Power supply equipment and its control methods, three-phase power supply system and its control methods

Abstract

The present invention provides a power supply device and its control method, a three-phase power supply system and its control method. The control method of the power supply device includes: configuring N modules to be connected in cascade, where N is a positive integer greater than or equal to 2, and each module includes a bidirectional switch unit and an uncontrolled rectifier bridge, and the bidirectional switch unit is connected to the midpoints of the two arms of the uncontrolled rectifier bridge; controlling each module to operate in one of three operating modes: modulation mode, bypass mode, and uncontrolled rectification mode. Among the N modules, m1 modules operate in the bypass mode, where 0 ≤ m1 ≤ M1; m2 modules operate in the uncontrolled rectification mode, where 0 ≤ m2 ≤ M2; m3 modules operate in the modulation mode and can achieve power factor correction, where 0 < m3; and m1 + m2 + m3 = N, M1 is the number of modules allowed to be bypassed by the system, and M2 is the number of modules allowed to perform uncontrolled rectification by the system. The present invention can reduce costs and improve reliability.

Description

Technical Field

[0001] This invention relates to power electronics technology, and in particular to a power supply device and its control method, a three-phase power supply system and its control method. Background Technology

[0002] Solid-state transformers (SSTs), also known as power electronic transformers, are devices that directly convert medium-voltage or high-voltage grid voltage into low-voltage output through power electronic circuits and high-frequency isolation transformers. They have significant advantages in size and light weight and have wide application value in power distribution networks, data centers, charging stations and other application scenarios.

[0003] Solid-state transformers (SSTs) typically consist of an AC-DC stage and a DC-DC stage. In current applications, such as data centers and charging stations, SSTs are usually used as unidirectional power supply systems, meaning power flows only from the grid to the load, not vice versa. In this unidirectional application, to save costs, the AC-DC stage often employs a PFC (Power Factor Correction) circuit.

[0004] like Figure 1A The diagram shows a single-phase PFC type SST, which consists of N modules, such as modules Cell 1 to Cell N. The inputs of the AC-DC stages of these modules (Cell 1 to Cell N) are cascaded, and the outputs of the DC-DC stages are connected in parallel. In unidirectional applications, the AC-DC stages typically employ a configuration such as... Figure 1B or Figure 1C or Figure 1D The PFC circuit shown is currently the industry standard for cost savings. Figure 1B The Totem-pole PFC circuit shown is an example. To improve system reliability, a bidirectional switch is usually added to the AC side, such as... Figure 1E The "bidirectional switch + Totem-pole" scheme shown means that when one module fails, the corresponding bidirectional switch of that module is turned on, the module is bypassed, and the other modules continue to operate stably.

[0005] The problem with existing unidirectional PFC-type SSTs is that, in order to improve system reliability, each module needs to be equipped with an additional bypass switch, which is also very expensive, increasing the cost of the entire system. Summary of the Invention

[0006] The purpose of this invention is to provide a power supply device and its control method, a three-phase power supply system and its control method, which can solve one or more defects of the prior art.

[0007] To achieve the above object, according to an embodiment of the present invention, the present invention provides a control method for a power supply device, which includes:

[0008] Configure N modules to be connected in cascade, where N is a positive integer greater than or equal to 2, and each of the modules includes a bidirectional switch unit and an uncontrolled rectifier bridge, and the bidirectional switch unit is connected to the midpoints of the two arms of the uncontrolled rectifier bridge;

[0009] Control each of the modules to operate in one of three operating modes: modulation mode, bypass mode, and uncontrolled rectification mode. Among the N modules, m1 modules operate in the bypass mode, where 0 ≤ m1 ≤ M1; m2 modules operate in the uncontrolled rectification mode, where 0 ≤ m2 ≤ M2; m3 modules operate in the modulation mode and can achieve power factor correction, where 0 < m3; where, m1 + m2 + m3 = N, M1 is the number of modules allowed to be bypassed by the system, and M2 is the number of modules allowed to perform uncontrolled rectification by the system.

[0010] In an embodiment of the present invention, the modules operating in the modulation mode adopt carrier phase shift modulation.

[0011] In an embodiment of the present invention, the carrier phases between the m3 modules operating in the modulation mode are sequentially different by 2π / m3.

[0012] In an embodiment of the present invention, the modules operating in the modulation mode also adopt current closed-loop and voltage feed-forward control; where, the calculation formula for the feed-forward voltage is:

[0013] [[ID=C19]]

[0014] V g is the grid voltage, i g is the grid current, sign is the sign function, V dch represents the output voltage of the hth module operating in the uncontrolled rectification mode.

