800V battery architecture high power density on-board charger

Abstract

The present invention relates to an 800V battery architecture high power density on-board charger, which is a two-stage structure on-board charger with a first-stage active power factor correction circuit and a second-stage isolated dual active bridge circuit. A bus capacitor C is connected in parallel between the two-stage circuits for storing low-frequency ripple. bus Using smaller bus capacitors improves system power density. The low-frequency ripple of the input power is stored in the bus capacitor, and the bus capacitor voltage varies with the stored low-frequency ripple period. Compared to active filters, this reduces the low-frequency ripple transmission path without adding additional power devices. At the same time, the DC power required for battery charging is accurately transmitted through dual active bridges. Since the battery end absorbs the DC component of the input power, the bus capacitor end absorbs the low-frequency ripple. Therefore, the same DC charging effect as traditional methods can be achieved.

Description

Technical Field

[0001] The present invention relates to a power electronics technology, and in particular to an 800V battery architecture high power density on-board charger. Background Art

[0002] With the rapid development and popularity of electric vehicles in recent years, conventional 400V power battery architectures have struggled to meet the demands for range and charging speed. Higher battery capacities and voltage architectures are becoming inevitable trends, and major electric vehicle manufacturers are currently developing 800V battery architectures. Onboard chargers are crucial for AC slow charging of power batteries. Because they are installed in vehicles, power density is crucial.

[0003] Figure 1 The schematic diagram of a two-stage on-board charger is shown. The first-stage active power factor correction circuit realizes the AC / DC function, and the second-stage isolated DC / DC circuit realizes the output of wide-range, precisely adjustable, low-ripple, high-quality DC power. Figure 2 The relationship between the input voltage and current of the on-board charger and the input power and output power is shown. When the unity power factor is guaranteed, the input power can be obtained by the input voltage v in (t) = U in sin(ωt) and input current i in (t) = I in sin(ωt) is calculated,

[0004]

[0005] From the above formula, we can get the input power P in (t) is a DC component P ave =U in I in / 2 superimposed with a low-frequency ripple P with twice the power frequency period ripple =-U in I in cos(2ωt) / 2, ω is the angular frequency. To ensure stable DC charging for the power battery, a larger DC bus capacitor C is usually required. bus Filter out the low-frequency ripple at the input, which seriously affects the power density of the on-board charger.

[0006] To reduce bus capacitance, researchers have proposed AC charging and active filtering solutions. AC charging transfers the input low-frequency ripple directly to the battery terminal to charge the battery, thereby reducing the demand for DC bus capacitance. However, the impact of AC charging current on battery capacity and life requires further in-depth verification. The active filter uses a bidirectional buck-boost circuit to transfer the low-frequency ripple to the auxiliary capacitor C.aux Above, such as Figure 3 As shown in the figure, since the system has no requirements for the auxiliary capacitor voltage, C aux The capacitance value can ensure that the voltage is as small as possible within a safe range. However, this method requires additional circuits, which increases system cost and control complexity.

[0007] A plug-in electric vehicle integrated charging system with active filtering (202010524083.X) proposes a method for reusing the three-phase converter in the motor to reduce DC bus capacitance. The three-phase converter can be viewed as a combination of a full-bridge and a half-bridge circuit. The full-bridge acts as a rectifier, while the half-bridge, along with external inductors and capacitors, forms an active filter. However, this reuse approach makes it difficult to optimize each system specifically. Although power devices are reused, the switching frequency is generally low, limiting the contribution to power density.

[0008] A method for suppressing high- and low-frequency ripple currents in electric vehicle single-phase onboard charging systems (201910580608.9) proposes a method for reusing the primary circuit of an auxiliary battery charger as an active filter for the onboard charger. However, this reuse method requires complete isolation of the onboard charger and the auxiliary battery charger, preventing their simultaneous use, limiting flexibility. Furthermore, the additional circuitry required to store low-frequency ripple increases the power transmission path, resulting in additional losses and reduced efficiency.

