Power modules provide efficient conversion of 400V and 800V systems for electric vehicles

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Power modules provide efficient conversion of 400V and 800V systems for electric vehicles

Posted Date: 2024-01-24

Currently, pure electric vehicles (BEV) and plug-in hybrid electric vehicles (PHEV) operate on a battery voltage of 800V, exceeding the conventional 400V series. The 800V battery is used to improve performance, reduce fast charging time, cope with increasing power consumption and extend cruising range.

A major challenge for electric vehicles using 800V batteries is that most of the public infrastructure for fast charging is not yet compatible with 800V batteries. Therefore, measures have been taken to equip 800V vehicles with built-in power adapters to enable 800V cars to be charged at conventional 400V charging stations. Bidirectional power modules are a way for 800V electric vehicles to support 400V infrastructure and are a unique voltage conversion method between 400V and 800V. Now, OEMs are solving this problem in different ways with various efficiencies.

The Porsche Taycan is the first mass-produced 800V electric vehicle and a pure electric vehicle released in 2019. This is a typical example of an 800V car being charged using a 400V charging infrastructure. A boost converter that converts the 400V input of the charger to a suitable 800V battery for the vehicle is installed on the vehicle and used as a DC on-board charger. This boost converter has a circuit that bypasses the input and output of the converter. When charging using an 800V charger, the boost converter will be bypassed and the 800V battery will be charged directly.

Figure 1: Porsche Taycan DC car charger connection

According to the manufacturer, when charging via an 800V charger, it takes about 20 minutes to charge the battery to 80% using 270kW fast charging. On the other hand, when using a 400V charger with a maximum capacity of 150kW, it takes approximately 35 minutes to charge the same amount of electricity.

Hyundai IONIQ 5 also uses an 800V main battery (available in 2021). The IONIQ 5 also has a boost function that can charge the vehicle's 800V battery using a regular 400V charger. But unlike the Porsche Taycan, it does not have a DC on-board charger and mainly uses a drive motor and an inverter to achieve the boost function (Figure 2).

Figure 2: Hyundai IONIQ 5 boost function configuration

A and B are the drive motor and inverter respectively. The fast charger is connected to the high-voltage terminal of the battery through switch S1 and to the neutral point of the motor through switch S2. When the vehicle is running, S1 and S2 will be turned on and A and B will operate as normal motors and inverters. When charging with a 400V charger, S2 is turned off, running motor A on the boost converter reactor and inverter B on the boost converter switch to charge the vehicle's 800V battery. If the charger supports 800V, closing S1 and opening S2 will bypass A and B and charge the 800V car battery directly. Using this method, a 400V charger can be used to charge an 800V vehicle without the need to install a dedicated boost converter.

The GM Hummer Electric Vehicle is a pure electric vehicle that will be produced starting in 2021. Unlike previous 800V pure electric vehicles, the high-voltage main battery is 400V. Although the car uses a 400V system, it is compatible with 800V chargers, improving fast charging performance.

Figure 3: GM Hummer electric vehicle battery configuration

It has a unique configuration (Figure 3) and supports 400V and 800V fast chargers. The 400V battery installed in the vehicle is divided into two 400V battery packs. Two 400V battery packs can be connected in parallel or in series via the connections of switches S1, S2 and S3. Under normal circumstances, including when the vehicle is running, only switches S1 and S2 are turned off, and the two battery packs are connected in parallel, which can be used as a 400V battery. The same is true when charging with a 400V charger. When supporting 800V charger, turn on the S1 and S2 switches and turn off only the S3 switch. The two battery packs will be connected in series and used as an 800V battery.

According to the manufacturer, it supports 800V chargers, which not only enables 350kW fast charging, but also allows the vehicle to travel 160 kilometers in just 10 minutes of charging.

Vicor’s battery virtualization solution

Power module manufacturer Vicor has come up with a unique "battery virtualization solution" using the company's high-density power modules. This is a boost converter technology that uses a 400V charger to charge an 800V battery, primarily using the company's proprietary bidirectional DC-DC converter that supports a fixed voltage conversion ratio.

The bidirectional fixed-ratio DC-DC converter is a converter without regulation (voltage stabilization) function. The input-output voltage ratio of the DC-DC converter is fixed, and the voltage can be expressed by the following equation:

Output voltage = input voltage x transformation ratio K

It is bidirectional, so it can be converted in reverse (when operating in reverse, output voltage = input voltage/K), and the internal series impedance is small, so it can be used as a transformer that can convert DC.

Figure 4: 37.5kW, 400V/800V fixed-ratio bidirectional converter

The battery virtualization solution places a fixed voltage conversion ratio bidirectional converter with a transformation ratio of 2 in front of the 800V battery, making the battery voltage of the 800V vehicle appear to be half of the 400V voltage (Figure 5). As charging proceeds, the voltage of an 800V battery will rise, and the voltage seen from the charger terminal will rise proportionately (1/2).

Figure 5: Vicor battery virtualization

The module (Figure 4) has an output power of 37.5kW, a peak efficiency of 99% and dimensions of 92 x 80 x 7.4 mm. Through parallel connection, high power and fast charging can be supported in a small space.

The advantage of using a bidirectional power module is that the 800V battery can power a 400V load when the battery is not charging.

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