[0015] In an embodiment of the present invention, when controlling each of the modules, it further includes:

[0016] Among the N modules, for the kth module, after the start of its control cycle, detect whether the kth module itself has a fault;

[0017] If there is no fault, the kth module selects to enter the modulation mode;

[0018] If there is a fault and the fault type is an open-circuit fault of the bidirectional switch unit, and when the number of modules already in the uncontrolled rectification mode among the N modules is less than M2, the kth module selects to enter the uncontrolled rectification mode, otherwise the system shuts down;

[0019] If there is a fault and the fault type is not a bidirectional switch unit open circuit fault, and the number of modules in the N modules that are already in the bypass mode is less than M1, the kth module will select to enter the bypass mode; otherwise, the system will shut down.

[0020] In one embodiment of the present invention, each module further includes a relay, which is connected in parallel with the bidirectional switching unit and located on the AC side of the module;

[0021] Specifically, when controlling each of the aforementioned modules:

[0022] If there is a fault in the k-th module and the fault type is a bidirectional switch unit open circuit fault, the relay is closed, causing the k-th module to enter the bypass mode.

[0023] In one embodiment of the present invention, the power supply device is cascaded and applied to a medium-voltage power grid system.

[0024] In one embodiment of the present invention, M1 is determined by the ratio of the grid voltage of the medium-voltage power grid system to the voltage that the port of a single module can withstand; M2 is determined by the degree of current distortion allowed by the system, and M2 does not exceed N / 2.

[0025] In one embodiment of the present invention, each module further includes a first capacitor connected in parallel to the DC terminal of the uncontrolled rectifier bridge; wherein, the bidirectional switching unit includes two IGBTs with body diodes connected in reverse series; or, the bidirectional switching unit includes two IGBTs without body diodes connected in parallel.

[0026] In one embodiment of the present invention, each module further includes a capacitor branch formed by a first capacitor and a second capacitor connected in series, the capacitor branch being connected in parallel with the uncontrolled rectifier bridge; wherein, the bidirectional switching unit includes a first IGBT, a second IGBT, a third IGBT, and a fourth IGBT connected in series, the first IGBT and the second IGBT being connected in reverse series to form a first switching assembly, the third IGBT and the fourth IGBT being connected in reverse series to form a second switching assembly, and the midpoint of the first switching assembly and the second switching assembly being connected to the midpoint of the first capacitor and the second capacitor.

[0027] In one embodiment of the present invention, each of the modules further includes a DC-DC converter module connected to the DC terminal of the uncontrolled rectifier bridge.

[0028] To achieve the above objectives, the present invention further provides a power supply device comprising: N cascaded modules, wherein N is a positive integer greater than or equal to 2, and each module includes a bidirectional switching unit and an uncontrolled rectifier bridge, wherein the bidirectional switching unit is connected to the midpoint of the two arms of the uncontrolled rectifier bridge; wherein each module is capable of operating in one of three operating modes: modulation mode, bypass mode, and uncontrolled rectifier mode, and the module operating in the modulation mode is capable of power factor correction.

[0029] In another embodiment of the present invention, each of the modules includes a first terminal and a second terminal, the first terminals of the N modules are cascaded, and the second terminals of the N modules are each connected to a DC-DC converter module.

[0030] In another embodiment of the invention, each module further includes a relay connected in parallel with the bidirectional switching unit.

[0031] In another embodiment of the invention, the power supply device is cascaded to a medium-voltage power grid system.

[0032] In another embodiment of the present invention, each of the modules further includes a first capacitor connected in parallel to the DC terminal of the uncontrolled rectifier bridge; wherein, the bidirectional switching unit includes two IGBTs with body diodes connected in reverse series; or, the bidirectional switching unit includes two IGBTs without body diodes connected in parallel.

[0033] In another embodiment of the present invention, each module further includes a capacitor branch formed by a first capacitor and a second capacitor connected in series, the capacitor branch being connected in parallel with the uncontrolled rectifier bridge; wherein, the bidirectional switching unit includes a first IGBT, a second IGBT, a third IGBT, and a fourth IGBT connected in series, the first IGBT and the second IGBT being connected in reverse series to form a first switching assembly, the third IGBT and the fourth IGBT being connected in reverse series to form a second switching assembly, and the midpoint of the first switching assembly and the second switching assembly being connected to the midpoint of the first capacitor and the second capacitor.

[0034] In another embodiment of the invention, among the N modules,

[0035] If any module is functioning correctly, that module will select to enter the modulation mode.

[0036] If any module has a fault and the fault type is a bidirectional switch unit open circuit fault, and the number of modules in the N modules that are already in the uncontrolled rectification mode is less than M2, then the module will enter the uncontrolled rectification mode; otherwise, the system will shut down.

[0037] If any module has a fault and the fault type is not a bidirectional switch unit open circuit fault, and the number of modules in the N modules that are already in the bypass mode is less than M1, then the module will enter the bypass mode; otherwise, the system will shut down.

[0038] To achieve the above objectives, the present invention further provides a three-phase power supply system, comprising:

[0039] The three power supply devices described above are connected to the three phases of a three-phase power supply via a Y-connection or a delta connection.

