A single-stage multi-path dc access converter and a control method thereof

Abstract

The application provides a single-stage multi-path direct current access converter and a control method thereof. Each direct current side conversion circuit is connected to a first side of an alternating current side conversion circuit through a corresponding primary winding of a multi-winding transformer. Since the equivalent impedance of each primary winding of the multi-winding transformer is greater than the equivalent impedance of a secondary winding, each direct current side conversion circuit can be independently controlled, and multi-path direct current access can be realized. Furthermore, each direct current side conversion circuit is used to realize AC / DC conversion, the turn ratio of the primary winding and the secondary winding of the multi-winding transformer can realize the corresponding transformation ratio of the primary voltage and the secondary voltage, the alternating current side conversion circuit can realize AC frequency conversion, and single-stage conversion can be realized, thereby improving conversion efficiency.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a single-stage multi-channel DC-DC converter and its control method. Background Technology

[0002] Photovoltaic inverters, or microinverters, have gained widespread attention due to their elimination of the bottleneck effect of series-connected photovoltaic modules and their ability to achieve module-level operation, maintenance, and MPPT (Maximum Power Point Tracking). The basic structure involves one inverter connecting to one photovoltaic module, which can be called a one-to-one inverter. To further reduce the use of connectors, one-to-many inverters have been developed based on the one-to-one inverter. Considering cost and practicality, one-to-two and one-to-four inverters are the most common, meaning one inverter connects to two or four photovoltaic modules.

[0003] However, in current multi-split inverters based on integrated transformers, the decoupling of power transmission between photovoltaic modules is mostly achieved through software algorithms. As the number of ports increases, power decoupling becomes increasingly complex and difficult, making it impossible to expand the number of ports further. Summary of the Invention

[0004] In view of this, this application provides a single-stage multi-channel DC-DC converter and its control method, which adopts hardware power decoupling, is simple to implement, does not increase the complexity of software algorithms, and thus makes it easier to further expand the number of ports.

[0005] To achieve the above objectives, this application provides the following technical solution:

[0006] The first aspect of this application provides a single-stage multi-channel DC-DC converter, comprising: a multi-winding transformer, an AC-side conversion circuit, and at least two DC-side conversion circuits; wherein...

[0007] The AC side of each DC-side conversion circuit is connected to the corresponding primary winding of the multi-winding transformer.

[0008] The secondary winding of the multi-winding transformer is connected to the first side of the AC-side conversion circuit;

[0009] Each of the DC-side conversion circuits is used to invert the DC power it receives, or to rectify the AC power it receives.

[0010] The AC-side conversion circuit is used for AC frequency conversion;

[0011] The equivalent impedance of each primary side of the multi-winding transformer is greater than the equivalent impedance of the secondary side.

[0012] Optionally, the equivalent leakage inductance of each primary side of the multi-winding transformer is greater than the equivalent leakage inductance of the secondary side.

[0013] Optionally, the primary-side equivalent leakage inductance originates from: the primary-side leakage inductance of the multi-winding transformer, or the primary-side leakage inductance of the multi-winding transformer and the inductance integrated therewith.

[0014] Optionally, the equivalent leakage inductance of the secondary side is zero; or,

[0015] The equivalent leakage inductance on the secondary side originates from: the leakage inductance on the secondary side of the multi-winding transformer, or the leakage inductance on the secondary side of the multi-winding transformer and the inductance integrated therewith.

[0016] Optionally, it also includes an impedance element disposed between the AC side and the corresponding primary winding of each of the DC-side conversion circuits.

[0017] Optionally, the impedance element includes: an inductor, or an inductor and a capacitor.

[0018] Optionally, it also includes an impedance element disposed between the secondary winding and the first side of the AC-side conversion circuit.

[0019] Optionally, the multi-winding transformer is a single-phase multi-winding transformer or a three-phase multi-winding transformer.

[0020] Optionally, in the three-phase multi-winding transformer, the primary windings of each phase of each group of three-phase primary windings are respectively used to connect the corresponding phase of the AC side of the DC-side conversion circuit, and their other ends are all connected to the reference ground.

[0021] Each phase secondary winding of the three-phase multi-winding transformer is connected at both ends to the corresponding phase on the first side of the AC-side conversion circuit, and the middle taps are connected.

[0022] Optionally, when the multi-winding transformer is a single-phase multi-winding transformer, the DC-side conversion circuit is a half-bridge circuit or a full-bridge circuit.

[0023] When the multi-winding transformer is a three-phase multi-winding transformer, the DC-side conversion circuit is a three-phase bridge circuit.

[0024] Optionally, the AC-side conversion circuit is either a frequency conversion circuit or a matrix conversion circuit.

[0025] Optionally, when the multi-winding transformer is a single-phase multi-winding transformer:

[0026] The AC-side conversion circuit is a half-bridge conversion circuit, with its switch bridge arm and capacitor bridge arm connected in parallel between the two ends of the second side of the AC-side conversion circuit; the switch bridge arm includes two bidirectional switches that serve as the upper and lower half-bridge arms respectively, and the capacitor bridge arm includes two capacitor modules connected in series with the same capacitance; the midpoint of the switch bridge arm and the midpoint of the capacitor bridge arm serve as the two ends of the first side of the AC-side conversion circuit respectively; or,

[0027] The AC-side conversion circuit is a full-bridge conversion circuit, wherein its two switching bridge arms are connected in parallel between the two ends of the second side of the AC-side conversion circuit; the midpoints of the two switching bridge arms respectively serve as the two ends of the first side of the AC-side conversion circuit; or,

[0028] The AC-side conversion circuit is a three-phase bridge conversion circuit, in which the three switch bridge arms are connected in parallel between the two ends of the first side of the AC-side conversion circuit; the midpoints of the three switch bridge arms are respectively used as the ends of the second side of the AC-side conversion circuit.

