CN112868172B

CN112868172B - Three-level power conversion system and method

Info

Publication number: CN112868172B
Application number: CN201980065582.2A
Authority: CN
Inventors: 朱辉斌; 戴和平
Original assignee: Huawei Digital Power Technologies Co Ltd
Current assignee: Huawei Digital Power Technologies Co Ltd
Priority date: 2018-11-26
Filing date: 2019-11-26
Publication date: 2022-07-12
Anticipated expiration: 2039-11-26
Also published as: EP3881422A4; CN112868172A; EP3881422A1; WO2020108460A1

Abstract

A system includes a first three-level power converter having output terminals coupled to a three-level voltage bus arrangement and input terminals for coupling with a solar panel array, an inverter coupled between the three-level voltage bus arrangement and a power grid, and a second three-level power converter coupled between the three-level voltage bus arrangement and an energy storage unit.

Description

Three-level power conversion system and method

Cross Reference to Related Applications

This patent application claims priority from U.S. provisional application No. 62/771,438 entitled "three level power conversion system and method" filed on 26.11.2018, the entire contents of which are incorporated herein by reference.

Technical Field

The present disclosure relates to a three-level power bus apparatus and method, and in particular embodiments, to a three-level power bus apparatus and method for transferring energy in a solar energy conversion system.

Background

Renewable energy sources include solar, wind, tidal, and the like. The solar energy conversion system may comprise a plurality of solar panels connected in series or in parallel. The output of the solar panel may generate a direct current (dc) voltage that may vary depending on various factors, such as time of day, location, and sun-tracking ability. To regulate the output of the solar panel, the output of the solar panel may be coupled to a dc/dc converter to produce a regulated output voltage at the output of the dc/dc converter. In addition, solar panel can be connected with standby battery system through battery charging controlling means. Daytime, the standby battery is charged through the output end of the solar panel. The backup battery provides power to a load coupled to the solar panel when the power utility fails or the solar panel is an off-grid power system.

Since most applications can be designed to operate on 120 volt alternating current (ac) power, solar inverters are used to convert the variable dc output of the photovoltaic module to 120 volt ac power. Multiple multi-level inverter topologies can be employed to achieve high power and efficient conversion of solar energy to utility power. In particular, a high power ac output may be achieved by converting a plurality of low voltage dc power supplies into the high power ac output by synthesizing stepped voltage waveforms using a series of power semiconductor switches.

Multilevel inverters can be classified into three categories, namely diode-clamped multilevel inverters, flying capacitor multilevel inverters, and cascaded H-bridge multilevel inverters. In addition, the multilevel inverter may employ different Pulse Width Modulation (PWM) techniques, such as Sinusoidal PWM (SPWM), selective harmonic elimination PWM, space vector modulation, and the like. Multilevel inverters are a versatile power topology for high and medium power applications such as utility interfaces for renewable power sources, flexible ac transmission systems, medium voltage motor drive systems, and the like.

Diode-clamped multilevel inverters are commonly referred to as three-level Neutral Point Clamped (NPC) inverters. A three-level NPC inverter requires two capacitors in series to be coupled between the input dc bus. Each capacitor is charged to an equal potential. Further, the three-level NPC inverter may include four switching elements and two clamping diodes. The clamping diode helps to reduce the voltage stress on the switching element to a capacitor voltage level.

The NPC inverter generates an ac output using a step waveform. This step waveform is similar to the desired sinusoidal waveform. Therefore, the output voltage of the NPC inverter may have a low Total Harmonic Distortion (THD). In addition, the step waveform can reduce voltage stress. Therefore, electromagnetic compatibility (EMC) performance of the NPC inverter may be improved.

Disclosure of Invention

These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present disclosure which provide a three-level voltage bus for improving performance of solar energy systems.

According to an embodiment, an apparatus includes a first voltage bus, a second voltage bus, and a third voltage bus. The first voltage bus is connected to a plurality of three-level power conversion units. The second voltage bus is connected to the plurality of three-level power conversion units. The third voltage bus is connected to the plurality of three-level power conversion units. The first voltage bus and the third voltage bus are regulated by at least one of the three-level power conversion units with reference to the second voltage bus.

The plurality of three-level power conversion units include a three-level boost converter, a three-level buck converter, an inverter, and an inductor-inductor-capacitor (LLC) converter, and wherein output/input terminals of the three-level boost converter, the three-level buck converter, the inverter, and the LLC converter are connected together by a first voltage bus, a second voltage bus, and a third voltage bus. The three-level boost converter is connected between the solar panel array and the first, second, and third voltage buses. The three-level buck converter is connected between the energy storage unit and the first, second, and third voltage buses. The inverter is connected between the grid and the first, second, and third voltage buses. The LLC converter is connected between the dc load and the first, second, and third voltage buses.

The energy storage unit is a battery-based energy storage unit. The dc load includes a charger for charging the electric vehicle. In some embodiments, the inverter is a neutral point clamped inverter, and wherein a neutral point of the inverter is connected to the second voltage bus. In an alternative embodiment, the inverter comprises a first neutral point clamped inverter, a second neutral point clamped inverter, and a third neutral point clamped inverter. The first neutral point clamped inverter is connected to a first phase of the three-phase power system through a first star-delta transformer. The second neutral point clamped inverter is connected to a second phase of the three phase power system through a second star-delta transformer. A third neutral point clamped inverter is connected to a third phase of the three phase power system through a third star-delta transformer. The neutral lines of the first, second, and third star-to-triangle transformers are connected to a second voltage bus.

In some embodiments, the plurality of three-level power conversion units includes a first three-level boost converter, a second three-level boost converter, an inverter, and a three-level buck converter connected together by a first voltage bus, a second voltage bus, and a third voltage bus. In an alternative embodiment, the plurality of three-level power conversion units includes a first LLC converter, a second LLC converter, an inverter, and a three-level boost converter connected together by a first voltage bus, a second voltage bus, and a third voltage bus.

In some embodiments, the plurality of three-level power conversion units includes an LLC converter, a dual-output LLC converter, an inverter, and a three-level boost converter connected together by a first voltage bus, a second voltage bus, and a third voltage bus. The three-level boost converter is connected between the dual-active bridge converter and the first, second, and third voltage buses. The first output and the second output of the dual output LLC converter are stacked together. A common node of the first output terminal and the second output terminal of the dual output LLC converter is connected to a second voltage bus.

According to another embodiment, a method includes transferring energy from a power source to a three-level voltage bus device through a first three-level power converter. The method further comprises transferring energy from the three-level voltage bus arrangement to the grid through the inverter, and transferring energy between the three-level voltage bus arrangement and the energy storage unit through the second three-level power converter.

The method further comprises the following steps: transferring energy from a three-level voltage bus device to a load through an LLC power converter; adjusting the voltage of the three-level voltage bus device; and configuring the second three-level power converter to function as a bi-directional power converter to transfer energy between the three-level voltage bus device and the energy storage unit.

