A multi-channel bidirectional AC / DC converter based on an active midpoint clamp converter

Abstract

This invention discloses a multi-channel bidirectional AC / DC converter based on an active neutral point clamping (ANPC) converter, comprising: N (N is a positive integer) active neutral point clamping (ANPC) three-phase converters and N three-phase phase-shifting transformers; the arm voltages of the active neutral point clamping converters are modulated using a dual-variable method of phase shift angle and modulation angle; the phase difference between the fundamental voltage of the corresponding phase of the first three-phase phase-shifting transformer and the fundamental voltage of the primary phase is lagging, and the phase angles of the corresponding phase voltages of the N phase-shifting transformers are sequentially different; the control signals of the corresponding phases of the N three-phase converters are sequentially different, so as to achieve the same phase of the secondary fundamental voltage of each three-phase transformer. This invention can improve the adaptability of the converter to the power grid and provides a solution for achieving SST (Synchronous Transmission System) with good controllability, high reliability, mature technology, good inheritance, and low life-cycle cost.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter. Background Technology

[0002] Power electronics technology is now widely used in power applications, including DC transmission, new energy power generation, microgrids, electrochemical energy storage, static var compensating, AC / DC hybrid power distribution, DC power distribution, and "photovoltaic-storage-DC-flexible" systems. High-power AC / DC power converters ranging from hundreds of kilovolt-amperes to tens of megavolt-amperes, which can be directly connected to 10kV or 35kV medium voltage or even higher voltage levels, have been extensively researched and applied.

[0003] The existing high-power AC / DC power converters suitable for medium-voltage access mainly have two technical solutions: power frequency transformer isolation access and medium-voltage direct connection.

[0004] A high-power bidirectional AC / DC converter with power frequency transformer isolation consists of a power frequency transformer and a high-frequency switching power electronic converter. The power frequency transformer provides electrical isolation and voltage matching. The high-frequency switching power electronic converter, including two-level, three-level, or multi-level converters and modular multilevel (MMC) topologies, converts DC to AC power from hundreds to tens of kilovolts. Its power devices typically require sinusoidal pulse width modulation (SPWM), including space vector modulation, to achieve sinusoidal control of the AC side voltage or current waveform and matching control of the AC and DC side voltage magnitudes. Furthermore, due to the performance limitations of current high-frequency fully controlled switching devices, when the DC side voltage exceeds a certain value (e.g., 2000V and above), a highly complex high-level circuit topology or multiple three-level or lower-level circuit topologies with DC side series connection is required. When using DC side series connection, appropriate series voltage equalization measures are needed, and a high-frequency DC / DC converter is also required for electrical isolation, or the power frequency input transformer is divided into multiple transformers. In summary, conventional power frequency transformer-isolated high-power bidirectional AC / DC converters have disadvantages such as high switching frequency of power devices, low system efficiency, and large transformer size and weight.

[0005] High-power converters directly connected to the grid mainly include MMC converters and cascaded H-bridge inverters (CHB). Currently, CHB is the primary solution used in medium-voltage direct-connection scenarios, while MMC is more often used for higher voltage levels. CHB was initially used for medium-voltage active filtering and reactive power compensation, and later expanded to electrochemical energy storage and static synchronous phase regulation. In these scenarios, the discrete DC sides of the cascaded H-bridge are supported by capacitors or batteries. Its characteristic is that it does not require transformer isolation, but it lacks a unified DC-side circuit. In recent years, the application of CHB in high-power photovoltaic power plants has also been studied. However, due to the insulation capacity of photovoltaic panels, high-frequency DC converters are usually required to achieve electrical isolation between the photovoltaic cells and the discrete DC sides of the H-bridge. High-power isolated DC converters, especially those with a wide operating voltage range, struggle to achieve high efficiency over a wide range, and the insulation problem of their high-frequency isolation transformers is also significant. Another important application scenario for CHB is the currently widely discussed solid-state transformer (SST, or power electronic transformer (PET)). Solid-state AC / DC transformers used in AC / DC bidirectional converters employ a CHB (Chain-Bridge) design on the AC side. Each H-bridge connects to one end of a resonant or non-resonant converter using a dual active bridge. The other ends of all dual active bridges are connected in parallel to form the DC side. The dual active converters achieve high-frequency electrical isolation and voltage matching. AC / AC solid-state transformers are based on AC / DC solid-state transformers, with an additional bidirectional DC / AC converter stage added to the DC side. Solid-state transformers possess significant advantages such as high power density, good controllability, adaptability to new energy sources and energy storage, and high efficiency. They have received considerable attention and are considered a crucial technological development direction and trend to meet the electricity demands driven by the development of computing power.However, despite this, SST based on the aforementioned multi-stage high-frequency power conversion still faces many significant core bottlenecks, mainly including: ① Reliability and mass production issues with key components. Firstly, in high-frequency, high-voltage environments, the loss, insulation, and partial discharge resistance of the magnetic materials (such as ultra-thin silicon steel, amorphous / nanocrystalline, ferrite, etc.) of one of its core components, the high-power intermediate-frequency or high-frequency transformer (several kHz and above), are extremely difficult to solve, resulting in poor mechanical characteristics and low product yield. Secondly, another core component, SiC... MOSFETs are currently not only expensive, but also prone to gate oxide degradation over long-term operation; ② They lack operational verification, unified standards, and complex maintenance, and their system reliability cannot yet meet the primary high reliability requirements of power applications and data center power supply scenarios. There are still many fundamental issues to be resolved before they can be widely adopted; ③ Although high-frequency isolated DC-DC bidirectional converters can achieve soft switching, they cannot guarantee soft switching across the entire operating range, and their AC side CHB is a high-frequency hard switch, so there are still di / dt and du / dt problems caused by high-frequency switching, i.e., electromagnetic compatibility issues; ④ The initial investment cost of the system is still significantly higher than that of traditional power frequency isolated converters. Although there are benefits such as saving space and shortening the construction period, even without considering the difference in maintenance costs, based on the current application boundary conditions, the investment payback period is at least 20 years, which is not yet economical.

