Single-phase three-level buck-boost inverter

Abstract

The invention relates to a transformerless single-phase DC / AC inverter which is high in efficiency, three in level, high in power density and wide in input voltage range.

Description

Technical Field

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

[0002] In particular, the present invention relates to a transformerless single-phase buck-boost inverter for deriving a single-phase AC output voltage from a DC input power source. Background Art

[0003] The electrical energy obtained from a regulated or unregulated DC voltage / current source is converted into an AC voltage / current via an inverter with or without a transformer, and is transmitted to the grid or to a load independent of the grid. The transformer inverter provides galvanic isolation between the DC input source and the AC output, and can suppress leakage current from the DC input source. Transformerless inverters are at a disadvantage in terms of size, weight, efficiency, and cost. In transformerless inverters, cost, size, and weight are reduced by removing the transformer from the system, and efficiency is improved by reducing the power loss caused by the transformer. Various power converter topologies, switching strategies, and filtering methods are considered to suppress leakage current drawn from the input power supply in transformerless inverters.

[0004] An inverter with a wide input voltage range is preferred in order to minimize the effect of large changes in the input DC voltage on the output AC voltage. If the input DC voltage level is below the peak value of the AC voltage required for the output, the inverter is expected to exhibit a step-up characteristic, and if the input DC voltage level is above the output AC voltage peak, the inverter is expected to exhibit a step-down characteristic.

[0005] As a result of research on this topic, see US7411802B2. This application describes a method for converting a DC voltage from a DC voltage source (especially a photovoltaic DC voltage source) into an AC voltage. However, there is no mention of a transformerless, high-efficiency, three-level, high-power-density, wide-input-voltage-range single-phase three-level buck-boost DC / AC inverter structure.

[0006] Therefore, due to the above-mentioned shortcomings and inadequacies of current solutions regarding this subject matter, a need exists for developments in the related art. Summary of the invention

[0007] The present invention aims to solve the above-mentioned disadvantages by being inspired by the current situation.

[0008] The main object of the present invention is to prevent capacitive leakage current from flowing from the DC voltage source to the output.

[0009] Another object of the present invention is to utilize a single DC source at the input to provide the functions of voltage step-up, voltage step-down, and conversion of AC power into voltage form.

[0010] Another object of the present invention is to obtain a single-phase AC output voltage from a DC input power source within the scope of a buck-boost inverter.

[0011] Another object of the present invention is to provide a regulated and stable AC voltage at the output for wide voltage variations at the inverter input.

[0012] In order to achieve the above-mentioned object, the present invention is a transformerless, high-efficiency, three-level, high-power-density, wide-input voltage range single-phase three-level buck-boost DC / AC inverter, characterized in that it includes a transformerless single-phase buck-boost inverter, which has high power density, provides a single-phase AC output voltage, and includes a T1 semiconductor switch, which prevents capacitive leakage current from flowing from a DC input power supply to the output.

[0013] The structures and characteristic features of the present invention will be clearly understood through the following drawings and the detailed description made with reference to these drawings, and thus should be evaluated by considering these drawings and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is an illustrative diagram of a single-phase three-level buck-boost inverter which is the subject of the present invention.

[0015] Figure 2 It is an illustration of the prior art.

[0016] Figure 3 It is an illustration of the prior art.

[0017] Figure 4 It is an illustration of the prior art.

[0018] Figure 5 is an illustrative diagram of a single-phase three-level buck-boost inverter which is the subject of the present invention.

[0019] Figure 6 is an exemplary diagram of a switching signal when the peak value of the output voltage of the subject invention is lower than the input voltage.

[0020] Figure 7 is an exemplary diagram of a switching signal when the peak value of the output voltage of the subject invention is higher than the input voltage.