[0029] Optionally, when the multi-winding transformer is a three-phase multi-winding transformer, the AC side conversion circuit includes: three conversion circuits;

[0030] Each of the two sides of the aforementioned conversion circuit serves as the corresponding phase on both sides of the AC-side conversion circuit.

[0031] Optionally, each of the aforementioned conversion circuits includes: a rectifier bridge and a half-bridge circuit;

[0032] The AC side of the rectifier bridge serves as the first phase of the AC-side conversion circuit, the DC side of the rectifier bridge is connected to both ends of the half-bridge circuit, and the midpoint of the half-bridge circuit serves as the second phase of the AC-side conversion circuit.

[0033] Optionally, it further includes: an AC-side filter circuit disposed on the second side of the AC-side conversion circuit; and / or,

[0034] Each DC-side filter circuit is respectively set on the DC side of each DC-side conversion circuit.

[0035] A second aspect of this application provides a control method for a single-stage multiplex DC-DC converter, applied to a single-stage multiplex DC-DC converter as described in any of the first aspects above, the control method comprising:

[0036] Obtain the electrical parameters on both sides of the single-stage multi-channel DC-DC converter and determine the power transmission direction required by the single-stage multi-channel DC-DC converter;

[0037] Based on the electrical parameters on both sides and the power transmission direction, determine the switching frequency and inner and outer phase shift angles of the single-stage multi-channel DC-DC converter;

[0038] Based on the switching frequency and the internal and external phase shift angles, control signals for each switch of the single-stage multi-channel DC-DC converter are generated and output to realize phase shift control of the single-stage multi-channel DC-DC converter.

[0039] Optionally, the switching frequency is the frequency at which the primary impedance of the multi-winding transformer in the single-stage multi-channel DC-DC converter becomes inductive.

[0040] Optionally, the inner and outer phase shift angles include: the inner and outer phase shift angles of each DC-side conversion circuit in the single-stage multi-channel DC-DC converter;

[0041] Each of the aforementioned outward phase shift angles is determined based on the power transmission direction;

[0042] Each of the aforementioned inner phase shift angles and each of the aforementioned outer phase shift angles are independent of each other.

[0043] The single-stage multi-channel DC-DC converter provided in this application has its AC side of each DC-side conversion circuit connected to the corresponding primary winding of a multi-winding transformer, and the secondary winding of the multi-winding transformer connected to the first side of the AC-side conversion circuit. Since the equivalent impedance of each primary side of the multi-winding transformer is greater than the equivalent impedance of the secondary side, power decoupling between each DC-side conversion circuit can be achieved in hardware, and each DC-side conversion circuit can be independently controlled, thereby enabling multi-channel DC access. Moreover, each DC-side conversion circuit is used to realize AC-DC conversion, the turns ratio of the primary and secondary windings of the multi-winding transformer can realize the corresponding transformation ratio of the primary and secondary voltages, and the AC-side conversion circuit can perform AC frequency conversion, thereby realizing single-stage conversion and improving conversion efficiency. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the structure of a single-stage multi-channel DC-DC converter provided in an embodiment of this application;

[0046] Figure 2 The fundamental equivalent circuit diagram of a single-stage multi-channel DC-DC converter provided in the embodiments of this application;

[0047] Figure 3 Another structural schematic diagram of a single-stage multi-channel DC-DC converter provided in an embodiment of this application;

[0048] Figure 4a A schematic diagram of a DC-side converter circuit provided in an embodiment of this application;

[0049] Figure 4b Another schematic diagram of the DC-side conversion circuit provided in the embodiments of this application;

[0050] Figure 4c Another schematic diagram of the DC-side conversion circuit provided in the embodiments of this application;

[0051] Figure 5a A structural diagram of an AC-side conversion circuit provided in an embodiment of this application;

[0052] Figure 5b Another structural diagram of the AC-side conversion circuit provided in the embodiments of this application;

[0053] Figure 5c Another structural diagram of the AC-side conversion circuit provided in the embodiments of this application;

[0054] Figure 5d Another structural diagram of the AC-side conversion circuit provided in the embodiments of this application;

[0055] Figure 6 A detailed circuit diagram of a single-stage multi-channel DC-DC converter provided in an embodiment of this application;

[0056] Figure 7 A specific fundamental equivalent circuit diagram of a single-stage multi-channel DC-DC converter provided in the embodiments of this application;

[0057] Figure 8a A waveform diagram of the drive signal of a single-stage multi-channel DC-DC converter provided in an embodiment of this application during the positive half-cycle of the power grid.

[0058] Figure 8b A waveform diagram of the drive signal of a single-stage multi-channel DC-DC converter provided in an embodiment of this application during the negative half-cycle of the power grid.

[0059] Figure 9 A flowchart of a control method for a single-stage multi-channel DC-DC converter provided in an embodiment of this application;

[0060] Figure 10 Another waveform diagram of the drive signal of the single-stage multi-channel DC-DC converter provided in the embodiments of this application during the positive half-cycle of the power grid. Detailed Implementation

[0061] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0063] This application provides a single-stage multi-channel DC-DC converter that employs hardware power decoupling, which is simple to implement and does not increase the complexity of software algorithms, thereby making it easier to further expand the number of ports.

[0064] See Figure 1 The single-stage multi-channel DC-DC converter includes: a multi-winding transformer 100, an AC-side conversion circuit 102, and at least two DC-side conversion circuits 101; wherein:

[0065] The AC side of each DC-side conversion circuit 101 is connected to the corresponding primary winding of the multi-winding transformer 100, and its DC side serves as one DC interface of the single-stage multi-channel DC-DC converter, connected to the corresponding DC power supply (e.g., Figure 1 The DC interfaces shown (DC1, DC2, ..., DCn) can be connected to a DC power supply, a DC load, or a combination thereof, depending on the specific application environment. In practical applications, the DC power supply can be a photovoltaic cell module, a power battery, or a fuel cell, and the DC load can be a power battery in a charging state, etc. Furthermore, each DC-side conversion circuit 101 can also be equipped with a corresponding DC-side filter circuit 103 on its DC side.

