A charging circuit

Abstract

The present invention provides a charging circuit, which includes a DCDC circuit and a power adjustment circuit. The DCDC circuit includes a power supply DC1, switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, and a transformer T. The positive and negative electrodes of the power supply DC1 are connected to the switching transistors Q1, Q2, Q3, and Q4. The power adjustment circuit includes a battery bat, a switching transistor K1, and a diode D1. The switching transistor K1 and the diode D1 are connected in parallel across both ends of a capacitor C1. In the present invention, the charging current of the battery varies with the duty cycle D of the conduction of the switching transistor K1; the output power of the power adjustment circuit is low, thereby improving the efficiency and reducing the energy consumption; compared with the existing LLC and buck in series, since only part of the power passes through the power adjustment circuit and the stress on the switching transistor is small, the overall loss is small. Therefore, the efficiency of the circuit is increased by about 13%.

Description

Technical Field

[0001] The present invention relates to the technical field of charging circuits, and in particular to a charging circuit that can improve charging efficiency. Background Art

[0002] With the proposal of the dual-carbon requirements, energy-efficient and energy-saving energy has also developed rapidly. In particular, the number of lithium battery charging vehicles has doubled, posing new requirements for high-efficiency lithium battery charging converters. Common converter topologies include phase-shifted full-bridge, hard-switching full-bridge topologies, or LLC and buck / boost two-stage cascaded structures. Although the former two can achieve wide-range battery charging, they have low efficiency and low switching frequency, making it difficult to achieve high power density and restricting their application scope. The latter uses a two-stage cascaded structure. The LLC operates at the quasi-resonant point and has high efficiency, and the buck / boost regulates the voltage to achieve a wide-range output, but the cost increases and the control becomes complex. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present invention provides a charging circuit, and the present invention can improve the efficiency of the circuit.

[0004] The technical solution of the present invention is: a charging circuit, including a DCDC circuit and a power adjustment circuit. The DCDC circuit includes a power supply DC1, switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, and a transformer T. The positive and negative poles of the power supply DC1 are connected to the switching transistors Q1, Q2, Q3, Q4. Among them, the switching transistors Q1, Q2 are connected in parallel with the switching transistors Q3, Q4, the switching transistors Q1, Q2 are connected in series, and the switching transistors Q3, Q4 are connected in series.

[0005] The mid-nodes of the switching transistors Q1, Q2 and the mid-nodes of the switching transistors Q3, Q4 are respectively connected to the transformer T. One end of the secondary side of the transformer T is connected in parallel with the switching transistors Q5, Q6, and the other end of the secondary side of the transformer T is connected in parallel with the switching transistors Q7, Q8.

[0006] The other ends of the switching transistors Q5, Q6, Q7, Q8 are connected to the power adjustment circuit.

[0007] The power adjustment circuit includes a battery bat, a switching transistor K1, and a diode D1. One end of the switching transistor K1 is connected to the diode D1, the other end of the diode D1 is connected to the positive electrode of the battery bat, and the negative electrode of the battery bat is also connected to the switching transistor K1.

[0008] Preferably, the DCDC circuit further includes a resonant inductor Lr and a resonant capacitor Cr. The resonant inductor Lr is disposed between the switching transistors Q3, Q4 and the transformer T, and the resonant capacitor Cr is disposed between the switching transistors K1, K2 and the transformer T.

[0009] Preferably, a capacitor C1 is further connected in parallel to one side of the switching transistors Q7, Q8, and the capacitor C1 is connected in parallel to the diode D1 and the switching transistor K1.

[0010] Preferably, a capacitor C2 is further disposed between the negative electrode of the battery bat and the switching transistor K1.

[0011] Preferably, an inductor L1 is further disposed between the switching transistor K1 and the battery bat.

[0012] Preferably, the DCDC circuit operates near the resonance point. The turn-on time of the switching transistors of the DCDC circuit is half of the switching period, and the DCDC circuit operates at the highest efficiency operating point.

[0013] Preferably, the switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, and the switching transistor K1 are GAN devices, SIC devices, IGBT devices, or MOS devices.

[0014] Principle of the power adjustment circuit:

[0015] S1. During charging, the capacitor C1 charges the battery bat and the capacitor C2. At this time, the current of the battery bat is I 1 , and the switching period of the switching transistor K1 is T. Then, the charging charge Q c1 of the capacitor C1 to the capacitor C2 is:

[0016] Q c1 = I 1 * T;

[0017] S2. When the switching transistor K1 is closed, the closing time is D*T. The capacitor C2 charges the inductor L1. During this process, the discharging charge Q c2 of the capacitor C2 is:

[0018]

[0019] Wherein, C 2 is the capacitance value of the capacitor C2, U c2 is the voltage across the capacitor C2, D is the conduction duty ratio of the switching transistor K1, and L 1 is the inductance value of the inductor L1;

[0020] S3. When the switch K1 is turned off, the capacitor C2 and the inductor L1 charge the capacitor C1 through the diode D1; during this process, the capacitor C2 discharges the charge Q c3 is:

[0021]

[0022] S4. The entire switching period is T, and the charging and discharging charges of the capacitor C2 are equal, that is:

[0023] Q c1 = Q c2 + Q c3

[0024] Q c1 = C 2 * U c2

[0025] U c1 = U bat + U c2

[0026] Among them, U c1 is the voltage across the capacitor C1, and U bat is the voltage across the battery.

