Hybrid transformer with ac / ac converter performing single-stage power conversion and control method of hybrid transformer

Abstract

A hybrid transformer according to one embodiment comprises: a low-frequency transformer; and an AC / AC converter, wherein the AC / AC converter comprises: a first leading leg operating with a first pulse signal and a first lagging leg operating with a second pulse signal delayed from the first pulse signal, and a first full bridge circuit generating a primary side voltage from an AC input using the first leading leg and the first lagging leg; a high-frequency transformer transmitting a secondary side voltage delayed by a phase difference from the primary side voltage; and a second full bridge circuit comprising a second leading leg operating with a third pulse signal and a second lagging leg operating with a fourth pulse signal delayed from the third pulse signal, and transmitting an AC output from the secondary side voltage using the second leading leg and the second lagging leg. The control circuit may include a first pulse signal and a second pulse signal based on PI control for a first DC voltage based on the first full-bridge circuit, and a third pulse signal and a fourth pulse signal based on PI control for an output voltage based on the low-frequency transformer and the AC / AC converter, so that the phase difference between the first side voltage and the second side voltage reaches a target phase difference.

Description

Technology Field

[0001] In the following, a technology for power conversion through a hybrid transformer in which a low-frequency transformer and a converter are connected in series is provided, based on power electronics technology. Background Technology

[0003] In power transmission, on-load tap changers (OLTC) and reactive power compensation devices based on power semiconductor switches, such as STATCOMs, Dynamic Voltage Restorers (DVRs), and Unified Power Quality Conditioners (UPQCs), can be used to maintain power quality. While OLTCs offer the advantage of a long lifespan, they present difficulties in precise or rapid control because they rely on transformer taps for control. However, unlike OLTCs, STATCOMs, DVRs, and UPQCs incorporate semiconductor switches; consequently, they enable precise and accurate control through the high-speed switching of semiconductor switches and allow for a reduction in the volume of power conversion devices. Nevertheless, the use of semiconductor switches results in lower power conversion reliability compared to conventional compensation devices. To address this low reliability issue, hybrid transformers have been proposed. A hybrid transformer refers to a transformer in which a separate converter is connected in series or parallel to an existing low-frequency transformer. Since most power is transmitted through the low-frequency transformer, power conversion losses caused by the separate converter connected to the transformer can be minimized. Furthermore, since power transmission is possible via the low-frequency transformer even if the converter fails, it can be excellent in terms of reliability. Accordingly, measures are required to reduce the size of the converter combined with the existing low-frequency transformer and to increase the power conversion efficiency of said converter. means of solving the problem

[0005] A hybrid transformer according to one embodiment comprises a low-frequency transformer; and an AC / AC converter, wherein the AC / AC converter comprises: a first leading leg operating with a first pulse signal and a first lagging leg operating with a second pulse signal delayed from the first pulse signal, and a first full bridge circuit generating a primary side voltage from an AC input using the first leading leg and the first lagging leg; a high-frequency transformer transmitting a secondary side voltage delayed by a phase difference from the primary side voltage; and a second full bridge circuit comprising a second leading leg operating with a third pulse signal and a second lagging leg operating with a fourth pulse signal delayed from the third pulse signal, and transmitting an AC output from the secondary side voltage using the second leading leg and the second lagging leg. The control circuit may include a first pulse signal and a second pulse signal based on PI control for a first DC voltage based on the first full-bridge circuit, and a third pulse signal and a fourth pulse signal based on PI control for an output voltage based on the low-frequency transformer and the AC / AC converter, so that the phase difference between the first side voltage and the second side voltage reaches a target phase difference value.

[0006] The first full-bridge circuit of the hybrid transformer according to one embodiment can transmit the primary side voltage based on the duty ratio of the first leading leg and the duty ratio of the first lagging leg.

[0007] The duty ratio of the first leading leg and the duty ratio of the first lagging leg of the hybrid transformer according to one embodiment may be the same.

[0008] The control circuit of the hybrid transformer according to one embodiment can determine the duty ratio of the first pulse signal and the second pulse signal from PI control for the first DC voltage based on the error between the first DC voltage and the first reference voltage.

[0009] The control circuit of the hybrid transformer according to one embodiment can match the phase of the input current and input voltage of the AC input applied to the first full-bridge circuit based on the PI control result for the first DC voltage and the phase value of the AC input voltage.

[0010] The control circuit of the hybrid transformer according to one embodiment can determine the target phase difference based on PI control for the second DC voltage based on the second full-bridge circuit.

[0011] The control circuit of the hybrid transformer according to one embodiment can determine the target phase difference from PI control for the second DC voltage based on the error between the second DC voltage and the second reference voltage.

[0012] The control circuit of the hybrid transformer according to one embodiment can determine the duty ratio of the third pulse signal and the fourth pulse signal from PI control for the output voltage based on the error between the output voltage and the output reference voltage.

[0013] The control circuit of the hybrid transformer according to one embodiment can match the phases of the output voltage and the output current based on the PI control result for the output voltage.

[0014] A power control method using a hybrid transformer according to one embodiment comprises: a first leading leg connected to the secondary side of a low-frequency transformer and operating with a first pulse signal and a first lagging leg operating with a second pulse signal delayed from the first pulse signal, and a first full bridge circuit connected to the primary side of a high-frequency transformer using the first leading leg and the first lagging leg to generate a primary side voltage from an AC input; and a step of transmitting a secondary side voltage delayed by a phase difference from the primary side voltage to the secondary side of the high-frequency transformer based on the generated primary side voltage. The method may include: a second leading leg operating with a third pulse signal and a second lagging leg operating with a fourth pulse signal delayed compared to the third pulse signal, and a second full-bridge circuit connected to the secondary side of the high-frequency transformer, wherein the second leading leg and the second lagging leg are used to transmit an AC output from the secondary side voltage; a step of determining the duty ratio of the first pulse signal and the second pulse signal based on PI control for a first DC voltage based on the first full-bridge circuit so that the phase difference between the primary side voltage and the secondary side voltage reaches a target phase difference value; and a step of determining the duty ratio of the third pulse signal and the fourth pulse signal based on PI control for an output voltage based on the low-frequency transformer and the AC output.

