WO2020213037A1 - Power conversion device, power conversion system, and program - Google Patents

Abstract

This power conversion device (1) comprises a power converter (10), an AC circuit breaker (CB), a switching control unit (240), and a breaker control unit (250). The power converter (10) includes an arm. The arm includes a plurality of unit converters connected in series. Each of the plurality of unit converters includes a capacitor whose charging/discharging can be switched by a switching element. The AC circuit breaker (CB) is connected between an AC system and the power converter (10). When the absolute value of the AC voltage (Vd) is larger than a first threshold value or smaller than a second threshold value (< the first threshold value), the switching control unit (240) outputs a gate block command (GB) to stop the switching operation of the switching element. When the absolute value is larger than a third threshold value (> the first threshold value) and the absolute value does not instantaneously change according to the output of the gate block command (GB), the breaker control unit (250) opens the AC circuit breaker (CB).

Description

Power converters, power conversion systems, and programs

Embodiments of the present invention relate to power conversion devices, power conversion systems, and programs.

In recent years, a modular multi-level converter (hereinafter referred to as MMC: Modular Multilevel Converter), which is one of the power converters, has been put into practical use. The MMC is a power converter that includes an arm unit including a plurality of unit converters connected in series, and can handle high voltage and large capacity by adding the outputsable voltages of the unit converters. The power converter is connected between, for example, an AC system and a DC system, and converts electric power to each other.

If an abnormality such as an accident occurs in the AC system or DC system to which the power converter is connected, the power converter will continue to operate so as not to impair the stability of the voltage and frequency of the AC system (operate quickly after the abnormality is resolved). It is required to properly select whether to restart the power converter) or to stop the protection so as to suppress the failure of the power converter depending on the degree of abnormality. The control / protection of the power converter in the event of an abnormality is, for example, a method of stopping (gate blocking) the switching control of the semiconductor element provided in the power converter, or an AC cutoff provided between the power converter and the AC system. It is realized by a method of switching the vessel to the open state. Since the opening / closing operation of the AC circuit breaker is slower than the switching control of the semiconductor element, the power converter can quickly resume the operation (can continue the operation) after the abnormality is resolved when the switching control of the semiconductor element is stopped. When the AC circuit breaker was switched to the open state, the operation could not be resumed promptly (the operation could not be continued) after the abnormality was resolved.

Japanese Unexamined Patent Publication No. 2019-22313

An object to be solved by the present invention is to provide a power conversion device, a power conversion system, and a program capable of improving operation continuity in the event of a system accident.

The power conversion device of the embodiment can convert alternating current and direct current to each other. The power converter includes a power converter, an AC circuit breaker, a switching control unit, and a circuit breaker control unit. The power converter includes an arm. The arm includes a plurality of unit converters connected in series. Each of the plurality of unit converters includes a capacitor whose charge and discharge can be switched by a switching element. The AC circuit breaker is connected between the AC system that supplies the AC and the power converter. The switching control unit controls the switching element. The cutoff control unit controls the AC circuit breaker. When the absolute value of the AC voltage is larger than the first threshold value or smaller than the second threshold value (the second threshold value is smaller than the first threshold value), the switching control unit outputs a gate block command. Stop the switching operation of the switching element. When the absolute value is larger than the third threshold value (the third threshold value is larger than the first threshold value), the circuit breaker control unit causes the gate block command to be output by the switching control unit. When the absolute value does not change instantaneously, when the AC circuit breaker is opened and the absolute value changes instantaneously as the gate block command is output by the switching control unit. , Do not open the AC circuit breaker.

It is a figure which shows an example of the structure of the power conversion apparatus 1 of embodiment. It is a figure which shows an example of the structure of the power converter 10 of an embodiment. It is a figure which shows an example of the structure of a cell CL. It is a figure which shows typically an example of the processing of the AC information calculation unit 210 of embodiment. It is a figure which shows typically an example of the process of the gate command part 240 of embodiment. It is a figure which shows typically an example of the process of the circuit breaker control part 250 of embodiment. It is a figure which shows an example of the operation of the conventional power conversion apparatus. It is a figure which shows an example of the operation of the power conversion apparatus 1 of this embodiment. It is a flowchart which shows an example of the process which concerns on the generation of the 1st gate signal gtp, and the 2nd gate signal gtn of the power conversion apparatus 1 of this embodiment. It is a flowchart which shows an example of the process which concerns on the output of the gate block command signal GB of the power conversion apparatus 1 of this embodiment. It is a flowchart which shows an example of the process which concerns on the output of the circuit breaker open command signal CBT of the power conversion apparatus 1 of this embodiment. It is a figure which shows an example of the processing operation of the 3rd filter 224 of the modification 1. It is a figure which shows an example of the structure of the power conversion apparatus 1 in the modification 2. It is a figure which shows an example of the structure of the circuit breaker control unit 250a which concerns on the modification 2. It is a figure which shows an example of the structure of the power conversion system in the modification 3.

Hereinafter, the power conversion device, the power conversion system, and the program of the embodiment will be described with reference to the drawings.

(Embodiment)
[Configuration of power converter 1]
FIG. 1 is a diagram showing an example of the configuration of the power conversion device 1 of the embodiment. The power conversion device 1 is provided at the interconnection point between the AC system and the DC system, and mutually converts the AC power supplied by the AC system and the DC power supplied by the DC system. The power converter 1 includes a power converter 10 and a converter control device 20.

[About power converter 10]
The power converter 10 is connected to the AC system via the AC circuit breaker CB. The AC circuit breaker CB is controlled to an open state (open state) or a closed state (not an open state) by the converter control device 20 described later. In the open state (open state), the AC circuit breaker CB is controlled to the off state or the cutoff state, and in the closed state (not the open state), the AC circuit breaker CB is turned on or in the conductive state. It is to be controlled. The AC circuit breaker CB connects the AC system and the power converter 10 in the closed state, and shuts off the AC system and the power converter 10 in the open state. The power converter 10 mutually converts AC power and DC power based on the control of the converter control device 20. The power converter 10 is, for example, a modular multilevel converter (hereinafter, MMC: Modular Multilevel Converter). FIG. 2 is a diagram showing an example of the configuration of the power converter 10 of the embodiment. The power converter 10 includes a plurality of leg LGs between the positive electrode of the DC system (terminal P shown) and the negative electrode of the DC system (terminal N shown). The number of leg LGs corresponds to, for example, the number of phases of AC power supplied by the AC system. In the present embodiment, the AC system supplies three-phase, three-wire AC power of the first phase (R phase shown in the figure), the second phase (S phase shown in the figure), and the third phase (T phase shown in the figure). Therefore, the power converter 10 includes a leg LGr corresponding to the R phase, leg LGs corresponding to the S phase, and a leg LGt corresponding to the T phase. In the following description, when the leg LGr, the leg LGs, and the leg LGt are not distinguished from each other, they are collectively referred to as "leg LG".