[0021] Reference numerals

[0022] 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12: terminals

[0023] T1, T2, T3, T4, T5, T6, T7, T8: semiconductor switches

[0024] Vdc, Vdc1, Vdc2: DC power supply

[0025] L1, L2, Lg: Inductors

[0026] D1, D2, D3, D4: semiconductor switches (diodes)

[0027] Cf, C1, C2: capacitors

[0028] Vg: Output AC voltage

[0029] 501:DC input power supply

[0030] 502, 503, 504, 506, 507, 510, 511: Semiconductor switches

[0031] 505, 508: Inductor

[0032] 509, 512: Semiconductor switch (diode)

[0033] 513: Capacitor

[0034] 514: Inductor

[0035] 515: AC output voltage DETAILED DESCRIPTION

[0036] In this detailed description, in order to clarify the subject matter, preferred embodiments of the single-phase three-level buck-boost inverter of the present invention are described only by way of example.

[0037] Capacitive leakage current may flow from a DC voltage source with a large surface area (such as a solar panel) to the output. In the circuit structure before the single-phase three-level buck-boost inverter, the capacitive leakage current from the input source is prevented by separating the DC input terminal from the output terminal. In the single-phase three-level buck-boost inverter, the DC input terminals (1, 2) are separated from the output terminals (11, 12) to prevent capacitive leakage current from the input source. In addition to this feature, with the help of the single-phase three-level buck-boost inverter, the required midpoint between the terminals (1, 2) at the input is no longer required. With the help of the single-phase three-level buck-boost inverter, a single DC source at the input can be used to achieve the functions of voltage boost, voltage reduction, and conversion of AC into voltage form. The topology of the single-phase three-level buck-boost inverter does not include any electrolytic capacitors. Since the input can be directly powered by a single source, there is no need to customize the inverter input. Since there is no electrolytic capacitor connected in series at the inverter input, a balancing algorithm is not required.

[0038] A transformerless single-phase buck inverter is provided for obtaining a single-phase AC output voltage from a DC input power source within the scope of a single-phase three-level buck-boost inverter.

[0039] exist Figure 1 A circuit structure presented as a single-phase three-level buck-boost inverter is shown in FIG. A transformerless inverter is developed, which consists of a transformer connected to its terminals (1, 2) ( Figure 1 The single-phase three-level buck-boost inverter is powered by a DC source at the terminals (1, 2) in the inverter, and generates an output voltage in the form of a single-phase AC sine wave at its terminals (11, 12) within the scope of the single-phase three-level buck-boost inverter. The output filter is located between the terminals (9, 10) and (11, 12). The active switch, the passive diode and the inductor are located between the terminals (1, 2) and (9, 10). The single-phase three-level buck-boost inverter is an inverter with a wide input voltage range because it has both buck characteristics and boost characteristics. The single-phase three-level buck-boost inverter is an inverter with high power density because it does not contain electrolytic capacitors and has at most two high-frequency switching semiconductors at the same time.

[0040] Figure 2 The single-phase transformerless inverter in has both buck and boost characteristics. Relative to the wide voltage change at the inverter input, a regulated and stable AC voltage can be obtained at the output. With the help of an appropriate switching strategy, the leakage current originating from the DC input source can be suppressed. On the other hand, the upper DC power supply supplies power to the output in the area where the output voltage is positive, while the lower DC power supply supplies power to the output in the area where the output voltage is negative. Although this topology has buck and boost characteristics, the need for independent input power supplies for the positive and negative half-cycles results in reduced input voltage utilization.

[0041] Figure 3 A buck-boost inverter powered by a single DC voltage source is shown. In this inverter structure, the input voltage utilization is higher than Figure 2 In the inverter, the power flow for the positive and negative half cycles is provided by using two series capacitors at the input instead of two DC power supplies. It is important in this inverter structure that the voltages on the series capacitors at the input of the inverter structure are balanced so that the output AC voltage is stable and regulated. The high current flowing through the capacitors makes the size of the capacitors large. Although Figure 3 The inverter in the embodiment is a transformerless inverter, but the capacitor in its structure will increase the size of the inverter and reduce the power density.

[0042] exist Figure 2In the inverter shown in , two DC sources are required at the input, so voltage balancing between the sources is required. This situation makes the system at the inlet customized according to the topology.

[0043] exist Figure 3 In the inverter shown in , two series electrolytic capacitors are required despite using a single source at the input. An additional control algorithm must be applied to maintain voltage balance across the electrolytic capacitors in this inverter. Electrolytic capacitors not only increase the size of the circuit but also limit the life of the product.