[0015] In a power control method using a hybrid transformer according to one embodiment, the step of generating the primary side voltage may include the step of generating the primary side voltage based on the duty ratio of the first leading leg and the duty ratio of the first lagging leg.

[0016] In a power control method using a hybrid transformer according to one embodiment, the duty ratio of the first leading leg and the duty ratio of the first lagging leg may be the same.

[0017] In a power control method using a hybrid transformer according to one embodiment, the step of determining the duty ratio of the first pulse signal and the second pulse signal may include the step of PI controlling the first DC voltage based on the error between the first DC voltage and the first reference voltage.

[0018] In a power control method using a hybrid transformer according to one embodiment, the step of determining the duty ratio of the first pulse signal and the second pulse signal may include the step of matching the phase of the input current and input voltage of the AC input applied to the first full-bridge circuit based on the PI control result for the first DC voltage and the phase value of the AC input voltage.

[0019] In a power control method using a hybrid transformer according to one embodiment, the step of determining the duty ratio of the third pulse signal and the fourth pulse signal may include the step of determining the target phase difference based on PI control for the second DC voltage based on the second full-bridge circuit.

[0020] In a power control method using a hybrid transformer according to one embodiment, the step of determining the duty ratio of the third pulse signal and the fourth pulse signal may include the step of determining the target phase difference from PI control for the second DC voltage based on the error between the second DC voltage and the second reference voltage.

[0021] In a power control method using a hybrid transformer according to one embodiment, the step of determining the duty ratio of the third pulse signal and the fourth pulse signal may include the step of PI controlling the output voltage based on the error between the output voltage and the output reference voltage.

[0022] In a power control method using a hybrid transformer according to one embodiment, the step of determining the duty ratio of the third pulse signal and the fourth pulse signal may include the step of matching the phases of the output voltage and the output current based on the PI control result for the output voltage. Brief explanation of the drawing

[0024] FIGS. 1a to 1c illustrate a hybrid transformer corresponding to a comparative example. FIG. 2 shows the structure of a proposed hybrid transformer according to one embodiment. Figure 3 shows the specific circuit structure of the AC / AC converter included in the hybrid transformer shown in Figure 2. Figure 4 shows the equivalent circuit of the AC / AC converter illustrated in Figure 3. FIG. 5 shows a block diagram of the operation control of an AC / AC converter through a control circuit according to one embodiment. FIGS. 6a to 6f show result graphs through the operation of a hybrid transformer according to one embodiment. Specific details for implementing the invention

[0025] Specific structural or functional descriptions of the embodiments are disclosed for illustrative purposes only and may be modified and implemented in various forms. Accordingly, actual implementations are not limited to the specific embodiments disclosed, and the scope of this specification includes modifications, equivalents, or substitutions included in the technical concept described by the embodiments.

[0026] Terms such as "first" or "second" may be used to describe various components, but these terms should be interpreted solely for the purpose of distinguishing one component from another. For example, the first component may be named the second component, and similarly, the second component may be named the first component.

[0027] When it is stated that a component is "connected" to another component, it should be understood that it may be directly connected to or coupled with that other component, or that there may be other components in between.

[0028] The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to specify the existence of the described features, numbers, steps, actions, components, parts, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0029] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this specification.

[0030] Hereinafter, embodiments will be described in detail with reference to the attached drawings. In the description with reference to the attached drawings, identical components are given the same reference numeral regardless of the drawing number, and redundant descriptions thereof will be omitted.

[0032] FIGS. 1a to 1c illustrate comparative examples of a hybrid transformer according to one embodiment.

[0033] FIG. 1a shows a comparative example (100a) of a hybrid transformer according to one embodiment.

[0034] For reference, the hybrid transformer may be a device that regulates the voltage delivered to the secondary side of the low-frequency transformer (110a) by connecting a converter (120a) in parallel to the secondary side of the low-frequency transformer (110a) and connecting the output of the converter (120a) in series with the secondary side of the low-frequency transformer (110a) through the low-frequency transformer (130a).

[0035] A comparative embodiment (100a) may include a converter (120a) and a low-frequency transformer (130a) connected in series to the secondary side of a low-frequency transformer (110a) as a hybrid transformer. In the comparative embodiment (100a), the converter (120a) and the low-frequency transformer (130a) connected to the secondary side of the low-frequency transformer (110a) may have a structure in which they are connected in a magnetic coupling manner. For example, the comparative embodiment (100a) in a magnetic coupling manner may include a two-stage power conversion structure of AC / DC and DC / AC back-to-back converters (120a) as well as an additional low-frequency transformer (130a). In the comparative embodiment (100a), the converter (120a) may receive a portion of the secondary side voltage of the low-frequency transformer (110a) to perform a two-stage power conversion, converting the AC voltage into a DC voltage and converting the converted DC voltage into an AC voltage. The voltage converted in two stages can be transferred to the secondary side of the low-frequency transformer (110a) according to the number of turns (or windings) of the primary and secondary sides of the low-frequency transformer (130a). The power conversion efficiency according to the comparative example (100a) can be calculated through the following mathematical formula 1. For reference, the power conversion efficiency of the transformer can represent the ratio of output power to input power for the transformer, and the power lost during power conversion (transfer) by the transformer can be identified through the efficiency value.

[0037]

[0039] In mathematical formula 1, This can represent the efficiency of the low-frequency transformer (110a). This can represent the efficiency of the converter (120a). Is It can represent the processing ratio processed by the converter (120a) for the power input to the low-frequency transformer (110a). In other words, is the input power for the low-frequency transformer (110a), may represent power delivered to the converter. For example, if the processing ratio of the converter (120a) and the low-frequency transformer (130a) for the power input to the comparative example (100a) is 10%, can correspond to a value of 0.1. For example, is 0.1, and when the efficiency of the low-frequency transformer (110a) corresponds to 99% and the efficiency of the converter (120a) and the low-frequency transformer (130a) corresponds to 96%, the efficiency of the comparative example (100a) can correspond to 98.6%. In other words, the power ratio processed by the converter (120a) and the low-frequency transformer (130a) The smaller the value, the closer the low-frequency transformer (110a) can operate to a high power conversion efficiency. Therefore, as the power conversion ratio by the converter (120a) increases, the efficiency of the comparative example (100a) may decrease.

