DCDC converter suitable for wide voltage input range

Abstract

The present invention relates to a DCDC converter suitable for a wide voltage input range, comprising a first BUCK-BOOST unit and a second BUCK-BOOST unit, wherein the inputs of the first BUCK-BOOST unit and the second BUCK-BOOST unit are both connected to the voltage input terminal of the DCDC converter, and the outputs thereof are respectively connected to one end of the primary coil of a transformer; the driving signals of the first BUCK-BOOST unit and the second BUCK-BOOST unit are staggered by half a driving cycle, so that a full-bridge topology is formed for the primary coil of the transformer, and an alternating voltage or current is provided for the primary coil of the transformer. The DCDC converter suitable for a wide voltage input range of the present invention has the following beneficial effects: its structure is relatively simple and the input voltage range is relatively wide.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and more particularly to a DCDC converter suitable for a wide voltage input range. Background Art

[0002] High-voltage DC / DC converters have high operating voltages, which results in large switching losses, restricting efficiency improvements. At the same time, in high-voltage applications, soft switching needs to be achieved to reduce turn-on and turn-off losses, increase operating frequency, and reduce volume and weight. Existing phase-shifted full-bridge and LLC circuits can achieve high-voltage soft switching. However, the LLC circuit is mainly suitable for narrow-range input applications, while the front bridge arm of the phase-shifted full-bridge circuit is easy to achieve soft switching, while the lagging bridge arm is not easy to achieve. For wider input applications, both circuits are not applicable. Although some existing wide-range circuits can solve the problem of wide-range input, they have a complex structure and can only achieve partial soft switching of the front-stage circuit, and do not achieve soft switching of all switch tubes. Therefore, the existing DC / DC converters have the defects of a relatively complex structure and a narrow input voltage range. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a DCDC converter with a relatively simple structure and a wide input voltage range suitable for a wide voltage input range in view of the above-mentioned defects of the prior art that the structure is relatively complex and the input voltage range is relatively narrow.

[0004] The technical solution adopted by the present invention to solve the technical problem is: construct a DCDC converter suitable for a wide voltage input range, including a first BUCK-BOOST unit and a second BUCK-BOOST unit, the inputs of the first BUCK-BOOST unit and the second BUCK-BOOST unit are both connected to the voltage input end of the DCDC converter, and the outputs thereof are respectively connected to one end of the primary coil of a transformer; the driving signals of the first BUCK-BOOST unit and the second BUCK-BOOST unit are staggered by half a driving cycle, so that the connection parts of the first BUCK-BOOST unit and the second BUCK-BOOST unit and the primary coil of the transformer form a full-bridge topology for the primary coil of the transformer, and provide an alternating voltage or current for the primary coil of the transformer.

[0005] Furthermore, the first BUCK-BOOST unit includes a first bridge arm and a third bridge arm, the midpoints of the first bridge arm and the third bridge arm are connected through a first inductor, the first BUCK-BOOST unit obtains an input DC voltage through two ends of the first bridge arm, and outputs it from the midpoint of the third bridge arm after conversion between the first bridge arm and the third bridge arm; the second BUCK-BOOST unit includes a second bridge arm and a fourth bridge arm, the midpoints of the second bridge arm and the fourth bridge arm are connected through a second inductor, the second BUCK-BOOST unit obtains an input DC voltage through two ends of the second bridge arm, and outputs it from the midpoint of the fourth bridge arm after conversion between the second bridge arm and the fourth bridge arm.

[0006] Furthermore, the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm respectively include two controlled switch devices connected in series with each other, the connection point of the two switch ends in series is the midpoint of the bridge arm, and the two switch ends that are not connected to each other are the two ends of the bridge arm; the control end of each switch device in each bridge arm has a different switch control signal.

[0007] Furthermore, the full-bridge topology includes a full-bridge LLC resonant circuit.

