Power converter, power conversion method, and program

Abstract

To provide a power converter, a power conversion method, and a program which can efficiently suppress a harmonic component of a prescribed frequency band.SOLUTION: A power converter of an embodiment calculates a voltage harmonic component of an integral multiple of harmonic order to a commercial frequency, and the total harmonic distortion of voltage. The power converter compares the voltage harmonic component and the total harmonic distortion of voltage by each harmonic order with preset two voltage harmonic reference values, and determines a magnitude relation thereof. The power converter calculates a current target value by each three-phase on the basis of the three-phase AC voltage so as to realize a transfer function including an RLC component of an AC filter capable of suppressing a harmonic component. The power converter extracts a filter parameter of a conversion source of the RLC component from a table storing filter parameters on the basis of the magnitude relation, and corrects the RLC component based on the extracted filter parameter.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a power conversion device, a power conversion method, and a program. [Background technology]

[0002] In power voltage self-commutated converter systems, harmonic suppression systems are required to suppress the increasing residual harmonics in power systems. Conventional voltage self-commutated converters suppress harmonics by extracting harmonic components contained in the load current and voltage and outputting a current that compensates for the harmonic components from the voltage self-commutated converter. In particular, a technology is known that virtually realizes a state in which an AC filter is connected in parallel with a voltage self-commutated converter. The current harmonics flowing through the virtual AC filter are calculated based on the RLC components of the virtual AC filter, and the current harmonics are superimposed on the current output by the voltage self-commutated converter, thereby allowing the voltage self-commutated converter to function as a virtual AC filter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 092812 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem that the present invention aims to solve is to provide a power conversion device, a power conversion method, and a program that can efficiently suppress harmonic components in a specified frequency band using a self-commutated converter, even when system conditions change, such as when residual harmonics increase or decrease or short-circuit capacity changes. [Means for solving the problem]

[0005] A power conversion device according to an embodiment is connected to an AC system. The power conversion device includes a voltage harmonic calculation unit, a harmonic determination unit, a filter calculation unit, and a filter parameter correction unit. The voltage harmonic calculation unit performs frequency analysis on three-phase AC voltages, which are voltages of the AC system for each of the three phases, to calculate voltage harmonic components of orders that are integer multiples of a commercial frequency and a voltage total harmonic distortion factor. The harmonic determination unit compares the voltage harmonic components and the voltage total harmonic distortion factor for each order with preset first and second voltage harmonic reference values, and determines a first magnitude relationship between the voltage harmonic components and the voltage total harmonic distortion factor for each order and the first and second voltage harmonic reference values. The filter calculation unit calculates a current target value for each of the three phases based on the three-phase AC voltage to achieve a transfer function including an RLC component of an AC filter capable of suppressing harmonic components. The filter parameter correction unit extracts the filter parameters from a filter parameter table that stores filter parameters from which the RLC components are converted, based on the voltage harmonic components and the first magnitude relationship, and corrects the RLC components based on the extracted filter parameters. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a configuration diagram of a power conversion device 100 according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the configuration of a filter parameter correction unit 170 according to the first embodiment. [Figure 3] FIG. 10 is a diagram illustrating an example of a voltage filter parameter table. [Figure 4] 5 is a flowchart showing an example of the processing flow of a filter parameter correction unit 170 according to the first embodiment. [Figure 5] FIG. 10 is a diagram showing an example of a change in the voltage harmonic component Vhn due to correction of the RLC component of the virtual AC filter. [Figure 6] FIG. 1 is a configuration diagram of a power conversion device 100 according to a second embodiment. [Figure 7]FIG. 10 is a diagram showing the configuration of a filter parameter correction unit 270 according to a second embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of a current filter parameter table. [Figure 9] 10 is a flowchart showing an example of the flow of processing by a filter parameter correction unit 270 according to the second embodiment. [Figure 10] FIG. 10 is a diagram showing an example of a change in the current harmonic component Ihn due to correction of the RLC component of the virtual AC filter. [Figure 11] FIG. 2 is a diagram showing an example of the hardware configuration of a control device 120 or 220 according to each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, a power conversion device, a power conversion method, and a program according to an embodiment will be described with reference to the drawings. In the drawings, the power lines of the three phases are not distinguished from one another but are represented as single lines. The three phases are represented by the symbols a, b, and c, respectively.

[0008] (First embodiment) [Configuration of power conversion device] 1 is a configuration diagram of a power conversion device 100 according to the first embodiment. The power conversion device 100 includes a self-commutated converter 110 and a control device 120 that controls the self-commutated converter 110.

[0009] The self-commutated converter 110 converts DC to AC and vice versa. The AC side of the self-commutated converter 110 is connected to an AC bus 2 (AC system), and the DC side is connected to a DC system (not shown). Note that in Fig. 1, devices other than the self-commutated converter 110 connected to the AC bus 2 are omitted.

[0010] The self-excited converter 110 is a converter that uses self-extinguishing elements. The self-excited converter 110 has current interruption capability and can operate regardless of the AC voltage on the AC system side. Examples of self-extinguishing elements that can be used include voltage-driven self-extinguishing elements such as IGBTs (Insulated Gate Bipolar Transistors) and IEGTs (Injection Enhanced Gate Transistors). The self-excited converter 110 performs switching operations based on voltage command values ​​Vcov_a, Vcov_b, and Vcov_c for each of the three phases input from the control device 120, and converts DC and AC into each other.

[0011] The voltage of the AC bus 2, that is, the system voltages Va, Vb, and Vc for each of the three phases, are detected by a voltage detector 30 configured with a VT (Voltage Transformer) or the like. Once the system voltages Va, Vb, and Vc for each of the three phases are detected by the voltage detector 30, the detected voltages Va, Vb, and Vc are input to the control device 120. Va, Vb, and Vc are examples of "three-phase AC voltages."