[0006] To address the efficiency improvement issue of power frequency isolated high-power bidirectional converters, the applicant proposed a high-power bidirectional converter scheme based on a multi-pulse structure in previous research (see: A. Xu and S. Xie, "A Multipulse-Structure-Based Bidirectional PWM Converter for High-Power Applications," in IEEE Transactions on Power Electronics, vol. 24, no. 5, pp. 1233-1242, May 2009.). This bidirectional AC / DC converter adopts a multi-channel structure, with a three-phase bridge converter and a phase-shifting transformer forming the power channels. The power switches in each channel use a switching frequency three times the base frequency, and sequential sampling space vector modulation (SVM) technology is used between multiple channels. It features low switching frequency, good sinusoidal AC current waveform, and can achieve rapid dynamic adjustment performance. While ensuring excellent stable and dynamic electrical performance, the system efficiency is higher than that of conventional power frequency isolated high-frequency PWM modulation converters (see: Xu Aiguo, Research on Regenerative Braking Energy Utilization Technology for Urban Rail Transit, Doctoral Dissertation, Nanjing University of Aeronautics and Astronautics, 2009.9).

[0007] Based on a multi-pulse high-power converter, the sole proprietorship of the first inventor, Mag-Anbe Electric Technology Co., Ltd., has proposed a medium-voltage direct-link uninterrupted flexible AC / DC hybrid power supply system (Invention Patent Application No.: CN202111584724.1, Authorization Announcement No.: CN114336933B). This system includes a multi-channel converter consisting of N three-phase bridge bidirectional AC / DC converters and N phase-shifting transformers, a regulated DC converter, a battery charge / discharge converter, and a battery. The N three-phase bridge bidirectional AC / DC converters are controlled uniformly. During rectification operation, the power transistors are fully off or commutated / off when the current crosses zero. During inverter operation, the power transistors employ 180° open-loop control, with the switching frequency being the fundamental frequency. This hybrid power supply system includes medium-voltage and low-voltage AC distribution systems, as well as regulated and unregulated DC buses, facilitating the connection of DC electrical equipment and new energy power generation equipment. Energy can flow in multiple directions, thus enabling flexible uninterruptible power supply (UPS) for both AC and DC systems. The core component of this system is a multi-channel bidirectional AC / DC converter with a power frequency switch. The system uses a power frequency transformer to achieve electrical isolation and direct connection to medium voltage.

[0008] While the aforementioned existing technology of power frequency isolated multi-channel high-power bidirectional converter has outstanding advantages such as high reliability and high power conversion efficiency, its AC / DC converter may not be able to perform voltage regulation, or the low switching frequency SVM technology used has high harmonic content and is not applicable when regulating voltage over a wide range, and its adaptability to changes in AC grid voltage is poor. Therefore, its practical application is also limited to a certain extent. Summary of the Invention

[0009] Purpose of the invention: This invention provides a multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter to achieve wide voltage range operation of the converter, improve the adaptability of the converter to the power grid, and provide a solution for achieving SST with good controllability, high reliability, mature technology, good inheritance and low life cycle cost.

[0010] Technical solution: The present invention provides a multi-channel bidirectional AC / DC converter based on an active neutral point clamping converter, comprising: N (N is a positive integer) active neutral point clamping (ANPC) three-phase converters and N three-phase phase shifting transformers;

[0011] Each ANPC three-phase converter consists of two series capacitors connected in parallel to the DC bus and three active neutral clamping bridge arms consisting of six power switches and their anti-parallel diodes. The four power switches and their anti-parallel diodes of each active clamping bridge arm are connected in series to form the main bridge arm, and the other two power switches and their diodes are connected in series to form the clamping bridge arm. The upper two and lower two power switches and their anti-parallel diodes of the main bridge arm form its upper bridge arm and lower bridge arm, respectively. The middle connection point of the upper bridge arm and the lower bridge arm is the AC side node of the main bridge arm. The two ends of the clamping bridge arm are connected to the middle nodes of the two power switches of the upper bridge arm and the two power switches of the lower bridge arm, respectively. The middle connection point of the two power switches of the clamping bridge arm is connected to the middle node of the series capacitor.

