WO2020079817A1 - Power conversion device, power conversion system, power conversion method, and program - Google Patents

Abstract

The power conversion device according to an embodiment has an arm unit in which one or more unit converters each including a capacitor and a switching element connected in parallel are connected in series. A generation unit selectively generates a triangular wave carrier signal having the frequency of any of a first frequency obtained by multiplying an AC frequency by a first non-integer value, a second frequency obtained by multiplying the AC frequency by a second non-integer value greater than or equal to the first non-integer value, and a third frequency higher than the second frequency. A control unit controls the switching element on the basis of the triangular wave carrier signal. A switching unit causes the triangular wave carrier signal having the first frequency to be generated if the absolute value of the AC voltage is within a predetermined range, causes the triangular wave carrier signal having the third frequency to be generated during a first period if the absolute value of the AC voltage is not within the predetermined range, and causes the triangular wave carrier signal having the second frequency to be generated during a second period if the generation unit is not generating the triangular wave carrier signal having the third frequency.

Description

POWER CONVERSION DEVICE, POWER CONVERSION SYSTEM, POWER CONVERSION METHOD, AND PROGRAM

The embodiment of the present invention relates to a power conversion device, a power conversion system, a power conversion method, and a program.

In recent years, as a power converter, a modular multilevel converter (MMC converter: Modular Multilevel Converter) has been put into practical use. The MMC converter is a power conversion device that includes an arm unit that includes a plurality of unit converters connected in series, and is capable of handling high voltage and large capacity by adding the voltages that can be output from each unit converter. is there. The power conversion device is connected between, for example, an AC system and a DC system, and converts power.

Here, when the MMC converter includes a unit converter that is a half-bridge cell type two-level converter, switching control of the unit converter uses a triangular wave carrier as a modulation method for generating a PWM (Pulse Width Modulation) voltage. A comparison method may be used. In this case, when the frequency of the triangular wave carrier signal (that is, the switching frequency of the unit converter) is a low frequency and approaches an integral multiple of the frequency of the AC system interconnected with the power converter, the capacitor of the half bridge cell is It may be difficult to stabilize the voltage balance. Therefore, conventionally, there is known a technique of setting the triangular wave carrier frequency to a non-integer multiple of about 2 to less than 4 times the AC system frequency or increasing the frequency to 4 times or more.

However, in the power converter, when the switching frequency per unit converter becomes high, the scale of power loss accompanying power conversion becomes large. Therefore, when the triangular wave carrier frequency is set to a high frequency that is four times or more as high as the AC system frequency, It is difficult to reduce the loss due to the power conversion of the conversion device. On the other hand, if a non-integer multiple of less than 4 times the AC system frequency is set from the viewpoint of lowering the loss, the control performance of voltage and current deteriorates because of the low frequency. Therefore, when a system failure occurs in the AC system or DC system to be interconnected, it may be difficult for the power conversion device to continue operating. In order to deal with this, there is known a technique of temporarily setting the triangular wave carrier frequency to a high frequency in the event of a system fault, but the total heat generation amount due to the loss due to power conversion continues to increase, or immediately after the fault is cleared. It was sometimes difficult to recover driving.

International Publication No. 2009/086927 JP-A-2014-18015 Japanese Patent Laid-Open No. 2018-133950

An object of the present invention is to provide a power conversion device, a power conversion system, a power conversion method, and a program that can improve the operation continuity at the time of a system fault while reducing the power loss related to power conversion. To do.

An object of the present invention is to provide a power conversion device, a power conversion system, a power conversion method, and a program capable of improving the operation continuity at the time of a system fault while reducing the power loss related to power conversion. Is to provide.

The power converter of the embodiment is a power converter capable of mutually converting DC and AC, and has an arm unit, a generation unit, a control unit, and a switching unit. The arm unit is connected in series with at least one unit converter including a capacitor and a switching element that are connected in parallel with each other. The generating unit includes a first frequency obtained by multiplying the alternating current frequency by a first non-integer value, a second frequency obtained by multiplying the alternating current frequency by a second non-integer value equal to or greater than the first non-integer value, and the second frequency. A triangular wave carrier signal of any one of the third frequency, which is a frequency higher than two frequencies, is selectively generated. The control unit controls the switching element based on the triangular wave carrier signal generated by the generation unit. The switching unit switches to which frequency the triangular wave carrier signal is generated by the generation unit, and when the absolute value of the AC voltage is in a predetermined range, the switching unit switches the triangular wave carrier of the first frequency. When a signal is generated and the absolute value of the alternating voltage is not within the predetermined range, the triangular wave carrier signal of the third frequency is generated for the first period, and the absolute value of the alternating voltage is within the predetermined range. And the generator does not generate the triangular wave carrier signal of the third frequency, the triangular wave carrier signal of the second frequency is generated during the second period.

It is a figure which shows an example of a structure of the power converter device 1 of embodiment. It is a figure which shows an example of a structure of the power converter 10. It is a figure which shows an example of a structure of the cell CL. It is a figure which shows notionally an example of a process of the alternating current information calculation part 210 of embodiment. It is a figure which shows notionally an example of a process of the carrier frequency switching instruction | command part 230 of embodiment. It is a figure which shows notionally an example of a process of the carrier frequency switching part 240 of embodiment. It is a graph which shows an example of the relation of the 1st frequency fc1, the 2nd frequency fc2, and the 3rd frequency fc3, and the 1st period TM1 and the 2nd period TM2. 6 is a graph showing an example of various signals generated by the converter control device 20. It is a figure which shows an example of operation | movement of the power converter device 1 at the time of an AC system accident. Flowchart showing an example of the operation of the power converter 1 of the embodiment (No. 1) Flowchart showing an example of the operation of the power conversion device 1 of the embodiment (Part 2) It is a figure which shows notionally the process of the carrier frequency switching instruction | command part 230a of the modification 1. It is a figure which shows notionally the process of the carrier frequency switching instruction | command part 230b of the modification 2. It is a figure which shows an example of a structure of the converter control apparatus 20b of the modification 3. 13 is a diagram showing an example of a usage environment of the power conversion device 1 in Modification Example 4. FIG.

A power conversion device, a power conversion system, a power conversion method, and a program according to the embodiments will be described below with reference to the drawings.

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

[About the power converter 10]
The power converter 10 mutually converts AC power and DC power under the control of the converter control device 20. The power converter 10 is, for example, a modular multilevel converter (hereinafter, MMC converter: Modular Multilevel Converter). FIG. 2 is a diagram showing an example of the configuration of the power converter 10. The power converter 10 includes a plurality of legs LG between a positive electrode of the DC system (a terminal P shown in the figure) and a negative electrode of the DC system (a terminal N shown in the figure). The number of legs LG corresponds, for example, to 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 a first phase (R phase shown), a second phase (S phase shown), and a third phase (T phase shown). Therefore, the power converter 10 includes the leg LGr corresponding to the R phase, the leg LGs corresponding to the S phase, and the 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 a transformer (a transformer TR shown in the figure). Specifically, the leg LGr is connected to the R phase, the leg LGs is connected to the S phase, and the leg LGt is connected to the T phase. In the following description, a connection point between the leg LGr and the R phase will be referred to as a connection point CPr, a connection point between the leg LGs and the S phase will be referred to as a connection point CPs, and a connection between the leg LGt and the T phase will be described. The point is described 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 referred to as the connection point CP.