[0066] The multi-winding transformer 100 can be a single-phase multi-winding transformer (such as...). Figure 1(As shown in the diagram), it can also be a three-phase multi-winding transformer, depending on the specific application environment; moreover, its secondary winding is connected to the first side of the AC-side conversion circuit 102; the second side of the AC-side conversion circuit 102 serves as the AC interface of the single-stage multi-channel DC-DC converter, used to connect to an AC source or AC load. The AC source can be the power grid. In practical applications, the second side of the AC-side conversion circuit 102 can be connected to the AC source or AC load through a corresponding AC-side filter circuit 104.

[0067] The specific working principle is as follows:

[0068] During forward power transmission, the high-frequency operation of the semiconductor power devices in each DC-side conversion circuit 101 converts the DC voltage output from the corresponding DC power supply into a pulsating voltage. Each pulsating voltage is then transmitted to the corresponding primary winding in the high-frequency multi-winding transformer 100. After passing through the high-frequency multi-winding transformer 100, each high-frequency pulsating voltage is coupled to the AC-side conversion circuit 102, which then performs AC frequency conversion, for example, transmitting AC power according to the frequency required by the power grid or AC load. This achieves the conversion from high-frequency (e.g., 100kHz) AC power to low-frequency (e.g., power frequency 50Hz, 60Hz) AC power. Finally, the power is connected to the power grid or AC load through filtering and other circuits, realizing a single-stage conversion.

[0069] During reverse power transmission, the AC-side conversion circuit 102 converts the low-frequency AC power from the AC source into high-frequency AC power, which is then transmitted to each DC-side conversion circuit 101 through the multi-winding transformer 100. Each DC-side conversion circuit 101 rectifies the AC power it receives and outputs it to each DC load.

[0070] The single-stage multi-channel DC-DC converter provided in this embodiment realizes AC-DC conversion through each DC-side conversion circuit 101. The turns ratio of the primary and secondary windings of the multi-winding transformer 100 can realize the corresponding transformation ratio of the primary and secondary voltages. The AC-side conversion circuit 102 can perform AC frequency conversion, thereby realizing single-stage conversion. It has high transmission efficiency potential and small product size.

[0071] Furthermore, each primary winding of the multi-winding transformer 100 is connected to a corresponding DC-side conversion circuit 101, enabling the single-stage multi-channel DC-DC converter to connect to multiple DC power supplies or DC loads. However, multi-port converters built based on transformer magnetic integration suffer from coupling between the power outputs of their ports, making control increasingly complex and even impossible as the number of ports increases. To achieve flexible expansion of transformer magnetic integration, this embodiment clamps the voltage at the secondary port of the transformer by setting the equivalent impedance of the primary and secondary sides, thereby achieving approximate hardware decoupling of the power outputs at each port of the magnetically integrated multi-port converter. This greatly simplifies control and makes expansion to 2 to n ports possible. The specific principle of setting the equivalent impedance of the primary and secondary sides of the transformer is described below:

[0072] Any circuit that relies on phase shifting of square waves across a transformer to transfer power can have its fundamental equivalent circuit, calculated after adjusting the transformer's primary and secondary sides, drawn as follows: Figure 2 The form shown, where, (x = 1, 2, 3, 4) is the fundamental equivalent voltage of the high-frequency pulsating voltage of any bridge arm. This is the fundamental voltage of the power grid. Taking forward power transmission as an example, (x = 1, 2, 3, 4) is the output current of any DC-side converter circuit 101. It is the input current of the AC-side converter circuit 102, Z x (x = 1, 2, 3, 4) and Z o These are the equivalent impedances connected to each bridge arm. For example, Z1 is the equivalent impedance between the AC side of the first DC-side converter circuit 101 and its corresponding primary winding, while Z2 to Z4 are the equivalent impedances between the AC side of the other DC-side converter circuits 101 and their corresponding primary windings, respectively. o It is the equivalent impedance between the first side and the secondary winding of the AC-side conversion circuit 102.

[0073] Voltage at common connection point in equivalent circuit This can be represented as expression 1:

[0074]

[0075] The current transmitted in each branch can be expressed as expression 2:

[0076]

[0077] In actual work, Z will be x (x = 1, 2, 3, 4) are designed to be equal, let Z1 = Z2 = ... = Z n =Z, and substituting expression 1 into expression 2, we can obtain the relationship between each port and the impedance Z and the voltage at each port, which can be expressed as expression 3:

[0078]

[0079] It can be seen from Expression 3 that, the current expression of each port branch includes, in addition to the non-coupling term on the left of the plus sign that is only related to the voltage of the local port and the port impedance, a coupling term on the right of the plus sign that is related to the voltage of each port. To eliminate the coupling term, one approach is to make the result of the operation of each port voltage in the parentheses equal to 0 through software control. However, this approach will impose restrictions on other control objectives of the circuit; and as the number of ports increases, the implementation difficulty becomes higher and higher. This imposes a limitation on the scalable number of ports of the magnetically integrated multi-port converter, which is usually 2 to 3. To achieve easy scalability of the number of ports without causing control difficulties, this embodiment adopts the equivalent impedance setting of the primary and secondary sides of the transformer to realize hardware decoupling. The principle is to slightly deform Expression 3 to obtain Expression 4:

[0080]

[0081] As shown in Expression 4, to eliminate the coupling term, it can be designed such that Z o << Z to make the denominator of the coupling term very large so as to approximately eliminate the coupling term. When Z o << Z, the denominator of the coupling term can be considered to be much larger than the numerator term. At this time, Expression 4 can be approximately written as Expression 5, and it can be seen that the coupling term has been eliminated:

[0082]

[0083] Therefore, expanding the number of ports according to this design principle will not bring difficulties to the implementation of software control, and it is easy to expand more ports.

