Buck-boost wide-input wide-output bidirectional DC-DC converter based on T network

Abstract

The invention provides a buck-boost wide-input wide-output bidirectional DC-DC converter based on a T network, and the converter comprises an inversion unit which is used for converting a DC input voltage source or current source into an AC signal; the voltage conversion unit is provided with N cascaded T networks, and N is a positive integer; wherein each T network realizes conversion between voltage and current, the independent gain of each T network is determined through parameter design, and the total gain of the N T networks is the product of the gains of the T networks; and the rectifying unit is used for converting the alternating current signal into a direct current signal. The system has wide-range input and output capability, supports bidirectional flow of energy, and ensures that the system can keep excellent performance under various working conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of DC / DC converters, and in particular relates to a T-network-based, step-up and step-down bidirectional DC-DC converter with wide input and output. Background Art

[0002] In recent years, with the rapid development of the electric vehicle industry and the increasing proportion of new energy in modern energy networks, high-efficiency DC-DC converters have become a key technology that needs to be solved in the fields of electric vehicle charging and new energy grid connection. However, the existing technologies have the following main problems:

[0003] 1. During the charging process of electric vehicles, since the battery voltage varies greatly with the state of charge (SOC) (for example, a 400V battery system may reach 450V when fully charged, but may be as low as 300V after discharge), it is difficult for existing converters to achieve a wide output voltage range and high conversion efficiency at the same time, thus affecting the charging speed and system stability.

[0004] 2. The output voltage of new energy power generation (such as photovoltaic power generation) is significantly affected by environmental conditions. The output voltage fluctuation range of a single photovoltaic cell is small, but the overall output voltage is greatly affected by changes in light. The existing DC-DC converter has low conversion efficiency under wide input conditions and it is difficult to maintain efficient energy conversion.

[0005] 3. Traditional resonant converters usually rely on variable frequency modulation to adapt to changes in input or output voltage. However, when the voltage range is wide, not only does it need to cover a larger frequency conversion range, but it is also easy to deviate from the optimal operating point, resulting in complex closed-loop control, reduced system dynamic performance and increased design difficulty.

[0006] 4. In addition, most existing DC-DC converters only support one-way energy transmission. In future electric vehicles V2G (vehicle-to-grid), energy storage systems and microgrids, converters are required to have the ability to flow energy in both directions to achieve charge and discharge management and grid-assisted regulation. However, traditional technologies are difficult to meet this requirement at the same time.

[0007] Therefore, how to achieve a wide input and output voltage range, simplify the control strategy to ensure that the system can still operate stably when the load changes, and realize two-way energy flow while maintaining high efficiency and stability, so as to meet the requirements of applications such as electric vehicle charging, energy storage management and new energy grid connection, has become a technical problem that needs to be solved urgently. Summary of the invention

[0008] The purpose of the present invention is to address the deficiencies in the above-mentioned background technology and to provide a T-network-based, step-up and step-down bidirectional DC-DC converter with wide input and output capabilities, which supports bidirectional energy flow and ensures that the system can maintain excellent performance under various working conditions.

[0009] The technical solution adopted by the present invention is: a T-network-based wide-input and wide-output bidirectional DC-DC converter capable of buck-boost and buck-boost, comprising:

[0010] An inverter unit, used to convert a DC input voltage source or current source into an AC signal;

[0011] A voltage conversion unit is provided with N cascaded T networks, where N is a positive integer; each T network realizes the conversion between voltage and current, its individual gain is determined by parameter design, and the total gain of the N T networks is the product of the gains of each T network;

[0012] A rectifier unit, used for converting an AC signal into a DC signal;

[0013] Wherein, after the DC input is converted into an AC signal by the inverter unit, a preset conversion mode is implemented by the voltage conversion unit, and a DC signal with a constant current or constant voltage characteristic is output by the rectifier unit;

[0014] In another working mode, an external DC power source is connected to the DC output terminal of the rectifier unit, and the DC energy is transmitted to the DC input terminal through reverse conversion, so as to charge the input side and realize bidirectional energy flow.

[0015] In the above technical solution, the T network includes three branches, the middle branch is provided with a capacitor, and the middle branch is provided with a capacitor; the inductance of at least one side of the two side branches is a coupled inductor and matches the impedance of the middle capacitor.

[0016] In the above technical solution, at least one T network in the voltage conversion unit is an isolated T network; the isolated T network cascades a transformer on the basis of the T network to achieve electrical isolation and voltage conversion between the input end and the output end, and the excitation inductance of the transformer does not participate in the resonance, and the transformer ratio is n, where n is a positive integer; the voltage gain of the isolated T network is n times the gain of the corresponding non-isolated T network.

[0017] In the above technical solution, when the number of T networks is an odd number: when the input end is a voltage source input, the bidirectional DC-DC converter automatically achieves a constant current output; when the input end is a current source input, the bidirectional DC-DC converter automatically achieves a constant voltage output.

[0018] When the number of T networks is an even number: when the input end is a voltage source input, the bidirectional DC-DC converter automatically achieves a constant voltage output; when the input end is a current source input, the bidirectional DC-DC converter automatically achieves a constant current output.

