Electric vehicle fast charging circuit and control method

Abstract

The present invention discloses a fast charging circuit and a control method for an electric vehicle. The fast charging circuit for the electric vehicle includes a switching switch, a direct charging branch, an on-board charger branch, and a battery pack. The switching switch is connected to an external charging pile, and the direct charging branch or the on-board charger branch is selected to charge the battery pack. The control method specifically includes: first connecting the charging pile with the direct charging branch, and charging the battery pack through the direct charging branch; then disconnecting the direct charging branch, connecting the charging pile with the on-board charger branch, and charging the battery pack through the on-board charger branch. The present invention adds a small amount of components to the design of a conventional charger, and uses the on-board charger to fully charge the remaining power. The method does not require the user to manually switch to a slow charging pile, and does not require the entire vehicle to add boosting components. The method has the advantages of simple and practical operation, simple circuit structure, and low cost.

Description

Technical Field

[0001] The present invention relates to the field of electric vehicles, and in particular to a circuit and a control method for rapidly charging an electric vehicle by utilizing existing modules for power distribution and upgrading conventional designs at a relatively low cost. Background Art

[0002] The maximum output voltage of the current fast charging piles on the market is 750V, while the power battery of large electric vehicles such as buses and public transportation is about 785V when fully charged. There are two countermeasures for chargers at home and abroad. One is to stop charging after charging to 750V. The other is to add a boost module to the fast charging circuit to increase the voltage to 800V or above to fully charge the missing part. Figure 1 The figure shows a schematic diagram of how charging piles currently used in China and abroad charge new energy vehicles. During slow charging, the charging pile generates alternating current (AC), which is converted by the charging module into direct current (HV) to charge the power battery. During fast charging, the charging pile generates direct current (HV) to charge the power battery directly. Some products include a boost module to ensure a full charge of the power battery during fast charging.

[0003] These two solutions have their own shortcomings. Solution 1 affects customer experience, while Solution 2 is costly, increases weight and space, and its only function is to fully charge 36V. Therefore, most manufacturers choose Solution 1 without processing.

[0004] Therefore, how to design a charging circuit with fast charging, easy operation, simple structure and low cost is a technical problem that needs to be solved urgently in the industry. Summary of the Invention

[0005] In order to solve the above-mentioned defects in the prior art, the present invention proposes a fast charging circuit and a control method for an electric vehicle.

[0006] The technical solution adopted by the present invention is to design a fast charging circuit for electric vehicles, which includes a switching switch, a direct charging branch, an on-board charger branch, and a battery pack. The switching switch is connected to an external charging pile to select the direct charging branch or the on-board charger branch to charge the battery pack.

[0007] The direct charging branch is a DC bus.

[0008] The on-board charger branch adopts one of Vienna, totem pole, bridge PFC and bridgeless PFC.

[0009] The charging pile can be a DC charging pile, and the switch can select the direct charging branch or the on-board charger branch. When the on-board charger branch adopts a PFC module with two bridge arms, the positive output of the DC charging pile is connected to the midpoint of one bridge arm of the PFC module, and the negative output of the DC charging pile is connected to the midpoint of the remaining bridge arm of the PFC module. When the on-board charger branch adopts a PFC module with three bridge arms, the positive output of the DC charging pile is connected to the midpoint of two bridge arms of the PFC module, and the negative output of the DC charging pile is connected to the midpoint of the remaining bridge arm of the PFC module.

[0010] The charging pile can also be an AC charging pile, and the switch only switches on the on-board charger branch.

[0011] The present invention also designs a control method for an electric vehicle fast charging circuit. The fast charging circuit adopts the above-mentioned electric vehicle fast charging circuit. The control method specifically includes: first connecting the charging pile with the direct charging branch, and charging the battery pack through the direct charging branch; then disconnecting the direct charging branch, connecting the charging pile with the on-board charger branch, and charging the battery pack through the on-board charger branch.

[0012] The battery pack is charged through the direct charging branch. When the battery pack voltage reaches 750V, the direct charging branch is disconnected and the on-board charger branch is used to charge the battery pack. When the battery pack voltage reaches 800V, the charging is terminated.

[0013] The battery pack is charged through the direct charging branch. When the battery pack voltage reaches the maximum charging voltage of the charging pile, the direct charging branch is disconnected and the on-board charger branch is used to charge the battery pack. Charging is terminated when the battery pack voltage reaches 100% of the rated voltage of the battery pack.