[0084] It can be derived that the single-stage multi-channel DC access converter provided in this embodiment does not require a complex control algorithm to realize software power decoupling, and only through the above-mentioned impedance setting of the primary and secondary sides of the transformer, the power decoupling between the DC-side conversion circuits 101 is realized on the hardware, so that each DC-side conversion circuit 101 can realize independent control, and further realize multi-channel independent DC access; moreover, this embodiment adopts a single-stage magnetic integration structure, which realizes multi-channel DC access in the form of single-stage conversion, and can improve the conversion efficiency. In addition, each DC-side conversion circuit 101 shares the secondary winding of the transformer and the secondary semiconductor elements (that is, the AC-side conversion circuit 102), which maximizes the sharing of components and structural parts, and reduces the system cost per watt.

[0085] Based on the previous embodiment, in practical applications, the equivalent impedance of the secondary side of the multi-winding transformer 100 can be directly set to be less than a preset low threshold, for example, the equivalent impedance of the secondary side of the multi-winding transformer 100 can be zero; or, the equivalent impedance of the secondary side of the multi-winding transformer 100 can be set to be less than the equivalent impedance of each primary side of the multi-winding transformer 100 and the difference is greater than a preset high threshold, that is, the equivalent impedance of the secondary side of the multi-winding transformer 100 is much smaller than the equivalent impedance of each primary side; both can achieve power decoupling between each DC-side conversion circuit, so that multiple photovoltaic energy sources can achieve multiple independent DC access.

[0086] The preset low threshold is less than the preset high threshold. In practical applications, the preset low threshold can be a small value slightly greater than zero, and the preset high threshold can be a large value. The values ​​of both can be determined according to the specific application situation, and there is no limitation here.

[0087] To achieve the aforementioned setting of the equivalent impedance of the primary and secondary sides of each multi-winding transformer 100, the equivalent leakage inductance of the primary side of each multi-winding transformer 100 can be set to be greater than the equivalent leakage inductance of the secondary side; specifically, this can be achieved by adjusting the equivalent leakage inductance of the primary side of the multi-winding transformer 100 (e.g., ...). Figure 3 The equivalent leakage inductance of the secondary side (Lk1 to Lkn) shown in the diagram can be set to achieve this. For example, the equivalent leakage inductance of the secondary side of the multi-winding transformer 100 can be directly set to be less than the preset low threshold, or less than the equivalent leakage inductance of each primary side and the difference between them is greater than the preset high threshold. The equivalent leakage inductance of the primary side can originate from the primary leakage inductance of the multi-winding transformer 100, or the primary leakage inductance of the multi-winding transformer 100 and the inductor integrated therewith. When the equivalent leakage inductance of the secondary side is not zero, it can originate from the secondary leakage inductance of the multi-winding transformer 100, or the secondary leakage inductance of the multi-winding transformer 100 and the inductor integrated therewith; the specific application environment determines the appropriate setting, and all are within the scope of protection of this application.

[0088] Or see Figure 1 Furthermore, corresponding impedance elements 105 can be set between the AC side of each DC-side conversion circuit 101 and its corresponding primary winding to achieve the above-mentioned primary and secondary equivalent impedance settings.

[0089] In practical applications, each impedance element 105 can be an inductor, or other forms can be selected, such as using an inductor and a capacitor (e.g. Figure 1 As shown in the figure, the inductor and capacitor can be connected in series or in other ways; moreover, the impedance of each impedance element 105 can be the same or different, depending on the specific application environment, and all are within the protection scope of this application.

[0090] It should be noted that the leakage inductance setting for the multi-winding transformer 100 and the additional addition of each impedance element 105 mentioned above can coexist, as long as the above power decoupling can be achieved, and all are within the protection scope of this application.

[0091] Due to the need for hardware decoupling of power transmission in each branch of the multi-port magnetic integrated circuit, no impedance needs to be connected between the AC-side conversion circuit 102 and the secondary winding port of the multi-winding transformer. Alternatively, even if an impedance is connected between the AC-side conversion circuit 102 and the secondary winding port of the multi-winding transformer, its equivalent impedance will be much smaller than the impedance values ​​of each primary arm. That is, in practical applications, it is not ruled out that a secondary-side impedance element can be set between the secondary winding and the AC-side conversion circuit 102. This element can exist when there is no impedance element on the primary side, and power decoupling can be achieved through the aforementioned leakage inductance setting. Alternatively, it can exist simultaneously with the primary-side impedance element, and power decoupling can be achieved through the aforementioned leakage inductance setting and / or the setting of the primary-side impedance element. It depends on the specific application environment, and all of these are within the scope of protection of this application.

[0092] Based on the above embodiments, this embodiment provides some specific optional implementations of the DC-side conversion circuit 101 and the AC-side conversion circuit 102 in the single-stage multi-channel DC-DC converter, such as:

[0093] When the multi-winding transformer 100 is a single-phase multi-winding transformer 100, the DC-side conversion circuit 101 can adopt a half-bridge circuit (e.g., according to the power level). Figure 4a (as shown) or full-bridge circuit (such as) Figure 4b (As shown).

[0094] When the multi-winding transformer 100 is a three-phase multi-winding transformer, such as Figure 4c As shown, the primary windings of each phase of the three-phase multi-winding transformer 100 are connected, either directly or via an impedance element (an inductor is used as an example in the figure), to the corresponding phase on the AC side of the DC-side conversion circuit 101, with their other ends connected to reference ground. The secondary windings of each phase of the three-phase multi-winding transformer are connected at both ends to the corresponding phase on the first side of the AC-side conversion circuit 102, with their intermediate taps connected. Alternatively, the DC-side conversion circuit 101 can be a three-phase bridge circuit, with the midpoint of each phase bridge arm directly or via a corresponding impedance element connected to the primary winding of the corresponding phase of the multi-winding transformer 100.