The three-level voltage bus apparatus includes: a first voltage bus, a second voltage bus, and a third voltage bus, the first voltage bus, the second voltage bus, and the third voltage bus connected to the first three-level power converter, the second three-level power converter, the inverter, and the LLC power converter, and wherein the first voltage bus and the third voltage bus are regulated with reference to the second voltage bus.

The first three-level power converter is a three-level boost converter comprising four switches connected in series, and wherein midpoints of the four switches of the three-level boost converter are connected to the second voltage bus. The second three-level power converter is a three-level buck converter including four switches connected in series, and wherein midpoints of the four switches of the three-level buck converter are connected to the second voltage bus. The inverter is a neutral point clamped inverter having a neutral point connected to the second voltage bus. The LLC power converter includes four switches connected in series, and wherein midpoints of the four switches of the LLC power converter are connected to the second voltage bus.

In accordance with another embodiment, a system includes a first three-level power converter having output terminals connected to a three-level voltage bus arrangement and input terminals for coupling with a solar panel array. The system further includes an inverter connected between the three-level voltage bus device and the grid, and a second three-level power converter connected between the three-level voltage bus device and the energy storage unit.

The three-level voltage bus arrangement includes a first voltage bus, a second voltage bus, and a third voltage bus. The first voltage bus is connected to the positive output terminal of the first three-level power converter. The second voltage bus is connected to a neutral point of the first three-level power converter. The third voltage bus is connected to the negative output terminal of the first three-level power converter, and wherein the voltages on the first voltage bus, the second voltage bus, and the third voltage bus are regulated by the first three-level power converter.

The system further comprises an LLC converter connected between the direct current load and the three-level voltage bus device. The dc load includes a plurality of electric vehicles.

An advantage of embodiments of the present disclosure is that a three-level voltage bus connects a plurality of three-level power conversion units, thereby improving the efficiency, reliability, and cost of the solar energy system.

The foregoing has outlined rather broadly the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims.

Drawings

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

fig. 1 illustrates a block diagram of a three-level power conversion system, in accordance with various embodiments of the present disclosure;

FIG. 2 illustrates a block diagram of a first implementation of a portion of the three-level power conversion system shown in FIG. 1, in accordance with various embodiments of the present disclosure;

FIG. 3 illustrates a schematic diagram of the three-level power conversion system shown in FIG. 2, in accordance with various embodiments of the present disclosure;

FIG. 4 illustrates a block diagram of a second implementation of the portion of the three-level power conversion system shown in FIG. 2, according to various embodiments of the present disclosure;

fig. 5 illustrates a schematic diagram of the three-level power conversion system illustrated in fig. 4, in accordance with various embodiments of the present disclosure;

FIG. 6 illustrates a block diagram of a first implementation of another portion of the three-level power conversion system shown in FIG. 1, in accordance with various embodiments of the present disclosure;

fig. 7 illustrates a schematic diagram of the three-level power conversion system illustrated in fig. 6, in accordance with various embodiments of the present disclosure;

FIG. 8 illustrates a block diagram of a second implementation of another portion of the three-level power conversion system shown in FIG. 1, in accordance with various embodiments of the present disclosure;

fig. 9 illustrates a schematic diagram of the three-level power conversion system shown in fig. 8, in accordance with various embodiments of the present disclosure;

fig. 10 illustrates a block diagram of a third implementation of another portion of the three-level power conversion system shown in fig. 1, in accordance with various embodiments of the present disclosure;

fig. 11 illustrates a schematic diagram of the three-level power conversion system illustrated in fig. 10, in accordance with various embodiments of the present disclosure;

fig. 12 illustrates a block diagram of another portion of the three-level power conversion system shown in fig. 1, in accordance with various embodiments of the present disclosure;

fig. 13 illustrates a schematic diagram of the three-level power conversion system shown in fig. 12, in accordance with various embodiments of the present disclosure;

fig. 14 illustrates a block diagram of another three-level power conversion system, in accordance with various embodiments of the present disclosure;

fig. 15 illustrates a schematic diagram of the three-level power conversion system shown in fig. 14, in accordance with various embodiments of the present disclosure;

fig. 16 shows a block diagram of another three-level power conversion system, in accordance with various embodiments of the present disclosure;

fig. 17 illustrates a schematic diagram of a portion of the three-level power conversion system illustrated in fig. 16, in accordance with various embodiments of the present disclosure;

fig. 18 illustrates a schematic diagram of another portion of the three-level power conversion system illustrated in fig. 16, in accordance with various embodiments of the present disclosure;

fig. 19 shows a block diagram of another three-level power conversion system, in accordance with various embodiments of the present disclosure;

FIG. 20 illustrates a schematic diagram of a portion of the three-level power conversion system shown in FIG. 19, in accordance with various embodiments of the present disclosure;

fig. 21 illustrates a schematic diagram of another portion of the three-level power conversion system illustrated in fig. 19, in accordance with various embodiments of the present disclosure; and

fig. 22 illustrates a flow diagram of a method for controlling the three-level power conversion system shown in fig. 1, in accordance with various embodiments of the present disclosure.

Corresponding numerals and symbols in the various drawings generally refer to corresponding parts unless otherwise indicated. The drawings are drawn for clarity of illustration of relevant aspects of various embodiments and are not necessarily drawn to scale.

Detailed Description

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to preferred embodiments in a particular context (i.e., a three-level inverter). However, the present disclosure may also be applied to various multi-level inverters including a five-level inverter, a seven-level inverter, a nine-level inverter, and the like. Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings.

Fig. 1 illustrates a block diagram of a three-level power conversion system, according to various embodiments of the present disclosure. The three-level power conversion system 100 includes a three-level boost converter 110, a three-level buck converter 120, an inverter 130, and an inductor-capacitor (LLC) converter 140. As shown in fig. 1, the level up converter 110, the three-level down converter 120, the inverter 130, and the LLC converter 140 are connected together by a three-level voltage bus arrangement. The three-level voltage bus arrangement includes a plurality of voltage buses configured as energy buffers in the three-level power conversion system 100.

As shown in fig. 1, the first voltage bus 101, the second voltage bus 102, and the third voltage bus 103 are connected between the three-level boost converter 110 and the inverter 130. Throughout the specification, the first voltage bus 101 may alternatively be referred to as a positive voltage bus, as indicated by the letter p. The second voltage bus 102 may alternatively be referred to as a midpoint voltage bus, as indicated by the letter m. The third voltage bus 103 may alternatively be referred to as a negative voltage bus, as indicated by the letter n. The first voltage bus 101, the second voltage bus 102, and the third voltage bus 103 are part of a three-level voltage bus arrangement. The first voltage bus 101 and the third voltage bus 103 are symmetrical with respect to the second voltage bus 102.

The three-level voltage bus arrangement further extends to other power converters. As shown in fig. 1, the

voltage bus

151, 152, 153 is connected between the three-level buck converter 120 and the LLC converter 140. The

voltage buses

151, 152, 153 are electrically connected to the

voltage buses

101, 102, 103, respectively. In other words, the

voltage buses

101 and 151 may be collectively referred to as a single entity. Likewise, the

voltage buses

102 and 152 may be collectively referred to as a single entity, and the

voltage buses

103 and 153 may be collectively referred to as a single entity.