[0019] In the above technical solution, when the input of the bidirectional DC-DC converter is a voltage source and the output is a constant current, the gain of a single non-isolated T network is the reciprocal of the impedance of its intermediate branch;

[0020] When the input of the bidirectional DC-DC converter is a current source and the output is a constant voltage, the gain of a single non-isolated T network is the impedance of its middle branch;

[0021] The gain, type, and number of T networks are selected based on the input and output requirements of the bidirectional DC-DC converter.

[0022] The present invention also provides a control method for a T-network-based step-up / step-down wide-input and wide-output bidirectional DC-DC converter, comprising the following steps:

[0023] In the forward working mode, the DC input voltage source or current source is converted into an AC signal by controlling the inverter unit, and the AC signal is converted into a DC output via a voltage conversion unit and a rectifier unit composed of N cascaded T networks;

[0024] In the reverse working mode, when the external DC power supply is connected to the DC output terminal, the external DC power supply is converted into an AC signal, processed by the voltage conversion unit, and then transmitted to the DC input side, thereby realizing charging of the input side.

[0025] The above technical solution also includes the following steps:

[0026] The switching frequency of the inverter unit is fixed according to the power supply condition on the input side and the power demand on the output side of the bidirectional DC-DC converter;

[0027] By adjusting the phase shift angle between the bridge arms in the inverter unit, closed-loop control of the output DC voltage or output DC current is achieved.

[0028] The present invention also provides a power conversion system, comprising:

[0029] a first DC power supply;

[0030] A second DC power supply;

[0031] The bidirectional DC-DC converter described in the above technical solution is configured to realize bidirectional energy transmission between the first DC power supply and the second DC power supply, and realizes the functions of wide input and wide output through the cascaded T network and its gain design.

[0032] In the above technical solution, the first DC power supply is a DC energy storage device, including but not limited to: a battery energy storage system for household or industrial use, a backup power system, a distributed energy storage unit, or an energy storage device based on a fuel cell or other DC energy conversion technology.

[0033] In the above technical solution, the second DC power supply is a DC power supply system, including but not limited to a power grid system, a photovoltaic power generation system, a DC energy storage system or a distributed DC microgrid.

[0034] The beneficial effects of the present invention are as follows: the present invention provides a bidirectional DC-DC converter with a simple structure and high efficiency, which realizes wide-input and wide-output DC power conversion through an inverter unit, a voltage conversion unit (composed of N cascaded T networks) and a rectifier unit; it has two working modes, forward (power supply) and reverse (charging), to realize bidirectional energy flow, and meet various application requirements such as vehicle-to-grid interconnection (V2G) and energy storage systems; it adapts to the input of a DC voltage source or a current source, and ensures that the system can output DC power with constant current or constant voltage characteristics in different working modes.

[0035] Furthermore, the present invention achieves impedance matching with the middle capacitor by adopting a three-branch structure in a typical T network and using coupled inductors to replace independent inductors on one or both sides; the number and complexity of components are reduced, thereby reducing costs and improving system reliability and energy conversion efficiency.

[0036] Furthermore, the present invention introduces an isolated T network, and realizes electrical isolation and voltage conversion between the input end and the output end by cascading transformers on the basis of the T network; the excitation inductance of the transformer does not participate in the resonance, thereby reducing the transformer loss, and the voltage gain of the isolated T network is effectively improved through the transformation ratio n, thereby improving the flexibility and safety of the system.

[0037] Furthermore, the present invention utilizes the odd or even number of T network cascades to automatically match the conversion requirements of different input sources: when the number of T networks is an odd number, constant current output under voltage source input or constant voltage output under current source input can be achieved; when the number of T networks is an even number, the output modes are interchangeable; this design enables the converter to automatically adapt to different input conditions, simplifies the control strategy, and improves the stability and applicability of the conversion.

[0038] Furthermore, the present invention determines the gain by selecting the inverse or positive value of the impedance of the middle branch in a single non-isolated T network according to different working modes, thereby achieving accurate gain design; the overall gain of the converter is determined only by the product of the gains of each T network, thereby ensuring that the conversion ratio is stable and not significantly affected by load changes, thereby improving the overall energy conversion efficiency.

[0039] Furthermore, the present invention provides a control method, which converts a DC input (voltage source or current source) into an AC signal in a forward mode, and then cascades and rectifies it through a T network to output DC energy; in a reverse mode, an external DC power supply is connected and converted into an AC signal, which is then processed by a voltage conversion unit and transmitted to the input side to charge the input side, thereby realizing bidirectional energy flow and enhancing the application flexibility of the system.

[0040] Furthermore, the present invention realizes closed-loop control of the output DC voltage or DC current through further control steps, such as fixing the switching frequency of the inverter unit and adjusting the phase shift angle between the bridge arms; improves the dynamic response and stability of the system, ensures that the working state can be accurately adjusted during the bidirectional energy transmission process, and meets different power supply and charging requirements.

[0041] Furthermore, the present invention constructs an electric power conversion system for energy interconnection between multiple DC power supplies, so that the first DC power supply and the second DC power supply can perform bidirectional energy transmission through a bidirectional DC-DC converter; by utilizing a cascaded T network and its gain design, the functions of wide input and wide output are realized, the adaptability and application range of the system are enhanced, and it is suitable for energy exchange between various DC systems.

