Apparatus and method for controlling ac / dc solid-state transformer

Abstract

The present invention relates to an AC / DC semiconductor transformer control device and method, wherein the AC / DC semiconductor transformer control device comprises a voltage acquisition unit for acquiring a DC side voltage from a semiconductor transformer including a DC / DC converter, and a DC / DC converter control unit for generating an average power command for controlling the average value of the DC side voltage based on the DC side voltage, generating a pulsating power command for controlling the pulsating value of the DC side voltage, and generating a control signal for the DC / DC converter based on the average power command and the pulsating power command, wherein in a situation where the AC voltage applied to the semiconductor transformer exceeds a reference value, the average value of the DC side voltage increases and the pulsating value of the DC side voltage decreases, and the average power command and the pulsating power command are generated in such a way that the average value of the DC side voltage increases and the pulsating value of the DC side voltage decreases.

Description

Technology Field

[0001] This invention relates to an AC / DC semiconductor transformer control device and a control method for an AC / DC semiconductor transformer. Background Technology

[0002] A semiconductor transformer is a device designed to perform power conversion using semiconductor elements. It utilizes high-speed switching power semiconductor devices (e.g., Insulated Gate Bipolar Transistors (IGBTs) or Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs)) to convert alternating current (AC) to direct current (DC) or vice versa. Since semiconductor transformers perform power conversion using semiconductor elements, they offer advantages such as miniaturization and weight reduction, low heat loss, and the ability to be easily applied to various voltages and frequencies through precise control. In particular, the adoption of semiconductor transformers has been steadily increasing recently due to the growing use of renewable energy, the development of smart grids, and the introduction of electric vehicle charging systems.

[0003] Semiconductor transformers connected to a single-phase AC system may include an AC / DC converter and a DC / DC converter electrically connected to the AC / DC converter; it is common for the AC / DC converter to switch using a carrier-based pulse-width modulation method. Carrier-based pulse-width modulation is a technique that generates a switching signal by comparing an AC command voltage synthesized by a controller with a triangular wave carrier.

[0004] FIG. 10 is a graph illustrating an example of a waveform for voltage in a carrier-based pulse width modulation (Carrier-based PWM) method. Referring to FIG. 10, in carrier-based pulse width modulation, the carrier voltage (V_c) has the form of a triangular wave, and the command voltage (V_r) has the form of a sine wave. If the command voltage (V_r) is greater than the carrier voltage (V_c), the inverter outputs a voltage (DC link voltage) of a predetermined magnitude (V_dc), and if not, outputs zero voltage. Here, for normal modulation to be possible, the magnitude of the command voltage (V_r) must be smaller than the magnitude of the carrier voltage (V_c). To properly express this, a modulation index (MI) defined as shown in Equation 1 below can be defined.

[0005] [Mathematical Formula 1]

[0006]

[0007] Here, the operation in which an inverter performs modulation with a modulation index (MI) less than 1 is called linear modulation. However, depending on the situation, the magnitude of the command voltage (V_r) may become larger than the magnitude of the carrier voltage (V_c). In this case, the possible output voltage of the inverter exceeds the DC link voltage (V_dc), and the modulation index (MI) also becomes equal to or greater than 1, making it impossible to perform linear modulation normally. This is commonly referred to as over-modulation.

[0008] Inverters are generally connected to the grid voltage, and the magnitude of this grid voltage often rises instantaneously within the normal range, causing the modulation index (MI) to increase and potentially exceed 1. In other words, overmodulation may occur. Conventionally, to solve this problem, the average value of the DC link voltage (V_dc) was increased in accordance with the rise in the grid voltage. However, if only the average value of the DC link voltage (V_dc) is increased, the 2nd harmonic ripple voltage remains unchanged, causing the maximum value of the DC link voltage (V_dc) to increase. An increase in the maximum value of the DC link voltage (V_dc) necessitates designing circuit components within the inverter's DC link, such as DC-link capacitors, snubber capacitors, and semiconductor switch elements, with higher voltage ratings than before, leading to problems such as increased component volume, increased overall device size, and additional costs. Meanwhile, there is also a method of limiting the output voltage of the inverter to relatively reduce the increase in the maximum value of the DC link voltage (V_dc). According to this, while it has the advantage of not requiring an increase in the size of components within the inverter's DC section, it has the disadvantage that the inverter's output power is significantly limited. Prior art literature

[0009] [Patent Document 0001] Method and apparatus for controlling a semiconductor transformer (Registration No.: 10-2624204, Applicant: Packtech Co., Ltd., Publication Date: 2023.06.01) [Patent Document 0002] Bidirectional isolated DC-DC converter and its control apparatus and operation method (Publication No.: 10-2022-0085934, Applicant: Hyundai Mobis Co., Ltd., Publication Date: 2022.06.23) The problem to be solved

[0010] The problem is to provide an AC / DC semiconductor transformer control device and a control method for an AC / DC semiconductor transformer that can appropriately control the DC voltage when the system AC voltage increases so that the inverter does not operate with overmodulation. means of solving the problem

[0011] To solve the above-mentioned problem, an AC / DC semiconductor transformer control device and a control method for an AC / DC semiconductor transformer are provided.

[0012] The AC / DC semiconductor transformer control device includes a voltage acquisition unit for acquiring a DC link voltage from a semiconductor transformer including a DC / DC converter, and a DC / DC converter control unit for generating an average power command to control the average value of the DC link voltage based on the DC link voltage, generating a pulsating power command to control the pulsating value of the DC link voltage, and generating a control signal for the DC / DC converter based on the average power command and the pulsating power command, wherein in a situation where the AC voltage applied to the semiconductor transformer exceeds a reference value, the average power command and the pulsating power command can be generated such that the average value of the DC link voltage increases and the pulsating value of the DC link voltage decreases.

[0013] The above DC / DC converter control unit controls the average value of the DC link voltage to increase when the system voltage increases above the rated voltage, and may also generate an average power command such that the average value of the DC link voltage increases linearly with a slope greater than the slope of the increase of the average value of the DC link voltage when the AC voltage applied to the semiconductor transformer exceeds a reference value.

[0014] The above DC / DC converter control unit may acquire a grid voltage at least at one point in time from the voltage acquisition unit and acquire a DC link voltage average value command signal corresponding to the grid voltage based on the grid voltage, and may acquire the DC link voltage average value command signal by detecting the average voltage corresponding to the grid voltage using a predetermined function or graph that is defined differently for each of the normal situation, the voltage rise situation, and the reference exceedance situation.

[0015] The above DC / DC converter control unit may be configured to pass the DC link voltage through a notch filter to extract a DC component from the DC link voltage and obtain an average voltage value, subtract the DC link voltage average value command signal from the average voltage value to obtain a combination result, and input the combination result into a function for PI control to generate an average power command.

[0016] The above DC / DC converter control unit may generate a pulsating power command to control the pulsating value of the DC link voltage using a linear function between the absolute value and the pulsating value of the system voltage.

[0017] The above DC / DC converter control unit may obtain a pulsation value of the DC terminal voltage corresponding to the above DC terminal voltage and calculate a proportionality constant, wherein the proportionality constant is given as the ratio of the DC terminal pulsation voltage to the output terminal pulsation voltage, obtain the output terminal voltage from the above voltage acquisition unit, obtain a pulsation value for the above output terminal voltage, and subtract the pulsation value of the above DC terminal voltage from the result of multiplying the proportionality constant and the pulsation value for the above output terminal voltage.