In some embodiments, the voltages on the voltages p, m, n are fully regulated by at least one converter of the three-level power conversion system 100. In some embodiments, a three-level boost converter 110 may be used to maintain and regulate the voltage across the voltages p, m, n. In an alternative embodiment, a three-level buck converter 120 may be used to maintain and regulate the voltage across the voltages p, m, n. Furthermore, a combination of a three-level boost converter 110 and a three-level buck converter 120 may be used to maintain and regulate the voltages on the voltages p, m, n. Alternatively, the three-level boost converter 110 and the three-level buck converter 120 may be used to regulate the voltages on the voltages p, m, n in an alternating manner.

In some embodiments, the three-level boost converter 110 is configured to be coupled to a solar panel array 150. As shown in fig. 1, the three-level boost converter 110 is connected between the solar panel array 150 and the three-level voltage bus device. The output of solar panel array 150 includes two voltage levels. The three-level boost converter 110 is capable of converting two voltage levels to three voltage levels, i.e., p, m, n as shown in fig. 1. Furthermore, the three-level boost converter 110 is capable of regulating the voltage on the voltage buses p, m, n depending on design requirements and different applications. Further, the three-level boost converter 110 may be configured as a bi-directional power converter by which a dc voltage may be established across the output terminals of the solar panel array 150 during abnormal operating conditions (e.g., PID repair/recovery processes).

The implementation of the three-level boost converter 110 may vary according to different applications and design requirements. In some embodiments, the three-level boost converter 110 may include two input inductors (e.g., a three-level boost converter 111 as shown in fig. 3 below). In an alternative embodiment, the three-level boost converter 110 may include a single input inductor (e.g., the three-level boost converter 112 shown in fig. 5 below).

In some embodiments, the three-level buck converter 120 is configured to be coupled to the energy storage unit 160. As shown in fig. 1, the three-level buck converter 120 is connected between the energy storage unit 160 and the three-level voltage bus device. In some embodiments, the three-level buck converter 120 is configured to operate as a bi-directional power converter. During the energy storage phase, energy is transferred from the three-level voltage bus arrangement to the energy storage unit 160 via the three-level buck converter 120. The three-level buck converter 120 acts as a buck power converter. On the other hand, during the energy release phase, energy is transferred from the energy storage unit 160 to the three-level voltage bus arrangement via the three-level buck converter 120. A detailed circuit configuration of the three-level buck converter 120 will be described below with reference to fig. 3.

It should be noted that during the de-energized phase, the three-level buck converter 120 acts as a boost power converter. Furthermore, the three-level buck converter 120 is able to regulate the voltage on the voltage bus lines p, m, n.

In some embodiments, inverter 130 is configured to be coupled to a three-phase power grid, such as an ac power grid 170. As shown in fig. 1, the inverter 130 is connected between an ac grid 170 and a three-level voltage bus arrangement. Alternatively, the inverter 130 may be configured to be coupled to a single-phase alternating current load.

In some embodiments, the inverter 130 may be a Neutral Point Clamped (NPC) inverter. A detailed circuit configuration of the NPC inverter will be described below with reference to fig. 9. Alternatively, the inverter 130 may be an Active Neutral Point Clamped (ANPC) inverter. A detailed circuit configuration of the ANPC inverter will be described below with reference to fig. 7.

In some embodiments, the LLC converter 140 is configured to be coupled to a dc load. As shown in fig. 1, the LLC converter 140 is connected between a load 180 and a three-level voltage bus device. The LLC converter 140 converts the three voltage levels into two voltage levels, which are applied to downstream converters. The LLC converter 140 functions as a three-level dc/dc power converter. A detailed circuit configuration of the LLC converter 140 will be described below with reference to fig. 13.

It should be noted that the LLC converter described above is merely an exemplary converter and is not intended to limit the present embodiments. The power conversion unit between the load 180 and the three-level voltage bus device may be implemented as various power converters, such as a full-bridge converter, a half-bridge converter, a forward converter, a flyback converter, any combination thereof, and the like.

In some embodiments, the energy storage unit 160 may be a battery energy storage system including a plurality of rechargeable batteries, a fuel cell, any combination thereof, or the like. Alternatively, the energy storage unit 160 may be implemented as other suitable energy storage systems. For example, the energy storage unit 160 may include a compressed air energy storage system, a flywheel energy storage system, a pumped storage system, an ultracapacitor system, any combination thereof, and the like.

In some embodiments, the load 180 may refer to a downstream converter coupled to the output of the LLC converter 140. More specifically, the downstream converter may be a plurality of chargers for charging the electric vehicle.

In operation, one of the three-level power converters of fig. 1 can measure and regulate the voltage on the voltage buses (e.g., positive voltage bus p, negative voltage bus n, and/or midpoint voltage bus m), thereby controlling the voltage balance of the three voltage buses. Accordingly, the inverters (e.g., inverter 130) of the three-level power conversion system 100 no longer need to address the voltage bus imbalance problem and/or the load imbalance problem. This may save costs. In addition, the regulated bus voltage helps to improve circuit performance of the three-level power conversion system 100.

Furthermore, the energy storage unit 160 may help to improve the performance of the three-level power conversion system 100. In particular, the solar panel array 150 and the energy storage unit 160 are both coupled to the same three-level voltage bus device and form an integrated power conversion system. In such an integrated power conversion system, the power capacity of the solar panel array 150 and the power capacity of the energy storage unit 160 may be configured according to a predetermined dc-to-ac ratio to achieve maximum solar panel energy harvesting at the lowest cost.

One advantageous feature of the three-level power conversion system shown in fig. 1 is that by employing a three-level voltage bus, a three-level power converter (e.g., three-level boost converter 110 and/or three-level buck converter 120) can regulate both the positive voltage bus p and the negative voltage bus n. The regulation of the bus voltage comes from inherent capability without additional cost. Therefore, the inverter 130 no longer needs to deal with the capacitor voltage balancing problem. This configuration saves costs. Furthermore, this configuration may simplify the PWM control scheme, thereby reducing switching losses and improving reliability of the three-level power conversion system 100.

Another advantage of the three-level power conversion system shown in fig. 1 is the constant regulation of the midpoint voltage bus m. The midpoint of such regulation may be provided directly to inverter 130 as a neutral or neutral point. Through the neutral line, the inverter 130 can operate under 100% three-phase unbalanced load conditions. For grid-independent or micro-grid applications, the availability of the neutral line and the ability to operate under 100% three-phase unbalanced load conditions are advantageous features. This reduces costs compared to conventional solutions, such as four-phase inverters as an alternative solution. Furthermore, the system configuration of fig. 1 may not require a load transformer. In contrast, the three-level power conversion system 100 may provide system isolation on the grid feeder using transformer isolation barriers to reduce the overall cost of the three-level power conversion system 100.