[0008] Furthermore, the output end of the first BUCK-BOOST unit is connected to one end of the primary coil of the transformer through a first capacitor, and the output end of the second BUCK-BOOST unit is connected to the other end of the primary coil of the transformer through a third inductor; the switch device control signals of the third bridge arm and the fourth bridge arm enable the third bridge arm and the fourth bridge arm and the primary coil of the transformer to form a full-bridge LLC resonant circuit to provide alternating current for the primary coil of the transformer; the endpoints of the third bridge arm and the fourth bridge arm are connected in parallel, and one of the parallel-connected endpoints is connected to the equipotential on the primary side of the transformer; and a second capacitor is also connected in parallel between the two endpoints of the third bridge arm and the fourth bridge arm after the parallel connection.

[0009] Furthermore, the first BUCK-BOOST unit and the second BUCK-BOOST unit both adopt fixed-frequency phase modulation control; in the fixed-frequency phase modulation control, the switching frequencies of all switching devices are set frequencies, and the driving signals of the first BUCK-BOOST unit and the second BUCK-BOOST unit are staggered by half a period of the driving signal.

[0010] Furthermore, the driving signal of the first BUCK-BOOST unit includes a first BUCK driving signal and a first BOOST driving signal, which are respectively used to drive the switching devices of the BUCK and BOOST parts of the first BUCK-BOOST unit; the driving signal of the second BUCK-BOOST unit includes a second BUCK driving signal and a second BOOST driving signal, which are respectively used to drive the switching devices of the BUCK and BOOST parts of the second BUCK-BOOST unit.

[0011] Furthermore, the first BOOST driving signal is provided by the control unit, and the first BUCK driving signal obtains its duty cycle from the output voltage of the first BUCK-BOOST unit and its phase angle from the phase angle of the input voltage, thereby forming the driving signal; the second BOOST driving signal is provided by the control unit, and the second BUCK driving signal obtains its duty cycle from the output voltage of the second BUCK-BOOST unit and its phase angle from the phase angle of the input voltage, thereby forming the driving signal.

[0012] Furthermore, the first BOOST driving signal acts on the third bridge arm, and the first BUCK driving signal acts on the first bridge arm; the second BOOST driving signal acts on the fourth bridge arm, and the second BUCK driving signal acts on the second bridge arm.

[0013] Furthermore, the first BOOST driving signal and the second BOOST driving signal are both 0.5; the duty ratio of the first BUCK driving signal and the second BUCK driving signal is DT S or 1-DT S , where DT S It is the duty cycle of the upper switch device of the first bridge arm or the second bridge arm obtained by detecting the output voltage of the BUCK-BOOST unit.

[0014] The DCDC converter suitable for a wide voltage input range of the present invention has the following beneficial effects: due to the staggered parallel connection of two BUCK-BOOST units, the input voltage is input into two BUCK-BOOST topologies, so its input range can vary widely; at the same time, according to the two BUCK-BOOST units connected as above, a full-bridge circuit is formed for the primary coil of the transformer, and an alternating current is applied to the coil, so overall, a separate full-bridge switch tube is saved, so its structure is relatively simple. Therefore, its structure is relatively simple and the input voltage range is relatively wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a circuit diagram of a DCDC converter in an embodiment of a DCDC converter suitable for a wide voltage input range of the present invention;

[0016] Figure 2 is a working waveform diagram of each switch device in the embodiment;

[0017] Figure 3 4 is a diagram showing the corresponding relationship between the driving waveform and the current waveform of the first BUCK-BOOST unit in the embodiment. DETAILED DESCRIPTION