A certain phase of the three phases of AC power supplied by the AC system is connected to the leg LG via the transformer TR. Specifically, the R phase is connected to the leg LGr, the S phase is connected to the leg LGs, and the T phase is connected to the leg LGt. In the following description, the connection point between the leg LGr and the R phase is described as the connection point CPr, the connection point between the leg LGs and the S phase is described as the connection point CPs, and the connection between the leg LGt and the T phase is described. The point is referred to as a connection point CPt. In the following description, when the connection point CPr, the connection point CPs, and the connection point CPt are not distinguished from each other, they are simply described as the connection point CP.

Further, in the following description, the portion having the same potential as the terminal P of the DC voltage output by the power converter 10 is also described as the terminal P of the leg LG, and the portion having the same potential as the terminal N of the DC voltage is described. It is also described as the terminal N of the leg LG. Further, the area from the terminal P of the leg LG to the connection point of each phase is also described as a positive arm unit. Further, the area from the connection point of each phase to the terminal N of the leg LG is also described as a negative arm unit.

Each leg LG has the same configuration as each other. In the following description, the configuration related to the leg LGr is given an "r" at the end of the code, the configuration related to the leg LGs is given an "s" at the end of the code, and the configuration related to the leg LGt is given an "s". , Add "t" to the end of the code. Further, when it is not possible to distinguish which leg LG has the configuration, "r", "s", or "t" is omitted. Hereinafter, the leg LGr will be described on behalf of each leg LG.

The leg LGr has n cell CLs (cells CL1-1r to CL1-nr and cells CL2-1r to CL2-nr shown in the figure) and a plurality of reactors in the positive arm unit and the negative arm unit, respectively. It is provided with an RT (reactors RT1r and RT2r shown). n is a natural number. The cells CL1-1r to CL1-nr and the reactor RT1r are connected in series to the positive arm unit of the leg LGr from the terminal P toward the connection point CPr in the order described. Further, to the negative arm unit of the leg LGr, the reactor RT2r and the cells CL2-1r to CL2-nr are connected in series in the order described from the connection point CPr toward the terminal N. The reactor RT and the transformer TR may be replaced with a transformer having a special winding structure having a leakage reactance that only replaces the function of the reactor.

The leg LGr includes a current detector (not shown) that detects the positive arm current (shown, R-phase positive current Ipr) flowing from the connection point CP to the terminal P, and a negative current flowing from the terminal N to the connection point CP. A current detector (not shown) for detecting the side arm current (R-phase negative side current Inr (not shown)) may be provided.

[About cell CL]
FIG. 3 is a diagram showing an example of the configuration of the cell CL. The cell CL is, for example, a half-bridge circuit. As shown in FIG. 3, the cell CL includes, for example, a plurality of switching elements Q (switching elements Q1 to Q2 shown), a number of diodes D (diodes D1 to D2 shown) corresponding to the switching element Q, and a capacitor. It has C. The switching element Q is, for example, an insulated gate bipolar transistor (hereinafter, IGBT: Insulated Gate Bipolar Transistor). However, the switching element Q is not limited to the IGBT. The switching element Q may be any self-extinguishing switching element capable of realizing a converter or an inverter. In this embodiment, a case where the switching element Q is an IGBT will be described.

The switching element Q1 and the switching element Q2 are connected in series with each other. The switching element Q1 and the switching element Q2 and the capacitor C are connected in parallel with each other. Each switching element Q and the diode D are connected in parallel with each other. Specifically, the switching element Q1 and the diode D1 are connected in parallel with each other, and the switching element Q2 and the diode D2 are connected in parallel with each other.

In FIG. 3, the cell CL includes a positive electrode terminal connected to the terminal P side of the leg LG and a negative electrode terminal connected to the terminal N side. The positive electrode terminal of the cell CL is connected to the connection point between the switching element Q1 and the switching element Q2, and the negative electrode terminal of the cell CL is connected to the emitter terminal of the switching element Q2. In the following description, the voltage generated between the positive electrode terminal and the negative electrode terminal of the cell CL will be referred to as the cell voltage Vcl.

Each switching element Q is provided with a switching terminal (not shown) for switching on / off of the switching element Q, and the switching terminal is connected to the converter control device 20 to input a control signal. Specifically, the first gate signal gtp is input to the switching element Q1 as a control signal, and the second gate signal gtn is input to the switching element Q2 as a control signal. By switching each switching element Q on or off based on the control signal, the capacitor C included in the cell CL is charged or discharged. Further, the cell CL is provided with a voltage detector (not shown) that detects the capacitor voltage Vc, which is the voltage of the capacitor C.

When the control signal for turning on the switching element Q is expressed as "1" and the control signal for turning off the switching element Q is expressed as "0", the cell voltage Vcl is when (gtp, gtn) = (1, 0). , It corresponds to the capacitor voltage Vc, and when (gtp, gtn) = (0, 1), it is 0 [V]. By switching the switching element Q included in each leg LG in this way, a multi-level waveform can be generated.

It should be noted that setting the switching element Q to (gtp, gtn) = (1, 1) is prohibited because the capacitor C is short-circuited. Further, in order to prevent the switching element Q from transiently (gtp, gtn) = (1, 1) during switching, the switching element Q is usually transiently (gtp, gtn) for a very short time. It is controlled to the state (dead time) of = (0, 0). However, the time during which the switching element Q is controlled to the state (dead time) of (gtp, gtn) = (0, 0) is sufficiently shorter than the switching cycle, and thus is omitted from the following description. .. Further, when the switching control of the switching element Q is stopped, it is realized by fixing it in the state of (gtp, gtn) = (0,0). In the following description, a state in which the first gate signal gtp and the second gate signal gtn are fixed at (gtp, gttn) = (0, 0) is also described as a gate block state.

[About the converter control device 20]
Returning to FIG. 1, the converter control device 20 includes a control unit 200 and a gate signal generation unit 300. In the control unit 200, for example, a hardware processor such as a CPU (Central Processing Unit) executes a program (software) stored in a storage unit (not shown) to execute an AC information calculation unit 210 and a first filter 220. The second filter 222, the third filter 224, the voltage command value calculation unit 230, the gate command unit 240, and the circuit breaker control unit 250 are realized as functional units. In addition, some or all of these components are hardware (circuits) such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), GPU (Graphics Processing Unit), etc. It may be realized by the part (including circuitry), or it may be realized by the cooperation of software and hardware.

The AC information calculation unit 210 acquires information indicating the voltage (R-phase voltage Vr, S-phase voltage Vs, and T-phase voltage Vt shown in the figure) detected by the detector CS that detects the voltage of each phase of the AC system. , The AC system active voltage Vd and the AC system invalid voltage Vq are calculated based on the acquired information. Further, the AC information calculation unit 210 repeats the calculation so that the calculated value of the AC system invalid voltage Vq becomes zero as a calculation for following and synchronizing the AC system voltage. As a result, the AC information calculation unit 210 calculates the AC frequency fpll and the AC system voltage phase theta. The AC frequency fpl is the frequency of the AC system voltage to which the power converter 10 is connected. Further, the AC system voltage phase theta is a value indicating the phase of a reference phase having the AC voltage. The details of the processing of the AC information calculation unit 210 will be described later.