Another advantage of the three-level power conversion system shown in fig. 1 is that the system configuration shown in fig. 1 can reduce leakage current from the solar panel array 150. In order to detect ground faults and improve the safety of solar energy systems, the solar energy industry requires that the solar panel array and the energy storage cell subsystem must be floating. In a floating system, having a separate negative rail between the solar converter (e.g., three-level boost converter 110) and the energy storage converter (e.g., three-level buck converter 120) is an advantageous feature. This configuration helps to avoid high leakage currents from the solar panel array, thereby reducing the size of the common mode filter required.

It should also be noted that a symmetrical PWM control scheme may be employed in the three-level power conversion system 100. Symmetric PWM control schemes can be applied to three-level boost converters and three-level buck converters. Due to the symmetrical PWM control scheme, the three-level boost converter 110 in the system may have a lower common node voltage than other three-level boost power converters. The lower common node voltage helps to reduce the cost of the EMI filter.

Another advantage of the three-level power conversion system shown in fig. 1 is that the lower switch of the three-level power conversion unit can be used as a ground fault circuit breaker. For example, when a ground fault is detected, some (e.g., lower switches) or all of the active switches of the three-level buck converter and/or the three-level boost converter may be turned off to prevent the ground fault from spreading to other circuit branches. This is an important feature of floating systems.

Another advantage of connecting the three-level voltage bus arrangement to the three-level boost converter 110 and the solar panel array 150 is that a dc voltage can be freely generated on the terminals of the solar panel array, which can be used for potential induced attenuation (PID) compensation of the solar panel array. Furthermore, connecting the three-level voltage bus arrangement to the three-level boost converter may generate a dc voltage on the terminals of the solar panel array during the PID repair/restoration process.

Furthermore, as an energy buffer, a three-level voltage bus device may see line frequency ripple caused by an ac load coupled to the inverter. The three-level voltage bus arrangement may also see a two-wire frequency ripple under unbalanced load conditions when a neutral line is provided to the ac output. For these reasons and other transient response requirements, larger capacitors coupled to the three-level voltage bus devices are required. The energy from the energy storage unit 160 may help reduce bus voltage ripple. In particular, energy from the energy storage unit may help to reduce second line frequency harmonics during unbalanced load conditions. Since the energy storage unit may help to reduce ripple on the voltage bus, the size of the capacitor coupled to the voltage bus may be reduced.

The three-level voltage bus arrangement may be formed from a plurality of stacked bus layers. The midpoint layer may be placed between the positive voltage bus layer and the negative voltage bus layer. This bus layer configuration helps to reduce the actual insulation voltage stress, thereby improving the insulation stress margin and system reliability.

Fig. 2 illustrates a block diagram of a first implementation of a portion of the three-level power conversion system shown in fig. 1, in accordance with various embodiments of the present disclosure. The three-level boost converter 111 and the three-level buck converter 120 are placed on opposite sides of the three-level voltage bus arrangement. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. The three-level boost converter 111 is used to convert the two-level voltage generated by the solar panel array 150 into a three-level voltage. The three-level buck converter 120 serves to convert the three-level voltage into a two-level voltage applied to the energy storage unit 160.

Fig. 3 illustrates a schematic diagram of the three-level power conversion system shown in fig. 2, according to various embodiments of the present disclosure. The three-level boost converter 111 includes a plurality of switches, two input inductors, two input capacitors, and two output capacitors.

As shown in fig. 3, the first input capacitor CIN1 and the second input capacitor CIN2 are connected in series between two output terminals of a solar panel array (as shown in fig. 2). In some embodiments, the first input capacitor CIN1 and the second input capacitor CIN2 have the same capacitance. Thus, the voltage applied to the input capacitors is equally distributed across each capacitor. More particularly, the output voltage of the first input capacitor CIN1 with respect to the common node of capacitors CIN1 and CIN2 is VIN/2. Similarly, the output voltage of the second input capacitor CIN2 with respect to the common node of capacitors CIN1 and CIN2 is-VIN/2. According to some embodiments, a common node of capacitors CIN1 and CIN2 is connected to midpoint voltage bus m. Throughout the specification, the common node of capacitors CIN1 and CIN2 may alternatively be referred to as the neutral point of a three-level power conversion system.

It should be noted that although fig. 1 illustrates three-level boost converter 111 having two input capacitors (e.g., first capacitor C1 and second capacitor C2), three-level boost converter 111 may accommodate any number of input capacitors. The number of input capacitors shown herein is limited only to clearly illustrate the inventive aspects of the various embodiments. The present disclosure is not limited to any particular number of input capacitors. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.

The three-level boost converter 111 includes switches S11, S12, S13, S14 connected in series between the positive voltage bus p and the negative voltage bus n. As shown in fig. 3, the first inductor L1 is connected to a common node of switches S11 and S12. The second inductor L2 is connected to the common node of switches S13 and S14. The common node of switches S12 and S13 is connected to the common node of capacitors CIN1 and CIN 2. A first output capacitor C1 is connected between the positive voltage bus p and the midpoint voltage bus m. A second output capacitor C2 is connected between the midpoint voltage bus m and the negative voltage bus n.

The first input capacitor CIN1, the first inductor L1, the switches S11-S12, and the first output capacitor C1 form a first boost converter. The first boost converter is used to regulate the voltage between the positive voltage bus p and the midpoint voltage bus m. The second input capacitor CIN2, the second inductor L2, the switches S13-S14, and the second output capacitor C2 form a second boost converter. The second boost converter is used to regulate the voltage between the midpoint voltage bus m and the negative voltage bus n. The combination of the first boost converter and the second boost converter functions as a three-level boost converter.

The three-level buck converter 120 includes a plurality of switches, one inductor, two input capacitors, and one output capacitor. As shown in fig. 3, the three-level buck converter 120 includes switches S15, S16, S17, S18 connected in series between the positive voltage bus p and the negative voltage bus n. An output inductor L3 is connected to the common node of switches S15 and S16. It should be noted that the output inductor L3 may be split into two separate inductors according to different applications and design requirements. For example, the first output inductor is connected to a common node of switches S15 and S16. The second output inductor is connected to a common node of switches S17 and S18.

The first input capacitor C3 is connected between the positive voltage bus p and the midpoint voltage bus m. A second input capacitor C4 is connected between the midpoint voltage bus m and the negative voltage bus n. The common node of switches S16 and S17 is connected to the common node of capacitors C3 and C4.

The input capacitors C3-C4, the output inductor L3, the switches S15-S18, and the output capacitor Co form a three-level buck converter. In particular, a three-level buck converter is used to receive three voltage levels p, m, n and generate a two-level voltage that is applied to the battery energy storage system.

According to an embodiment, the switches (e.g., switches S11-S18) may be Insulated Gate Bipolar Transistor (IGBT) devices. Alternatively, the switching element may be any controllable switch, such as a metal oxide semiconductor field-effect transistor (MOSFET) device, an Integrated Gate Commutated Thyristor (IGCT) device, a gate turn-off thyristor (GTO) device, a Silicon Controlled Rectifier (SCR) device, a junction field-effect transistor (JFET) device, a MOS Controlled Thyristor (MCT) device, and so on.