[0040] In the comparative example (100a), since the two-stage power conversion of the converter (120a) is performed, the power conversion efficiency and power density may decrease, and the volume of the entire comparative example (100a) may increase due to the volume occupied by the low-frequency transformer (130a).

[0042] FIG. 1b is a specific circuit diagram of a back-to-back converter included in the comparative example of FIG. 1a.

[0043] The back-to-back converter (120a) included in the comparative example (100a) may include a device that converts an AC input to DC and converts the converted DC back to an AC output. The back-to-back converter (120a) may include a primary side (150b) full-bridge circuit, a DC link (160b) connected to the primary side (150b) full-bridge circuit, and a secondary side (170b) full-bridge circuit connected to the DC link (160b). The back-to-back converter (120a) may include an input AC power source and a plurality of switches connected to the AC power source on the primary side (150b). For example, the back-to-back converter (120a) may include an AC power source (e.g., V) on the primary side (150b). P,in It may include switches (e.g., S1, S2, S3, S4) connected to the back-to-back converter (120a). The switches included in the back-to-back converter (120a) may include semiconductor switches capable of high-speed switching. The back-to-back converter (120a) can convert the voltage from the AC power source into DC and store it in the DC link (160b) by controlling the duty cycle of the switches on the primary side (150b). The DC link (160b) may include, for example, a capacitor, but is not limited thereto. The back-to-back converter (120a) can supply the DC voltage stored in the DC link (160b) to the secondary side (170b). The secondary side (170b) of the back-to-back converter (120a) may include a plurality of switches (e.g., S5, S6, S7, S8). The back-to-back converter (120a) controls the duty cycle of the secondary side (170b) switches to convert the DC voltage supplied by the DC link (160b) into an AC output voltage (e.g., V P,out It can be converted to ).

[0044] In other words, since the back-to-back converter (120a) can perform two-stage power conversion by converting AC power to DC and then converting DC back to AC, the power efficiency may be reduced.

[0046] FIG. 1c shows a comparative example (100c) of a hybrid transformer according to one embodiment.

[0047] The comparative embodiment (100c) may include a low-frequency transformer (110c) and a converter (120c) connected in series to the secondary output of the low-frequency transformer (110c). The comparative embodiment (100c) may represent a structure in which the low-frequency transformer (110c) and the converter (120c) are connected in a direct connection manner. The converter (120c) may include an AC / DC converter, a DC / DC converter (130c), and a DC / AC converter. In the converter (120c), the left and right sides may be isolated with respect to the DC / DC converter (130c). In the comparative embodiment (100c), the converter (120c) may perform three stages of power conversion. According to Equation 1 described in FIG. 1a, the power conversion efficiency of the comparative embodiment (100c) may decrease as the number of power conversion stages increases.

[0048] Accordingly, unlike the comparative embodiments (100a, 100c), a converter that repeats a single power conversion is connected to a low-frequency transformer, and unlike the comparative embodiment (100a), a hybrid transformer structure is proposed in which a separate low-frequency transformer (130a) is not additionally attached.

[0050] FIG. 2 shows the structure of a proposed hybrid transformer according to one embodiment.

[0051] A hybrid transformer (200) according to one embodiment may include a device that transmits an input voltage supplied from the primary side to the secondary side. The hybrid transformer (200) may include a circuit in which the input portion of an AC / AC converter (220) is connected in parallel with the secondary side of a low-frequency transformer (210), and the output portion of an AC / AC converter (220) is connected in series with the secondary side of a low-frequency transformer (210). The hybrid transformer (200) may include a device that regulates the total output voltage of the secondary side of the hybrid transformer (200) by regulating (or controlling) the output voltage of the AC / AC converter (220).

[0052] The low-frequency transformer (210) may include a transformer that takes a voltage of 60 Hz or less as input, but is not limited thereto.

[0053] The AC / AC converter (220) can generate a converted AC output by performing a single-stage power conversion on a portion of the AC input transmitted from the primary side to the secondary side of the low-frequency transformer (210). Unlike the comparative embodiment (100a) shown in FIG. 1a, the AC / AC converter (220) may include a converter structure in which the DC link capacitor arranged between the AC / DC converter and the DC / AC is removed. For example, the AC / AC converter (220) can perform a single-stage power conversion for the AC input by removing the DC link capacitor. The structure of the AC / AC converter (220) with the DC link capacitor removed is merely one embodiment and is not limited thereto. However, the AC / AC converter (220) is described below based on the structure with the DC link capacitor removed.

[0054] For example, the voltage delivered to the secondary side of the low-frequency transformer (210) from the hybrid transformer (200) (e.g., V P,in ) can be input to the AC / AC converter (220). Based on the voltage delivered to the secondary side, the hybrid transformer (200) controls a portion of the delivered power through the AC / AC converter (220) to obtain a desired output voltage (e.g., V) on the secondary side of the hybrid transformer (200). out It can generate ). The specific circuit configuration of the AC / AC converter (220) included in the hybrid transformer (200) will be described in detail below in FIG. 3.

[0056] Figure 3 shows the specific circuit structure of the AC / AC converter included in the hybrid transformer shown in Figure 2.

[0057] An AC / AC converter (220) according to one embodiment may include a first leading leg (310) that operates with a first pulse signal and a first lagging leg (311) that operates with a second pulse signal delayed from the first pulse signal, and may include a first full bridge circuit (312) that generates a primary side voltage from an AC input using the first leading leg (310) and the first lagging leg (311).

[0058] The first full-bridge circuit (312) can rectify an AC input based on the operation control of switches included in the first leading leg (310) and the first lagging leg (311). For example, the first full-bridge circuit (312) can rectify the AC input to generate a DC voltage in the capacitor of the first full-bridge circuit (312).