[0018] The above DC / DC converter control unit may be configured to obtain the pulsating power command using a predetermined transfer function based on the result of subtracting the pulsating value of the DC terminal voltage from the result of multiplying the proportionality constant and the pulsating value for the output terminal voltage.

[0019] A control method for an AC / DC semiconductor transformer may include the steps of obtaining a DC side voltage from a semiconductor transformer including a DC / DC converter, generating an average power command for adjusting the average value of the DC side voltage and a pulsating power command for adjusting the pulsating value of the DC side voltage based on the DC side voltage, and generating a control signal for the DC / DC converter based on the average power command and the pulsating power command, wherein the step of generating an average power command for adjusting the average value of the DC side voltage and a pulsating power command for adjusting the pulsating value of the DC side voltage from the DC side voltage may include the step of generating the average power command and the pulsating power command such that, in a situation where the AC voltage applied to the semiconductor transformer exceeds a reference value, the average value of the DC side voltage increases and the pulsating value of the DC side voltage decreases. Effects of the invention

[0020] According to the AC / DC semiconductor transformer control device and the control method of the AC / DC semiconductor transformer described above, when the system AC voltage applied to the AC / DC semiconductor transformer increases, the voltage of the DC side is appropriately controlled so that the inverter of the AC / DC semiconductor transformer does not operate with overmodulation.

[0021] According to the AC / DC semiconductor transformer control device and the AC / DC semiconductor transformer control method described above, by controlling the magnitude of the 2nd harmonic pulsating voltage while increasing the average value of the DC link voltage so that the maximum value of the DC link voltage is maintained constant, it is possible to prevent the maximum value of the DC link voltage from increasing as the average value of the DC link voltage increases.

[0022] According to the AC / DC semiconductor transformer control device and the AC / DC semiconductor transformer control method described above, as the increase in the maximum value of the DC side voltage can be prevented, the need to design the DC-link capacitor, snubber capacitor, and semiconductor switch element of the DC side of the inverter to have a high voltage rating is reduced, and accordingly, the overall circuit size can be reduced and the problem of increased costs can also be solved.

[0023] According to the AC / DC semiconductor transformer control device and the AC / DC semiconductor transformer control method described above, by controlling the pulsation of the DC side voltage, the maximum value of the DC side voltage can be maintained and adjusted to a certain range or lower, thereby obtaining the advantage of not needing to limit the output power of the inverter.

[0024] According to the AC / DC semiconductor transformer control device and the control method of the AC / DC semiconductor transformer described above, by simultaneously controlling the average value of the DC link voltage and the 2nd harmonic pulsation value, the problem in which the multi-level inverter cannot perform linear modulation as the modulation index exceeds 1 as the magnitude of the single-phase system voltage increases, and consequently, normal control algorithm operation becomes impossible, can also be resolved. Brief explanation of the drawing

[0025] FIG. 1 is a block diagram of an embodiment of an AC / DC semiconductor transformer system including an AC / DC semiconductor transformer and an AC / DC semiconductor transformer control device. FIG. 2 is a graph showing the change over time of the average DC voltage and the second harmonic pulsating voltage controlled by an AC / DC semiconductor transformer control device according to one embodiment. Figure 3 is a graph diagram illustrating an example of the operation of DC link voltage control when the AC input voltage magnitude increases. FIG. 4 is a graph diagram illustrating the control of the average value of the DC side voltage according to one embodiment. FIG. 5 is a graph diagram illustrating second harmonic pulsating voltage control according to one embodiment. FIG. 6 is a block diagram of a voltage average value control unit and a voltage pulsation value control unit according to one embodiment. FIG. 7 is a graph showing the average DC voltage value and the second harmonic pulsation value command according to one embodiment. Figure 8 is a first graph showing an example of an operation simulation waveform of an AC / DC semiconductor transformer system according to a rise in system voltage. Figure 9 is a second graph showing an example of a simulation waveform of the operation of an AC / DC semiconductor transformer system according to a rise in system voltage. FIG. 10 is a flowchart of a control method for an AC / DC semiconductor transformer according to one embodiment. Figure 11 is a graph illustrating an example of a waveform for voltage in a carrier-based pulse width modulation (Carrier-based PWM) method. Specific details for implementing the invention

[0026] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0027] The terms used in this specification will be briefly explained, and the present invention will be described in detail. The terms used in this invention have been selected to be as widely used as possible, taking into account their functions in the invention; however, these terms may vary depending on the intent of those skilled in the art, case law, the emergence of new technologies, etc. Additionally, in specific cases, terms may be arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, terms used in this invention should be defined not merely by their names, but based on the meanings they possess and the content of the invention as a whole. When a part in the specification is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Furthermore, terms such as "part," "module," and "unit" used in the specification refer to a unit that processes at least one function or operation, and may be implemented as software, hardware components such as FPGAs or ASICs, or a combination of software and hardware. However, the terms "part," "module," and "unit" are not limited to software or hardware. "Parts," "modules," "units," etc. may be configured to reside in an addressable storage medium or configured to operate on one or more processors. Thus, by example, the terms "parts," "modules," "units," etc. include components such as software components, object-oriented software components, class components, and task components, as well as processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables.Terms containing ordinal numbers, such as "first," "second," etc., may be used to describe various components, but the components are not limited by the terms. The terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component. The term "and / or" includes a combination of multiple related items or any one of the multiple related items. A singular expression may include a plural expression unless there is an obvious exception in the context. Additionally, the underscore (_) typically indicates that the character added after the underscore is a subscript of the character located before the underscore, and the caret (^) indicates that the character added after the caret is a superscript of the character located before the caret; however, depending on the situation, they may be used with a different meaning.

[0028] Below, embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. Additionally, parts of the drawings that are irrelevant to the description are omitted to clearly explain the invention.

[0029] Hereinafter, with reference to FIGS. 1 to 9, an AC / DC semiconductor transformer, an AC / DC semiconductor transformer control device, and an AC / DC semiconductor transformer system including these embodiments will be described.

[0030] FIG. 1 is a block diagram of an embodiment of an AC / DC semiconductor transformer system including an AC / DC semiconductor transformer and an AC / DC semiconductor transformer control device.

[0031] Referring to FIG. 1, an AC / DC semiconductor transformer system (10) according to one embodiment may include an AC / DC semiconductor transformer (100) that is connected to an external grid (90) and load (120) and converts AC power into DC power, and a control unit (200) that generates a control signal for the AC / DC semiconductor transformer (100) and controls the AC / DC semiconductor transformer (100). Additionally, the AC / DC semiconductor transformer system (100) may further include a measurement unit (300) that measures and obtains necessary information (e.g., voltage, etc.) from the transformer (100) and transmits the obtained information to the control unit (200). At least two of the transformer (100), the control unit (200), and the measurement unit (300) may, depending on the embodiment, be configured to transmit electrical signals in one or both directions through a trace, a circuit line, a cable, or a wireless communication network (which may include a short-range communication network such as Wi-Fi or Bluetooth, a mobile communication network such as LTE or 5G, or a satellite communication network, etc.).

[0032] The external system (90) may be a single-phase AC system according to the embodiment, but is not limited thereto.

