Single-phase three-level buck-boost inverter

Abstract

The present invention relates to a transformerless, high-efficiency, high-output density, high-input voltage range, single-phase DC / AC inverter.

Description

Technical Field

[0001] The present invention relates to a single-phase three-level buck-boost inverter.

[0002] In particular, the present invention relates to a single-phase three-level buck-boost inverter that obtains a single-phase AC output from a DC input power source.

Background Art

[0003] Electrical energy obtained from a controlled or uncontrolled DC voltage / current source is converted into AC voltage / current via an inverter (regardless of the presence or absence of a transformer) and transferred to a grid or a load circuit independent of the grid. A transformer inverter can electrically isolate a DC input source from an AC output and suppress leakage current caused by the DC input source. A transformerless inverter has disadvantages in terms of volume, weight, efficiency, and cost. In a transformerless inverter, cost, volume, and weight are reduced by removing the transformer from the system, and efficiency is improved by reducing the power loss induced by the transformer. Various geometric arrangements, switching plans, and filtering methods of power converters for suppressing leakage current generated from an input power source have been considered.

[0004] An inverter with a wide input voltage range is suitable in terms of minimizing the effect of greatly changing the output AC voltage. When the input DC voltage level is smaller than the peak value of the desired AC voltage at the output, the inverter is expected to exhibit boost characteristics. When the input DC voltage level is larger than the peak value of the desired AC voltage at the output, the inverter is expected to exhibit buck characteristics.

[0005] When investigating the subject of the present invention, Patent Document 1 was found. This application describes a method for converting a DC voltage from a DC voltage source - particularly a photovoltaic DC voltage source - into an AC voltage. However, there is no mention of a transformerless, high-efficiency, three-level, high-output density, wide-input voltage range, and single-phase three-level buck-boost DC / AC inverter.

[0006] That is, the current solutions for the subject matter of the present application have the above-mentioned drawbacks, and since the current solutions for the subject matter of the present application are inefficient, development is needed in this technical field.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention aims to solve the above-mentioned drawbacks as suggested by the current situation.

[0009] The main object of the present invention is to prevent capacitive leakage current from flowing into the output from a DC voltage source.

[0010] Another object of the present invention is to boost the voltage, step down the voltage, and convert an alternating current into a function of voltage form by a single DC power source provided at the input.

[0011] Another object of the present invention is to obtain a single-phase AC output voltage from a DC input power source within the range of a buck-boost inverter.

[0012] Another object of the present invention is to provide a stable AC voltage controlled at the output against a wide range of voltage variations at the inverter input.

Means for Solving the Problems

[0013] To meet the above object, the present invention is a transformerless, high-efficiency, three-level, high-output density, single-phase three-level buck-boost DC / AC inverter that provides a single-phase AC output voltage and includes a semiconductor switch T1 that prevents capacitive leakage current from flowing from the DC input power supply to the output. The inverter is characterized by comprising a high-output density transformerless single-phase buck-boost inverter.

[0014] The structural and inherent features of the present invention will be clearly understood from the following drawings and the detailed description with reference to these drawings. Therefore, the evaluation shall be made in consideration of these drawings and the detailed description.

Brief Description of the Drawings

[0015]

Figure 1

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Embodiments for Carrying Out the Invention

[0016] In this detailed description, for the sole purpose of clarifying the object of the invention, preferred embodiments of the single-phase three-level buck-boost inverter of the present invention will be described by way of example.