[0042] Furthermore, the present invention limits the first DC power supply to a DC energy storage device (including household / industrial battery energy storage, backup power supply, distributed energy storage unit or fuel cell, etc.), broadening the application scope of the converter in the energy storage system; by combining with a bidirectional DC-DC converter, efficient bidirectional energy transmission is achieved, providing technical support for applications such as charging and discharging management of the energy storage system and vehicle-grid interconnection.

[0043] Furthermore, the present invention limits the second DC power supply to a DC power supply system (including a power grid, photovoltaic power generation, DC energy storage or a distributed DC microgrid, etc.), further expanding the applicability of the converter in a variety of DC power supply scenarios; through efficient voltage conversion and bidirectional energy flow, energy complementarity and optimal configuration between DC systems are achieved, which helps to improve the overall energy utilization efficiency and meet the needs of modern energy networks for efficient power conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is the circuit topology diagram of the double-T network DC-DC converter, showing the circuit schematic and control block diagram;

[0045] Figure 2a A schematic diagram of a basic typical T-type module and its equivalent dual-port transmission network;

[0046] Figure 2b The basic typical T-type module and its equivalent dual-port transmission network diagram b;

[0047] Figure 3a Schematic diagram of ZPA module under CC or CV a;

[0048] Figure 3b b is a schematic diagram of the ZPA module under CC or CV;

[0049] Figure 4a A is a typical T network diagram;

[0050] Figure 4b It is a typical T network diagram b;

[0051] Figure 5a Schematic diagram a of coupled inductor T network;

[0052] Figure 5b Schematic diagram b of coupled inductor T network;

[0053] Figure 5c is a schematic diagram of a coupled inductor T network c;

[0054] Figure 5d d is a schematic diagram of the coupled inductor T network;

[0055] Figure 6a It is the schematic diagram of isolated T network a;

[0056] Figure 6b It is the schematic diagram of isolated T network b;

[0057] Figure 7 It is a typical battery charging curve. The two curves represent the transformation of voltage and current respectively, and the horizontal axis is the charging time;

[0058] Figure 8 is a control block diagram of the present invention;

[0059] Fig. 9 It is the control principle diagram of the present invention. DETAILED DESCRIPTION

[0060] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments to facilitate a clear understanding of the present invention, but they do not constitute a limitation on the present invention.

[0061] Example 1

[0062] like Figure 1 As shown, the present invention provides a T-network-based, step-up and step-down bidirectional DC-DC converter with wide input and wide output, comprising:

[0063] Inverter unit (i.e. Figure 1 The full-bridge inverter module shown in FIG. 1 is used to convert a DC input voltage source or current source into an AC signal;

[0064] Voltage conversion unit (i.e. Figure 1 The resonant cavity shown in ), which is provided with N cascaded T networks, N is a positive integer; wherein each T network realizes the conversion between voltage and current, its individual gain is determined by parameter design, and the total gain of the N T networks is the product of the gains of each T network;

[0065] Rectification unit (ie Figure 1 The full-bridge rectifier module shown in FIG. 1 is used to convert an AC signal into a DC signal;

[0066] Wherein, after the DC input is converted into an AC signal by the inverter unit, a preset conversion mode is implemented by the voltage conversion unit, and a DC signal with a constant current or constant voltage characteristic is output by the rectifier unit;

[0067] In another working mode, an external DC power source is connected to the DC output terminal of the rectifier unit, and the DC energy is transmitted to the DC input terminal through reverse conversion, so as to charge the input side and realize bidirectional energy flow.

[0068] Specifically, in the voltage conversion unit, a two-port network is usually used to realize voltage conversion. A common two-port network is a T-type network (such as Figure 2a As shown). A T-type network usually consists of three branches, the impedances of which are Z 1 , Z 2 , Z 3 (like Figure 2a When the input of the T-type network is a voltage source, the output can be turned into a constant current source by configuring the appropriate parameters. Similarly, when the input of the T-type network is a current source, the output can be turned into a constant voltage source by configuring the appropriate parameters. In order to analyze the characteristics of the T-type network, add a load Ro to the T-type network (as shown in Figure 1). Figure 2a shown).

[0069] like Figure 2b As shown, according to the KCL and KVL principles, when the input voltage U of the T-type network in 、Input current I in , output voltage U o , output current I o When , the input-output relationship of the T-type network is:

[0070]

[0071] When the impedance of the T-type network is composed of inductance or capacitance, that is, Z 1 , Z 2 , Z 3 When both are pure imaginary numbers, T 11 and T 22 is a pure real number, T 12 and T21 is a pure imaginary number. At the same time, it can be seen from the reciprocal two-port network that T 11 T 22 -T 12 T 21 =1.

[0072] When the input of the T-type network is a voltage source, a constant current output can be achieved. According to formula (1), the following conditions must be met: T11 = 0, that is, Z 1 +Z 2 = 0. On this basis, if we want to further achieve zero phase angle (ZPA) output, that is, the input voltage and input current of the T-type network are in phase, we need to further satisfy Z 2 +Z 3 = 0. Therefore, the conditions and characteristics that need to be satisfied by the T-type network can be obtained as shown in formula (2).