[0095] In practical applications, the DC-side conversion circuit 101 can also adopt other conversion structures that convert DC voltage into high-frequency pulsating voltage. These are just two examples and are not limited to this one.

[0096] Regardless of the structure used, each DC-side conversion circuit 101 can be composed of power semiconductor devices such as MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or IGBT (Insulated Gate Bipolar Transistor) with anti-parallel diodes, but is not limited to these.

[0097] For this AC-side conversion circuit 102, since it needs to handle AC voltages with polarity changes, it can be selected according to its power rating, such as... Figures 5a to 5d Various frequency conversion structures are shown. Specifically, when each multi-winding transformer 100 is a single-phase multi-winding transformer, the AC side conversion circuit 102 can specifically adopt a hybrid conversion circuit composed of bidirectional switching bridge arms and capacitor bridge arms (such as...). Figure 5a (As shown), a converter circuit composed of all bidirectional switching bridge arms can also be used (such as...). Figure 5b and Figure 5c (As shown). In a three-phase AC load application scenario, if each multi-winding transformer 100 is a single-phase multi-winding transformer, then the AC side conversion circuit 102 can be a frequency converter composed of three bidirectional switching bridge arms (e.g., Figure 5c (as shown); if each multi-winding transformer 100 is a three-phase multi-winding transformer, then the AC side conversion circuit 102 may include three conversion circuits (such as...). Figure 5d (As shown).

[0098] See Figure 5a Each multi-winding transformer 100 is a single-phase multi-winding transformer. The AC-side conversion circuit 102 is a half-bridge conversion circuit, with its switching arm and capacitor arm connected in parallel between the two ends of the second side of the AC-side conversion circuit 102. The switching arm includes two bidirectional switches connected in series. The bidirectional switch composed of switching transistors SS1 and SS2 serves as the upper half-bridge arm, and the bidirectional switch composed of switching transistors SS3 and SS4 serves as the lower half-bridge arm. The capacitor arm includes two capacitor modules C1 and C2 connected in series with the same capacity. The midpoints of the switching arm and the capacitor arm respectively serve as the two ends of the first side of the AC-side conversion circuit 102.

[0099] See Figure 5bEach multi-winding transformer 100 is a single-phase multi-winding transformer 100. The AC-side conversion circuit 102 is a full-bridge conversion circuit, with its two switching bridge arms connected in parallel between the two ends of the second side of the AC-side conversion circuit 102. Each switching bridge arm includes two bidirectional switches connected in series; in one switching bridge arm, the bidirectional switch composed of switching transistors Ss1 and Ss2 serves as the upper half-bridge arm, and the bidirectional switch composed of switching transistors Ss3 and Ss4 serves as the lower half-bridge arm; in the other switching bridge arm, the bidirectional switch composed of switching transistors Ss1' and Ss2' serves as the upper half-bridge arm, and the bidirectional switch composed of switching transistors Ss3' and Ss4' serves as the lower half-bridge arm. The midpoints of the two switching bridge arms are respectively used as the two ends of the first side of the AC-side conversion circuit 102. Capacitor module C3 belongs to... Figure 1 The AC side filter circuit 104 shown is illustrated.

[0100] See Figure 5c Each multi-winding transformer 100 is a single-phase multi-winding transformer. The AC-side conversion circuit 102 is a three-phase bridge conversion circuit, with its three switching bridge arms connected in parallel between the two ends of the first side of the AC-side conversion circuit 102. Each switching bridge arm includes two bidirectional switches connected in series. In one switching bridge arm, the bidirectional switch composed of switching transistors Ss1 and Ss2 serves as the upper half-bridge arm, and the bidirectional switch composed of switching transistors Ss3 and Ss4 serves as the lower half-bridge arm. In another switching bridge arm, the bidirectional switch composed of switching transistors Ss1' and Ss2' serves as the upper half-bridge arm, and the bidirectional switch composed of switching transistors Ss3' and Ss4' serves as the lower half-bridge arm. In the third switching bridge arm, the bidirectional switch composed of switching transistors Ss1" and Ss2" serves as the upper half-bridge arm, and the bidirectional switch composed of switching transistors Ss3" and Ss4" serves as the lower half-bridge arm. The midpoints of the three switch bridge arms serve as the second terminals of the AC-side conversion circuit 102; furthermore, each pair of terminals on the second side of the AC-side conversion circuit 102 is connected to corresponding capacitor modules C5 to C7, all of which belong to... Figure 1 The AC side filter circuit 104 shown is illustrated.

[0101] See Figure 5d At this time, each multi-winding transformer 100 is a three-phase multi-winding transformer. The AC-side conversion circuit 102 includes: three conversion circuits; the two sides of each conversion circuit respectively serve as the corresponding phases on both sides of the AC-side conversion circuit 102. In practical applications, each conversion circuit can be configured as follows: Figure 5dAs shown, it includes: a rectifier bridge 201 and a half-bridge circuit 202. The AC side of the rectifier bridge 201 serves as the first phase of the AC-side conversion circuit 102. The DC side of the rectifier bridge 201 is connected to both ends of the half-bridge circuit 202. The midpoint of the half-bridge circuit 202 serves as the second phase of the AC-side conversion circuit 102. Specifically, in one conversion circuit, the AC side of its rectifier bridge 201 serves as the first phase A of the AC-side conversion circuit 102, and the midpoint of its half-bridge circuit 202 serves as the second phase A of the AC-side conversion circuit 102; in another conversion circuit, the AC side of its rectifier bridge 201 serves as the first phase B of the AC-side conversion circuit 102, and the midpoint of its half-bridge circuit 202 serves as the second phase B of the AC-side conversion circuit 102; in a third conversion circuit, the AC side of its rectifier bridge 201 serves as the first phase C of the AC-side conversion circuit 102, and the midpoint of its half-bridge circuit 202 serves as the second phase C of the AC-side conversion circuit 102. Each rectifier bridge 201 can be... Figure 5d The rectifier bridge shown can be composed of diodes; it can also be a full-bridge structure composed of controllable semiconductor switches such as MOSFETs or IGBTs to achieve bidirectional energy transfer; it depends on the specific application environment, and all of them are within the protection scope of this application.