[0017] A transformerless, high-efficiency, three-level, high-output density, single-phase three-level buck-boost DC / AC inverter without a DC connection capacitor includes a single DC input power supply connected between a first terminal and a second terminal, a first semiconductor switch connected between the first terminal and a third terminal, a second semiconductor switch connected between the third terminal and a fourth terminal, a third semiconductor switch connected between the second terminal and the fourth terminal, a first inductor connected between the third terminal and a fifth terminal, a second inductor connected between the second terminal and a sixth terminal, a fourth semiconductor switch connected between the fifth terminal and the fourth terminal, a fifth semiconductor switch connected between the sixth terminal and the fourth terminal, a sixth semiconductor switch and an eighth semiconductor switch connected in series between the fifth terminal and a ninth terminal, a seventh semiconductor switch and a ninth semiconductor switch connected in series between the sixth terminal and the ninth terminal, and drive control means. At most two of the first semiconductor switch to the ninth semiconductor switch are turned on simultaneously at high frequency. At least the first semiconductor switch, the second semiconductor switch, the third semiconductor switch, the fourth semiconductor switch, the fifth semiconductor switch, the sixth semiconductor switch, and the seventh semiconductor switch are MOSFETs or IGBTs. The drive control means operates the first semiconductor switch and the second semiconductor switch at high frequency in the positive half-cycle of the buck mode of the inverter, maintains the third semiconductor switch, the fifth semiconductor switch, the sixth semiconductor switch, and the eighth semiconductor switch in the on state, and maintains the fourth semiconductor switch, the seventh semiconductor switch, and the ninth semiconductor switch in the off state. operates the first semiconductor switch and the third semiconductor switch at high frequency in the negative half-cycle of the buck mode of the inverter, maintains the second semiconductor switch, the fourth semiconductor switch, the seventh semiconductor switch, and the ninth semiconductor switch in the on state, and maintains the fifth semiconductor switch, the sixth semiconductor switch, and the eighth semiconductor switch in the off state. In the positive half-cycle of the boost mode of the inverter, operate the fourth semiconductor switch and the eighth semiconductor switch at high frequency, maintain the first semiconductor switch, the fifth semiconductor switch, and the sixth semiconductor switch in the on state, and maintain the second semiconductor switch, the third semiconductor switch, the seventh semiconductor switch, and the ninth semiconductor switch in the off state. In the negative half-cycle of the boost mode of the inverter, operate the fifth semiconductor switch and the ninth semiconductor switch at high frequency, maintain the first semiconductor switch, the fourth semiconductor switch, and the seventh semiconductor switch in the on state, and maintain the second semiconductor switch, the third semiconductor switch, the sixth semiconductor switch, and the eighth semiconductor switch in the off state. Prevent the capacitive leakage current from flowing from the DC input power supply to the output by turning off the first semiconductor switch in the zero-crossing region of the AC voltage at the output.

[0018] From a DC voltage source with a large surface area such as a solar cell panel, capacitive leakage current may flow into the output. In a circuit structure prior to a single-phase three-level buck inverter, capacitive leakage current generated from the input power supply is prevented by separating the DC input terminals and the output terminals. In a single-phase three-level buck inverter, capacitive leakage current caused by the input power supply is prevented by separating the DC input terminal ( First terminal (1), second terminal (2) ) and the output terminal ( Eleventh terminal (11), twelfth terminal (12) ). In addition to this feature, in a single-phase three-level buck inverter, Between the first terminal (1) and the second terminal (2) the required midpoint between them becomes unnecessary. The boost function, buck function, and conversion function of the DC current to an AC voltage by one DC power supply provided at the input are possible with a single-phase three-level buck inverter. The single-phase three-level buck inverter does not include an electrolytic capacitor in its circuit structure. Since the input can be directly supplied from a single power supply, there is no need to customize the inverter input. Since there is no electrolytic capacitor connected in series to the inverter input, a balancing algorithm is also unnecessary.

[0019] Within the range of a single-phase three-level buck-boost inverter, a transformerless single-phase buck inverter is provided for obtaining a single-phase AC output voltage (501) from a DC input power supply (515) .

[0020] The circuit structure as a single-phase three-level buck-boost inverter is shown in FIG. 1. Powered from a DC power supply connected to the terminal Child ( of FIG. 1, a transformerless inverter that generates a single-phase AC sine wave output voltage at the terminal ( First terminal (1), second terminal (2) ) within the range of a single-phase three-level buck-boost inverter was developed. The output filter is Between the eleventh terminal (11) and the twelfth terminal (12) and Between the ninth terminal (9) and the tenth terminal (10) andBetween the eleventh terminal (11) and the twelfth terminal (11) is between. The active switch, passive diode, and inductor are First terminal (1) and second terminal (2) and Ninth terminal (9) and tenth terminal (10) is arranged between. The single-phase three-level buck inverter is an inverter with a wide input voltage range because it has both buck and boost functions. The single-phase three-level buck-boost inverter does not include an electrolytic capacitor and has at most two high-frequency switching semiconductors at the same time, so it is an inverter with high output density.

[0021] The single-phase transformerless inverter in Figure 2 has buck and boost functions. A stable AC voltage can be obtained at the output for a wide voltage change at the inverter input. The leakage current generated from the DC input power supply can be suppressed by appropriate switching measures. On the other hand, the upper DC power supply supplies power to the output in the region where the output voltage is positive, and the lower DC power supply supplies power to the output in the region where the output voltage is negative. Although this circuit has buck and boost functions, separate input power supplies are required for the positive and negative half-cycles, so the utilization rate of the input voltage decreases.

[0022] Figure 3 shows a buck inverter powered by a single DC voltage source. In this inverter structure with a higher input voltage utilization rate than the inverter in Figure 2, two series capacitors are used instead of two DC power supplies at the input to provide the output current for the positive and negative half-cycles. In this inverter structure, it is important that the voltages of the input series capacitors are balanced, which stabilizes and adjusts the output AC voltage. If the current flowing through the capacitor is large, the size of the capacitor will also be large. Although the inverter in Figure 3 is a transformerless inverter, the presence of the capacitor increases the volume and reduces the output density.

[0023] In the inverter of Figure 2, since two DC power supplies are required at the input, it is necessary to balance the voltages between the power supplies. This situation leads to customizing the inlet system according to the circuit.

[0024] In the inverter of FIG. 3, although one power supply is used for the input, two series electrolytic capacitors are required. In this inverter, an additional control algorithm must be applied to keep the voltages of the electrolytic capacitors balanced. Electrolytic capacitors not only increase the circuit size but also limit the product life.

[0025] The inverter of FIG. 4 solves the problem of using large electrolytic capacitors in the inverter of FIG. 3. With the help of the added semiconductor switches T1, T2, T3, and T4 in the input, the current passing through the capacitors can be reduced, and the size of the capacitors can be decreased. However, since this inverter uses four additional switches, the cost increases and the control algorithm becomes complex.

[0026] The single-phase inverter considered in the single-phase three-level buck-boost inverter structure is shown in FIG. 5 together with the numbers of the materials used.

[0027] When the voltage level of the DC input power supply (501) is higher than the peak value of the output AC voltage (515) (FIG. 6), First Semiconductor switch Th ( 502), Second semiconductor switch (503) and First Inductor Ta ( 505), a DC / DC buck converter is used to form the sinusoidal shape of the output voltage in the positive half-cycle of the output voltage. In the positive half-cycle of the output voltage, Sixth Semiconductor switch Th ( 510) is on, Seventh Semiconductor switch Th ( 511) is off.

[0028] When the voltage level of the DC input power supply (501) is higher than the peak value of the output AC voltage (FIG. 6); in the negative half-cycle of the output voltage, First Semiconductor switch Th ( 502), Third semiconductor switch (504) and Second Inductor Ta ( 508), a DC / DC buck converter is formed. In this case, Fourth Semiconductor switch Th ( 506), Fifth semiconductor switch (507) is off, Eighth Semiconductor switch Th ( 509), And the ninth semiconductor switch (512) is on. In the negative half cycle of the output voltage, Sixth Semiconductor switch Th ( 510) is off, Seventh Semiconductor switch Th ( (511) is on.

[0029] When the voltage level of the DC input power supply (501) is higher than the peak value of the output AC voltage, the inverter operates in a buck mode to generate a sinusoidal output voltage.

[0030] When the voltage level of the DC input power supply (501) is lower than the peak value of the output AC voltage (Fig. 7), in the positive half cycle of the output voltage, in the region where the output AC voltage is lower than the DC input voltage level, First Semiconductor switch Th ( 502), Second semiconductor switch (503) and First Inductor Ta ( 505) are used to create a voltage waveform with a DC / DC buck converter. In the region where the output AC voltage is higher than the DC input voltage level, First Inductor Ta ( 505), Fourth semiconductor switch (506), and Eighth semiconductor switch (509) semiconductor switches are used to create a voltage waveform with a DC / DC boost converter. In the positive half cycle of the output voltage, Sixth Semiconductor switch Th ( 510) is on, Seventh Semiconductor switch Th ( (511) is off.