[0033] The transformer (100) may include an AC / DC converter (101) connected to an external system (90) and a DC / DC converter (102) which is electrically connected to the AC / DC converter (101) on one side and connected to a load (120) on the other side. At this time, the AC / DC converter (101) and the DC / DC converter (102) are interconnected through two lines, and a branch line is arranged between the two lines, with one end connected to one line and the other end connected to another line, and a predetermined capacitor (111, hereinafter referred to as the first capacitor) may be installed in the branch line. Additionally, another capacitor (112, hereinafter referred to as the second capacitor) is arranged between the load (120) and the DC / DC converter (102), and the second capacitor (112) may be connected in parallel with the load (120). The first capacitor (111) and the second capacitor (112) may each have a capacitance (C_MV, C_LV) of a predetermined size. In this case, the capacitance (C_MV) of the first capacitor (111) and the capacitance (C_LV) of the second capacitor (111, 112) may be the same or different. A voltage of a predetermined size (V_MV, hereinafter DC terminal voltage value) may be applied to the first capacitor (111), and likewise, a different voltage of a predetermined size (V_LV, hereinafter output terminal voltage value) may be applied to the second capacitor (112). The instantaneous DC terminal voltage value (V_MV) and the instantaneous output terminal voltage value (V_LV) may be the same or different. In addition, depending on the situation, the instantaneous DC-link voltage (V_MV) may be a medium-voltage (MV) and / or the instantaneous output-link voltage (V_LV) may be a low-voltage (LV), but is not limited thereto. The instantaneous DC-link voltage (V_MV) and the instantaneous output-link voltage (V_LV) may vary depending on the type or situation of the system, design conditions, or the choice of the user or designer.If necessary, an inductor (110) having a predetermined inductance (L_f) may be further disposed between the external grid (90) and the AC / DC converter (101). According to an embodiment, the AC / DC converter (101) may include a multi-level inverter in which a plurality of full-bridge converters are connected in series. Here, the full-bridge converters may be arranged to equally divide and share the entire AC voltage. Additionally, the DC / DC converter (102) may include a dual-active bridge converter (DAB) capable of bidirectional power transfer.

[0034] The control unit (200) is configured to control the operation of at least one of the C / DC converter (101) and the DC / DC converter (102), and according to one embodiment, it may be configured to include an AC / DC converter control unit (201), a voltage acquisition unit (210), and a DC / DC converter control unit (200).

[0035] The AC / DC converter control unit (201) generates a control signal for the AC / DC converter (101) based on the current (i_g) and voltage (V_g, hereinafter referred to as the grid voltage) input from the external grid (90), and transmits this to the AC / DC converter (101), thereby enabling the AC / DC converter (101) to output a current of a predetermined voltage according to the control signal. If necessary, the AC / DC converter control unit (201) may also generate a control signal based on a target current (i^*_g).

[0036] The voltage acquisition unit (210) receives and acquires at least one voltage measured by the measurement unit (300) and transmits them to the DC / DC converter control unit (220), and can provide a corresponding voltage to each of the voltage average value control unit (230) and the voltage ripple value control unit (240). For example, the voltage acquisition unit (210) acquires the DC terminal voltage instantaneous value (V_MV) and the output terminal voltage instantaneous value (V_LV), transmits the DC terminal voltage instantaneous value (V_MV) to both the voltage average value control unit (230) and the voltage ripple value control unit (240), and transmits the output terminal voltage instantaneous value (V_LV) to the voltage ripple value control unit (240). Additionally, the voltage acquisition unit (210) may further measure and acquire the grid voltage (V_g). The system voltage (V_g) may be provided to both the voltage average value control unit (230) and the voltage pulsation value control unit (240).

[0037] FIG. 2 is a graph illustrating the change over time of the average DC-side voltage and the second harmonic pulsation voltage controlled by an AC / DC semiconductor transformer control device according to one embodiment. In FIG. 2, the x-axis represents time (t) and the y-axis represents voltage (V). Additionally, z1 represents a normal AC-side voltage condition, and V_MV,conv represents the average DC-side voltage condition. z2 represents a condition where the AC-side voltage has risen at time t1, and V_MV,pro represents the average DC-side voltage condition where the voltage has risen.

[0038] The DC / DC converter control unit (220) can generate a control signal for the DC / DC converter (102) based on information, i.e., voltage, received from the voltage acquisition unit (210), and transmit the generated control signal to the DC / DC converter (102).

[0039] According to one embodiment, the DC / DC converter control unit (220) increases the average value (V_MV,conv, V_MV,pro) of the DC link voltage in response to a significant increase in the grid voltage applied at any point in time (t) or during any period as shown in FIG. 2, while simultaneously adjusting the magnitude of the second harmonic pulsation voltage, so that the maximum value of the DC link voltage (V_MV) remains the same or approximately the same after the grid voltage has increased, or / or is smaller than a certain value, thereby ensuring that the modulation index (M1) does not exceed 1, and accordingly, the AC / DC converter (101) can perform pre-modulation. Specifically, in a situation (z1) where the DC link voltage (V_MV) is normally output at a predetermined average value (V_MV,conv), if the system voltage suddenly rises at a predetermined time (t1), the AC / DC converter (101) is limited to a modulation index (MI) of 1, so the control quality is inevitably degraded. In this case, the DC / DC converter control unit (220) raises the DC link voltage (V_MV) from the original average value (V_MV,conv) to a relatively large average value (V_MV,pro) while simultaneously reducing the pulsation of the DC link voltage, thereby ensuring that the maximum value of the DC link voltage remains constant even in a situation (z2) after an abnormality occurs, so that the modulation index (MI1) can have a predetermined value of 1 or less.

[0040] According to one embodiment, such reduction of DC link voltage pulsation may be achieved by transferring the second harmonic power pulsation to the second capacitor (112) through the DC / DC converter (102) to reduce the pulsation of the DC link voltage (V_MV) applied to the first capacitor (111). For example, when the magnitude of the grid voltage increases, the DC / DC converter control unit (220) increases the average value of the DC link voltage (V_MV) according to a given predetermined function so that the modulation index (MI) of the inverter operates below a certain value. If the grid voltage increases further and the maximum value of the DC link voltage (V_MV) including the second harmonic ripple reaches the limit value of the DC link voltage (V_MV), the average value of the DC link voltage is increased while the second harmonic voltage ripple is reduced, and the voltage is reduced to a minimum value set according to the situation. By transmitting the second harmonic power of the DC link voltage (V_MV) to the output terminal voltage (V_LV) through the DC / DC converter (102), the second harmonic voltage ripple of the DC link voltage (V_MV) can be controlled.

[0041] A DC / DC converter control unit (220) according to one embodiment may include a voltage average value control unit (230), a voltage ripple value control unit (240), and a signal combination unit (250). The inputs of the voltage average value control unit (230) and the voltage ripple value control unit (240), respectively, may be directly or indirectly connected to a voltage acquisition unit (210). Additionally, the outputs of the voltage average value control unit (230) and the voltage ripple value control unit (240), respectively, may be connected to a signal combination unit (250).

[0042] The voltage average value control unit (230) is the average of the DC terminal voltage ( Signal for control to adjust ) , hereinafter referred to as the average power command) can be generated and output. That is, the average value of the DC link voltage ( ) is adjusted to be maintained, increased, or decreased according to the operation of the voltage average value control unit (230).

[0043] The voltage pulsation value control unit (240) is provided to control the pulsation value (ΔV_DC) of the DC link voltage, and more specifically, a signal for controlling the magnitude of the pulsation value (ΔV_DC), such as a pulsation power command ( It can generate and output ). In other words, the pulsation value (ΔV_DC) of the DC voltage is adjusted so that its value increases, decreases, or is maintained by the operation of the voltage pulsation value control unit (240).

[0044] The signal combination unit (250) is an average power command ( ) and pulsating power command( ) is received from the voltage average value control unit (230) and the voltage pulsation value control unit (240), respectively, and the average power command ( ) and pulsating power command( A control signal for the DC / DC converter (102) can be generated based on a combination of ). According to one embodiment, the signal combining unit (250) has an average power command ( ) and pulsating power command( A control signal for the DC / DC converter (102) may be finally generated by summing the values ​​and multiplying by a predetermined constant (-K, where K is 0, and depending on the embodiment, the predetermined constant may be positive). Here, the predetermined constant (-K) may be defined according to the type of DC / DC converter (102). If the DC / DC converter (102) is a dual active bridge converter, the control signal for the DC / DC converter (102) may include a phase command value for phase control of the DC / DC converter (102).

[0045] Referring to FIGS. 3 to 5 below, the average value of the DC terminal voltage (V_DC) according to the situation, depending on the operation of the DC / DC converter control unit (220) described above ( Let us explain in more detail an example in which the ) and pulsation value (ΔV_DC) are controlled.

[0046] FIG. 3 is a graph illustrating an example of the operation of DC link voltage control when the AC input voltage magnitude increases. FIG. 4 is a graph illustrating the DC link voltage average value control according to an example, and FIG. 5 is a graph illustrating the 2nd harmonic pulsation voltage control according to an example.

[0047] In Fig. 3, the x-axis represents time, and the y-axis represents voltage. V_g,M on the x-axis of Fig. 3 is a predefined reference value for the system voltage, where the reference value (V_g,M) may include the system voltage value when the average value of the DC-link voltage (V_DC) rises under the condition that the output power of the AC-link is the rated power, and the maximum value of the sum of the DC-link voltage (V_DC) and the 2nd harmonic ripple voltage reaches the limit value (V_DC,lim) (the point where V_g=V_g,M in Fig. 3). V_g,n is the design value of the magnitude of the AC-link voltage in the steady state, and V_g,max is the design value of the maximum value of the AC-link voltage. z3 represents a situation where the system voltage is less than or equal to the rated voltage (hereinafter referred to as the steady state), and z4 represents a situation where the system voltage increases but is less than the predefined reference value (V_g,M) (hereinafter referred to as the voltage rise situation). z5 represents a situation where the system voltage exceeds a predefined reference value (V_g,M) (hereinafter referred to as the reference exceeding situation), and z6 signifies the situation after the maximum value of the sum of the DC link voltage (V_DC) and the 2nd harmonic ripple voltage has reached the limit value (V_DC,lim). In addition, the y-axis is the design value of the average value of the steady-state DC link voltage, and V_DC,lim is the limit value of the DC link voltage. The limit value of the DC link voltage (V_DC,lim) may be defined by the user or designer, or it may be a value given by the AC / DC semiconductor transformer system (10), AC / DC semiconductor transformer (100), or DC / DC converter (102), etc. ΔV_DC represents the magnitude of the pulsation (i.e., the pulsation value).

[0048] Meanwhile, in FIGS. 4 and 5, the x-axis represents the magnitude of the system voltage (V_g). In FIG. 4, the y-axis represents the average value of the DC link voltage (V_DC), and in FIG. 5, the x-axis represents the magnitude of the system voltage (V_g), while the y-axis represents the 2nd harmonic ripple value (ΔV_DC). In FIGS. 4 and 5, V_g,n and V_g,max represent, respectively, the design value of the steady-state AC link voltage magnitude and the design value of the AC link voltage maximum value, as described above. In FIG. 4 is the design value of the average of the steady-state DC link voltage, as in Fig. 3. represents the design value of the DC link voltage limit. In Fig. 5, ΔV_DC,n is the design value for the steady-state DC link voltage ripple, and ΔV_DC,m represents the smallest value of the ripple. z7 and z10 in Figs. 4 and 5, respectively, are for the steady-state situation, z8 and z11 are for the voltage rise situation, and z9 and z12 are for the reference overshoot situation.

[0049] As illustrated in FIGS. 3 to 5, under normal conditions (z3, z7, z10), the system voltage (V_g) is less than or equal to the rated voltage (V_g,n) (V_g ≤ V_g,n). In this case, the average DC link voltage (V_DC) is the design value of the average value of the normal state DC link voltage designed as described in Equation 2 below ( It becomes the same as ).

[0050] [Mathematical Formula 2]

[0051]

[0052] In addition, as described in Equation 3 below, the pulsating voltage (ΔV_DC) of the DC section is controlled to be smaller than the design value (ΔV_DC,n).

[0053] [Mathematical Formula 3]

[0054]

[0055] In voltage rise situations (z4, z8, and z11), the system voltage (V_g) increases above the rated voltage (V_g,n) but becomes smaller than the reference value (V_g,M) (V_g,n ≤ V_g ≤ V_g,M). In this case, in the corresponding sections (z4, z8, and z11), the average value of the DC link voltage increases linearly with respect to the system voltage (V_g) at a predetermined slope (a_1, see Equations 13 and 14 described later). Accordingly, the modulation index (MI) can be maintained at a generally constant value.

[0056] Meanwhile, if the inverter of the AC / DC converter (101) maintains its rated power output while the average value of the DC link voltage increases, the second harmonic ripple in the corresponding situations (z4, z8, and z11) is slightly reduced, as shown in FIG. 5. Specifically, the input power (P_g) of the inverter connected to the single-phase AC system (90) has a DC component ( ) and alternating current components( It is given as the sum of ), which can be given as mathematical formula 4 below.

[0057] [Mathematical Formula 4]

[0058]

[0059] In Equation 4, v_g is the system voltage and i_g is the system current, ω_g is the system angular frequency, φ represents the phase angle of the system current (i_g), and t represents time. In Equation 4, the system voltage (v_g) and the system current (i_g) can be given as Equations 5 and 6 below, respectively.

[0060] [Mathematical Formula 5]

[0061]

[0062] [Mathematical Formula 6]

[0063]

[0064] As stated in Equation 4 above, the power (P_g) of a single-phase AC system has a DC component ( ) and AC components pulsating as the 2nd harmonic of each system frequency ( It is given as the sum of ), and the magnitude of the second harmonic pulsating power of the single-phase power (P_g) is determined by the magnitudes of the grid voltage (v_g) and grid current (v_i). If second harmonic pulsating power is supplied to the AC / DC converter (101) including the inverter, the voltage of the DC link capacitor (111), i.e., the DC link voltage (V_MV), also has a DC component and a second harmonic pulsating component. In this case, the relationship for the second harmonic pulsating component of the DC link voltage (V_MV) can be given as Equation 7 below.

