Next-generation 800V battery architecture on-board charger input low-frequency ripple transfer method

Abstract

The present invention provides a method for transferring low-frequency ripple input to a next-generation 800V battery architecture on-board charger. For power batteries with an 800V battery architecture, the present invention transfers the DC component of the input power and the low-frequency ripple to the battery end with a higher voltage, reducing the system's demand for DC bus capacitance and improving the auxiliary capacitor's ripple storage capacity. The first-stage interleaved parallel Buck circuit of the reused two-stage DC converter is used as an active filter for the on-board charger to transfer low-frequency ripple to provide DC charging for the power battery. The entire system can improve the power density of the system without introducing additional devices.

Description

Technical Field

[0001] The present invention relates to a method for transferring low-frequency ripple input to a next-generation 800V battery-based onboard charger, and belongs to the technical field of onboard chargers for electric vehicles. Background Art

[0002] With the rapid development and popularity of electric vehicles in recent years, concerns about battery life and charging speed have become topics of concern. Higher battery capacities and higher battery voltage architectures are inevitable trends. Onboard chargers and DC converters are key components of electric vehicles and are both connected to the power battery, making power density crucial.

[0003] like Figure 1 As shown in the figure, in the commonly used two-stage on-board charger, the first stage active power factor correction circuit realizes the AC / DC function, and the second stage is an isolated DC / DC circuit that outputs a wide range of accurately adjustable, low ripple, high-quality DC power. Figure 2 As shown, under the condition of ensuring unity power factor, the input power P in (t) can be determined by the input voltage v in (t) = U in sin(ωt) and input current i in (t) = I in sin(ωt) is calculated as shown below:

[0004]

[0005] From the above formula, we can get: input power P in (t) is a DC component Superimpose a low-frequency ripple with twice the power frequency period In order to ensure stable DC charging for the power battery, a larger DC bus capacitor C is usually required. bus Filter out low-frequency ripple at the input, which seriously affects the power density of the system.

[0006] In order to reduce the DC bus capacitance C bus To improve the system power density, researchers proposed a solution of AC charging and active filter. ripple Directly transmit to the battery end to charge the battery, thereby reducing the DC bus capacitance C bus However, the impact of AC charging current on battery capacity and life still needs further verification. The active filter uses a bidirectional Buck-boost circuit to convert low-frequency ripple P ripple Transfer to auxiliary capacitor C aux Above, such as Figure 3 As shown. Since the system has a large auxiliary capacitor Caux There is no voltage requirement, so the auxiliary capacitor C aux The capacitance value can ensure that its voltage is as small as possible within a safe range. However, this method requires the introduction of additional components, which increases the cost, and the commonly used lower bus voltage reduces the auxiliary capacitor C aux energy storage capacity.

[0007] The invention patent application with publication number CN113400959A, published on 20210917, proposes a method of reusing the three-phase inverter in the motor to improve the system power density. The three-phase converter can be regarded as a combination of a full-bridge and a half-bridge circuit. During the charging process of the power battery, the full-bridge can be used as a rectifier and the half-bridge can form an active filter with the motor winding and an external capacitor. The operating mode of the on-board charger and the motor is switched by three four-quadrant switches. However, this reuse method is difficult to optimize each system in a targeted manner. Although power devices are reused, the switching frequency is generally low.

[0008] Electric vehicles also have a low-voltage auxiliary battery that provides energy for the vehicle's low-voltage loads. The power battery recharges the low-voltage auxiliary battery through the vehicle's DC converter. An invention patent application published on November 12, 2019, with publication number CN110445227A, proposes a method for reusing the DC converter's primary circuit as an active filter for an onboard charger. However, this method is only applicable to a half-bridge configuration with a DC-blocking capacitor on the DC converter's primary side. As low-voltage loads increase, a full-bridge primary-side configuration becomes more suitable for high-power applications and is therefore required. This method also requires the introduction of an additional switching switch G on the DC converter's secondary side. Furthermore, because the battery's terminal voltage varies over a wide range during use, the DC converter needs to provide a wide gain range and step-down ratio. Figure 4 The two-stage structure shown is widely used due to its greater control freedom and design flexibility. Figure 4 In the DC converter shown, the first-stage interleaved parallel Buck circuit provides voltage regulation, and the second-stage uncontrolled DCX structure provides voltage reduction and isolation functions.