[0014] The beneficial effects of the technical solution provided by the present invention are:

[0015] The present invention adds a small number of components to the design of a conventional charger and uses an on-board charger to fully charge the remaining power. It does not require the user to manually switch to a slow charging pile, and does not require the addition of boosting components to the entire vehicle. It has the advantages of easy and practical operation, simple circuit structure, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention is described in detail below with reference to the embodiments and accompanying drawings, in which:

[0017] Figure 1 It is a prior art circuit diagram;

[0018] Figure 2 This is a principle block diagram of a preferred embodiment of the present invention;

[0019] Figure 3 It is a three-phase AC voltage waveform diagram;

[0020] Figure 4 This is a schematic diagram of the current flow when the on-board charger branch uses a three-arm PFC module AC input;

[0021] Figure 5 This is a schematic diagram of the current flow when the on-board charger branch adopts a three-arm PFC module DC input. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] In response to the bottlenecks mentioned in the background technology, the present invention adds a switching switch while minimizing the cost, and utilizes the original on-board charger to boost the voltage to fully charge the power battery.

[0024] The invention discloses a fast charging circuit for electric vehicles, see Figure 2 The block diagram shows a switching switch, a direct charging branch, an onboard charger branch, and a battery pack. The switching switch is connected to an external charging station to select whether to charge the battery pack via the direct charging branch or the onboard charger branch. In a preferred embodiment, the direct charging branch is a DC bus.

[0025] Figure 2 The technical solution is to attach Figure 1 The boost device in the circuit is removed and replaced with a direct charging branch.

[0026] When charging, first connect the charging pile to the direct charging branch, and quickly charge the battery pack through the direct charging branch. When it is almost full, disconnect the direct charging branch, connect the charging pile to the on-board charger branch, and slowly charge the battery pack through the on-board charger branch. The on-board charger branch can increase the voltage to charge the remaining capacity until the battery pack is fully charged.

[0027] The onboard charger branch circuit can adopt one of the following topologies, including but not limited to Vienna, totem pole, bridge PFC, and bridgeless PFC. Any switching power supply topology that can use HV input can be applied to this invention, not limited to the three-phase circuit exemplified in the application.

[0028] In a preferred embodiment, the charging pile is a DC charging pile, and the switching switch can select the direct charging branch or the on-board charger branch.

[0029] When the battery pack voltage is low, the switch switches on the direct charging branch, and the charging pile directly charges the battery pack at HV200V~750V.

[0030] When the battery pack voltage is 750V, it is still 35V away from the full charge voltage of 785V. The control switch switches the charging pile line to the on-board charger, and the on-board charger increases the 750V fast charge voltage to 800V to charge the battery.

[0031] Based on the capacity of a conventional battery, a full charge of 35V voltage provides approximately 3.5 kWh of electricity.

[0032] If the car is equipped with a 22KW onboard charger, the time required to charge 3.5 kWh is: .

[0033] If the car is equipped with a 44KW onboard charger, the time required to charge 3.5 kWh is: .

[0034] The battery pack can be fully charged in just 5-10 minutes, and the cost is limited to a pair of high-voltage relays and the corresponding distribution busbars, making it far more cost-effective than installing a set of booster equipment. Furthermore, eliminating one piece of equipment reduces the risk of failure, which helps improve the reliability of the entire vehicle.

[0035] In an embodiment in which the charging pile adopts a DC charging pile, the on-board charger branch adopts a PFC module with two bridge arms; the positive output electrode of the DC charging pile is connected to the midpoint of one bridge arm in the PFC module, and the negative output electrode of the DC charging pile is connected to the midpoint of the remaining bridge arm in the PFC module.

[0036] In another embodiment where the charging pile adopts a DC charging pile (see Figure 4 and Figure 5 ), the on-board charger branch adopts a PFC module with three bridge arms; the positive output of the DC charging pile is connected to the midpoint of two bridge arms in the PFC module, and the negative output of the DC charging pile is connected to the midpoint of the remaining bridge arm in the PFC module.

[0037] Feasibility analysis of AC port input HV voltage:

[0038] The charging module needs to be rectified after AC input before it can work. In theory, it can use HV input.

[0039] Take three-phase AC input as an example, as shown in the attached Figure 3 As shown, it is the three-phase voltage waveform. Figure 4 This is a circuit diagram showing the flow of currents into L2 and L3 and the outflow of current from L1 when the on-board charger branch adopts a three-arm PFC module. Figure 5 This is a circuit diagram showing the flow of currents into L1 and L2 and the outflow of current from L3 when the on-board charger branch adopts a three-arm PFC module.