[0102] In practical applications, each of the above-mentioned capacitor modules can be a single capacitor or multiple capacitors connected in series or parallel; it depends on the specific application environment, and all are within the protection scope of this application.

[0103] Furthermore, the AC-side conversion circuit 102 can also utilize other conversion structures capable of voltage reversal, such as various forms of matrix conversion circuits, as long as they can achieve adaptive connection with the corresponding AC source or AC load. It should be noted that... Figures 5a to 5d The power devices selected are merely examples. In actual applications, MOSFETs or IGBTs can be selected as needed. For instance, since the AC-side conversion circuit 102 processes the sum of the power from n input channels, it requires high voltage and high power. If MOSFETs cannot meet the requirements, high-voltage devices such as IGBTs can be used. Alternatively, to improve efficiency, SiC (silicon nitride), GaN (gallium nitride), or a hybrid device composed of IGBT and SiC can be selected, depending on the specific application environment. All of these are within the scope of protection of this application.

[0104] Figure 6 Taking a 4-input converter as an example, this paper shows a converter with an H-bridge structure on the primary side and a hybrid circuit of switching bridge arms and capacitor bridge arms on the secondary side.

[0105] See Figure 6Each DC-side conversion circuit includes switching transistors Sp11 to Sp14, Sp21 to Sp24, Sp31 to Sp34, and Sp41 to Sp44, respectively, and each DC-side filter circuit includes a capacitor module Cpv. Because this type of inverter is connected to photovoltaic modules (such as...) Figure 6 The DC1 to DC4 shown are generally of the same model, so the impedance of the four input bridge arms can be designed to be equal. Figure 6 The diagram illustrates how each H-bridge is connected to the corresponding primary winding of the multi-winding transformer 100 via an inductor Ls acting as an impedance element. Each inductor Ls can be designed to have the same inductance. In practical applications, the impedance element can also be implemented by connecting an inductor and a capacitor in series. Alternatively, corresponding impedance elements can be provided on the primary and secondary sides of each multi-winding transformer 100.

[0106] See Figure 6 Its secondary side uses a half-bridge frequency converter with split capacitors, which can reduce EMI (Electromagnetic Interference). That is, its AC-side conversion circuit consists of switching transistors Ss11 to Ss14 and capacitor modules C1 and C2, with C1 and C2 designed to use the same capacitors; its AC-side filtering circuit includes inductor module Lg and capacitor module Cg.

[0107] Will Figure 6 The inverter primary-side components shown are referred to the secondary-side components, resulting in the following: Figure 7 The fundamental equivalent circuit shown is as follows, in which, (x = 1, 2, 3, 4) is the fundamental equivalent voltage of the high-frequency pulsating voltage of any bridge arm. It is the fundamental voltage of the power grid. (x = 1, 2, 3, 4) is the output current of any DC-side converter circuit 101. ω is the input current of the AC-side converter circuit 102, w is the angular frequency of the switching transistor in the circuit, Ls' and Cs' are the equivalent inductance and equivalent capacitance values ​​of the impedance components connected to each DC-side converter circuit 101 after conversion, and Cg is the capacitance of the secondary side of the multi-winding transformer. The selection of the primary and secondary bridge arm impedance values ​​needs to follow the following principle to ensure hardware decoupling of power transmission between branches:

[0108]

[0109] When choosing other types of impedance structures, the selection should also be based on the aforementioned limitation that the impedance of the secondary bridge arm after conversion and equivalent is 0 or much smaller than the impedance value of the primary bridge arm.

[0110] Depend on Figure 7 It can be seen that the adjustment to and The phase difference between the phases determines the power transferred from each branch to the grid. Therefore, this circuit can employ fixed-frequency phase-shift control, meaning the control strategy for the AC-side conversion circuit 102 and each DC-side conversion circuit 101 can be a fixed-frequency phase-shift control strategy. Furthermore, the operating frequency of each semiconductor device, i.e., each switch in the AC-side conversion circuit 102 and each DC-side conversion circuit 101, should be selected to make the primary-side equivalent impedance of the multi-winding transformer 100 inductive, thus providing conditions for the device to perform ZVS (Zero Voltage Switch). When the above hardware decoupling design principles are met, each branch can be considered independent, thus enabling independent control of each branch.

[0111] Based on the above description Figure 6 The circuit shown can use the following modulation methods, such as Figure 8a and Figure 8b As shown:

[0112] The switching transistors in each DC-side conversion circuit 101 and AC-side conversion circuit 102 are driven with a 50% duty cycle, and a certain dead time is set between the complementary drive signals.

[0113] In each DC-side converter circuit 101, the switching transistors of the upper and lower half-arms of each bridge arm operate complementaryly, and the drive signals of the switching transistors of different half-arms in different bridge arms differ by an inward phase shift angle. (See also...) Figure 8a and Figure 8b Taking the DC1 input as an example, its switching transistors Sp11 and Sp12 work in a complementary manner, and its switching transistors Sp13 and Sp14 work in a complementary manner. The drive signal of the switching transistor Sp11 leads the drive signal of the switching transistor Sp14 by an angle β.