[0031] When the voltage level of the DC input power supply (501) is lower than the peak value of the output AC voltage (Fig. 7); in the negative half cycle of the output voltage, in the region where the absolute value of the output AC voltage is lower than the DC input voltage level, First Semiconductor switch Th ( 502), Third semiconductor switch (504) and Second Inductor Ta (Create a voltage waveform with a DC / DC buck converter composed of (508). In the region where the output AC voltage is higher than the absolute value of the DC input voltage level, Second inductor Ta ( (508), Fifth semiconductor switch (507), and Ninth semiconductor switch Create a voltage waveform with a DC / DC boost converter composed of the semiconductor switches of (512). During the negative half-cycle of the output voltage Sixth semiconductor switch Th ( (510) is off, Seventh semiconductor switch Th ( (511) turns on.

[0032] When the voltage level of the input DC power supply (501) is lower than the peak value of the output AC voltage, in order to make the output voltage sinusoidal, the inverter outputs the AC power Voltage ( (515) and the DC input power Source ( (501) operates in the buck mode in the region below the voltage level. The output AC power Voltage ( (515) and the DC input power Source ( (501) operates in the boost mode in the region above the voltage level.

[0033] While the inverter is operating in the buck mode, First semiconductor switch Th ( (502) And the second semiconductor switch (503) is switched at a high frequency (1 kHz to 1 MHz band) during the positive half-cycle of the output voltage, Third semiconductor Switch (504), Fifth semiconductor switch (507), Sixth semiconductor switch (510), And the eighth semiconductor switch (509) are in the conducting state, Fourth semiconductor Body ( (506), Seventh semiconductor switch (511), and Ninth semiconductor switch (512) are in the off state.

[0034] While the inverter is operating in the buck mode, during the negative half-cycle of the output voltage First semiconductor switch Th ( (502) And the third semiconductor switch (504) is switched at a high frequency (1 kHz to 1 MHz band),Second Semiconductor switch Th ( 503), Fourth semiconductor switch (506), Seventh semiconductor switch (511), and Ninth semiconductor switch (512) conduct, Fifth Semiconductor switch Th ( 507), Sixth semiconductor switch (510), And the eighth semiconductor switch (509) enter the off state.

[0035] While the inverter is operating in boost mode, Fourth Semiconductor switch Th ( 506) And the eighth semiconductor switch (509) is switched at a high frequency (in the band of 1 kHz to 1 MHz) during the positive half-cycle of the output voltage, First semiconductor switch (502), Fifth semiconductor switch (507), And the sixth semiconductor switch (510) semiconductors are in the on state, Second semiconductor switch (503), Third semiconductor switch (504), Seventh semiconductor switch (511), and Ninth semiconductor switch (512) semiconductor switches are in the off state.

[0036] While the inverter is operating in boost mode, during the negative half-cycle of the output voltage Fifth Semiconductor switch Th ( 507) And the ninth semiconductor switch (512) is switched at a high frequency (in the 1 kHz to 1 MHz band), First Semiconductor Switch (502), Fourth semiconductor switch (506), and the seventh semiconductor switch (511) are in the on state, Second Semiconductor Switch (503), Third semiconductor switch (504), Sixth semiconductor switch (510), and the eighth semiconductor switch (509) enter the off state.

[0037] Capacitor Sa( 513) and inductor Ta( 514) are used to filter the transmission of high-frequency components generated in the inverter considered within the range of a single-phase three-level buck-boost inverter.

[0038] The high-frequency leakage capacitive current instantaneously drawn from the input power supply in the zero-crossing region of the output AC voltage is for a single-phase three-level buck inverter First semiconductor switch (502) is prevented by. First Semiconductor switch Chi ( 502) is turned off, and the electrical connection between the input terminal and the output terminal is interrupted in the zero-crossing region of the output voltage. Therefore, the problem of capacitive leakage current generated from the input DC power supply that occurs in a transformerless inverter is suppressed by the present invention.

[0039] In a single-phase three-level buck-boost inverter, since two semiconductor switches are switched at a high frequency during one switching period, the thermal power loss due to switching is small.