[0027] As can be seen from the above, the charging current I 1 of the battery bat changes with the duty cycle D of the conduction of the switch K1.

[0028] The beneficial effects of the present invention are:

[0029] 1. The charging current of the battery of the present invention changes with the duty cycle D of the conduction of the switch K1; it has the advantage of adjusting the charging current in a wide range, and the output power of the power adjustment circuit is low, thereby improving the efficiency and reducing the energy consumption;

[0030] 2. Compared with the existing LLC and buck in series, since the power adjustment circuit of the present invention only conducts part of the power and the stress on the switch is small, the overall loss is small. Therefore, the efficiency of the circuit is increased by about 13%, and the volume and cost are reduced by more than 50%. Description of the Drawings

[0031] Figure 1 is the circuit diagram of the present invention;

[0032] Figure 2 is the circuit diagram of the switch K1 of the power adjustment circuit of the present invention when it is turned on;

[0033] Figure 3 is the circuit diagram of the switch K1 of the power adjustment circuit of the present invention when it is turned off. Detailed Embodiments

[0034] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings:

[0035] As Figure 1 shown, the present invention provides a charging circuit, including a DCDC circuit and a power adjustment circuit. The DCDC circuit includes a power supply DC1, switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, and a transformer T. The positive and negative electrodes of the power supply DC1 are connected to the switching transistors Q1, Q2, Q3, and Q4. Among them, the switching transistors Q1, Q2 are connected in parallel with the switching transistors Q3, Q4. The switching transistors Q1, Q2 are connected in series, and the switching transistors Q3, Q4 are connected in series.

[0036] The midpoints of the switching transistors Q1, Q2 and the midpoints of the switching transistors Q3, Q4 are respectively connected to the transformer T. One end of the secondary side of the transformer T is connected in parallel with the switching transistors Q5, Q6, and the other end of the secondary side of the transformer T is connected in parallel with the switching transistors Q7, Q8. The other ends of the switching transistors Q5, Q6, Q7, Q8 are connected to the power adjustment circuit. A capacitor C1 is also connected in parallel on one side of the switching transistors Q7, Q8.

[0037] Preferably in this embodiment, the DCDC circuit further includes a resonant inductor Lr and a resonant capacitor Cr. The resonant inductor Lr is arranged between the switching transistors Q3, Q4 and the transformer T, and the resonant capacitor Cr is arranged between the switching transistors K1, K2 and the transformer T.

[0038] In this embodiment, the power adjustment circuit includes a battery bat, a switching transistor K1, and a diode D1. The switching transistor K1 and the diode D1 are connected in parallel across the capacitor C1, and one end of the switching transistor K1 is connected to the diode D1. The other end of the diode D1 is connected to the positive electrode of the battery bat, and the negative electrode of the battery bat is also connected to the switching transistor K1.

[0039] Preferably in this embodiment, a capacitor C2 is further arranged between the negative electrode of the battery bat and the switching transistor K1.

[0040] Preferably in this embodiment, an inductor L1 is further arranged between the switching transistor K1 and the positive electrode of the capacitor C2. The negative electrode of the battery bat is also connected to the positive electrode of the capacitor C2 and the inductor L1.

[0041] Preferably, in this embodiment, the DCDC circuit operates near the resonance point, the turn-on time of the switching transistor of the DCDC circuit is half of the switching period, and the DCDC circuit operates at the highest efficiency operating point.

[0042] Preferably, the switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, and the switching transistor K1 are GAN devices, SIC devices, IGBT devices, or MOS devices.

[0043] As Figure 2 and 3 shown, the working process of the charging circuit is as follows:

[0044] S1. During charging, the capacitor C1 charges the battery bat and the capacitor C2. At this time, the current of the battery bat is I 1 , the switching period of the switching transistor K1 is T, then the charging charge Q c1 of the capacitor C1 to the capacitor C2 is:

[0045] Q c1 = I 1 * T;

[0046] S2. When the switching transistor K1 is closed, the closing time is D * T, and the capacitor C2 charges the inductor L1. During this process, the discharging charge Q c2 of the capacitor C2 is:

[0047]

[0048] where C 2 is the capacitance value of the capacitor C2, U c2 is the voltage across the capacitor C2, D is the conduction duty cycle of the switching transistor K1, and L 1 is the inductance value of the inductor L1;

[0049] S3. When the switching transistor K1 is turned off, the capacitor C2 and the inductor L1 charge the capacitor C1 through the diode D1; during this process, the discharging charge Q c3 of the capacitor C2 is:

[0050]

[0051] S4. The entire switching period is T, and the charging and discharging charges of the capacitor C2 are equal, that is:

[0052] Q c1 = Q c2 + Q c3

[0053] Q c1 = C 2 * U c2

[0054] U c1 = U bat + U c2

[0055] wherein, U c1 is the voltage across capacitor C1, and U bat is the voltage across the battery.

