Figure 1. F1 Insights
For the F1 DC-DC Converter, these are the specifications we need to know:
- Voltage in: the voltage supplied by the battery.
- Voltage out: the voltage required by the electric motor.
- Converter Power: the power rating of the converter in Watts.
- Magnetizing Inductance: the inductance of the transformer.
- Switching Frequency: the frequency at which the switches in the converter will operate.
- Leakage Inductance: the inductance of the transformer that is not coupled to the primary or secondary windings.
- Turns Ratio: the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.
🔎 The topology chosen for the F1 DC-DC Converter can depend on different factors such as efficiency, cost, size, and performance requirements. For instance, if high efficiency and low EMI are crucial, the PSFB or LLC topologies are often preferred. The PSFB topology is commonly used for high-power applications due to its ability to handle high voltages and currents, while the LLC topology is favored for medium to high-power applications as it provides high efficiency and a wide input voltage range. Ultimately, the choice of topology depends on the specific application requirements and trade-offs between different factors.
📉 Assuming that the F1 DC-DC Converter needs to step down the voltage from the battery to the electric motor, we can use different topologies. Here is an example of the design parameters for the F1 DC-DC Converter:
- Voltage in: 400 V.
- Voltage out: 200 V.
- Converter power: 10 kW.
- Magnetizing inductance: 1.6 mH.
- Switching frequency: 100 kHz.
- Leakage inductance: 6 uH.
- Turns ratio: 1:2.
Based on these design parameters, we can select the appropriate components and calculate the required values for the circuit elements, including the Inductors, Capacitors, and Resistors. We can also use simulation software to verify the design and analyze its performance under different conditions.
⚙️ Design Process
Before continuing with the design process, the chosen topology must be identified and designed using similar approaches as previous designs. Once the topology has been established, further optimization can then be performed in order to achieve the desired performance specifications.
🤔 The first approach: Topology
As we embark on the task of designing a DC-DC Converter, we must take into account the possible variations in topology. For this purpose, we will explore the PSFB and LLC topologies. Let's begin with the PSFB Half-Bridge Center Tapped topology, which has fewer components and less current on the secondary side, allowing for a more compact design. We create an original design that we can use for all topologies and introduce some cooling. However, we discover that the temperature in this design is excessively high, leading us to investigate alternative topologies.
Next, we examine the PSFB Full Bridge topology, which is a well-established topology with much literature. We input the same parameters, design and obtain remarkable results, achieving a design that is capable of handling the required operation point. We can now proceed to optimize the design, which we will discuss in the following section. For now, let’s just focus on the selection of topology.
⚡ If our ultimate goal is to achieve maximum efficiency, we can opt for one of the most efficient topologies, namely the LLC topology. By employing resonant Converters, we can reduce losses and overall temperature and, as a result, have a more compact design. Therefore, we decide to go for an LLC Full-Bridge topology, and after uploading the design, we obtain results that confirmed its superiority in every aspect. We can now start the design process for our LLC Full-Bridge topology.
💡 Design
You can have a look at the design here. The original design uses the PSFB Half-Bridge topology. To fit the wires in the winding window, I use a customized PQ65/54 core made of 3C97 material, and this is the design that we will optimize.
Now that we've switched to the LLC topology, the distribution of losses has changed significantly, allowing us to reduce the core size to a standard PQ65/54 or PQ65/44 with a lower profile. By adjusting the turns and core size, we can achieve 10 turns on the primary side and 5 on the secondary, resulting in a design similar to Figure 2 with the custom core option.