[0040] To achieve the above objectives, the present invention further provides a control method for a three-phase power supply system, comprising:

[0041] Configure three power supply devices as described above, and connect them to the three phases of a three-phase power supply via a Y-connection;

[0042] When a module operating in uncontrolled rectification mode exists in one of the power supply devices connected to a certain corresponding power supply device, zero-sequence voltage is injected into the AC ports of the other two power supply devices connected to the corresponding power supply devices.

[0043] The power supply device of the present invention utilizes N cascaded modules to form a cascaded circuit. Each module of the cascaded circuit is an HPFC circuit including a bidirectional switching unit and an uncontrolled rectifier bridge. By controlling the switches in the bidirectional switching unit, power factor correction (PFC) can be achieved, and multiplexing bypass switches can be implemented (i.e., the switches in the bidirectional switching unit can also have a bypass function), thereby reducing costs and improving reliability.

[0044] The present invention also proposes a three-phase power supply system based on the cascaded circuit, and a fault-tolerant control method applicable to the cascaded circuit. When a bidirectional switching unit of a certain module has an open circuit fault, zero-sequence voltage can be injected to make the current waveform good and improve the fault-tolerant operation capability of the system.

[0045] This invention offers significant advantages by applying the cascaded circuit to a medium-voltage power grid system, and by providing a bypass function to the switch in the bidirectional switching unit.

[0046] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. Attached Figure Description

[0047] The above and other features and advantages of the present invention will become more apparent from a detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0048] Figure 1A A schematic diagram of the structure of a unidirectional PFC type SST in an existing power supply system;

[0049] Figures 1B-1D They are respectively Figure 1A A schematic diagram of the PFC circuit used in the AC-DC stage;

[0050] Figure 1E for Figure 1A A schematic diagram of the PFC circuit using the "bidirectional switch + Totem-pole" scheme adopted in the AC-DC stage;

[0051] Figure 2 This is a schematic diagram of the circuit structure of the power supply device according to the first preferred embodiment of the present invention;

[0052] Figure 3 This is a flowchart illustrating the control method of the power supply device of the present invention;

[0053] Figure 4 This is a schematic diagram of the current closed-loop and voltage feedforward control of the module in modulation mode of the present invention.

[0054] Figure 5 This is a schematic diagram of the module fault-tolerant processing flow of the power supply device of the present invention;

[0055] Figure 6 This is a circuit structure diagram of a power supply device according to a second preferred embodiment of the present invention, wherein each module further includes a DC-DC converter module;

[0056] Figure 7 This is a schematic diagram of the simulation waveforms of each module of the power supply device based on the second preferred embodiment of the present invention from the modulation mode to the bypass mode.

[0057] Figure 8 This is a schematic diagram of the simulation waveforms of each module of the power supply device based on the second preferred embodiment of the present invention, from the modulation mode to the uncontrolled rectification mode.

[0058] Figure 9 This is a circuit structure diagram of a power supply device according to a third preferred embodiment of the present invention, wherein each module also has a relay;

[0059] Figure 10 This is a circuit structure diagram of a power supply device according to a fourth preferred embodiment of the present invention, wherein the bidirectional switching unit in each module includes four IGBTs connected in series;

[0060] Figure 11 This is a schematic diagram of the structure of a three-phase power supply system based on the power supply device of the present invention;

[0061] Figure 12This is a schematic diagram illustrating how, in the three-phase power supply system of the present invention, when a module operating in uncontrolled rectification mode exists in one phase power supply device, zero-sequence voltage can be injected into the AC ports of the other two phase power supply devices to achieve current PFC control function.

[0062] Figure 13 This is a schematic diagram illustrating the simulation effect of a three-phase power supply system based on the present invention. Detailed Implementation

[0063] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that the invention will be thorough and complete, and the concept of the exemplary embodiments will be fully conveyed to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed description will be omitted.

[0064] In describing the elements / components / etc. described and / or illustrated herein, the terms “a,” “an,” “the,” “the,” and “at least one” are used to indicate the presence of one or more elements / components / etc. The terms “comprising,” “including,” and “having” are used to indicate an open-ended inclusion and to mean that additional elements / components / etc. may exist in addition to those listed. Relative terms, such as “upper” or “lower,” may be used in the embodiments to describe the relative relationship of one component of the icon to another component. It is understood that if the device of the icon is flipped so that it is upside down, the component described as being on the “upper” side will become the component on the “lower” side. Furthermore, the terms “first,” “second,” etc., in the claims are used only as illustrative marks and are not intended to limit the number of objects to which they apply.

[0065] like Figure 2 The diagram illustrates the circuit structure of a power supply device 100 according to a first preferred embodiment of the present invention. The power supply device 100 can be cascaded into a medium-voltage power grid system, for example, but the invention is not limited thereto. Figure 2 In the illustrated embodiment, the power supply device 100 may include N cascaded modules 10, such as modules Cell 1, Cell 2, ..., Cell N shown in the figure, where N is a positive integer greater than or equal to 2. Each module 10 may include a first terminal 101 and a second terminal 102. The first terminals 101 of the N modules 10 are cascaded and may be further connected to a power source 20. The power source 20 may be, for example, but is not limited to, an AC power grid, and may have a voltage V. g The second terminal 102 of the N modules 10 can be, for example, a DC output terminal and can be connected to a DC load, and each DC output terminal can have a voltage V. dc1 Vdc2 ... V dcN .