Further, in the following description, a portion having the same potential as the terminal P of the DC voltage output by the power converter 10 is also referred to as a terminal P of the leg LG, and a portion having the same potential as the terminal N of the DC voltage, Also referred to as the terminal N of the leg LG. Further, a portion from the terminal P of the leg LG to the connection point of each phase is also referred to as a positive arm unit. Further, a portion 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 suffixed with “r”, the configuration related to the leg LGs is suffixed with “s”, and the configuration related to the leg LGt is suffixed to , "T" is added to the end of the code. In addition, when it is not necessary 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 includes n cells CL (the illustrated cells CL1-1r to CL1-nr and cells CL2-1r to CL2-nr) and a plurality of reactors in the positive arm unit and the negative arm unit, respectively. RT (reactors RT1r, RT2r shown). n is a natural number. To the positive arm unit of the leg LGr, the cells CL1-1r to CL1-nr and the reactor RT1r are connected in series in the stated order from the terminal P toward the connection point CPr. Further, a reactor RT2r and cells CL2-1r to CL2-nr are connected in series from the connection point CPr to the terminal N in the negative arm unit of the leg LGr in the order shown. It should be noted that the reactor RT and the transformer TR may be replaced with a transformer having a special winding structure having a leak reactance sufficient to substitute the function of the reactor.

The leg LGr includes a current detector (not shown) that detects a positive arm current (not 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 (illustrated, R-phase negative side current Inr) 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 (illustrated switching elements Q1 to Q2), a number of diodes D (illustrated diodes D1 to D2) corresponding to the switching elements Q, and capacitors. And C. The switching element Q is, for example, an Insulated Gate Bipolar Transistor (IGBT). However, the switching element Q is not limited to the IGBT. The switching element Q may be any element as long as it is a self-turn-off switching element that can realize 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, 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 terminal of the cell CL is connected to the connection point between the switching element Q1 and the switching element Q2, and the negative 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 has a switching terminal (not shown) for switching the switching element Q on and off, and the switching terminal is connected to the converter control device 20 and a control signal is input. Specifically, the switching element Q1 receives the first gate signal gtp as a control signal, and the switching element Q2 receives the second gate signal gtn as a control signal. The capacitors C included in the cells CL are charged or discharged by switching each switching element Q on or off based on the control signal. 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 is expressed as “0”, the cell voltage Vcl is (gtp, gtn) = (1, 0) , Which is the same as the capacitor voltage Vc, and (gtp, gtn) = (0, 1), it is 0 [V]. In this way, by switching the switching element Q included in each leg LG, it is possible to generate a multi-level waveform.

Note that setting the switching element Q to (gtp, gtn) = (1,1) is prohibited because it short-circuits the capacitor C. Further, in order to prevent the switching element Q from transiently (gtp, gtn) = (1, 1) during switching, the switching element Q is normally transiently (gtp, gtn) for a very short time. = (0, 0) is controlled (dead time). 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 therefore will be omitted from the following description. . Further, when the switching control of the switching element Q is stopped, it is realized by fixing the state of (gtp, gtn) = (0, 0).

[Converter controller 20]
Returning to FIG. 1, the converter control device 20 includes a control unit 200 and a gate signal generation unit 300. The control unit 200, for example, by a hardware processor such as a CPU (Central Processing Unit) executing a program (software) stored in a storage unit (not shown), the AC information calculation unit 210 and the voltage command value calculation. The unit 220, the carrier frequency switching command unit 230, the carrier frequency switching unit 240, and the triangular wave carrier generation unit 250 are realized as functional units. 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), and GPU (Graphics Processing Unit). Part; including circuitry), or may be realized by cooperation of software and hardware.

The AC information calculation unit 210 calculates the voltages (R-phase voltage Vr, S-phase voltage Vs, and T-phase voltage Vt shown) detected by a device (detector CS shown) that detects the voltage of each phase of the AC system. The information shown is acquired, and the AC system effective voltage Vd and the AC system reactive voltage Vq are calculated based on the acquired information. In addition, the AC information calculation unit 210 repeats the calculation as a calculation for following and synchronizing with the AC system voltage so that the calculated value of the AC system reactive voltage Vq becomes zero. Thereby, the AC information calculation unit 210 calculates the AC frequency fpll and the AC system voltage phase theta. The AC frequency fpll is the frequency of the AC system voltage with which the power converter 10 is interconnected. The AC system voltage phase theta is a value indicating the phase of a reference phase having the AC voltage. Details of the processing of the AC information calculation unit 210 will be described later.

The voltage command value calculator 220 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 calculator 210. Based on the AC system active voltage Vd, the AC system reactive voltage Vq, and the AC system voltage phase theta, the active power PE output by the power converter 10 and the reactive power QE have a predetermined active power command value PE *. Then, the cell voltage command value Vcl * for instructing the cell voltage Vcl of each cell CL is calculated so that the reactive power command value QE * is obtained.

The carrier frequency switching command unit 230 is a signal that commands the frequency of the triangular wave carrier signal based on the AC system effective voltage Vd calculated by the AC information calculation unit 210 and a command from the external system (external command SYS shown). The first pulse switching command SW1 and the second pulse switching command SW2 shown in the figure are output to the carrier frequency switching unit 240. The triangular wave carrier signal is a signal used when the switching control signal of the switching element Q is generated by the triangular wave comparison method. In the triangular wave comparison method, the frequency of the triangular wave carrier signal and the switching frequency match. In the following description, the frequency of the triangular wave carrier signal is also referred to as the switching frequency. The external system is, for example, a protection device for the power conversion device 1. Details of the processing of the carrier frequency switching command unit 230 will be described later.

The carrier frequency switching unit 240, based on the AC frequency fpll calculated by the AC information calculation unit 210, the first pulse switching command SW1 and the second pulse switching command SW2 output by the carrier frequency switching command unit 230, A command value (hereinafter, carrier command frequency fc *) that indicates the switching frequency of the power converter 10 is selected and output to the triangular wave carrier generation unit 250. Details of the processing of the carrier frequency switching unit 240 will be described later.

The triangular wave carrier generation unit 250 generates a triangular wave carrier signal Tri * for each cell CL based on the carrier command frequency fc * output by the carrier frequency switching unit 240. This triangular wave carrier signal Tri * is a signal in which the phase is uniformly shifted for each cell CL in order from one end to the other end of the cells CL connected in series to the arm unit.

Note that the phase shift order of the triangular wave carrier signal Tri * does not necessarily have to match the serial connection order of the cells CL, as long as they are evenly phase-shifted between arbitrary cells CL belonging to the same arm unit. . Therefore, the phase shift order of the triangular wave carrier signal Tri * can be arbitrarily changed. In the following description, the case where the phase shift order of the triangular wave carrier signal Tri * is the series connection order of the cells CL will be described as an example.

The gate signal generation unit 300 is based on the cell voltage command value Vcl * of each cell CL calculated by the voltage command value calculation unit 220 and the triangular wave carrier signal Tri * for each cell CL generated by the triangular wave carrier generation unit 250. Then, the first gate signal gtp and the second gate signal gtn for each cell CL are generated and output to the power converter 10. Details of the triangular wave carrier signal Tri * generated by the triangular wave carrier generation unit 250, the first gate signal gtp, and the second gate signal gtn will be described later.

Below, the contents of the processing of each part of the power converter 10 will be explained.

[About AC information calculation unit 210]
FIG. 4 is a diagram conceptually illustrating 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 voltages (R-phase voltage Vr, S-phase voltage Vs, and T-phase voltage Vt shown) detected by the detector CS. The conversion unit 211 converts (calculates) the acquired R-phase voltage Vr, S-phase voltage Vs, and T-phase voltage Vt into an AC system effective voltage Vd and an AC system reactive voltage Vq, using Equation (1). . The AC system voltage phase theta is a value output by an oscillator 214 described later, and is a value indicating the voltage phase of a certain reference phase (R phase in this example) of the AC system.

