WO2023234898A1

WO2023234898A1 - Three-phase, three-level, transformerless, t-typ inverter with bipolar buck-boost converter on the dc side

Info

Publication number: WO2023234898A1
Application number: PCT/TR2023/050465
Authority: WO
Inventors: Eyyup DEMİRKUTLU; İres İSKENDER
Original assignee: Aselsan Elektroni̇k Sanayi̇ Ve Ti̇caret Anoni̇m Şi̇rketi̇
Priority date: 2022-06-01
Filing date: 2023-05-24
Publication date: 2023-12-07

Abstract

The invention relates to a transformerless inverter with high efficiency, low volume, low weight, high power density, wide input voltage range, ease of application for control and modulation algorithms, which can reduce leakage currents for three-phase systems. While 5 of the 17 semiconductor switches (402, 403, 404, 406, 407) included in the invention are switched at high frequency (in the 1 kHz - 1MHz band range), 6 of them (411, 414, 415, 418, 419, 422) are switched at the output voltage frequency (50Hz - 400Hz) and the other 6 switches (412, 413, 416, 417, 420, 421) are switched at twice the output voltage frequency (100Hz - 800Hz).

Description

THREE-PHASE, THREE-LEVEL, TRANSFORMERLESS, T-TYP INVERTER WITH BIPOLAR BUCK-BOOST CONVERTER ON THE DC SIDE

Technical Field

The invention relates to a transformerless inverter with high efficiency, low volume, low weight, high power density, wide input voltage range, ease of application for control and modulation algorithms, which can reduce leakage currents for three-phase systems.

Prior Art

Inverters with or without transformer are used to convert DC input voltage to AC output voltage. Transformerless inverters, compared to transformer inverters are advantageous in terms of size, volume, weight, cost and efficiency. The leakage capacitive currents can be prevented from being drawn from the input power source as transformer inverters can isolate input and output terminals galvanically. Transformerless inverters are also disadvantageous in terms of leakage currents drawn from the input power source besides the advantages they have. Various power converter topologies, switching strategies and filtering methods so as to suppress the leakage currents drawn from the input power supply in transformerless inverters, are taken into consideration.

The “H5 inverter” (U.S. Pat. No. 7,411 ,802 B2), which provides an effective solution for reducing leakage currents, can be seen in Figure 4. The semiconductor switch placed between the DC Input terminals and the H bridge ensures that the leakage currents are reduced by separating the DC terminals and the AC terminals from each other during the time intervals when the inverter needs to roam freely. This topology, which can produce single-phase AC output voltages, is widely known and many research studies have been carried out.

The inverter shown in Figure 4 can produce solutions in applications where single-phase AC output voltages are needed. It is a transformerless inverter that is preferred especially based on its performance in reducing capacitive leakage currents. In order to adapt this inverter to a three-phase system, it is possible to produce a solution by using a singlephase inverter for each phase. However, in this case; problems arise such as the necessity of transferring the neutral line to the output, controlling the phases with independent power converters, and controlling the current circulations between the phases. In addition, in the case of using three single-phase inverters, a total of nine switches operate at high frequency, and six switches are switched at high frequency in the same time interval.

Figure 5 shows a power system consisting of two converters. The output DC voltage is obtained by increasing the input DC voltage with the DC/DC converter in the first stage. Three-phase AC output voltages are obtained with the DC/AC three-phase, two-level inverter in the second stage. High peak amplitude capacitive leakage currents are drawn instantly from the inverter input in the zero vector operating regions of the three-phase two-level DC/AC inverter in this power system. In order to prevent these leakage currents, two switches are added in series with the inverter input DC bus terminals in Figure 5. Thus, the input currents drawn as a result of simultaneous conduction of the upper part of the parallel switches in the zero vector regions of the inverter or the simultaneous conduction of the parallel switches in the lower part can be reduced. Although this topology can provide a solution for the prevention or suppression of capacitive leakage currents, it is disadvantageous in terms of efficiency and power density. Although the inverter in Figure 5 is a transformerless inverter, the DC bus capacitor between the two converters causes the volume of the inverter to increase and the power density to decrease. The number of switches switched at high frequency in this inverter is ten.