[0073]

[0074] Among them, G vi Represents the gain when voltage source input is constant current output, Z in(cc) Indicates the input impedance during constant current output.

[0075] When the input of the T-type network is a constant current source, to achieve a constant current output, according to formula (1), it is necessary to satisfy T 22 =0, that is, Z 1 +Z 3 = 0. If you want to further implement ZPA output, you must satisfy Z 2 =∞. Therefore, the conditions and characteristics that the CC and ZPA outputs of the T-type network need to meet when the input is a constant current source are shown in equation (3).

[0076]

[0077] Among them, G ii Represents the gain when the current source inputs a constant current output, Z in(cc) Indicates the input impedance during constant current output.

[0078] When the T-type network input is a constant voltage source, to achieve a constant voltage output, according to formula (1), it is necessary to satisfy T 12 =0, that is, Z 1 +Z 3 = 0. If we want to further realize ZPA output, according to formula (1), we need to further satisfy Z 2 =∞. Therefore, the conditions and characteristics that the CV and ZPA outputs of the T-type network need to satisfy when the input is a constant voltage source are shown in equation (4).

[0079]

[0080] Among them, G vv Represents the gain when the voltage source inputs a constant voltage output, Z in(cv) Indicates the input impedance when constant voltage is output.

[0081] When the T-type network input is a constant current source, to achieve a constant voltage output, according to formula (1), it is necessary to satisfy T 21 =0, that is, Z 2 +Z 3 = 0. If the ZPA output is to be further satisfied, then according to formula (1), Z 1 +Z 2 = 0. Therefore, the conditions and characteristics that the CV and ZPA outputs of the T-type network need to satisfy when the input is a constant current source are shown in equation (5).

[0082]

[0083] Among them, G iv Represents the gain when the current source inputs a constant voltage output, Z in(cv) Indicates the input impedance when constant voltage is output.

[0084] From the above analysis, it can be seen that only two types of T modules can achieve ZPA under CC or CV, one is the resonant T module and the other is the symmetrical T module, such as Figure 3a and Figure 3b shown.

[0085] The above four situations are listed in the table for easy comparison.

[0086] Table 1 Basic T network input and output characteristics

[0087]

[0088]

[0089] A typical T-type network unit usually consists of three branches, and the impedances on these three branches are Z 1 , Z 2 , Z 3 (like Figure 4a Here, Z i (i=1,2,3), such as Figure 4b As shown, it is usually a single inductor or capacitor. For complex scenarios, Z i (i=1,2,3) can also be a series-parallel combination of inductors and capacitors, which can be equivalent to a single inductor or capacitor branch at different operating frequencies. The derivation and calculation process of its CC, CV and ZPA properties is the same as the above T network.

[0090] This embodiment proposes a new T network. The T network includes three branches, the middle branch is provided with a capacitor, and the middle branch is provided with a capacitor; the inductance of at least one side of the two side branches is a coupled inductor and matches the impedance of the middle capacitor. For the case where the two sides of the typical T network are inductors and the middle is a capacitor, this embodiment uses a coupled inductor to replace the inductors on both sides of the typical T network. By matching the impedance of the coupled inductor and the capacitor, a new T network can be formed, which can reduce the number of components. The detailed implementation process is as follows. Figure 5a-5d As shown, Figure 5a This is an equivalent schematic diagram of the same decoupling of the same-named terminals;

[0091] Figure 5b It is a schematic diagram of an equivalent T network with the same terminals as the others; Figure 5c This is an equivalent schematic diagram of opposite decoupling of the same-named terminals; Figure 5d This is a schematic diagram of an equivalent T network with opposite ends of the same name. The derivation and calculation process of its CC, CV and ZPA properties is the same as the above T network.

[0092] Based on the above two T networks, the typical T network and the T network with coupled inductance, this embodiment further proposes an isolated T network, such as Figure 6a As shown, the transformer is behind the T network or as Figure 6b The transformer is shown before the T network.

[0093] That is, a transformer is cascaded on the basis of the above two T networks. Here, the transformer's excitation inductance does not participate in resonance, and the transformer only plays the role of electrical isolation and voltage conversion. The derivation and calculation process of its CC, CV and ZPA properties is the same as the above T network.

[0094] At least one T network in the voltage conversion unit is an isolated T network; the isolated T network is cascaded with a transformer on the basis of the T network to achieve electrical isolation and voltage conversion between the input end and the output end, and the excitation inductance of the transformer does not participate in the resonance, and the transformer ratio is n, where n is a positive integer; due to the introduction of a transformer, the voltage gain of the isolated T network is n times the gain of the corresponding non-isolated T network.

[0095] Specifically, when the input of the bidirectional DC-DC converter is a voltage source and the output is a constant current, the gain of a single non-isolated T network is the inverse of the impedance of its middle branch;

[0096] When the input of the bidirectional DC-DC converter is a current source and the output is a constant voltage, the gain of a single non-isolated T network is the impedance of its middle branch;

[0097] The gain, type, and number of T networks are selected based on the input and output requirements of the bidirectional DC-DC converter.