[0012] In the ANPC converter, the outer switches of each main bridge arm (the upper switch of the upper bridge arm and the lower switch of the lower bridge arm) operate in a complementary switching mode, meaning that when one is on, the other is off. A dead time interval is maintained between their switching transitions to prevent shoot-through. The inner switches of each main bridge arm (the lower switch of the upper bridge arm and the upper switch of the lower bridge arm) operate in a complementary switching mode. The two switches of the clamping bridge arm operate in a complementary switching mode, with the upper switch of the clamping bridge arm switching synchronously with the lower switch of the lower bridge arm and the lower switch of the clamping bridge arm. The two power switches of the upper bridge arm of the main bridge arm use phase-shift control, meaning that the control signal of the lower switch has the same waveform as the control signal of the upper switch, but its phase leads or lags by a certain phase shift angle. ;

[0013] Each power switch in the ANPC converter uses a single modulation angle. Switching control is performed, meaning the control signal consists of three switching pulses within each power frequency cycle. The phase at the first turn-on is taken as the reference (0 phase), corresponding to time 0. The turn-off point of the first switching pulse corresponds to phase lead. A certain modulation angle That is, t=( At time ω1 (ω1 = 2πf1, where f1 is the fundamental frequency of the AC side), the turn-on time of the second switching pulse is... / ω1, continues until the half-cycle point when π / ω1 is turned off, in ( The third activation at time ) / ω1, in / ω1 is turned off;

[0014] The control signals for the power transistors of the three bridge arms within each ANPC converter are sequentially different. ;

[0015] Each phase of each phase of the phase-shifting transformer includes one primary winding and two or one secondary winding. The three-phase primary windings are connected in a delta or star configuration to form a three-phase node on the primary side of the transformer. These three-phase nodes are connected to the corresponding AC side nodes of the ANPC converter. The secondary windings are connected in a zigzag configuration, so that the voltage phase formed after the zigzag connection has a certain phase difference from the voltage phase of the primary winding. The secondary sides of N phase-shifting transformers are connected in a star or delta configuration after being connected in series to form a three-phase AC side circuit.

[0016] The phase difference between the fundamental voltage of the corresponding phase secondary side and the fundamental voltage of the primary side of the first three-phase phase-shifting transformer is lagging. The turns ratios of the primary and secondary windings of N phase-shifting transformers are such that the effective values ​​of the fundamental voltages of the primary side voltage and the secondary side voltage of the zigzag connection are equal or all in the same proportion, and the phase shift angles of the corresponding phases of the phase-shifting transformers differ sequentially. And the calculation determines it;

[0017] The control signals of corresponding phases of N three-phase ANPC converters are sequentially phase-differentiated. This is to ensure that the secondary fundamental voltage of each three-phase transformer has the same phase.

[0018] Furthermore, in steady state, the phase shift angle and modulation angle of all ANPC converters are the same. Their magnitudes can be directly calculated based on the AC side voltage amplitude and phase requirements, meaning that the control signals for each power transistor do not need to be obtained using the sinusoidal pulse width modulation (SVPWM, or SVM) method based on vector control (VC).

[0019] Furthermore, each three-phase ANPC converter and its corresponding phase-shifting transformer constitute a power channel (or module). Each channel can independently achieve bidirectional AC / DC conversion. The converter output line voltage of a channel contains only the fundamental frequency and harmonics with frequencies of 6k±1 (k=1,2,3,…) times the fundamental frequency. The relationship between the fundamental voltage amplitude and the average DC voltage is as follows: The relationship between the amplitude of the nth harmonic voltage and the average value of the DC voltage is as follows: .

[0020] Furthermore, phase shift angle The range of variation is Modulation angle The range of variation is .

[0021] Furthermore, phase shift angle and modulation angle Adjusting the ratio between the AC-side fundamental voltage and the DC-side voltage individually or / and simultaneously, i.e., for voltage amplitude control, phase shift angle. It is also used to adjust the phase of the output voltage of the ANPC converter. .

[0022] Furthermore, the AC sides of the N power channels are connected in series, while the DC sides can be connected in parallel, in series, in a combination of series and parallel, in a combination of independent and independent connections, and / or in series. When the DC sides are not all connected in parallel, appropriate measures are usually required to ensure that the average DC voltage of each channel is basically equal.

