Power converting apparatus

Abstract

A power conversion device according to one embodiment of the present invention comprises a converter including at least one upper switch and at least one lower switch, and an auxiliary power supply unit that supplies driving power to the upper switch and the lower switch, wherein the auxiliary power supply unit includes a bootstrap circuit that supplies driving power to the upper switch using a first driving power supply that supplies driving power to the lower switch.

Description

Technology Field

[0001] The present invention relates to a power converter, and more specifically, to a power converter that operates in multiple operating modes. Background Technology

[0002] Solar power generation is an eco-friendly energy method that is becoming widely adopted as a replacement for conventional chemical or nuclear power generation. Solar power generation systems include standalone types, where batteries are connected to a converter, and grid-connected types, where they are linked to the power grid. Generally, standalone systems consist of solar cells, storage batteries, and power converters, while grid-connected systems are configured to connect to commercial power sources to exchange power with load grid lines.

[0003] The maximum power point of a solar cell module varies depending on factors such as sunlight intensity and temperature. To operate the solar cell at its maximum power point, Module-Level Power Electronics (MLPE) can be used to perform Maximum Power Point Tracking (MPPT) control at the module level. MLPE performs maximum power point tracking by converting the power received from the solar cell, but depending on the situation, it may be necessary to output the input voltage directly as an output voltage without power conversion.

[0004] Therefore, in order to optimize solar cell modules, technology is required to implement the MLPE to operate in various operating modes. The problem to be solved

[0005] The technical problem that the present invention aims to solve is to provide a power converter that operates in multiple operating modes. means of solving the problem

[0006] To solve the above technical problem, a power conversion device according to one embodiment of the present invention comprises: a converter including at least one upper switch and at least one lower switch; and an auxiliary power supply unit that supplies driving power to the upper switch and the lower switch, wherein the auxiliary power supply unit includes a bootstrap circuit that supplies driving power to the upper switch using a first driving power supply that supplies driving power to the lower switch.

[0007] Additionally, the bootstrap circuit includes a capacitor that is charged by receiving power from the first driving power source; and a diode connected between the first driving power source and the capacitor, wherein the capacitor is connected to a node between the upper switch and the lower switch, and when the lower switch is turned on, a closed loop is formed connecting the first driving power source, the diode, the capacitor, and the lower switch, so that power is received from the first driving power source and charged, and when the lower switch is turned off, power received from the first driving power source and charged can be supplied to the driving power of the upper switch.

[0008] Additionally, the converter operates in a first mode in which the upper switch and the lower switch conduct complementarily at a first frequency, or in a second mode in which the upper switch and the lower switch conduct complementarily at a second frequency, and the first frequency may be different from the second frequency.

[0009] In addition, the second frequency may be smaller than the first frequency.

[0010] In addition, the second frequency may be 1 / 4 or less of the first frequency.

[0011] In addition, the first frequency may be 20 kHz or higher.

[0012] In addition, the second frequency can be set according to the input / output voltage, current, and temperature of the converter.

[0013] Additionally, the converter includes a first section in which the upper switch conducts and a second section in which the lower switch conducts, and the converter operates such that in the second mode, the ratio of the first section to the second section is a first ratio, and the first ratio may be such that the first section is longer than the second section.

[0014] In addition, the converter can gradually change the ratio of the first section and the second section when changing modes.

[0015] In addition, in the second mode, the difference between the voltage of the input portion of the converter and the voltage of the output portion of the converter may be less than or equal to the first threshold voltage value.

[0016] Additionally, the converter operates in a third mode in which the lower switch is connected for at least one cycle, and when the upper switch is connected between the lower switch and the output (+) terminal, the upper switch can be simultaneously connected to the lower switch for at least one cycle in the third mode.

[0017] Additionally, the converter includes at least one of a buck converter, a boost converter, and a buck-boost converter, and in the third mode, the buck converter may have only the lower switch connected, the boost converter may have both the upper switch and the lower switch connected, and the buck-boost converter may have both the output-side upper switch and the lower switch connected.

[0018] Additionally, the device includes an input unit that receives a first voltage; and an output unit that outputs an output voltage of the converter, wherein the converter operates in a first mode that converts the first voltage into a second voltage, or in a second mode that outputs the first voltage to the output unit, and the output unit can output the second voltage in the first mode and output the first voltage in the second mode.

[0019] In addition, the converter operates in a third mode that creates a bypass path in the output section, and the output section can output a third voltage input from the output side in the third mode.

[0020] To solve the above technical problem, a power conversion device according to another embodiment of the present invention includes a plurality of power circuits constituting a multi-level, and each of the power circuits includes the power conversion device described above. Effects of the invention

[0021] According to embodiments of the present invention, a power converter can be used in multiple operating modes, such as a power conversion mode, an input / output connection mode, and a bypass mode. An input / output connection mode or a bypass mode can be implemented or enhanced using a power conversion circuit. When operating the power conversion circuit in a power conversion mode or an input / output connection mode, an auxiliary power circuit that supplies driving power to an upper switch and a lower switch can be implemented simply and inexpensively using a bootstrap circuit. Brief explanation of the drawing

[0022] Figure 1 is a diagram illustrating maximum power point tracking control. FIG. 2 is a block diagram of a power conversion device according to one embodiment of the present invention. FIGS. 3 to 11 are drawings for explaining a power conversion device according to an embodiment of the present invention. FIG. 12 is a block diagram including an auxiliary power supply unit of a power conversion device according to an embodiment of the present invention. FIGS. 13 to 17 are drawings for explaining a power conversion device according to an embodiment of FIG. 12. FIG. 18 is a block diagram of a power conversion device in which a plurality of power circuits are configured as multi-levels according to an embodiment of the present invention. FIGS. 19 to 21 are drawings for explaining a power conversion device according to an embodiment of FIG. 18. Specific details for implementing the invention

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0024] However, the technical concept of the present invention is not limited to some of the described embodiments but can be implemented in various different forms, and within the scope of the technical concept of the present invention, one or more of the components among the embodiments may be selectively combined or substituted.