[0012] When the control device 120 receives the system voltages Va, Vb, and Vc for each of the three phases from the voltage detector 30, the control device 120 outputs voltage command values ​​Vcon_a, Vcon_b, and Vcon_c to the self-commutated converter 110.

[0013] The control device 120 includes, for example, a target value calculation unit 130, a filter unit 140, a voltage compensation control unit 150, and a converter control unit 160. These components are realized by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Furthermore, some or all of these components may be realized by hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), a GPU (Graphics Processing Unit), or an SOC (System On Chip), or may be realized by a combination of software and hardware.

[0014] The target value calculation unit 130 calculates the d-axis current target value Idref based on the required power, which is the active power that the self-commutated converter 110 supplies to the AC bus 2 (AC system). The d-axis is a virtual coordinate axis representing the active power. The q-axis, which will be described later, is a virtual coordinate axis representing the reactive power.

[0015] The voltage compensation control unit 150 includes a constant voltage control unit 152 , a fault-time reactive power output control unit 154 , and a constant reactive power control unit 156 .

[0016] The constant voltage control unit 152 calculates a reactive power target value Qv_ref for maintaining the voltage of the AC system constant based on the system voltages Va, Vb, and Vc for each of the three phases detected by the voltage detector 30.

[0017] The fault-time reactive power output control unit 154 outputs a reactive power target value Qcon_ref for bringing reactive power closer to a desired value more quickly than the constant voltage control unit 152 when the average value, effective value, or other statistical value, or all of the system voltages Va, Vb, and Vc, or the average value, effective value, or other statistical value, falls below a first fault voltage reference value or exceeds a second fault voltage reference value. The effective value is the square of the sum of the squares of the respective values. The first fault reference value and the second fault voltage reference value are set, for example, based on the voltage determined to be a system fault.

[0018] A reactive power target value Qref obtained by adding the reactive power target value Qv_ref output by the constant voltage control unit 152 and the reactive power target value Qcon_ref output by the fault-time reactive power output control unit 154 is input to a constant reactive power control unit 156. The constant reactive power control unit 156 calculates and outputs a q-axis current target value Iqref for bringing the reactive power at the bus 2 closer to the reactive power target value Qref. The constant voltage control unit 152 and the constant reactive power control unit 156 perform feedback control such as PID control, for example.

[0019] The filter unit 140 includes, for example, a filter calculation unit 142, a coordinate conversion unit 144, and HPF (high-pass filter) units 146d and 146q.

[0020] The filter calculation unit 142 calculates the current target values ​​for each of the three phases based on the system voltages Va, Vb, and Vc for each of the three phases detected by the voltage detector 30 and the filter parameter Fill_RLC output by the filter parameter correction unit 170, which will be described later, so as to realize a transfer function including the RLC components of a filter that can suppress harmonic components in a predetermined frequency band. The harmonic components in the predetermined frequency band are harmonic components in the frequency band to be suppressed.

[0021] The filter calculation unit 142 calculates a current target value for each of the three phases so that the self-commutated converter 110 can substitute for the functions of these AC filters 20. The AC filters 20 whose functions are substituted by the self-commutated converter 110 may be referred to as virtual AC filters.

[0022] Here, the description will be focused on one of the three phases. The AC filter 20 is often an electric circuit in which a resistance R, an inductance L, and a capacitor C are connected in series (hereinafter referred to as an RLC series circuit), or an electric circuit in which multiple RLC series circuits are connected in parallel. Therefore, assuming that the virtual AC filter is an RLC series circuit (or a circuit that approximates this), the electric circuit equation of the virtual AC filter is expressed by equation (1) using the respective magnitudes (RLC components) of the resistance R, inductance L, and capacitor C.

[0023]

number

[0024] By Laplace transforming equation (1) using the Laplace operator s, we obtain the transfer function Fil(s) shown in equation (2), which has the same characteristics as an RLC series circuit: Fil(s)=(R+Ls+1 / Cs).

[0025]

number

[0026] The filter calculation unit 142 calculates the harmonic current i(t) flowing through the virtual AC filter from the AC voltage V(t) by applying the inverse of the transfer function Filall(s) of the virtual AC filter to the time domain. By performing this for each of the three phases, the filter calculation unit 142 calculates the current target values ​​Iaf, Ibf, and Icf for each of the three phases based on the system voltages Va, Vb, and Vc for each of the three phases.

[0027] The coordinate conversion unit 144 converts the current target values ​​Iaf, Ibf, and Icf for each of the three phases calculated by the filter calculation unit 142 into a d-axis current target value Idf# and a q-axis current target value Iqf#. There are no particular restrictions on the conversion method used by the coordinate conversion unit 144, and the coordinate conversion unit 144 performs the above conversion using, for example, a known method. The d-axis current target value Idf# is an example of a first d-axis current target value, and the q-axis current target value Iqf# is an example of a first q-axis current target value. In this process, the fundamental frequency component in the AC system is converted into a DC component.

[0028] The HPF (high pass filter) units 146d and 146q remove low frequency components, including DC components, from the d-axis current target value Idf#. The HPF unit 146q removes low frequency components, including DC components, from the q-axis current target value Iqf#. As a result, the fundamental frequency component in the AC system is removed. The HPF unit 146d outputs the d-axis current target value Idref#, and the HPF unit 146q outputs the q-axis current target value Iqref#. These current target values ​​are components of the current target values ​​of the self-commutated converter 110 that are used to realize the function of an active filter.

[0029] The filter parameter correction unit 170 outputs, from the system voltages Va, Vb, and Vc for each of the three phases detected by the voltage detector 30, filter parameter values ​​that are the basis for conversion of the RLC components of the virtual AC filter used in the filter calculation unit 142 to bring the amount of harmonic compensation closer to a desired value.