[0023] Furthermore, when the AC side of the N power channels is connected in series and the DC side voltage is equal, the fundamental voltage of the output voltage of each channel is superimposed in phase, and the harmonics are attenuated or completely eliminated after superposition. That is, theoretically, the AC side voltage of the N-channel converter only contains 6Nk±1 (k=1,2,3,…) harmonics, and under the same phase shift angle and modulation angle, the relative relationship between the remaining harmonic content and the fundamental content is consistent with that of the single channel.

[0024] Furthermore, the converter uses an AC-side series inductor (L) filter, inductor-capacitor (LC) filter, or various low-pass filters with specific harmonic traps to filter out harmonic components in the AC-side voltage or current. The filter inductor directly connected to the AC side of the converter can be an external inductor or directly utilize the transformer leakage inductance and line inductance equivalent to the secondary side of the phase-shifting transformer. The inductor connected to the AC grid (or other AC-side power sources) can be an external inductor and / or line inductance.

[0025] Furthermore, one or more sets of windings with the same structure and connection method as the aforementioned transformer secondary windings but with a certain ratio of turns can be added to each phase-shifting transformer. These sets of windings can be connected in series to form another set of three-phase AC systems, which can be used to connect AC loads or power supplies that require electrical isolation and have different voltage levels.

[0026] Furthermore, the power switching transistors are silicon-based insulated gate bipolar transistors (Si IGBTs), silicon or silicon carbide-based metal-oxide-semiconductor field-effect transistors (Si / SiC MOSFETs), or other types of fully controllable semiconductor power devices.

[0027] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: simple modulation signal calculation and implementation, very low switching losses and strong current overload capacity, high sinusoidal AC side voltage and / or current at low switching frequencies, and low power transistor voltage stress. It provides a solution for existing power frequency isolated multi-channel high-power bidirectional converters to achieve wide-range adjustment of the magnitude and phase of the AC side fundamental voltage based on dual-variable control of phase shift angle and modulation angle, significantly improving its adaptability to AC grid voltage changes. It lays the foundation for realizing power electronic interface converters with grid support capabilities using advanced control strategies such as grid-type control. It has good application prospects in high-power AC / DC power conversion applications connected to the grid, including but not limited to photovoltaic power generation, electrochemical energy storage, reactive power compensation and microgrids, as well as high-voltage DC power supply for data centers, rail transit traction power supply and AC uninterruptible power supply applications. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the multi-channel bidirectional converter circuit topology and the bridge arm line voltage waveform of a single three-phase ANPC converter according to the present invention.

[0029] Figure 2 This is a schematic diagram of the modulation signals of the six power transistors in one arm of the three-phase ANPC circuit in the converter of this invention.

[0030] Figure 3 This is a timing diagram of the modulation signals of the Sc1 power transistors of the C-phase bridge arm of the N three-phase ANPC converters in this invention.

[0031] Figure 4 This is a waveform diagram of the line voltage output of a single three-phase ANPC converter of the present invention. , ).

[0032] Figure 5 This invention relates to a single three-phase ANPC converter. =0、 A graph showing the relationship between the fundamental effective value of the output line voltage and the DC voltage during changes.

[0033] Figure 6 This invention relates to a single three-phase ANPC converter. =0、 A graph showing the relationship between the fundamental effective value of the output line voltage and the DC voltage during changes.

[0034] Figure 7 This invention relates to a single three-phase ANPC converter. , A graph showing the relationship between the fundamental effective value of the output line voltage and the DC voltage during changes.

[0035] Figure 8 This invention relates to a single three-phase ANPC converter. =0、 A graph showing the relationship between the effective value of the main harmonics in the changing output line voltage and the DC voltage.

[0036] Figure 9 This invention relates to a single three-phase ANPC converter. =0、 A graph showing the relationship between the effective value of the main harmonics in the changing output line voltage and the DC voltage.

[0037] Figure 10 This invention relates to a single three-phase ANPC converter. , The graph showing the relationship between the effective value of the main harmonics in the output line voltage and the DC voltage, and the graph showing the total harmonic content (within the 50th order).

[0038] Figure 11 This is a schematic diagram of the system structure in the embodiment.

[0039] Figure 12 The example uses an ANPC circuit employing an insulated gate bipolar transistor (IGBT).

[0040] Figure 13 This is the per-unit value of the AC side voltage synthesized by the four channels in series in the embodiment (in words). = The output voltage when =0 is used as the reference. =0、 (When changing).

[0041] Figure 14 This is the per-unit value of the AC side voltage synthesized by the four channels in series in the embodiment (in words). = The output voltage when =0 is used as the reference. =0、 (When changing).

[0042] Figure 15 This is the per-unit value of the AC side voltage synthesized by the four channels in series in the embodiment (in words). = The output voltage when =0 is used as the reference. , (When changing).

[0043] Figure 16 This refers to the single harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. =0、 (When changing).

[0044] Figure 17This refers to the single harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. =0、 (When changing).

[0045] Figure 18 This refers to the single harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. , (When changing).