[0025] In addition, terms used in the embodiments of the present invention (including technical and scientific terms) may be interpreted in a sense that is generally understood by those skilled in the art to which the present invention belongs, unless explicitly and specifically defined otherwise. Terms that are commonly used, such as terms defined in advance, may be interpreted in consideration of their meaning in the context of the relevant technology.

[0026] Furthermore, the terms used in the embodiments of the present invention are for the purpose of describing the embodiments and are not intended to limit the present invention.

[0027] In this specification, the singular form may include the plural form unless specifically stated otherwise in the text, and when described as "at least one of A and B and C (or more than one)," it may include one or more of all combinations that can be formed from A, B, and C.

[0028] In addition, terms such as first, second, A, B, (a), (b), etc., may be used when describing the components of the embodiments of the present invention. These terms are used merely to distinguish the components from other components and are not intended to limit the essence, order, or sequence of the components.

[0029] And, where it is stated that a component is 'connected', 'combined', or 'connected' to another component, this may include not only cases where the component is directly 'connected', 'combined', or 'connected' to the other component, but also cases where it is 'connected', 'combined', or 'connected' due to another component located between the component and the other component.

[0030] Furthermore, when described as being formed or placed "above" or "below" each component, "above" or "below" includes not only cases where two components are in direct contact with each other, but also cases where one or more other components are formed or placed between the two components. Additionally, when expressed as "above" or "below," it may include the meaning of a downward direction as well as an upward direction relative to a single component.

[0031] Variations according to the present embodiment may include some components of each embodiment and some components of other embodiments. That is, a variation may include one of the various embodiments, but with some components omitted and some components of a corresponding other embodiment included. Or, the opposite may be true. Features, structures, effects, etc. described in the embodiments are included in at least one embodiment and are not necessarily limited to only one embodiment. Furthermore, features, structures, effects, etc. exemplified in each embodiment may be combined or modified and implemented in other embodiments by a person with ordinary knowledge in the field to which the embodiments belong. Therefore, details regarding such combinations and modifications should be interpreted as being included within the scope of the embodiments.

[0033] A power conversion device according to an embodiment of the present invention may be a device that converts power generated from a photovoltaic power generation panel into power suitable for a load or battery. A photovoltaic cell that performs photovoltaic power generation may be expressed as a cell string unit in which a plurality of cells are connected in series.

[0034] A cell string may include at least one cell, and if it includes multiple cells, the multiple cells may be connected in series. The cell string may be a solar cell string containing solar cells. The solar cell string may form a solar panel. Solar cells perform photovoltaic (PV) power generation by utilizing the photoelectric effect. The photoelectric effect is the emission of electrons when light of a specific frequency or higher strikes a specific metal material; power is generated by forming a pn junction using a P-type semiconductor and an n-type semiconductor, and generating an electric current using the electrons generated by the photoelectric effect. Solar cells are formed using silicon, etc., and may be formed in the form of a wafer. Solar cells are located in open areas or on the exterior walls or rooftops of buildings where they can receive sunlight well, and generate power using sunlight. In this case, the solar cells may be formed as BIPV (Building Integrated Photovoltaics) that are integrated with the building.

[0035] Since the amount of power generated by a single solar cell is insufficient for use by loads or power grids, multiple solar cells are connected in series to form a solar cell string, thereby generating power of a suitable size for use. A solar cell string can serve as the basic unit for generating power. A solar power generation panel can be formed by arranging multiple cell strings, which are the basic units, into panels. Solar cells exhibit different voltage-current characteristics depending on sunlight intensity, temperature, etc., as shown in Fig. 1, and the Maximum Power Point (MPP) also fluctuates. (Power generated = Voltage x Current) A power converter plays the role of controlling the solar cell to operate at the Maximum Power Point (MPP), which is the operating point where the power is maximum under each condition. This is called Maximum Power Point Tracking (MPPT), and the efficiency of solar power generation can be increased by utilizing MPPT. In solar power generation, depending on the characteristics of the relationship between current and voltage, and between voltage and power, the maximum power may not be the maximum voltage, but rather the power at approximately 80% of the maximum voltage. Since this maximum power point continuously changes depending on the magnitude of the voltage and current generated by the solar panel, it is necessary to continuously identify the point where the maximum power can be generated. In other words, to track the maximum power rather than the maximum voltage, the magnitudes of the voltage and current can be varied to achieve the maximum power. That is, the voltage can be decreased and the current increased in the direction of increasing power, or the voltage can be increased and the current decreased.

[0036] To perform maximum power point tracking for multiple cell strings, individual control for each cell string may be required. For example, if a specific cell string has foreign matter obstructing light reception or is shaded, the level of power generation may differ from that of other cell strings; therefore, in addition to operation modes that convert the power output from the cell string, operations other than power conversion may be required. It may be necessary to output power directly without conversion or to bypass the corresponding cell string. For each situation, a device capable of multiple operation modes is required that can operate in the most suitable mode for the power output from each cell string.

[0037] A power conversion device according to an embodiment of the present invention may operate in multiple modes, including a power conversion mode (first mode), an input / output connection mode (second mode), and a bypass mode (third mode), in order to operate in the most suitable mode for each situation. In addition to the power conversion mode, the input / output connection mode, and the bypass mode, other operating modes may be further included depending on the design.

[0038] FIG. 2 is a block diagram of a power converter according to an embodiment of the present invention, and FIGS. 3 to 11 are drawings for explaining a power converter according to an embodiment of the present invention.

[0039] A power conversion device (100) according to one embodiment of the present invention is composed of an input unit (110), a power conversion unit (120), an output unit (130), an input / output connection unit (140), and a bypass unit (150), and may include a monitoring unit, an auxiliary power supply unit, a temperature sensor, a control unit, a coupling circuit, and a wireless transceiver.

[0040] The input unit (110) receives a first voltage. The input unit (110) can be connected to a cell string to receive the first voltage.

[0041] The power conversion unit (120) converts the first voltage into a second voltage. When the first voltage is input to the input unit, the power conversion unit (120) converts the first voltage into a second voltage according to the power conversion mode. The first voltage may be higher or lower than the second voltage. The power conversion unit (120) may convert the received first voltage into a second voltage higher than the first voltage or into a second voltage lower than the first voltage. Alternatively, it may convert the first current into a second current. Here, the first current may be higher or lower than the second current. The power conversion unit (120) may include a converter for converting power.

[0042] The output unit (130) outputs the output voltage of the power conversion unit (120). The output unit (130) outputs a second voltage that is converted and output from the power conversion unit (120).

[0043] In the power conversion mode, which performs maximum power point tracking on the input power and converts the power, power conversion is performed through the input unit (110), power conversion unit (120), and output unit (130). Maximum power point tracking is performed so that the power of the cell string connected to the input unit (110) becomes the maximum power.

[0044] The input / output connection unit (140) connects the input unit (110) to the output unit (130). In order to perform an input / output connection mode that transmits the input voltage directly to the output side without converting it depending on the situation, the input / output connection unit (140) connects the input unit (110) and the output unit (130) in the input / output connection mode. For example, if some of the cell strings among a plurality of cell strings generate a lower voltage than other cell strings due to shading or the like, it is necessary to output the voltage of the other cell strings as is without power conversion to reduce the voltage difference between each cell string, thereby reducing losses and increasing efficiency. At this time, the input / output connection unit (140) connects the input unit (110) and the output unit (130) to perform the input / output connection mode. Since the first voltage received in the input / output connection mode is output as is, the voltage output from the output unit (130) becomes the first voltage of the input unit (110).

[0045] The bypass unit (150) creates a bypass path in the output unit (130) that bypasses the power conversion unit (120) or the input / output connection unit (140). It can operate in an input / output connection mode that outputs the input voltage as is without performing power conversion, as well as in a bypass mode that creates a bypass path so that the output unit (130) is connected only to the output side in order to bypass the power conversion unit (120) and the input / output connection unit (140). The bypass mode serves to discharge the output voltage of the power conversion device or maintain it below a preset voltage or at 0 V. In the bypass mode, the bypass unit (150) creates a bypass path in the output unit (130) to prevent current input from the output unit (130) from flowing to the power conversion unit (120).

[0046] For example, when the current of the output section (130) is greater than the current of the input section (110), the bypass section (150) can provide a bypass path for the current corresponding to the difference. For example, when a failure occurs in a photovoltaic power generation module including a cell string, or when the input section is not connected and there is no input current to the power converter, the bypass section (150) can provide a bypass path for the output current. In particular, when a hot spot occurs in the photovoltaic power generation module, the bypass section (150) can provide a bypass path for the output current to lower the current value flowing through the photovoltaic power generation module and suppress heat generation. Through this, if a current greater than the current that the photovoltaic power generation module can output is forcibly conducted, it is possible to prevent the impedance of the photovoltaic power generation module from increasing and the amount of heat generated from increasing.

[0047] The output unit (130) outputs the first voltage, the second voltage, or the third voltage input from the output side according to the operation of the power conversion unit (120), the input / output connection unit (140), or the bypass unit (150) which operate according to each mode. That is, in the power conversion mode, the second voltage output from the power conversion unit (120) is output; in the input / output connection mode, the first voltage received by the input unit (110) is output as is, as it is directly connected to the input unit (110); and in the bypass mode, the third voltage input to the output side is output regardless of the voltage of the power conversion unit (120) or the input unit (110).

[0048] The power conversion unit (120), input / output connection unit (140), and bypass unit (150) can be operated by a control unit, and the control unit can transmit a control signal to each component to operate in the most suitable mode according to information such as input / output voltage and current, temperature, etc. Additionally, they can operate in the corresponding mode according to a control signal from an external control unit or input from a user.

[0049] A power conversion device (100) according to an embodiment of the present invention may be implemented as shown in FIG. 3, comprising a power conversion circuit (120), an input / output connection circuit (Contactor, 140) that connects an input section and an output section by bypassing the power conversion circuit (120), and a bypass circuit (Bypass circuit, 150) that creates a bypass path to an output section (130) by connecting both ends of the output section. The input / output connection circuit (140) is a type of bypass circuit that bypasses, or bypasses, the power conversion circuit (120), but to distinguish it from the bypass circuit (150), it is referred to as an input / output connection circuit (140) or a contactor.

[0050] A power conversion device (100) according to an embodiment of the present invention may include various configurations to operate in multiple operation modes, as shown in FIG. 4.

[0051] It may include an auxiliary power supply that generates auxiliary power using the voltage of the input section (110) or the voltage of the output section (130). The auxiliary power supply may receive one or more of the voltages of the input or output sections of the power converter and generate a single or multiple power sources. The generated power source may be a voltage typically used by semiconductor devices, such as 3.3V, 5V, 12V, etc. Some of the power sources may have a floating potential from the ground of the power converter. The auxiliary power supply may be composed of a single or multiple power conversion circuits. For example, it may include at least one of a fly-back converter, a buck converter, a boost converter, a linear regulator, and a charge pump, or may be composed of a combination thereof.

[0052] The monitoring circuit can measure at least one of the current of the input unit (110), the voltage of the input unit (110), the current of the output unit (130), and the voltage of the output unit (130).

[0053] Memory may include non-volatile memory for storing information. Physical / software identification information, monitoring correction information, failure history, etc., may be stored in the memory.

[0054] It may include a thermal sensor for temperature measurement. The thermal sensor can measure the temperature of the power converter. In particular, the thermal sensor can measure the temperature of MOFSETs, diodes, power semiconductor devices, and magnetic components such as transformers and inductors, or the temperature of adjacent areas, in a contact or non-contact manner.

[0055] The control circuit can control each component of the power converter using information received from the power converter and from the outside. At this time, depending on the circuit of the power converter (120), an additional current detection circuit may be used to detect the current of the inductor included in the power converter (120). The control circuit can activate a protection function based on the detected voltage, current, and temperature information. For example, when overvoltage or overcurrent is detected, specific parameters may be limited or the operation of the power converter may be stopped. In addition, when overheating is detected, the output power of the power converter may be lowered or stopped.

[0056] The control unit is responsible for detecting various parameters, controlling the power circuit, communicating with external equipment, and storing information. It can recognize signals input from the monitoring unit by converting them to an Analog-to-Digital Converter (ADC) and control the power circuit by outputting PWM or GPIO. Additionally, based on the signals input from the monitoring unit, it can control the power circuit to track the operating point where the power supplied by the PV module reaches its maximum. Based on the signals detected by the monitoring unit, it can implement overvoltage and overcurrent protection functions and transmit and receive information by communicating with external devices. Wired and wireless methods can be used as communication means. In the case of the wired method, an additional terminal for connecting a communication cable may be provided, and in the case of the wireless method, a wireless transceiver may be additionally provided for communication. When using a Power Line Communication (PLC), a coupling circuit may be additionally provided at the (+) or (-) terminal of the output terminal. The transmitted information may include parameters detected by the power converter, the presence and history of faults, physical / software identification information, and calibration information of the monitoring circuit. A capacitor may additionally be used between the (+) and (-) terminals of the power circuit to remove noise.

[0057] The power conversion unit (120) may include a converter comprising at least one upper switch and at least one lower switch. Power conversion is performed by controlling the on / off of the upper switch and the lower switch. At this time, the upper switch and the lower switch may conduct complementarily to each other. Each switch may be controlled by a time to maintain turn-on, i.e., a constant duty ratio. Here, the duty ratio refers to the ratio of being turned on within a certain period, and is also called the duty ratio. Each switch may be a switching element that operates by receiving a driving power input, and the switching element may be a semiconductor switching element such as an FET, MOSFET, or IGBT.

[0058] The power conversion unit (120) may include a DC-DC converter, and may include at least one of a buck converter, a boost converter, and a buck-boost converter. As shown in FIG. 5(A), the power conversion unit (120) may be implemented as a buck converter that lowers the voltage, composed of an upper switch, a lower switch, and an inductor. In this case, the input current can be converted into a high current. Additionally, as shown in FIG. 5(B), it may be implemented as a boost converter that raises the voltage, composed of an inductor, an upper switch, and a lower switch. In this case, the input current can be converted into a low current. Additionally, as shown in FIG. 5(C), it may be implemented as a buck-boost converter that lowers or raises the voltage, composed of a first upper switch, a first lower switch, an inductor, a second upper switch, and a second lower switch. A capacitor may be connected in parallel to the input and output terminals of each converter.

[0059] The input / output connection unit (140) may include a switching element that connects the input unit (110) and the output unit (130). By connecting the input unit (110) and the output unit (130), the input voltage and current are output to the output unit (130) without conversion. At this time, a mechanical switching element such as a relay or a semiconductor switching element such as a MOSFET or a diode may be used as the switching element, either individually or in combination. The input / output connection unit (140) may include an inductor and a capacitor for noise reduction.

[0060] The input / output connection unit (140) may include at least one of two MOSFETs connected in series via a common source or common drain, and a body diode having a cathode connected to the input unit (110). The input / output connection unit (140) may be implemented with various switching elements as shown in FIG. 6. As shown in FIG. 6(A), it may be implemented as a mechanical switch, or as shown in FIG. 6(B), when implemented as a MOSFET including a body diode, the body diode may be connected between the input unit (110) and the output unit (130) so that the cathode is connected to the input unit (110). Additionally, when implemented with two MOSFETs, they may be connected in series via a common source as shown in FIG. 6(C) or connected in series via a common drain as shown in FIG. 6(D). Stability may be increased by connecting two MOSFETs in series via a common source or common drain.

[0061] The bypass section (150) may include a switching element that connects the (+) terminal and the (-) terminal of the output section (130). At this time, the bypass section (150) may include at least one of a MOSFET including a diode whose cathode is connected to the (+) terminal of the output section and a body diode whose cathode is connected to the (+) terminal of the output section. The bypass section (150) connects the (+) terminal and the (-) terminal of the output section (130), and must be connected so that current flows from the (-) terminal to the (+) terminal in order to form a path to the output section. To this end, as shown in FIG. 7, it may include a diode or a body diode. As shown in FIG. 7(A), the cathode may be implemented as a diode connected to the (+) terminal of the output section; as shown in FIG. 7(B), the cathode may be implemented as a MOSFET including a body diode connected to the (+) terminal of the output section; as shown in FIG. 7(C), a MOSFET including a diode and a body diode may be connected in parallel; or as shown in FIG. 7(D), a diode and a different type of switching element may be connected in parallel.

[0062] As described above, depending on the operation of the power conversion unit (120), the input / output connection unit (140), and the bypass unit (150), the power conversion device can be configured to operate in multiple operation modes, such as power conversion mode, input / output connection mode, and bypass mode. Through this, it can operate in the most suitable mode depending on the situation.

[0063] In order to enable the power conversion device (100) to operate in multiple operation modes, the converter can be implemented to operate in multiple operation modes, such as a power conversion mode, an input / output connection mode, and a bypass mode. To this end, the converter includes at least one upper switch and at least one lower switch.

[0064] The converter can operate in a first mode (power conversion mode) in which the input unit (110) converts a first voltage received into a second voltage, a second mode (input / output connection mode) in which the first voltage is output to the output unit (130), and a third mode (bypass mode) in which a bypass path is created in the output unit (130). Depending on the operation of the converter according to each mode, the output unit (130) can output the second voltage in the power conversion mode, the first voltage in the input / output connection mode, and the third voltage input from the output side in the bypass mode.

[0065] The converter can convert the first voltage to the second voltage by conducting the upper switch and the lower switch complementarily in the power conversion mode. The power conversion mode is a general operation of the converter in which the upper switch and the lower switch are conducted according to a duty cycle based on the voltage or current of the power to be converted, and accordingly, the input first voltage is converted to the second voltage.

[0066] In the input / output connection mode, the converter can output the first voltage to the output section by keeping the upper switch on and the lower switch off. In the input / output connection mode, the input section (110) and the output section (130) are directly connected. At this time, the upper switch is connected between the input section (110) and the output section (130), so the upper switch is kept on and the lower switch is turned off to maintain the state in which the input section (110) and the output section (130) are connected.

[0067] As shown in FIG. 8, when the converter is implemented as a buck converter, a boost converter, and a buck-boost converter, respectively, the input and output sections can be directly connected by keeping only the upper switch on in the input / output connection mode. As shown in FIG. 8(A), the buck converter has a path formed through the input section (110), the upper switch, the inductor, and the output section (130), so that the first voltage of the input section (110) is output to the output section (130) without power conversion. As shown in FIG. 8(B), the boost converter has a path formed through the input section (110), the inductor, the upper switch, and the output section (130), so that the first voltage of the input section (110) is output to the output section (130) without power conversion. As shown in FIG. 8(C), the buck-boost converter has a path formed through an input section (110), a first upper switch, an inductor, a second upper switch, and an output section (130), so that the first voltage of the input section (110) is output to the output section (130) without power conversion. The inductor located on the input-output connection path can perform the function of a filter for noise reduction, thereby enabling more stable power delivery.

[0068] At this time, the input unit (110) and the output unit (130) are connected in the input / output connection mode, and a switching element connected in parallel with the converter may be included. The input / output connection mode can be implemented by connecting the converter and the input / output connection unit (140) in parallel. Since the converter and the input / output connection unit (140) each form an input / output connection path, current stress and heat generation of the device can be reduced. As shown in FIG. 9, a plurality of input / output connection paths can be formed by connecting a switching element, such as a MOSFET including a body die, in parallel to the input / output terminals of the buck converter (A), boost converter (B), and buck-boost converter (C).

[0069] When the converter operates in bypass mode, depending on the type of converter, the on / off of the upper switch or the lower switch can be controlled to form a bypass path in the output section (130).

[0070] In bypass mode, if the converter is a buck converter, only the lower switch is connected; if it is a boost converter, both the upper switch and the lower switch are connected; and if it is a buck-boost converter, both the upper switch and the lower switch on the output side are connected, thereby creating a bypass path. As shown in FIG. 10(A), the buck converter has only the lower switch connected, so a bypass path is formed through the output (-) terminal, the lower switch, the inductor, and the output (+) terminal, and the voltage input to the output (-) terminal is output directly to the output (130). As shown in FIG. 10(B), the boost converter has a bypass path formed through the output (-) terminal, the lower switch, the upper switch, and the output (+) terminal, so the voltage input to the output (-) terminal is output directly to the output (130). As shown in FIG. 10(C), the buck-boost converter forms a bypass path through the output (-) terminal, the second lower switch, the second upper switch, and the output (+) terminal, so that the voltage input to the output (-) terminal is output directly to the output (130). At this time, the first upper switch must be turned off, but the first lower switch can be selectively turned on and off. When the first lower switch is on, an additional bypass path can be formed through the output (-) terminal, the first lower switch, the inductor, the second upper switch, and the output (+) terminal.

[0071] At this time, a switching element may be included that connects the (+) terminal and (-) terminal of the output section in bypass mode and is connected in parallel with the converter. By connecting the converter and the bypass section (150) in parallel, a bypass mode can be implemented. Since the converter and the bypass section (150) each form a bypass path, current stress and heat generation of the element can be reduced. As shown in FIG. 11, multiple bypass paths can be formed by connecting switching elements, such as diodes, in parallel to the input / output terminals of the buck converter (A), boost converter (B), and buck-boost converter (C).

[0072] When operating a converter comprising at least one upper switch and at least one lower switch in a power conversion mode, an input / output connection mode, and a bypass mode, the converter may have the connection state of the upper switch and the lower switch changed at least once during a first cycle in the power conversion mode, only the upper switch connected for at least the first cycle in the input / output connection mode, and the lower switch connected for at least the first cycle in the bypass mode. When the upper switch is connected between the lower switch and the output terminal (+), the upper switch may be connected simultaneously with the lower switch for at least the first cycle in the bypass mode. When the power conversion device (100) is implemented as a converter and operates in each mode, the operating time of each switch of the converter may vary depending on the operating mode.

[0073] When the power conversion unit (120), input / output connection unit (140), and bypass unit (150) are operating, they operate according to the operation of each configuration, but when the converter operates in the first to third modes, the operating time of each switch is different.

[0074] In the power conversion mode, the power conversion unit (120) operates to provide an output value different from the input value (e.g., voltage or current). For example, an input value with low current and high voltage can be converted into an output value with low voltage and high current. The opposite is also possible. The power conversion unit (120), implemented as a converter, changes the conduction state of the upper switch and the lower switch at least once within a first cycle, which is a switching cycle. Here, the first cycle may be variable. For example, the first cycle may be set according to the detected voltage, current, temperature, etc. Power is converted by performing a switching operation with a set duty cycle within the first cycle.

[0075] In the input / output connection mode, the input / output connection unit (140) operates to provide an output value identical to the input value. For example, the input current and the output current may be identical. When the power conversion unit (120) is implemented as a converter, the converter may replace the function of the input / output connection unit (140) or operate in parallel with the input / output connection unit (140). Since the connection of the upper switch must be maintained in the input / output connection mode, the upper switch may maintain a conductive state for a longer period than the first cycle.

[0076] In bypass mode, the bypass section (150) operates to provide an electrical path between the (-) terminal and the (+) terminal of the output section. For example, if the output current of the power circuit is greater than the current input from the PV module, the bypass circuit can provide a conduction path for the current corresponding to the difference. For example, when the PV module is faulty or unconnected and there is no input current to the power circuit, the bypass circuit can provide an output current conduction path. When a hot-spot occurs in the PV module, the bypass section (150) provides a bypass path for the output current to lower the current value flowing through the PV module, thereby suppressing heat generation in the PV module. Through this, it is possible to prevent an increase in heat generation caused by an increase in the impedance of the PV module when a current greater than the current that the PV module can output is forcibly conducted. When the power conversion section (120) is implemented as a converter, the converter can replace the function of the bypass section (150) or operate by being connected in parallel with the bypass section (150). In bypass mode, the connection between the output (-) terminal and the (+) terminal must be maintained, so the lower switch can maintain the conduction state of the switching element for a longer period than the first cycle. If the converter is a buck converter, only the lower switch maintains conduction for a longer period than the first cycle, and if the converter is a boost converter, both the upper switch and the lower switch maintain conduction for a longer period than the first cycle, and if the converter is a buck-boost converter, the second upper switch and the second lower switch can maintain conduction for a longer period than the first cycle.

[0077] The power converter (100) may set an operating mode based on parameters detected by a monitoring unit or a temperature sensor. Additionally, the operating mode may be set based on information received from the outside via communication. If necessary, additional modes may be used in addition to the three operating modes. For example, an additional mode for protecting the power converter may be used. When changing modes, a transient period may exist and may be defined as a separate mode if necessary.

[0078] FIG. 12 is a block diagram including an auxiliary power supply unit of a power converter according to an embodiment of the present invention. The power converter (200) may include a converter (210) including at least one upper switch (211) and at least one lower switch (212), and may include an auxiliary power supply unit (220) that supplies driving power to the upper switch (211) and the lower switch (212). At this time, the auxiliary power supply unit (220) includes a bootstrap circuit (222) that supplies driving power to the upper switch (211) using a first driving power supply (221) that supplies driving power to the lower switch (212). Here, the description focuses primarily on the configuration that supplies driving power to the upper switch (211) and lower switch (212) of the converter (210), and it is obvious that the auxiliary power unit (220) can also supply auxiliary power to configurations other than the upper switch (211) and lower switch (212) of the converter (210).

[0079] The auxiliary power supply unit (220) supplies driving power to the upper switch (211) and lower switch (212) of the converter (210). Each switch may be a switching element that operates by receiving driving power, and an auxiliary power supply is required to operate each switch. The switching element may be a semiconductor switching element such as a Si or SiC series MOSFET, GaN HEMT, or IGBT.

[0080] The auxiliary power supply unit (220) may supply auxiliary power to the upper switch (211) using an isolated converter, etc., rather than a bootstrap circuit (222). In this case, the auxiliary power supply unit may include a primary circuit that receives a voltage from at least one output terminal of a plurality of cell strings, an isolated converter that outputs a voltage to a first secondary circuit according to the voltage of the primary circuit, and a plurality of first secondary circuits that supply driving power to each of the upper switches of the plurality of converters using the voltage output from the isolated converter. In this case, the upper switch may be supplied with driving power independently of whether the lower switch is operated.

[0081] The power converter (100) according to the embodiment of FIG. 12 can simply supply driving power to the upper switch (211) using a bootstrap circuit (222). To this end, the auxiliary power supply unit (220) includes a first driving power (221) that supplies driving power to the lower switch (212) and a bootstrap circuit (222) that generates driving power to be supplied to the upper switch (211) using the first driving power (221). When the upper switch (211) and the lower switch (212) are implemented as MOSFETs as in FIG. 13, driving power must be supplied to a driving circuit that supplies a driving voltage to the gate. The driving circuit supplies a gate voltage to the gate of each switch according to a driving signal from a control unit such as an MCU or a PWM controller. Here, the driving signal may use a PWM signal having a 3.3V or 5V level.

[0082] As shown in FIG. 13, when the converter (210) is a buck converter, the source terminal of the lower switch can be directly connected to the negative terminal of the first driving power supply, so that the auxiliary power supply can be used directly during driving. However, since the source terminal of the upper switch is not directly connected to the negative terminal of the first driving power supply, the gate driver cannot directly use the auxiliary power supply, so a separate driving power supply must be generated by using a bootstrap circuit.

[0083] Even if the converter (210) is a boost converter (A) or a buck-boost converter (B) as in FIG. 14, it includes an upper switch, and to supply power to the upper switch, the auxiliary power supply unit (220) may include a bootstrap circuit.

[0084] The bootstrap circuit (222) includes a capacitor that is charged by receiving power from the first driving power source (221); and a diode connected between the first driving power source (221) and the capacitor. Here, the capacitor is connected to a node between the upper switch (211) and the lower switch (212), and when the lower switch (212) is turned on, a closed loop is formed connecting the first driving power source (221), the diode, the capacitor, and the lower switch (212) to receive power from the first driving power source (221) and charge it, and when the lower switch (212) is turned off, the power charged by receiving power from the first driving power source (221) can be supplied as the driving power of the upper switch (211).

[0085] As shown in FIG. 15, the bootstrap circuit (222) may include a diode (223) and a capacitor (224). One end of the capacitor (224) is connected to the first driving power source (221) through the diode (223), and the other end is connected to a node (225) between the upper switch (211) and the lower switch (212). When the lower switch (212) is turned on, a closed loop is formed connecting the first driving power source (221), the diode (223), the capacitor (224), and the lower switch (212), and power is input from the first driving power source (221) to charge. At this time, the upper switch (211) is turned off, so the capacitor (224) is only charged.

[0086] Afterwards, when the lower switch (212) is turned off, the lower switch (212) is opened, and the loop connected to the first driving power source (221), diode (223), capacitor (224), and lower switch (212) is disconnected, and a closed loop is formed between the capacitor (224) and the upper switch (211), so that the power charged in the capacitor (224) is discharged and supplied as the driving power source to the upper switch (211).

[0087] As shown in FIG. 16, the driving power of the upper switch (211) can be supplied to the converter (210) in a boost converter (A) or a buck-boost converter (B) using the first driving power (221) and bootstrap circuit (222) of the corresponding lower switch (212).

[0088] That is, in order to supply driving power to the upper switch (211) using the bootstrap circuit (222), the capacitor must be charged. Therefore, it is impossible to continuously conduct the upper switch without the operation of the lower switch, and the output voltage of the bootstrap must be maintained by conducting the lower switch even for a short time.

[0089] That is, the driving power of the upper switch (211) is dependent on the on / off operation of the corresponding lower switch (212). If sufficient time is not secured for the lower switch (212) to conduct, the power supplied through the bootstrap circuit (222) is less than the power consumed by the gate driver, so a sufficient voltage level cannot be maintained. In addition, the half-bridge structure does not turn on the upper switch (211) and the lower switch (212) simultaneously to prevent a short circuit that can cause circuit damage known as a shoot-through condition. As a result, there is a limitation in continuously conducting the upper switch (211) when generating the driving power of the upper switch (211) using the bootstrap circuit (222).

[0090] Accordingly, for a converter (210) that receives driving power from an auxiliary power supply unit (220) including a bootstrap circuit (222) to operate in an input / output connection mode, the first section in which the upper switch (211) is conductive must be maintained for as long as possible, while including a second section in which the lower switch (212) is conductive. Through this, in the first section, the converter (210) provides an output value identical to the input value, and in the second section, the driving power of the upper switch (211) is charged through the bootstrap circuit (222).

[0091] The converter (210) may operate in an input / output connection mode such that the ratio of the first section and the second section is the first ratio. Here, the first ratio may be such that the first section is longer than the second section. The first ratio may be set to a preset value according to the specifications of the converter (210). Here, the ratio of the second section may be set to a minimum ratio for charging the capacitor (224) to supply driving power to the upper switch (211). For example, the second section may be set to 1% and the first section to 99%. Or, the second section may be set to 0.1% and the first section to 99.9%.

[0092] Additionally, the first ratio of the first section and the second section may be variable. For example, when changing modes to suppress the inrush current generated in the bootstrap circuit (222), the ratio of the first section and the second section may be gradually increased or decreased.

[0093] In the input / output connection mode, a first ratio can be set so that the difference between the voltage of the input portion of the converter (210) and the voltage of the output portion of the converter (210) is less than or equal to a first threshold voltage value. The first threshold voltage value may be pre-set or set by the user. The first threshold voltage value may be an error range. A first ratio can be calculated and applied so that the difference between the voltages of the input portion and the output portion is within a pre-set error range. The first ratio can be calculated and set through simulation or calculation.

[0094] In the converter (210), the upper switch (211) and the lower switch (212) can conduct complementarily at a first frequency in the power conversion mode, and in the input / output connection mode, the upper switch (211) and the lower switch (212) can conduct complementarily at a second frequency.

[0095] In the input / output connection mode, the second frequency in which the first and second sections are repeated may be different from the first frequency, which is the switching frequency of the switching element in the power conversion mode.

[0096] In power conversion mode, it operates at a first frequency having a high frequency to reduce voltage / current ripple generated during the power conversion process or to reduce the size of passive components such as inductors, transformers, and capacitors. For example, the first frequency can be a frequency of 20 kHz or higher, which is higher than the human audible frequency.

[0097] On the other hand, in the input / output connection mode, there are fewer constraints on voltage / current ripple and the size of passive components. Therefore, there is no need to use a high frequency, and it can operate at a second frequency that has a low frequency. The lower the second frequency, the lower the frequency of switching losses occurring during the on / off process of the switching element, and thus, an increase in efficiency due to the reduction of switching losses can be expected. To sufficiently secure the effect of reducing switching losses, the second frequency may be 1 / 4 times or less of the first frequency. For example, the first frequency may be 20 kHz to 100 kHz, and the second frequency may be 0.001 Hz to 10 kHz or less.

[0098] Here, the second frequency can be set according to the input / output voltage, current, and temperature of the converter. Additionally, a jittering function may be used to reduce electromagnetically generated noise, and the second frequency may use a frequency other than 20 to 20 kHz to avoid audible frequencies.

[0099] As shown in FIG. 17, in the input / output connection mode (A), the first section in which the upper switch (211) conducts is longer than the second section in which the lower switch (212) conducts, and the second frequency that repeats the first and second sections may be lower than the first frequency of the power conversion mode (B). It can also be seen that the ratio of the first section is longer in the input / output connection mode (A) than in the power conversion mode (B). In this way, by operating differently depending on the operation mode, the converter (210) can operate in multiple operation modes.

[0100] FIG. 18 is a block diagram of a power converter in which a plurality of power circuits are configured at a multi-level according to an embodiment of the present invention, and FIG. 19 to 21 are drawings for explaining a power converter according to the embodiment of FIG. 18.

[0101] Detailed descriptions of each power circuit (310 to 330) of a power converter (300) in which a plurality of power circuits (310 to 330) are configured at multiple levels correspond to the power converter (100) of FIGS. 2 to 11 and the power converter (200) of FIGS. 12 to 17, and redundant descriptions below will be omitted.

[0102] Multiple power circuits (310 to 330) are configured in a multi-level manner and can be individually connected to each cell string constituting a photovoltaic power generation module. Each power circuit may be Module-Level Power Electronics (MLPE). As shown in FIG. 19, the power converter can also be connected in a multi-level manner with other power converters to output power to an inverter or a load.

[0103] Multiple power circuits (310 to 330) can be connected in a cascode to form a multi-level. Here, a cascode refers to a form in which output terminals are connected in multiple stages, and the output terminals of the power circuits are stacked according to the cascode connection to form a multi-level. A multi-level refers to a structure in which the output signals of each power circuit are combined into a single signal and output. At this time, the (-) terminal of the output terminal of the upper level power circuit is sequentially connected to the (+) terminal of the output terminal of the adjacent lower level power circuit, so that the output from the highest level power circuit to the lowest level power circuit is combined and output as a single signal.