[0059] The first leading leg (310) of the first full-bridge circuit (312) can be connected to one end of the high-frequency transformer (350) at node (a), and the first lagging leg (311) can be connected to the other end of the high-frequency transformer (350) at node (b).

[0060] The first full-bridge circuit (312) may include a plurality of switches in the first leading leg (310). For example, the first leading leg (310) of the first full-bridge circuit (312) may include two switches (e.g., S1, S1'). In the first leading leg (310), switches (S1) and (S1') may be connected in series at node (a). For reference, the switches (S1, S1', S2, S2') may include semiconductor switches. For example, the switches (S1, S1', S2, S2') may each be modeled as devices in which a MOSFET, a diode, and a capacitor are connected in parallel. For example, the drain terminal of a switch may be connected in parallel with the cathode of a diode and one end of a capacitor, and the source terminal of a switch may be connected in parallel with the anode of a diode and the other end of a capacitor. This is merely an example and does not limit the structure of the switches to this. The switches of the first leading leg (310) can be controlled by a predetermined duty ratio through a control circuit described below. For example, a switch (e.g., S1) of the first leading leg (310) can be controlled by a duty ratio of 'd1'. A switch (S1) controlled by a duty ratio of 'd1' can be turned on in a section corresponding to d1 (e.g., T1Xd1) within a period (e.g., T1). For example, d1 can be a real number between 0 and 1. The switches of the first leading leg (310) can be controlled based on a pulse signal, and the pulse signal may indicate a high level in a section corresponding to d1 during the period and a low level in other sections. A switch (e.g., S1') of the first leading leg (310) can be controlled by a duty ratio of '1-d1'. When a switch (e.g., S1) is controlled with a duty cycle of 'd1' and a switch (e.g., S1') is controlled with a duty cycle of '1-d1', when S1 is ON, S1' is OFF, and when S1 is OFF, S1' can be ON.However, the operation duty ratio of the switches included in the first leading leg (310) is not limited to this.

[0061] The first full-bridge circuit (312) may include a plurality of switches in the first lagging leg (311). For example, the first lagging leg (311) may include two switches (e.g., S2, S2'). The switches of the first lagging leg (311) may be controlled by a predetermined duty cycle through a control circuit described below. For example, a switch (e.g., S2) of the first lagging leg (311) may be controlled by a duty cycle of 'd2', and a switch (e.g., S2') may be controlled by a duty cycle of '1-d2'. For example, the duty cycle of the first leading leg (310) and the duty cycle of the first lagging leg (311) may be the same. As another example, the duty cycle of the first leading leg (310) and the duty cycle of the first lagging leg (311) may be different from each other, but the following description mainly explains the case where the duty cycles are the same. The operation according to the duty cycle of the switches included in the first lagging leg (311) overlaps with the first leading leg (310) described above, so it is omitted.

[0062] The switches of the first lagging leg (311) can be operated with a phase difference from the first leading leg (310). For example, the switches of the first leading leg (310) and the first lagging leg (311) can be operated with a phase difference of 180 degrees. For example, if the operating phase of the switch (e.g., S1) of the first leading leg (310) corresponds to 'a', the operating phase of the switch (e.g., S2) of the first lagging leg (311) can correspond to 'a+180 degrees'. The AC / AC converter (220) can reduce input current ripple by operating the first leading leg (310) and the first lagging leg (311) with a phase difference of 180 degrees through a control circuit. For reference, the fact that the first leading leg (310) and the first lagging leg (311) operate with a phase difference may include the operation of switching on and off with a time interval, but this is merely an example and is not limiting.

[0063] The first full-bridge circuit (312) can receive an AC input from the secondary side of a low-frequency transformer. For example, the first full-bridge circuit (312) receives an AC voltage and alternating current An AC input corresponding to it can be supplied from the secondary side of the low-frequency transformer. The first full-bridge circuit (312) can generate a first DC voltage (315) in a capacitor based on the supplied AC input. For example, the first full-bridge circuit (312) can supply capacitors (e.g., C1, C2) connected to the primary side (301) of the high-frequency transformer (350). A first DC voltage (315) corresponding to can be generated.

[0064] The instantaneous input voltage for the AC / AC converter (220) can be calculated by the following mathematical formula 2 based on the first DC voltage (315) generated based on the first full-bridge circuit (312), the duty cycle of the first leading leg (310), and the duty cycle of the first lagging leg (311).

[0066]

[0067] In mathematical formula 2, V can represent the instantaneous input voltage for the AC / AC converter (220). DC1 can represent a first DC voltage (315) generated based on the first full-bridge circuit (312). d1(t) can represent the operating duty ratio of a switch (e.g., S1) included in the first leading leg (310), and d2(t) can represent the operating duty ratio of a switch (e.g., S2) included in the first lagging leg (311). Equation 2 is explained under the assumption that the duty ratio of the first leading leg (310) and the duty ratio of the first lagging leg (3110) are the same. Therefore, d1(t) and d2(t) are both d 12 It can be expressed as (t).

[0069] In addition, the instantaneous input voltage for the AC / AC converter (220) can be calculated using the following mathematical formula 3 through a phasor diagram.

[0071]

[0073] In mathematical formula 3, can represent the instantaneous input voltage for the AC / AC converter (220). In Equation 3, Is It can represent. Also, in mathematical formula 3, Is It can represent. In this case, is the angular frequency of the system, and Each is the peak value of the AC input voltage and the inductor (e.g., L) due to the AC input. p It can represent the peak value of the current flowing through ).

[0075] Based on the above mathematical formulas 2 and 3, the duty cycle can be calculated using the following mathematical formula 4.

[0076]

[0077] In mathematical formula 4, Is The modulation index can be represented by a value such as . According to Equation 4, the AC / AC converter (220) can control the first DC voltage (315) by controlling the duty cycle. In other words, the AC / AC converter (220) can control the first DC voltage (315) by controlling the operating duty cycle of the first leading leg (310) and the first lagging leg (311) of the first full-bridge circuit (312), and by controlling the first DC voltage (315), the primary side voltage (e.g., Can generate ).

