A dc-dc converter, system and control method with continuous input current

Abstract

This invention belongs to the field of power electronics technology and discloses a DC-DC converter, system, and control method with continuous input current. The converter includes: an input voltage source Vin, an input capacitor Co, a switching transistor S, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a first inductor L1, a second inductor L2, a third inductor L3, a first capacitor C1, a second capacitor C2, a third capacitor C3, an output capacitor C4, and a load R1. The topology of this invention achieves continuous input current, high voltage gain, low switching stress, and high efficiency. Furthermore, the topology is simple, using only one active switch, which simplifies the drive and control circuitry. It is suitable as a front-end converter in a photovoltaic parallel system.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a DC-DC converter, system, and control method with continuous input current. Background Technology

[0002] Photovoltaic systems are favored for their cleanliness, noiselessness, and low maintenance costs. However, the output voltage of a single photovoltaic cell is extremely low (approximately 0.5-0.8V), requiring them to be connected in series to form modules. In practical applications, the output voltage of photovoltaic modules is typically still at a low level (15-45V), making it difficult to directly meet the needs of medium- and high-voltage applications such as DC microgrids. Therefore, high-gain DC-DC converters are required to boost the voltage.

[0003] While traditional boost converters are simple in structure, they require extremely high duty cycles (e.g., >0.9) for high-gain applications, leading to severe semiconductor device stress, efficiency degradation, and electromagnetic interference (EMI). Although isolated converters can achieve high gain through transformer turns ratio, they suffer from drawbacks such as large size, high cost, and voltage spikes caused by leakage inductance. Non-isolated high-gain topologies, such as those based on voltage multipliers, switched inductors, and switched capacitors, have become a research hotspot. However, some existing high-gain topologies still have problems, such as: discontinuous input current, which is detrimental to photovoltaic cell operation and requires large-capacity input filters; excessive switching voltage or current stress; excessive number of components, resulting in complex structures; or voltage gain that still cannot meet the requirements of certain applications.

[0004] Therefore, there is an urgent need for a non-isolated DC-DC converter topology that can achieve high voltage gain at a moderate duty cycle, has continuous input current, low switching stress, relatively simple structure, and high efficiency.

[0005] Chinese Patent Publication No. CN111092548A, entitled "A High-Gain Cuk DC-DC Converter with Inductor-Capacitor Switching Network," includes a basic Cuk converter and several inductor-capacitor switching network units. Each inductor-capacitor switching network unit contains an inductor, a capacitor, and two diodes. This patent application can increase the voltage gain by adding different numbers of inductor-capacitor switching networks, but the structure of this patent application is complex and not easy to control. Summary of the Invention

[0006] To overcome the problems existing in the prior art, the present invention aims to provide a DC-DC converter, system, and control method with continuous input current. The topology of the present invention achieves continuous input current, high voltage gain, low switching stress, and high efficiency. Furthermore, the topology of the present invention is simple in structure, using only one active switch, which simplifies the drive and control circuitry. It is suitable as a front-end converter in a photovoltaic parallel system.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a DC-DC converter with continuous input current, comprising: an input voltage source Vin, an input capacitor Co, a switching transistor S, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a first inductor L1, a second inductor L2, a third inductor L3, a first capacitor C1, a second capacitor C2, a third capacitor C3, an output capacitor C4, and a load R1; The positive terminal of the input voltage source Vin is connected to the first terminal of the first inductor L1. The second terminal of the first inductor L1 is connected to the anode of the first diode D1 and the anode of the second diode D2. The cathode of the first diode D1 is connected to the first terminal of the second inductor L2, the cathode of the second diode D2, the first terminal of the first capacitor C1, the collector of the switch S, the second terminal of the second inductor L2, the anode of the third diode D3, and the first terminal of the second capacitor C2. The second terminal of the second capacitor C2 is connected to the second terminal of the third inductor L3 and the first terminal of the output capacitor C4. The second terminal of the third diode D3 is connected to the first terminal of the third inductor L3, the anode of the fourth diode D4, and the first terminal of the third capacitor C3. The cathode of the fourth diode D4 is connected to the second terminal of the fourth capacitor C4 and the anode of the fifth capacitor D5. The cathode of the fifth capacitor D5 is connected to the first terminal of the input capacitor Co and the first terminal of the load R1. The negative terminal of the input voltage source Vin is connected to the second terminal of the first capacitor C1, the emitter of the switch S, the second terminal of the third capacitor C3, the second terminal of the input capacitor Co, and the second terminal of the load R1.