[0098] Preferably,

[0099] When the voltage conversion unit is a single T-type network:

[0100] (1) When the T network is a non-isolated T network, the gain of a single T network is shown in Table 1 above. That is:

[0101]

[0102] Among them, G vi Indicates the gain when voltage source input is constant current output; G iv Represents the gain when current source input is constant voltage output.

[0103] (2) When the T network uses an isolated T network, the gain of a single T network is n times as shown in Table 1 above. That is,

[0104]

[0105] in, Indicates the gain when voltage source input is constant current output; Represents the gain when current source input is constant voltage output.

[0106] When the voltage conversion unit is cascaded with two T-type networks:

[0107] (1) When the T network is a non-isolated T network, the gain of two T networks in cascade is:

[0108]

[0109] Among them, G vv Indicates the gain when the voltage source inputs a constant voltage output; G ii Represents the gain when a current source inputs a constant current output.

[0110] (2) When one of the T networks is an isolated T network, the purpose of the isolated T network is mainly to achieve electrical isolation. Generally, an isolated T network and a non-isolated T network can be combined. The gain when two T networks are cascaded is:

[0111]

[0112] in, It represents the gain when the voltage source input is constant voltage output, where n represents the transformer ratio, G vi (1) represents the gain of the first-stage T network when the voltage source input is constant current output, G iv (2) represents the gain of the second-stage T network constant current source input and constant voltage output; It represents the gain when the current source inputs a constant current output, where n represents the transformer ratio, G iv(1) represents the gain of the first-stage T network when the current source is input and the output is constant voltage, and Gvi(2) represents the gain of the second-stage T network when the constant voltage source is input and the output is constant current.

[0113] When the voltage conversion unit is a cascade of multiple T-type networks:

[0114] (1) When the T network is a non-isolated T network, the gain of two T networks in cascade is:

[0115]

[0116] Among them, G vv Indicates the gain when the voltage source inputs a constant voltage output, G vi Indicates the gain when voltage source input is constant current output; G ii Indicates the gain when the current source inputs a constant current output, G iv It indicates the gain when the current source inputs a constant voltage output. It can be found that when the number of T networks is even, the input is a voltage source and the output is a constant voltage source, and the input is a current source and the output is a constant current source; when the number of T networks is odd, the input is a voltage source and the output is a constant current source, and the input is a current source and the output is a constant voltage source. In this way, by reasonably designing the number of T networks, the expected function can be achieved.

[0117] (2) When the T network is an isolated T network, the purpose of the isolated T network is mainly to play the role of electrical isolation. Generally, an isolated T network is selected and combined with N-1 non-isolated T networks. The gain when multiple T networks are cascaded is:

[0118]

[0119] Where n is the transformation ratio of the transformer, It represents the gain when the voltage source input is constant voltage output. Indicates the gain when voltage source input is constant current output; Indicates the gain when the current source inputs a constant current output, indicating Gain when current source input and constant voltage output. It can be found that when the number of T networks is even, the input is a voltage source and the output is a constant voltage source, and the input is a current source and the output is a constant current source; when the number of T networks is odd, the input is a voltage source and the output is a constant current source, and the input is a current source and the output is a constant voltage source. In this way, by reasonably designing the number of T networks, the expected function can be achieved.

[0120] Example 2

[0121] The present invention proposes a novel step-up and step-down wide input and wide output bidirectional DC-DC converter (as shown in the attached figure) Figure 1As shown in the figure, it includes three parts, namely, an inverter unit, a voltage conversion unit and a rectifier unit. The inverter unit converts the DC input voltage into an AC voltage. The voltage conversion unit converts the voltage source into a current source, or the current source into a voltage source, by adopting a reasonable structure and configuring parameters reasonably. The number of conversion modules can actually be configured according to needs. For example, when the output is a voltage, the input voltage source can be converted into a current source by the first module, and then the current source can be converted into a voltage source. In this way, the voltage-to-voltage conversion can be achieved. The voltage conversion unit realizes the conversion from AC to AC. As a DC-DC converter, a third part, the rectifier unit, is also required, that is, to convert AC into the target DC. The rectifier unit can adopt uncontrolled rectification and fully controlled rectification circuits. If the energy flows in one direction, uncontrolled rectification can be used. If the energy flows in both directions, fully controlled rectification is used.

[0122] In the full-bridge inverter unit, Q1, Q4 and Q2, Q3 form two bridge arms respectively, and adopt complementary PWM control with dead zone respectively, and the duty cycle of each switch tube is 50%. The PWM control phase difference of the two bridge arms is θ, so the output voltage fundamental wave of the inverter is:

[0123]

[0124] Among them U in-DC is the DC input voltage.

[0125] In the voltage conversion unit, the input AC square wave power is converted by the T network and effectively adjusted to another voltage level of sine wave power for output. From left to right, it is the first-level T network, the transformer, and the second-level T network.