[0065] [Mathematical Formula 7]

[0066]

[0067] In mathematical equation 7, C_DC is the capacitance of the first capacitor (111). That is, the second harmonic pulsation component of the DC link voltage (V_MV) is proportional to the product of the grid voltage (V_g) and the current (I_g), and the average value of the DC link capacitance (C_DC), grid angular frequency (ω_g), and the DC component of the DC link voltage (V_MV) It can be seen that it is inversely proportional to ). In other words, if the output power of the inverter in the AC / DC converter (101) decreases, the ripple voltage decreases relatively, but conversely, if the output power of the inverter increases, the ripple voltage also increases. Therefore, while the AC / DC converter (101) maintains the rated power output (i.e., P_g is constant), the average value of the DC link voltage ( When ) increases, the pulsation value (ΔV_DC) decreases accordingly without separate control. Accordingly, in the voltage rise situation (z11), the second harmonic pulsation appears in a somewhat reduced form as shown in FIG. 5.

[0068] In voltage rise situations (z4, z8, and z11), the reference value (V_g,M), and the average value of the DC link voltage corresponding to the reference value (V_g,M) The pulsation value (ΔV_DC,M) of the DC link voltage corresponding to ) and the reference value (V_g,M) can be given as Equations 8 to 10 below, respectively.

[0069] [Mathematical Formula 8]

[0070]

[0071] In mathematical equation 8, V_DC,lim represents the limit value of the DC link voltage as described above.

[0072] [Mathematical Formula 9]

[0073]

[0074] In Equation 9, MI_1 is the modulation index in the voltage rise situation (z4, z8, and z11). Average value of the DC link voltage ( ) may also be obtained from the design value of the AC / DC semiconductor transformer system (10) according to the embodiment.

[0075] [Mathematical Formula 10]

[0076]

[0077] In mathematical formula 10 The input power (P_g) is a DC component, C_DC is the capacitance of the first capacitor (111), and ω_g is the system angular frequency. Here, the average value of the DC link voltage ( If the remaining part excluding ) is substituted with the variable k, the pulsation value (ΔV_DC,M) of the DC link voltage can be expressed as the rightmost side.

[0078] Substituting mathematical formula 10 into mathematical formula 8 yields the following mathematical formula 11.

[0079] [Mathematical Formula 11]

[0080]

[0081] From Equation 11, the average value of the DC link voltage ( The solution to ) can be given as in the following mathematical formula 12.

[0082] [Mathematical Formula 12]

[0083]

[0084] Based on this, the DC link voltage average value control function according to the system voltage (V_g) is the system voltage (V_g) and the average value ( It can be given as a linear function of the relationship, but can be given in the form of a first-order function as shown in Equation 13 below.

[0085] [Mathematical Formula 13]

[0086]

[0087] In Equation 13, the slope (a_1) and y-intercept (b_1) may be Equation 14 and Equation 15 below, respectively.

[0088] [Mathematical Formula 14]

[0089]

[0090] [Mathematical Formula 15]

[0091]

[0092] The voltage average value control unit (230) provides an average power command based on the given DC voltage average value control function ( ) can be obtained and output. Meanwhile, in the corresponding sections (z4, z8 and z11), the pulsating power command (by the voltage pulsation value control unit (240) The creation of ) may not be performed.

[0093] The criteria exceeding situation (z5, z9, and z12) is a situation where the system voltage (V_g) exceeds the reference voltage (V_g,M) but is smaller than the maximum value of the system voltage (V_g,max) (V_g,M≤V_g≤V_g,max), and in the corresponding section (z5, z9, and z12), the average value of the DC link voltage ( ) increases with respect to the system voltage (V_g) with a slope (a_2) that is smaller than the slope (a_1) of the voltage rise situation (z8), and the 2nd harmonic pulsation value of the DC link voltage is controlled to be relatively reduced by the voltage pulsation value control unit (240). The DC link voltage average value control function in the reference exceeding situations (z5, z9, and z12) is the absolute value and average value ( of the system voltage (V_g) as shown in Equation 16 below. It may also be provided in the form of a linear function between ).

[0094] [Mathematical Formula 16]

[0095]

[0096] In Equation 16, the slope (a_2) and the y-intercept (b_2) may each be defined by Equation 17 and Equation 18.

[0097] [Mathematical Formula 17]

[0098]

[0099] [Mathematical Formula 18]

[0100]

[0101] In this case, since the slope (a_2) for the average value of the DC link voltage is relatively smaller than the slope (a_1) in the voltage rise situation (z4, z8, and z11), the modulation index (MI_2) in the corresponding situation (z5, z9, and z12) becomes somewhat larger than the modulation index (MI_1) in the voltage rise situation (z4, z8, and z11). Even in this case, the modulation index (MI_2) must be controlled to have a value less than 1. To this end, according to one embodiment, the modulation index (MI_2) may be given to satisfy the condition of Equation 19 below.

[0102] [Mathematical Formula 19]

[0103]

[0104] That is, the modulation index (MI_2) in the exceedance situation (z5, z9, and z12) is greater than the value obtained by dividing the maximum value of the grid voltage (V_g,max) by the limit value of the DC link voltage (V_DC,lim), and the maximum value of the grid voltage (V_g,max) is greater than the average value of the DC link voltage ( It may be given as a value smaller than the value divided by ).

[0105] Meanwhile, the second harmonic pulsation control function for the DC link voltage (V_DC) can be given in the form of a first-order function between the absolute value of the system voltage (V_g) and the pulsation value (ΔV_DC), as described in Equation 20 below.

[0106] [Mathematical Formula 20]

[0107]

[0108] The slope (c_1) and y-intercept (d_1) of Equation 20 can be given as Equations 21 and 22 below, respectively.

[0109] [Mathematical Formula 21]

[0110]

[0111] [Mathematical Formula 22]

[0112]

[0113] The subsequent section (z6) is the section where the system voltage (V_g) is at its maximum, and when entering the section (z6), the DC / DC converter control unit (220) [is the] average value of the DC side voltage ( ) is the maximum value, i.e., the voltage limit value( The DC / DC converter (102) is controlled to maintain the ) and maintain the 2nd harmonic pulsation value at the minimum value (ΔV_DC,min).

[0114] Hereinafter, with reference to FIG. 6, an embodiment of the DC / DC converter control unit (220) will be described in more detail, using the example where the DC terminal voltage instantaneous value (V_MV) is an intermediate level voltage and the output terminal voltage instantaneous value (V_LV) is a low level voltage.

[0115] FIG. 6 is a block diagram of a voltage average value control unit and a voltage pulsation value control unit according to one embodiment.

[0116] A voltage average value control unit (230) according to one embodiment, as shown in FIG. 6, comprises a voltage average value command determining unit (231) connected to a voltage acquisition unit (210), a voltage average value determining unit (233) connected to a voltage acquisition unit (210), and a signal (231, 233) output from each of the voltage average value command unit (231) and the voltage average value determining unit (233) connected to both of them. , A first combination unit (235) that receives ), and a signal output from the first combination unit (235), and an average power command ( It may include a PI control unit (237) that outputs ).

[0117] The voltage average value command determination unit (231) receives a system voltage (V_g) at least once from the voltage acquisition unit (210), and based on the received system voltage (V_g), a signal ( , hereinafter DC link voltage average value command signal) is obtained, and the obtained DC link voltage average value command signal ( ) is transmitted to the first combination unit (235). Here, the DC terminal voltage average value command signal ( ) can be given differently depending on the normal situation (z7), the voltage rise situation (z8), and the reference exceedance situation (z9), as shown in FIG. 4.