The first filter 220 performs the first filter processing (one of the filter processing) on the absolute value of the AC system active voltage Vd calculated by the AC information calculation unit 210, and outputs the value Vdf1. Further, the first filter 220 performs the first filter processing on the AC system invalid voltage Vq calculated by the AC information calculation unit 210, and acquires the value Vqf1. The first filter 220 is, for example, a general low-pass filter that removes high-frequency components while passing low-frequency components contained in the AC system active voltage Vd and the AC system invalid voltage Vq, and a specific frequency. It is realized by a band removal filter that removes a band, or a combination of a low frequency pass filter and a band removal filter.

The second filter 222 performs the second filter processing (one of the filter processing) on the absolute value of the AC system active voltage Vd calculated by the AC information calculation unit 210, and outputs the value Vdf2. For example, a general low-pass filter or the like can be applied to the second filter 222.

The third filter 224 performs a third filter process (one of the filter processes) on the absolute value of the AC system active voltage Vd calculated by the AC information calculation unit 210, and outputs the value Vdf3. The third filter 224 applies, for example, a general low-pass filter.

The second filter 222 and the third filter 224 are designed so that the time constant of the second filter 222 is at least shorter than the time constant of the third filter 224. Designing the time constant to be short includes the case where the input is output as it is without the second filter processing and the AC system effective voltage Vd is output as the value Vdf2.

The time constant of the first filter 220 is designed independently of the time constant of the second filter 222 and the time constant of the third filter 224. Further, the third filter processing of the first filter 220, the second filter 222, and the third filter 224 may be a digital filter that realizes the passing characteristics of a desired frequency component by software, or parts such as an operational amplifier and a capacitor. May be used in combination as an analog filter realized by hardware. Further, the band-stop filter may be introduced for the purpose of removing the influence of a specific harmonic when the generation of a specific harmonic becomes large due to the conditions of the interconnected AC system. In the band removal filter, the filter constant is designed according to the frequency band to be removed and the removal level thereof.

Here, the normal AC system voltage may include harmonic components such as 5 times or 7 times the rated frequency in addition to the rated frequency of 50 [Hz] or 60 [Hz]. In addition, when an AC system accident occurs, the amplitude including the rated frequency may change suddenly. If the time constant of the first filter 220 is long, the response of the current control to these harmonics and fluctuations is delayed, which makes it difficult for the power converter to operate stably, which may lead to protection stoppage or failure. Therefore, the time constant of the first filter 220 is appropriately designed so as not to be in an unstable operating state due to noise or the like while having the required current control performance.

The voltage command value calculation unit 230 is calculated by the AC information calculation unit 210 and each state of the power converter 10 (for example, the positive side currents Ipr to Ipt, the negative side currents Inr to Int, and each capacitor voltage Vc). Based on the AC system voltage phase theta, the value Vdf1 acquired by the first filter 220, and the value Vqf1, the active power PE output by the power converter 10 and the active power QE are predetermined active powers. The cell voltage command value Vcl * that indicates the cell voltage Vcl of each cell CL is calculated so that the command value PE * and the ineffective power command value QE * are obtained.

Here, the voltage command value calculation unit 230 has an AC system active voltage Vd that becomes a substantially constant value (DC component) and an AC system invalid voltage Vq that becomes almost zero in the case of a sinusoidal wave in which the AC system voltage is stable. Based on the above, the voltage command value to be output by the power converter 10 is calculated so that the active power PE output by the power converter 10 and the ineffective power QE match the predetermined set values. At this time, it is preferable to calculate the voltage command value to be output by the power converter 10 based on the AC system active voltage Vd from which the noise that causes disturbance is removed and the AC system invalid voltage Vq. The voltage command value calculation unit 230 has a value Vdf1 and a value output by the first filter 220 after removing high-frequency noise while passing low-frequency components such as the DC component of the AC system active voltage Vd and the AC system invalid voltage Vq. Based on Vqf1, the voltage command value to be output by the appropriate power converter 10 is calculated.

The gate command unit 240 causes the gate signal generation unit 300 to output the gate block command signal GB to all the cell CLs of the power converter 10 based on the value Vdf2 output by the second filter 222. The conditions for the gate command unit 240 to output the gate block command signal GB will be described later.

The circuit breaker control unit 250 outputs the circuit breaker open command signal CBT based on the value Vdf3 output by the third filter 224. The AC circuit breaker CB is controlled to the open state when the circuit breaker open command signal CBT is output by the converter control device 20. Hereinafter, controlling the AC circuit breaker CB in the open state by the converter control device 20 is also described as "opening the AC circuit breaker CB". The conditions for the circuit breaker control unit 250 to output the circuit breaker open command signal CBT will be described later.

The gate signal generation unit 300 generates a first gate signal gtp and a second gate signal gttn for each cell CL based on the cell voltage command value Vcl * of each cell CL calculated by the voltage command value calculation unit 230. , Output to the power converter 10.

Hereinafter, the processing contents of each part included in the converter control device 20 will be described.

[About AC information calculation unit 210]
FIG. 4 is a diagram schematically showing an example of processing of the AC information calculation unit 210 of the embodiment. The AC information calculation unit 210 includes a conversion unit 211, a PI calculation unit 212, an addition unit 213, and an oscillator 214 as functional units.

The conversion unit 211 acquires information indicating the voltage detected by the detector CS (R-phase voltage Vr, S-phase voltage Vs, and T-phase voltage Vt shown). The conversion unit 211 converts (calculates) the acquired R-phase voltage Vr, S-phase voltage Vs, and T-phase voltage Vt into AC system effective voltage Vd and AC system invalid voltage Vq using the equation (1). .. The AC system voltage phase theta is a value output by the oscillator 214 described later, and is a value indicating the voltage phase of a reference phase (R phase in this example) of the AC system.

The PI calculation unit 212 has a frequency difference (hereinafter, frequency) between the frequency of the AC system voltage to which the power converter 10 is connected and the reference AC system frequency fs0 based on the AC system invalid voltage Vq converted by the conversion unit 211. The difference Δfpll) is calculated. The frequency difference Δfpll takes a positive value when the frequency of the AC system voltage is higher than the reference AC system frequency fs0, and takes a negative value when the frequency is lower than the reference AC system frequency fs0. The reference AC system frequency fs0 is the rated frequency of the interconnected AC system, and is, for example, a constant of 50 [Hz] or 60 [Hz]. The frequency difference Δfpll continues to increase or decrease until the calculated value of the AC system invalid voltage Vq input to the PI calculation unit 212 becomes zero, and is the value of the difference between the actual AC system frequency and the reference AC system frequency fs0. Converges to.

The addition unit 213 adds the frequency difference Δfpll calculated by the PI calculation unit 212 to the reference AC system frequency fs0.

The oscillator 214 outputs an AC system voltage phase theta that repeatedly and monotonically increases from a minimum value of 0 to a maximum value of 2π according to the frequency of the AC frequency fpll calculated by the addition unit 213. As described above, the AC system voltage phase theta is used for converting the AC system effective voltage Vd and the AC system invalid voltage Vq of the conversion unit 211 and generating the cell voltage command value Vcl *.