[0126] Among them, the first-level T network can realize the transformation from voltage source to current source by adjusting the inductance L p1 , L p2 , capacitor C p1 The parameters can control the current gain of the first-stage T network output, G iv It represents the current gain in the process of transforming the voltage source to the current source of the first-stage T network. The magnetizing inductance of the intermediate transformer does not participate in the resonance. The transformer plays the role of electrical isolation and voltage conversion here. n represents the transformation ratio of the transformer.

[0127] The second-stage T network can realize the transformation from current source to current source by adjusting the inductor L s1 ,L s2 , capacitor C s1 The parameters can control the voltage gain of the second-stage T network output, G iv It represents the voltage gain of the second-stage T network during the transformation from current source to voltage source. In this way, the total gain of the double-T network can be expressed as:

[0128] G vv =G iv *n*G iv

[0129] The rectifier unit can use uncontrolled rectification and fully controlled rectification circuits. If the energy flows in one direction, uncontrolled rectification can be used. If the energy flows in two directions, fully controlled rectification can be used. According to the fundamental wave approximation analysis method, the equivalent resistance R of the AC end can be obtained. ab The equivalent resistance R of the DC output o relation:

[0130]

[0131] Then the AC output of the double-T network circuit I ab and U ab , the battery DC current I can be rectified by the double-T network o-dc and DC voltage U o-dc According to the fundamental wave approximation analysis method, we can get:

[0132]

[0133] Based on the above analysis, the relationship between the total DC output voltage and the DC input voltage can be obtained as follows:

[0134]

[0135] It can be seen that the output voltage of the dual-T network is a function of the input voltage, phase shift angle θ, and dual-T network gain. By reasonably adjusting the input voltage / current, the phase shift angle between the two bridge arms of the full-bridge inverter unit, and the T network gain, wide input and wide output can be achieved. Here, Uin-DC is the DC source input voltage, which can be adjusted within a certain range at the DC source input end to meet the DC source access of different voltage levels; θ is the phase shift angle between the two half-bridge bridge arms of the full-bridge inverter unit, which can be used only through a simple PID controller to achieve phase shift control and adjust the voltage flowing into the dual-T network; G vv is the voltage gain of the dual-T network in the middle. The converter proposed in this embodiment, the symmetrical dual-T network has the potential to support bidirectional energy flow, which means that it may be applied to vehicle-to-grid (V2G) technology to enable electric vehicles to reversely supply power to the grid during peak power consumption.

[0136] The present invention proposes a dual-T network topology DC-DC converter with an isolation transformer. In the network, the transformer realizes electrical isolation between input and output, thereby improving the safety and stability of the system. By designing the excitation inductance of the transformer to be very large, much larger than the value of the resonant inductance on both sides thereof, it can be considered that the transformer only plays the functions of electrical isolation and voltage conversion in the dual-T network, which greatly simplifies the design of the resonant networks on both sides of the transformer and is also conducive to reducing the loss of the transformer part.

[0137] The DC-DC converter of the dual-T network topology has the function of stepping up and down, and can adapt to a wide range of input and output. It works in a fixed frequency mode and has the characteristics of constant voltage output, ensuring that the output voltage is stable and independent of load changes, simplifying the closed-loop control design. By adjusting the phase shift angle, the voltage of the input dual-T network can be effectively changed, and the output voltage can be accurately adjusted to the preset value. At the same time, it exhibits excellent dynamic performance due to its constant voltage characteristics. At the same time, considering that the battery equipment is charged in the constant current charging stage at the beginning, its equivalent internal resistance increases with the increase of voltage during the charging process, and closed-loop control can be used to make it a constant current output at the beginning stage, that is, to keep the ratio of the charging voltage to the equivalent internal resistance of the battery unchanged, so that constant current charging can be achieved. In this way, the designed dual-T network topology can charge the entire charging process of the battery, and the control is simple and the dynamic performance is good.

[0138] Example 3

[0139] The present invention also provides a control method for a T-network-based step-up / step-down wide-input and wide-output bidirectional DC-DC converter, comprising the following steps:

[0140] In the forward working mode, the DC input voltage source or current source is converted into an AC signal by controlling the inverter unit, and the AC signal is converted into a DC output via a voltage conversion unit and a rectifier unit composed of N cascaded T networks;

[0141] In the reverse working mode, when the external DC power supply is connected to the DC output terminal, the external DC power supply is converted into an AC signal, processed by the voltage conversion unit, and then transmitted to the DC input side, thereby realizing charging of the input side.

[0142] The above technical solution also includes the following steps:

[0143] The switching frequency of the inverter unit is fixed according to the power supply condition on the input side and the power demand on the output side of the bidirectional DC-DC converter;

[0144] By adjusting the phase shift angle between the bridge arms in the inverter unit, closed-loop control of the output DC voltage or output DC current is achieved.