It should be noted that when switches S11-S18 are implemented with MOSFET devices, the body diodes of switches S11-S18 may be used to provide a freewheeling path. On the other hand, when the switches S11-S18 are implemented by IGBT devices, a separate freewheeling diode needs to be connected in parallel with its corresponding switch.

As shown in fig. 3, diodes D11, D12, D13, D14, D15, D16, D17, D18 are required to provide a reverse conduction path for the three-level power conversion system. In other words, diodes D11-D18 are anti-parallel diodes. In some embodiments, diodes D11-D18 are co-packaged with their respective IGBT devices. In an alternative embodiment, diodes D11-D18 are placed external to their respective IGBT devices.

It should also be noted that while each bidirectional switch shown in fig. 3 is formed of a diode and an IGBT device connected in an anti-parallel arrangement, those of ordinary skill in the art will recognize numerous variations, substitutions, and modifications. For example, the bidirectional switch may be implemented by some new semiconductor switches (e.g., an anti-parallel reverse-blocking type IGBT device arrangement).

In operation, both three-level boost converter 111 and three-level buck converter 120 may be configured as bidirectional power converters. For example, if desired, the three-level boost converter 111 may be used as a three-level buck converter to establish a dc voltage on the terminals of the solar panel array. The three-level buck converter 120 may function as a three-level boost converter to transfer power from the battery box to the three-level voltage bus device.

It should be noted that throughout the specification, the three-level boost converter and the three-level buck converter may be configured as bidirectional power converters. In other words, depending on the direction of power flow, a three-level boost converter may be used as a three-level buck converter. Also, a three-level buck converter may be used as a three-level boost converter.

In operation, a symmetrical PWM control scheme may be applied to the three-level power conversion system shown in fig. 3 when the battery coupled to the three-level buck converter is floating. In other words, the grounding requirement is not necessary for the battery terminals. On the other hand, when the battery coupled to the three-level buck converter is not floating, an asymmetric PWM control scheme may be applied to the three-level power conversion system shown in fig. 3. In other words, the grounding requirement is necessary for the battery terminals.

Fig. 4 illustrates a block diagram of a second implementation of the portion of the three-level power conversion system shown in fig. 2, according to various embodiments of the present disclosure. The block diagram shown in fig. 4 is similar to the block diagram shown in fig. 2, except that the implementation of the three-level boost converter is different. The three-level boost converter 112 is used in place of the three-level boost converter 111 shown in fig. 2. A detailed schematic of the three-level boost converter 112 will be discussed below with reference to fig. 5.

Fig. 5 illustrates a schematic diagram of the three-level power conversion system shown in fig. 4, in accordance with various embodiments of the present disclosure. The three-level boost converter 112 is similar to the three-level boost converter 111 shown in fig. 3, except that the two input inductors of the three-level boost converter 111 have been combined into a single inductor. As shown in FIG. 5, input capacitor CIN is connected between the first terminal of input inductor L1 and the common node of switches S13-S14. A second terminal of the input inductor L1 is connected to a common node of switches S11-S12. The operation principle of the three-level boost converter 112 is similar to that of the three-level boost converter 111, and therefore, the description thereof is omitted to avoid redundancy.

Fig. 6 illustrates a block diagram of a first implementation of another portion of the three-level power conversion system shown in fig. 1, according to various embodiments of the present disclosure. In some embodiments, the three-level boost converter 110 shown in fig. 1 is implemented as a three-level boost converter 112. The inverter 130 shown in fig. 1 is implemented as an ANPC inverter 131. The grid 170 is replaced by a single-phase ac load 171. The three-level boost converter 112 and the ANPC inverter 131 are connected together by a three-level voltage bus arrangement. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. The three-level boost converter 112 is used to convert the two-level voltage generated by the solar panel array 150 into a three-level voltage. The ANPC inverter 131 serves to convert the three-level voltage into a multi-level voltage applied to the ac load 171.

Fig. 7 illustrates a schematic diagram of the three-level power conversion system shown in fig. 6, according to various embodiments of the present disclosure. The three-level boost converter 112 has been discussed in detail above with reference to fig. 3 and thus will not be described in detail here.

The ANPC inverter 131 includes six switches and an output inductor LA. As shown in fig. 7, the switches S21, S22, S23, S24 are connected in series between the positive voltage bus p and the negative voltage bus n. Switches S25 and S26 are connected in series between a common node of switches S21-S22 and a common node of switches S23-S24. The common node of switches S25 and S26 is connected to the midpoint voltage bus m. The common node of switches S22 and S23 is connected to output inductor LA. The operating principles of ANPC inverters are well known and will not be discussed here to avoid repetition.

Fig. 8 illustrates a block diagram of a second implementation of another portion of the three-level power conversion system shown in fig. 1, according to various embodiments of the present disclosure. The block diagram shown in fig. 8 is similar to the block diagram shown in fig. 6, except that the inverter is implemented as an NPC inverter 132. A schematic diagram of the NPC inverter 132 will be described in detail below with reference to fig. 9.

Fig. 9 illustrates a schematic diagram of the three-level power conversion system shown in fig. 8, according to various embodiments of the present disclosure. The schematic of fig. 9 is similar to that of fig. 7, except that switches S25 and S26 have been replaced by two diodes D25 and D26. The operating principle of NPC inverters is well known and therefore will not be described in detail here to avoid repetition.

Fig. 10 illustrates a block diagram of a third implementation of another portion of the three-level power conversion system shown in fig. 1, according to various embodiments of the disclosure. The block diagram shown in fig. 10 is similar to the block diagram shown in fig. 6, except that the inverter is implemented as a three-phase ANPC inverter 130. The load is a three-phase grid. A schematic diagram of the three-phase ANPC inverter 130 will be described in detail below with reference to fig. 11.

Fig. 11 illustrates a schematic diagram of the three-level power conversion system illustrated in fig. 10, according to various embodiments of the present disclosure. The three-level power conversion system includes a three-level boost converter 112 and a three-phase ANPC inverter 130. As shown in fig. 11, the three-level boost converter 112 and the three-phase ANPC inverter 130 are connected together by a three-level voltage bus arrangement. The three-level boost converter 112 has been discussed in detail above with reference to fig. 3 and thus will not be described in detail here.

The three-phase ANPC inverter 130 includes a first phase inverter 220, a second phase inverter 230, and a third phase inverter 240. The first phase inverter 220 includes switches S21, S22, S23, S24 connected in series between the positive voltage bus p and the negative voltage bus n. The first phase inverter 220 also includes switches S25 and S26 connected in series between the common node of S21-S22 and the common node of S23-S24. The common node of S25-S26 is connected to the midpoint voltage bus m. The first output filter is placed between the common node of S22-S23 and the first star-delta transformer 125. The first output filter is formed by inductor LA and capacitor C20. A capacitor C20 is connected in parallel with the star side of the first star-to-triangle transformer 125. The delta side of the first star-delta transformer 125 is connected to the first phase (phase a) of the three-phase grid (as shown in fig. 10).