[0114] In the AC-side conversion circuit 102, when the instantaneous value of the grid voltage is greater than zero, the diodes of the upper half-bridge arm (Ss1) pointing towards the grid and the diodes of the lower half-bridge arm (Ss3) pointing towards the secondary winding operate complementaryly, while the other switches are directly connected. When the instantaneous value of the grid voltage is less than zero, the diodes of the upper half-bridge arm (Ss2) pointing towards the secondary winding and the diodes of the lower half-bridge arm (Ss4) pointing towards the grid operate complementaryly, while the other switches are directly connected. Furthermore, the drive signals of the switches in each DC-side conversion circuit 101 are respectively phase-shifted by an external phase angle compared to the drive signals of the switches in the AC-side conversion circuit 102. Taking the DC1 input as an example, when the grid voltage is positive, switches Ss1 and Ss3 operate complementaryly, switches Ss2 and Ss4 are always on, and the drive signal of switch Sp11 leads the drive signal of switch Ss1 by an angle α (signal waveform as shown). Figure 8a(As shown); When the mains voltage is negative, switches Ss2 and Ss4 work complementaryly, switches Ss1 and Ss3 are always on, and the drive signal of switch Sp11 leads the drive signal of switch Ss4 by an angle α (signal waveform as shown). Figure 8b (As shown). Figure 8a and Figure 8b In the diagram, V1 is the output voltage of the DC-side converter circuit 101 corresponding to DC1. g It is the secondary voltage of the multi-winding transformer 100, i res It is the current of a multi-winding transformer 100.

[0115] The drive signal logic for each input from DC2 to DC4 is the same as that for DC1, but the specific values ​​of α and β for each input are independent of each other, that is, each inner phase shift angle and each outer phase shift angle are independent of each other. Each input is controlled by two degrees of freedom (α and β angles) because by combining the two degrees of freedom, the effective value of the bridge arm output current can be reduced when transmitting the same power, thereby optimizing the conduction loss.

[0116] The single-stage multi-channel DC-DC converter provided in this embodiment adopts a single-stage structure with independent dual-degree-of-freedom modulation between each input, which helps to improve the system power transmission efficiency.

[0117] Another embodiment of this application provides a control method for a single-stage multiplex DC-DC converter, which is applied to the single-stage multiplex DC-DC converter as described in any of the above embodiments. This control method is as follows: Figure 9 As shown, it specifically includes:

[0118] S101. Obtain the electrical parameters on both sides of the single-stage multi-channel DC-DC converter and determine the power transmission direction required by the single-stage multi-channel DC-DC converter.

[0119] The electrical parameters on both sides include at least one of the voltage, current and power on both sides of the single-stage multi-channel DC-DC converter, depending on the specific application environment.

[0120] The power transmission directions required by this single-stage multi-channel DC-DC converter include: the forward transmission direction when power is inverted from its DC interface to its AC interface, and the reverse transmission direction when power is rectified from its AC interface to its DC interface.

[0121] S102. Based on the electrical parameters on both sides and the power transmission direction, determine the switching frequency and inner and outer phase shift angles of the single-stage multi-channel DC-DC converter.

[0122] Once the switching frequency is determined, the operating period Ts of each switch in the single-stage multi-channel DC-DC converter can be determined.

[0123] Preferably, the switching frequency is a frequency that makes the primary side impedance of the multi-winding transformer in the single-stage multi-channel DC access converter inductive, thereby providing conditions for ZVS of the device.

[0124] The inner and outer phase shift angles include: the inner phase shift angle (i.e., β described in the above embodiments) and the outer phase shift angle (i.e., α described in the above embodiments) for each DC side conversion circuit in the single-stage multi-channel DC access converter; each outer phase shift angle is determined according to the power transmission direction, still taking Figure 6 the case where DC1 shown in the following operates when the grid voltage is positive as an example, referring to Figure 10 , by adjusting the lead and lag of the outer phase shift angle α, the power transmission direction can be controlled. When the power area S1 > S2, the topology realizes forward power transmission; when the power area S1 < S2, the topology realizes reverse power transmission; Figure 10 in the figure, V1 is the output voltage of the DC side conversion circuit corresponding to DC1, V p is the primary side voltage of the multi-winding transformer, i k is the primary side current of the multi-winding transformer, and the existence of the power area S3 can provide energy for soft switching.

[0125] Moreover, each inner phase shift angle and each outer phase shift angle are mutually independent respectively.

[0126] S103. Generate and output control signals for each switching tube of the single-stage multi-channel DC access converter according to the switching frequency and the inner and outer phase shift angles, so as to realize phase shift control of the single-stage multi-channel DC access converter.

[0127] This control method can realize the phase shift control of the single-stage multi-channel DC access converter. For the specific principle of the phase shift control, reference may be made to the above embodiments, which will not be repeated here; moreover, through the mutual independence of each inner phase shift angle and each outer phase shift angle, the control method can also realize the optimization of conduction loss.

[0128] For the same and similar parts among the various embodiments in this specification, reference may be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and relevant parts can be referred to the part description of the method embodiments. The systems and system embodiments described above are only illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. A person of ordinary skill in the art can understand and implement it without creative work.

[0129] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0130] The features described above in the disclosed embodiments can be substituted for or combined with each other to enable those skilled in the art to implement or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A single-stage multi-channel DC-DC converter, characterized in that, include: A multi-winding transformer, an AC-side conversion circuit, and at least two DC-side conversion circuits; wherein, The AC side of each DC-side conversion circuit is connected to the corresponding primary winding of the multi-winding transformer. The secondary winding of the multi-winding transformer is connected to the first side of the AC-side conversion circuit; Each of the DC-side conversion circuits is used to invert the DC power it receives, or to rectify the AC power it receives. The AC-side conversion circuit is used for AC frequency conversion; The equivalent impedance of each primary side of the multi-winding transformer is greater than the equivalent impedance of the secondary side. The equivalent impedance of the secondary side of the multi-winding transformer is less than a preset low threshold, or the equivalent impedance of the secondary side of the multi-winding transformer is less than the equivalent impedance of each primary side of the multi-winding transformer and the difference is greater than a preset high threshold, wherein the preset low threshold is less than the preset high threshold.

2. The single-stage multi-channel DC-DC converter according to claim 1, characterized in that, The equivalent leakage inductance of each primary winding of the multi-winding transformer is greater than that of the secondary winding.