[0018] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0019] like Figure 1 As shown, in an embodiment of a DCDC converter suitable for a wide voltage input range of the present invention, the DCDC converter includes a first BUCK-BOOST unit (including Figure 1 Q1, Q2, Q9 and Q10 in the second BUCK-BOOST unit (including Figure 1 The inputs of the first BUCK-BOOST unit and the second BUCK-BOOST unit are both connected to the voltage input terminal of the DCDC converter (the voltage input terminal is Figure 1 The outputs are connected to one end of the primary coil of the transformer Tr; see Figure 2, the driving signals of the first BUCK-BOOST unit and the second BUCK-BOOST unit are staggered by half a driving cycle (i.e., the phase of one driving signal is 180 degrees ahead or behind the phase of the other driving signal), so that the connection part of the first BUCK-BOOST unit, the second BUCK-BOOST unit and the primary coil of the transformer forms a full-bridge topology for the primary coil of the transformer, providing an alternating voltage or current for the primary coil of the transformer. This arrangement is connected to the BUCK-BOOST circuit for the input voltage end, so that even if the input voltage fluctuates greatly, the voltage or current applied to the primary coil of the transformer can meet the set requirements through the BUCK-BOOST circuit, so that the DCDC converter is not sensitive to the input voltage and can be used in a variety of occasions or harsh environments. At the same time, through the control of the driving waveform of the BUCK-BOOST unit or circuit, on the basis of realizing the input voltage adjusted in a wider range, the switching action of the switching device connected to the primary coil of the transformer forms a full-bridge switch driving topology for the primary coil of the transformer, thereby greatly improving the variable range of the input voltage and realizing a relatively simple driving structure.

[0020] In this embodiment, if Figure 1 As shown, the first BUCK-BOOST unit includes a first bridge arm (composed of Figure 1 Q1 and Q2 in the bridge) and the third bridge arm (composed of Figure 1 The first bridge arm and the third bridge arm are connected at midpoints through a first inductor L2. The first BUCK-BOOST unit obtains an input DC voltage through both ends of the first bridge arm, and after conversion between the first bridge arm and the third bridge arm, it is output from the midpoint of the third bridge arm and electrically connected to one end of the primary coil of the transformer. The second BUCK-BOOST unit includes a second bridge arm (composed of Figure 1 Q3 and Q4 in the bridge arm) and the fourth bridge arm (composed of Figure 1 The second bridge arm and the fourth bridge arm are connected at the midpoint through the second inductor L1, and the second BUCK-BOOST unit obtains the input DC voltage through the two ends of the second bridge arm, and after the conversion between the second bridge arm and the fourth bridge arm, it is output from the midpoint of the fourth bridge arm and electrically connected to the other end of the primary coil of the transformer. Specifically, Figure 1As shown, the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm each include a controlled switch device connected in series with two switch ends, the connection point of the two switch ends (i.e., the series connection point of the two switch devices) is the midpoint of the bridge arm, and the two unconnected switch ends are the two ends of the bridge arm; the control end of each switch device in each bridge arm has a different switch control signal. Figure 2 The specific waveforms of these switching devices (switching tubes) under one situation are shown.

[0021] In this embodiment, in order to further improve the performance of the DCDC converter and realize the soft switching of all switching devices, the full-bridge topology includes a full-bridge LLC resonant circuit. Specifically, the output end of the first BUCK-BOOST unit is connected to one end of the primary coil of the transformer through the first capacitor Cr, and the output end of the second BUCK-BOOST unit is connected to the other end of the primary coil of the transformer through the third inductor Lr; and the switch device control signals of the third bridge arm and the fourth bridge arm make the third bridge arm and the fourth bridge arm and the primary coil of the transformer form a full-bridge LLC resonant circuit to provide alternating current for the primary coil of the transformer; wherein the endpoints of the third bridge arm and the fourth bridge arm are connected in parallel, and one of the paralleled endpoints is connected to the equipotential on the primary side of the transformer; and a second capacitor Cbus is also connected in parallel between the two endpoints of the third bridge arm and the fourth bridge arm after the parallel connection.

[0022] For the driving signal of the entire converter, the first BUCK-BOOST unit and the second BUCK-BOOST unit both adopt fixed-frequency phase modulation control; in the fixed-frequency phase modulation control, the switching frequencies of all switching devices are set frequencies, and the driving signals of the first BUCK-BOOST unit and the second BUCK-BOOST unit are staggered by half a cycle of the driving signal. The driving signal of the first BUCK-BOOST unit includes a first BUCK driving signal and a first BOOST driving signal, which are respectively used to drive the switching devices of the BUCK and BOOST parts of the first BUCK-BOOST unit; the driving signal of the second BUCK-BOOST unit includes a second BUCK driving signal and a second BOOST driving signal, which are respectively used to drive the switching devices of the BUCK and BOOST parts of the second BUCK-BOOST unit.