The second phase inverter 230 includes switches S31, S32, S33, S34 connected in series between the positive voltage bus p and the negative voltage bus n. The second phase inverter 230 also includes switches S35 and S36 connected in series between the common node of S31-S32 and the common node of S33-S34. As shown in FIG. 11, the common node of S35-S36 is connected to the midpoint voltage bus m. The second output filter is placed between the common node of S32-S33 and the second star-delta transformer 135. The second output filter is formed by inductor LB and capacitor C30. A capacitor C30 is connected in parallel with the star-side of the second star-to-triangle transformer 135. The delta side of the second star-delta transformer 135 is connected to a second phase (phase B) of the three-phase grid.

The third phase inverter 240 includes switches S41, S42, S43, S44 connected in series between the positive voltage bus p and the negative voltage bus n. The third phase inverter 240 also includes switches S45 and S46 connected in series between the common node of S41-S42 and the common node of S43-S44. As shown in FIG. 11, the common node of S45-S46 is connected to the midpoint voltage bus m. The third output filter is placed between the common node of S42-S43 and the third star-delta transformer 145. The third output filter is formed by inductor LC and capacitor C40. A capacitor C40 is connected in parallel with the star side of the third star-to-triangle transformer 145. The delta side of the third star-delta transformer 145 is connected to the third phase (C-phase) of the three-phase grid.

In operation, the three-level power conversion system shown in fig. 11 is capable of regulating three phases under various conditions (e.g., unbalanced and non-linear load conditions). Furthermore, the three-level power conversion system shown in fig. 11 is compatible with driving the single-phase ac transformer of a modular three-phase system under a balanced control regime.

In some embodiments, the three-level power conversion system shown in fig. 11 provides a neutral point ready for grounding when neutral grounding is desired. When a three-phase unbalanced load is present, an energy storage unit (not shown, but shown in fig. 1) coupled to the three-level power conversion system shown in fig. 11 may be used to actively compensate for second harmonics on the three-level voltage bus arrangement, thereby reducing the capacity requirements of the capacitors coupled to the three-level voltage bus arrangement.

Fig. 12 illustrates a block diagram of another portion of the three-level power conversion system shown in fig. 1, in accordance with various embodiments of the present disclosure. The three-level boost converter 112 and the LLC converter 140 are placed on opposite sides of the three-level voltage bus arrangement. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. The three-level boost converter 112 is used to convert the two-level voltage generated by the solar panel array 150 into a three-level voltage. The three-level boost converter 110 is capable of regulating the voltage on the voltage buses p, m, n. The LLC converter 140 is used to convert the three-level voltage into a two-level voltage that is applied to the load 180. The LLC converter 140 is a three-level LLC resonant converter. The load 180 may include a plurality of chargers for charging a plurality of electric vehicles.

Fig. 13 illustrates a schematic diagram of the three-level power conversion system shown in fig. 12, according to various embodiments of the present disclosure. The three-level power conversion system shown in fig. 13 includes a three-level boost converter 112 and an LLC converter 140. As shown in fig. 13, the three-level boost converter 112 and the LLC converter 140 are connected together by a three-level voltage bus arrangement. The three-level boost converter 112 has been discussed in detail above with reference to fig. 3 and thus will not be described in detail here.

The LLC converter 140 includes a switching network 161, a resonant tank 162, a transformer 163, a rectifier 164, and an output filter 165. As shown in fig. 13, the switching network 161, the resonant tank 162, the transformer 163, the rectifier 164, and the output filter 165 are coupled to each other and connected in cascade between the input capacitors C3, C4 and the load RL.

The switching network 161 includes switches S1, S2, S3, S4 connected in series between the positive voltage bus p and the negative voltage bus n. As shown in FIG. 13, the common node of switches S2 and S3 is connected to the midpoint voltage bus m. The common node of switches S1 and S2 is connected to a first terminal of a transformer 163 through a resonant tank 162. The common node of switches S3 and S4 is connected to the second terminal of transformer 163.

The resonant tank 162 can be implemented in a variety of ways. For example, the main resonant tank includes a series resonant inductor Lr, a parallel resonant inductor Lm, and a series resonant capacitor Cr.

The series resonant inductor and the parallel resonant inductor may be implemented as external inductors. Those skilled in the art will recognize that many variations, substitutions, and modifications are possible. For example, the series resonant inductor may be implemented as a leakage inductance of the transformer 163.

In summary, the resonant tank 162 includes three key resonant elements, namely, a series resonant inductor, a series resonant capacitor, and a parallel resonant inductor. This configuration is commonly referred to as an LLC resonant converter. According to the operating principle of an LLC resonant converter, the resonant tank 162 facilitates zero voltage switching of the primary side switching element and zero current switching of the secondary side switching element at a switching frequency approximately equal to the resonant frequency of the resonant tank 162.

The LLC converter 140 may also include a transformer 163, a rectifier 164, and an output filter 165. The transformer 163 provides electrical isolation between the primary side and the secondary side of the LLC converter 140. According to an embodiment, the transformer 163 may be composed of two transformer windings, i.e., a primary transformer winding NP and a secondary transformer winding NS as shown in fig. 13. Alternatively, the transformer 163 may have a center tapped secondary, thereby having three transformer windings, including a primary transformer winding, a first secondary transformer winding, and a second secondary transformer winding.

It should be noted that the transformers described above and throughout the specification are examples only and should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the transformer 163 may also include various bias windings and gate drive auxiliary windings.

The rectifier 164 converts the alternating polarity waveform received from the output of the transformer 163 into a single polarity waveform. When the transformer 163 is a center-tapped secondary, the rectifier 164 may be formed of a pair of switching elements such as n-type metal oxide semiconductor (NMOS) transistors. Alternatively, the rectifier 164 may be formed of a pair of diodes. On the other hand, when transformer 163 is a single secondary winding, rectifier 164 may be a full-wave rectifier coupled to the single secondary winding of transformer 163.

Furthermore, rectifier 164 may be formed from other types of controllable devices, such as Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices, Bipolar Junction Transistor (BJT) devices, Super Junction Transistor (SJT) devices, Insulated Gate Bipolar Transistor (IGBT) devices, gallium nitride (GaN) based power devices, and so forth. The detailed operation and structure of the rectifier 114 is well known in the art and therefore will not be discussed here.

The output filter 165 is used to attenuate the switching ripple of the LLC converter 140. The output filter 165 may be an L-C filter formed of an inductor and a plurality of capacitors according to the operation principle of the isolated dc/dc converter. Those skilled in the art will recognize that certain isolated dc/dc converter topologies (e.g., forward converters) may require an L-C filter. On the other hand, some isolated dc/dc converter topologies (e.g., LLC resonant converters) may include an output filter formed by a capacitor. Those skilled in the art will also recognize that different output filter configurations are suitable for different power converter topologies where appropriate. Variations in the configuration of the output filter 165 are within the various embodiments of the present disclosure.