[0066] The specific circuits of each module in this invention are described in detail below using module Cell 1 as an example. In this invention, each module 10 is an HPFC circuit and includes a bidirectional switching unit 11 and an uncontrolled rectifier bridge 12. The bidirectional switching unit 11 connects the midpoints N1 and N2 of the two arms 121 and 122 of the uncontrolled rectifier bridge 12. In this embodiment, the bidirectional switching unit 11 may, for example, include two IGBTs with body diodes connected in reverse series, i.e., switches Q1 and Q2. However, it is understood that in other embodiments, the bidirectional switching unit 11 may also include two IGBTs without body diodes connected in parallel, which is not intended to limit the invention. In other embodiments, each module 10 may also include a first capacitor 13, which may be connected in parallel to the DC terminal of the uncontrolled rectifier bridge 12. The circuit structures of modules Cell 2, ..., Cell N are the same as those of module Cell 1 and will not be described again here.

[0067] In this invention, because the circuit formed by adding a bidirectional switching unit 11 between the midpoints N1 and N2 of the two arms 121 and 122 of the uncontrolled rectifier bridge 12 resembles the letter H, and this circuit can achieve power factor correction (PFC), it can be called an "HPFC circuit". This invention allows adjustment of the switches in the bidirectional switching unit 11 (e.g., ...) Figure 2 The duty cycle of switches Q1 and Q2 in the illustrated embodiment enables the HPFC circuit to achieve power factor correction (PFC).

[0068] In particular, each of the modules 10 is capable of operating in one of three modes: modulation mode, bypass mode, and uncontrolled rectification mode. Specifically, in modulation mode, the bidirectional switching unit 11 and the uncontrolled rectifier bridge 12 operate simultaneously, enabling power factor correction (PFC); in bypass mode, the bidirectional switching unit 11 of the module 10 is turned on to bypass the uncontrolled rectifier bridge 12; and in uncontrolled rectification mode, the bidirectional switching unit 11 of the module 10 is turned off, with only the uncontrolled rectifier bridge 12 performing rectification.

[0069] The power supply device of this invention adopts an HPFC circuit structure, which multiplexes the bypass function with the PFC function, reducing costs compared with existing technologies such as "bidirectional switch + Totem-pole"; and the uncontrolled rectifier bridge has no shoot-through problem, improving system reliability; at the same time, the introduction of the uncontrolled rectifier mode enhances the fault-tolerant control capability of the system.

[0070] Furthermore, in combination Figure 2 ,like Figure 3 As shown, it shows the control method 300 of the power supply device of the present invention, which mainly includes:

[0071] Step S31: Configure N modules 10 to be connected in cascade, where N is a positive integer greater than or equal to 2, and each module 10 includes a bidirectional switch unit 11 and an uncontrolled rectifier bridge 12. The bidirectional switch unit 11 is connected to the midpoints N1 and N2 of the two bridge arms 121 and 122 of the uncontrolled rectifier bridge 12.

[0072] Step S32: Control each module 10 to operate in one of three operating modes: modulation mode, bypass mode, and uncontrolled rectification mode. Among the N modules 10, m1 modules operate in the bypass mode, where 0 ≤ m1 ≤ M1; m2 modules operate in the uncontrolled rectification mode, where 0 ≤ m2 ≤ M2; m3 modules operate in the modulation mode and can achieve power factor correction, where 0 < m3; where m1 + m2 + m3 = N, M1 is the number of modules allowed to be bypassed by the system, and M2 is the number of modules allowed to be uncontrolled rectified by the system.

[0073] In Figure 2 In the shown embodiment, M1 can be determined, for example, by the ratio of the grid voltage of the medium-voltage power grid system to the port voltage of a single module. For example, when the total grid voltage is 10 kV, assuming the rated voltage of each module is 1 kV and there are N = 12 module cascades in the system, the number of modules allowed to be bypassed is M1 = 2. M2 can be determined, for example, by the degree of current distortion allowed by the system, and M2 does not exceed N / 2.

[0074] By controlling the switches in the bidirectional switch unit 11, the present invention can achieve power factor correction (PFC) and can also achieve multiplexing of the bypass switch (that is, the switches in the bidirectional switch unit 11 can also have the function of bypass). The bypass function and the PFC function are multiplexed. Compared with the prior art "bidirectional switch + Totem-pole" (as Figure 1E shown), etc., the cost can be reduced and the reliability can be improved.