[0008] Optionally, the switching transistor S is an IRFP460 type or CoolMOS type MOSFET switching transistor.

[0009] Optionally, both the input capacitor Co and the output capacitor C4 are aluminum electrolytic capacitors.

[0010] Optionally, the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, and the fifth diode D5 are all MUR460 type fast recovery diodes.

[0011] Optionally, the first inductor L1, the second inductor L2, and the third inductor L3 are all iron-silicon-aluminum magnetic ring type inductors.

[0012] Optionally, the first capacitor C1, the second capacitor C2, and the third capacitor C3 are all CBB or MKP type film capacitors.

[0013] Optionally, the minimum value Lmin of the first inductor L1 is:

[0014] Where IL is the average current, Vin is the input voltage, D is the duty cycle, fs is the switching frequency, and ΔiL is the allowable inductor current ripple rate.

[0015] Optionally, the minimum value of the output capacitor C4 is:

[0016] Where Io is the input current, D is the duty cycle, fs is the switching frequency, and ΔVo is the allowable output voltage ripple.

[0017] Secondly, the present invention provides a photovoltaic parallel power generation system, comprising multiple DC-DC converters with continuous input current connected in parallel, wherein each DC-DC converter with continuous input current is independently connected to a photovoltaic module as an input power source Vin.

[0018] Thirdly, the present invention provides a control method for a DC-DC converter with continuous input current, comprising the following steps: Step 1: Turn on the switch S, and the input power supply Vin excites the first inductor L1. The first capacitor C1 and the third capacitor C3 discharge through the second inductor L2 and the third inductor L3. The energy is transferred to the second inductor L2, the third inductor L3, the second capacitor C2 and the fourth capacitor C4. The fourth capacitor C4 supplies power to the load R1. Step 2: Turn off the switch S, demagnetize the first inductor L1, the second inductor L2 and the third inductor L3 and transfer energy to the load R1, the first capacitor C1, the second capacitor C2, the third capacitor C3 and the output capacitor C4, and charge the first capacitor C1 and the third capacitor C3. Step one and step two alternate in a loop.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves high voltage gain at a low duty cycle, mitigating the drawbacks of high duty cycles. It reduces current stress on photovoltaic sources or batteries, extending their lifespan and reducing input filtering requirements. The relatively low voltage and current stress on the power switches and diodes improves efficiency and reliability. Furthermore, it uses only one active switch, simplifying the drive and control circuitry.

[0020] Furthermore, this invention selects MOSFETs as power switches, whose high-frequency switching characteristics can further reduce conduction losses and improve converter efficiency.

[0021] Furthermore, the optimized topology and low-stress characteristics of this invention enable the converter to maintain high efficiency over a wide load range. This invention is applicable to parallel systems and is suitable for application in photovoltaic parallel steady-state power output (SPO) systems that require modularity and high reliability. Attached Figure Description

[0022] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely schematic to aid in understanding the invention and do not specifically limit the shapes and proportions of the components. In the drawings: Figure 1 This is a circuit topology diagram of the converter according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the switching transistor conduction mode according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the switch turn-off mode according to an embodiment of the present invention; Detailed Implementation To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0025] When an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments. The use of the term "horizontal" does not imply that the component is required to be absolutely horizontal, but rather that it may be slightly tilted. "Horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it may be slightly tilted.

[0026] It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification and appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0028] The present invention will now be described in detail with reference to the accompanying drawings.