[0044] Figure 4 The inverter in Figure 3 The problem of using large electrolytic capacitors in the inverter in . With the help of T1, T2, T3 and T4 semiconductor switches added to the input, the current through the capacitor is reduced and the size of the capacitor can be reduced. However, this inverter uses four additional switches, which increases the cost and complicates the control algorithm.

[0045] The single-phase inverter is considered to be a single-phase three-level buck-boost inverter structure. Figure 5 The single-phase inverter and the quantity of materials used are shown together.

[0046] When the voltage level of the DC input power source (501) is higher than the peak value of the output AC voltage (515) Figure 6 ); in the positive half cycle of the output voltage, a DC / DC buck converter including semiconductor switches T1 (502), T2 (503) and inductor L1 (505) is used to form a sinusoidal waveform of the output voltage. In the positive half cycle of the output voltage, the semiconductor switch T6 (510) is turned on and the semiconductor switch T7 (511) is turned off.

[0047] When the voltage level of the DC input power supply (501) is higher than the peak value of the output AC voltage ( Figure 6 ); in the negative half cycle of the output voltage, the output voltage is formed by a DC / DC buck converter including semiconductor switches T1 (502), T3 (504) and inductor L2 (508). In this case, semiconductor switches T4 (506), T5 (507) are turned off, and semiconductor switches D1 (509), D2 (512) are turned on. In the negative half cycle of the output voltage, semiconductor switch T6 (510) is turned off, and semiconductor switch T7 (511) is turned on.

[0048] In case the voltage level of the DC input power source (501) is higher than the peak value of the output AC voltage; the inverter operates in buck mode to generate an output voltage in the form of a sine wave.

[0049] When the voltage level of the DC input power supply (501) is lower than the peak value of the output AC voltage ( Figure 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, the voltage waveform is generated using a DC / DC buck converter including semiconductor switches T1 (502), T2 (503) and an inductor L1 (505). In the region where the output AC voltage is higher than the DC input voltage level, the voltage waveform is generated using a DC / DC boost converter including inductor L1 (505), T4 (506), and D1 (509) semiconductor switches. In the positive half cycle of the output voltage, the semiconductor switch T6 (510) is turned on and the semiconductor switch T7 (511) is turned off.

[0050] When the voltage level of the DC input power supply (501) is lower than the peak value of the output AC voltage ( Figure 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, the voltage waveform is generated using a DC / DC buck converter consisting of semiconductor switches T1 (502), T3 (504) and inductor L2 (508). In the region where the output AC voltage is higher than the absolute value of the DC input voltage level, the voltage waveform is generated using a DC / DC boost converter consisting of an L2 (508) inductor, T5 (507), and D2 (512) semiconductor switch. In the negative half cycle of the output voltage, the semiconductor switch T6 (510) is turned off and the semiconductor switch T7 (511) is turned on.

[0051] In the case where the voltage level of the input DC power supply (501) is lower than the peak value of the output AC voltage; in order to generate an output voltage in the form of a sine wave, the inverter operates in a buck mode for a region lower than the voltage level of the output AC voltage Vg (515) and the DC input power supply Vdc (501). The inverter operates in a boost mode for a region higher than the voltage level of the output AC voltage Vg (515) and the DC input power supply Vdc (501).

[0052] When the inverter operates in buck mode, the semiconductor switches T1 (502) and T2 (503) are switched at a high frequency (within a frequency band of 1 kHz to 1 MHz) in the positive half cycle of the output voltage, the semiconductor switches T3 (504), T5 (507), T6 (510), and D1 (509) are turned on, and the semiconductor switches T4 (506), T7 (511), and D2 (512) are turned off.

[0053] When the inverter operates in buck mode, the semiconductor switches T1 (502) and T3 (504) are switched at a high frequency (1kHz to 1MHz band) in the negative half cycle of the output voltage, the T2 (503), T4 (506), T7 (511), and D2 (512) semiconductors are turned on, and the T5 (507), T6 (510), and D1 (509) semiconductor switches are turned off.