This inverter in Figure 5 can produce a natural solution for reducing capacitive leakage currents. This power converter requires the use of electrolytic capacitors in the DC bus. Electrolytic capacitors not only increase the size of the circuit, but also limit the lifetime of the product. In case the number of switches switched at high frequency (in the 1 kHz - 1 MHz band range) is 10 in the inverter, this results in high switching losses.

As a result, due to the abovementioned disadvantages and the insufficiency of the current solutions regarding the subject matter, a development is required to be made in the relevant technical field.

Aim of the Invention The invention reveals a transformerless inverter with high efficiency, low volume, low weight, high power density, wide input voltage range, ease of application for control and modulation algorithms, which can reduce leakage currents for three-phase systems.

An inverter has been developed within the scope of the invention, which is fed from a direct current source connected to the input terminals and which produces, reduces and amplifies output voltages in the form of a three-phase alternating current sine wave between the output terminals.

The capacitive leakage current reduction feature of the single-phase transformerless inverter shown in Figure 4 is preserved in the topology (Figure 1 ) introduced within the scope of this invention. A solution is revealed with the invention shown in Figure 1 or reducing the capacitive leakage currents drawn from the input DC power supply forthree- phase applications.

Electrolytic capacitors in the topology in Figure 5 cause the volume and weight of the power converter to increase and economic life to decrease. In the present invention, the need to use an electrolytic capacitor at the input is eliminated. Thus, it is possible to extend the inverter lifetime. Volume, cost and weight are reduced with the deactivation of electrolytic capacitors.

While 5 of the 17 semiconductor switches (402, 403, 404, 406, 407) included in the invention are switched at high frequency (in the 1 kHz - 1 MHz band range), 6 of them (411 , 414, 415, 418, 419, 422) are switched at the output voltage frequency (50Hz - 400Hz) and the other 6 switches (412, 413, 416, 417, 420, 421) are switched at twice the output voltage frequency (100Hz - 800Hz). The present invention has fewer high frequency switching switches compared to the inverter shown in Figure 5. The modulation algorithm of the circuit structure within the scope of the invention is much simpler.

DC input terminals and AC output terminals are separated in the zero vector regions of the inverter, preventing instantaneous high leakage currents from the input power supply with the help of the switch (402). The invention has a high power density due to the absence of an electrolytic capacitor. The invention is an inverter with a wide input voltage range, as it has both buck and boost features. The present invention converts the DC input voltage taken from the solar panel or DC power source or battery to three-phase AC voltages, allowing it to be used for feeding electronic equipment or for transferring energy to the grid.

Three-phase AC voltages obtained from the network or from the alternator or turbine can be used to charge batteries or feed DC electronic loads.

The present invention can be used in battery charging units of electric vehicles, in converting non-regulated AC voltages obtained from wind turbines to regulated DC output voltage due to its two-way operation.

The inverter revealed within the scope of the present invention can be used in renewable energy, military land/sea/air vehicles, rail systems, medical devices, electric vehicle applications.

The structural and characteristic features of the present invention will be understood clearly by the following drawings and the detailed description made with reference to these drawings.

Description of the Figures

Figure 1 shows the circuit diagram of the inventive inverter.

Figure 2 shows the voltage waveforms formed at the terminals between the regulation section and the decoupling section of the inverter according to the invention.

Figure 3 shows the switching signals of the switches in the decoupling section of the inverter according to the invention.

Figure 4 shows the circuit diagram of the inverter that produces a solution for reducing leakage currents in the prior art.

Figure 5 shows the circuit diagram of a power system consisting of two converters in the prior art.

The figures are not required to be scaled and the details which are not necessary for understanding the present invention may be neglected. Description of the Part References

401. Power source (Vin)

429. Va

430. Vb

431. Vc

Diodes: 409, 410

Inductors: 405, 408, 426, 427, 428

Capacitors: 423, 424, 425

Terminals: 1 , 2, ... , 14

Semiconductor switches: 402, 403, 404, 406, 407, 411 , 412, ... , 422

Detailed Description of the Invention

In this detailed description, the preferred embodiments of the invention are described only for clarifying the subject matter in a manner such that no limiting effect is created.

A transformerless three-phase three-level buck-boost inverter is provided to obtain three- phase AC output voltages from the DC input power supply within the scope of the invention The three-phase inverter disclosed in the present invention is shown in Figure 1 with the numbers of the materials used. The input power supply (401) between the input terminals (1 , 2) provides regulated or unregulated DC voltage.