The PI calculation unit 212, based on the AC system reactive voltage Vq converted by the conversion unit 211, the frequency difference between the frequency of the AC system voltage with which the power converter 10 is interconnected and the reference AC system frequency fs0 (hereinafter, referred to as frequency). 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 it is lower than the reference AC system frequency fs0. The reference AC system frequency fs0 is a 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 reactive 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. Converge to.

The adder 213 adds the frequency difference Δfpll calculated by the PI calculator 212 to the reference AC system frequency fs0. In the following description, the frequency obtained by adding the frequency difference Δfpll to the reference AC system frequency fs0 is referred to as AC frequency fpll.

The oscillator 214 outputs an AC system voltage phase theta that monotonically increases from the minimum value 0 to the maximum value 2π according to the frequency of the AC frequency fpll calculated by the adding 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 reactive voltage Vq of the conversion unit 211 and for generating the cell voltage command value Vcl *.

Through the above-described 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 reactive voltage Vq in the conversion unit 211 becomes zero, and thus the AC system synchronized with the AC system voltage. The frequency fpll and the AC system voltage phase theta are obtained.

As will be described later, the switching frequency of the switching element Q may be controlled so as to be proportional to the AC frequency fpll. Here, when the state of the AC system becomes unstable and the frequency difference Δfpll fluctuates outside the normal range, the calculated value fpll of the AC frequency also fluctuates, and the switching frequency of the switching element Q falls outside the normal range. Beyond that, there is a risk that the power conversion device 1 may not operate stably. To prevent this, the PI calculation unit 212 sets the frequency difference Δfpll to the + limit value Δfpll_limit when the frequency difference Δfpll is larger than the limit value (hereinafter, the limit value Δfpll_limit), and sets the frequency difference Δfpll_limit to the −limit value Δfpll_limit. Δfpll may be output as −limit value Δfpll_limit. In this case, the addition unit 213 can limit the AC frequency fpll to a frequency in the range of the reference AC system frequency fs0 + the limit value Δfpll_limit to the reference AC system frequency fs0−the limit value Δfpll_limit. The limit value Δfpll_limit is, for example, a positive value smaller than the reference AC system frequency fs0.

[About carrier frequency switching command unit 230]
FIG. 5: is a figure which shows notionally an example of a process of the carrier frequency switching instruction | command part 230 of embodiment. The carrier frequency switching command unit 230 includes a first comparator 231, a determination unit 232, a first pulse output unit 233, and a second pulse output unit 234 as functional units. The first comparator 231 compares the absolute value of the AC system effective voltage Vd calculated by the AC information calculation unit 210 with the voltage upper limit value Vth_H and the voltage lower limit value Vth_L. The first comparator 231 outputs the system voltage abnormality signal ERR when the absolute value of the AC system effective voltage Vd is larger than the voltage upper limit value Vth_H or when the absolute value of the AC system effective voltage Vd is smaller than the voltage lower limit value Vth_L. Output. When the absolute value of the AC system effective voltage Vd is larger than the voltage upper limit value Vth_H, or the absolute value of the AC system effective voltage Vd is smaller than the voltage lower limit value Vth_L, a system fault occurs in the AC system and the AC system This is a state in which the amplitude of each phase voltage shows an abnormal value or the phases are unbalanced. The range indicated by the voltage upper limit value Vth_H to the voltage lower limit value Vth_L is an example of a “predetermined range” that the absolute value of the AC system effective voltage Vd can take.

The first comparator 231 compares the combined voltage vector Vdq obtained by the equation (2) with a predetermined threshold value, and the value of the combined voltage vector Vdq is greater than a predetermined upper threshold value or less than a predetermined lower threshold value. If it is smaller, the system voltage abnormality signal ERR may be output.

The determination unit 232 determines whether or not the system voltage abnormality signal ERR has been output by the first comparator 231 or whether the external command SYS has been output by the external system. The determination unit 232 outputs the system voltage abnormality signal ERR to the first pulse output unit 233 when either the system voltage abnormality signal ERR or the external command SYS is output.

When the determination unit 232 outputs the system voltage abnormality signal ERR, the first pulse output unit 233 outputs the first pulse switching command SW1 only for the first period TM1 after the system voltage abnormality signal ERR is output. Further, the first pulse output unit 233 outputs the first pulse switching command SW1 when the external command SYS is output even when the first comparator 231 does not detect a system fault.

When the system voltage abnormality signal ERR is output by the first comparator 231, the second pulse output unit 234 outputs the second pulse switching command SW2 only for the second period TM2 after the system voltage abnormality signal ERR is output. To do.

[About carrier frequency switching unit 240]
FIG. 6 is a diagram conceptually illustrating an example of processing of the carrier frequency switching unit 240 of the embodiment. The carrier frequency switching unit 240 includes a first switching unit 241, a multiplication unit 242, and a second switching unit 243 as functional units. The first switching unit 241 switches the non-integer value output to the multiplication unit 242 to either one of the first non-integer value N1 and the second non-integer value N2. The first switching unit 241 outputs the first non-integer value N1 to the multiplication unit 242 when the first pulse switching command SW1 is not output, and the second non-integer value N1 when the first pulse switching command SW1 is output. The integer value N2 is output. The first non-integer value N1 and the second non-integer value N2 are positive values that are not integers. In addition, the first non-integer value N1 is a value smaller than the second non-integer value N2.

The multiplying unit 242 multiplies the AC frequency fpll by the non-integer value output by the first switching unit 241. In the following description, the frequency obtained by multiplying the AC frequency fpll by the first non-integer value N1 is referred to as the first frequency fc1, and the frequency obtained by multiplying the AC frequency fpll by the second non-integer value N2 is referred to as the first frequency fc1. It is described as 2 frequencies fc2.

The second switching unit 243 sets the frequency output to the triangular wave carrier generation unit 250 as the carrier command frequency fc * to the frequency output by the multiplication unit 242 (first frequency fc1 or second frequency fc2) and the third frequency fc3. And switch to either one of. When the second pulse switching command SW2 is not output, the second switching unit 243 outputs the first frequency fc1 or the second frequency fc2 output by the multiplication unit 242 as the carrier command frequency fc *, and the second pulse When the switching command SW2 is output, the third frequency fc3 is output as the carrier command frequency fc *. The third frequency fc3 is a predetermined frequency.

Hereinafter, the relationship between the first frequency fc1, the second frequency fc2, and the third frequency fc3, and the first period TM1 and the second period TM2 will be described. FIG. 7 is a graph showing an example of the relationship between the first frequency fc1, the second frequency fc2, the third frequency fc3, and the first period TM1 and the second period TM2. The horizontal axis of FIG. 7 shows the carrier command frequency fc *, and the vertical axis shows the time (hereinafter, continuous control time) that can be continuously controlled by the switching frequency of the carrier command frequency fc *. W1 is a waveform showing the relationship between the carrier command frequency fc * and the continuous control time.

Generally, in the power converter 10, as the carrier command frequency fc * increases, the amount of heat generation per unit time (that is, power conversion loss) occurs, and the larger the power conversion loss, the shorter the continuous control time. Therefore, when the allowable heat generation amount due to the power conversion loss is fixed, the relationship between the carrier command frequency fc * and the continuous control time is approximately inversely proportional as shown by the waveform W1.