[0029] like Figure 1 As shown, a DC-DC converter with continuous input current according to the present invention includes: an input voltage source Vin, an input capacitor Co, a switching transistor S, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a first inductor L1, a second inductor L2, a third inductor L3, a first capacitor C1, a second capacitor C2, a third capacitor C3, an output capacitor C4, and a load R1; The positive terminal of the input voltage source Vin is connected to the first terminal of the first inductor L1. The second terminal of the first inductor L1 is connected to the anode of the first diode D1 and the anode of the second diode D2. The cathode of the first diode D1 is connected to the first terminal of the second inductor L2, the cathode of the second diode D2, the first terminal of the first capacitor C1, the collector of the switch S, the second terminal of the second inductor L2, the anode of the third diode D3, and the first terminal of the second capacitor C2. The second terminal of the second capacitor C2 is connected to the second terminal of the third inductor L3 and the first terminal of the output capacitor C4. The second terminal of the third diode D3 is connected to the first terminal of the third inductor L3, the anode of the fourth diode D4, and the first terminal of the third capacitor C3. The cathode of the fourth diode D4 is connected to the second terminal of the fourth capacitor C4 and the anode of the fifth capacitor D5. The cathode of the fifth capacitor D5 is connected to the first terminal of the input capacitor Co and the first terminal of the load R1. The negative terminal of the input voltage source Vin is connected to the second terminal of the first capacitor C1, the emitter of the switch S, the second terminal of the third capacitor C3, the second terminal of the input capacitor Co, and the second terminal of the load R1.

[0030] This invention achieves high voltage gain at a low duty cycle, mitigating the drawbacks of high duty cycles. It reduces current stress on photovoltaic sources or batteries, extending their lifespan and reducing input filtering requirements. The relatively low voltage and current stress on the power switches and diodes improves efficiency and reliability. Furthermore, it uses only one active switch, simplifying the drive and control circuitry.

[0031] Example 1 A high-gain non-isolated DC-DC converter with continuous input current includes: an input voltage source Vin, an input capacitor Co, a switching transistor S, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a first inductor L1, a second inductor L2, a third inductor L3, a first capacitor C1, a second capacitor C2, a third capacitor C3, an output capacitor C4, and a load R1; The positive terminal of the input voltage source Vin is connected to the first terminal of the first inductor L1. The second terminal of the first inductor L1 is connected to the anode of the first diode D1 and the anode of the second diode D2. The cathode of the first diode D1 is connected to the first terminal of the second inductor L2, the cathode of the second diode D2, the first terminal of the first capacitor C1, the collector of the switch S, the second terminal of the second inductor L2, the anode of the third diode D3, and the first terminal of the second capacitor C2. The second terminal of the second capacitor C2 is connected to the second terminal of the third inductor L3 and the first terminal of the output capacitor C4. The second terminal of the third diode D3 is connected to the first terminal of the third inductor L3, the anode of the fourth diode D4, and the first terminal of the third capacitor C3. The cathode of the fourth diode D4 is connected to the second terminal of the fourth capacitor C4 and the anode of the fifth capacitor D5. The cathode of the fifth capacitor D5 is connected to the first terminal of the input capacitor Co and the first terminal of the load R1. The negative terminal of the input voltage source Vin is connected to the second terminal of the first capacitor C1, the emitter of the switch S, the second terminal of the third capacitor C3, the second terminal of the input capacitor Co, and the second terminal of the load R1.

[0032] The input capacitor Co and the output capacitor C4 are both filter capacitors. The first capacitor C1, the second capacitor C2, and the third capacitor C3 are all used to achieve voltage boosting and energy transfer.

[0033] In this embodiment, the DC-DC converter with continuous input current controls the switching transistor S to turn on and off, and alternately operates in two modes in Continuous Conduction Mode (CCM) to achieve high gain of input voltage and maintain continuous input current.

[0034] Mode 1 (Switching transistor S is on): such as Figure 2 As shown, when the switching transistor S is turned on, its channel forms a low-impedance path, and the input voltage V... in The current is directly applied across inductor L1, allowing the current in inductor L1 to rise rapidly and linearly, storing energy. Diodes D1 and D3 are off, while D2 and D4 are on. The input power supply Vin energizes inductor L1, while capacitors C1 and C3 discharge through inductors L2 and L3, transferring energy to inductors L2 and L3, capacitor C2, and capacitor C4. The output power is supplied to load R1 via capacitor C4.