[0046] Figure 19 This refers to the total harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. =0、 (When changing).

[0047] Figure 20 This refers to the total harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. =0、 (When changing).

[0048] Figure 21 This refers to the total harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. , (When changing).

[0049] Figure 22 It shows the AC side voltage waveform of the converter synthesized by four channels under several typical control angles during off-grid inverter operation, as well as the AC port voltage waveform after LC filtering. Detailed Implementation

[0050] A multi-channel bidirectional AC / DC converter based on active neutral-point clamping (ANPC) converters includes: N (N is a positive integer) active neutral-point clamping (ANPC) three-phase converters and N three-phase phase-shifting transformers. The converter power circuit structure and the arm voltage modulation method are illustrated below. Figure 1 As shown;

[0051] Each ANPC three-phase converter consists of two series capacitors connected in parallel to the DC bus and three active neutral clamping bridge arms, each composed of six power switches and their anti-parallel diodes. In each active clamping bridge arm, the four power switches and their anti-parallel diodes are connected in series to form the main bridge arm, while the other two power switches and their diodes are connected in series to form the clamping bridge arm. The upper two and lower two power switches and their anti-parallel diodes in the main bridge arm form its upper and lower bridge arms, respectively. The midpoint of the upper and lower bridge arms is the AC side node of the main bridge arm. The two ends of the clamping bridge arm are connected to the midpoints of the two power switches in the upper and lower bridge arms, respectively. The midpoint of the two power switches in the clamping bridge arm is connected to the midpoint of the series capacitor. The control signals for the power switches in the three bridge arms of each ANPC converter are sequentially phased. ;

[0052] like Figure 2 As shown: The outer switches of each main bridge arm of the converter (i.e., the upper switch of the upper bridge arm and the lower switch of the lower bridge arm) adopt a complementary switching mode (i.e., when one is on, the other is off, and there is a certain dead time between the switching of the two power switches to prevent the two power switches from shooting through). The inner switches of each main bridge arm (i.e., the lower switch of the upper bridge arm and the upper switch of the lower bridge arm) are complementary switches. The two switches of the clamping bridge arm are complementary switches, and its upper switch switches synchronously with the lower switch of the lower bridge arm of the main bridge arm, and its lower switch switches synchronously with the upper switch of the upper bridge arm of the main bridge arm. The two power switches of the upper bridge arm of the main bridge arm adopt phase shift control, that is, the control signal of the lower switch has the same waveform as the control signal of the upper switch, but the phase leads or lags by a certain phase shift angle. Each power switch uses a switching frequency (f1) three times the fundamental frequency of the AC side voltage. That is, the control signal consists of three switching pulses in each power frequency cycle. The phase at the first turn-on is taken as the reference (0 phase, corresponding to time 0), and the turn-off point of the first switching pulse corresponds to phase lead. A certain modulation angle That is, t=( At time ω1 (ω1=2πf1), the turn-on time of the second switching pulse is... / ω1, continues until the half-cycle point when π / ω1 is turned off, in ( The third activation at time ) / ω1, in / ω1 is turned off.

[0053] Each phase of each phase of the phase-shifting transformer includes one primary winding and two or one secondary winding. The three-phase primary windings are connected in a delta or star configuration to form a three-phase node on the primary side of the transformer. These three-phase nodes are connected to the corresponding AC side nodes of the ANPC converter. The secondary windings are connected in a zigzag configuration, so that the voltage phase formed after the zigzag connection has a certain phase difference from the voltage phase of the primary winding. The secondary sides of N phase-shifting transformers are connected in a star or delta configuration after being connected in series to form a three-phase AC side circuit.

[0054] The phase difference between the fundamental voltage of the corresponding phase secondary side and the fundamental voltage of the primary side of the first three-phase phase-shifting transformer is lagging. The turns ratios of the primary and secondary windings of N phase-shifting transformers are such that the effective values ​​of the fundamental voltages of the primary side voltage and the secondary side voltage of the zigzag connection are equal or all in the same proportion, and the phase shift angles of the corresponding phases of the phase-shifting transformers differ sequentially. And the calculation determines it;

[0055] The control signals of corresponding phases of N three-phase converters are sequentially phase-differentiated. This ensures that the secondary fundamental voltage phase of each three-phase transformer is the same. The S-phase of the C-phase bridge arm of the N three-phase ANPC converters... c1 The timing diagram of the control signal for the power transistor is as follows: Figure 3 As shown.

[0056] Figure 1 The single three-phase ANPC converter in the middle adopts Figure 2 When the given power transistor control signal is given, its output line voltage is (based on the upper transistor S of the upper arm of the main bridge arm of phase A). A1 The control signal is first activated at time zero, and the upper arm lower tube S of the main bridge arm is defined. A2 The control signal lags behind S A1 When the control signal is received, the phase shift angle α is positive; conversely, when it is negative, the phase shift angle α is negative; and when it is synchronized, the phase shift angle α is 0.