[0078] An AC / AC converter (220) according to one embodiment may include a high-frequency transformer (350) that delivers a secondary voltage delayed by a phase difference from the primary voltage. For example, the primary side (301) of the high-frequency transformer (350) may be connected to a circuit in which a first full-bridge circuit (312) and capacitors (e.g., C1, C2) are connected in series. The high-frequency transformer (350) may receive a primary voltage generated based on a first DC voltage (315) at the primary side (301).

[0079] The high-frequency transformer (350) may include an inductor on the primary side (301). For example, the high-frequency transformer (350) has an inductance value on the primary side (301). It may include an inductor corresponding to. Based on the inductor included on the primary side, the high-frequency transformer (350) can store energy from an AC input in the primary side (301) and then transfer it to the secondary side (302). Based on the primary side voltage of the primary side (301), the high-frequency transformer (350) can transfer a secondary side voltage (e.g., a voltage on the secondary side (302) that is delayed by a phase difference from the primary side voltage (e.g., ) can be generated. A method for generating a secondary voltage by transferring energy (or voltage) from the primary side (301) to the secondary side (302) by a high-frequency transformer (350) is specifically explained in FIG. 4.

[0080] For reference, the high-frequency transformer (350) according to one embodiment may include a transformer operating at 100 kHz or higher, but is not limited thereto.

[0081] An AC / AC converter (220) according to one embodiment may include a second leading leg (320) that operates with a third pulse signal and a second lagging leg (321) that operates with a fourth pulse signal delayed from the third pulse signal, and may include a second full-bridge circuit (322) that transmits an AC output from a secondary side voltage using the second leading leg (320) and the second lagging leg (321).

[0082] The second full-bridge circuit (322) may have a symmetrical structure with respect to the first full-bridge circuit (312) and the high-frequency transformer (350). For example, the second full-bridge circuit (322) may include two switches (e.g., S3, S3') in the second leading leg (320). Additionally, the second full-bridge circuit (322) may include two switches (e.g., S4, S4') in the second lagging leg (321). The switches included in the second full-bridge circuit (322) may be controlled by a predetermined duty cycle through a control circuit described below. For example, switches S3 and S3' included in the second leading leg (320) may be controlled by the control circuit with duty cycles of 'd3' and '1-d3', respectively. At the same time, switches S4 and S4' included in the second lagging leg (321) can be controlled through a control circuit with duty ratios of 'd4' and '1-d4', respectively. For example, the duty ratio of the second leading leg (320) and the duty ratio of the second lagging leg (321) may be the same.

[0083] The switches of the second lagging leg (321) can be controlled with a phase difference from the second leading leg (320). For example, the switches of the second leading leg (320) and the second lagging leg (321) can be controlled with a phase difference of 180 degrees. For example, if the operating phase of the switch (e.g., S3) of the second leading leg (320) corresponds to 'b', the operating phase of the switch (e.g., S4) of the second lagging leg (321) can correspond to 'b+180 degrees'. The AC / AC converter (220) can reduce output current ripple by operating the second leading leg (320) and the second lagging leg (321) with a phase difference of 180 degrees through a control circuit.

[0084] The second full-bridge circuit (322) can be connected to the secondary side (302) of the high-frequency transformer (350). The second full-bridge circuit (322) can generate an AC output by controlling the operation of the second leading leg (320) and the second lagging leg (321) through a control circuit from the secondary side voltage received from the secondary side (302). For example, the second full-bridge circuit (322) can generate a second DC voltage (325) on a capacitor based on the secondary side voltage. For example, the second full-bridge circuit (322) on capacitors (e.g., C3, C4) A second DC voltage (325) corresponding to can be generated. The AC / AC converter (220) can control the second DC voltage (325) by controlling the duty ratio of the second leading leg (320) and the second lagging leg (321). Additionally, by controlling the second DC voltage (325), the AC / AC converter (220) can generate a secondary voltage (e.g., v cd AC voltage from ) and alternating current It can generate an AC output corresponding to.

[0085] According to one embodiment, the AC / AC converter (220) may include a control circuit (not shown) that determines the duty cycle of a first pulse signal and a second pulse signal based on PI control for a first DC voltage (315) based on a first full-bridge circuit (312) so that the phase difference between the primary side voltage and the secondary side voltage reaches a target phase difference value, and determines the duty cycle of a third pulse signal and a fourth pulse signal based on PI control for an output voltage based on a low-frequency transformer and the AC / AC converter (220). The control circuit will be described in detail below in FIG. 5.

[0087] Figure 4 shows the equivalent circuit of the AC / AC converter illustrated in Figure 3.

[0088] An equivalent circuit of an AC / AC converter (220) according to one embodiment may be composed of a power source having a primary side voltage value (410), an inductor (401), and a power source having a secondary side voltage value (420). In other words, the AC / AC converter (220) has a leakage inductance (e.g., It can be simplified into an equivalent circuit with an inductor having ) and two power sources connected. Considering the first harmonic of the primary side voltage (410) and the first harmonic of the secondary side voltage (420), they can be calculated using the following Equations 5 and 6, respectively.

[0090]

[0091]

[0092] In mathematical formulas 5 and 6, and Each can represent the primary side voltage (410) and the secondary side voltage (420). It can represent the switching angular frequency. This can represent a phase difference between the primary side voltage (410) and the secondary side voltage (420). For reference, the phase difference between the primary side voltage (410) and the secondary side voltage (420) may correspond to the phase difference between the operating phase of a switch included in the first leading leg of the first full-bridge circuit and the operating phase of a switch included in the second leading leg of the second full-bridge circuit. This can be expressed as an equation relating to the duty cycles of the switches included in the first full-bridge circuit and the second full-bridge circuit, respectively, as shown in Equation 7 below. For reference, it can be assumed that the duty cycles of the switches included in the first leading leg and the first lagging leg of the first full-bridge circuit are the same, and the duty cycles of the switches included in the second leading leg and the second lagging leg of the second full-bridge circuit are the same.

[0093]

[0095] Based on mathematical formulas 5 to 7, the RMS values ​​of the primary side voltage (410) and the secondary side voltage (420), respectively, can be calculated using the following mathematical formulas 8 and 9.