[0030] 2 is a configuration diagram of a filter parameter correction unit 170 according to the first embodiment. The filter parameter correction unit 170 includes, for example, a voltage harmonic calculation unit 172, a harmonic determination unit 174, a parameter table reference unit 176, and a parameter upper limit limiter unit 178.

[0031] The voltage harmonic calculation unit 172 performs frequency analysis on the system voltages Va, Vb, and Vc for each of the three phases detected by the voltage detector 30, and calculates voltage harmonic components Vhn of orders that are integer multiples of the fundamental frequency. The voltage harmonic components Vhn are composed of n parameters: a first-order (fundamental) component Vh_1, a second-order component Vh_2, ..., and an nth-order component Vh_n. Furthermore, the voltage harmonic calculation unit 172 calculates a voltage total harmonic distortion (THD) Vh_thd, which is the ratio of the fundamental to the sum of all harmonic components, from the voltage harmonic components Vhn. Here, the frequency analysis may be, for example, a discrete Fourier transform (DFT) or a fast Fourier transform (FFT).

[0032] The harmonic determination unit 174 compares the voltage total harmonic distortion factor Vh_thd calculated by the voltage harmonic calculation unit 172 and the voltage harmonic components Vhn of each order with preset voltage reference values ​​1 and 2 to determine which is larger. That is, the harmonic determination unit 174 compares the voltage total harmonic distortion factor Vh_thd with voltage reference values ​​1 and 2, and compares the voltage harmonic components Vhn of each order with voltage reference values ​​1 and 2. Then, the harmonic determination unit 174 outputs a determination signal F_Num and each of the harmonic components Vh_thd and Vhn according to the magnitude relationship. The voltage reference value 1 is an example of a "first voltage harmonic reference value," and the voltage reference value 2 is an example of a "second voltage harmonic reference value." The magnitude relationships between the voltage total harmonic distortion factor Vh_thd and the voltage harmonic components Vhn of each order, and the voltage reference value 1 and the voltage reference value 2 are examples of "first magnitude relationships." Here, an on-delay timer may be used to determine the magnitude relationships.

[0033] For example, the harmonic determination unit 174 sets the determination signal F_Num to 1 when either the voltage total harmonic distortion factor Vh_thd or the voltage harmonic component Vhn of each order is equal to or greater than the voltage reference value 1 or less than the voltage reference value 2. The condition under which the determination signal F_Num becomes 1 is an example of a "predetermined condition."

[0034] Furthermore, if either the voltage total harmonic distortion factor Vh_thd or the voltage harmonic component Vhn of each order is equal to or greater than the voltage reference value 2 and less than the voltage reference value 1, the harmonic determination unit 174 sets the determination signal F_Num=2.

[0035] The voltage reference value to be compared with the voltage total harmonic distortion factor Vh_thd may be different from the voltage reference value to be compared with each order of the voltage harmonic component Vhn.

[0036] The parameter table reference unit 176 extracts one filter parameter value from a preset voltage filter parameter table based on the determination signal F_Num output by the harmonic determination unit 174, the voltage total harmonic distortion factor Vh_thd, the voltage harmonic components Vhn of each order, and the current filter parameter value para_S.

[0037] 3 is a diagram showing an example of a voltage filter parameter table. As shown in the figure, the voltage filter parameter table is a table in which a filter capacitance para_S and a sharpness para_Q are associated with a filter parameter value para_S and each order of a voltage harmonic Vhn. The filter capacitance para_S and the sharpness para_Q are filter parameters that are used to convert the RLC components of a virtual AC filter used in the filter calculation unit 142.

[0038] In the voltage filter parameter table, multiple filter capacitances para_S and sharpness factors para_Q are determined according to the filter parameter value para_S and each order of voltage harmonics Vhn. For example, in Figure 3, there are X voltage harmonics Vhn of each order, which are designated Vhn_T1, Vhn_T2, ..., Vhn_TX in ascending order. There are Y filter parameters, designated S_T1, S_T2, ..., S_TY. The filter capacitances para_S and sharpness factors para_Q are determined for each matrix of Vhn_T1, Vhn_T2, ..., Vhn_TX and S_T1, S_T2, ..., S_TY. The voltage filter parameter table is an example of a "first filter parameter table."

[0039] When the judgment signal F_Num is 1, the parameter table reference unit 176 selects one matrix from the voltage filter parameter table, extracts filter parameters (filter capacitance para_S and sharpness para_Q) from that matrix, and outputs them to the downstream parameter upper limiter unit 178.

[0040] Specifically, the parameter table reference unit 176 selects, from among Vhn_T1, Vhn_T2, ..., Vhn_TX, a value that is closest to the voltage harmonic component Vhn of each order calculated by the voltage harmonic calculation unit 172, and selects, from among S_T1, S_T2, ..., S_TY, a value that is closest to the current filter parameter value para_S. In other words, one matrix is ​​selected from the voltage filter parameter table. Then, the parameter table reference unit 176 extracts the filter parameters (filter capacitance para_S and sharpness para_Q) stored in the matrix.

[0041] When the determination signal F_Num is 2, the parameter table reference unit 176 does not use the voltage filter parameter table, but instead holds the current filter parameters (filter capacitance para_S and sharpness para_Q) as they are and outputs them to the parameter upper limiter unit 178 at the subsequent stage.

[0042] The parameter upper limit limiter unit 178 performs filter capacity upper limit processing according to the rated capacity Qrate of the self-excited converter 110 and the reactive power output command value Qref based on the reactive power target value Qref output from the voltage compensation control unit 150 and the filter parameters (filter capacity para_S and sharpness para_Q) calculated by the parameter table reference unit 176, and converts the filter parameter Fill_RLC into the RLC component of the virtual AC filter and outputs it.