[0057] (1)

[0058] The line voltage does not contain 3rd and multiples of 3 harmonics, and when When it is used, the nth harmonic can be eliminated.

[0059] As can be seen from equation (1), with S A1 The rise time of the first switching pulse of the control signal is used as a reference, and the fundamental phase angle of the transformer primary voltage (i.e., the line voltage output by the ANPC converter) is... As shown in equation (2) (with lag as positive):

[0060] (2)

[0061] From equation (2), we can obtain that under certain conditions... Next, according to It can make exist to The changes between these ranges mean that when applying grid connection, if... Phase synchronized with grid voltage, regulation It can achieve full-range adjustment of the phase difference angle between the converter's internal potential and the grid voltage, that is, it can be achieved through direct adjustment. It enables bidirectional, rapid, and stable regulation of active power.

[0062] Figure 4 This is a waveform diagram of the line voltage output of a single three-phase ANPC converter of the present invention. , ). Figure 5 This invention relates to a single three-phase ANPC converter. =0、 A graph showing the relationship between the fundamental effective value of the output line voltage and the DC voltage during changes. Figure 6 This invention relates to a single three-phase ANPC converter. =0、 A graph showing the relationship between the fundamental effective value of the output line voltage and the DC voltage during changes. Figure 7 This invention relates to a single three-phase ANPC converter. , A graph showing the relationship between the fundamental effective value of the output line voltage and the DC voltage during changes. Figure 8 This invention relates to a single three-phase ANPC converter. =0、 A graph showing the relationship between the effective value of the main harmonics in the changing output line voltage and the DC voltage. Figure 9 This invention relates to a single three-phase ANPC converter. =0、 A graph showing the relationship between the effective value of the main harmonics in the changing output line voltage and the DC voltage. Figure 10 This invention relates to a single three-phase ANPC converter. , The graphs show the relationship between the effective values ​​of the main harmonics in the output line voltage and the DC voltage, as well as the total harmonic content (within the 50th order). These graphs demonstrate how controlling... , It can control the ratio of AC fundamental voltage to DC voltage, and within the range of fundamental voltage variation from 0 to maximum value, the single and total harmonic content in AC voltage is limited.

[0063] The following combination Figures 11-22 An embodiment of the present invention (N=4) is described below:

[0064] A four-channel bidirectional AC / DC converter based on an active neutral-point clamping converter includes four three-phase ANPC converters and four phase-shifting transformers. All ANPC converters are connected to the same DC bus. The primary windings of the transformers have the same number of turns and are connected in a delta configuration, while the secondary windings are connected in a star configuration after being connected in series. Figure 11 As shown. In this embodiment, the power switching transistors in the three-phase ANPC converter are insulated-gate bipolar transistors (IGBTs). Figure 12 This is the ANPC circuit using IGBTs in the embodiment. Figure 11 The converters in the first to fourth groups are shown from top to bottom. For the first group of converters, after the secondary side of the transformer is connected in a zigzag manner, the phase voltage output from the secondary side lags behind the primary side voltage. (Right now The phase voltage output from the secondary side of the transformer corresponding to the second group of converters lags behind the primary voltage. For the third group of converters, after the secondary side of the transformer is connected in a zigzag manner, the phase voltage output from the secondary side leads the primary voltage. The phase voltage output from the secondary side of the transformer corresponding to the fourth group of converters leads the primary voltage. Because the control signals for each converter group are sequentially delayed... (Right now After phase shifting via a convoluted wiring process, the fundamental voltage outputs from the secondary sides of each transformer are in phase, while the harmonic voltages cancel each other out due to the phase shifting and superposition. For the transformer corresponding to the first group of converters, to achieve... Due to voltage lag, the turns ratios of the two sets of secondary windings to the primary windings of the transformer are k1:1 and k2:1, respectively. For the transformer corresponding to the second set of converters, in order to achieve... Due to voltage lag, the turns ratios of the two sets of secondary windings to the primary windings of the transformer are k3:1 and k4:1, respectively. The transformer in the third converter has the same number of turns as the transformer in the second converter, differing only in the winding connection method. Similarly, the transformer in the fourth converter has the same number of turns as the transformer in the first converter, differing only in the winding connection method. The fundamental frequency of the output phase voltage of each channel should be the same to achieve power distribution; therefore, k1=0.703, k2=0.442, k3=0.916, and k4=0.151.

[0065] The secondary voltage of the first transformer lags behind the primary voltage phase. The phase voltage output after the secondary voltages of the four transformers are superimposed in series is:

[0066] (3)

[0067] In equation (3), m is the ratio of the effective value of the fundamental voltage of the primary side of each transformer to the effective value of the fundamental voltage of the secondary side of the zigzag connection, which can be called the voltage ratio of the transformer.