[0040] Depending on whether the output AC voltage is lower or higher than the input DC voltage, by switching two different switches at a high frequency during the positive and negative cycles of the output AC voltage and the operation period of the buck-boost mode, the thermal load of the heat sink is surely dispersed.

[0041] In a single-phase three-level buck inverter, it is not necessary to connect one or two electrolytic capacitors in series to the input terminal of the transformerless inverter structure. Therefore, by not using an electrolytic capacitor, the total volume of the inverter is reduced and the output density is increased. Generally, the short life of the electrolytic capacitor is also the cause of the short life of the output converter that requires an electrolytic capacitor. Therefore, the inverter introduced by the present invention that does not require an electrolytic capacitor has a long life.

[0042] In the structure of a single-phase three-level buck-boost inverter First semiconductor switch , the second semiconductor switch, the third semiconductor switch, the fourth semiconductor switch, the fifth semiconductor switch, the sixth semiconductor switch, and the seventh semiconductor switch can use MOSFETs and IGBTs of silicon or silicon carbide technology. The anti-parallel diodes in the switch can also be externally attached.

[0043] Included in the single-phase, three-level, buck-boost inverter structure Eighth semiconductor switch and ninth semiconductor switchcan be used in silicon or silicon carbide technology.

[0044] The MOSFET can be used as an IGBT in silicon or silicon carbide technology instead of D1 and D2 included in the single-phase three-level buck-boost inverter structure. Thus, the thermal losses of these switches can be reduced. Furthermore, by using a controllable semiconductor instead of the D1 and D2 diodes, the inverter can operate in two directions. An inverter that can convert an input DC voltage to an output AC voltage can also convert a single-phase AC voltage to a regulated DC voltage.

[0045] A single-phase, three-level, buck-boost inverter can convert a DC input voltage taken from a solar panel, DC power supply, or battery into a single-phase AC voltage and can be used for powering electronic devices or feeding power into the grid.

[0046] An AC voltage obtained from a network, AC generator, or turbine can be used for charging a battery or powering a DC electronic load.

[0047] Since the single-phase three-level buck inverter can operate in two directions, it is used when converting an unregulated AC voltage obtained from a wind turbine into a regulated DC output voltage and in battery charging devices for electric vehicles.

[0048] The inverters disclosed within the scope of the single-phase three-level buck inverter are used in applications such as renewable energy, military land, sea, and air vehicles, railway systems, medical devices, and electric vehicles.

[0049] A single-phase three-level buck-boost inverter and a transformerless, high-efficiency, three-level, high-power density, wide input voltage range, single-phase DC / AC inverter are provided.

Description of Symbols

[0050] 1 : First Terminal 2 : Second terminal 3 : Third terminal 4 : Fourth terminal 5 : Fifth terminal 6 : Sixth terminal 7 : Seventh terminal 8 : Eighth terminal 9 : Ninth terminal 10 : Tenth terminal 11 : Eleventh terminal 12 : Twelfth terminal T1, T2, T3, T4, T5, T6, T7, T8: Semiconductor switches Vdc, Vdc1, Vdc2: DC power supplies L1, L2, Lg: Inductors D1, D2, D3, D4: Semiconductor switches (diodes) Cf, C1, C2: Capacitors Vg: Output AC voltage 501: DC input power supply 502 : First Semiconductor switches 503 : Second semiconductor switch 504 : Third semiconductor switch 506 : Fourth semiconductor switch 507 : Fifth semiconductor switch 510 : Sixth semiconductor switch 511 : Seventh semiconductor switch 505 : First Inductor 508 :Second inductor 509 : Eighth Semiconductor switch (diode) 512 : Ninth semiconductor switch (diode) 513: Capacitor 514: Inductor 515: AC output power supply

Claims

【Claim 1】 A traceless, high-efficiency, three-level, high-output-density, single-phase three-level buck-boost DC / AC inverter with a wide input voltage range, comprising a traceless single-phase buck-boost inverter with high output density, the traceless single-phase buck-boost inverter with high output density provides a single-phase AC output voltage, and includes a semiconductor switch T1 that prevents capacitive leakage current from flowing from the DC input power supply to the output, characterized in that it is a single-phase three-level buck-boost DC / AC inverter.

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