[0043] When the filter parameter para_S exceeds the difference (Qrate-Qref) between the rated capacity Qrate and the reactive power output command value Qref, the parameter upper limit limiter unit 178 performs upper limit processing to set para_S to (Qrate-Qref).

[0044] Here, as shown in equation (3), the voltage and angular frequency ω_s (=2πf) can be converted into RLC components using the tuning order n, filter capacitance S, and sharpness Q. Because there are filters corresponding to each order, the RLC components are calculated using the filter capacitance S and sharpness Q, which are filter parameters referenced in the voltage filter parameter table.

[0045]

number

[0046] The converter control unit 160 calculates voltage command values ​​Vcov_a, Vcov_b, and Vcov_c for each of the three phases to be given to the self-excited converter 110 based on the input final d-axis current target value Id* and final q-axis current target value Iq*, and outputs them to the self-excited converter 110.

[0047] The final d-axis current target value Id* is added to the d-axis current target value Idref output by the target value calculation unit 130 and the d-axis current target value Idref# output by the HPF unit 146d. The final q-axis current target value Iq* is added to the q-axis current target value Iqref# output by the HPF unit 146q and the q-axis current target value Iqref output by the constant reactive power control unit 156.

[0048] [Processing flow] A series of processing steps performed by the filter parameter correction unit 170 according to the first embodiment will be described below with reference to a flowchart. FIG. 4 is a flowchart illustrating an example of the processing steps performed by the filter parameter correction unit 170 according to the first embodiment. Information related to the RLC components of the AC filter 20 (virtual AC filter) is stored in advance in the storage device of the control device 120. The filter calculation unit 142 calculates Filcl(s) based on the RLC components of the filter k that needs to be realized, and calculates Filall(s). The filter parameter correction unit 170 corrects the RLC components based on the voltage harmonic components Vhn.

[0049] First, the voltage harmonic calculation unit 172 performs frequency analysis on the system voltages Va, Vb, and Vc for each of the three phases detected by the voltage detector 30, and calculates voltage harmonic components Vhn of orders that are integer multiples of the fundamental frequency from 1 to n, and voltage total harmonic distortion (THD) Vh_thd (step S100).

[0050] Next, the harmonic determination unit 174 compares the voltage total harmonic distortion factor Vh_thd calculated by the voltage harmonic calculation unit 172 and the voltage harmonic components Vhn of each order with the preset voltage reference value 1 and voltage reference value 2, and determines which is larger (step S102).

[0051] As described above, when either the voltage total harmonic distortion Vh_thd or the voltage harmonic component Vhn of each order is equal to or greater than the voltage reference value 1 or less than the voltage reference value 2, the judgment signal F_Num indicating the magnitude relationship becomes 1.

[0052] In other words, if the voltage total harmonic distortion factor Vh_thd is greater than or equal to the voltage reference value 1, if the voltage harmonic components Vhn of each order are greater than or equal to the voltage reference value 1, if the voltage total harmonic distortion factor Vh_thd is less than the voltage reference value 2, or if the voltage harmonic components Vhn of each order are less than the voltage reference value 2, the judgment signal F_Num will be 1.

[0053] Furthermore, when either the voltage total harmonic distortion factor Vh_thd or the voltage harmonic component Vhn of each order is equal to or greater than the voltage reference value 2 and less than the voltage reference value 1, the determination signal F_Num becomes 2.

[0054] When the judgment signal F_Num is 1, the parameter table reference unit 176 extracts filter parameters (filter capacitance para_S and sharpness para_Q) from the voltage filter parameter table using the voltage harmonic components Vhn of each order calculated by the voltage harmonic calculation unit 172 and the current filter parameter value para_S (step S104).

[0055] On the other hand, if the determination signal F_Num is 2, the parameter table reference unit 176 does not use the voltage filter parameter table, and keeps the current filter parameters (filter capacitance para_S and sharpness para_Q) as they are (step S106).

[0056] Next, the parameter upper limit limiter unit 178 performs filter capacity upper limit processing (processing in which the upper limit is (Qrate-Qref)) according to the rated capacity Qrate of the self-excited converter 110 and the reactive power output command value Qref, based on the reactive power target value Qref output from the voltage compensation control unit 150 and the filter parameters (filter capacity para_S and sharpness para_Q) output from the parameter table reference unit 176 (step S108).

[0057] Next, the parameter upper limit limiter unit 178 converts the filter parameters (filter capacitance para_S and sharpness para_Q) output from the parameter table reference unit 176 into RLC components and outputs them as filter parameters Fill_RLC to the filter calculation unit 142 (step S110). As a result, the RLC components of the virtual AC filter used in the filter calculation unit 142 are corrected (updated) to the filter parameters Fill_RLC.

[0058] FIG. 5 is a diagram showing an example of changes in voltage harmonic component Vhn due to correction of the RLC component of the virtual AC filter. In the initial state, voltage harmonic component Vhn is in the range of less than voltage reference value 1 and greater than or equal to voltage reference value 2. When voltage harmonic component Vhn of each order increases due to system change 1, it may exceed voltage reference value 1. In such a case, when filter parameters are corrected (parameter correction 1 in the diagram), voltage harmonic component Vhn is suppressed to be equal to or less than voltage reference value 1. Suppose that system change 2 then causes voltage harmonic component Vhn to be less than voltage reference value 2. In contrast, when filter parameters are corrected (parameter correction 2 in the diagram), voltage harmonic component Vhn is increased to be equal to or greater than voltage reference value 2, and the filter capacitance of the self-commutated converter 110 is suppressed.