[0035] Mode 2 (Switching transistor S is off): such as Figure 3As shown, diodes D1 and D3 are conducting, while diodes D2 and D4 are cut off. Inductors L1, L2, and L3 begin to demagnetize, transferring their stored energy to the load R1, capacitors C1, C2, C3, and C4. Simultaneously, inductors L1, L2, and L3 charge capacitors C1 and C3. When switch S is off, its body diode suppresses voltage spikes, protecting the circuit.

[0036] This alternating operating mode enables the converter to achieve efficient energy transfer and voltage boost. Its ideal voltage gain is... The gain is significantly higher than that of traditional Boost converters. An actual gain model is presented through analysis of non-ideal factors (parasitic parameters, diode voltage drop). Analysis shows that voltage and current stresses on the semiconductor device are effectively controlled.

[0037] This invention also provides a design method for key parameters that ensure the operation of CCM.

[0038] Based on the principles of charge conservation and volt-second balance, the relationship between the voltage gain (M) and duty cycle (D) of the converter under ideal conditions is expressed by the following formula:

[0039] Among them, V in V is the input voltage. o This is the output voltage. This gain is four times that of a conventional Boost converter at the same duty cycle.

[0040] Under non-ideal conditions, taking into account the equivalent series resistance of the inductor, the on-resistance of the switch, and the forward voltage drop of the diode, the actual voltage gain (Mnon) of the converter is... The ideal expression is:

[0041] Among them, R L R1 is the equivalent parasitic resistance, and V is the load resistance. D This represents the forward voltage drop of the diode. When the duty cycle is below 65%, the non-ideal gain is basically the same as the ideal gain; when the duty cycle is above 65%, the influence of non-ideal factors becomes significant.

[0042] To ensure CCM operation and control ripple, component parameters need to be designed appropriately. For example, in this embodiment, the input voltage V is set... in =50V, output voltage V o =200V (D=50%), output current I o =0.5A (P) o=100W), switching frequency f s =50kHz, inductor current ripple rate set to 20%, output voltage ripple rate set to 5%. The formula for calculating the minimum value Lmin of the first inductor L1 is:

[0043] Among them, I L V is the average current. in Where is the input voltage, D is the duty cycle, and f is the input voltage. s Δi is the switching frequency. L The allowable inductor current ripple rate.

[0044] Optionally, in this embodiment, the allowable inductor current ripple rate Δi L Take 20%.

[0045] The minimum value of the output capacitor C4 is:

[0046] Where Io is the input current, D is the duty cycle, fs is the switching frequency, and ΔVo is the allowable output voltage ripple.

[0047] The voltage and current stresses of the switching transistor S and the first diode D1, second diode D2, third diode D3 and fourth diode D4 are effectively suppressed. The normalized voltage stress is less than 0.5 times the output voltage and the normalized current stress is less than 2.5 times the output current. This is beneficial for selecting semiconductor devices with low stress specifications, reducing costs and switching losses.

[0048] The efficiency (η) of the DC-DC converter with continuous input current is calculated by taking into account inductor copper loss, semiconductor device conduction loss and switching loss. At a typical operating point with an output power of 200W and a duty cycle of 50%, the efficiency can reach more than 90%.

[0049] Example 2 A photovoltaic parallel power generation system includes multiple DC-DC converters with continuous input current, each converter being independently connected to a photovoltaic module as an input power source Vin. This system is suitable for DC microgrid interfaces.

[0050] Optionally, in each embodiment, three DC-DC converters with continuous input current are connected in parallel, and each DC-DC converter with continuous input current is connected to a photovoltaic panel as an input power source Vin, together supplying power to a 400V DC microgrid.