Further, in general, when the carrier command frequency fc * takes a value that is an integer multiple of the AC frequency fpll or a value close to an integer multiple in the low frequency region of the constant K × AC frequency fpll or less, the power converter 10 causes the capacitor voltage Vc It becomes difficult to maintain the balance. On the other hand, even if the carrier command frequency fc * takes an integer multiple of the AC frequency fpll or a value close to an integer multiple in a high frequency region higher than the constant K × AC frequency fpll, the power converter 10 uses the capacitor. The balance of the voltage Vc can be maintained. The constant K is, for example, a value of “4” or more, and the first non-integer value N1 and the second non-integer value N2 are values less than the constant K. That is, the first non-integer value N1 and the second non-integer value N2 are, for example, non-integer values of about “2” to “4” (for example, 2.1 to 2.9 and 3.1 to 3.9). ).

The first frequency fc1 and the second frequency fc2 are frequencies in a low frequency region equal to or less than a constant K × AC frequency fpll, but the AC frequency fpll is multiplied by a first non-integer value N1 or a second non-integer value N2. Frequency. Therefore, the power converter 10 can maintain the balance of the capacitor voltage Vc even if switching control is performed by the switching frequency of the carrier command frequency fc * of the first frequency fc1 or the second frequency fc2.

When the switching loss when the carrier command frequency fc * is the second non-integer value N2 × AC frequency fpll is small, the difference between the second non-integer value N2 and the first non-integer value N1 is made sufficiently small. Alternatively, the difference between the second non-integer value N2 and the first non-integer value N1 may be “0” (that is, the second non-integer value N2 = the first non-integer value N1).

The third frequency fc3 is a frequency higher than the first frequency fc1 and the second frequency fc2, and is a frequency in a high frequency range equal to or higher than the constant K × AC frequency fpll. The third frequency fc3 may be an integral multiple of the AC frequency fpll or a non-integer multiple of the AC frequency fpll. In the above description, the case where the third frequency fc3 is a predetermined frequency (that is, a fixed value) has been described. However, a value obtained by multiplying the AC frequency fpll by an integer equal to or greater than a constant K or a non-integer equal to or greater than the constant K May be

Hereinafter, the relationship between the first period TM1 and the second period TM2 will be described. As described above, the carrier frequency switching unit 240 has the third frequency fc3 during the second period TM2 in which the second pulse switching command SW2 is output (that is, during the time period during which the system fault continues). Is output as the carrier command frequency fc *. The third frequency fc3 is a frequency in a high frequency range, and thus has a large power loss per unit time. Therefore, it is difficult for the power converter 10 to continue operating for a long period of time. Therefore, the carrier frequency switching unit 240 outputs the third frequency fc3 for a short period (in this example, the second period TM2).

The second period TM2 is, for example, a period until the AC circuit breaker provided in the AC system disconnects the fault circuit and the fault is eliminated. The second period TM2 may be set based on a past accident case or a predetermined recovery time, and is, for example, a period of several times the AC system voltage cycle. The second period TM2 may be a period during which heat generated by switching control at the third frequency fc3 can be cooled according to the cooling function of the power converter 10.

In addition, the carrier frequency switching unit 240 outputs the second pulse switching command SW2 and does not output the first pulse switching command SW1 (that is, the second period TM2 after the occurrence of the system fault). The second frequency fc2 is output as the carrier command frequency fc * during the first period TM1 to the second period TM2 after the lapse of time or during the first period TM1 after receiving the external command SYS). . Since the second frequency fc2 is a frequency in the lower frequency range than the third frequency fc3, the power loss per unit time is smaller than that of the third frequency fc3. Therefore, the power converter 10 can continue to operate the power converter 10 for a longer period than the third frequency fc3. Therefore, the first period TM1 is longer than the second period TM2.

In addition, as described above, the carrier frequency switching unit 240 sets the first frequency fc1 to the carrier command frequency when the first pulse switching command SW1 and the second pulse switching command SW2 are not output (that is, in the normal state). Output as fc *. The power converter 10 has a cooling function that allows constant switching control with the first frequency fc1.

[About gate signal]
FIG. 8 is a graph showing an example of various signals generated by the converter control device 20. In FIG. 8, a waveform W11 indicates a j-th (j is a natural number) cell CL (hereinafter, cell CL (j)) of the cell CL connected in series to a certain arm unit of the power converter 10. It is a waveform showing the change over time of the triangular wave carrier signal Tri (j) * used for generating the 1-gate signal gtp (j). The waveform W12 is a waveform showing a change over time of the cell voltage command value Vcl * which is a command value of the voltage generated between the positive electrode terminal and the negative electrode terminal of the cell CL (j). The waveform W13 is the triangular wave carrier signal Tri (j + 1) used to generate the first gate signal gtp (j + 1) of the cell CL (hereinafter, cell CL (j + 1)) connected in series adjacent to the cell CL (j). It is a waveform showing the change with time of *. A waveform W14 is a waveform showing a temporal change of a cell voltage command value Vcl (j + 1) *, which is a command value of a voltage generated between the positive electrode terminal and the negative electrode terminal of the cell CL (j + 1). The waveform W15 is a waveform showing the change over time of the first gate signal gtp (j). The waveform W16 is a waveform showing the change over time of the first gate signal gtp (j + 1).

As shown by the waveforms W11 and W13, the triangular wave carrier signal Tri (j) * and the triangular wave carrier signal Tri (j + 1) * are triangular wave waveforms having a cycle of 1 / carrier command frequency fc *. In FIG. 8, the triangular wave carrier signal Tri (j) * is made dimensionless so that the maximum value thereof coincides with the capacitor voltage Vc of the cell CL, and is shown by the range of 0 to 1. Further, as shown by the waveforms W12 and W14, the cell voltage command value Vcl (j) * and the cell voltage command value Vcl (j + 1) * are substantially equal. The cell voltage command value Vcl (j) * is made dimensionless with the capacitor voltage Vc of the cell CL as a reference, and is represented by a range of 0 to 1, like the triangular wave carrier signal Tri *.

The gate signal generation unit 300 generates the first gate signal gtp and the second gate signal gtn by phase shift PWM (Pulse Width Modulation). As shown by the waveforms W11 and W13, when the number of cells CL for each arm unit is n, the gate signal generator 300 sets the phases of the triangular wave carrier signals Tri * assigned to the cells CL of the arm units to 2π / n. Shift one by one. n is the number of cells CL (n [pieces] in this example) connected in series to the arm unit. Therefore, the triangular wave carrier signal Tri (j) * and the triangular wave carrier signal Tri (j + 1) * of the cell CL (j) and the cell CL (j + 1) adjacent in phase have a time of 1 / (n × fc *). Just a gap occurs.

The gate signal generation unit 300 compares the triangular wave carrier signal Tri (j) * with the cell voltage command value Vcl (j) *, and when Vcl (j) * <Tri (j) *, the first gate signal gtp. (J) is changed to “0” (that is, the switching element Q1 of the cell CL (j) is turned off), and when Vcl (j) *> Tri (j) *, the first gate signal gtp (j) is changed. It is changed to "1" (that is, the switching element Q1 of the cell CL (j) is turned on). Similarly, the gate signal generation unit 300 compares the triangular wave carrier signal Tri (j + 1) * with the cell voltage command value Vcl (j + 1) * to change the first gate signal gtp (j + 1). The second gate signal gtn of the switching element Q2 is a logical inversion signal of the first gate signal gtp.

Based on the first gate signal gtp and the second gate signal gtn generated by the gate signal generator 300, the power converter 10 determines the change timing of the first gate signal gtp of each cell CL in the arm unit. Is shifted to generate a multi-level voltage of maximum n levels as a combined voltage of the arm unit.