[0054] When the inverter operates in boost mode, semiconductor switches T4 (506) and D1 (509) are switched at a high frequency (1kHz to 1MHz frequency band) in the positive half cycle of the output voltage, T1 (502), T5 (507), and T6 (510) semiconductors are turned on, and T2 (503), T3 (504), T7 (511), and D2 (512) semiconductor switches are turned off.

[0055] When the inverter operates in boost mode, semiconductor switches T5 (507) and D2 (512) are switched at a high frequency (1kHz to 1MHz band) in the negative half cycle of the output voltage, T1 (502), T4 (506), and T7 (511) semiconductors are turned on, and T2 (503), T3 (504), T6 (510), and D1 (509) semiconductor switches are turned off.

[0056] Capacitor Cf (513) and inductor Lg (514) are used to filter the transfer of high frequency components generated by the inverter, which is considered to be within the range of a single-phase three-level buck-boost inverter.

[0057] In a single-phase three-level buck-boost inverter, a high-frequency capacitive leakage current drawn instantaneously from an input power supply in a zero-crossing region of an output AC voltage is prevented by a T1 (502) semiconductor switch. The semiconductor switch T1 (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 present invention can suppress the problem of capacitive leakage current drawn from an input DC power supply that occurs in a transformerless inverter.

[0058] The fact that the single-phase three-level buck-boost inverter has two semiconductor switches switched at a high frequency in one switching cycle ensures that thermal power losses due to switching are low.

[0059] Switching two different switches at high frequency in positive and negative cycles of the output AC voltage and in the operation cycle in buck-boost mode depending on whether the output AC voltage is lower or higher than the input DC voltage ensures distribution of the thermal load on the heat sink.

[0060] With the help of a single-phase three-level buck-boost inverter, it is not necessary to connect a single or two electrolytic capacitors in series to the input terminals of the transformerless inverter structure. Therefore, with the deactivation of the electrolytic capacitors, the overall volume of the inverter is reduced and the power density is increased. In general, the fact that electrolytic capacitors do not have a long life also leads to a short life of power converters that require electrolytic capacitors. In this context, the inverter introduced according to the present invention that does not require electrolytic capacitors has a long life.

[0061] The semiconductor switches (T1, T2, T3, T4, T5, T6, T7) in the single-phase three-level buck-boost inverter structure can be used as MOSFETs, IGBTs in silicon or silicon carbide technology. The anti-parallel diodes that may be present in the switches can be added externally.

[0062] The diodes (D1 and D2) included in the single-phase three-level buck-boost inverter structure can be used in silicon or silicon carbide technology.

[0063] MOSFETs are used as IGBTs in silicon or silicon carbide technology instead of D1 and D2 in the single-phase three-level buck-boost inverter structure. Therefore, the heat loss of these switches can be reduced. In addition, by using controllable semiconductors instead of D1 and D2 diodes, the inverter can be operated in both directions. An inverter that can convert an input DC voltage into an output AC voltage can also convert a single-phase AC voltage into a regulated DC voltage.

[0064] A single-phase three-level buck-boost inverter converts a DC input voltage taken from a solar panel or DC power source or battery into a single-phase AC voltage, allowing the inverter to be used to power electronic devices or transfer energy to the grid.

[0065] The AC voltage obtained from the network, an alternator or a turbine is used to charge the battery or to power a DC electronic load.

[0066] Since the single-phase three-level buck-boost inverter can operate in both directions, it is used to convert the unregulated AC voltage obtained from wind turbines into a regulated DC output voltage and is used in battery charging units for electric vehicles.

[0067] The inverter disclosed in the scope of single phase three level buck-boost inverter is used for renewable energy, military land / sea / air stop tools, railway systems, medical devices, electric transportation applications.

[0068] Provided are 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.

Claims

1. A transformerless, high-efficiency, three-level, high-power-density, wide-input-voltage-range single-phase three-level buck-boost DC / AC inverter, characterized in that include: · Transformerless single-phase buck-boost inverter with high power density, the transformerless single-phase buck-boost inverter oProvide single-phase AC output voltage, o includes T1 (502) a semiconductor switch that prevents capacitive leakage current from flowing from a DC input power source to an output.

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