[0075] In the present invention, further, the modules operating in the modulation mode can also eliminate the influence of the port voltage of the modules in the uncontrolled rectification mode through current closed-loop and voltage feed-forward control to achieve the PFC function. For example, the current closed-loop and voltage feed-forward control as shown in Figure 4 can be adopted. In the figure, I dref is the d-axis current reference, which reflects the active power and can be set according to needs; cosθ A is the cosine function of the grid voltage angle, I gref is the AC current reference, which is synchronized with the grid voltage; I g is the grid current feedback, P is the current proportional controller, Vbkref V is the reference value for the modulation voltage of the kth module in modulation mode. ff This is voltage feedforward. Wherein, the feedforward voltage V... ff The calculation formula is:

[0076]

[0077] Among them, V g For grid voltage; i g For grid current; sign is the sign function, i.e., when i g When >0, sign(i) g )=1, when i g When <0, sign(i) g )=-1, when i g When = 0, sign(i g ) = 0; V dch This represents the output voltage of the h-th module in uncontrolled rectification mode. In the formula, the subscript h indicates that the h-th module is in uncontrolled rectification mode, and there are a total of m2 modules in uncontrolled rectification mode. The numerator is the grid voltage minus the total port voltage of the m2 modules in uncontrolled rectification mode. The denominator N-m1-m2 represents the number of modules in modulation mode, i.e., m3, meaning that the total voltage corresponding to the numerator is evenly distributed among the modules in modulation mode.

[0078] Furthermore, all modules operating in modulation mode can employ carrier phase-shift modulation. Specifically, this can be achieved through the modulation voltage reference value V. bkref Compared with the carrier wave, a bidirectional switching drive signal is generated. Furthermore, for (N-m1-m2) modules operating in modulation mode, the carrier phases between modules can successively differ by 2π / (N-m1-m2). In other words, for m3 modules operating in modulation mode, the carrier phases between them can successively differ by 2π / m3.

[0079] Furthermore, the present invention also provides a fault-tolerant control method for a power supply device based on a cascaded HPFC circuit. For example... Figure 5As shown, it shows the fault-tolerant control processing flow during the control cycle of the k-th module. Among the N modules, for the k-th module, after the start of its control cycle, it detects whether there are any faults in the k-th module itself, such as faults like DC_Link overvoltage and module overtemperature. If there are no faults, the k-th module selects to enter the modulation mode. If there are faults, they are classified and processed according to the fault situation: If it is an open-circuit fault of the bidirectional switch unit, it is necessary to judge the number of modules in the uncontrolled rectification mode in the system at this time. When the number of modules m2 in the uncontrolled rectification mode among the N modules is less than M2, the k-th module can choose to enter the uncontrolled rectification module, and the number of modules in the uncontrolled rectification mode increases by 1 (i.e., m2 + 1), otherwise the system shuts down. If it is not an open-circuit fault of the bidirectional switch unit, it is necessary to judge the number of modules in the bypass mode in the system at this time. When the number of modules m1 in the bypass mode among the N modules is less than M1, the k-th module can choose to enter the bypass mode, and the number of modules in the bypass mode increases by 1 (i.e., m1 + 1), otherwise the system should shut down.

[0080] As Figure 6 shown, it shows the circuit structure of the power supply device 100-1 according to the second preferred embodiment of the present invention, which can form a single-phase SST for example. In this embodiment, each module 10 in the power supply device 100-1 may further include a DC-DC conversion module 14, which is connected to the DC terminal of the uncontrolled rectifier bridge 12, and the outputs of the DC-DC conversion modules 14 are connected in parallel to form the total port voltage Vo output.

[0081] For this embodiment, when there is an open-circuit fault in the bidirectional switch unit 11 of the module 10 itself, the front-stage AC-DC (such as the uncontrolled rectifier bridge 12) of the module 10 is in the uncontrolled rectification mode, and DC-Link voltage equalization control can be performed through the rear-stage DC-DC (such as the DC-DC conversion module 14). Figure 7 and Figure 8 The simulation conditions for the simulation waveforms of the single-phase SST embodiment based on the present invention: The single-phase SST includes 4 modules in cascade, that is, it includes modules Cell 1 to Cell 4, where it is simulated that the 4th module Cell 4 has a fault and bypasses; the peak value of the grid voltage is 4500V; Vdc = 1580V; Vo = 980V; the DC-DC conversion module 14 is an LLC converter, and its transformer turns ratio n:1 = 3:2; the capacitance value Cdc of the first capacitor 13 is 100 μF; the capacitance value Co of the output capacitor is 5 μF; the switching frequency of the AC-DC (i.e., the HPFC circuit) is 5 kHz, the carriers of the 4 modules are mutually staggered by 90 degrees, the resonant frequency of the LLC converter is 100 kHz, and fixed switching frequency control; the output of the LLC converter is connected to a 20Ω resistive load.

[0082] Figure 7The waveform shown is a simulation of the transition from modulation mode to bypass mode based on the second preferred embodiment of the present invention. The waveform shows that around 100ms, module Cell 4 enters bypass mode, for example, due to a fault. Because module Cell 4 is out of operation, its DC-Link voltage drops, while the DC-Link voltages of other modules (Cell 1 to Cell 3) remain relatively stable and operate at a uniform voltage. Other current and voltage waveforms are generally normal. This demonstrates the feasibility of switching from normal modulation mode to bypass mode using the structure and method of the present invention.