By the above processing, the AC information calculation unit 210 repeats the calculation of the AC system voltage phase theta so that the calculated value of the AC system invalid voltage Vq in the conversion unit 211 becomes zero, so that the AC is synchronized with the AC system voltage. The frequency fpll and the AC system voltage phase theta are calculated.

If the state of the AC system becomes unstable and the frequency difference Δfpll fluctuates outside the normal range, the power converter 1 may not be able to operate stably. In order to prevent this, the PI calculation unit 212 sets the frequency difference Δfpll to + limit value Δfpll_limit when the frequency difference Δfpll is larger than the limit value (hereinafter, limit value Δfpll_limit), and when it is smaller than the-limit value Δfpll_limit, the frequency difference Δfpll may be output as a −limit value Δfpll_limit. In this case, the addition unit 213 can limit the AC frequency fpl to a frequency in the range of the reference AC system frequency fs0 + limit value Δfpll_limit to the reference AC system frequency fs0-limit value Δfpll_limit. The limit value Δfpll_limit is, for example, a positive value smaller than the reference AC system frequency fs0.

[About Gate Command Unit 240]
FIG. 5 is a diagram schematically showing an example of processing of the gate command unit 240 of the embodiment. The gate command unit 240 includes a first comparator 242 and a timer 244 as functional units. The first comparator 242 compares the value Vdf2 output by the second filter 222 with the predetermined AC system voltage upper limit value Vth_H and the AC system voltage lower limit value Vth_L. The AC system voltage upper limit value Vth_H is, for example, the maximum value of the AC voltage of the AC system in which the power converter 10 can continue operation without impairing the stability of the voltage and frequency of the AC system. Further, the lower limit value Vth_L of the AC system voltage is, for example, the minimum value of the AC voltage of the AC system in which the power converter 10 can continue operation without impairing the stability of the voltage and frequency of the AC system. The AC system voltage upper limit value Vth_H is an example of the “first threshold value”. Further, the AC system voltage lower limit value Vth_L is an example of the "second threshold value".

The first comparator 242 outputs a system voltage abnormality signal ERR when the value Vdf2 is larger than the AC system voltage upper limit value Vth_H or when the value Vdf2 is smaller than the AC system voltage lower limit value Vth_L. When the value Vdf2 is larger than the AC system voltage upper limit value Vth_H or smaller than the AC system voltage lower limit value Vth_L, for example, a system accident occurs in the AC system and the amplitude of each phase voltage of the AC system is an abnormal value. Is shown, or the phases are unbalanced.

The first comparator 242 compares the combined voltage vector Vdqf2 calculated using the equation (2) with a predetermined threshold value, and when the value of the combined voltage vector Vdqf2 is larger than the predetermined upper limit threshold value, or a predetermined value. When it is smaller than the lower limit threshold value, the system voltage abnormality signal ERR may be output. However, Vqf2 is a value obtained by subjecting the AC system invalid voltage Vq to the second filter processing of the second filter 222.

When the system voltage abnormality signal ERR is output by the first comparator 242, the timer 244 outputs the gate block command signal GB only for a predetermined period TM1 after the system voltage abnormality signal ERR is output. The predetermined period TM1 is set to, for example, a time of about several AC cycles in which AC system accidents are generally eliminated. The predetermined period TM1 is an example of a “predetermined period” in which counting is started after the gate block command signal GB is output.

[About the circuit breaker control unit 250]
FIG. 6 is a diagram schematically showing an example of processing of the circuit breaker control unit 250 of the embodiment. The circuit breaker control unit 250 includes a comparator 252 as a functional unit. The comparator 252 compares the value Vdf3 with a predetermined circuit breaker open threshold V_CBT. The circuit breaker open threshold V_CBT cuts off the AC system and the power converter 10 (that is, the power converter 10) in order to suppress the failure of the power converter 10 due to the influence of an abnormality such as an AC system accident. This is the maximum value of the AC voltage of the AC system when it is required to protect. The circuit breaker opening threshold V_CBT is an example of a “third threshold”.

The comparator 252 outputs a circuit breaker opening command signal CBT when the absolute value of the value Vdf3 is larger than the circuit breaker opening threshold value V_CBT. When the value Vdf3 is larger than the circuit breaker open threshold value V_CBT, for example, a system accident occurs in the AC system, the amplitude of each phase voltage of the AC system shows an abnormal value, or the phases are unbalanced. It is in a state. The circuit breaker open threshold value V_CBT is set to a value larger than the AC system voltage upper limit value Vth_H.

The comparator 252 compares the combined voltage vector Vdqf3 calculated using the equation (3) with a predetermined threshold value, and when the value of the combined voltage vector Vdqf3 is larger than the predetermined threshold value, sets the circuit breaker opening threshold value V_CBT. It may be configured to output. However, the value Vqf3 is a value obtained by subjecting the AC system invalid voltage Vq to the third filter processing of the third filter 224.

The AC circuit breaker CB is controlled to the open state when the circuit breaker open threshold value V_CBT is input, and shuts off (disconnects) the AC system and the power converter 10. This is because when the AC system voltage rises outside the normal range and exceeds a certain value, the capacitor C of each cell CL included in the power converter 10 is overcharged exceeding the voltage withstand capacity of the cell CL. This is to prevent. When the power converter 10 is in the gate block state, assuming that the line voltage on the secondary side (arm unit side) of the transformer TR, which is proportional to the AC system voltage, is voltage Vs2 and the number of cell CL series for each arm unit is n. The capacitor C is overcharged to the capacitor voltage Vc shown in the equation (4).

That is, the capacitor voltage Vc is overcharged in proportion to the AC system voltage. If the AC system voltage becomes even larger than the circuit breaker open threshold value V_CBT and the capacitor voltage Vc exceeds the voltage withstand voltage of the cell CL, the cell CL may fail. In order to prevent this, the AC circuit breaker CB is opened to cut off the AC system from the power converter 10.

[Operation when an abnormality occurs: Conventional power converter]
FIG. 7 is a diagram showing an example of the operation of the conventional power conversion device. The waveform W11 is a waveform showing a change over time in the active power that the conventional power conversion device accommodates in the AC system or the DC system. Hereinafter, the value of the active power interchanged by the conventional power converter and the power converter 10 shows a positive value when the active power is interchanged from the AC system side to the DC system side, and is AC from the DC system side. When the active power is accommodated on the grid side, it shall show a negative value. In the following description, the active power accommodated by the conventional power converter or the power converter 10 is also simply referred to as "active power". The waveform W12 is a waveform showing a change over time in the absolute value of the AC system active voltage Vd. The waveform W13 is a waveform indicating the presence or absence of output of the gate block command signal GB. The waveform W14 is a waveform indicating the presence / absence of output of the circuit breaker opening command signal CBT.

As the waveform W11 shows, the active power is stable at a constant value (-1.0 [pu] in the figure) until time t0. As shown by the waveform W12, the absolute value of the AC system active voltage Vd is a constant value (1.0 [pu] in the figure) until time t0. Further, as the waveform W13 shows, the gate block command signal GB is not output until time t0 (that is, it is invalid), and as the waveform W14 shows, the circuit breaker open command signal CBT is at time t0. Until then, it has not been output (that is, it is invalid). Therefore, the conventional power converter is not interrupted by the AC circuit breaker CB, and the switching control is continued and the power is interchanged based on the control of the converter control device 20.

