1" to "0"). Depends on at least one. The V _FRT depends on the distance from the power converter 105 to the location where the accident occurred, and at least one of Δω and ω _pp depends on the state after the accident is resolved. Therefore, according to the mode selection process, the operation mode is selected based on at least one of the position where the accident occurred and the state after the accident is resolved, so that the stability of the power system can be expected to be improved.

Hereinafter, the mode selection process will be described in detail.

For example, when the power conversion device 105 is started, the normal mode, which is the default operation mode, is selected as the operation mode (step 501).

The selection unit 207 determines whether or not FLG _FRT = 1 in the normal mode (step 502). If the determination result of step 502 is false (step 502: No), the operation mode remains the normal mode.

When the determination result of step 502 is true (step 502: Yes), the selection unit 207 selects the FRT mode (step 503).

The selection unit 207 determines whether or not FLG _FRT = 0 in the FRT mode (step 504). If the determination result of step 503 is false (step 504: No), the operation mode remains the FRT mode. This is because the situation of having an accident continues. That is, the FRT mode continues at least until FLG _FRT = 0 (specifically, for example, until _Vmag becomes a predetermined value (for example, 0.9) or more).

In the FRT mode, if the determination result of step 504 is true (step 504: Yes), the selection unit 207 selects to exit the FRT mode. This is because FLG _FRT = 0, that is, the state has returned to the state without accidents. At that time, the selection unit 207 determines whether or not _VFRT < _VTH is selected in order to determine whether to select the normal mode or the VSG mode (step 505). As described above, V _FRT depends on the position where the accident occurs, but V _FRT < _VTH means that the position where the accident occurs is close.

If the determination result in step 505 is false (step 505: No), the selection unit 207 selects the normal mode (step 501). This is to avoid that VSG control is performed even when the V _FRT is larger than the V _TH (the position where the accident occurs is far from the power conversion device 105), and as a result, the power generation efficiency is lowered.

Therefore, when the determination result of step 505 is true (step 505: YES), the selection unit 207 selects the VSG mode (step 506).

The selection unit 207 determines whether or not Δω <Δω _TH and ω _pp <ω _pp TH in the VSG mode (step 507). If the determination result of step 507 is false (step 507: No), the operation mode remains the VSG mode. This is because it was judged that the condition after the accident was resolved was not stable. That is, the VSG mode continues until at least Δω <Δω _TH and ω _pp <ω _pp TH.

In other words, if the determination result of step 507 is true (step 507: No), the selection unit 207 selects to exit the VSG mode. For example, the selection unit 207 selects a normal mode (step 501).

The above is the description of the mode selection process. The selection unit 207 outputs an operation mode command indicating the operation mode selected in the mode selection process.

In the mode selection process, for example, at least one of the following may be adopted.
-In FRT mode, step 504 is skipped. Step 505: When No, step 504 is performed, and when Step 504: No, step 503 (selection of FRT mode) is performed.
-In the VSG mode, it is determined whether FLG _FRT = 0 or not between step 506 and step 507, and in the case of step 507: No, at least one of them. When FLG _FRT = 1, step 503 (selection of FRT mode) is performed.

FIG. 6 shows an example of the configuration of the designation unit 205.

The designation unit 205 has a plurality of blocks 601 to 604. The block 601 determines the content of the normal control (control in the case of the normal mode) based on the local information (V _a , V _b , V _c , I _a , I _b and I _c ). The block 602 determines the content of the FRT control (control in the case of the FRT mode) based on the local information. The block 603 determines the content of VSG control (control in the case of VSG mode) based on the local information. The contents of each of the FRT control and the VSG control can be determined according to the existing method.

The operation mode command output from the selection unit 207 is input to the designation unit 205. The block 604 (mode selector) selects the control content corresponding to the operation mode indicated by the input operation mode command from the normal control content, the FRT control content, and the VSG control content. The block 604 generates a control signal indicating the selected control content, and outputs the generated control signal.

Example 2 of the present invention will be described. At that time, the differences from the first embodiment will be mainly described, and the common points with the first embodiment will be omitted or simplified.

FIG. 7 shows an example of the configuration of the detection unit according to the second embodiment.

The detection unit 700 outputs ΔΘ _FRT instead of V _FRT . That is, the abnormal state includes ΔΘ _FRT instead of V _FRT . Is ΔΘ _FRT , which is the phase angle deviation. The ΔΘ _FRT depends on the stability of the RES 102 or BESS 104 connected to the power converter 105 including the detector 700. That is, in the second embodiment, the stability of the RES 102 or the BESS 104 is considered instead of the distance to the position where the accident occurs. The larger the ΔΘ _FRT , the more unstable the RES102 or BESS104.

Specifically, the detection unit 700 has blocks 701 to 704 instead of blocks 405, 406 and 413. The block 701 (S / H) holds the frequency by sampling when the FLG _FRT changes from “0” to “1”. As a result, the frequency before the accident occurs is detected and maintained. The block 702 compares the frequency (ω) derived from the SRF-PLL400 with the frequency before the accident occurs. The block 703 outputs a phase angle deviation (ΔΘ _FRT ) based on the comparison result (frequency difference). When the accident resolution is completed (when the FLG _FRT changes from "1" to "0"), the ΔΘ _FRT is sampled and held.

FIG. 8 shows an example of the mode selection process according to the second embodiment.

In the FRT mode, instead of performing step 505, the selection unit 800 in the determination unit 810 determines whether or not ΔΘ _FRT > ΔΘ _TH (step 805). ΔΘ _TH is a threshold value of ΔΘ _FRT , and is one of one or more threshold values set by the host controller 106.

When the determination result of step 805 is true (step 805: Yes), the selection unit 800 selects the VSG mode (step 506). This is because a large ΔΘ _FRT means that the RES 102 or BESS 104 connected to the power conversion device 105 including the selection unit 800 is likely to be unstable. If the determination result in step 805 is false (step 805: No), the selection unit 800 selects the normal mode because FLG _FRT = 0 according to the example of FIG. 8 (step 501).

Example 3 of the present invention will be described. At that time, the differences from the first and second embodiments will be mainly described, and the common points with the first and second embodiments will be omitted or simplified.

FIG. 9 shows a part of an example of the mode selection process according to the third embodiment.

In Example 3, at least one of step 505 and step 805 is performed. For example, in the case of step 505: Yes or step 805: Yes, the VSG mode is selected (step 506). In the case of step 505: No and step 805: No, the normal mode is selected (step 501).

Although some examples have been described above, these are examples for the purpose of explaining the present invention, and the scope of the present invention is not limited to these examples. The present invention can also be practiced in various other forms. For example, the control unit 202 may exist in an external device such as the host control device 106 in place of or in addition to the power conversion device 105.

105: Power converter

Claims (9)

A power conversion unit that operates according to a control signal input to convert DC power from RES (Renewable Energy Source) or BESS (Battery Energy Storage System) in the power system to AC power.
It is provided with a power conversion control unit that inputs a control signal of the power conversion unit to the power conversion unit.
The power conversion control unit
Of the accident flag indicating whether or not an accident has occurred and the amplitude value indicating the amplitude and the phase change value indicating the amount of phase change , based on the AC power as the output of the power conversion unit. Detecting an accident state including at least one and a frequency change value which is a value indicating the amount of change in frequency ,
When the accident flag in the detected accident state indicates the occurrence of an accident , FRT (Fault Ride Through) mode and VSG (Virtual Synchronous), which are stabilized operation modes that contribute to the stabilization of the power system , respectively. Select the FRT mode from the Generator) mode and select
Whether or not to select the VSG mode is controlled based on at least one of the amplitude value and the phase change value in the detected accident state.
Controls whether or not to cancel the selection of the VSG mode based on the frequency change value in the detected accident state.
Power converter. At least one of the fact that the amplitude value is less than the amplitude threshold value, which is the threshold value of the amplitude value, and that the phase change value exceeds the phase threshold value, which is the threshold value of the phase change value, is satisfied. If so, the power conversion control unit selects the VSG mode.
The power conversion device according to claim 1 . The power conversion control unit further selects the VSG mode when the accident flag does not indicate the occurrence of an accident.
The power conversion device according to claim 2 . When it is satisfied that the frequency change value is less than the frequency threshold value which is the threshold value of the frequency change value, the power conversion control unit deselects the VSG mode.
The power conversion device according to claim 1 . The frequency change value includes a frequency deviation and a pp frequency (peak-to-peak frequency).
As the frequency threshold value, there are a deviation threshold value which is the threshold value of the frequency deviation and a pp threshold value which is the threshold value of the pp frequency.
The frequency change value is less than the frequency threshold value is at least one of the frequency deviation being less than the deviation threshold value and the pp frequency being less than the pp threshold value.
The power conversion device according to claim 4 . The control of whether or not to select the VSG mode and the control of whether or not to cancel the selection of the VSG mode are the values of at least one of the detected accident states other than the accident flag and the value. Based on thresholds and relationships,
The threshold value is a value set by a higher-level control device that is a device for acquiring power network information including information indicating the state of the power network included in the power system.
The power conversion device according to claim 1 . The threshold value is a value determined by the higher-level control device based on the acquired power grid information.
The power conversion device according to claim 6 . The value indicated by the accident flag is at least one of a value related to voltage amplitude and a value related to frequency specified from AC power as an output of the power conversion unit, and a threshold value set to the at least one value. It is a value determined according to the relationship of
The power conversion device according to claim 1. It is a power conversion control method that controls a power conversion device that converts DC power output by RES (Renewable Energy Source) or BESS (Battery Energy Storage System) in a power system into AC power.
Based on the AC power after power conversion , the computer has at least one of an accident flag indicating whether or not an accident has occurred, an amplitude value indicating an amplitude, and a phase change value indicating the amount of phase change. Detects an accident state including one and a frequency change value which is a value indicating the amount of change in frequency .
When the computer indicates that an accident has occurred in the detected accident state , the FRT (Fault Ride Through) mode and VSG, which are stabilized operation modes that contribute to the stabilization of the power system, respectively. Select the FRT mode from the (Virtual Synchronous Generator) mode .
The computer controls whether or not to select the VSG mode based on at least one of the amplitude value and the phase change value in the detected accident state.
The computer controls whether or not to deselect the VSG mode based on the frequency change value in the detected accident state.
Power conversion control method.

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