[0023] Among them, the first BOOST driving signal (i.e. Figure 2 The driving waveform or driving signal of Q9 and Q10 in the embodiment is provided by the control unit (it is worth mentioning that the generation of such a driving signal can be easily realized for the control unit of the existing DCDC power supply, and only needs to be set in advance), and the first BUCK driving signal (i.e. Figure 2 The driving waveform or driving signal of Q1 and Q2 in the first BUCK-BOOST unit is obtained by obtaining its duty cycle from the output voltage of the first BUCK-BOOST unit and its phase angle from the phase angle of the input voltage, thereby forming the driving signal; the second BOOST driving signal (i.e. Figure 2 The driving waveform or driving signal of Q11 and Q12 in the embodiment is provided by the control unit, and the second BUCK driving signal (i.e. Figure 2 The driving waveform or driving signal of Q3 and Q4 in the embodiment of the present invention is obtained by obtaining its duty cycle from the output voltage of the second BUCK-BOOST unit and obtaining its phase angle from the phase angle of the input voltage, thereby forming the driving signal.

[0024] As mentioned above, the first BOOST drive signal acts on the third bridge arm, and the first BUCK drive signal acts on the first bridge arm; the second BOOST drive signal acts on the fourth bridge arm, and the second BUCK drive signal acts on the second bridge arm. The first BOOST drive signal and the second BOOST drive signal are both 0.5; the duty ratio of the first BUCK drive signal and the second BUCK drive signal is DT S or 1-DT S , where DT S The duty cycle of the upper switch device of the first bridge arm or the second bridge arm is obtained by detecting the output voltage of the BUCK-BOOST unit. In this embodiment, the upper switch device refers to the switch device connected to the positive terminal of the input power supply in the bridge arm (i.e., the first bridge arm or the second bridge arm). Figure 1 In this case, it refers to Q1 and Q3; that is, DT S It refers to the duty cycle of Q1 and Q3 obtained by detecting their corresponding output voltages respectively; while 1-DT S is the driving signal duty cycle of the lower switch device on the bridge arm (i.e. Figure 1 The duty cycle of the Q2 and Q4 drive signals in the DT is shown in Figure 1. Taking the first BUCK-BOOST unit formed by Q1, Q2, Q9, and Q10 as an example, the above DT S See the process or principle of obtaining Figure 3 Since Q9 and Q10 work at a fixed 50% duty cycle, Q1 and Q2 work in a complementary state, where the duty cycle of Q1 is defined as D Q1 , conduction time D Q1 T s The entire drive is staggered by 180 degrees. For the first BUCK-BOOST unit mentioned above, the mathematical relationship of a switching cycle can be obtained based on the volt-second balance of the voltage across the inductor:

[0025] V i (t1-t0)=(Vo -V i )(t2-t1)+V o (t3-t2)

[0026] After sorting, we can get:

[0027] V i (t2-t0)=V o (t3-t1)

[0028] t2-t0 is the on-time of Q1, and t3-t1 is the fixed 50% on-time.

[0029]

[0030] Among them, M is the ratio of output voltage to input voltage, that is, voltage gain. Therefore, in actual operation, the above DT S , that is, D Q1 The gain of the output voltage closed-loop feedback can be obtained. The second BUCK-BOOST unit is roughly the same as the first BUCK-BOOST unit, and the above DT is also obtained through the voltage gain of its own circuit. S value.