[0118] According to one embodiment, the voltage average value command determining unit (231) uses a predetermined function to obtain a DC terminal voltage average value command signal (corresponding to the system voltage (V_g) ) may also be obtained. Here, a predetermined function may be defined differently for each normal situation (z7), voltage rise situation (z8), and reference exceedance situation (z9), as shown in the graph in FIG. 4. The voltage average value command determination unit (231), for example, according to the situation (z7, z8, z9), determines an average voltage ( corresponding to the system voltage (V_g) based on a predetermined function. Calculate ) or use the graph of Fig. 4, etc. to obtain the average voltage (corresponding to the system voltage (V_g) By detecting ), the DC link voltage average value command signal corresponding to the system voltage (V_g) ) may also be obtained. Here, a predetermined function may be given by combining, for example, Equation 2, Equation 13, and Equation 16. The voltage average value command determining unit (231) obtains a DC link voltage average value command signal ( ) obtain and transfer it to the first combination unit (235).

[0119] The voltage average value determining unit (233) receives the instantaneous value (V_MV) of the DC terminal voltage and, based on the received instantaneous value (V_MV) of the DC terminal voltage, determines the voltage average value ( ) is obtained and output. According to one embodiment, the voltage average value determining unit (233) passes the DC terminal voltage (V_MV) through a predetermined filter (e.g., a notch filter with a frequency of 120 Hz) and obtains a voltage average value ( ), that is, it can also extract and acquire the DC component and output it. The output average voltage value ( ) is transmitted to the first combination part (235).

[0120] The first combination unit (235) receives a DC side voltage average value command signal (from the voltage average value command determining unit (231) In ), the voltage average value received from the voltage average value determining unit (233) The combination result can be obtained by subtracting ) and the combination result can be transmitted to the PI control unit (237).

[0121] The PI control unit (237) has an average power command ( ) obtain, and average power command( ) can be transmitted to the signal combining unit (250). The PI control unit (237) uses a predetermined transfer function for PI control to obtain an average power command ( You can also obtain ).

[0122] According to one embodiment, the transfer function of the PI control unit (237) may be defined by the following mathematical formula 23.

[0123] [Mathematical Formula 23]

[0124]

[0125] In mathematical formula 23, K_p and K_i represent the proportional gain and integral gain, respectively. ω_c is the bandwidth of the PI control unit (237). is the output voltage command ( ) is the voltage command (i.e., target voltage) used in the calculation, and V_DC is the actual DC link voltage. s represents a variable in the frequency domain. ζ represents the damping ratio.

[0126] A voltage pulsation value control unit (240) according to one embodiment may include, as shown in FIG. 6, a DC terminal voltage pulsation value determining unit (241) connected to a voltage acquisition unit (210), a proportionality constant determining unit (242) connected to a voltage acquisition unit (210), an output terminal voltage pulsation value determining unit (243) connected to a voltage acquisition unit (210), a second combination unit (245) connected to the DC terminal voltage pulsation value determining unit (241), the proportionality constant determining unit (242), and the voltage pulsation value determining unit (243), and a resonance control unit (247) connected to the second combination unit (245).

[0127] The DC-side voltage pulsation value determining unit (241) receives the DC-side voltage instantaneous value (V_MV) at least once from the voltage acquisition unit (210), and can acquire the DC-side voltage pulsation value (ΔV_MV) corresponding to the DC-side voltage instantaneous value (V_MV) and transmit it to the second combination unit (245). In one embodiment, the voltage pulsation value determining unit (241) may use a predetermined filter (e.g., a bandpass filter with a frequency of 120 Hz) to extract and acquire only the second harmonic pulsation voltage component corresponding to the DC-side voltage instantaneous value (V_MV) from the DC-side voltage instantaneous value (V_MV). The extracted DC-side voltage pulsation value (ΔV_MV) can be used as a feedback value in the second combination unit (245).

[0128] The proportionality constant determining unit (242) obtains a proportionality constant (α) for generating a command value for the DC section's second harmonic pulsating voltage (ΔV_MV) using the output section's second harmonic pulsating voltage (ΔV_LV). According to the generated proportionality constant (α), the phase of the DC section's pulsating voltage (ΔV_MV) and the phase of the output section's pulsating voltage (ΔV_LV) can be maintained identically. According to one embodiment, the proportionality constant (α) is calculated by adding the DC section pulsating voltage command (V_T) to the sum (V_T) of the DC section's pulsating voltage (ΔV_MV) and the output section's pulsating voltage (ΔV_LV), as described in Equation 24 below. After subtracting ), DC link pulsating voltage command ( It can be obtained by dividing by the value obtained as a result of subtracting ).

[0129] [Mathematical Formula 24]

[0130]

[0131] In other words, the proportionality constant (α) may be the ratio of the DC link ripple voltage (ΔV_MV) to the output link ripple voltage (ΔV_LV). Here, the DC link ripple voltage command ( ) can be given, for example, by mathematical formula 19. That is, the DC link pulsating voltage command ( ) may also be given as a result obtained by substituting the measured system voltage (V_g) into Equation 19. In this case, the proportionality constant determining unit (242) uses the graph shown in FIG. 5 to obtain the DC link pulsating voltage command ( It is also possible to obtain ).

[0132] The output terminal voltage ripple value determination unit (243) receives an output terminal voltage instantaneous value (V_LV) at least once from the voltage acquisition unit (210), obtains an output terminal voltage ripple value (ΔV_LV) for the output terminal voltage instantaneous value (V_LV), and transmits it to the second combination unit (245). The output terminal voltage ripple value (ΔV_LV) may also be obtained by extracting it from the output terminal voltage instantaneous value (V_LV) using a predetermined filter, similar to the DC terminal voltage ripple value (ΔV_MV). Here, the filter used may be the same as or different from the filter used in the DC terminal voltage ripple value determination unit (241), depending on the embodiment. For example, the filter of the output terminal voltage ripple value determination unit (243) may include a bandpass filter with a frequency of 120 Hz. The pulsation value (ΔV_LV) of the extracted output terminal voltage can be transmitted to the second combination unit (245) and can be used as a command value in the second combination unit (245).

[0133] The second combination unit (245) can obtain at least one combination result using the DC terminal voltage pulsation value (ΔV_MV) transmitted from the DC terminal voltage pulsation value determining unit (241), the proportionality constant (α) transmitted from the proportionality constant determining unit (242), and the output terminal voltage pulsation value (ΔV_LV) transmitted from the output terminal voltage pulsation value determining unit (243), and can transmit the combination result to the resonance control unit (247). According to one embodiment, the second combination unit (245) may obtain a combination result by multiplying the proportionality constant (α) and the output terminal voltage pulsation value (ΔV_LV) and subtracting the DC terminal voltage pulsation value (ΔV_MV) from the multiplied result.

[0134] The resonance control unit (247) provides a corresponding pulsating power command based on the combination result of the second combination unit (245). ) can be obtained. According to one embodiment, the resonance control unit (247) uses a predetermined transfer function for resonance control to obtain a pulsating power command ( ) can be computed, and the specified transfer function may include, for example, a function expressed by the following mathematical formula 25.

[0135] [Mathematical Formula 25]

[0136]

[0137] In mathematical formula 25, K_r represents the gain of the resonance control unit (247), and s represents a variable in the frequency domain. ω_g is the bandwidth of the resonance control unit (247).

[0138] The pulsating power command obtained by the resonance control unit (247) ) can be transmitted to the signal combination unit (250).

[0139] The signal combination unit (250) receives the average power command ( ) obtains, and pulsating power command ( from resonance control unit (247) After obtaining ), as described above, power command ( ) and pulsating power command( A control signal for the DC / DC converter (102) can be generated based on ).