[0083] Figure 8 The simulation waveforms show the transition from modulation mode to uncontrolled rectification mode based on the second preferred embodiment of the present invention. The waveforms show that around 100ms, module Cell4 enters uncontrolled rectification mode, for example, due to a bidirectional switch open-circuit fault. Since module Cell4 in uncontrolled rectification mode stops PWM modulation, the bridge arm voltage changes from a high-frequency PWM wave to a low-frequency square wave. Meanwhile, the DC-Link voltages of all modules (Cell 1 to Cell 4) are basically able to operate stably with equal voltage distribution. Other current and voltage waveforms are also basically normal. This demonstrates the feasibility of switching from normal modulation mode to uncontrolled rectification mode using the structure and method of the present invention.

[0084] like Figure 9 The diagram illustrates the circuit structure of the power supply device 100-2 according to a third preferred embodiment of the present invention. In this embodiment, a relay 15 is further provided on the AC side of each module 10. When an open-circuit fault occurs in the switch (e.g., IGBT) of the bidirectional switching unit 11, the relay 15 can be closed to put the corresponding module into bypass mode. Using the relay for bypass has lower losses than using the IGBT in the bidirectional switching unit for bypass. Therefore, when controlling each module, for the k-th module, if there is a fault and the fault type is an open-circuit fault in the bidirectional switching unit, the relay can preferably be closed to put the k-th module into bypass mode.

[0085] like Figure 10 The diagram illustrates the circuit structure of a power supply device 100-3 according to a fourth preferred embodiment of the present invention. In this embodiment, each module 10 further includes a capacitor branch 13' formed by a first capacitor 131 and a second capacitor 132 connected in series. The capacitor branch 13' is connected in parallel to the DC terminal of the uncontrolled rectifier bridge 12, wherein the first capacitor 131 has a voltage V across it. dclp The second capacitor 132 has a voltage V across its terminals. dclnFurthermore, each bidirectional switching unit 11 in module 10 may include a first IGBT 11-11, a second IGBT 11-12, a third IGBT 11-21, and a fourth IGBT 11-22 connected in series. The first IGBT 11-11 and the second IGBT 11-12 are connected in reverse series to form a first switching assembly 11-1, and the third IGBT 11-21 and the fourth IGBT 11-22 are connected in reverse series to form a second switching assembly 11-2. The midpoint N3 of the first switching assembly 11-1 and the second switching assembly 11-2 is connected to the midpoint N4 of the first capacitor 131 and the second capacitor 132. Thus, two IGBTs connected in series can be used instead of... Figure 2 An IGBT in the illustrated embodiment can be formed as follows: Figure 10 The three-level HPFC embodiment shown can reduce the withstand voltage requirement of a single IGBT.

[0086] like Figure 11 The diagram illustrates the structure of a three-phase power supply system 200 based on the power supply device of the present invention. The three-phase power supply system 200 includes three power supply devices 100A, 100B, and 100C, which can be connected to the three phases of a three-phase power supply 30 via a Y-connection or a delta connection. Figure 11 In the illustrated embodiment, the circuit structure of the three power supply devices 100A, 100B, and 100C can be, for example, as follows: Figure 6 The circuit structure shown, and the three power supply devices 100A, 100B and 100C are connected to the three phases (V) of the three-phase power supply 30. gA V gB V gC The three-phase SST is formed by a Y-connection. It is understood that, in other embodiments, the circuit structure of the three power supply devices 100A, 100B, and 100C can also be, for example... Figure 2 , Figure 9 or Figure 10 The structures shown, or other circuit structures derived from variations of the present invention, are not intended to limit the scope of the invention.

[0087] In this invention, for three-phase power supply systems with Y-connection or delta connection, the fault-tolerant control logic of each phase is the same as that of single-phase SST, and will not be described again here.

[0088] In this invention, for a Y-connected three-phase power supply system, when a module is operating in uncontrolled rectification mode, the zero-sequence voltage injection method can be used to achieve current PFC control. More specifically, when a module operating in uncontrolled rectification mode exists in one phase of the power supply device, zero-sequence voltage can be injected into the AC ports of the other two phases of the power supply device. A schematic diagram of zero-sequence voltage injection is shown below. Figure 12As shown, assuming that one module in phase A is in uncontrolled rectification mode, the modulation wave voltage of that phase cannot be infinitely close to zero near the zero crossing. In order to ensure that the current is not distorted, the same voltage, namely zero-sequence voltage, needs to be injected into the other two phases so that the line voltage does not contain harmonics.