[0096]

[0097]

[0099] Based on mathematical formulas 8 and 9, the RMS current flowing through the inductor (401) Assuming this, the average power can be calculated using the following mathematical formula 10.

[0100]

[0101] In mathematical equation 10, P can represent the average power delivered to the load through the hybrid transformer, and Is and It can represent the phase difference between them.

[0102] The peak voltage applied to the inductor (401) based on the primary side voltage (410) In the case of [this], the relationship shown in mathematical formula 11 below may hold.

[0103]

[0104] In mathematical formula 11, is a reactance based on the switching angular frequency and the inductance value of the inductor (401). It can represent.

[0106] Based on mathematical formulas 10 and 11, the average power P transferred from the primary side to the secondary side of the high-frequency transformer in the AC / AC converter (220) can be calculated as shown in mathematical formula 11 below.

[0107]

[0108] As explained above, in mathematical formula 12 can represent the phase difference between the primary side voltage (410) and the secondary side voltage (420). Based on Equation 12, the AC / AC converter (220) can control the power transferred from the primary side to the secondary side by the high-frequency transformer by controlling (or determining) the phase difference between the primary side voltage (410) and the secondary side voltage (420) through the control circuit described below.

[0110] FIG. 5 shows a block diagram of the operation control of an AC / AC converter through a control circuit according to one embodiment.

[0111] An AC / AC converter according to one embodiment has a primary side voltage (e.g., v ab ) and secondary voltage (e.g., v cd It may include a control circuit (not shown) that determines the duty ratio of the first pulse signal and the second pulse signal based on PI control for the first DC voltage (501) based on the first full-bridge circuit so that the phase difference between them reaches the target phase difference (530), and determines the duty ratio of the third pulse signal and the fourth pulse signal based on PI control for the output voltage based on the low-frequency transformer and the AC / AC converter.

[0112] A control circuit according to one embodiment may include a voltage controller and a current controller. For example, the control circuit may be configured with a structure in which the voltage controller and the current controller are connected in series.

[0113] The control circuit is based on proportional-integral (PI) control for the first DC voltage (501) based on the first full-bridge circuit, and the input voltage (e.g., v) supplied to the AC / AC converter from the low-frequency transformer p,in ) and input current (e.g., i p,in Unit power factor control between ) can be performed. For example, the control circuit can perform PI control for the first DC voltage (501) based on the error between the first DC voltage (501) and the first reference voltage (502). Based on the result of the PI control for the first DC voltage (501), the control circuit can control the first DC voltage (501) to follow the first reference voltage (502).

[0114] For reference, as an example, the first reference voltage (502) is assumed to be generally an AC voltage of 220V, It can be determined as above.

[0115] The control circuit can match the phase of the input current and input voltage of the AC input applied to the first full-bridge circuit based on the PI control result for the first DC voltage (501) and the phase value of the AC input. For example, the control circuit can generate a command input current by multiplying the output value based on the PI control for the first DC voltage (501) by the value obtained by dividing the input voltage by the peak value of the input voltage. For example, the control circuit can multiply the output value based on the PI control for the first DC voltage (501) (v p,in / V p,inBy multiplying by ), the command input current of a sine waveform with added phase information of the input voltage (e.g., i p,in,ref It can generate ). The control circuit can perform unity power factor control by PI controlling the input current based on the error between the command input current and the input current. For example, the control circuit [controls] the command input current (e.g., i p,in,ref ) and input current (e.g., i p,in Input the error between ) into the PI controller, and i in the direction in which the error decreases. p,in By controlling the value, i p,in and v p,in Unitary power factor control that matches the phase can be performed. The control circuit can determine the duty ratio of the first pulse signal and the second pulse signal through a comparison between the PI output generated based on the first DC voltage (501) and the unitary power factor control and the triangular wave (carrier). For example, the control circuit Based on the error between a triangular wave with frequency and a PI output, a pulse signal can be generated that corresponds to a logic high (e.g., 1) when the PI output is greater than the triangular wave, and to a logic low (e.g., 0) when the PI output is smaller than the triangular wave. However, this is merely an example of generating a pulse signal, and the method of implementing a pulse signal by comparing a triangular wave and a PI output may include the opposite case where a logic low corresponds when the PI output is greater than the triangular wave, and the method of generating a pulse signal is not limited to the above examples.

[0116] For example, the pulse signal can correspond to a PWM signal (503), and the control circuit can determine the duty ratio of the first pulse signal and the second pulse signal corresponding to the phase difference between the first leading lag and the first lagging lag based on the PWM signal (503).

[0117] In summary, the control circuit controls the first DC voltage (501) on the primary side of the high-frequency transformer to follow the first reference voltage, and performs unity power factor control so that the phase of the input current is equal to the phase of the input voltage, thereby enabling the switches included in the first leading leg and the second lagging leg to operate with the duty ratio of the first pulse signal and the second pulse signal through the PWM signal (503).

[0119] A control circuit according to one embodiment can determine a target phase difference (530) based on PI control for a second DC voltage (510) based on a second full-bridge circuit. For example, the control circuit can determine the target phase difference (530) from PI control for the second DC voltage (510) based on an error between the second DC voltage (510) and the second reference voltage (521). For example, the control circuit V corresponding to the second DC voltage (510). DC2 V corresponding to the second reference voltage (521) DC2,ref By inputting the error between to the PI controller, the target phase difference (530) corresponds to It can determine. As explained in Equation 12 above, the AC / AC converter is Based on this, power transferred from the primary side to the secondary side can be controlled. The control circuit can achieve a target phase difference (530) through the phase difference between a triangular wave (carrier) used to generate a PWM signal (503) for controlling a switch included in the first full-bridge circuit and a triangular wave (carrier) used to generate a PWM signal (520) for controlling a switch included in the second full-bridge circuit.

[0120] For reference, the target phase difference (530) may represent the phase difference between the primary side voltage applied to the primary side of the high-frequency transformer and the secondary side voltage output to the secondary side, and the target phase difference (530) may also represent the operating phase difference between the legs of the switch included in the primary side first full-bridge circuit and the switch included in the secondary side second full-bridge circuit. For example, the target phase difference (530) may represent the operating phase difference between the switch included in the first leading leg and the switch included in the second leading leg.