Fig. 14 illustrates a block diagram of another three-level power conversion system, in accordance with various embodiments of the present disclosure. The three-level power conversion system 1400 is similar to the three-level power conversion system 100 shown in fig. 1, except that the LLC converter 140 of fig. 1 has been replaced by a three-level boost converter 112. As shown in fig. 14, the three-level boost converter 112 is connected between the power supply 155 and the three-level voltage bus device. In some embodiments, power source 155 is a solar panel array. In an alternative embodiment, the power source 155 may be implemented as an energy storage unit such as a battery box.

Fig. 15 illustrates a schematic diagram of the three-level power conversion system shown in fig. 14, according to various embodiments of the present disclosure. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. As shown in fig. 15, a three-level boost converter 111 is connected between the solar panel array and the three-level voltage bus device. The three-level buck converter 120 is connected between the battery box and the three-level voltage bus device. The three-level boost converter 112 is connected between the power supply and the three-level voltage bus device. As shown in fig. 15, the power supply may be implemented as a solar panel array or a battery box. The ANPC inverter 131 is connected between the load and the three-level voltage bus device. The power conversion unit shown in fig. 15 has been described above, and thus, will not be described in detail here.

Fig. 16 illustrates a block diagram of another three-level power conversion system, in accordance with various embodiments of the present disclosure. The three-level power conversion system 1600 is similar to the three-level power conversion system 100 shown in fig. 1, except that the solar panel array of fig. 1 has been replaced with a power supply 155. Further, the LLC converter 140 is connected between the power supply 155 and the three-level voltage bus device, and the three-level boost converter 112 is connected between the energy storage unit 160 and the three-level voltage bus device. In some embodiments, power source 155 is a power source connected to a power grid. In an alternative embodiment, the power source 155 may be implemented as an energy storage unit such as a battery box.

Fig. 17 illustrates a schematic diagram of a portion of the three-level power conversion system shown in fig. 16, in accordance with various embodiments of the present disclosure. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. The portion of the three-level power conversion system shown in fig. 17 includes the LLC converter 140 and the ANPC inverter 131. As shown in fig. 17, the LLC converter 140 is connected between the power supply and the three-level voltage bus device. The ANPC inverter 131 is connected between the three-level voltage bus device and the load.

Fig. 18 illustrates a schematic diagram of another portion of the three-level power conversion system illustrated in fig. 16, in accordance with various embodiments of the present disclosure. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. The portion of the three-level power conversion system shown in fig. 18 includes a three-level boost converter 112 and an LLC converter 140. As shown in fig. 18, a three-level boost converter 112 is connected between the energy storage unit (shown in fig. 16) and the three-level voltage bus device. The LLC converter 140 is connected between the three-level voltage bus means and the load RL. In some embodiments, the load includes a plurality of chargers for charging a plurality of electric vehicles.

Fig. 19 illustrates a block diagram of another three-level power conversion system, in accordance with various embodiments of the present disclosure. Three-level power conversion system 1900 is similar to three-level power conversion system 100 shown in fig. 1, except that the three-level boost converter of fig. 1 has been replaced by a dual-output LLC converter 141. Furthermore, the three-level buck converter of fig. 1 has been replaced by a cascaded Dual Active Bridge (DAB) converter 190 and a three-level boost converter 113.

Fig. 20 illustrates a schematic diagram of a portion of the three-level power conversion system shown in fig. 19, according to various embodiments of the present disclosure. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. The portion of the three-level power conversion system shown in fig. 20 includes a dual-output LLC converter 141 and an ANPC inverter 131. As shown in fig. 20, a dual output LLC converter 141 is connected between the solar panel array and the three-level voltage bus device. The ANPC inverter 131 is connected between the three-level voltage bus device and the load. The three-level voltage bus arrangement serves as an energy buffer between the dual-output LLC converter 141 and the ANPC inverter 131.

The dual output LLC converter 141 includes a primary side circuit and a secondary side circuit. The primary side circuitry of the dual output LLC converter 141 is similar to the primary side circuitry of the LLC converter 140 shown in fig. 13, and therefore is not described in detail to avoid repetition. The secondary side circuit includes a first secondary winding NS1, a second secondary winding NS2, a first rectifier 146, a second rectifier 148, a first output capacitor Co1, and a second output capacitor Co 2. The first rectifier 146 includes diodes D51, D61, D71, D81. As shown in fig. 20, the second rectifier 148 includes diodes D52, D62, D72, D82.

As shown in fig. 20, the first secondary winding NS1, the first rectifier 146, and the first output capacitor Co1 form a first output of the dual output LLC converter 141. The second secondary winding NS2, the second rectifier 148, and the second output capacitor Co2 form a second output of the dual output LLC converter 141. The first output terminal and the second output terminal are stacked together and further coupled to a three-level voltage bus arrangement. A common node of the first output terminal and the second output terminal is connected to the midpoint voltage bus line m.

Fig. 21 illustrates a schematic diagram of another portion of the three-level power conversion system illustrated in fig. 19, in accordance with various embodiments of the present disclosure. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. The portion of the three-level power conversion system shown in fig. 21 includes a DAB converter 190, a three-level boost converter 113, and an LLC converter 140. The three converters are connected in cascade between the input capacitors CIN1, CIN2 and the load RL.

As shown in fig. 21, the DAB converter 190 is connected between the energy storage unit (the battery box shown in fig. 19) and the three-level boost converter 113. The three-level boost converter 113 is connected to a three-level voltage bus arrangement. The LLC converter 140 is connected between the three-level voltage bus means and the load RL. In some embodiments, the load includes a plurality of chargers for charging a plurality of electric vehicles.

DAB converter 190 is similar to LLC converter 140 except that DAB converter 190 does not include a resonant capacitor. The operating principle of a DAB-converter is well known and will therefore not be discussed here.

The three-level boost converter 113 is similar to the three-level boost converter 112 described above, except that the input inductor is from transformer T1. More specifically, the resonant inductor Lr of the DAB converter 190 serves as an input inductor of the three-level boost converter 112.

Fig. 22 illustrates a flow diagram of a method for controlling the three-level power conversion system shown in fig. 1, in accordance with various embodiments of the present disclosure. The flow chart shown in fig. 22 is merely an example, and should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, various steps shown in FIG. 22 can be added, removed, replaced, rearranged, and repeated.

At step 2202, a plurality of power conversion units are coupled to a three-level voltage bus device. The three-level voltage bus arrangement includes a positive voltage bus p, a midpoint voltage bus m, and a negative voltage bus n. The power conversion unit includes a three-level boost converter, a three-level buck converter, an inverter, an LLC converter, and the like.

At step 2204, energy of the power supply is transferred to the three-level voltage bus device by the three-level power converter. In some embodiments, the power source is a solar panel array. The three-level power converter is a three-level boost converter. In some embodiments, the three-level power converter is capable of detecting voltages on the buses p, m, n and adjusting the voltages based on the detected voltages.

At step 2206, energy of the three-level voltage bus device is transmitted to the grid through the inverter. In some embodiments, the inverter is an NPC inverter. Alternatively, the inverter is an ANPC inverter. Furthermore, the grid may be a single phase grid. The inverter is implemented as a single-phase inverter. Alternatively, the grid may be a three-phase grid. The inverter is implemented as a three-phase inverter.