[0009] In summary, to increase the power density of onboard chargers, it is necessary to divert the input low-frequency power ripple to reduce the busbar capacitor volume. Existing solutions all have certain limitations. Therefore, using a simpler, more efficient, and cost-effective solution to divert low-frequency power ripple and improve system power density is of great practical significance. Summary of the Invention

[0010] In order to improve the power density of the on-board charger, an 800V battery architecture high power density on-board charger is proposed.

[0011] The technical solution of the present invention is: an 800V battery architecture high power density on-board charger, which is a two-stage structure on-board charger with a first-stage active power factor correction circuit and a second-stage isolated dual active bridge circuit, and a bus capacitor C for storing low-frequency ripple is connected in parallel between the two-stage circuits. bus .

[0012] Preferably, the output power of the first-stage active power factor correction circuit is a DC component superimposed with a low-frequency ripple, and the DC component is transmitted to the connected battery terminal through the second-stage isolated dual active bridge circuit, and the bus capacitor C bus By changing the capacitor voltage to store low-frequency ripple energy, the maximum energy stored in the bus capacitor in one cycle is E r The calculation is as follows:

[0013]

[0014] Among them U in and i in are the AC input voltage and input current values ​​respectively, ω is the input grid angular frequency, T S is the input grid power frequency period.

[0015] Preferably, the ripple energy stored as needed is equal to the energy stored in the process of bus capacitor voltage fluctuating between the maximum and minimum values, and the required bus capacitor values ​​corresponding to on-board chargers of different power levels are obtained, and the bus capacitor is selected according to the calculated values.

[0016] Preferably, the minimum value of the bus capacitor voltage is higher than the maximum value of the AC input.

[0017] The beneficial effects of the present invention are as follows: the present invention provides an 800V battery architecture high power density on-board charger, which uses a smaller capacity bus capacitor to improve the system power density for power batteries with an 800V battery architecture. The low-frequency ripple of the input power is stored in the bus capacitor, and the bus capacitor voltage varies with the stored low-frequency ripple period. Compared with active filters, the low-frequency ripple transmission path is reduced without adding additional power devices. At the same time, the DC power required for battery charging is accurately transmitted through dual active bridges. Since the battery end absorbs the DC component of the input power, the bus capacitor end absorbs the low-frequency ripple. Therefore, the same DC charging effect as the traditional method can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of a two-stage on-board charger;

[0019] Figure 2 This is the relationship between the input voltage and current of the on-board charger and the input power and output power;

[0020] Figure 3 is the active filter diagram;

[0021] Figure 4 This is a topological diagram of the on-board charger of the present invention;

[0022] Figure 5 Schematic diagram of the relationship between input power, output power, AC input voltage and bus capacitor voltage of the circuit of the present invention;

[0023] Figure 6 A diagram showing the busbar capacitance values ​​required for on-board chargers of different power levels according to the present invention;

[0024] Figure 7 This is the simulation waveform diagram of the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0026] like Figure 4 The topology diagram of the vehicle charger of the present invention is shown as an example of the totem pole PFC active power factor correction circuit. The active power factor correction circuit output is connected in parallel with the bus capacitor. The second stage circuit is an isolated dual active bridge circuit. Its topology is the same as the traditional vehicle charger with two stages, so no additional components are added. However, the first stage active power factor correction circuit output is connected in parallel with a capacitor C with a smaller capacitance. bus Because the larger filter capacitor in the traditional circuit is not used, the difference from the traditional method is that the output bus voltage of the first-stage active power factor correction circuit presents periodic changes. The bus capacitor C bus It is mainly used to filter out high-frequency ripple related to the switching frequency and store low-frequency ripple. For 800V voltage architecture, C bus The voltage can vary in a wider range, so a better energy storage effect can be achieved. The second-stage isolated DC / DC circuit uses a dual active bridge structure to provide isolation and precise adjustment of output power. In order to achieve the effect of providing DC charging to the battery, the power P required to be transmitted in the second stage is o Therefore, this solution can reduce the design complexity of magnetic components. bus Compared with the active filter solution, the shortened power transmission path can effectively reduce the conduction loss. Figure 5 The diagram shows the relationship between the circuit's input power, output power, AC input voltage, and bus capacitor voltage. The input power can be viewed as a DC component superimposed on a low-frequency ripple. The DC component is transferred to the battery terminal by the second-stage dual-active bridge circuit. The low-frequency ripple remains in the bus capacitor C. bus Therefore, the maximum energy E that the bus capacitor needs to store or release in one cycle r like Figure 5 The shaded area is shown in the figure, and the calculation is as follows:

[0027] Where T S is the input grid power frequency period.