[0104] In addition, as shown in FIG. 20, multiple power circuits can be connected to each of the multiple pairs of output terminals of a single photovoltaic power generation panel to form a multi-level circuit. At this time, the input terminals input to the power converter (300) may be multiple pairs, but the output terminals may be a single pair depending on the connection of the power circuits configured as a multi-level circuit.

[0105] Each power circuit (310 to 330) may include a power conversion unit, an input / output connection unit, and a bypass unit, and may operate in multiple operation modes such as a power conversion mode, an input / output connection mode, and a bypass mode, or may include a converter that operates in a power conversion mode, an input / output connection mode, and a bypass mode. The operation modes of each power circuit (310 to 330) may have independently determined modes, or in some cases, may all operate in the same mode.

[0106] It may include a multi-level bypass unit (340) that creates a bypass path at a multi-level output terminal that bypasses all of the multiple power circuits (310 to 330). Instead of bypassing each power circuit (310 to 330) individually, the multi-level bypass unit (340) creates a path that bypasses all of the multiple power circuits constituting the multi-level.

[0107] In addition, it may include an individual monitoring unit that monitors each input / output terminal of a plurality of power circuits, as well as a multi-level monitoring unit that monitors the output terminal of the entire plurality of power circuits.

[0108] Additionally, as shown in FIG. 21, it may include an auxiliary power supply unit that supplies driving power to each of the multiple power circuits (310 to 330). In this case, each power circuit (310 to 330) includes a converter comprising at least one upper switch and at least one lower switch, and the driving power supplied to each power circuit (310 to 330) is the driving power of the lower switch, and the driving power can be supplied to the upper switch using a bootstrap circuit.

[0109] Each power circuit (310 to 330) may be configured as a buck converter, and the buck converter may implement the functions of power conversion mode, input / output connection mode, and bypass mode. A driving circuit is connected to each switching element included in the converter, and the driving circuit controls the conduction state of the switching element. The driving power for the lower switch is supplied through an auxiliary power circuit, and the driving power for the upper switch is generated through a bootstrap circuit. When the power circuit operates in the input / output connection mode, it may include a first section in which the upper switch conducts for a long time and a second section in which the lower switch conducts for a short time. At this time, the second frequency that repeats the first section and the second section may be lower than the first frequency, which is the switching frequency in the power conversion mode.

[0111] Those skilled in the art related to the embodiments described above 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 foregoing description, and all variations within the scope of equivalence should be interpreted as being included in the invention.

Claims

Claim 1 A power conversion device comprising: a converter including at least one upper switch and at least one lower switch; and an auxiliary power supply unit that supplies driving power to the upper switch and the lower switch, wherein the auxiliary power supply unit includes a bootstrap circuit that supplies driving power to the upper switch using a first driving power supply that supplies driving power to the lower switch, and wherein the converter operates in a third mode in which the lower switch maintains a turned-on state for at least a first period, and when the converter includes a boost converter, the upper switch maintains a turned-on state simultaneously with the lower switch for at least the first period in the third mode. Claim 2 In claim 1, the bootstrap circuit comprises: a capacitor that is charged by receiving power from the first driving power source; and a diode connected between the first driving power source and the capacitor, wherein the capacitor is connected to a node between the upper switch and the lower switch, and when the lower switch is turned on, a closed loop is formed connecting the first driving power source, the diode, the capacitor, and the lower switch, so as to receive power from the first driving power source and charge it, and when the lower switch is turned off, the power charged by receiving power from the first driving power source is supplied to the driving power source of the upper switch. Claim 3 In claim 1, the converter operates in a first mode in which the upper switch and the lower switch conduct complementarily at a first frequency, or in a second mode in which the upper switch and the lower switch conduct complementarily at a second frequency, and the first frequency is different from the second frequency. Claim 4 In paragraph 3, the second frequency is a power converter that is smaller than the first frequency. Claim 5 In paragraph 3, a power converter in which the second frequency is 1 / 4 or less of the first frequency. Claim 6 In paragraph 3, the power converter having a first frequency of 20 kHz or higher. Claim 7 In paragraph 3, the second frequency is a power converter set according to the input / output voltage, current, and temperature of the converter. Claim 8 In paragraph 3, the converter comprises a first section in which the upper switch conducts and a second section in which the lower switch conducts, and the converter operates such that in the second mode, the ratio of the first section to the second section is a first ratio, and the first ratio is such that the first section is longer than the second section. Claim 9 In claim 8, the converter is a power conversion device that gradually changes the ratio of the first section and the second section when changing modes. Claim 10 In paragraph 3, a power converter in which the difference between the voltage of the input portion of the converter and the voltage of the output portion of the converter in the second mode is less than or equal to a first threshold voltage value. A power converter connected simultaneously with the lower switch for at least the first cycle. Claim 11 delete Claim 12 A power conversion device according to claim 1, wherein the converter comprises at least one of a buck converter, a boost converter, and a buck-boost converter, and in the third mode, the buck converter maintains only the lower switch in a turned-on state, and the buck-boost converter maintains both the output-side upper switch and the lower switch in a turned-on state. Claim 13 A power conversion device according to claim 1, comprising: an input unit receiving a first voltage; and an output unit outputting an output voltage of the converter, wherein the converter operates in a first mode for converting the first voltage into a second voltage or in a second mode for outputting the first voltage to the output unit, and wherein the output unit outputs the second voltage in the first mode and outputs the first voltage in the second mode. Claim 14 In paragraph 13, the converter operates in the third mode that creates a bypass path in the output section, and the output section outputs a third voltage input from the output side in the third mode. Claim 15 A multi-level power converter comprising a plurality of power circuits constituting a multi-level, wherein each power circuit comprises a power converter of any one of claims 1 to 10 and claims 12 to 14.

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