In step 2208, energy of the three-level voltage bus arrangement is transferred to the load by the LLC converter. In some embodiments, the load includes a plurality of chargers for charging a plurality of electric vehicles. The LLC converter is a three-level LLC resonant converter.

At step 2208, energy is transferred between the three-level voltage bus means and the energy storage unit by the three-level buck converter. In some embodiments, the three-level buck converter is a bi-directional converter. In the energy storage phase, energy is transferred from the three-level voltage bus arrangement to the energy storage unit. During the discharge phase, energy is transferred from the energy storage unit to the three-level voltage bus arrangement. During the de-energized phase, the three-level buck converter is able to detect the voltages on the buses p, m, n and adjust the voltages based on the detected voltages.

Although embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.

For example, in one embodiment, a system is disclosed that includes a first three-level power converter device having output terminals connected to a three-level voltage bus device and input terminals for coupling with a solar panel array, an inverter device connected between the three-level voltage bus device and a power grid, and a second three-level power converter device connected between the three-level voltage bus device and an energy storage unit. The use of the term "coupled" is intended to include both direct and indirect connections of the various devices.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. Accordingly, the specification and figures are to be regarded only as illustrative of the present disclosure as defined by the appended claims and are intended to cover any and all modifications, variations, combinations, or equivalents that fall within the scope of the present disclosure.

Claims

1. A three-level voltage bus apparatus comprising:

a first voltage bus coupled to a plurality of three-level power conversion units;

a second voltage bus coupled to the plurality of three-level power conversion units; and

a third voltage bus coupled to the plurality of three-level power conversion units, wherein the first voltage bus and the third voltage bus are regulated with reference to the second voltage bus by at least one of the plurality of three-level power conversion units, the plurality of three-level power conversion units including an inductance-capacitance (LLC) converter coupled between a DC load and the first voltage bus, the second voltage bus, and the third voltage bus.

2. The apparatus of claim 1, wherein:

the plurality of three-level power conversion units includes a three-level boost converter, a three-level buck converter, an inverter, and wherein output/input terminals of the three-level boost converter, the three-level buck converter, the inverter, and the LLC converter are coupled together by the first voltage bus, the second voltage bus, and the third voltage bus.

3. The apparatus of claim 2, wherein:

the three-level boost converter is coupled between a solar panel array and the first, second, and third voltage buses;

the three-level buck converter is coupled between an energy storage unit and the first, second, and third voltage buses;

the inverter is coupled between a power grid and the first, second, and third voltage buses.

4. The apparatus of claim 3, wherein:

the energy storage unit is a battery-based energy storage unit; and

the dc load includes a charger for charging an electric vehicle.

5. The apparatus of claim 3 or 4, wherein:

the inverter is a neutral point clamped inverter, and wherein a neutral point of the inverter is coupled to the second voltage bus.

6. The apparatus of claim 3 or 4, wherein:

the inverter comprises a first neutral point clamped inverter, a second neutral point clamped inverter, and a third neutral point clamped inverter, and wherein:

the first neutral point clamped inverter is coupled to a first phase of a three-phase power system through a first star-delta transformer;

the second neutral point clamped inverter is coupled to a second phase of the three-phase power system through a second star-to-delta transformer; and

the third neutral-clamped inverter is coupled to a third phase of the three-phase power system through a third star-to-delta transformer.

7. The apparatus of claim 6, wherein:

the neutral lines of the first, second, and third star-to-triangle transformers are coupled to the second voltage bus.

8. The apparatus of claim 1, wherein:

the plurality of three-level power conversion units includes a first three-level boost converter, a second three-level boost converter, an inverter, and a three-level buck converter coupled together by the first voltage bus, the second voltage bus, and the third voltage bus.

9. The apparatus of claim 1, wherein:

the plurality of three-level power conversion units includes a first LLC converter, a second LLC converter, an inverter, and a three-level boost converter coupled together by the first voltage bus, the second voltage bus, and the third voltage bus.

10. The apparatus of claim 1, wherein:

the plurality of three-level power conversion units includes an LLC converter, a dual-output LLC converter, an inverter, and a three-level boost converter coupled together by the first voltage bus, the second voltage bus, and the third voltage bus.

11. The apparatus of claim 10, wherein:

the three-level boost converter is coupled between a dual-active bridge converter and the first voltage bus, the second voltage bus, and the third voltage bus; and

a first output and a second output of the dual output LLC converter are stacked together, and wherein a common node of the first output and the second output of the dual output LLC converter is coupled to the second voltage bus.

12. A three-level power conversion method, comprising:

transferring energy from a power source to a three-level voltage bus device through a first three-level power converter;

transmitting energy from the three-level voltage bus device to a grid through an inverter;

transferring energy between the three-level voltage bus device and an energy storage unit through a second three-level power converter;

energy is transferred from the three-level voltage bus device to a load through the LLC power converter.

13. The method of claim 12, further comprising:

adjusting a voltage of the three-level voltage bus device.

14. The method of claim 12 or 13, wherein:

the three-level voltage bus apparatus includes: a first voltage bus, a second voltage bus, and a third voltage bus coupled to the first three-level power converter, the second three-level power converter, the inverter, and the LLC power converter, and wherein the first voltage bus and the third voltage bus are regulated with reference to the second voltage bus.

15. The method of claim 13, wherein:

the first three-level power converter is a three-level boost converter comprising four switches coupled in series, and wherein midpoints of the four switches of the three-level boost converter are coupled to a second voltage bus;

the second three-level power converter is a three-level buck converter including four switches coupled in series, and wherein midpoints of the four switches of the three-level buck converter are coupled to the second voltage bus;

the inverter is a neutral point clamped inverter having a neutral point coupled to the second voltage bus; and

the LLC power converter comprises four switches coupled in series, and wherein midpoints of the four switches of the LLC power converter are coupled to the second voltage bus.

16. The method of claim 12 or 13, further comprising:

configuring the second three-level power converter to function as a bi-directional power converter to transfer energy between the three-level voltage bus device and the energy storage unit.

17. A three-level power conversion system comprising:

a first three-level power converter having output terminals coupled to the three-level voltage bus arrangement and input terminals for coupling with the solar panel array;

an inverter coupled between the three-level voltage bus device and a power grid;

a second three-level power converter coupled between the three-level voltage bus device and an energy storage unit;

an LLC converter coupled between a DC load and the three-level voltage bus means.

18. The system of claim 17, wherein the three-level voltage bus means comprises:

a first voltage bus coupled to a positive output terminal of the first three-level power converter;

a second voltage bus coupled to a neutral point of the first three-level power converter; and

a third voltage bus coupled to a negative output terminal of the first three-level power converter, and wherein voltages on the first voltage bus, the second voltage bus, and the third voltage bus are regulated by the first three-level power converter.

19. The system of claim 17, wherein:

the dc load includes a plurality of electric vehicles.