[0089] Based on the present invention, as follows Figure 11 The simulation results of the three-phase SST embodiment shown are as follows: Figure 13 As shown. In this embodiment, the simulation conditions are: 3-phase SST, 4 modules per phase, where the bidirectional switching unit of the 4th module of phase C enters uncontrolled rectification mode after an open-circuit fault occurs at 15ms; between 15ms and 20ms, there is a transition process of fault detection and mode switching, during which the carrier phase shift angle and control strategy cannot be switched in time, resulting in a small segment of current-distorted waveform; afterwards, after current closed-loop control that takes into account the influence of the uncontrolled rectification port voltage and injects zero-sequence voltage as provided in this invention, the current waveform returns to normal. This simulation effect shows that injecting zero-sequence voltage into the bridge arm voltage can improve the THD of the circuit waveform and allow the module to operate in uncontrolled rectification mode.

[0090] In summary, the power supply device and system based on a cascaded HPFC circuit proposed in this invention can be composed of a bidirectional switching unit and an uncontrolled rectifier bridge. The switches in the bidirectional switching unit can multiplex bypass and PFC functions, reducing costs compared to existing solutions such as "bidirectional switch + Totem-pole". The uncontrolled rectifier bridge of this invention eliminates the shoot-through problem, improving reliability.

[0091] This invention also proposes a fault-tolerant control method applicable to the cascaded HPFC circuit and a three-phase SST based on the cascaded HPFC circuit. When a bidirectional switching unit of one of the modules experiences an open-circuit fault, it can select to enter either an uncontrolled rectification mode or a bypass mode. The introduction of the uncontrolled rectification mode can enhance the fault-tolerant control capability of the system.

[0092] For a Y-connected three-phase power supply system, when a module is running in uncontrolled rectification mode, this invention can also use the zero-sequence voltage injection method to realize the current PFC control function, so that the current waveform is good, thereby further improving the fault-tolerant operation capability of the system and making this invention more advantageous.

[0093] Exemplary embodiments of the present invention have been specifically illustrated and described above. It should be understood that the present invention is not limited to the disclosed embodiments; rather, the present invention is intended to cover various modifications and equivalent arrangements contained within the spirit and scope of the appended claims.

Claims

1. A control method for a power supply device, characterized in that, Comprising: Configuring N modules to be cascaded, where N is a positive integer greater than or equal to 2, and each of the modules includes a bidirectional switch unit and an uncontrolled rectifier bridge, and the bidirectional switch unit is connected to the midpoints of the two arms of the uncontrolled rectifier bridge; Controlling each of the modules to operate in one of three operating modes: a modulation mode, a bypass mode, and an uncontrolled rectification mode. Among the N modules, m1 modules operate in the bypass mode, where 0 ≤ m1 ≤ M1; m2 modules operate in the uncontrolled rectification mode, where 0 ≤ m2 ≤ M2; m3 modules operate in the modulation mode and can achieve power factor correction, where 0 < m3; and m1 + m2 + m3 = N, M1 is the number of modules that the system allows to be bypassed, and M2 is the number of modules that the system allows to perform uncontrolled rectification; In the module operating in the modulation mode, the bidirectional switch unit and the uncontrolled rectifier bridge operate simultaneously to perform power factor correction; in the module operating in the bypass mode, the bidirectional switch unit is turned on to bypass the uncontrolled rectifier bridge; in the module operating in the uncontrolled rectification mode, the bidirectional switch unit is turned off, and only the uncontrolled rectifier bridge performs rectification operation.

2. The control method for the power supply device according to claim 1, characterized in that, The module operating in the modulation mode uses carrier phase shift modulation.

3. The control method for the power supply device according to claim 2, characterized in that, The carrier phases between the m3 modules operating in the modulation mode differ from each other by 2π / m3 in sequence.

4. The control method for the power supply device according to claim 1, characterized in that, The module operating in the modulation mode also uses current closed-loop and voltage feedforward control; where the calculation formula for the feedforward voltage is: V g For grid voltage, i g V represents the grid current, sign is the sign function, and V dch This represents the output voltage of the h-th module in uncontrolled rectification mode.

5. The control method for the power supply device according to claim 1, characterized in that, When controlling each of the modules, it further includes: Among the N modules, for the kth module, after the start of its control period, it is detected whether the kth module itself has a fault; If there is no fault, the kth module selects to enter the modulation mode; If there is a fault and the fault type is an open-circuit fault of the bidirectional switch unit, and when the number of modules that have already been in the uncontrolled rectification mode among the N modules is less than M2, the kth module selects to enter the uncontrolled rectification mode, otherwise the system stops; If there is a fault and the fault type is not an open-circuit fault of the bidirectional switch unit, and when the number of modules that have already been in the bypass mode among the N modules is less than M1, the kth module selects to enter the bypass mode, otherwise the system stops.

6. The control method of the power supply device according to claim 5, wherein: Each of the modules further includes a relay, which is connected in parallel with the bidirectional switch unit and is located on the AC side of the module; Wherein, when controlling each of the modules: For the kth module, if there is a fault and the fault type is an open-circuit fault of the bidirectional switch unit, the relay is closed, so that the kth module enters the bypass mode.