[0051] Unless otherwise specified, the equipment components involved in the above embodiments are all conventional equipment components, and the structural settings, working methods or control methods involved are all conventional settings, working methods or control methods in the art unless otherwise specified.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A DC-DC converter with continuous input current, characterized in that, include: Input voltage source Vin, input capacitor Co, switching transistor S, first diode D1, second diode D2, third diode D3, fourth diode D4, fifth diode D5, first inductor L1, second inductor L2, third inductor L3, first capacitor C1, second capacitor C2, third capacitor C3, output capacitor C4, and load R1; The positive terminal of the input voltage source Vin is connected to the first terminal of the first inductor L1. The second terminal of the first inductor L1 is connected to the anode of the first diode D1 and the anode of the second diode D2. The cathode of the first diode D1 is connected to the first terminal of the second inductor L2, the cathode of the second diode D2, the first terminal of the first capacitor C1, the collector of the switch S, the second terminal of the second inductor L2, the anode of the third diode D3, and the first terminal of the second capacitor C2. The second terminal of the second capacitor C2 is connected to the second terminal of the third inductor L3 and the first terminal of the output capacitor C4. The second terminal of the third diode D3 is connected to the first terminal of the third inductor L3, the anode of the fourth diode D4, and the first terminal of the third capacitor C3. The cathode of the fourth diode D4 is connected to the second terminal of the fourth capacitor C4 and the anode of the fifth capacitor D5. The cathode of the fifth capacitor D5 is connected to the first terminal of the input capacitor Co and the first terminal of the load R1. The negative terminal of the input voltage source Vin is connected to the second terminal of the first capacitor C1, the emitter of the switch S, the second terminal of the third capacitor C3, the second terminal of the input capacitor Co, and the second terminal of the load R1.

2. A DC-DC converter with continuous input current according to claim 1, characterized in that, The switching transistor S is an IRFP460 or CoolMOS type MOSFET switching transistor.

3. A DC-DC converter with continuous input current according to claim 1, characterized in that, Both the input capacitor Co and the output capacitor C4 are aluminum electrolytic capacitors.

4. A DC-DC converter with continuous input current according to claim 1, characterized in that, The first diode D1, the second diode D2, the third diode D3, the fourth diode D4, and the fifth diode D5 are all MUR460 type fast recovery diodes.

5. A DC-DC converter with continuous input current according to claim 1, characterized in that, The first inductor L1, the second inductor L2 and the third inductor L3 are all iron-silicon-aluminum magnetic ring type inductors.

6. A DC-DC converter with continuous input current according to claim 1, characterized in that, The first capacitor C1, the second capacitor C2, and the third capacitor C3 are all CBB or MKP type film capacitors.

7. A DC-DC converter with continuous input current according to claim 1, characterized in that, The minimum value Lmin of the first inductor L1 is: Where IL is the average current, Vin is the input voltage, D is the duty cycle, fs is the switching frequency, and ΔiL is the allowable inductor current ripple rate.

8. A DC-DC converter with continuous input current according to claim 1, characterized in that, The minimum value of the output capacitor C4 is: Where Io is the input current, D is the duty cycle, fs is the switching frequency, and ΔVo is the allowable output voltage ripple.

9. A photovoltaic parallel power generation system, characterized in that, It includes multiple DC-DC converters with continuous input current as described in any one of claims 1 to 8 connected in parallel, each DC-DC converter with continuous input current being independently connected to a photovoltaic module as an input power source Vin.

10. A control method for a DC-DC converter with continuous input current as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Turn on the switch S, and the input power supply Vin excites the first inductor L1. The first capacitor C1 and the third capacitor C3 discharge through the second inductor L2 and the third inductor L3. The energy is transferred to the second inductor L2, the third inductor L3, the second capacitor C2 and the fourth capacitor C4. The fourth capacitor C4 supplies power to the load R1. Step 2: Turn off the switch S, demagnetize the first inductor L1, the second inductor L2 and the third inductor L3 and transfer energy to the load R1, the first capacitor C1, the second capacitor C2, the third capacitor C3 and the output capacitor C4, and charge the first capacitor C1 and the third capacitor C3. Step one and step two alternate in a loop.

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