[0009] In summary, to reduce DC bus capacitance, it is necessary to transfer the input power's low-frequency ripple to increase system power density. Existing solutions all have limitations. Therefore, using a simpler and more efficient solution to transfer low-frequency ripple and increase system power density is of great practical significance. Summary of the Invention

[0010] The technical problem to be solved by the present invention is: to suppress the low-frequency ripple P ripple To provide DC charging for power batteries, the traditional two-stage structure of the on-board charger requires the introduction of a large DC bus capacitor, which seriously affects the system power density.

[0011] To address the above technical issues, the present invention provides a next-generation 800V battery-based onboard charger input low-frequency ripple transfer method. The method utilizes a three-stage circuit topology, including a first-stage AC / DC circuit for converting AC to DC, a second-stage isolated DC / DC circuit for voltage regulation and isolation, and a third-stage Buck circuit that reuses the first-stage interleaved parallel Buck circuit in the two-stage DC converter.

[0012] The input power of the first-stage AC / DC circuit contains DC components, low-frequency ripple, and high-frequency ripple. The DC bus capacitor C between the first-stage AC / DC circuit and the second-stage isolated DC / DC circuit bus Only the high-frequency ripple related to the switching frequency in the input power is filtered out, and the low-frequency ripple is transferred to the battery end; the third-stage Buck circuit acts as an active filter for the on-board charger to store the low-frequency ripple, and the output capacitor of the third-stage Buck circuit serves as an auxiliary capacitor C aux Absorb low frequency ripple.

[0013] Preferably, the auxiliary capacitor C aux Peak voltage V peak Expressed as:

[0014]

[0015] Where U in Indicates the peak value of the input AC voltage, I in represents the peak value of the input AC current, and ω represents the angular frequency of the AC input;

[0016] When the battery voltage is constant, establish the auxiliary capacitor C under different power conditions. aux Capacitance and peak voltage V peak Based on the relationship curve, the auxiliary capacitor C required by the on-board charger of the target power level at the current battery voltage is calculated. aux Capacitance value.

[0017] Preferably, the auxiliary capacitor C aux The voltage V aux (t) is expressed as:

[0018] Preferably, if the inductor of the third-stage Buck circuit operates in discontinuous conduction mode, the duty cycle D required by the main switch when calculating different power transmission directions based on the power required to be transmitted is:

[0019]

[0020] Where, L represents the inductance of the third-stage Buck circuit, Vb Indicates the power battery terminal voltage, V aux Indicates the auxiliary capacitor voltage.

[0021] For power batteries with 800V battery architectures, this invention shifts the DC component of input power and low-frequency ripple to the higher-voltage battery terminal, reducing the system's DC bus capacitance requirements. The interleaved parallel Buck circuit in the first stage of a two-stage DC converter is reused as an active filter for the onboard charger, shifting low-frequency ripple to provide DC charging for the power battery. This system improves power density without the need for additional components. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The commonly used two-stage structure of the on-board charger is shown;

[0023] Figure 2 The relationship between the input voltage, current and power of the on-board charger is shown;

[0024] Figure 3 The use of active filters to divert low-frequency ripple is illustrated;

[0025] Figure 4 The structure of a commonly used DC converter is shown;

[0026] Figure 5 illustrates the topological structure used in the present invention;

[0027] Figure 6 The relationship between the output power of the third-stage Buck circuit and the input low-frequency ripple is shown;

[0028] Figure 7 It shows that when the battery voltage is 870V, the auxiliary capacitor C aux Capacitance and peak voltage V peak the relationship between;

[0029] Figure 8 Indicates that during one cycle, the auxiliary capacitor voltage V aux (t) and the output power of the third-stage Buck circuit;

[0030] Figure 9 The simulation waveform of the solution proposed in the present invention is illustrated. DETAILED DESCRIPTION

[0031] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0032] like Figure 5 As shown in the figure, the topology used in the present invention is divided into three levels. The first-level AC / DC circuit realizes the function of converting AC to DC, and its input power contains DC component, low-frequency ripple and high-frequency ripple. The second-level isolated DC / DC circuit provides voltage regulation and isolation functions. In order to achieve better low-frequency ripple transfer and better steady-state performance, the present invention transfers the input low-frequency ripple to the battery end with higher voltage. The DC bus capacitor C bus Only high-frequency ripple associated with the switching frequency needs to be filtered out, significantly reducing the required capacity. To provide DC charging for the power battery, the third-stage Buck circuit reuses the first-stage interleaved parallel Buck circuit in the two-stage DC converter structure as an active filter for the on-board charger to store low-frequency input ripple.