[0031] From another perspective, the interleaved parallel Buck-Boost LLC cascade converter circuit adopted by the present invention has a front stage composed of two Buck circuits interleaved in parallel, wherein Q1, Q2 and L2 constitute one Buck circuit, and Q3, Q4 and L1 constitute another Buck circuit; its rear stage is composed of a full-bridge LLC resonant circuit, wherein the front bridge arm of the phase-shifted full bridge is composed of Q9 and Q10, and a Buck-Boost circuit is formed at point B through L2 and the Buck circuit composed of Q1 and Q2. The rear bridge arm is composed of Q11 and Q12, and at point A, another Buck-Boost circuit is formed through L2 and the Buck circuit composed of Q3 and Q4. The two Buck-Boost circuits are connected in parallel by sharing the full-bridge switch tube with the above-mentioned full-bridge LLC resonant converter, and are output through transformer T1 and a synchronous rectification circuit.

[0032] In the above circuit, the control method used is fixed frequency phase modulation control. Taking the Buck-Boost circuit composed of Q1, Q2, Q9 and Q10 (i.e. the first Buck-Boost unit) as an example, first, keep the switching frequency of all switches unchanged, and set the duty cycle D of Q9 and Q10 to S9 and D S10 The duty cycle D of Q1 is obtained by output voltage feedback. S1 , and the duty cycle of Q2 is 1-D S1 , and then the corresponding phase angle δ is obtained by detecting the input voltagei The control method of the Buck-Boost circuit composed of Q3, Q4, Q11 and Q12 (i.e., the second Buck-Boost unit) is the same as above, but the control of the Buck-Boost circuit composed of Q1, Q2, Q9 and Q10 is staggered by half a cycle, thereby achieving the purpose of staggered parallel control. The specific working waveform is as follows Figure 2 Taking the first BUCK-BOOST unit as an example, the order in which the switches are turned on is Q1→Q10→Q9→Q2→Q1, and the order in which the switches are turned on in the second BUCK-BOOST unit is Q3→Q12→Q11→Q4→Q1.

[0033] It can be clearly seen from the above description that in this embodiment, the staggered parallel Buck-Boost LLC cascade converter circuit combines two Buck-Boost circuits and a full-bridge LLC resonant converter together, so that the circuit that requires 16 switch tubes to implement can be implemented by only 8 switch tubes, reducing the switching elements and drive circuits by half. At the same time, the above control method is implemented by the above switch device, so that the staggered parallel Buck-Boost LLC cascade converter can achieve a wide range of input / output in high-power applications, and in the full working range, each switch tube can achieve ZVS (zero-crossing switch), which greatly reduces the switching loss and improves the overall efficiency and power density of the converter. That is, the soft switching of all switch tubes in a wide range of high-voltage and high-power converters is realized, reducing switching losses and improving power density. In addition, the realization of soft switching can increase the switching operating frequency and further reduce the volume and weight of the converter. Therefore, whether from the perspective of the BUCK-BOOST unit or from the perspective of the front and rear stage BUCK and full bridge, the organic combination of the unit circuits, the connection relationship between the unit circuits, the resonant topology and the drive signal in this embodiment enables it to achieve the reduction of switching devices and soft switching of all switching devices on the basis of being applicable to a larger range of input voltage changes, thereby improving the performance of the entire converter under high frequency and high voltage conditions.

[0034] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A DCDC converter suitable for a wide voltage input range, characterized in that: The invention comprises a first BUCK-BOOST unit and a second BUCK-BOOST unit, wherein the inputs of the first BUCK-BOOST unit and the second BUCK-BOOST unit are both connected to the voltage input terminal of the DCDC converter, and the outputs thereof are respectively connected to one end of the primary coil of the transformer; the driving signals of the first BUCK-BOOST unit and the second BUCK-BOOST unit are staggered by half a driving cycle, so that the connection parts of the first BUCK-BOOST unit and the second BUCK-BOOST unit and the primary coil of the transformer form a full-bridge topology for the primary coil of the transformer, thereby providing an alternating voltage for the primary coil of the transformer. or current; the first BUCK-BOOST unit includes a first bridge arm and a third bridge arm, the midpoints of the first bridge arm and the third bridge arm are connected through a first inductor, the first BUCK-BOOST unit obtains an input DC voltage through the two ends of the first bridge arm, and outputs it from the midpoint of the third bridge arm after conversion between the first bridge arm and the third bridge arm; the second BUCK-BOOST unit includes a second bridge arm and a fourth bridge arm, the midpoints of the second bridge arm and the fourth bridge arm are connected through a second inductor, the second BUCK-BOOST unit obtains an input DC voltage through the two ends of the second bridge arm, and outputs it from the midpoint of the fourth bridge arm after conversion between the second bridge arm and the fourth bridge arm.