[0059] According to the first embodiment described above, the power conversion device 100 performs frequency analysis on the system voltages Va, Vb, and Vc to calculate voltage harmonic components Vhn of orders that are integer multiples of the commercial frequency and voltage total harmonic distortion factor Vh_thd. The power conversion device 100 compares the voltage harmonic components Vhn and voltage total harmonic distortion factor Vh_thd with preset voltage reference values ​​1 and 2 to determine the magnitude relationship between them. The power conversion device 100 calculates current target values ​​Iaf, Ibf, and Icf for each of the three phases to achieve a transfer function including RLC components of an AC filter capable of suppressing harmonic components. Based on the magnitude relationship, the power conversion device 100 extracts filter parameters from a voltage filter parameter table that stores filter parameters (filter capacitance para_S and sharpness para_Q) from which the RLC components are converted. The power conversion device 100 corrects the RLC components based on the extracted filter parameters. This makes it possible to efficiently respond to changes in system conditions such as short-circuit capacity and increases or decreases in residual harmonics.In addition, it is possible to achieve harmonic suppression by changing filter parameters and switching virtual AC filters based on voltage harmonics and arbitrary reference values ​​(voltage reference values ​​1 and 2).

[0060] (Second embodiment) The second embodiment will be described below. In the first embodiment described above, a filter parameter is extracted from a voltage filter parameter table according to a comparison result between each order of the voltage harmonic component Vhn and an arbitrary reference value (voltage reference value 1, 2), and the RLC component is corrected using the extracted filter parameter.

[0061] In contrast, the second embodiment differs from the first embodiment in that filter parameters are extracted from the voltage filter parameter table or the current filter parameter table described above in accordance with the comparison result between the current harmonic distortion factor Ihn of each order and an arbitrary reference value (current reference value 1, 2), and the RLC component is corrected using the extracted filter parameters. The following description will focus on the differences from the first embodiment, and a description of the points in common with the first embodiment will be omitted. In the description of the second embodiment, the same parts as in the first embodiment will be described with the same reference numerals.

[0062] 6 is a configuration diagram of a power conversion device 100 according to the second embodiment. The power conversion device 100 includes a self-commutated converter 110 and a control device 220 that controls the self-commutated converter 110.

[0063] In the second embodiment, in addition to the voltage detector 30, a current detector 40 is also attached to the AC bus 2. The current detector 40 detects system currents Ia, Ib, and Ic for each of the three phases. Ia, Ib, and Ic are examples of "three-phase AC current."

[0064] The control device 220 outputs voltage command values ​​Vcon_a, Vcon_b, and Vcon_c to the self-excited converter 110 based on the system currents Ia, Ib, and Ic for each of the three phases detected by the current detector 40 .

[0065] The control device 220 includes a target value calculation unit 130 , a voltage compensation control unit 150 , a filter unit 240 , a filter parameter correction unit 270 , and a converter control unit 160 .

[0066] The filter section 240 includes a filter calculation section 142, a limiter section 143, a coordinate conversion section 144, and HPF sections 146d and 146q.

[0067] When the harmonic determination unit 274 outputs a determination signal F_Num=3, the limiter unit 143 sets the numerical value If_limit output by the filter parameter correction unit 270 as the upper limit. The determination signal F_Num=3 is output when the current harmonic component Ihn of each order is equal to or greater than the current reference value 1. If_limit is an arbitrarily determined limit value, a value that is set in advance for the rated current. Furthermore, If_limit may be the difference between the rated current and the system currents Ia, Ib, and Ic for each of the three phases detected by the current detector.

[0068] 7 is a configuration diagram of a filter parameter correction unit 270 according to the second embodiment. The filter parameter correction unit 270 includes a voltage harmonic calculation unit 172, a current harmonic calculation unit 172I, a harmonic determination unit 274, a parameter table reference unit 276, and a parameter upper limit limiter unit 278.

[0069] The voltage harmonic calculation unit 172 performs frequency analysis on the system voltages Va, Vb, and Vc for each of the three phases detected by the voltage detector 30, and calculates voltage harmonic components Vhn of orders that are integer multiples of the fundamental frequency from 1 to n. Furthermore, the voltage harmonic calculation unit 172 calculates the voltage total harmonic distortion factor Vh_thd.

[0070] The current harmonic calculation unit 172I performs frequency analysis on the system currents Ia, Ib, and Ic for each of the three phases detected by the current detector, and calculates current harmonic components Ihn of orders that are integer multiples of the fundamental frequency. Ihn consists of n parameters: a first-order (fundamental wave) component Ih_1, a second-order component Ih_2, ..., an n-order component Ih_n.

[0071] The harmonic determination unit 174 compares the voltage total harmonic distortion factor Vh_thd calculated by the voltage harmonic calculation unit 172 and the voltage harmonic components Vhn of each order with preset voltage reference values ​​1 and 2, and determines which is larger or smaller. That is, the harmonic determination unit 174 compares the voltage total harmonic distortion factor Vh_thd with the voltage reference values ​​1 and 2, and compares the voltage harmonic components Vhn of each order with the voltage reference values ​​1 and 2.

[0072] Furthermore, the harmonic determination unit 174 compares the current harmonic components Ihn of each order calculated by the current harmonic calculation unit 172I with preset current reference values ​​1 and 2, and determines which is larger.

[0073] Then, the harmonic determination unit 174 outputs a priority mode F_mode, a determination signal F_Num, and each of the harmonic components Vh_thd, Vhn, and Ihn according to the two types of magnitude relationships. Current reference value 1 is an example of a "first current harmonic reference value," and current reference value 2 is an example of a "second current harmonic reference value." The magnitude relationships between the current harmonic component Ihn and current reference value 1 and current reference value 2 are an example of a "second magnitude relationship."

[0074] For example, the harmonic determination unit 174 sets the determination signal F_Num=1 when either the voltage total harmonic distortion Vh_thd or the voltage harmonic component Vhn of each order is equal to or greater than the voltage reference value 1 or is less than the voltage reference value 2.