Hereafter, it is assumed that an abnormality occurs at time t0. This abnormality occurs, for example, when another power converter that supplies active power to the conventional power converter suddenly stops during the operation of the power converter 10.

As the waveform W11 shows, when an abnormality occurs in which another power converter stops, the active power decreases sharply. The active power becomes almost 0 [pu] between the time t0 and the time t2, for example.

As the waveform W12 shows, the absolute value of the AC system active voltage Vd decreases as the active power accommodated by the conventional power conversion device decreases. This is because the decrease in active power becomes a disturbance, and the same function as the voltage command value calculation unit 230 of the conventional power conversion device cannot be optimally operated. Further, as shown by the waveform W12, at time t1, the absolute value of the AC system effective voltage Vd is smaller than the AC system voltage lower limit value Vth_L. Therefore, as shown in the waveform W13, the gate command unit 240 outputs the gate block command signal GB from time t1.

The power converter 10 is controlled to the gate block state in response to the output of the gate block command signal GB by the gate command unit 240. Along with this, as shown by the waveform W12, the absolute value of the AC system active voltage Vd rises sharply and exceeds the circuit breaker opening threshold value V_CBT. Therefore, as shown by the waveform W14, the circuit breaker control unit 250 outputs the circuit breaker opening command signal CBT, the circuit breaker CB is opened, and the conventional power conversion device is cut off from the AC system. When the AC circuit breaker CB is opened, the operation cannot be restarted at least until the AC circuit breaker CB is turned on again. Further, since the opening of the AC circuit breaker CB is generally recognized as a serious failure in which the power converter 10 cannot be connected, the AC circuit breaker CB is not automatically turned on again, and confirmation by the operator may be required. As described above, if the power converter 10 is stopped for a long period of time, the stability of the voltage and frequency of the AC system may be impaired, and the power supply may be stopped in a wide range.

As described above, a series of events in which the absolute value of the AC system active voltage Vd decreases as the active power decreases, and then the absolute value of the AC system active voltage Vd rises sharply as the gate block state is switched. Is caused by the fact that the voltage of the AC system fluctuates greatly due to the response of the power converter 10, and is particularly likely to occur when the scale of the AC system to be connected is small and the short-circuit capacity is small. When the short-circuit capacitance is small, the back impedance on the upper side of the system from the interconnection point to the generator is large, so that the voltage of the AC system at the interconnection point is easily affected by the output voltage fluctuation of the power converter 10. Conventionally, the large-capacity power converter 10 has been connected to a backbone system having a large short-circuit capacity, but in the future, with the increase in the introduction of renewable energy, small-scale generator groups and the like will be connected. It may be connected to a small system. In this case, it is expected that the phenomenon in which the absolute value of the AC system active voltage Vd rises sharply becomes more apparent as the gate block state is switched to as described above. Therefore, in the conventional power conversion device, the power supply may be stopped in a wide range.

[Operation when an abnormality occurs: Power converter 1]
FIG. 8 is a diagram showing an example of the operation of the power conversion device 1 of the present embodiment. The waveform W21 is a waveform showing a time-dependent change in the active power that the power conversion device 1 accommodates in the AC system or the DC system. The waveform W22 is a waveform showing a time-dependent change in the value Vdf3 output by the third filter 224. In FIG. 8, the waveform W22 is shown superimposed on the waveform W12. The waveform W23 is a waveform indicating the presence or absence of output of the gate block command signal GB. The waveform W24 is a waveform indicating the presence / absence of output of the circuit breaker opening command signal CBT.

Waveforms W21 to W24 show the same changes as the above-mentioned waveforms W11 to W14 until time t0.

As the waveform W21 shows, when an abnormality occurs in which another power converter stops at time t0, the active power sharply decreases. The active power becomes almost 0 [pu] between the time t0 and the time t2, for example.

As the waveform W22 shows, the value Vdf3 decreases as the active power accommodated by the power converter 1 decreases, and becomes a value smaller than the lower limit value Vth_L of the AC system voltage at time t1'. Here, as shown by the waveform W22, since the high frequency component is removed from the value Vdf3 as compared with the absolute value of the AC system active voltage Vd indicated by the waveform W21, the time t1'is at the same time as the time t1 or It is a time after the time t1. As shown in the waveform W23, the gate command unit 240 outputs the gate block command signal GB from the time t1'.

The power converter 10 is controlled to the gate block state in response to the output of the gate block command signal GB by the gate command unit 240. Along with this, as the waveform W22 shows, the value Vdf3 does not rise sharply like the absolute value of the AC system active voltage Vd due to the third filter processing of the third filter 224, so that the circuit breaker open threshold value V_CBT even instantaneously. Does not exceed. Therefore, the circuit breaker control unit 250 does not output the circuit breaker opening command signal CBT, and the AC circuit breaker CB is not opened. In this case, after the abnormality is resolved, the power conversion device 1 can restart the operation only by releasing the gate block command signal GB and without turning on the AC circuit breaker CB again.

[Operation flow]
FIG. 9 is a flowchart showing an example of processing related to the generation of the first gate signal gtp and the second gate signal gtt of the power conversion device 1 of the present embodiment. The flowchart shown in FIG. 9 is executed, for example, constantly or repeatedly at predetermined time intervals. First, the AC information calculation unit 210 acquires information indicating the voltage of each phase of the AC system (R phase voltage Vr, S phase voltage Vs, and T phase voltage Vt) from the detector CS (step S100). The AC information calculation unit 210 converts the acquired AC system effective voltage Vd and AC system invalid voltage Vq based on the acquired voltage of each phase of the AC system (step S102). Next, the first filter 220 performs the first filter processing on the absolute values of the AC system active voltage Vd and the AC system invalid voltage Vq calculated by the AC information calculation unit 210, and outputs the values Vdf1 and the value Vqf1. (Step S104).

Next, the voltage command value calculation unit 230 calculates each state of the power converter 10 (for example, the positive side currents Ipr to Ipt, the negative side currents Inr to Int, and each capacitor voltage Vc) and the AC information calculation unit 210. Based on the AC system voltage phase theta, the value Vdf1 acquired by the first filter 220, and the value Vqf1, the active power PE output by the power converter 10 and the active power QE are predetermined. The cell voltage command value Vcl * that indicates the cell voltage Vcl of each cell CL is calculated so that the active power command value PE * and the ineffective power command value QE * are obtained (step S106). Next, the gate signal generation unit 300 sets the first gate signal gtp and the second gate signal gttn for each cell CL based on the cell voltage command value Vcl * of each cell CL calculated by the voltage command value calculation unit 230. Is generated and output to the power converter 10 (step S108).