[0145] Specifically, when the number of T networks is an odd number, when the input terminal is a voltage source input, constant current output can be automatically achieved. According to the fundamental wave approximation method, the relationship between the total DC output current and the DC input voltage is:

[0146]

[0147] Here, U in-DC is the DC source input voltage, which can be adjusted within a certain range to meet the needs of DC sources with different voltage levels; θ is the phase shift angle between the two bridge arms of the full-bridge inverter unit, which can be controlled by a simple PID controller to adjust the voltage flowing into the T network; G vi Indicates the gain when the voltage source inputs a constant current output; by reasonably adjusting the input voltage / current, the phase shift angle between the two bridge arms of the full-bridge inverter unit, and the T network gain, wide input and wide output can be achieved. Under fixed frequency regulation, the network automatically has the function of constant current output. If you want to achieve a constant voltage function, you can use a closed-loop PID controller to achieve phase shift control, change the output current of the converter, and ensure that the product of the output current and the load remains unchanged, so that the constant voltage function can be achieved.

[0148] When the number of T networks is an odd number, and the input terminal is a current source input, constant voltage output can be automatically achieved. According to the fundamental wave approximation method, the relationship between the total DC output voltage and the DC input current is:

[0149]

[0150] Here, I in-DC is the DC source input current, which can be adjusted within a certain range to meet the needs of DC sources with different current levels; θ is the phase shift angle between the two bridge arms of the full-bridge inverter unit, which can be controlled by a simple PID controller to adjust the voltage flowing into the T network; G iv Indicates the gain when the voltage source inputs a constant current output; by reasonably adjusting the input voltage / current, the phase shift angle between the two bridge arms of the full-bridge inverter unit, and the T network gain, wide input and wide output can be achieved. Under fixed frequency regulation, the network automatically has the function of constant voltage output. If you want to achieve a constant current function, you can use a closed-loop PID controller to achieve phase shift control, change the output voltage of the converter, and ensure that the ratio of the output voltage to the load remains unchanged, so that the constant current function can be achieved.

[0151] When the number of T networks is even, and the input terminal is a voltage source input, constant voltage output can be automatically achieved. According to the fundamental wave approximation method, the relationship between the total DC output voltage and the DC input voltage is:

[0152]

[0153] Here, U in-DC is the DC source input voltage, which can be adjusted within a certain range to meet the requirements of DC sources with different voltage levels; θ is the phase shift angle between the two bridge arms of the full-bridge inverter unit, which can realize phase shift control through a simple PID controller to adjust the voltage flowing into the T network; G vv Indicates the gain when the voltage source inputs a constant current output; by reasonably adjusting the input voltage / current, the phase shift angle between the two bridge arms of the full-bridge inverter unit, and the T network gain, wide input and wide output can be achieved. Under fixed frequency regulation, the network automatically has the function of constant voltage output. If you want to achieve a constant current function, you can use a closed-loop PID controller to achieve phase shift control, change the output voltage of the converter, and ensure that the ratio of the output voltage to the load remains unchanged, so that the constant current function can be achieved.

[0154] When the number of T networks is even, and the input terminal is a current source input, constant current output can be automatically achieved. According to the fundamental wave approximation method, the relationship between the total DC output current and the DC input current is:

[0155]

[0156] Here, I in-DC is the DC source input current, which can be adjusted within a certain range to meet the needs of DC sources with different current levels; θ is the phase shift angle between the two bridge arms of the full-bridge inverter unit, which can be used to achieve phase shift control through a simple PID controller to adjust the voltage flowing into the T network; G ii Indicates the gain when the voltage source inputs a constant current output; by reasonably adjusting the input voltage / current, the phase shift angle between the two bridge arms of the full-bridge inverter unit, and the T network gain, wide input and wide output can be achieved. Under fixed frequency regulation, the network automatically has the function of constant current output. If you want to achieve a constant voltage function, you can use a closed-loop PID controller to achieve phase shift control, change the output current of the converter, and ensure that the product of the output current and the load remains unchanged, so that the constant voltage function can be achieved.

[0157] In summary, the T network converter can provide an efficient, stable and flexible solution for the charging management of electric vehicle energy storage batteries through its unique constant voltage / constant current output, fixed gain and closed-loop regulation functions, promoting the sustainable development of the electric vehicle industry.

[0158] Example 4

[0159] The present invention also provides a power conversion system, comprising:

[0160] a first DC power supply;

[0161] A second DC power supply;

[0162] The bidirectional DC-DC converter is configured to realize bidirectional energy transmission between the first DC power supply and the second DC power supply, and realizes the functions of wide input and wide output through the cascaded T network and its gain design.

[0163] The first DC power source is a DC energy storage device, including but not limited to: a battery energy storage system for home or industrial use, a backup power system, a distributed energy storage unit, or an energy storage device based on a fuel cell or other DC energy conversion technology.

[0164] The second DC power supply is a DC power supply system, including but not limited to a power grid system, a photovoltaic power generation system, a DC energy storage system or a distributed DC microgrid.

[0165] Theoretically, the T-network converter has the potential to support bidirectional energy flow, which means it is possible to be applied to vehicle-to-grid (V2G) technology to enable electric vehicles to reversely supply power to the grid during peak hours. In actual deployment, it is usually necessary to combine advanced technical components such as bidirectional intelligent control devices and smart meters to ensure efficient, stable and safe bidirectional energy exchange between electric vehicles and the grid. Through the optimization and integration of these technical means, the T-network converter is expected to play an important role in V2G applications.