[0075] Furthermore, if either the voltage total harmonic distortion factor Vh_thd or the voltage harmonic component Vhn of each order is equal to or greater than the voltage reference value 2 and less than the voltage reference value 1, the harmonic determination unit 174 sets the determination signal F_Num=2.

[0076] Furthermore, the harmonic determination unit 174 sets the determination signal F_Num=3 when the current harmonic component Ihn of each order is equal to or greater than the current reference value 1. Furthermore, the harmonic determination unit 174 sets the priority mode F_mode=I. F_mode=I is a current priority mode, in which a current filter parameter table, which will be described later, is referenced.

[0077] Furthermore, the harmonic determination unit 174 sets the determination signal F_Num=4 when the current harmonic component Ihn of each order is less than the current reference value 2. Furthermore, the harmonic determination unit 174 sets the priority mode F_mode=V. F_mode=V is a voltage priority mode, in which the above-mentioned voltage filter parameter table is referenced.

[0078] Furthermore, the harmonic determination unit 174 sets the determination signal F_Num to 5 when the current harmonic component Ihn of each order is equal to or greater than the current reference value 2 and less than the current reference value 1. Furthermore, the harmonic determination unit 174 maintains the priority mode F_mode as the previous mode.

[0079] The parameter table reference unit 276 switches the filter parameter table to be referenced between the voltage filter parameter table and the current filter parameter table according to the priority mode F_mode. Then, the parameter table reference unit 276 extracts filter parameters from either the filter parameter table based on the determination signal F_Num output by the harmonic determination unit 274, the harmonic values ​​Vh_thd, Vhn, Ihn, and the current filter parameter value para_S.

[0080] 8 is a diagram showing an example of a current filter parameter table. As shown in the figure, the current filter parameter table is a table in which the filter capacitance para_S and the sharpness para_Q are associated with the filter parameter value para_S and the current harmonic component Ihn of each order.

[0081] In the current filter parameter table, multiple filter capacitances para_S and sharpness factors para_Q are determined according to the filter parameter value para_S and the current harmonic component Ihn of each order. For example, in FIG. 8, there are X current harmonic components Ihn of each order, which are designated Ihn_T1, Ihn_T2, ..., Ihn_TX in ascending order. There are Y filter parameters, designated S_T1, S_T2, ..., S_TY. The filter capacitances para_S and sharpness factors para_Q are determined for each matrix of Ihn_T1, Ihn_T2, ..., Ihn_TX and S_T1, S_T2, ..., S_TY. The current filter parameter table is an example of a "second filter parameter table."

[0082] When the judgment signal F_Num is 1, the parameter table reference unit 176 selects one matrix from the voltage filter parameter table, extracts filter parameters (filter capacitance para_S and sharpness para_Q) from that matrix, and outputs them to the downstream parameter upper limiter unit 178.

[0083] If the determination signal F_Num is 2 or 5, the parameter table reference unit 176 does not use the voltage filter parameter table, but instead holds the current filter parameters (filter capacitance para_S and sharpness para_Q) as they are and outputs them to the parameter upper limiter unit 178 in the subsequent stage.

[0084] When the judgment signal F_Num is 3, the parameter table reference unit 176 selects one matrix from the current filter parameter table, extracts filter parameters (filter capacitance para_S and sharpness para_Q) from that matrix, and outputs them to the downstream parameter upper limiter unit 178.

[0085] The step size of each order of the current harmonic component Ihn in the current filter parameter table may be different from the step size of each order of the current harmonic Vhn in the voltage filter parameter table described above, as long as the same effect is obtained. The priority mode F_mode may be switched in response to an external switching command, or may be fixed in advance so as not to be switched.

[0086] The parameter upper limit limiter unit 278 performs filter capacity upper limit processing according to the rated capacity Qrate of the self-excited converter 110 and the reactive power output command value Qref based on the reactive power target value Qref output by the voltage compensation control unit 150, the priority mode F_mode output by the parameter table reference unit 276, and the filter parameters (Para_S, Para_Q), and converts the filter parameter Fill_RLC into the RLC component of the filter and outputs it.

[0087] When the filter parameter para_S exceeds the difference (Qrate-Qref) between the rated capacity Qrate and the reactive power output command value Qref, the parameter upper limit limiter unit 278 performs upper limit processing to set para_S to (Qrate-Qref). Furthermore, when the priority mode F_mode is the current priority mode F_mode=I, the parameter upper limit limiter unit 278 may output a preset current upper limit value for each order.

[0088] [Processing flow] A series of processing steps performed by the filter parameter correction unit 270 according to the second embodiment will be described below with reference to a flowchart. FIG. 9 is a flowchart illustrating an example of the processing steps performed by the filter parameter correction unit 270 according to the second embodiment. Information related to the RLC components of the AC filter 20 (virtual AC filter) is stored in advance in a storage device of the control device 220. The filter calculation unit 142 calculates Fil(s) based on the RLC components of the filter k that needs to be realized, and calculates Filall(s). The filter parameter correction unit 270 corrects the RLC components based on the voltage harmonic components Vhn and the current harmonic components Ihn.

[0089] First, the current harmonic calculation unit 172I performs frequency analysis on the system currents Ia, Ib, and Ic for each of the three phases detected by the current detector, and calculates current harmonic components Ihn of orders that are integer multiples of the fundamental frequency from 1 to n (step S200).

[0090] Next, the harmonic determination unit 274 compares the current harmonic components Ihn of each order calculated by the current harmonic calculation unit 172I with preset current reference values ​​1 and 2, and determines which is larger (step S202).

[0091] For example, if the current harmonic component Ihn of each order is less than the current reference value 2, the harmonic determination unit 274 sets the determination signal F_Num=4, and further switches the priority mode F_mode to the voltage priority mode F_mode=V (step S204).