FIG. 10 is a flowchart showing an example of processing related to the output of the gate block command signal GB of the power conversion device 1 of the present embodiment. The flowchart shown in FIG. 10 is executed, for example, constantly or repeatedly at predetermined time intervals. First, the AC information calculation unit 210 acquires information indicating the voltage of each phase of the AC system (R phase voltage Vr, S phase voltage Vs, and T phase voltage Vt) from the detector CS (step S200). The AC information calculation unit 210 converts the acquired AC system effective voltage Vd based on the voltage of each phase of the AC system (step S202). Next, the second filter 222 performs the second filter processing on the absolute value of the AC system active voltage Vd calculated by the AC information calculation unit 210, and outputs the value Vdf2 (step S204).

Next, the gate command unit 240 determines whether or not the value Vdf2 output by the second filter 222 exceeds (exceeds) the AC system voltage upper limit value Vth_H (step S206). When the gate command unit 240 determines that the value Vdf2 exceeds the AC system voltage upper limit value Vth_H, the gate command unit 240 outputs the gate block command signal GB (step S208). When the gate command unit 240 determines that the value Vdf2 does not exceed the AC system voltage upper limit value Vth_H, the gate command unit 240 determines whether or not the value Vdf2 is lower than the AC system voltage lower limit value Vth_L (step S210). When the gate command unit 240 determines that the value Vdf2 is lower than the AC system voltage lower limit value Vth_L, the gate command unit 240 outputs the gate block command signal GB (step S208). When the value Vdf2 is equal to or less than the AC system voltage upper limit value Vth_H and not more than or equal to the AC system voltage lower limit value Vth_L, the gate command unit 240 does not output the gate block command signal GB and ends the process.

FIG. 11 is a flowchart showing an example of processing related to the output of the circuit breaker opening command signal CBT of the power conversion device 1 of the present embodiment. The flowchart shown in FIG. 11 is executed, for example, constantly or repeatedly at predetermined time intervals. First, the AC information calculation unit 210 acquires information indicating the voltage of each phase of the AC system (R phase voltage Vr, S phase voltage Vs, and T phase voltage Vt) from the detector CS (step S300). The AC information calculation unit 210 converts the acquired AC system effective voltage Vd based on the acquired voltage of each phase of the AC system (step S302). Next, the third filter 224 performs the third filter processing on the absolute value of the AC system active voltage Vd calculated by the AC information calculation unit 210, and outputs the value Vdf3 (step S304).

Next, the circuit breaker control unit 250 determines whether or not the value Vdf3 output by the third filter 224 exceeds (exceeds) the circuit breaker opening threshold value V_CBT (step S306). When the circuit breaker control unit 250 determines that the value Vdf3 exceeds the circuit breaker opening threshold value V_CBT, the circuit breaker control unit 250 outputs the circuit breaker opening command signal CBT (step S308). When the circuit breaker control unit 250 determines that the value Vdf3 does not exceed the circuit breaker opening threshold value V_CBT, the circuit breaker control unit 250 ends the process.

[Summary of Embodiment]
As described above, the power conversion device 1 of the present embodiment is an AC circuit breaker based on the value Vdf3 obtained by applying the third filter processing of the third filter 224, which is a low-pass filter, to the AC system active voltage Vd. Determine the necessity of opening the CB. As a result, the power conversion device 1 of the present embodiment prevents the unnecessary AC circuit breaker CB from being opened due to the instantaneous system overvoltage caused by the gate block of the cell CL, and shortens the time required for restarting the operation. It is possible to improve the continuity of operation in the event of a system accident.

Further, in the power conversion device 1 of the present embodiment, when a system overvoltage for a relatively long time exceeding the settling time constant of the third filter 224 occurs, the value Vdf3 output by the third filter 224 opens the circuit breaker. Since the threshold value V_CBT is exceeded, the AC circuit breaker CB can be opened. As a result, the power conversion device 1 of the present embodiment can prevent the capacitor voltage Vc from exceeding the withstand voltage of the cell CL as the capacitor C of the cell CL is overcharged.

Further, the power converter 1 of the present embodiment determines the gate block of the power converter 10 based on the value Vdf2 obtained by subjecting the AC system active voltage Vd to the processing of the second filter 222. The processing of the second filter 222 is independent of the processing of the third filter 224, and the time constant of the second filter 222 is shorter than the time constant of the third filter 224, or the AC system input as the value Vdf2. The effective voltage Vd is directly output. Therefore, in the power converter 1 of the present embodiment, when an abnormality occurs in the system voltage, the value Vdf2 immediately responds, the power converter 10 shifts to the gate block state, and the capacitor voltage Vc becomes normal. It is possible to suppress a state in which the operation cannot be maintained within the operable range and a state in which the operation of the power converter 10 is stopped due to a sudden change in the converter current (positive side current Ip or negative side current In). In particular, since the converter current has a shorter response time constant than the capacitor voltage Vc, the power converter 1 of the present embodiment immediately shifts to the gate block state when an abnormality occurs in the system voltage. As a result, the current can be cut off and the operation of the power converter 10 can be suppressed more appropriately.

Further, the power converter 1 of the present embodiment is a power converter based on the value Vdf1 and the value Vqf1 obtained by subjecting the AC system active voltage Vd and the AC system invalid voltage Vq to the first filter processing of the first filter 220. 10 voltage and current are controlled. The first filter processing of the first filter 220 is independent of the second filter processing of the second filter 222 and the third filter processing of the third filter 224. Therefore, the power conversion device 1 of the present embodiment has the required control performance, and the first filter 220 is designed with arbitrary characteristics so as not to cause an unstable operating state due to noise or the like. Stable operation can be performed even when the AC system voltage contains harmonic components or when an AC system accident occurs and the amplitude of the AC system voltage suddenly changes.

From the above, the power converter 1 of the present embodiment can suppress the opening of the AC circuit breaker CB which does not contribute to the protection of the power converter 10 while maintaining the operation performance at the time of normal operation and system accident without impairing the operation performance. , It is possible to improve the continuity of operation in the event of a system accident.

(Modification example 1)
Hereinafter, the processing of the third filter 224 of the first modification will be described with reference to the drawings. In the embodiment, the third filter 224 is a general low-pass filter, and the case where the AC system active voltage Vd outputs the value Vdf3 obtained by removing the momentary overvoltage signal at the time of the gate block has been described. In the third filter 224 of the first modification, a case where the momentary overvoltage signal is algorithmically removed will be described. The same components as those in the above-described embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 12 is a diagram showing an example of the processing operation of the third filter 224 of the modified example 1. The waveform W41 is a waveform showing an example of the time-dependent change of the AC system active voltage Vd. The waveform W42 is a waveform showing another example of the change with time of the AC system active voltage Vd. The waveform W43 is a waveform showing an example of the time-dependent change of the value Vdf3. The waveform W44 is a waveform showing another example of the change with time of the value Vdf3. The waveform W42 and the waveform W44 are waveforms related to the first event, and the waveforms W41 and W43 are waveforms related to the second event.