[0121] A control circuit according to one embodiment can determine the duty cycle of the third pulse signal and the fourth pulse signal based on PI control for the output voltage (513) based on the low-frequency transformer and the AC / AC converter. In other words, the control circuit can determine the duty cycle of the third pulse signal and the fourth pulse signal by controlling a PWM signal (520) that operates switches included in the second full-bridge circuit based on the output voltage (513) of the hybrid transformer. The control circuit can determine the duty cycle of the third pulse signal and the fourth pulse signal from PI control for the output voltage (513) based on the error between the output voltage (513) and the output reference voltage (512). For example, the control circuit V out Output voltage (513) and V corresponding to out,ref By inputting the error between the output reference voltage (512) corresponding to V into the PI controller, V out This V out,refIt can be controlled to follow. The control circuit can match the phases of the output voltage (513) and the output current based on the PI control result for the output voltage (513). The control circuit can perform PI control on the output current by inputting the error between the output current and the PI control result based on the error between the output voltage (513) and the output reference voltage (512) to the PI controller. For example, the control circuit can input the PI control result for the error between the output voltage (513) and the output reference voltage (512) and i s,out By inputting the error between the corresponding output currents into the PI controller, unity power factor control can be performed to match the phase of the output current with the phase of the output voltage.

[0122] In summary, the control circuit can perform power control of the hybrid transformer by determining the target phase difference (530) based on the second DC voltage (510), and at the same time, based on the output voltage (513), the output voltage (513) and output current (e.g., i s,out Unitary power factor control can be performed to control ) in phase.

[0124] FIGS. 6a to 6f show result graphs through the operation of a hybrid transformer according to one embodiment.

[0125] Figures 6a to 6f are graphs of the operation results of a hybrid transformer designed based on Table 1 below.

[0126] parameters P 3kW L l 100 μH f s 50kHz High-frequency transformer turn ratio 7:2 Low frequency transformer turn ratio 1:1 Input voltage 220VAC Primary side secondary side V DC1 700VDC V out , V DC2 200VDC L p 0 μH L s , C s 700 μH, 16 μF L1, L2 1.2 mH L3, L4 1.2 mH C1, C2 470 μF C3, C4 680 μH

[0127] The parameters included in Table 1 above may represent values ​​corresponding to the parameters included in the AC / AC converter (220) of FIG. 3, and below, the AC / AC converter (220) of FIG. 3 is described as being designed based on Table 1 above. FIG. 6a shows a result graph (600a) of the input voltage and input current for the AC / AC converter in a hybrid transformer designed based on Table 1. The graph (600a) illustrates the result of the input current and input voltage being controlled in phase by the hybrid transformer, and may represent the result of unity power factor control.

[0128] FIG. 6b illustrates a graph (600b) controlled by the phase difference between the primary side voltage and the secondary side voltage of a high-frequency transformer included in a hybrid transformer. In the graph (600b), the primary side voltage (e.g., V ab ) and secondary voltage (e.g., V cd ) can identify that a phase difference exists.

[0129] FIG. 6c illustrates a graph (600c) for the output voltage and output current of an AC / AC converter included in a hybrid transformer. The graph (600c) shows the output voltage (e.g., v s,out ) and output current (e.g., i s,out ) illustrates the result of being controlled in phase.

[0130] Figure 6d is a graph (600d) of the output voltage and output current of the hybrid transformer.

[0131] FIG. 6e is a graph (600e) of the first DC voltage generated in the capacitor of the first full bridge included in the AC / AC converter and the second DC voltage generated in the capacitor of the second full bridge.

[0132] Figure 6f is a graph of the output power (600f) delivered to the load by the hybrid transformer.

[0133] In summary, Figures 6a through 6f show the simulation result graphs for a 3kW hybrid transformer. In the hybrid transformer designed based on Table 1, the AC / AC converter receives 220VAC (peak 311V) from the low-frequency transformer, and V DC1 and V DC2 It can be controlled at 700VDC and 200VDC. At the same time, the AC / AC converter can control the input and output of the AC / AC converter as well as the output of the hybrid transformer to a unity power factor by performing current control. Unity power factor control for the output of the hybrid transformer can be performed through duty control and phase control of the switches included in the first full-bridge circuit and the switches included in the second full-bridge circuit. Due to the duty control of the switches included in the first full-bridge circuit and the switches included in the second full-bridge circuit, the voltage applied to the high-frequency transformer can have a three-level form. The output voltage of the AC / AC converter designed based on Table 1 is controlled to 21.5VAC (peak 30.4V), and the output voltage of the hybrid transformer is controlled to 242VAC (peak 342V), thereby allowing the hybrid transformer to supply 3kW to the load.

[0135] In this document, each of the phrases such as "A or B", "at least one of A and B", "at least one of A or B", "A, B or C", "at least one of A, B and C", and "at least one of A, B, or C" may include any one of the items listed together in the corresponding phrase, or all possible combinations thereof.

[0136] Although the embodiments have been described above with reference to the limited drawings, those skilled in the art can apply various technical modifications and variations based thereon. For example, suitable results may be achieved even if the described techniques are performed in a different order than described, and / or if the components of the described system, structure, device, circuit, etc. are combined or assembled in a form different from described, or replaced or substituted by other components or equivalents.

[0137] Therefore, other implementations, other embodiments, and equivalents to the claims also fall within the scope of the claims set forth below.

