Abstract— This paper describes a novel method for verifying the filter design of high voltage components. Current approaches rely on dedicated component tests and neglect the interaction of the overall high voltage system. Through a holistic system simulation, it is possible to identify resonance points for the single components depending on their physical location within the car. This information can be used to improve the filter design as well as optimizing the switching strategies of the components.

I. INTRODUCTION
The high voltage system (HVS) of a battery electric vehicle (BEV) consists of a high voltage battery pack, at least one inverter to drive the electric machine and several auxiliary consumers, e.g. climate compressor and heating elements, which are connected via a cable harness. Due to the capacitive and inductive elements of the circuit, it is inevitable that resonance points occur. Norms such as LV123 or VW80300 define the maximum voltage ripple that a component is allowed to generate, and they also define the voltage ripple that a component must withstand [1]. A unified test setup is used to get comparable results. The goal of this setup is to emulate the HVS. However, this test setup is very simple and consists only of a simple voltage source in series with a resistor and an inductance. The inductance and resistor are supposed to mimic the impedance of the HVS as shown in Fig. 1.
However, as depicted in Fig. 2 in a real BEV several components are connected as to form the HVS. They interact with each other and can lead to resonances that are not observable with the simplified test setup. As a result, a component can pass the initial tests defined by the norms but once the components are connected, the system behavior changes and failures can occur.
The goal of virtual system integration is to bypass the single component tests by performing a holistic system analysis via simulation.
Fig. 1: Type 2 Test Setup according to VW 80 3000
Fig. 2: Example for HVS

II. DIGITAL HVS TWIN
The basic fundament to perform virtual system integration is a digital twin of the HVS which is capable of emulating the physical behavior of the target system. In our scope of application, the focus lies on the electrical interaction between the single HV components in context of voltage ripple at the input of each component, the load current of the interlink capacitors and the differential and common mode chokes. The main goal is to identify the effect of control strategies, modulation techniques and switching frequencies on the overall system behavior. The switching frequency of the power electronics injects the distortion with the highest frequency. State-of-the-art drive inverters use a switching frequency of up to 20 kHz and DCDC converts usually use a switching frequency of 100 kHz. To include the effect of the 2nd harmonic of the DCDC inverters switching frequency, the physical model needs a high fidelity until at least 200 kHz. All models presented in this paper are validated against measurements in a frequency range of up to 200 kHz or higher. This also means that EMI effects are currently not considered. (Even though the approach used in the virtual system integration is also valid for EMI simulations, but the complexity of the resulting simulation model is way too high.)
Fig. 3 gives an example of the simulation models which are used for the HVS simulation. A detailed explanation and examples will be shown in the final paper. In short, the following physical models are modelled in Matlab/Simulink using the Simscape Electrical Toolbox:
• Input filter of each component, such as climate compressor, heaters, OBCs, DCDCs and inverters: the schematics are provided by the supplier and transferred into a model in Simscape. Already existing components are also measured, and the impedance curve is compared with the simulation to validate its fidelity. For new car projects, the filter model of takeover parts can be reused, or similar components can be used for simulation to estimate the initial behavior.
• HV cables: Each cable type was at first modelled using FEM to extract the relevant parameters for its representation according to the telegrapher’s equations. In addition, measurements were performed to validate model fidelity. The cable parameter set up can be used to simulate each cable with various lengths to evaluate the effect on the overall HVS.
• Electric machine: The behavior is simulated by using flux based ud/uq equations. The machine is connected to a three-phase inverter to evaluate the interaction between DC and AC side.
• Inverter: The control algorithms and switching strategies of the calibration used in the car are used to achieve realistic behavior as it is intended in the real car. [2]
Fig. 3: Physical Models of High Voltage Components

III. VIRTUAL SYSTEM INTEGRATION
The digital HVS twin enables simulations of specific drive scenarios or tests defined by norms such as LV123 or VW80300. This method has two main advantages. First, the tests can be performed before real hardware is available. