TW201944695A - Power conversion device and power conversion control method - Google Patents

Abstract

The present invention maintains the stability of a power system even when increasing a renewable energy source (RES) and a battery energy storage system (BESS) in the power system. This power conversion device has a power conversion control unit that controls a power conversion unit for converting DC power to AC power, said DC power being received from an RES or a BESS in a power system. The power conversion control unit detects, on the basis of the AC power output from the power conversion unit, an accident state including an accident flag indicating whether an accident has occurred or not. The power conversion control unit selects, on the basis of the detected accident state, an operation mode, which is indicated by a control signal input to the power conversion unit, from among a plurality of operation modes including one or more stabilization operation modes contributing in stabilizing the power system.

Description

Power conversion device and power conversion control method

Generally speaking, the present invention relates to the control of power conversion, and 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, power systems have tended to increase the amount of electricity generated by RES. RES's power generation system depends on factors that cannot be controlled like weather, so BESS has also attracted attention.

Patent Document 1 discloses a technique for controlling a micro-grid constituted by a plurality of micro-grid resources. Specifically, it discloses a control method for independent operation of each micro-grid resource in a state where power can be generated.
[Prior technical literature]
[Patent Literature]

[Patent Document 1] WO2017 / 067585 Patent Gazette

[Questions to be Solved by the Invention]

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

If RES or BESS is added to the power system, in order to maintain the balance of power supply and demand, synchronous power generators are listed from the power system. Regardless of RES or BESS, it is generally a generator without inertia. RES or BESS is replaced by a synchronous generator, and it will worry about the stability of the power system.

[Means for solving problems]

The power conversion device includes a power conversion control unit that controls the 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 an accident has occurred based on the AC power output by the power conversion unit. The power conversion control unit selects control inputted to the power conversion unit from a plurality of operation modes including one or more stabilization operation modes that contribute to the stabilization of the power system based on the detected accident state. The operating mode indicated by the signal.

[Inventive effect]

Even if RES or BESS is added to the power system, the stability of the power system can be expected to be maintained.

Hereinafter, several embodiments of the present invention will be described using drawings. In addition, in the following description, when the same type of requirements are not distinguished from each other, the common component symbols in the reference symbols are used, and when the same type of requirements are distinguished, the reference symbols are used. For example, when RES is not distinguished, it is called "RES102", and when RES is distinguished, it is called "RES102A" or "RES102B", for example.

[Example 1]

FIG. 1 shows an example of the overall configuration of a system including a 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, RES 102, and BESS 104. 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, RES 102, and BESS 104 may not have a generator.

A power conversion device 105 (for example, 105A and 105B) is interposed between the RES 102 (for example, 102A and 102B) and the power grid 100. 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 network 100.

The power generation of at least RES 102 or BESS 104 in the power system is controlled or managed by a higher-level control device 106 like an energy management center. The higher-level control device 106 manages the power network 100 as indicated by reference numeral 107. For example, the higher-level control device 106 acquires the power network information including information indicating the status of the power network 100 on a periodic or irregular basis. The higher-level control device 106 determines one or more threshold values to be set in each power conversion device 105 based on the obtained power network information. As indicated by reference numeral 108, each power conversion device 105 sets and determines more than one threshold value. As will be described later, the operation mode is switched based on the one or more threshold values. However, such a threshold value may be specified from the higher-level control device 106. The higher-level control device 106 can obtain the power network information. The higher-level control device 106 is based on the obtained power network information (for example, based on the power network information and based on the prediction of the power generation of at least one of RES 102 and BESS 104) to determine the power conversion. Because of one or more threshold values used by the device 105, it can be expected that the operation mode of each power conversion device 105 is maintained in a mode corresponding to the state of the power network 100. The details of more than one threshold will be described later. Moreover, in this embodiment, more than one threshold value is set by the higher-level control device 106 (further, at least one of the more than one threshold value is updated based on the obtained power network information), or more than one threshold value may be used. At least one of the threshold values is set as a fixed value in advance.

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

The power conversion device 105 includes a power conversion control unit (hereinafter, a control unit) 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. 202. At least a part of the control section 202 may be implemented by the processor executing one or more computer programs, or may be implemented by more than one hardware circuit (for example, FPGA (Field-Programmable Gate Array) or ASIC (Application) Specific Integrated Circuit)). Regarding the control unit 202, the description of each function described below is one example, and a plurality of functions may be summarized 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 the BESS 104 and the power network 100. The power conversion unit 201 converts DC power from the RES 102 or the BESS 104 into AC power according to a control signal from the control unit 202. AC power is supplied to the power grid 100. As described above, the power network 100 is indicated by reference numeral 107 and managed by the higher-level control device 106.

The control unit 202 includes a detection unit 203 that detects the state of the accident, a determination unit 204 that determines the operation mode, and a designation unit 205 that specifies the operation mode (specifically, sends a control signal indicating the content of the control to the power conversion unit 201 according to the operation mode). .

The detection unit 203 detects and outputs an accident state including an accident flag indicating whether an accident has occurred, based on at least part of the information related to the AC power that is the output of the power conversion unit 201, that is, local information. The outputted accident state is input to the determination unit 204.

The decision unit 204 includes a communication unit 206 that accepts one or more thresholds from an external device such as the higher-level control device 106, as indicated by reference numeral 108, and a selection unit 207 that has been accepted by the communication unit 206. One or more threshold values are selected (determined) from a plurality of operation modes (including a plurality of operation modes of one or more stabilization operation modes contributing to the stabilization of the power system) based on the accident state from the detection unit 203. The operation mode indicated by the control signal to the power conversion unit 201. The selection unit 207 outputs a control command indicating a selected operation mode, that is, an operation mode command.

The designation unit 205 receives local information and an operation mode command, and responds to the operation mode command to generate a control signal. The control signal is a signal indicating the content of the control 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.

The control unit 202 can contribute to the maintenance of the stability of the power system even if the RES 102 or BESS 104 is added to the power system.

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

The power conversion unit 201 includes a power stage circuit 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). ) 部 304. The power generated by the RES 102 or the BESS 104 is transmitted through the power stage circuit 301 and further through the cable 302 between the power conversion unit 201 and the power network 100.

The input voltage value and input current value (DC voltage value and DC current value) of the power stage circuit 301 are derived by the input voltage transformer 3 and the input current transformer 4, and these values are converted by the input detection section 5. A signal representing an input voltage value V _dc and a signal representing an input current value I _{dc are formed} . Similarly, the output voltage value and output current value (AC voltage value and AC current value) of the power stage circuit 301 are derived by the output voltage transformer 6 and the output current transformer 7, and these values are output by the output detection section 8. , Into signals representing output voltage values V _a , V _b and V _c and signals representing output current values I _a , I _b and I _c . Contains _{V a, V b, V c} , it a, I b and I _c of the information, is outputted as a local-based 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 outputted local information is input from the designation section 205 to the PWM section 304. The PWM section 304 generates a pulse for controlling the power stage circuit 301 according to 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 an accident has occurred. V _FRT is an example of a value related to the voltage amplitude (V _mag ). Specifically, it is the lowest value of V _mag . Δω and ω _pp are examples of frequency-dependent values. Δω is a frequency deviation (ω is a frequency). ω _pp is the pp frequency (peak-to-peak frequency).

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

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

An example of a part of the local information, that is, three-phase voltage values (V _a , V _b, and V _c ) is input to the detection unit 203. Block 401 transforms the input V _a , V _b and V _c into a fixed reference coordinate system (V _α , V _β ) by Park transformation.

Blocks 402 and 402 calculate V _mag based on V _α and V _β . The block 404 (comparator) compares the calculated V _mag and a specific value (for example, 0.9 [pu]).

When V _{mag is} lower than a specific value (for example, 0.9), the block 404 changes the value of FLG _FRT from "0" (meaning that no accident occurred) to "1" (meaning that the accident occurred) ). Moreover, whether or not FLG _FRT = 1 is determined may be determined instead of V _mag or added, and corresponding to the relationship between ω (for example, Δω) and a specific threshold. In the case of an accident, because it affects V _mag or ω (for example, Δω), the accident is determined based on the relationship between at least one of V _mag and ω (for example, Δω) and the threshold value of the value. What happens is effective. Block 405 obtains the lowest value of V _mag . In the case where the delay signal of the FLG _FRT changes from "0" to "1" by block 413, block 406 (S / H (Sample and Hold)) samples and holds the lowest value of _Vmag . At the same time, the frequency (ω) and phase angle (Θ) of the voltage are derived from SRF-PLL400. Block 411 compares the frequency deviation (Δω) from the nominal value with the average frequency obtained from the nominal value (ω _n ) and the block 410, and then detects it. Moreover, the block 412 detects and outputs ω _pp . As a result, an accident state composed of FLG _FRT , V _FRT , Δω, and ω _pp is output. The outputted accident state is input to the determination unit 204. According to the accident status output when V _{mag is} lower than a specific value (for example, 0.9) (that is, during an accident), FLG _FRT = 1, and V _FRT (V _mag when FLG _FRT = 1 is obtained Lowest value), Δω, ω _pp . Moreover, in the SRF-PLL400, the block 407 is based on the feedback Θ, and transforms the fixed reference coordinate system (V _α and V _β ) into a rotating coordinate system (V _d and V _q ). Block 408 (proportional integrator) calculates ω from V _q . ω is input to block 411 which outputs Δω via block 410 (LPF (Low Pass Filter)), and is compared with ω _n . Moreover, ω is input to the block 412, and the block 412 outputs ω _pp . In addition, ω is input to the block 409. The block 409 calculates Θ (phase angle) based on ω. The calculated Θ is fed back to block 407.

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

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

Then, one or more threshold values used in the mode selection process from the higher-level control device 106 through the communication unit 206 are input to the selection unit 207. The input of the accident state and the input of more than one threshold value may be the same timing or different timings. The selection unit 207 can hold more than one threshold value. Examples of the one or more threshold values are the threshold value V _TH of V _FRT , the threshold value Δω _{TH of} Δω, and the threshold value ω _{p-pTH of} ω _pp .

The selection unit 207 performs a mode selection process. The outline of the mode selection process is as follows. That is, one or more stable operation modes include: FRT (Fault Ride Through) mode, and VSG (Virtual
Synchronous Generator) mode. The plurality of operation modes include the normal operation mode, which is the normal operation mode when no accident has occurred, in addition to these FRT mode and VSG mode. 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 to select the VSG mode based on the V _FRT . In the same process, the selection unit 207 controls whether to cancel the selection of the VSG mode (leave the VSG mode) based on at least one of Δω and ω _pp . The stability of the power system is in addition to the presence or absence of inertia, the distance from the power conversion device 105 to the location of the accident, and the state after the accident is resolved (after the FLG _FRT changes from "1" to "0"). At least 1 dependent. V _{FRT depends} on the distance from the power conversion device 105 to the location of the accident, and at least one of Δω and ω _pp depends on the state after the accident is resolved. Therefore, in accordance with the mode selection process, the operation mode is selected based on at least one of the occurrence position of the accident and the state after the accident is resolved, and the stability of the power system can be expected to improve.

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

For example, when the power conversion device 105 is started, the operation mode selects a preset operation mode, that is, a normal mode (step 501).

The selection unit 207 determines whether FLG _FRT = 1 in the normal mode (step 502). When the determination result in step 502 is false (step 502: No), the operation mode is maintained in the normal mode.

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

The selection unit 207 determines whether FLG _FRT = 0 in the FRT mode (step 504). When the determination result in step 503 is false (step 504: No), the operation mode is maintained in the FRT mode. This is because it continues to be in an accident state. That is, the FRT mode is continued at least until FLG _FRT = 0 (specifically, for example, until V _mag is a specific value (for example, 0.9) or more).

In the FRT mode, if the determination result in step 504 is true (step 504: Yes), the selection unit 207 selects to leave the FRT mode. FLG _FRT = 0, that is, the reason for returning to the state without accidents. At this time, the selection unit 207 determines whether V _FRT &lt; V _{TH to} determine whether to select the normal mode or the VSG mode (step 505). As described above, the V _FRT system is dependent on the location of the accident. However, the V _FRT <V _TH system means approaching the location of the accident.

When the determination result in step 505 is false (step 505: No), the selection unit 207 selects the normal mode (step 501). VSG control is performed until V _{FRT is} larger than V _TH (the accident occurs far from the power conversion device 105), and the ultimate goal is to avoid a reduction in power generation efficiency.

If the result of the determination in step 505 is true (step 505: Yes), the selection unit 207 selects the VSG mode (step 506).

The selection unit 207 determines whether Δω <Δω _TH and ω _pp <ω _p-pTH in the VSG mode (step 507). When the determination result in step 507 is false (step 507: No), the operation mode is maintained in the VSG mode. This is because it is determined that the state after the accident has resolved is unstable. That is, the VSG mode is continued at least until Δω <Δω _TH and ω _pp <ω _p-pTH .

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

This concludes 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 addition, in the mode selection processing, for example, at least one of the following can be used.
・ In FRT mode, step 504 is ignored. When step 505: No, proceed to step 504, and when step 504: no, proceed to step 503 (selection of FRT mode).
・ In the VSG mode, it is determined whether FLG _FRT = 0 between step 506 and step 507, and at least one of the cases of step 507: "No". When FLG _FRT = 1, step 503 (selection of FRT mode) is performed.

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

The designation unit 205 includes a plurality of blocks 601 to 604. In block 601 the local information system _{(V a, V b, V} c, I a, I b and I _c), based on the normal control decisions (in the case of control of the normal mode) content. Block 602 determines the content of FRT control (control in the case of FRT mode) based on local information. Block 603 determines the content of VSG control (control in the case of VSG mode) based on local information. The contents of FRT control and VSG control can be determined according to existing methods.

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

[Example 2]

A second embodiment of the present invention will be described. At this time, the differences from the first embodiment will be mainly described, and the common points with the first embodiment will be omitted or briefly explained.

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

The detection unit 700 based substituent V _FRT, output ΔΘ _FRT. That is, the abnormal state replaces V _FRT and includes ΔΘ _FRT . ΔΘ _{FRT is} the phase angle deviation. The ΔΘ _FRT depends on the stability of the RES 102 or the BESS 104 connected to the power conversion device 105 including the detection unit 700. That is, in Example 2, the stability of the RES 102 or the BESS 104 is considered instead of the distance up to the occurrence location of the accident. The larger ΔΘ _FRT , the more unstable the RES 102 or BESS 104 is.

The detection unit 700 is a specific aspect, and has blocks 701 to 704 instead of blocks 405, 406, and 413. Block 701 (S / H) samples and maintains the frequency when the FLG _FRT changes from "0" to "1". After this, the frequency before the accident is detected and maintained. Block 702 compares: the frequency (ω) derived from SRF-PLL400 and the frequency before the above-mentioned accident. 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"), ΔΘ _{FRT is} sampled and held.

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

In the FRT mode, instead of performing step 505, the selection unit 800 in the decision unit 810 determines whether 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 higher-level control device 106.

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

[Example 3]

A third embodiment of the present invention will be described. In this case, 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 briefly described.

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

In Embodiment 3, at least one of steps 505 and 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).

A number of embodiments have been described above, but these are examples for explaining the present invention, and are not intended to limit the scope of the present invention to only these embodiments. The invention can also be implemented in various other forms. For example, the control unit 202 may be an external device such as a higher-level control device 106 instead of or in addition to the power conversion device 105.

105‧‧‧Power Conversion Device

[Fig. 1] Fig. 1 shows an example of the overall configuration of a system including a power system according to Embodiment 1. [Fig.

FIG. 2 shows an example of a configuration of a power conversion device.

[Fig. 3] Fig. 3 shows an example of a configuration of a power conversion unit.

FIG. 4 shows an example of a configuration of a detection unit.

Fig. 5 shows an example of a mode selection process.

[Fig. 6] Fig. 6 shows an example of a configuration of a designation unit.

7 is a diagram showing an example of a configuration of a detection unit according to the second embodiment.

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

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

Claims (10)

A power conversion device including: The power conversion unit operates according to a control signal that is inputted to convert DC power from RES (Renewable Energy Source) or BESS (Battery Energy Storage System) into AC power; as well as A power conversion control unit that inputs a control signal of the power conversion unit to the power conversion unit; The aforementioned power conversion control section is: Detecting an accident state including an accident flag indicating whether an accident has occurred based on the AC power output by the power conversion unit; Based on the detected accident state, selecting the control signal based on the control signal input to the power conversion unit from a plurality of operation modes including one or more stabilization operation modes that contribute to the stabilization of the power system. The operation mode of the indicated control content. The power conversion device according to claim 1, wherein: The above one or more stable operation modes include: FRT (Fault Ride Through) mode and VSG (Virtual Synchronous Generator) mode; The aforementioned accident status, in addition to the aforementioned accident flag, also includes: At least one of a value representing an amplitude, that is, an amplitude value, and a value representing an amount of phase change, that is, a phase change value; and The value representing the amount of frequency change is also the frequency change value; The aforementioned power conversion control section is: Selecting the aforementioned FRT mode when the aforementioned accident flag in the aforementioned detected accident state indicates that an accident has occurred; Controlling whether to select the VSG mode based on at least one of the amplitude value and the phase change value in the detected accident state; Controlling whether to cancel the selection of the VSG mode based on the frequency change value in the detected accident state. The power conversion device according to claim 2, wherein: When at least one of the threshold value whose amplitude value does not reach the amplitude value, that is, the amplitude threshold value, and the phase change value which exceeds the phase change value, that is, the phase threshold value is satisfied, the power conversion control unit Select the aforementioned VSG mode. The power conversion device according to claim 3, wherein: The power conversion control unit further selects the VSG mode when the accident flag does not indicate that an accident has occurred. The power conversion device according to claim 2, wherein: When the frequency change value is less than the threshold value of the frequency change value, that is, the frequency threshold value is satisfied, the power conversion control unit cancels the selection of the VSG mode. The power conversion device according to claim 5, wherein: As the aforementioned frequency change value, there are a frequency deviation and a pp frequency (peak-to-peak frequency); As the aforementioned frequency threshold, the threshold having the aforementioned frequency deviation, that is, the deviation threshold, and the aforementioned pp frequency threshold, which is the pp threshold; The term that the frequency change value does not reach the frequency threshold value means that the frequency deviation is less than the deviation threshold value and the pp frequency is at least one of the pp threshold values. The power conversion device according to claim 2, wherein: The control of whether to select the VSG mode and whether to cancel the selection of the VSG mode are based on the relationship between at least one value other than the accident flag in the detected accident state and a threshold value of the value; The threshold value is a value set by a higher-level control device, which is a device that obtains power network information. The power network information includes information indicating the status of the power network included in the power system. The power conversion device according to claim 7, wherein: The threshold value is a value determined by the upper-level control device based on the obtained power network information. The power conversion device according to claim 1, wherein: The value indicated by the accident flag is a value corresponding to at least one of a value related to a voltage amplitude and a value related to a frequency specified from the AC power that is an output of the power conversion unit, and the at least one value The value is determined based on the relationship between the thresholds that have been set for one value. A power conversion control method includes controlling a power conversion device that converts DC power output from a RES (Renewable Energy Source) or BESS (Battery Energy Storage System) into AC power; Based on the AC power after power conversion, detecting the accident status including the accident flag indicating whether an accident has occurred; Based on the detected accident state, the operation mode of the power conversion device is selected from a plurality of operation modes including one or more stabilization operation modes that contribute to the stabilization of the power system.