[0028] Bus capacitance C bus The capacitor voltage will show periodic changes during the process of storing and releasing energy, such as Figure 5 Medium V CbusIf the minimum bus capacitor voltage is assumed to be V0, and this minimum value is higher than the maximum value of the AC input, then the maximum capacitor voltage V peak The power that needs to be transmitted can be calculated as follows:

[0029]

[0030] According to the relationship between capacitor voltage and instantaneous low-frequency ripple power, the instantaneous voltage V of the bus capacitor can be calculated. c (t) is:

[0031]

[0032] The first-stage active power factor correction circuit is essentially a Boost circuit. Its real-time input voltage V in and the output voltage V out Satisfaction relationship V out =V in / (1-D), the duty cycle D changes with the circuit output reference voltage. In the actual control process, the instantaneous duty cycle D of the AC / DC stage switch can adjust the bus capacitor voltage V c (t) To achieve the effect of storing low-frequency ripple, there is no need to change the control scheme of the first-stage active power factor correction circuit. If the minimum voltage of the bus capacitor is set to 350V and the maximum voltage is set to 900V, the ripple energy required to be stored is equal to the energy stored or released during the fluctuation of the bus capacitor voltage between the maximum and minimum values. According to the calculation of formulas (1) to (3), the required bus capacitor values ​​corresponding to on-board chargers of different power levels can be obtained, and the bus capacitor can be selected according to the calculated values. Figure 6 Figure 2 shows the required busbar capacitance values ​​for on-board chargers of different power levels. It can be seen that for a 3.3kW on-board charger, a busbar capacitance of 30μF can meet the requirement using the proposed method. This reduces the busbar capacitance by nearly a hundredfold compared to traditional methods, far exceeding the required busbar capacitance, thereby effectively improving the system's power density.

[0033] See the specific circuit structure of the example Figure 4 , where the input voltage v in (t) = 339sin(100πt), the battery voltage is 870V, the switching frequency is set to 100kHz, the bus capacitance is 30μF, and the transmission power is 3.3kW. Figure 7The simulation waveforms of the proposed solution are presented. The voltage and current inputs to the AC / DC circuit are both sinusoidal. By adjusting the duty cycle of the main switch in the active power factor correction circuit, the bus voltage is altered to store low-frequency ripple. A dual active bridge converter transmits the DC power required for battery charging. Simulation results demonstrate that the proposed method can achieve the same DC charging effect with a much smaller bus capacitor, without the need for additional components. This effectively reduces the bus capacitor capacity and increases the system's power density, validating the feasibility and superiority of the proposed method.

[0034] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. An 800V battery architecture high power density on-board charger, characterized in that: The two-stage on-board charger consists of a first-stage active power factor correction circuit and a second-stage isolated dual-active bridge circuit. A bus capacitor for storing low-frequency ripple is connected in parallel between the two stages. C bus ; The output power of the first-stage active power factor correction circuit is a DC component superimposed with a low-frequency ripple. The DC component is transmitted to the connected battery terminal through the second-stage isolated dual active bridge circuit. The bus capacitor C bus By changing the capacitor voltage to store low-frequency ripple energy, the maximum energy stored in the bus capacitor in one cycle E r The calculation is as follows: ， in U in and i in are the AC input voltage and input current values ​​respectively, ω is the input grid angular frequency, T S is the power frequency period of the input grid; The ripple energy to be stored is equal to the energy stored in the process of bus capacitor voltage fluctuating between the maximum and minimum values. The required bus capacitor values ​​corresponding to on-board chargers of different power levels are obtained, and the bus capacitor is selected based on the calculated values.

2. The 800V battery architecture high power density on-board charger according to claim 1, characterized in that: The minimum value of the bus capacitor voltage is higher than the maximum value of the AC input.

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