The inverter can be considered in two parts. The first section is the regulation section between the input terminals (1 , 2) and the other terminals (4, 8, 9). The second section is the unfolding section between the terminals (4, 8, 9) that limits the regulation section and the terminals (10, 11 , 12) after them.

Output filter capacitors (423, 424, 425) are located between terminal (10, 13), terminal (11 , 13), and terminal (12, 13). Inductors (405, 408) of DC/DC converters are located between terminal (3, 6) and terminal (5, 7). Active switches are located between the input and the boundary terminals between the inverter sections. The voltage waveforms formed at the terminals (4, 8, 9) located between the two sections are given in Figure 2. The waveforms given in this way are produced for balanced, 220Vrms phase-neutral and 50 Hz, three-phase AC voltages. The waveform of the envelope consisting of the highest values of the three-phase AC voltages is shown in the upper graph in Figure 2, the waveform of the envelope consisting of the lowest values is shown in the graph below, and the waveforms in the middle region are shown in the graph in the middle.

Semiconductor switches (402, 403, 404, 406, 407) in the regulation section are switched at high frequency (1 kHz - 1 MHz band), and the waveforms shown in Figure 2 are generated at their terminals (4, 8 and 9).

In Figure 2, the waveform terminal (8) in the upper graph, the waveform terminal (4) in the middle graph and the waveform terminal (9) in the lower graph are formed, semiconductor switches (402, 403, 404, 406, 407) in the regulation section are controlled.

Regulated waveforms at terminals (4, 8, 9) are separated and three-phase AC voltages are obtained at terminals (10, 11 , 12) by controlling the semiconductor switches (411 , 412, ...,422) in the decoupling section. The switching waveforms of the decoupling section are shown in Figure 3.

When voltage Va (429), voltage Vb (430), voltage Vc (431) or reference values are compared with each other, one switch (411) is on and other switches (412, 413, 414) are off in regions where voltage Va (429) is the highest. In the regions where the voltage Vb (430) is greatest, one switch (415) is on and the other switches (416, 417, 418) are off. In the regions where the voltage Vc (431) is greatest, one switch (419) is on and the other switches (420, 421 , 422) are off.

When voltage Va (429), voltage Vb (430), voltage Vc (431) or reference values are compared with each other, one switch (414) is on and other switches (411 , 412, 413) are off in regions where voltage Va (429) is the lowest. In the regions where the voltage Vb (430) is the lowest, one switch (418) is on and the other switches (415, 416, 417) are off. In the regions where the voltage Vc (431) is the lowest, one switch (422) is on and the other switches (419, 420, 421) are off. When voltage Va (429), voltage Vb (430), voltage Vc (431) or reference values are compared with each other, in regions where voltage Va (429) is in the middle, some switches (412, 413) are on and other switches (411 , 414) are off. In the regions where the voltage Vb (430) is the is in the middle, some (416, 417) are on and the other switches (415, 418) are off. In the regions where the voltage Vc (431) is the is in the middle, some switches (420, 421) are on and the other switches (419, 422) are off.

In three-phase grid-connected applications; the voltage Va (429) between the terminals (10, 14), the voltage Vb (430) between the terminals (11 , 14) and the voltage Vc (431 ) between the terminals (12, 14) are measured and compared with each other and arranged to be the largest, medium and smallest. These waveforms constitute the reference waveforms for the output voltages (4, 8, 9) of the regulation section.

In three-phase applications operating independently of the mains; reference signs are obtained for the voltages to be generated at the (4, 8, 9) terminals by comparing the reference voltages for the voltage Va (429) between terminals (10, 14), the voltage Vb (430) between terminals (11 , 14), and the voltage Vc (431) between terminals (12, 14) with each other.

Semiconductor switches (411 , 414, 415, 418, 419, 422) are switched via the Va (429), Vb (430) and Vc (431) voltage waveforms formed between the output terminals (10, 14), (11 , 14)and (12, 14) (Figure 3).

Semiconductor switches (412, 413, 416, 417, 420, 421) are switched at twice the frequency of Va (429), Vb (430) and Vc (431 ) voltage waveforms formed between the output terminals (10, 14), (11 , 14) and (12, 14) (Figure 3).