3. The single-stage multi-channel DC-DC converter according to claim 2, characterized in that, The primary-side equivalent leakage inductance originates from: the primary-side leakage inductance of the multi-winding transformer, or the primary-side leakage inductance of the multi-winding transformer and the inductance integrated therewith.

4. The single-stage multi-channel DC-DC converter according to claim 2, characterized in that, The equivalent leakage inductance of the secondary side is zero; or... The equivalent leakage inductance on the secondary side originates from: the leakage inductance on the secondary side of the multi-winding transformer, or the leakage inductance on the secondary side of the multi-winding transformer and the inductance integrated therewith.

5. The single-stage multi-channel DC-DC converter according to claim 1, characterized in that, Also includes: Impedance elements are disposed between the AC side and the corresponding primary winding of each DC-side conversion circuit.

6. The single-stage multi-channel DC-DC converter according to claim 5, characterized in that, The impedance element includes: an inductor, or an inductor and a capacitor.

7. The single-stage multi-channel DC-DC converter according to any one of claims 1 to 6, characterized in that, Also includes: An impedance element disposed between the secondary winding and the first side of the AC-side conversion circuit.

8. The single-stage multi-channel DC-DC converter according to any one of claims 1 to 6, characterized in that, The multi-winding transformer is either a single-phase multi-winding transformer or a three-phase multi-winding transformer.

9. The single-stage multi-channel DC-DC converter according to claim 8, characterized in that, In the three-phase multi-winding transformer, the primary windings of each of the three-phase primary windings are respectively connected to the corresponding phases of the AC side of the DC-side conversion circuit, and their other ends are all connected to the reference ground. Each phase secondary winding of the three-phase multi-winding transformer is connected at both ends to the corresponding phase on the first side of the AC-side conversion circuit, and the middle taps are connected.

10. The single-stage multi-channel DC-DC converter according to any one of claims 1 to 6, characterized in that, When the multi-winding transformer is a single-phase multi-winding transformer, the DC-side conversion circuit is a half-bridge circuit or a full-bridge circuit. When the multi-winding transformer is a three-phase multi-winding transformer, the DC-side conversion circuit is a three-phase bridge circuit.

11. The single-stage multi-channel DC-DC converter according to any one of claims 1 to 6, characterized in that, The AC-side conversion circuit is either a frequency conversion circuit or a matrix conversion circuit.

12. The single-stage multi-channel DC-DC converter according to claim 11, characterized in that, When the multi-winding transformer is a single-phase multi-winding transformer: The AC-side conversion circuit is a half-bridge conversion circuit, with its switch bridge arm and capacitor bridge arm connected in parallel between the two ends of the second side of the AC-side conversion circuit; the switch bridge arm includes two bidirectional switches that serve as the upper and lower half-bridge arms respectively, and the capacitor bridge arm includes two capacitor modules connected in series with the same capacitance; the midpoint of the switch bridge arm and the midpoint of the capacitor bridge arm serve as the two ends of the first side of the AC-side conversion circuit respectively; or, The AC-side conversion circuit is a full-bridge conversion circuit, wherein its two switching bridge arms are connected in parallel between the two ends of the second side of the AC-side conversion circuit; the midpoints of the two switching bridge arms respectively serve as the two ends of the first side of the AC-side conversion circuit; or, The AC-side conversion circuit is a three-phase bridge conversion circuit, in which the three switch bridge arms are connected in parallel between the two ends of the first side of the AC-side conversion circuit; the midpoints of the three switch bridge arms are respectively used as the ends of the second side of the AC-side conversion circuit.

13. The single-stage multi-channel DC-DC converter according to claim 11, characterized in that, When the multi-winding transformer is a three-phase multi-winding transformer, the AC side conversion circuit includes: three conversion circuits; Each of the two sides of the aforementioned conversion circuit serves as the corresponding phase on both sides of the AC-side conversion circuit.

14. The single-stage multi-channel DC-DC converter according to claim 13, characterized in that, Each of the aforementioned conversion circuits includes: a rectifier bridge and a half-bridge circuit; The AC side of the rectifier bridge serves as the first phase of the AC-side conversion circuit, the DC side of the rectifier bridge is connected to both ends of the half-bridge circuit, and the midpoint of the half-bridge circuit serves as the second phase of the AC-side conversion circuit.

15. The single-stage multi-channel DC-DC converter according to any one of claims 1 to 6, characterized in that, Also includes: An AC-side filter circuit is configured on the second side of the AC-side conversion circuit; and / or, Each DC-side filter circuit is respectively set on the DC side of each DC-side conversion circuit.

16. A control method for a single-stage multi-channel DC-DC converter, characterized in that, The control method, applied to a single-stage multiplex DC-DC converter as described in any one of claims 1 to 15, comprises: Obtain the electrical parameters on both sides of the single-stage multi-channel DC-DC converter and determine the power transmission direction required by the single-stage multi-channel DC-DC converter; Based on the electrical parameters on both sides and the power transmission direction, determine the switching frequency and inner and outer phase shift angles of the single-stage multi-channel DC-DC converter; Based on the switching frequency and the internal and external phase shift angles, control signals for each switch of the single-stage multi-channel DC-DC converter are generated and output to realize phase shift control of the single-stage multi-channel DC-DC converter.

17. The control method for a single-stage multi-channel DC-DC converter according to claim 16, characterized in that, The switching frequency is the frequency at which the primary-side equivalent impedance of the multi-winding transformer in the single-stage multi-channel DC-DC converter becomes inductive.

18. The control method for a single-stage multi-channel DC-DC converter according to claim 16 or 17, characterized in that, The inner and outer phase shift angles include: the inner and outer phase shift angles of each DC-side conversion circuit in the single-stage multi-channel DC-DC converter; Each of the aforementioned outward phase shift angles is determined based on the power transmission direction; Each of the aforementioned inner phase shift angles and each of the aforementioned outer phase shift angles are independent of each other.

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