[About operation in case of an accident]
FIG. 9: is a figure which shows an example of operation | movement of the power converter device 1 at the time of an AC system accident. Waveforms W21 to W23 are waveforms showing changes with time of the AC voltage of each phase of the AC system. The waveform W24 is a waveform showing a change with time of the AC system effective voltage Vd. The waveform W25 is a waveform showing the change over time of the first pulse switching command SW1. The waveform W26 is a waveform showing the change over time of the second pulse switching command SW2. The waveform W27 is a waveform showing the change over time of the carrier command frequency fc *. The waveform W28 is a waveform showing the maximum value of the capacitor voltage Vc. The waveform W29 is a waveform showing the minimum value of the capacitor voltage Vc.

Before the AC system accident occurs (before the time t0 shown in the figure), the AC voltage of each phase shown by the waveforms W21 to W23 is balanced between the phases, and the frequency is almost equal to the reference AC system frequency fs0. Further, as shown by the waveform W24, the AC system effective voltage Vd at this time is a constant value indicating the absolute value of the amplitude of the AC voltage. Further, the carrier frequency switching unit 240 outputs the first frequency fc1 as the carrier command frequency fc * in the normal state.

At time t0, with the occurrence of an accident in the AC system, the voltage of a certain phase (in this example, the R phase) of the AC voltage of each phase of the AC system indicated by the waveforms W21 to W23 is almost 0 [. V]. The R phase and the other two healthy phases (S phase and T phase in this example) are unbalanced. Along with this, the AC system effective voltage Vd oscillates at a frequency approximately twice the reference AC system frequency fs0, and falls below the voltage lower limit value Vth_L.

When the AC system effective voltage Vd falls below the voltage lower limit value Vth_L, the carrier frequency switching command unit 230 outputs the first pulse switching command SW1 only for the first period TM1 and the second pulse switching command only for the second period TM2. Output SW2. The carrier frequency switching unit 240 outputs the third frequency fc3 as the carrier command frequency fc * while the second pulse switching command SW2 is being output (that is, the second period TM2).

As shown by the waveforms W28 to W29, the disturbance immediately after the occurrence of the accident increases the variation in the capacitor voltage Vc in the arm unit (the difference generated between the waveform W28 and the waveform W29). Controlled by the first gate signal gtp and the second gate signal gtn with high time resolution based on the triangular wave carrier signal Tri * of the third frequency fc3, the capacitor voltage Vc converges quickly without increasing the variation. Can be made.

Generally, when the variation of the capacitor voltage Vc is increased, the capacitor voltage Vc may reach the overvoltage level and the operation of the power converter 10 may stop. In this case, the power converter 10 cannot restart the operation until the capacitor C is discharged and the capacitor voltage Vc returns to the normal level. According to the above-described processing, the power converter 10 performs the switching control with the third frequency fc3 for a short period (second period TM2), so that the operation continuity is improved without increasing the capacitor voltage Vc. You can

Next, when the accident is removed at time t1, the AC system effective voltage Vd may temporarily exceed the voltage upper limit value Vth_H. When the AC system effective voltage Vd rises, it becomes a disturbance, and the variation of the capacitor voltage Vc in the arm unit increases again. In FIG. 9, the second pulse switching command SW2 is stopped around time t1, and the carrier frequency switching unit 240 outputs only the first pulse switching command SW1. The period during which only the first pulse switching command SW1 is output is from time t1 to time t2 (that is, between the first period TM1 and the second period TM2). The carrier frequency switching unit 240 outputs the carrier command frequency fc * while the first pulse switching command SW1 is being output (that is, during the second period TM2 to the first period TM1 after the end of the second period TM2). And outputs the second frequency fc2.

As shown by the waveforms W28 to W29, although the variation in the capacitor voltage Vc in the arm unit increases due to the temporary increase in the AC system effective voltage Vd after the accident elimination, the power converter 10 uses the second frequency fc2. Is controlled by the first gate signal gtp and the second gate signal gtn, which have a higher time resolution than in the normal state based on the triangular wave carrier signal Tri *, and converge quickly without increasing the variation in the capacitor voltage Vc. Can be made.

According to the above-described processing, the power converter 10 performs the switching control with the second frequency fc2 only for a short period (first period TM1), so that the operation continuity is improved without increasing the capacitor voltage Vc. You can

Next, at time t2, the first pulse switching command SW1 is stopped, and the carrier frequency switching unit 240 outputs the first frequency fc1 as the carrier command frequency fc *. As a result, in the normal state, the power converter 10 can be stably operated by the carrier command frequency fc * in the low frequency range without lowering the power conversion efficiency and maintaining the balance of the capacitor voltage Vc. .

Although the AC system effective voltage Vd temporarily exceeds the voltage upper limit value Vth_H due to the elimination of the accident at the time t1, the carrier frequency switching command unit 230 causes the first pulse switching command SW1, immediately after the time t0. Since the second pulse switching command SW2 has already been output, the first pulse switching command SW1 and the second pulse switching command SW2 are not output again at this timing. However, when the AC system effective voltage Vd does not fall below the voltage lower limit value Vth_L at time t0, the carrier frequency switching command unit 230, at this timing, the first pulse switching command SW1 and the second pulse switching command SW2. May be output.

[Processing flow]
10 and 11 are flowcharts (No. 1) to (No. 2) showing an example of the operation of the power conversion device 1 of the embodiment. The flowchart shown in FIG. 10 and the flowchart shown in FIG. 11 are executed simultaneously in parallel. In FIG. 10, first, the conversion unit 211 acquires information indicating the voltage (R-phase voltage Vr, S-phase voltage Vs, and T-phase voltage Vt) of each phase of the AC system from the detector CS (step S100). The conversion unit 211 converts the AC system valid voltage Vd and the AC system reactive voltage Vq based on the acquired voltage of each phase of the AC system (step S102). The addition unit 213 adds the reference AC system frequency fs0 to the frequency difference Δfpll calculated by the PI calculation unit 212 based on the AC system reactive voltage Vq to calculate the AC frequency fpll (step S104). Further, the oscillator 214 outputs an AC system voltage phase theta that monotonically increases from the minimum value 0 to the maximum value 2π according to the frequency of the AC frequency fpll calculated by the adding unit 213 (step S106).

The first comparator 231 compares the absolute value of the AC system effective voltage Vd converted by the conversion unit 211 with the voltage upper limit value Vth_H and the voltage lower limit value Vth_L, and the absolute value of the AC system effective voltage Vd is the voltage. It is compared whether it is within a predetermined range from the upper limit value Vth_H to the voltage lower limit value Vth_L (step S108). When the comparison result of the first comparator 231 indicates that the absolute value of the AC system effective voltage Vd is within the predetermined range, the determination unit 232 determines whether or not the external command SYS is received from the external system (step S110). The determination unit 232 ends the process when the external command SYS is not received from the external system. When the determination result of the determination unit 232 indicates that the external command SYS is received, the first pulse output unit 233 outputs the first pulse switching command SW1 and advances the process to step S116.

If the absolute value of the AC system effective voltage Vd is outside the predetermined range, the first comparator 231 outputs the system voltage abnormality signal ERR (step S114). The first pulse output unit 233 outputs the first pulse switching command SW1 along with the output of the system voltage abnormality signal ERR, and the second pulse output unit 234 outputs the system voltage abnormality signal ERR. Accordingly, the second pulse switching command SW2 is output (step S114). Note that, in step S114, the timings at which the first pulse switching command SW1 and the second pulse switching command SW2 are output match.