2. The DCDC converter suitable for a wide voltage input range according to claim 1, characterized in that: The first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm respectively include two controlled switch devices connected in series at the switch ends, the connection point of the two switch ends in series is the midpoint of the bridge arm, and the two switch ends that are not connected to each other are the two ends of the bridge arm; the control end of each switch device has a different switch control signal.

3. The DCDC converter suitable for a wide voltage input range according to claim 2, characterized in that: The full-bridge topology includes a full-bridge LLC resonant circuit.

4. The DCDC converter suitable for a wide voltage input range according to claim 3, characterized in that: The output end of the first BUCK-BOOST unit is connected to one end of the primary coil of the transformer through a first capacitor, and the output end of the second BUCK-BOOST unit is connected to the other end of the primary coil of the transformer through a third inductor; the switch device control signals of the third bridge arm and the fourth bridge arm enable the third bridge arm and the fourth bridge arm and the primary coil of the transformer to form a full-bridge LLC resonant circuit to provide alternating current for the primary coil of the transformer; the endpoints of the third bridge arm and the fourth bridge arm are connected in parallel, and one of the parallel-connected endpoints is connected to the equipotential on one side of the primary of the transformer; and a second capacitor is also connected in parallel between the two endpoints of the third bridge arm and the fourth bridge arm after the parallel connection.

5. The DCDC converter suitable for a wide voltage input range according to claim 4, characterized in that: The first BUCK-BOOST unit and the second BUCK-BOOST unit both adopt fixed-frequency phase modulation control; in the fixed-frequency phase modulation control, the switching frequencies of all switching devices are set frequencies.

6. The DCDC converter suitable for a wide voltage input range according to claim 5, characterized in that: The driving signal of the first BUCK-BOOST unit includes a first BUCK driving signal and a first BOOST driving signal, which are respectively used to drive the switching devices of the BUCK and BOOST parts of the first BUCK-BOOST unit; the driving signal of the second BUCK-BOOST unit includes a second BUCK driving signal and a second BOOST driving signal, which are respectively used to drive the switching devices of the BUCK and BOOST parts of the second BUCK-BOOST unit.

7. The DCDC converter suitable for a wide voltage input range according to claim 6, characterized in that: The first BOOST driving signal is provided by a control unit, and the first BUCK driving signal obtains its duty cycle from the output voltage of the first BUCK-BOOST unit and obtains its phase angle from the phase angle of the input voltage, thereby forming the driving signal; the second BOOST driving signal is provided by a control unit, and the second BUCK driving signal obtains its duty cycle from the output voltage of the second BUCK-BOOST unit and obtains its phase angle from the phase angle of the input voltage, thereby forming the driving signal.

8. The DCDC converter suitable for a wide voltage input range according to claim 7, characterized in that: The first BOOST driving signal acts on the third bridge arm, and the first BUCK driving signal acts on the first bridge arm; the second BOOST driving signal acts on the fourth bridge arm, and the second BUCK driving signal acts on the second bridge arm.

9. The DCDC converter suitable for a wide voltage input range according to claim 7, characterized in that: The first BOOST driving signal and the second BOOST driving signal are both 0.5; the duty ratio of the first BUCK driving signal and the second BUCK driving signal is DT S or 1-DT S , where DT S It is the duty cycle of the upper switch device of the first bridge arm or the second bridge arm obtained by detecting the output voltage of the BUCK-BOOST unit.

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