[0068] The main harmonic components of the AC phase voltage synthesized by four-channel series are 24k±1 (k=1,2,3,…). The main harmonic components have high frequency and low content, and the total harmonic distortion (THD) is significantly reduced compared with the single-channel converter. High sinusoidal power can be achieved by using transformer leakage inductance or simple filter filtering.

[0069] The invented converter can modulate the angle Full-range control of output voltage. Modulation angle. The introduction of this does not change the harmonic frequency components of the output voltage, but only changes the amplitude of the harmonics. In any... Below, the per-unit value of the fundamental effective value of the AC side phase voltage synthesized by multi-channel series synthesis can be further obtained from equation (3). With modulation angle Relationship:

[0070] (4)

[0071] In equation (4), the benchmark value on which the standardization is based is this. Down, The effective value of the fundamental phase voltage when it is 0.

[0072] According to equation (4), we obtain and Relationship curves, such as Figure 13 That is, the per-unit value of the AC side voltage synthesized by the four channels in series in the embodiment (in words). = The output voltage when =0 is used as the reference. =0、 (When changing). Figure 13 Therefore, by utilizing the modulation angle The output voltage can be shifted from 0 to this phase angle. The voltage is adjusted within the maximum voltage range. Therefore, when used as a grid-connected converter, the adjustment... The magnitude of the converter's internal potential can be directly adjusted, which provides a good foundation for improving the system's dynamic and transient stability when applied to the grid.

[0073] From equation (3), we can also obtain the phase shift angle. It can affect the amplitude and phase of the fundamental frequency of the output voltage. Theoretically... The variation range is -π to π, allowing independent adjustment of the AC side voltage from 0 to the maximum output; more importantly, It can also control the phase of the output fundamental voltage (e.g.) Figure 1As shown Therefore, when used as a grid-connected converter, it is controlled... It can change the phase difference between the AC side voltage of the converter and the grid voltage, thereby controlling the active power while controlling the reactive power injected or consumed by the converter. This lays the foundation for implementing grid-connected power electronic equipment with grid support function by adopting control strategies such as grid-type control.

[0074] Figure 14 This is the per-unit value of the AC side voltage synthesized by the four channels in series in the embodiment (in words). = The output voltage when =0 is used as the reference. =0、 (When changing). Figure 15 This is the per-unit value of the AC side voltage synthesized by the four channels in series in the embodiment (in words). = The output voltage when =0 is used as the reference. , (When changing). Figure 16 This refers to the single harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. =0、 (When changing). Figure 17 This refers to the single harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. =0、 (When changing). Figure 18 This refers to the single harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. , (When changing). Figure 19 This refers to the total harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. =0、 (When changing). Figure 20 This refers to the total harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. =0、 (When changing). Figure 21 This refers to the total harmonic content (within the 50th order) of the AC side voltage synthesized by the four-channel series connection in the embodiment. , (When changing).

[0075] Figure 22 This diagram shows the AC side voltage waveforms of a converter synthesized from four channels under several typical control angles during off-grid inverter operation, as well as the AC port voltage waveforms after LC filtering (the natural resonant frequency of the filter is approximately 720Hz). From... Figure 22As can be seen, this converter has a high equivalent switching frequency and a high lowest harmonic frequency, meaning that a high sinusoidal AC output voltage waveform can be achieved using only a small filter. The figure also shows that the voltage amplitude and phase of the inverter output can be adjusted over a wide range by controlling the phase shift angle and modulation angle.