Inductors (426, 427, 428) and capacitors (423, 424, 425) are used to filter the transfer of high-frequency components produced by the inverter, which is considered within the scope of the invention, to the output.

The need for zero vectors is eliminated with the help of the present invention. In Figure 1 , there is no need for switches (411 , 415, 419) or other switches (414, 418, 422) to be transmitting at the same time. DC input voltage and three-phase AC voltages can be separated due to the fact that there is no need for a zero vector and switch (402) connected in series on the main branch is in cutoff during free circulation time intervals. Thus, the problem of capacitive leakage current drawn from the input DC power source, which occurs in transformerless inverters, is suppressed by the present invention.

Since the number of semiconductor switches switched at high frequency within a switching period is three in the buck mode within the scope of the invention and this number is five in booster mode, it is ensured that the thermal power losses due to switching are low.

There is no need to connect a single or two electrolytic capacitors in series to the input terminals of the transformerless inverter structure. Thus, the total volume of the inverter decreases and the power density increases with the deactivation of the electrolytic capacitors. In general, the fact that electrolytic capacitors do not have a long lifespan also causes a short lifespan of power converters that need electrolytic capacitors. In this context, the inverter introduced with the present invention, which does not need electrolytic capacitors, has a long life.

Semiconductor switches in the inventive structure can be used as MOSFET, IGBT in Silicon or Silicon Carbide technology. The reverse parallel diode, which can be found in the switch, can be added externally.

Diodes (409, 410) in the inventive structure can be used in Silicon or Silicon Carbide technology.

Instead of the diodes (409, 410) included in the invention, Silicon or Silicon Carbide technology can be used as MOSFET, IGBT. Thus, thermal losses on these switches can be reduced. In addition, the inverter can operate in two directions by using controllable semiconductors instead of diodes (409, 410). The inverter, which can convert input DC voltage to three-phase output AC voltages, can also convert three-phase AC voltages to regulated DC voltage.

A serial switch can be connected between the terminals (2, 5) such that the power flow from the terminal (5) to the other terminal (2). The number of switches can be shared between the switches and it may be possible to reduce the thermal load on the switch (402) by programming this serial switch to have the switching characteristic of the switch (402).

High frequency signals at the output of the regulation section can be filtered with a filter consisting of capacitors with one end each at terminals (4, 8, 9) and the other ends in star point. Thus, the load of the output filter consisting of inductors (426, 427, 428) and capacitors (423, 424, 425) can be reduced and the size of the output filter can be reduced.

Claims

CLAIMS A three-phase, three-level, transformerless buck-boost inverter, characterized by comprising;

• power supply (401 ), located between the input terminals (1 , 2), providing DC voltage with or without regulation,

• semiconductor switches (402, 403, 404, 406, 407) switched at high frequency and located in the regulation section, controlled to form waveforms at the terminals (4, 8, 9) between the regulation and decoupling sections,

• controlled to decouple the regulated waveforms at the terminals (4, 8, 9) in the decoupling section; o semiconductor switches (411 , 414, 415, 418, 419, 422) which are switched by the frequency of the voltage waveforms Va (429), Vb (430) and Vc (431), respectively, formed between the output terminals (10, 14), (11 , 14) and (12, 14), o semiconductor switches (412, 413, 416, 417, 420, 421 ) that switch at twice the frequency of the voltage waveforms Va (429), Vb (430) and Vc (431) formed between the output terminals (10, 14), (11 , 14) and (12, 14),

• inductors (426, 427, 428) and capacitors (423, 424, 425) that filter the transfer of generated high-frequency components to the output. The inverter according to claim 1 , characterized in that said semiconductor switches are silicon or silicon carbide MOSFET or IGBT. The inverter according to claim 1 , characterized by comprising a filter consisting of capacitors with one end at the terminals (4, 8, 9) and the other end at the star point, filtering high-frequency signals at the output of the regulation section. The inverter according to claim 1 , characterized by comprising diodes (409, 410) located between terminals (6, 8) and (7, 9). The inverter according to claim 1 , characterized by comprising a serial switch connected in such a way that the power flow is terminal (5) - terminal (2) to reduce the thermal load on the switch (402) at the input.