7. The control method for the power supply device according to claim 1, characterized in that, The power supply device is cascaded and applied to a medium-voltage power grid system.

8. The control method for the power supply device according to claim 7, characterized in that, M1 is determined by the ratio of the grid voltage of the medium-voltage power grid system to the port voltage of a single module; M2 is determined by the allowable current distortion degree of the system, and M2 does not exceed N / 2.

9. The control method of the power supply device according to claim 1, wherein: Each of the modules further includes a first capacitor, which is connected in parallel to the DC terminal of the uncontrolled rectifier bridge; The bidirectional switching unit comprises two IGBTs with body diodes connected in reverse series; or, the bidirectional switching unit comprises two IGBTs without body diodes connected in parallel.

10. The control method for the power supply device according to claim 1, characterized in that, Each module further includes a capacitor branch formed by connecting a first capacitor and a second capacitor in series, and the capacitor branch is connected in parallel with the uncontrolled rectifier bridge; The bidirectional switching unit includes a first IGBT, a second IGBT, a third IGBT, and a fourth IGBT connected in series. The first IGBT and the second IGBT are connected in reverse series to form a first switching assembly, and the third IGBT and the fourth IGBT are connected in reverse series to form a second switching assembly. The midpoint of the first switching assembly and the second switching assembly is connected to the midpoint of the first capacitor and the second capacitor.

11. The control method for the power supply device according to claim 1, characterized in that, Each of the modules further includes a DC-DC converter module connected to the DC terminal of the uncontrolled rectifier bridge.

12. A power supply device, characterized in that, include: N modules are cascaded together, where N is a positive integer greater than or equal to 2, and each module includes a bidirectional switching unit and an uncontrolled rectifier bridge, wherein the bidirectional switching unit is connected to the midpoint of the two arms of the uncontrolled rectifier bridge; Each of the modules can operate in one of three modes: modulation mode, bypass mode, and uncontrolled rectification mode. The module operating in the modulation mode can achieve power factor correction. In the modulation mode, the bidirectional switching unit and the uncontrolled rectifier bridge in the module operate simultaneously to perform power factor correction; in the bypass mode, the bidirectional switching unit in the module is turned on to bypass the uncontrolled rectifier bridge; in the uncontrolled rectification mode, the bidirectional switching unit in the module is turned off, and only the uncontrolled rectifier bridge performs rectification.

13. The power supply device according to claim 12, characterized in that, Each of the modules includes a first terminal and a second terminal. The first terminals of the N modules are cascaded, and the second terminals of the N modules are each connected to a DC-DC converter module.

14. The power supply device according to claim 12 or 13, characterized in that, Each of the modules further includes a relay connected in parallel with the bidirectional switching unit.

15. The power supply device according to claim 12, characterized in that, The power supply device is cascaded to a medium-voltage power grid system.

16. The power supply device according to claim 12, characterized in that, Each of the modules further includes a first capacitor, which is connected in parallel to the DC terminal of the uncontrolled rectifier bridge; The bidirectional switching unit comprises two IGBTs with body diodes connected in reverse series; or, the bidirectional switching unit comprises two IGBTs without body diodes connected in parallel.

17. The power supply device according to claim 12, characterized in that, Each module further includes a capacitor branch formed by connecting a first capacitor and a second capacitor in series, and the capacitor branch is connected in parallel with the uncontrolled rectifier bridge; The bidirectional switching unit includes a first IGBT, a second IGBT, a third IGBT, and a fourth IGBT connected in series. The first IGBT and the second IGBT are connected in reverse series to form a first switching assembly, and the third IGBT and the fourth IGBT are connected in reverse series to form a second switching assembly. The midpoint of the first switching assembly and the second switching assembly is connected to the midpoint of the first capacitor and the second capacitor.

18. The power supply device according to claim 12, characterized in that, In the N modules, If any module is functioning correctly, that module will select to enter the modulation mode. If any module has a fault and the fault type is a bidirectional switch unit open circuit fault, and the number of modules in the N modules that are already in the uncontrolled rectification mode is less than M2, then the module will enter the uncontrolled rectification mode; otherwise, the system will shut down. If any module has a fault and the fault type is not a bidirectional switch unit open circuit fault, and the number of modules in the N modules that are already in the bypass mode is less than M1, then the module will enter the bypass mode; otherwise, the system will shut down.

19. A three-phase power supply system, characterized in that, include: The three power supply devices as described in any one of claims 12 to 18 are connected to the three phases of a three-phase power supply via a Y-connection or a delta connection.

20. A control method for a three-phase power supply system, characterized in that, include: Configure three power supply devices as described in any one of claims 12 to 18, and connect them to the three phases of a three-phase power supply via a Y-connection; When a module operating in uncontrolled rectification mode exists in one of the power supply devices connected to a certain corresponding power supply device, zero-sequence voltage is injected into the AC ports of the other two power supply devices connected to the corresponding power supply devices.

Images