The third filter 224 of the first modification has a circuit breaker open threshold V_CBT when the AC system active voltage Vd does not exceed the circuit breaker open threshold V_CBT, or when the AC system active voltage Vd is m or more in the number of times the third filter process is executed. Is continuously exceeded, the AC system active voltage Vd is output as the value Vdf3, and the AC system active voltage Vd exceeds the circuit breaker open threshold V_CBT m times or more in the number of executions of the third filter processing (that is,). (Up to m-1 times) outputs the AC system active voltage Vd (hereinafter, the previous value effective voltage Vd _t-1 ) immediately before exceeding the circuit breaker opening threshold V_CBT as the value Vdf3. The third filter 224 repeatedly executes the third filter process every predetermined period Td. Here, m is set so that the time indicated by m × predetermined period Td is 1 or more and shorter than the time during which the capacitor C is overcharged. Hereinafter, the case where m = 3 will be described.

First, the case of the first event will be described. As shown by the waveform W42, the AC system active voltage Vd is below the circuit breaker open threshold value V_CBT until time t11, exceeds the circuit breaker open threshold value V_CBT from time t12 to time t13, and again after time t14. It is below the circuit breaker opening threshold V_CBT.

In this case, although the AC system active voltage Vd exceeds the circuit breaker opening threshold value V_CBT at time t12, the state of exceeding the AC system active voltage Vd does not continue three times or more in the number of executions of the third filter processing (time t12 is 1). The second time.). Therefore, as shown in the waveform W44, the third filter 224 outputs the AC system effective voltage Vd (that is, the previous value effective voltage Vd _t-1 ) at the time t11 as the value Vdf3 at the time t12.

Further, although the AC system active voltage Vd exceeds the circuit breaker opening threshold value V_CBT at time t13, the state of exceeding the AC system active voltage Vd does not continue three times or more in the number of executions of the third filter processing (time t13 is the second time). Therefore, as shown in the waveform W44, the third filter 224 outputs the previous value effective voltage Vd _t-1 again as the value Vdf3 at the time t13.

Further, since the AC system active voltage Vd does not exceed the circuit breaker open threshold value V_CBT after the time t14, the third filter 224 outputs the AC system active voltage Vd as the value Vdf3.

Next, the case of the second event will be described. As shown by the waveform W41, the AC system active voltage Vd is below the circuit breaker opening threshold value V_CBT until time t11, and exceeds the circuit breaker opening threshold value V_CBT after time t12.

In this case, as shown by the waveform W43, the third filter 224 outputs the previous value effective voltage Vd _t-1 as the value Vdf3 during the time t12 to t13, as in the first event.

Further, after the time t14, the AC system active voltage Vd exceeds the circuit breaker opening threshold value V_CBT, and the state of exceeding the breaker opening threshold value V_CBT continues three times or more in the number of executions of the third filter processing (time t14 is the third time. ). Therefore, as shown by the waveform W43, the third filter 224 outputs the AC system active voltage Vd as the value Vdf3 after the time t14.

[Summary of Modification 1]
As described above, the third filter 224 according to the power conversion device 1 of the modification 1 removes the overvoltage signal exceeding the instantaneous circuit breaker opening threshold value V_CBT less than the preset number of executions m × predetermined period Td. , Output to the circuit breaker control unit 250. As a result, the power converter 1 of the first modification can suppress the opening of the AC circuit breaker CB that does not contribute to the protection of the power converter 10. Further, the third filter 224 according to the power conversion device 1 of the modification 1 is used when a system overvoltage exceeding the circuit breaker opening threshold V_CBT for a relatively long time of preset number of executions m × predetermined period Td or more occurs. Can output the circuit breaker opening command signal CBT to the circuit breaker control unit 250 to suppress overcharging of the capacitor C included in the power converter 10.

Further, the power conversion device 1 of the modification 1 is based on the value Vdf3 obtained by subjecting the AC system active voltage Vd to the processing of the third filter 224 that algorithmically removes the instantaneous overvoltage signal, and is based on the AC circuit breaker CB. Judge open. As a result, the power converter 1 of the modification 1 protects the power converter 10 by an instantaneous system overvoltage or the like in which the charging energy for the capacitor C is small due to the transition of the power converter 10 to the gate block state. It is possible to suppress the opening of the AC circuit breaker CB, which does not contribute to the above, and improve the continuity of operation.

(Modification 2)
Hereinafter, the power conversion device 1 of the modification 2 will be described with reference to the drawings. The case where the circuit breaker control unit 250 of the above-described embodiment and the first modification determines whether or not to output the circuit breaker opening command signal CBT based on the value Vdf3 has been described. A case where the circuit breaker control unit 250 of the second modification determines whether or not to output the circuit breaker opening command signal CBT based on the value Vdf3 and the gate block command signal GB will be described. The same reference numerals are given to the above-described embodiments and the same configurations as those of the modified examples, and the description thereof will be omitted.

FIG. 13 is a diagram showing an example of the configuration of the power conversion device 1 in the modification 2. The power conversion device 1 of the second modification is provided with a circuit breaker control unit 250a instead of the circuit breaker control unit 250. Further, the gate command unit 240 of the second modification outputs the gate block command signal GB to the gate signal generation unit 300 and the circuit breaker control unit 250a.

FIG. 14 is a diagram showing an example of the configuration of the circuit breaker control unit 250a according to the second modification. The circuit breaker control unit 250a includes a comparator 252, a rise detection unit 254, a timer 256, and a logical operation unit 258 as functional units.

The rise detection unit 254 detects whether or not the gate block command signal GB has been output by the gate command unit 240. When the rise detection unit 254 detects that the gate block command signal GB has been output by the gate command unit 240, the rise detection unit 254 outputs a signal indicating the detection to the timer 256.

When a signal indicating that the timer 256 has been detected by the rise detection unit 254 is output, the timer 256 outputs "1" during the predetermined period TM2, and outputs "0" during the other period. The predetermined period TM2 is set to, for example, a sufficient time (for example, about several ms) required for a momentary AC system overvoltage to occur after the gate block command signal GB is output and the system voltage to return to the normal range. To. The predetermined period TM2 is an example of a “predetermined period” in which counting is started after the gate block command signal GB is output.

The logical operation unit 258 calculates the logical product based on the inverted value of the output of the timer 256 and the comparison result of the comparator 252 (breaker open command signal CBT; “1” with output, “0” without output). The calculated and calculated logical product is output as a breaker open command signal CBT (breaker open command signal CBT; “1” with output, “0” without output).

[Summary of Modification 2]
As described above, in the power conversion device 1 of the modification 2, the circuit breaker opening command signal CBT is output by the comparator 252 for a predetermined period TM2 after the gate block command signal GB is output by the gate command unit 240. Even if the circuit breaker control unit 250 is used, the circuit breaker release command signal CBT can be prevented from being output (that is, masked). As described above, in the third filter 224 according to the power conversion device 1 of the modification 2, the circuit breaker open command signal CBT is invalidated during the predetermined period TM2 regardless of the output of the comparator 252. Therefore, the input AC system active voltage Vd may be output as it is as the value Vdf3. As a result, the power converter 1 of the second modification temporarily invalidates the circuit breaker open command signal CBT based on the gate block command signal GB, and the power converter 10 due to the instantaneous system overvoltage caused by the gate block. It is possible to suppress the opening of the AC circuit breaker CB, which does not contribute to the protection of the AC circuit breaker, and improve the continuity of operation.