Claims

Claim 1 In a hybrid transformer, a low-frequency transformer; The apparatus includes an AC / AC converter, wherein the AC / AC converter comprises an input portion of the AC / AC converter connected in parallel with the secondary side of the low-frequency transformer and an output portion of the AC / AC converter connected in series with the secondary side of the low-frequency transformer, and comprises a first leading leg operating with a first pulse signal and a first lagging leg operating with a second pulse signal delayed from the first pulse signal, and generates a primary side voltage from an AC input using the first leading leg and the first lagging leg; a high-frequency transformer that transmits a secondary side voltage delayed by a phase difference from the primary side voltage; and a second full-bridge circuit that comprises a second leading leg operating with a third pulse signal and a second lagging leg operating with a fourth pulse signal delayed from the third pulse signal, and transmits an AC output from the secondary side voltage using the second leading leg and the second lagging leg.The control circuit includes a duty ratio of the first pulse signal and the second pulse signal based on PI control for the first DC voltage based on the first full-bridge circuit, and a duty ratio of the third pulse signal and the fourth pulse signal based on PI control for the output voltage based on the low-frequency transformer and the AC / AC converter, so that the phase difference between the first side voltage and the second side voltage reaches a target phase difference; the control circuit generates a command input current of a sine wave by multiplying the output value based on PI control for the first DC voltage by the value obtained by dividing the input voltage by the peak value of the input voltage, performs unity power factor control to match the phase between the input current of the AC input and the input voltage by performing PI control based on the error between the input current of the AC input applied to the first full-bridge circuit and the command input current, and, based on the result of PI control for the output voltage, the output voltage and the output current corresponding to the output voltage A hybrid transformer that performs unit power factor control to match the phase between them. Claim 2 In claim 1, the first full-bridge circuit is a hybrid transformer that generates the primary side voltage based on the duty ratio of the first leading leg and the duty ratio of the first lagging leg. Claim 3 A hybrid transformer according to paragraph 2, wherein the duty ratio of the first leading leg and the duty ratio of the first lagging leg are the same. Claim 4 A hybrid transformer according to claim 1, wherein the control circuit determines the duty ratio of the first pulse signal and the second pulse signal from PI control for the first DC voltage based on the error between the first DC voltage and the first reference voltage. Claim 5 In claim 4, the control circuit is a hybrid transformer that matches the phase of the input current and input voltage of the AC input applied to the first full-bridge circuit based on the PI control result for the first DC voltage and the phase value of the voltage of the AC input. Claim 6 A hybrid transformer according to claim 1, wherein the control circuit determines the target phase difference based on PI control for a second DC voltage based on the second full-bridge circuit. Claim 7 In claim 6, the control circuit determines the target phase difference from PI control for the second DC voltage based on the error between the second DC voltage and the second reference voltage, a hybrid transformer. Claim 8 A hybrid transformer according to claim 1, wherein the control circuit determines the duty ratio of the third pulse signal and the fourth pulse signal from PI control for the output voltage based on the error between the output voltage and the output reference voltage. Claim 9 In claim 8, the control circuit is a hybrid transformer that matches the phases of the output voltage and output current based on the PI control result for the output voltage. Claim 10 A power control method using a hybrid transformer comprises: a step of generating a primary side voltage from an AC input using the first leading leg and the first lagging leg by means of a first full bridge circuit connected to the primary side of a high-frequency transformer, wherein the first leading leg is connected to the secondary side of a low-frequency transformer and operates with a first pulse signal and operates with a second pulse signal delayed from the first pulse signal; a step of transmitting a secondary side voltage delayed by a phase difference from the primary side voltage to the secondary side of the high-frequency transformer based on the generated primary side voltage; and a step of transmitting an AC output from the secondary side voltage using the second leading leg and the second lagging leg by means of a second full bridge circuit connected to the secondary side of the high-frequency transformer, wherein the second leading leg is connected to a third pulse signal and operates with a fourth pulse signal delayed from the third pulse signal. Step; determining the duty ratio of the first pulse signal and the second pulse signal based on PI control for the first DC voltage based on the first full-bridge circuit so that the phase difference between the first side voltage and the second side voltage reaches a target phase difference; and determining the duty ratio of the third pulse signal and the fourth pulse signal based on PI control for the output voltage based on the low-frequency transformer and the AC output;A power control method comprising: a step of determining the duty ratio of the first pulse signal and the second pulse signal, wherein the step of determining the duty ratio of the first pulse signal and the second pulse signal comprises: a step of generating a command input current of a sine waveform by multiplying an output value based on PI control for the first DC voltage by a value obtained by dividing the input voltage by the peak value of the input voltage; and a step of performing unity power factor control to match the phase between the input current of the AC input and the input voltage by performing PI control based on the error between the input current of the AC input applied to the first full-bridge circuit and the command input current; and a step of determining the duty ratio of the third pulse signal and the fourth pulse signal comprises: a step of performing unity power factor control to match the phase between the output voltage and the output current corresponding to the output voltage based on the result of PI control for the output voltage. Claim 11 A power control method according to claim 10, wherein the step of generating the primary side voltage comprises the step of generating the primary side voltage based on the duty ratio of the first leading leg and the duty ratio of the first lagging leg. Claim 12 In claim 11, a power control method in which the duty ratio of the first leading leg and the duty ratio of the first lagging leg are the same. Claim 13 A power control method according to claim 10, wherein the step of determining the duty ratio of the first pulse signal and the second pulse signal includes the step of PI controlling the first DC voltage based on the error between the first DC voltage and the first reference voltage. Claim 14 A power control method according to claim 13, wherein the step of determining the duty ratio of the first pulse signal and the second pulse signal includes the step of matching the phase of the input current and input voltage of the AC input applied to the first full-bridge circuit based on the PI control result for the first DC voltage and the phase value of the voltage of the AC input. Claim 15 A power control method according to claim 10, wherein the step of determining the duty ratio of the third pulse signal and the fourth pulse signal comprises the step of determining the target phase difference based on PI control for the second DC voltage based on the second full-bridge circuit. Claim 16 A power control method according to claim 15, wherein the step of determining the duty ratio of the third pulse signal and the fourth pulse signal comprises the step of determining the target phase difference from PI control for the second DC voltage based on the error between the second DC voltage and the second reference voltage. Claim 17 A power control method according to claim 10, wherein the step of determining the duty ratio of the third pulse signal and the fourth pulse signal includes the step of PI controlling the output voltage based on the error between the output voltage and the output reference voltage. Claim 18 In claim 17, the step of determining the duty ratio of the third pulse signal and the fourth pulse signal comprises the step of matching the phases of the output voltage and the output current based on the PI control result for the output voltage.

Images