[0092] Furthermore, if the current harmonic component Ihn of each order is greater than or equal to the current reference value 2 and less than the current reference value 1, the harmonic determination unit 274 sets the determination signal F_Num=5, and further maintains the priority mode F_mode as the previous mode (step S205).

[0093] Furthermore, if the current harmonic component Ihn of each order is equal to or greater than the current reference value 1, the harmonic determination unit 274 sets the determination signal F_Num=3, and further switches the priority mode F_mode to the current priority mode F_mode=I (step S206).

[0094] Next, the harmonic determining unit 274 determines whether the priority mode F_mode is the voltage priority mode F_mode=V or the current priority mode F_mode=I (step S208).

[0095] For example, if the priority mode F_mode is determined to be the voltage priority mode F_mode=V in the processing of S208, the harmonic determination unit 274 compares the voltage total harmonic distortion factor Vh_thd calculated by the voltage harmonic calculation unit 172 and the voltage harmonic components Vhn of each order with the preset voltage reference value 1 and voltage reference value 2, and determines which is larger (step S210).

[0096] When the judgment signal F_Num is 1, the parameter table reference unit 276 extracts filter parameters (filter capacitance para_S and sharpness para_Q) from the voltage filter parameter table using the voltage harmonic components Vhn of each order calculated by the voltage harmonic calculation unit 172 and the current filter parameter value para_S (step S212).

[0097] On the other hand, if the determination signal F_Num is 2, the parameter table reference unit 276 does not use the filter parameter table and keeps the current filter parameters (filter capacitance para_S and sharpness para_Q) as they are (step S214).

[0098] On the other hand, if the priority mode F_mode is determined to be the current priority mode F_mode=I in the processing of S208, the harmonic determination unit 274 compares the current harmonic components Ihn of each order calculated by the current harmonic calculation unit 172I with the preset current reference value 1 and current reference value 2, and determines the magnitude relationship between them (step S216).

[0099] When the judgment signal F_Num is 3, the parameter table reference unit 276 extracts filter parameters (filter capacitance para_S and sharpness para_Q) from the current filter parameter table using the current harmonic components Ihn of each order calculated by the current harmonic calculation unit 172I and the current filter parameter value para_S (step S218).

[0100] On the other hand, if the determination signal F_Num is 5, the parameter table reference unit 276 does not use the filter parameter table and keeps the current filter parameters (filter capacitance para_S and sharpness para_Q) as they are (step S214).

[0101] Next, the parameter upper limit limiter unit 278 performs filter capacity upper limit processing (processing in which the upper limit is (Qrate-Qref)) according to the rated capacity Qrate of the self-excited converter 110 and the reactive power output command value Qref, based on the reactive power target value Qref output from the voltage compensation control unit 150 and the filter parameters (filter capacity para_S and sharpness para_Q) output from the parameter table reference unit 176 (step S220).

[0102] Next, the parameter upper limit limiter unit 278 converts the filter parameters (filter capacitance para_S and sharpness para_Q) output from the parameter table reference unit 276 into RLC components and outputs them as filter parameters Fill_RLC to the filter calculation unit 142 (step S222). As a result, the RLC components of the virtual AC filter used in the filter calculation unit 142 are corrected (updated) to the filter parameters Fill_RLC.

[0103] FIG. 10 is a diagram showing an example of changes in the current harmonic component Ihn due to correction of the RLC component of the virtual AC filter. In the initial state, the current harmonic component Ihn is in the range of less than current reference value 1 and greater than or equal to current reference value 2. When the current harmonic component Ihn of each order increases due to grid change 1, it may exceed current reference value 1. In such a case, when the filter parameters are corrected (parameter correction 1 in the diagram), the current harmonic component Ihn is suppressed to less than current reference value 1. Suppose that grid change 2 then causes the current harmonic component Ihn to fall below current reference value 2. In this case, the priority mode F_mode switches from the current priority mode F_mode=I to the voltage priority mode F_mode=V.

[0104] According to the second embodiment described above, the power conversion apparatus 100 performs frequency analysis on the grid currents Ia, Ib, and Ic to calculate current harmonic components Ihn of orders that are integer multiples of the commercial frequency. The power conversion apparatus 100 compares the current harmonic components Ihn of each order with preset current reference values ​​1 and 2 to determine the magnitude relationship between them. The power conversion apparatus 100 selects either a voltage filter parameter table or a current filter parameter table based on the magnitude relationship. The power conversion apparatus 100 extracts filter parameters from the selected filter parameter table. The power conversion apparatus 100 corrects the RLC components based on the extracted filter parameters. This makes it possible to efficiently respond to changes in grid conditions such as short-circuit capacity and increases or decreases in residual harmonics. Furthermore, harmonic suppression can be achieved by changing the filter parameters and switching the virtual AC filter based on the current harmonics and arbitrary reference values ​​(current reference values ​​1 and 2).

[0105] [Hardware configuration] FIG. 11 is a diagram illustrating an example of the hardware configuration of the control device 120 or 220 (hereinafter, collectively referred to as the control device 120) according to each embodiment. As illustrated, the control device 120 includes a communication controller 120-1, a CPU 120-2, a random access memory (RAM) 120-3 used as a working memory, a read-only memory (ROM) 120-4 for storing a boot program and the like, a storage device 120-5 such as a flash memory or a hard disk drive (HDD), and a drive device 120-6, all interconnected via an internal bus or a dedicated communication line. The communication controller 120-1 communicates with other devices. The storage device 120-5 stores a program 120-5a to be executed by the CPU 120-2. This program is loaded into the RAM 120-3 by a direct memory access (DMA) controller (not shown) or the like, and executed by the CPU 120-2. As a result, some or all of the target value calculation section 130, filter section 140, voltage compensation control section 150, converter control section 160, and filter parameter correction section 170 are realized.