[0140] According to one embodiment, the control unit (200) described above may be implemented in the form of an AC / DC semiconductor transformer control device. The control unit (200) or the AC / DC semiconductor transformer control device may be implemented using a device specifically designed to perform the processing, computation, and / or control described above, or may be implemented by using one or more processors alone or in combination, or may be implemented using at least one information processing device provided to include such processors. Here, the processor may include, for example, a Central Processing Unit (CPU), a Graphic Processing Unit (GPU), a Micro Controller Unit (MCU), an Application Processor (AP), and / or an Electronic Controlling Unit (ECU), but is not limited thereto. These processing or control devices may be implemented by using one or more semiconductor chips, circuits, or related components alone or in combination, for example. In addition, information processing devices may include, but are not limited to, power management systems, energy storage systems, desktop computers, laptop computers, hardware devices for servers, smartphones, tablet PCs, artificial intelligence processing units, home appliances, manned or unmanned vehicles, manned or unmanned aerial vehicles, medical devices, robots and / or industrial machinery devices, etc.

[0141] FIG. 7 is a graph showing the average value of the DC link voltage and the command of the second harmonic ripple value according to one embodiment, and FIG. 8 is a first graph showing an example of the operation simulation waveform of an AC / DC semiconductor transformer system according to the rise in grid voltage. In FIG. 7, the x-axis represents time (seconds). The y-axis on the left is for the average value of the DC link voltage, and the y-axis on the right is for the ripple value of the DC link voltage. FIG. 8 is a graph showing the change in grid voltage (v_g) and grid current (v_i) over time, a graph showing the change in the modulation index (MI) at the same time, and a graph showing the change in the DC link voltage (V_MV, C1) applied to the first capacitor (111) and the output terminal voltage (V_LV) applied to the second capacitor (112) at the same time.

[0142] A graph for obtaining commands for each of the average DC link voltage value and the second harmonic pulsation value may be predefined as shown in FIG. 7. Specifically, referring to the illustration in FIG. 7, the average value of the DC link voltage ( ) is initially given at 940V, but as the grid voltage rises, it gradually increases over approximately 0.5 seconds to reach 1085V. Meanwhile, the DC link voltage ripple value (ΔV_DC) is initially given at 110V and decreases to 15V over approximately 0.3 seconds as the grid voltage rises. In this case, the decrease in the DC link voltage ripple value (ΔV_DC) is due to the average value of the DC link voltage ( It may start later than the rise of ).

[0143] Referring to the illustration in FIG. 8, even though the magnitude of the grid voltage (V_g) gradually increases from 0.2 seconds to 0.7 seconds and rises to about 116% (top graph), it can be seen that the modulation index is generally controlled to about 0.9 by the AC / DC semiconductor transformer system (10) (middle graph). Meanwhile, due to the control operation described above, the DC side voltage (V_MV,C1) gradually increases its maximum value in the initial period (period of 0.2 to 0.4 seconds) in response to the increase in the grid voltage (V_g), but from the point of approximately 0.4 seconds (i.e., reference point (g_m,M)), its maximum value is generally maintained at the same value (bottom graph).

[0144] FIG. 9 is a second graph illustrating an example of a simulation waveform of the operation of an AC / DC semiconductor transformer system according to a rise in grid voltage. FIG. 9 shows a simulation waveform regarding the operation performed by the AC / DC semiconductor transformer system (10) when the AC / DC semiconductor transformer system (10) employs a dual active bridge converter as the DC / DC converter (102), and the magnitude of the grid voltage (V_g) rapidly rises to 116% over 0.05 seconds and then returns to a normal value. The x-axis of FIG. 9 represents time. FIG. 9 is a graph showing the change in system voltage (v_g) and system current (v_i) over time, sequentially from top to bottom, a graph showing the phase switching angle ratio during the same period, a graph showing the change in modulation index (MI) during the same period, a graph showing the change in DC terminal voltage (V_MV,C1) and output terminal voltage (V_LV) during the same period, a graph showing the current flowing through the dual active bridge converter during the same period, and a graph showing the change in power (P_ac) of the AC / DC converter (101).

[0145] Referring to the illustration in FIG. 9, it can be seen that even when the system voltage (V_g) fluctuates rapidly, the AC / DC semiconductor transformer (100) of the AC / DC semiconductor transformer system (10) is controlled stably and appropriately by the control unit (200). In particular, when the system voltage (V_g) increases, the ripple (ΔV_DC) of the DC terminal voltage (V_DC) decreases, and the maximum value of the DC terminal voltage (V_DC) is adjusted to match the design value (V_DC,lim), and to this end, the ripple (ΔV_DC) of the output terminal voltage (V_LC) increases.

[0146] An embodiment of a control method for an AC / DC semiconductor transformer will be described below with reference to FIG. 10.

[0147] FIG. 10 is a flowchart of a control method for an AC / DC semiconductor transformer according to one embodiment.

[0148] According to one embodiment of the control method for an AC / DC semiconductor transformer illustrated in FIG. 10, various values ​​for controlling the AC / DC semiconductor transformer are first obtained (400). For example, a design value for the average value of the steady-state DC terminal voltage ( ), design value for the pulsation value of the steady-state DC link voltage( ), design value for steady-state AC voltage( ), design value of maximum AC voltage ( ) and design values ​​of DC link voltage limit values( ) etc. can be determined. These values ​​can be obtained from AC / DC semiconductor transformers, systems comprising the same, and / or systems connected to these transformers or systems.

[0149] A modulation index (MI_1) for a voltage rise situation is determined (402). The modulation index (MI_1) can be set according to the choice of the user or designer, but is provided to have a value of 1 or less.

[0150] Once the modulation index (MI_1) is determined, a function or graph for calculating the average DC voltage and pulsation value for a voltage rise situation can be determined (404). Here, the function for calculating the average DC voltage may be given as in Equation 13, but may also be defined using various values ​​obtained in the process (400) described above. In addition, the function for calculating the pulsation value may be defined as in Equation 10. Meanwhile, the determined modulation index (MI_1) can be used to obtain a reference value (V_g,M) through Equation 9. Here, the reference value (V_g,M) is used for calculating the slope (a_1) and y-intercept (b_1) of Equation 13.

[0151] Another modulation index (MI_2) for a reference override situation may be determined (408). Here, the modulation index (MI_2) may be determined to satisfy the conditions of Equation 19, but may be defined to have a value less than 1. In other words, the modulation index (MI_2) for a reference override situation may be determined to have a value greater than the value obtained by dividing the maximum value of the grid voltage by the limit value of the DC link voltage, and a value less than the value obtained by dividing the maximum value of the grid voltage by the average value of the DC link voltage. The modulation index (MI_2) for a reference override situation may be greater than the modulation index (MI_1) for a voltage rise situation.

[0152] A function or graph for calculating the average value and pulsation value of the DC link voltage for a situation exceeding the standard may be determined (410). Here, the function for controlling the average value of the DC link voltage may be provided as in Equation 16 described above, and / or the function for calculating the pulsation value may be provided as in Equation 20 described above.