The second pulse output unit 234 continues to output the second pulse switching command SW2 from the time the second pulse switching command SW2 is output until the second period TM2 elapses (step S116). The second pulse output unit 234 stops the second pulse switching command SW2 after the second period TM2 has elapsed after outputting the second pulse switching command SW2 (step S118). The first pulse output unit 233 continues to output the first pulse switching command SW1 until the first period TM1 elapses after outputting the first pulse switching command SW1 (step S120). The first pulse output unit 233 stops the first pulse switching command SW1 after the first period TM1 has elapsed after outputting the first pulse switching command SW1 (step S122).

As shown in FIG. 11, the carrier frequency switching unit 240 determines whether or not the second pulse switching command SW2 is output (step S200). When the second pulse switching command SW2 is output, the carrier frequency switching unit 240 outputs the third frequency fc3 as the carrier command frequency fc * (step S202). When the second pulse switching command SW2 is not output, the carrier frequency switching unit 240 determines whether the first pulse switching command SW1 is output (step S204). Furthermore, when the first pulse switching command SW1 is output, the carrier frequency switching unit 240 outputs the second frequency fc2 as the carrier command frequency fc * (step S206). When the first pulse switching command SW1 and the second pulse switching command SW2 are not output, the carrier frequency switching unit 240 outputs the first frequency fc1 as the carrier command frequency fc * (step S208).

The triangular wave carrier generation unit 250 generates the triangular wave carrier signal Tri * for each cell CL based on the carrier command frequency fc * output from the carrier frequency switching unit 240 (step S210). The voltage command value calculation unit 220, based on the AC system effective voltage Vd, the AC system reactive voltage Vq, the AC system voltage phase theta, and the like calculated by the AC information calculation unit 210, the cell voltage command value Vcl * for each cell CL. Is generated (step S212). The gate signal generation unit 300, based on the triangular wave carrier signal Tri * generated by the triangular wave carrier generation unit 250 and the cell voltage command value Vcl * generated by the voltage command value calculation unit 220, the first for each cell CL. The gate signal gtp and the second gate signal gtn are generated (step S214). The power converter 10 performs switching control of the switching element Q based on the first gate signal gtp and the second gate signal gtn generated by the gate signal generation unit 300, and converts power.

[Summary of Embodiments]
As described above, the power conversion device 1 of the present embodiment controls the power converter 10 by the carrier command frequency fc * in the low frequency range in the normal time, thereby reducing the power conversion loss and reducing the capacitor voltage. It is possible to prevent the balance of Vc from being lost. In addition, the power conversion device 1 of the present embodiment controls the power converter 10 for a short period of time by the carrier command frequency fc * in the high frequency range at the time of a system fault, so that the total heat generation amount that is the integrated value of the power conversion loss. It is possible to prevent the capacitor voltage Vc from reaching the overvoltage level while suppressing an increase in the voltage. Therefore, the power conversion device 1 of the present embodiment can improve the operation continuity at the time of a system fault while reducing the power loss related to the power conversion.

Further, the power conversion device 1 of the present embodiment controls the power converter 10 by using the carrier command frequency fc * in different high frequency regions at the timing when the system fault occurs and the timing when the system fault converges to some extent. As a result, it is possible to further suppress an increase in the total heat generation amount, which is the integrated value of the power conversion loss. Further, the power conversion device 1 of the present embodiment controls the power converter 10 by the carrier command frequency fc * so as to finish in a shorter period as the carrier command frequency fc * is in a higher frequency range. It is possible to further suppress an increase in the total heat generation amount that is the integrated value of the power conversion loss. Furthermore, by controlling the power converter 10 using the carrier command frequency fc * having the highest frequency at the timing when the system fault has the greatest influence on the operation continuity, the operation continuity can be further improved. .

Further, the power conversion device 1 of the present embodiment controls the power converter 10 by the carrier command frequency fc * in the high frequency range based on the external command SYS received from the external system. As a result, the power conversion device 1 according to the present embodiment can quickly perform power conversion when the external protection device or the like of the power conversion device 1 precedes the power conversion device 1 or independently detects an abnormality such as a system accident. The power converter 10 can be controlled so that the converter 1 can continue operation.

Further, the power conversion device 1 of the present embodiment suppresses an increase in power conversion loss and reduces the cooling function of the power converter 10 as described above, thereby reducing the power conversion device 1 cost and size. Can be converted.

(Modification 1)
Hereinafter, with reference to the drawings, the carrier frequency switching command unit 230a of the first modification will be described. In the embodiment, the case where the carrier frequency switching command unit 230 outputs the first pulse switching command SW1 and the second pulse switching command SW2 based on the system voltage abnormality signal ERR and the external command SYS has been described. In the carrier frequency switching command unit 230a of Modification Example 1, further, based on the number of times (hereinafter, the number of counts ct) that the AC system effective voltage Vd deviates from the range indicated by the voltage upper limit value Vth_H and the voltage lower limit value Vth_L, A case where the first pulse switching command SW1 and the second pulse switching command SW2 are output will be described. The same components as those of the above-described embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 12 is a diagram conceptually showing the process of the carrier frequency switching command unit 230a of the first modification. The carrier frequency switching command unit 230a of the first modification is replaced with (or in addition to) the functional units included in the carrier frequency switching command unit 230, and the first comparator 231, the determination unit 232a, and the first pulse output unit. 233, a second pulse output unit 234, a number counter 235, a second comparator 236, and a third comparator 237 are provided as functional units. The frequency counter 235 sets a certain set time based on the information indicating that the comparison result of the first comparator 231 indicates that the AC system effective voltage Vd exceeds the voltage upper limit value Vth_H or falls below the voltage lower limit value Vth_L. The number of abnormalities in the system voltage within 10 seconds (for example, 10 seconds) is counted, and the counted number ct is output to the second comparator 236 and the third comparator 237.

It should be noted that the frequency counter 235 repeatedly measures the voltage upper limit value during another set time (for example, 1 [second]) that is sufficiently shorter than the set time of the count target because the AC system effective voltage Vd vibrates finely. When Vth_H deviates from the range indicated by the voltage lower limit value Vth_L or returns to the range, they are collectively counted as one system voltage abnormal state.

The second comparator 236 compares the count number ct output by the number counter 235 with the switching number first upper limit value SW_lim1. The second comparator 236 outputs a "False" signal when the count number ct does not exceed the switching number first upper limit value SW_lim1, and when the count number ct exceeds the switching number first upper limit value SW_lim1, " True ”signal.

The third comparator 237 compares the count number ct output by the number counter 235 with the switching number second upper limit value SW_lim2. The third comparator 237 outputs a "False" signal when the count number ct does not exceed the switching number second upper limit value SW_lim2, and when the count number ct exceeds the switching number second upper limit value SW_lim2, " True ”signal.

The determination unit 232a determines whether the first comparator 231 outputs the system voltage abnormality signal ERR and the second comparator 236 outputs the “False” signal. The first pulse output unit 233 outputs the system voltage abnormality signal ERR and the “False” signal by the determination unit 232a (that is, the count number ct does not exceed the switching number first upper limit value SW_lim1). , And outputs the first pulse switching command SW1 only during the first period TM1. In addition, the first pulse output unit 233 of the modified example 1 outputs the “True” signal by the second comparator 236 even when the system voltage abnormality signal ERR is output (that is, the count). When the number of times ct exceeds the switching number first upper limit value SW_lim1), the first pulse switching command SW1 is not output. The switching count first upper limit value SW_lim1 is a value indicating the number of times the power converter 10 can be controlled by the second frequency fc2.