[0106] Although several 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, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0107] 2...AC bus, 30...voltage detector, 40...current detector, 110...self-commutated converter, 120, 220...control device, 130...target value calculation unit, 140, 240...filter unit, 142...filter operation unit, 143...limiter unit, 144...coordinate conversion unit, 146d, 146q...high-pass filter unit, 150...voltage compensation control unit, 152...constant voltage control unit, 154...fault-time reactive power output control unit, 156...constant reactive power control unit, 160...converter control unit, 170, 270...filter parameter correction unit, 172...voltage harmonic calculation unit, 172I...current harmonic calculation unit, 174, 274...harmonic determination unit, 176, 276...parameter table reference unit, 178, 278...parameter upper limit limiter unit

Claims

1. A power conversion device connected to an AC system, a voltage harmonic calculation unit that calculates voltage harmonic components of orders that are integer multiples of a commercial frequency and a voltage total harmonic distortion factor by performing frequency analysis on three-phase AC voltages that are voltages of the AC system for each of the three phases; a harmonic determination unit that compares the voltage harmonic components and the voltage total harmonic distortion factor for each order with a first voltage harmonic reference value and a second voltage harmonic reference value that are set in advance, and determines a first magnitude relationship between the voltage harmonic components and the voltage total harmonic distortion factor for each order and the first voltage harmonic reference value and the second voltage harmonic reference value; a filter calculation unit that calculates a current target value for each of the three phases based on the three-phase AC voltage so as to realize a transfer function including an RLC component of an AC filter that can suppress harmonic components; a filter parameter correction unit that extracts the filter parameters from a filter parameter table that stores filter parameters from which the RLC components are converted, based on the voltage harmonic components and the first magnitude relationship, and corrects the RLC components based on the extracted filter parameters; A power conversion device comprising:

2. The filter parameter correction unit extracting the filter parameters from the filter parameter table when the first magnitude relationship satisfies a predetermined condition, and correcting the RLC components based on the extracted filter parameters; If the first magnitude relationship does not satisfy the predetermined condition, the filter parameters are retained; the predetermined condition is that the voltage harmonic components for each order are less than the second voltage harmonic reference value, the voltage total harmonic distortion is less than the second voltage harmonic reference value, the voltage harmonic components for each order are equal to or greater than the first voltage harmonic reference value, or the voltage total harmonic distortion is equal to or greater than the first voltage harmonic reference value; The power conversion device according to claim 1 .

3. a current harmonic calculation unit that calculates current harmonic components for each order by performing frequency analysis on three-phase AC current, which is a current of the AC system for each of the three phases; The harmonic determination unit comparing the current harmonic components for each order with a first current harmonic reference value and a second current harmonic reference value that are preset, and determining a second magnitude relationship between the current harmonic components for each order and the first current harmonic reference value and the second current harmonic reference value; The filter parameter correction unit selecting one of the plurality of filter parameter tables based on the second magnitude relationship; extracting the filter parameters from the extracted filter parameter table based on the voltage harmonic components, the current harmonic components, and the filter parameters, and correcting the RLC components based on the extracted filter parameters; 3. The power conversion device according to claim 1 or 2.

4. the plurality of filter parameter tables include a first filter parameter table and a second filter parameter table; the first filter parameter table is a table for voltage in which candidate filter parameters are associated with the voltage harmonic components and the filter parameters for each order; the second filter parameter table is a table for current in which candidate filter parameters are associated with the current harmonic components and the filter parameters for each order; The power conversion device according to claim 3 .

5. The filter parameter correction unit selecting the second filter parameter table from the plurality of filter parameter tables when the current harmonic components for each order are equal to or greater than the first current harmonic reference value; selecting the first filter parameter table from the plurality of filter parameter tables when the current harmonic component for each order is less than the second current harmonic reference value; retaining the filter parameters when the current harmonic components for each order are equal to or greater than the second current harmonic reference value and less than the first current harmonic reference value; The power conversion device according to claim 4.

6. A power conversion device connected to an AC system, By performing a frequency analysis on a three-phase AC voltage, which is a voltage of the AC system for each of the three phases, voltage harmonic components of orders that are integer multiples of a commercial frequency and a voltage total harmonic distortion factor are calculated; comparing the voltage harmonic components and the voltage total harmonic distortion for each order with a first voltage harmonic reference value and a second voltage harmonic reference value that are set in advance; determining a first magnitude relationship between the voltage harmonic components and the voltage total harmonic distortion for each order, and the first voltage harmonic reference value and the second voltage harmonic reference value; calculating a current target value for each of the three phases based on the three-phase AC voltage so as to realize a transfer function including an RLC component of an AC filter capable of suppressing harmonic components; extracting the filter parameters from a filter parameter table storing filter parameters from which the RLC components are converted, based on the voltage harmonic components and the first magnitude relationship; correcting the RLC components based on the extracted filter parameters; Power conversion methods.

7. The computer of the power conversion device connected to the AC system performing frequency analysis on three-phase AC voltages, which are voltages of the AC system for each of the three phases, to calculate voltage harmonic components of orders that are integer multiples of a commercial frequency and a voltage total harmonic distortion factor; comparing the voltage harmonic components and the voltage total harmonic distortion factor for each order with a first voltage harmonic reference value and a second voltage harmonic reference value that are set in advance; determining a first magnitude relationship between the voltage harmonic components and the voltage total harmonic distortion for each order, and the first voltage harmonic reference value and the second voltage harmonic reference value; calculating a current target value for each of the three phases based on the three-phase AC voltage so as to realize a transfer function including an RLC component of an AC filter capable of suppressing harmonic components; selecting the filter parameters from a filter parameter table storing filter parameters from which the RLC components are converted, based on the voltage harmonic components and the first magnitude relationship; correcting the RLC components based on the extracted filter parameters; A program to execute.

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