[0056] As can be seen from the above, the charging current I of the battery bat 1 varies with the duty cycle D of the conduction of the switching transistor K1;

[0057] For example, at a rated output voltage of 500V, the output power of the DCDC circuit is 10kw, the loss is 250W, and the efficiency is 97.56%; the output power of the power adjustment circuit is:

[0058] 10kw * U C2 / U C1 = 10kw * 10 / 50 = 2kw;

[0059] The loss is 134W, the efficiency is 93.72%, the total loss is 384W, and the total efficiency is 96.3%.

[0060] At an output voltage of 400V, the output power of the DCDC circuit is 4.166kw, the loss is 124W, and the efficiency is 97.0%; the output power of the power adjustment circuit is:

[0061] 4.166kw * U C2 / U C1 = 4.166kw * 2 / 4 = 2.083kw

[0062] The loss is 95W, the efficiency is 95.6%, the total loss is 219W, and the total efficiency is 95.0%.

[0063] The above embodiments and those described in the specification are only to illustrate the principles and the best embodiments of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A charging circuit, characterized in that: it includes a DCDC circuit and a power adjustment circuit. The DCDC circuit includes a power supply DC1, switching transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, and a transformer T. The positive and negative poles of the power supply DC1 are connected to switching transistors Q1, Q2, Q3, and Q4. Among them, switching transistors Q1 and Q2 are connected in parallel with switching transistors Q3 and Q4. Switching transistors Q1 and Q2 are connected in series, and switching transistors Q3 and Q4 are connected in series; the midpoints of switching transistors Q1 and Q2, and the midpoints of switching transistors Q3 and Q4 are respectively connected to the transformer T. One end of the secondary side of the transformer T is connected in parallel with switching transistors Q5 and Q6, and the other end of the secondary side of the transformer T is connected in parallel with switching transistors Q7 and Q8. The other ends of switching transistors Q5, Q6, Q7, and Q8 are connected to the power adjustment circuit. A capacitor C1 is also connected in parallel on one side of switching transistors Q7 and Q8; the power adjustment circuit includes a battery bat, a switching transistor K1, and a diode D1. Switching transistor K1 and diode D1 are connected in parallel across the two ends of capacitor C1. One end of switching transistor K1 is connected to diode D1, and the other end of diode D1 is connected to the positive pole of battery bat. The negative pole of battery bat is also connected to switching transistor K1; the DCDC circuit further includes a resonant inductor Lr and a resonant capacitor Cr. The resonant inductor Lr is arranged between switching transistors Q3 and Q4 and the transformer T, and the resonant capacitor Cr is arranged between switching transistors K1, K2 and the transformer T; a capacitor C2 is also arranged between the negative pole of battery bat and switching transistor K1; an inductor L1 is also arranged between switching transistor K1 and the positive pole of capacitor C2. The negative pole of battery bat is also connected to the positive pole of capacitor C2 and inductor L1; the DCDC circuit operates near the resonance point, and the on-time of the switching transistors of the DCDC circuit is half of the switching period.

2. A charging circuit according to claim 1, characterized in that: the working process of the charging circuit is as follows: S1), during charging, capacitor C1 charges battery bat and capacitor C2. At this time, the current of battery bat is I 1 , the switching period of switch tube K1 is T, then the charging charge Q of capacitor C1 to capacitor C2 c1 is as follows: Q c1 = I 1 * T; S2), when the switch tube K1 is closed, the closing time is D*T, and the capacitor C2 charges the inductor L1. During this process, the discharging charge Q of the capacitor C2 is: c2 as follows: ； Among them, C 2 is the capacitance value of capacitor C2, U c2 is the voltage across capacitor C2, D is the conduction duty cycle of switch tube K1, L 1 is the inductance value of inductor L1; S3. When the switching transistor K1 is turned off, the capacitor C2 and the inductor L1 charge the capacitor C1 through the diode D1; during this process, the capacitor C2 discharges a charge Q c3 is as follows: ； S4. The entire switching period is T, and the charging and discharging charges of capacitor C2 are equal, that is: Q c1 = Q c2 + Q c3 ; Q c1 = C 2 * U c2 ; U c1 = U bat + U c2 ; Among them, U c1 is the voltage across capacitor C1, and U bat is the voltage across the battery.

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