[0040] When three-phase input is used, the three tubes work alternately. Figure 4 As shown, the charger branch adopts a PFC module with three bridge arms, and the input is the current direction of AC. At this time, the three-phase input is Figure 3 At point A, currents from L1 and L2 flow in, and currents from L3 flow out (dashed arrows). The next state is point B, where currents from L2 flow in and currents from L1 and L3 flow out (solid arrows). Figure 5 This is a schematic diagram of the current flow when the on-board charger branch adopts a three-arm PFC module DC input.

[0041] This cycle alternates to form a DC voltage across the capacitor, which serves as the input to the subsequent DCDC stage. The DCDC step-up charges the power battery.

[0042] In order to improve the compatibility of the present invention, when the charging pile is an AC charging pile, the switch only selects the on-board charger branch.

[0043] In a preferred embodiment, the switching switch is a high-voltage relay.

[0044] A control method for an electric vehicle fast-charging circuit, wherein the fast-charging circuit adopts the above-mentioned electric vehicle fast-charging circuit, and the control method specifically comprises: first connecting a charging pile with a direct-charging branch to charge a battery pack through the direct-charging branch; then disconnecting the direct-charging branch, connecting the charging pile with an on-board charger branch, and charging the battery pack through the on-board charger branch.

[0045] The battery pack is charged through the direct charging branch. When the battery pack voltage reaches 750V, the direct charging branch is disconnected and the on-board charger branch is used to charge the battery pack. When the battery pack voltage reaches 800V, the charging is terminated.

[0046] The battery pack is charged through the direct charging branch. When the battery pack voltage reaches the maximum charging voltage of the charging pile, the direct charging branch is disconnected and the on-board charger branch is used to charge the battery pack. Charging is terminated when the battery pack voltage reaches 100% of the rated voltage of the battery pack.

[0047] The above embodiments are for illustration only and are not intended to be limiting. Any equivalent modifications or variations made thereto without departing from the spirit and scope of this application should be included in the scope of the claims of this application.

Claims

1. A fast charging circuit for electric vehicles, characterized in that: It includes a switching switch, a direct charging branch, an on-board charger branch, and a battery pack. The switching switch is connected to an external charging pile to select the direct charging branch or the on-board charger branch to charge the battery pack. When the charging pile is a DC charging pile, the switch can select the direct charging branch or the on-board charger branch; When the charging pile is an AC charging pile, the switch only switches on the on-board charger branch; When the charging pile is a DC charging pile, the battery pack is first charged through the direct charging branch. When the battery pack voltage reaches the maximum charging voltage of the charging pile, the direct charging branch is disconnected and the battery pack is charged using the on-board charger branch. Charging is terminated when the battery pack voltage reaches 100% of the rated voltage of the battery pack.

2. The electric vehicle fast charging circuit according to claim 1, characterized in that: The direct charging branch is a DC bus.

3. The electric vehicle fast charging circuit according to claim 1, characterized in that: The on-board charger branch adopts one of Vienna, totem pole, bridge PFC and bridgeless PFC.

4. The electric vehicle fast charging circuit according to claim 1, characterized in that: The on-board charger branch adopts a PFC module with two bridge arms; the positive output of the DC charging pile is connected to the midpoint of one bridge arm in the PFC module, and the negative output of the DC charging pile is connected to the midpoint of the remaining bridge arm in the PFC module.

5. The electric vehicle fast charging circuit according to claim 1, characterized in that: The on-board charger branch adopts a PFC module with three bridge arms; the positive output of the DC charging pile is connected to the midpoint of two bridge arms in the PFC module, and the negative output of the DC charging pile is connected to the midpoint of the remaining bridge arm in the PFC module.

6. A control method for a fast charging circuit of an electric vehicle, characterized in that: The fast charging circuit adopts the electric vehicle fast charging circuit according to any one of claims 1 to 5, and the control method specifically includes: First, connect the charging pile to the direct charging branch and charge the battery pack through the direct charging branch; Then disconnect the direct charging branch, connect the charging pile to the on-board charger branch, and charge the battery pack through the on-board charger branch.

7. The control method of the electric vehicle fast charging circuit according to claim 6, characterized in that: The battery pack is charged through the direct charging branch. When the battery pack voltage reaches 750V, the direct charging branch is disconnected and the on-board charger branch is used to charge the battery pack. When the battery pack voltage reaches 800V, the charging is terminated.

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