Claims

1. A multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter, characterized in that, include: N active neutral-point clamped ANPC three-phase converters and N three-phase phase-shifting transformers; Each ANPC three-phase converter consists of two series capacitors connected in parallel to the DC bus and three active neutral clamping bridge arms consisting of six power switches and their anti-parallel diodes. The four power switches and their anti-parallel diodes of each active clamping bridge arm are connected in series to form the main bridge arm, and the other two power switches and their diodes are connected in series to form the clamping bridge arm. The upper two and lower two power switches and their anti-parallel diodes of the main bridge arm form its upper bridge arm and lower bridge arm, respectively. The middle connection point of the upper bridge arm and the lower bridge arm is the AC side node of the main bridge arm. The two ends of the clamping bridge arm are connected to the middle nodes of the two power switches of the upper bridge arm and the two power switches of the lower bridge arm, respectively. The middle connection point of the two power switches of the clamping bridge arm is connected to the middle node of the series capacitor. In the ANPC converter, the outer switches of each main bridge arm (the upper switch of the upper bridge arm and the lower switch of the lower bridge arm) operate in a complementary switching mode, meaning that when one is on, the other is off. A dead time interval is maintained between their switching transitions to prevent shoot-through. The inner switches of each main bridge arm (the lower switch of the upper bridge arm and the upper switch of the lower bridge arm) operate in a complementary switching mode. The two switches of the clamping bridge arm operate in a complementary switching mode, with the upper switch of the clamping bridge arm switching synchronously with the lower switch of the lower bridge arm and the lower switch of the clamping bridge arm. The two power switches of the upper bridge arm of the main bridge arm use phase-shift control, meaning that the control signal of the lower switch has the same waveform as the control signal of the upper switch, but its phase leads or lags by a certain phase shift angle. ; Each power switch in the ANPC converter uses a single modulation angle. Switching control is performed, meaning the control signal consists of three switching pulses within each power frequency cycle. The phase at the first turn-on is taken as the reference (0 phase), corresponding to time 0. The turn-off point of the first switching pulse corresponds to phase lead. A certain modulation angle That is, t=( At time ω1 (ω1 = 2πf1, where f1 is the fundamental frequency of the AC side), the turn-on time of the second switching pulse is... / ω1, continues until the half-cycle point when π / ω1 is turned off, in ( The third activation at time ) / ω1, in / ω1 is turned off; The control signals for the power transistors of the three bridge arms within each ANPC converter are sequentially different. ; Each phase of each phase of the phase-shifting transformer includes one primary winding and two or one secondary winding. The three-phase primary windings are connected in a delta or star configuration to form a three-phase node on the primary side of the transformer. These three-phase nodes are connected to the corresponding AC side nodes of the ANPC converter. The secondary windings are connected in a zigzag configuration, so that the voltage phase formed after the zigzag connection has a certain phase difference from the voltage phase of the primary winding. The secondary sides of N phase-shifting transformers are connected in a star or delta configuration after being connected in series to form a three-phase AC side circuit. The phase difference between the fundamental voltage of the corresponding phase secondary side and the fundamental voltage of the primary side of the first three-phase phase-shifting transformer is lagging. The turns ratios of the primary and secondary windings of N phase-shifting transformers are such that the effective values ​​of the fundamental voltages of the primary side voltage and the secondary side voltage of the zigzag connection are equal or all in the same proportion, and the phase shift angles of the corresponding phases of the phase-shifting transformers differ sequentially. And the calculation determines it; The control signals of corresponding phases of N three-phase ANPC converters are sequentially phase-differentiated. This is to ensure that the secondary fundamental voltage of each three-phase transformer has the same phase.

2. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, In steady state, the phase shift angle and modulation angle of all ANPC converters are the same.

3. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, Each three-phase ANPC converter and its corresponding phase-shifting transformer constitute a power channel. Each channel can independently achieve bidirectional AC / DC conversion. The converter output line voltage of a channel contains only the fundamental frequency and harmonics with frequencies of 6k ± 1 (k = 1, 2, 3, ...) times the fundamental frequency. The relationship between the fundamental voltage amplitude and the average DC voltage is as follows: The relationship between the amplitude of the nth harmonic voltage and the average value of the DC voltage is as follows: .

4. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, Phase shift angle The range of variation is Modulation angle The range of variation is .

5. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, Phase shift angle and modulation angle Adjusting the ratio between the AC-side fundamental voltage and the DC-side voltage individually or / and simultaneously, i.e., for voltage amplitude control, phase shift angle. It is also used to adjust the phase of the output voltage of the ANPC converter. .

6. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, The AC side of N power channels is connected in series, and the DC side is connected in parallel, in series, in a combination of series and parallel, in a combination of independent, independent and parallel, and / or in series. When the DC side is not connected in parallel, appropriate measures are usually required to ensure that the average DC voltage of each channel is basically equal.

7. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, When N power channels are connected in series on the AC side and the DC side voltages are equal, the fundamental voltages of the output voltages of each channel are superimposed in phase, and the harmonics are attenuated or completely eliminated after superposition. That is, theoretically, the AC side voltage of the N-channel converter only contains 6Nk±1 (k=1,2,3,…) harmonics, and under the same phase shift angle and modulation angle, the relative relationship between the remaining harmonic content and the fundamental content is consistent with that of the single channel.

8. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, Its AC side series inductor L filter, inductor-capacitor LC filter or various low-pass filters with specific subharmonic traps to filter out harmonic components in AC side voltage or current, and the filter inductor directly connected to the AC side of the converter is an external inductor or directly utilizes the transformer leakage inductance and line inductance equivalent to the secondary side of the phase-shifting transformer. The inductor connected to the AC grid or other power sources on the AC side is an external inductor and / or line inductance.

9. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, One or more sets of windings with the same structure and connection method as the secondary windings of the aforementioned transformers, but with a certain ratio of turns, are added to each phase-shifting transformer. These sets of windings are connected in series to form another set of three-phase AC systems, which are used to connect AC loads or power supplies that require electrical isolation and have different voltage levels.

10. The multi-channel bidirectional AC / DC converter based on an active midpoint clamping converter as described in claim 1, characterized in that, The power switching transistors are silicon-based insulated-gate bipolar transistors, silicon or silicon carbide-based metal-oxide-semiconductor field-effect transistors, or other types of fully controllable semiconductor power devices.

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