[0033] As analyzed above, the input low-frequency ripple Among them, U in Indicates the peak value of the input AC voltage, I in Indicates the peak value of the input AC current, ω indicates the angular frequency of the AC input. In order to transfer this low-frequency ripple P ripple , providing DC charging for the power battery, the output power of the third-level Buck circuit needs to be consistent with the input low-frequency ripple P ripple cancel each other out, such as Figure 6 As shown, the shaded part represents the absorption of low-frequency ripple P ripple The maximum energy required to store E r It can be calculated by the following formula:

[0034]

[0035] Where, T s Indicates the period of AC input.

[0036] If the low-frequency ripple P of the third-stage Buck circuit is input ripple Can be auxiliary capacitor C aux Absorption, the auxiliary capacitor C aux Peak voltage V peak It can be calculated as follows:

[0037]

[0038] When the battery voltage is 870V, the auxiliary capacitor C aux Capacitance and peak voltage V peak The relationship between Figure 7 As shown. Figure 7 It can be seen that for a 3.3kW on-board charger, a 50μF auxiliary capacitor can meet the requirements. Since the energy stored in the auxiliary capacitor is the energy of the low-frequency ripple, the auxiliary capacitor voltage V aux The expression for (t) can be calculated as:

[0039]

[0040] like Figure 8 As shown: When the output power of the third-stage Buck circuit is less than zero, that is, the circuit works in the forward Buck mode, V aux (t) rise;

[0041] When the output power of the third-stage Buck circuit is greater than zero, that is, the circuit works in the reverse Boost mode, V aux (t)Descend.

[0042] If the inductor of the third-stage Buck circuit operates in discontinuous conduction mode, the duty cycle D required by the main switch in different power transmission directions can be calculated based on the power required to be transferred:

[0043]

[0044] Where, L represents the inductance of the third-stage Buck circuit, V b Indicates the power battery terminal voltage, V aux Indicates the auxiliary capacitor voltage.

[0045] like Figure 9 The simulation waveform of the proposed method is shown below. The input voltage v in (t) = 311sin(100πt), the battery voltage is 870V, the switching frequency is 100kHz, and the DC bus capacitor C bus The capacity is 44μF, auxiliary capacitor C aux The capacitance is 50μF and the transmission power is 3.3kW. The voltage and current of the first-stage AC / DC circuit input are both sinusoidal. The second-stage isolated DC / DC circuit transfers the DC component and low-frequency ripple of the input power to the battery end with a higher voltage, thereby reducing the voltage ripple of the DC bus. The input low-frequency ripple is transferred to the auxiliary capacitor C through the third-stage Buck circuit. aux The simulation results show that, using the method proposed in the present invention, a smaller bus capacitor can achieve a bus ripple less than 1.5V, verifying the feasibility and superiority of the method proposed in the present invention.

Claims

1. A next-generation 800V battery architecture on-board charger input low-frequency ripple transfer method, characterized by: A three-stage circuit topology is used, including a first-stage AC / DC circuit for achieving AC-DC conversion, a second-stage isolated DC / DC circuit for achieving voltage regulation and isolation, and a third-stage Buck circuit that reuses the first-stage interleaved parallel Buck circuit in the two-stage DC converter. The input power of the first-stage AC / DC circuit contains DC components, low-frequency ripple, and high-frequency ripple. The DC bus capacitor C between the first-stage AC / DC circuit and the second-stage isolated DC / DC circuit bus Only the high-frequency ripple related to the switching frequency in the input power is filtered out, and the low-frequency ripple is transferred to the battery end with higher voltage; the third-stage Buck circuit acts as an active filter for the on-board charger to store the low-frequency ripple, and the output capacitor of the third-stage Buck circuit acts as an auxiliary capacitor C aux Absorb low-frequency ripple; The auxiliary capacitor C aux Peak voltage V peak Expressed as: Where U in Indicates the peak value of the input AC voltage, I in represents the peak value of the input AC current, and ω represents the angular frequency of the AC input; When the battery voltage is constant, establish the auxiliary capacitor C under different power conditions. aux Capacitance and peak voltage V peak Based on the relationship curve, the auxiliary capacitor C required by the on-board charger of the target power level at the current battery voltage is calculated. aux Capacitance value; The auxiliary capacitor C aux The voltage V aux (t) is expressed as:

2. A next-generation 800V battery architecture on-board charger input low-frequency ripple transfer method as claimed in claim 1, characterized in that: If the inductor of the third-stage Buck circuit operates in discontinuous conduction mode, the duty cycle D required by the main switch for different power transfer directions is calculated based on the power required to be transferred: Where, L represents the inductance of the third-stage Buck circuit, V b Indicates the power battery terminal voltage, V aux Indicates the auxiliary capacitor voltage.

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