[0166] A typical battery charging curve is as follows: Figure 7 As shown in the figure, the initial charging of electric vehicles is constant current charging, and then gradually transitions to the constant voltage charging stage. When the battery voltage is lower than the maximum charging voltage of 450V, the current controller is activated to charge the battery in CC mode, and the voltage controller is deactivated. Once the battery voltage reaches its maximum charging voltage, the current controller is automatically disconnected, and the voltage controller is turned on to charge the battery in CV mode. The current or voltage controller is controlled by PID. In order to flexibly adapt to the needs of the battery in different charging stages, the corresponding control block diagram is designed, as shown in the figure. Figure 8 , Fig. 9 As shown, through proper optimization, the efficiency and stability of the charging process are ensured. The specific implementation process of different types of input power sources is analyzed below.

[0167] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A T-network-based, step-up and step-down bidirectional DC-DC converter with wide input and wide output, characterized in that: include: An inverter unit, used to convert a DC input voltage source or current source into an AC signal; A voltage conversion unit is provided with N cascaded T networks, where N is a positive integer; each T network realizes the conversion between voltage and current, its individual gain is determined by parameter design, and the total gain of the N T networks is the product of the gains of each T network; A rectifier unit, used for converting an AC signal into a DC signal; Wherein, after the DC input is converted into an AC signal by the inverter unit, a preset conversion mode is implemented by the voltage conversion unit, and a DC signal with a constant current or constant voltage characteristic is output by the rectifier unit; In another working mode, an external DC power source is connected to the DC output terminal of the rectifier unit, and the DC energy is transmitted to the DC input terminal through reverse conversion, so as to charge the input side and realize bidirectional energy flow.

2. The T-network-based buck-boost bidirectional DC-DC converter with wide input and output according to claim 1, characterized in that: The T network includes three branches, the middle branch is provided with a capacitor, and the middle branch is provided with a capacitor; the inductance of at least one side of the two side branches is a coupled inductance and matches the impedance of the middle capacitor.

3. The T-network-based buck-boost bidirectional DC-DC converter with wide input and wide output according to claim 1, characterized in that: At least one T network in the voltage conversion unit is an isolated T network; the isolated T network is cascaded with a transformer on the basis of the T network to achieve electrical isolation and voltage conversion between the input end and the output end, and the excitation inductance of the transformer does not participate in the resonance, and the transformer ratio is n, where n is a positive integer; the voltage gain of the isolated T network is n times the gain of the corresponding non-isolated T network.

4. The T-network-based buck-boost bidirectional DC-DC converter with wide input and output according to claim 1, characterized in that: When the number of T networks is an odd number: when the input end is a voltage source input, the bidirectional DC-DC converter automatically achieves a constant current output; when the input end is a current source input, the bidirectional DC-DC converter automatically achieves a constant voltage output. When the number of T networks is an even number: when the input end is a voltage source input, the bidirectional DC-DC converter automatically achieves a constant voltage output; when the input end is a current source input, the bidirectional DC-DC converter automatically achieves a constant current output.

5. The T-network-based buck-boost bidirectional DC-DC converter with wide input and wide output according to claim 2, characterized in that: When the input of the bidirectional DC-DC converter is a voltage source and the output is a constant current, the gain of a single non-isolated T network is the reciprocal of the impedance of its middle branch; When the input of the bidirectional DC-DC converter is a current source and the output is a constant voltage, the gain of a single non-isolated T network is the impedance of its middle branch; The gain, type, and number of T networks are selected based on the input and output requirements of the bidirectional DC-DC converter.

6. A control method for a T-network-based step-up / step-down wide-input wide-output bidirectional DC-DC converter, characterized in that: The following steps are involved: In the forward working mode, the DC input voltage source or current source is converted into an AC signal by controlling the inverter unit, and the AC signal is converted into a DC output via a voltage conversion unit and a rectifier unit composed of N cascaded T networks; In the reverse working mode, when the external DC power supply is connected to the DC output terminal, the external DC power supply is converted into an AC signal, processed by the voltage conversion unit, and then transmitted to the DC input side, thereby realizing charging of the input side.

7. The control method of a T-network-based buck-boost wide-input and wide-output bidirectional DC-DC converter according to claim 6, characterized in that: The following steps are also included: The switching frequency of the inverter unit is fixed according to the power supply condition on the input side and the power demand on the output side of the bidirectional DC-DC converter; By adjusting the phase shift angle between the bridge arms in the inverter unit, closed-loop control of the output DC voltage or output DC current is achieved.

8. A power conversion system, characterized in that: include: a first DC power supply; A second DC power supply; The bidirectional DC-DC converter described in any one of claims 1 to 5 is configured to realize bidirectional energy transmission between the first DC power supply and the second DC power supply, and realizes the functions of wide input and wide output through the cascaded T network and its gain design.

9. The power conversion system according to claim 8, characterized in that: The first DC power source is a DC energy storage device, including but not limited to: a battery energy storage system for home or industrial use, a backup power system, a distributed energy storage unit, or an energy storage device based on a fuel cell or other DC energy conversion technology.

10. The power conversion system according to claim 8, characterized in that: The second DC power supply is a DC power supply system, including but not limited to a power grid system, a photovoltaic power generation system, a DC energy storage system or a distributed DC microgrid.

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