The determination unit 232a determines whether or not the system voltage abnormality signal ERR is output by the first comparator 231 and the “False” signal is output from the third comparator 237. The second pulse output unit 234 outputs the system voltage abnormality signal ERR and the “False” signal by the determination unit 232a (that is, the count number ct does not exceed the switching number second upper limit SW_lim2). , And outputs the second pulse switching command SW2 only during the second period TM2. In addition, the second pulse output unit 234 of the modified example 1 outputs the “True” signal by the third comparator 237 even when the system voltage abnormality signal ERR is output (that is, the count). When the number of times ct exceeds the switching number second upper limit value SW_lim2), the second pulse switching command SW2 is not output. The switching count second upper limit value SW_lim2 is a value indicating the number of times the power converter 10 can be controlled by the third frequency fc3.

Note that the switching count first upper limit value SW_lim1 and the switching count second upper limit value SW_lim2 may be the same value or different values. Further, the switching number first upper limit value SW_lim1 and the switching number second upper limit value SW_lim2 may be indicated by time (period) instead of (or in addition to) the number of times. In this case, the upper limit value is a value indicating a time (period) during which the power converter 10 can be controlled by the second frequency fc2 or the third frequency fc3. The switching number first upper limit value SW_lim1 is an example of the “second predetermined number”, and the switching number second upper limit value SW_lim2 is an example of the “first predetermined number”.

Further, when the count frequency ct exceeds the switching frequency first upper limit value SW_lim1 or exceeds the switching frequency third upper limit SW_lim3, the carrier frequency switching unit 240 determines that the absolute value of the AC system effective voltage Vd falls within the predetermined range. Even if it exceeds, the first frequency fc1 is selected as the carrier command frequency fc *. In this case, the switching number first upper limit value SW_lim1 or the switching number third upper limit SW_lim3 is an example of the “third predetermined number”.

[Summary of Modification 1]
As described above, the power conversion device 1 of the first modification increases the total heat generation amount due to the power conversion loss by limiting the number of effective times of the first pulse switching command SW1 and the second pulse switching command SW2. It is possible to prevent the power converter 1 from stopping for a long time due to a failure due to heat generation. In addition, according to the power conversion device 1 of the first modification, when a system fault of the system connected to the power conversion device 1 or a system fault of the system notified by the external command SYS from the external system frequently occurs in a short time. Even in this case, it is possible to reduce the power loss related to the power conversion and improve the operation continuity at the time of a system fault within the range in which the total calorific value does not exceed the allowable value.

(Modification 2)
Hereinafter, with reference to the drawings, the carrier frequency switching command unit 230b of Modification 2 will be described. In the carrier frequency switching command unit 230a of Modification Example 1, further, based on the number of times (hereinafter, the number of counts ct) that the AC system effective voltage Vd deviates from the range indicated by the voltage upper limit value Vth_H and the voltage lower limit value Vth_L, The case where the first pulse switching command SW1 and the second pulse switching command SW2 are output has been described. In the carrier frequency switching command unit 230b of the second modification, a case where the operation of the power converter 10 is stopped based on the count number ct will be further described. In addition, about the structure similar to embodiment and the modification mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted.

FIG. 13 is a diagram conceptually showing the process of the carrier frequency switching command unit 230b of the second modification. The carrier frequency switching command unit 230b of Modification 2 further includes a fourth comparator 238 in addition to the functional units included in the carrier frequency switching command unit 230b. The fourth comparator 238 compares the count number ct output by the number counter 235 with the switching number third upper limit SW_lim3. The fourth comparator 238 outputs the stop command signal STP to the gate signal generation unit 300 when the count number ct exceeds the switching number third upper limit SW_lim3. The gate signal generation unit 300, when the stop command signal STP is output by the fourth comparator 238, a gate signal that causes the power converter 10 to stop power conversion (for example, (gtp, gtn) = (0, 0 )) Is generated and output.

The switching number third upper limit SW_lim3 is a value sufficiently larger than the switching number first upper limit value SW_lim1 and the switching number second upper limit value SW_lim2. Further, the switching upper limit third upper limit SW_lim3 may be indicated by time (period) instead of (or in addition to) the number of times. In this case, the upper limit value is a value indicating a time (period) during which the power converter 10 can be controlled by the carrier command frequency fc * (for example, the second frequency fc2 or the third frequency fc3) in the high frequency range. The switching count third upper limit SW_lim3 is an example of a “fourth predetermined count”.

[Summary of Modification 2]
As described above, in the power conversion device 1 of the modified example 2, when the number of counts (that is, the number of system voltage abnormal states within a certain set time) exceeds the switching count third upper limit SW_lim3, the power converter. The power conversion of 10 is stopped. Here, the case where the number of abnormalities in the system voltage is large is a case where the state of the system to be interconnected or the system informed by the external command SYS from the external system is unstable. Further, when the power conversion device 1 continues the power conversion when the system state is unstable, the capacitor voltage Vc may reach the overvoltage level. In this case, the power converter 10 stops the operation and the capacitor voltage The operation cannot be resumed unless Vc is discharged to the normal level. The power conversion device 1 of the modified example 2 stops the power converter 10 according to the number of the system voltage abnormality signal ERR, thereby reducing power loss, speeding up the operation restart at the time of a system failure, and improving the operation continuity. Can be made.

(Modification 3)
Hereinafter, the converter control device 20a of the third modification will be described with reference to the drawings. In the converter control device 20 of the embodiment, the voltage command value calculation unit 220 determines that the active power PE output by the power converter 10 and the reactive power QE have a predetermined active power command value PE * and reactive power. The case has been described in which the cell voltage command value Vcl * for instructing the cell voltage Vcl of each cell CL is calculated so as to be the command value QE *. In the converter control device 20a according to the modification 3, the voltage command value calculation unit 220 sets limits on the active power command value PE * and the reactive power command value QE * based on the presence / absence of the first pulse switching command SW1. The case will be described. In addition, about the structure similar to embodiment and the modification mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted.

FIG. 14 is a diagram illustrating an example of the configuration of the converter control device 20a according to the third modification. Instead of (or in addition to) the configuration included in the converter control device 20, the converter control device 20a according to the modification 3 has a voltage command value calculation unit 220, a carrier frequency switching command unit 230, and a carrier frequency switching unit 240. The triangular wave carrier generation unit 250 and the converter 260 are provided as functional units. The converter 260 limits the predetermined active power command value PE * and reactive power command value QE * when the first pulse switching command SW1 is output by the carrier frequency switching command unit 230. For example, when the first pulse switching command SW1 is output, the converter 260 changes the active power command value PE * from the active power upper limit command value + P * _lim to the active power lower limit command value −P * _lim. The reactive power command value QE * is limited to a range from the reactive power upper limit command value + Q * _lim to the reactive power lower limit command value −Q * _lim. Here, the value of P * _lim is less than the rated active power of the power converter 10, and the value of Q * _lim is less than the rated reactive power of the power converter 10.

The voltage command value calculation unit 220 calculates the cell voltage command value Vcl * based on the active power command value PE * and the reactive power command value QE * limited by the converter 260. As a result, it is possible to generate a gate signal that suppresses power loss proportional to the active power PE and the reactive power QE of the power converter 10.

[Summary of Modification 3]
As described above, in the power conversion device 1 of the modified example 3, the first pulse switching command SW1 is output, and the power converter 10 outputs the carrier command frequency fc * in the high frequency range (for example, the second frequency fc2 or the third frequency fc2). The power loss of the power converter 10 can be reduced in the state where the switching is controlled by the frequency fc3).