[0153] After a function for calculating the average value and pulsation value of the DC link voltage for the required situation is obtained through this method, when a transformer or a system equipped with it is connected to the grid, the grid voltage / grid current applied to the system is measured periodically or non-periodically, and a control signal for the DC / DC converter is generated according to the measured grid voltage, and the DC / DC converter is controlled (412). Specifically, an average power command is generated to adjust the average value of the DC link voltage based on the DC link voltage, and a pulsation power command is generated to adjust the pulsation value of the DC link voltage simultaneously or sequentially, and a control signal is generated based on the average power command and the pulsation power command. In this case, when the grid voltage is in a normal state, it is controlled normally, and when the grid voltage (AC input voltage) is less than the reference value but increases, the average power command and the pulsation power command are generated so that the average value of the DC link voltage increases in correspondence, and the DC / DC converter is controlled accordingly. Meanwhile, when the system voltage exceeds a reference value, average power commands and pulsation power commands are generated such that the average value of the DC link voltage increases at a lower slope compared to the normal state of the system voltage, and the pulsation value of the DC link voltage decreases; based on this, a control signal for the DC / DC converter is generated. Accordingly, the sum of the average value of the DC link voltage and the maximum value of the pulsation value can be adjusted so that it does not exceed a predetermined limit value.

[0154] The control method for an AC / DC semiconductor transformer according to the above-described embodiment may be implemented in the form of a program that can be driven by a computer device. The program may include instructions, libraries, data files and / or data structures, etc., either individually or in combination, and may be designed and manufactured using machine code or high-level language code. The program may be specially designed to implement the above-described method, or it may be implemented using various functions or definitions that are known and available to a person skilled in the art in the field of computer software. Furthermore, the computer device may be implemented to include a processor or memory, etc., that enable the realization of the program's functions, and may further include a communication device as needed. The program for implementing the control method for an AC / DC semiconductor transformer described above may be recorded on a recording medium readable by a device such as a computer. A computer-readable recording medium may include at least one type of physical storage medium capable of temporarily or non-temporarily storing one or more programs executed upon the call of a device such as a computer, such as a semiconductor storage medium such as ROM, RAM, SD card or flash memory (e.g., a solid-state drive (SSD)), a magnetic disk storage medium such as a hard disk or floppy disk, an optical recording medium such as a compact disk or DVD, or a magneto-optical recording medium such as a floptical disk.

[0155] Although various embodiments of an AC / DC semiconductor transformer control device and a control method for an AC / DC semiconductor transformer have been described above, the AC / DC semiconductor transformer control device and / or the control method thereof are not limited only to the embodiments described above. Various other devices or methods that can be implemented by a person skilled in the art by modifying and varying the embodiments described above may also be embodiments of the AC / DC semiconductor transformer control device or the control method for an AC / DC semiconductor transformer described above. For example, even if the described method(s) are performed in a different order than described, and / or the described component(s) such as a system, structure, device, or circuit are combined, connected, or combined in a form different from described, or are replaced or substituted by other components or equivalents, they may still be embodiments of the AC / DC semiconductor transformer control device and / or the control method for an AC / DC semiconductor transformer described above.

[0156] Those skilled in the art related to the embodiments of the present invention will understand that they may be implemented in modified forms without departing from the essential characteristics of the description. Therefore, the disclosed methods should be considered in an illustrative rather than a restrictive sense. The scope of the invention is defined by the claims, not by the detailed description of the invention, and all variations within the scope of the claims should be interpreted as being included within the scope of the invention. Explanation of the symbols

[0157] 10: AC / DC Semiconductor Transformer System 100: AC / DC Semiconductor Transformer 101: AC / DC Converter 102: DC / DC converter 200: Control unit 220: DC / DC converter control unit 230: Voltage average value control unit 240: Voltage pulsation value control unit 250: Signal combination unit

Claims

Claim 1 A voltage acquisition unit for acquiring a DC link voltage from a semiconductor transformer including a DC / DC converter; and a DC / DC converter control unit for generating an average power command to adjust the average value of the DC link voltage based on the DC link voltage, generating a pulsating power command to adjust the pulsating value of the DC link voltage, and generating a control signal for the DC / DC converter based on the average power command and the pulsating power command; wherein the DC / DC converter control unit generates the average power command and the pulsating power command such that, in a situation where the AC voltage applied to the semiconductor transformer exceeds a reference value, the average value of the DC link voltage increases and the pulsating value of the DC link voltage decreases. Claim 2 In claim 1, the DC / DC converter control unit controls the average value of the DC link voltage to increase when the system voltage increases above the rated voltage, and generates an average power command such that the average value of the DC link voltage increases linearly with a slope greater than the slope of the increase of the average value of the DC link voltage when the AC voltage applied to the semiconductor transformer exceeds a reference value. Claim 3 In paragraph 2, the DC / DC converter control unit acquires a grid voltage at least at one point in time from the voltage acquisition unit and acquires a DC link voltage average value command signal corresponding to the grid voltage based on the grid voltage, wherein the DC link voltage average value command signal is acquired by detecting the average voltage corresponding to the grid voltage using a predetermined function or graph defined differently for each of a normal situation, a voltage rise situation, and a reference exceedance situation, wherein the normal situation includes a situation in which the grid voltage is less than or equal to the rated voltage, and the voltage rise situation includes a situation in which the grid voltage increases but is less than a predetermined reference value, an AC / DC semiconductor transformer control device. Claim 4 In paragraph 3, the DC / DC converter control unit passes the DC link voltage through a notch filter to extract a DC component from the DC link voltage and obtain an average voltage value, subtracts the DC link voltage average value command signal from the average voltage value to obtain a combination result, and inputs the combination result into a function for PI control to generate an average power command, thereby forming an AC / DC semiconductor transformer control device. Claim 5 In claim 1, the DC / DC converter control unit is an AC / DC semiconductor transformer control device that generates a pulsating power command to control the pulsating value of the DC link voltage using a linear function between the absolute value and the pulsating value of the system voltage. Claim 6 In claim 1, the DC / DC converter control unit obtains a pulsating value of the DC terminal voltage corresponding to the DC terminal voltage and calculates a proportionality constant, wherein the proportionality constant is given as the ratio of the DC terminal pulsating voltage to the output terminal pulsating voltage, obtains the output terminal voltage from the voltage acquisition unit, obtains a pulsating value for the output terminal voltage, and subtracts the pulsating value of the DC terminal voltage from the result obtained by multiplying the proportionality constant and the pulsating value for the output terminal voltage. AC / DC semiconductor transformer control device. Claim 7 In claim 6, the DC / DC converter control unit is an AC / DC semiconductor transformer control device that obtains the pulsating power command using a predetermined transfer function based on the result of multiplying the proportionality constant and the pulsating value for the output terminal voltage by subtracting the pulsating value of the DC terminal voltage. Claim 8 A method for controlling an AC / DC semiconductor transformer, comprising: a step of obtaining a DC link voltage from a semiconductor transformer including a DC / DC converter; a step of generating an average power command for adjusting the average value of the DC link voltage and a pulsating power command for adjusting the pulsating value of the DC link voltage based on the DC link voltage; and a step of generating a control signal for the DC / DC converter based on the average power command and the pulsating power command; wherein the step of generating the average power command for adjusting the average value of the DC link voltage and the pulsating power command for adjusting the pulsating value of the DC link voltage from the DC link voltage comprises: a step of generating the average power command and the pulsating power command such that, in a situation where the AC voltage applied to the semiconductor transformer exceeds a reference value, the average value of the DC link voltage increases and the pulsating value of the DC link voltage decreases.

Images