(Modification 3)
Hereinafter, the power conversion device 1 of the modification 3 will be described with reference to the drawings. In the above-described embodiment and modification, a case where it is determined whether or not to output the circuit breaker opening command signal CBT based on the value Vdf3 and the gate block command signal GB has been described. In the power conversion system of the third modification, among the systems connected to the power conversion device 1, the own device is connected based on the gate block command signal GB output from the other power conversion device 1 connected to the DC side. A case of determining whether or not to output the breaker opening command signal CBT to the AC breaker CB will be described. The same reference numerals are given to the above-described embodiments and the same configurations as those of the modified examples, and the description thereof will be omitted.

FIG. 15 is a diagram showing an example of the configuration of the power conversion system in the modified example 3. In the third modification, the power conversion device 1α and the power conversion device 1β are connected to one end and the other end of the DC system, respectively. The power conversion device 1α is provided at the interconnection point between the first AC system and the DC system, and mutually converts the AC power supplied by the first AC system and the DC power supplied by the DC system. The power conversion device 1β is provided at the interconnection point between the second AC system and the DC system, and mutually converts the AC power supplied by the second AC system and the DC power supplied by the DC system. In the following description, when the power conversion device 1α and the power conversion device 1β are not distinguished from each other, it is simply described as “power conversion device 1”.

The gate command unit 240 according to the power conversion device 1 of the modification 3 converts the gate block command signal GB into the gate signal generation unit 300 and another power conversion device 1 (in this case, the power conversion device 1α to the power conversion device 1β, or Output from the power converter 1β to the power converter 1α). Further, the circuit breaker control unit 250a according to the power conversion device 1 of the modification 3 acquires the gate block command signal GB output by the other power conversion device 1.

The gate block command signal GB output by another power conversion device 1 is input to the rise detection unit 254 of the circuit breaker control unit 250a in the modification 3 instead of the gate command unit 240.

In the above description, the case where the two power conversion devices 1 are connected to one end and the other end of the DC system has been described, but the present invention is not limited to this. The power conversion device 1 may be connected to two or more power conversion devices 1 via a DC system, for example. In this case, the gate block command signal GB output by the gate command unit 240 related to the two or more power conversion devices 1 is input to the rise detection unit 254.

[Summary of Modification 3]
As described above, the power conversion device 1 of the modification 3 temporarily invalidates the breaker opening command signal CBT based on the gate block command signal GB acquired from the other power conversion device 1, and the other power. Suppresses the sudden decrease in active power due to the gate block of the converter 1 and the opening of the AC breaker CB that does not contribute to the protection of the power converter 10 due to the instantaneous system overvoltage caused by the gate block of the own device, improving operation continuity. Can be made to.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention as well as the invention described in the claims and the equivalent scope thereof.

1, 1α, 1β ... power converter, 10 ... power converter, 20 ... converter control device, 200 ... control unit, 210 ... AC information calculation unit, 211 ... conversion unit, 212 ... PI calculation unit, 213 ... addition unit , 214 ... oscillator, 220 ... first filter, 222 ... second filter, 224 ... third filter, 230 ... voltage command value calculation unit, 240 ... gate command unit, 242 ... first comparator, 244 ... timer, 250, 250a ... Circuit breaker control unit, 252 ... Comparer, 254 ... Detection unit, 256 ... Timer, 258 ... Logic calculation unit, 300 ... Gate signal generator, CB ... AC circuit breaker, CBT ... Circuit breaker open command signal, ERR ... System voltage abnormality signal, GB ... Gate block command signal, TM1, TM2 ... Predetermined period, V_CBT ... Circuit breaker open threshold, Vth_H ... AC system voltage upper limit value, Vth_L ... AC system voltage lower limit value, Vdf1 ... Value, Vdf2 ... Value, Vdf3 ... Value

Claims (10)

1. It is a power converter that can convert alternating current and direct current to each other.
   A power converter that includes one or more arms connected in series with a unit converter that includes a capacitor that can be charged and discharged by a switching element.
   An AC circuit breaker connected between the AC system that supplies the AC and the power converter,
   A switching control unit that controls the switching element,
   A circuit breaker control unit for controlling the AC circuit breaker is provided.
   The switching control unit
   When the absolute value of the AC voltage is larger than the first threshold value or smaller than the second threshold value (the second threshold value is smaller than the first threshold value), a gate block command is output to perform the switching operation of the switching element. Stop,
   When the absolute value is larger than the third threshold value (the third threshold value is larger than the first threshold value), the cutoff control unit is used.
   When the absolute value does not change instantaneously as the gate block command is output by the switching control unit, the AC circuit breaker is opened.
   When the absolute value changes instantaneously as the gate block command is output by the switching control unit, the AC circuit breaker is not opened.
   Power converter.
2. The switching control unit outputs a voltage command to the power converter based on a value obtained by subjecting the absolute value to a first filter process, a predetermined active power value, and a predetermined reactive power value. A value is calculated, and the switching element is controlled based on the calculated voltage command value.
   The power conversion device according to claim 1.
3. When the value obtained by performing the second filter processing on the absolute value is larger than the first threshold value or smaller than the second threshold value, the switching control unit outputs the gate block command to stop the switching element. ,
   When the value obtained by performing the third filter processing on the absolute value is larger than the third threshold value, the cutoff control unit opens the AC circuit breaker.
   The power conversion device according to claim 1 or 2.
4. The time constant of the third filtering process is shorter than the time constant of the second filtering process.
   The power conversion device according to claim 3.
5. At least one of the filtering processes is realized by a digital filter.
   The power conversion device according to any one of claims 1 to 4.
6. At least one of the filtering processes is realized by an analog circuit.
   The power conversion device according to any one of claims 1 to 5.
7. The third filtering process is realized by an algorithm for removing an instantaneous abnormal value of the absolute value.
   The power conversion device according to claim 3 or 4.
8. The cutoff control unit
   The AC circuit breaker is not opened for a predetermined period after the gate block command is output by the switching control unit.
   The power conversion device according to any one of claims 1 to 7.
9. A power conversion system including two or more power conversion devices according to any one of claims 1 to 8, wherein the DC sides of the two or more power conversion devices are connected to each other.
   The cutoff control unit does not open the AC circuit breaker for a predetermined period after the gate block command is output from another power conversion device connected to the DC side of the own device.
   Power conversion system.
10. A computer that has a power converter that includes an arm in which a unit converter that includes a capacitor whose charge and discharge can be switched by a switching element is connected in series, and realizes a power converter that can convert alternating current and direct current to each other.
    By controlling the switching element,
    The AC circuit breaker connected between the AC system that supplies the AC and the power converter is controlled.
    When the absolute value of the AC voltage is larger than the first threshold value or smaller than the second threshold value (the second threshold value is smaller than the first threshold value), a gate block command is output to perform the switching operation of the switching element. Stop,
    When the absolute value is larger than the third threshold value (the third threshold value is larger than the first threshold value),
    When the absolute value does not change instantaneously as the gate block command is output by the switching control unit, the AC circuit breaker is opened.
    When the absolute value changes instantaneously with the output of the gate block command by the switching control unit, the AC circuit breaker is not opened.
    A program that lets you do things.

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