(Modification 4)
Hereinafter, the power converter 1 of the modification 4 is demonstrated with reference to drawings. In the above-described embodiment and modification, the carrier frequency switching command unit 230 of the converter control device 20 is based on the external command SYS output from the external system such as the protection device of the power conversion device 1 and the carrier command frequency fc. The case of selecting the frequency as * has been described. In the power conversion device 1 of the modification 4, the carrier command frequency fc * is based on the signal output from another power conversion device 1 connected to the DC side in the system connected to the power conversion device 1. A case of selecting the frequency as will be described. In addition, about the structure similar to embodiment and the modification mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted.

15: is a figure which shows an example of the usage environment of the power converter device 1 in the modification 4. As shown in FIG. In the modified example 4, the power conversion device 1α and the power conversion device 1β are connected to one end and the other end of the DC system so as to face each other. The power converter 1α is provided at a connection 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 converter 1β is provided at a connection 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 Modification 4, the first pulse output unit 233 outputs the first pulse switching command SW1 to the carrier frequency switching unit 240 and the other power conversion device 1. Moreover, in the modified example 4, the carrier frequency switching command unit 230 acquires the first pulse switching command SW1 output by another power conversion device 1 as the external command SYS.

In the above example, 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, for example, two or more power conversion devices 1 via a DC system.

[Summary of Modification 4]
As described above, the power conversion device 1 of the modified example 4 selects the carrier command frequency fc * based on the external command SYS acquired from the other power conversion device 1, and the other power conversion device 1 in the opposite direction selects the carrier command frequency fc *. The influence of the detected AC system fault on the self-device and the system connected to the self-device can be quickly settled. Therefore, the power conversion device 1 of Modification 4 can improve the operation continuity at the time of a system fault while reducing the power loss.

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 spirit of the invention. These embodiments and their modifications are included in the invention described in the claims and the equivalents thereof as well as included in the scope and the gist of the invention.

Claims (15)

1. A power conversion device capable of mutually converting DC and AC,
   An arm unit in which at least one unit converter including a capacitor and a switching element connected in parallel to each other is connected in series;
   A first frequency obtained by multiplying the frequency of the alternating current by a first non-integer value, a second frequency obtained by multiplying the frequency of the alternating current by a second non-integer value equal to or greater than the first non-integer value, and higher than the second frequency. A generator for selectively generating a triangular wave carrier signal having any one of the third frequencies, which is the frequency,
   A control unit for controlling the switching element based on the triangular wave carrier signal generated by the generation unit,
   The generation unit, a switching unit for switching which frequency of the triangular wave carrier signal is generated, and,
   The switching unit, in the generation unit,
   When the absolute value of the AC voltage is within a predetermined range, the triangular wave carrier signal of the first frequency is generated,
   When the absolute value of the alternating voltage is not within the predetermined range, the triangular wave carrier signal of the third frequency is generated during the first period,
   When the absolute value of the AC voltage is not within the predetermined range and the generator does not generate the triangular wave carrier signal of the third frequency, the triangular wave carrier signal of the second frequency is generated during the second period. Generate,
   Power converter.
2. When the command value is obtained from another device when the absolute value of the AC voltage is within a predetermined range, the switching unit causes the triangular wave carrier signal of the second frequency to be generated during the second period. ,
   The power conversion device according to claim 1.
3. The second period is longer than the first period,
   The power conversion device according to claim 1 or 2.
4. The third frequency is a frequency obtained by multiplying the frequency of the alternating current by a third non-integer value equal to or higher than the second non-integer value.
   The power conversion device according to any one of claims 1 to 3.
5. The third frequency is a frequency obtained by multiplying the frequency of the alternating current by an integer value of the second non-integer value or more, and the integer value is 4 or more,
   The power conversion device according to any one of claims 1 to 3.
6. The third frequency is a predetermined fixed frequency,
   The power conversion device according to any one of claims 1 to 3.
7. The generation unit does not generate the triangular wave carrier signal having the third frequency when the number of times the absolute value of the AC voltage exceeds the predetermined range is a first predetermined number or more within a predetermined time,
   The power conversion device according to any one of claims 1 to 6.
8. The generating unit does not generate the triangular wave carrier signal having the second frequency when the number of times the absolute value of the AC voltage exceeds the predetermined range is a second predetermined number or more within a predetermined time.
   The power conversion device according to any one of claims 1 to 7.
9. If the number of times that the absolute value of the AC voltage exceeds the predetermined range is a third predetermined number of times or more within a predetermined time, the generation unit causes the absolute value of the AC voltage to exceed the predetermined range. Even if the triangular wave carrier signal of the first frequency is continuously generated,
   The power conversion device according to any one of claims 1 to 8.
10. If the number of times the absolute value of the AC voltage exceeds the predetermined range is a fourth predetermined number or more within a predetermined time,
    The control unit stops the operation of the switching element,
    The power conversion device according to any one of claims 1 to 9.
11. The control unit controls the switching element so that the current flowing through the arm unit becomes less than a predetermined current value when the triangular wave carrier signal of the second frequency or the third frequency is generated by the generation unit. Control,
    The power conversion device according to any one of claims 1 to 10.
12. The generator generates a triangular wave carrier signal of the second frequency during the second period based on a command signal from another AC / DC converter connected to the DC side of the own device,
    The command signal is a signal output when a system voltage abnormality occurs on the AC side of the other AC-DC converter.
    The power conversion device according to any one of claims 1 to 11.
13. A power conversion system comprising two or more power conversion devices according to any one of claims 1 to 11, wherein direct current sides of the two or more power conversion devices are connected to each other.
    The generator generates a triangular wave carrier signal of the second frequency during the second period based on a command signal from another AC / DC converter connected to the DC side of the own device,
    The command signal is a signal that is output when a system voltage abnormality occurs on the AC side of the AC / DC converter,
    Power conversion system.
14. A power converter including an arm unit in which at least one unit converter including a capacitor and a switching element, which are capable of mutually converting direct current and alternating current and are connected in parallel, are connected in series,
    A first frequency obtained by multiplying the frequency of the alternating current by a first non-integer value, a second frequency obtained by multiplying the frequency of the alternating current by a second non-integer value equal to or greater than the first non-integer value, and higher than the second frequency. Selectively generate a triangular wave carrier signal of any one of the third frequency, which is the frequency,
    Controlling the switching element based on the generated triangular wave carrier signal,
    By switching which frequency the triangular wave carrier signal is generated,
    When the absolute value of the AC voltage is within a predetermined range, the triangular wave carrier signal of the first frequency is generated,
    When the absolute value of the alternating voltage is not within the predetermined range, the triangular wave carrier signal of the third frequency is generated during the first period,
    When the absolute value of the AC voltage is not within the predetermined range and the triangular wave carrier signal of the third frequency is not generated, the triangular wave carrier signal of the second frequency is generated for the second period,
    Power conversion method.
15. A power conversion device including an arm unit in which at least one unit converter including a capacitor and a switching element, which are capable of mutually converting direct current and alternating current and are connected in parallel to each other, are connected in series,
    A first frequency obtained by multiplying the frequency of the alternating current by a first non-integer value, a second frequency obtained by multiplying the frequency of the alternating current by a second non-integer value equal to or greater than the first non-integer value, and higher than the second frequency. Selectively generate a triangular wave carrier signal of any one of the third frequency, which is the frequency,
    Based on the generated triangular wave carrier signal, to control the switching element,
    By switching which frequency the triangular wave carrier signal is generated,
    When the absolute value of the AC voltage is within a predetermined range, the triangular wave carrier signal of the first frequency is generated,
    When the absolute value of the alternating voltage is not within the predetermined range, the triangular wave carrier signal of the third frequency is generated during the first period,
    When the absolute value of the AC voltage is not within the predetermined range and the triangular wave carrier signal of the third frequency is not generated, the triangular wave carrier signal of the second frequency is generated for the second period.
    program.

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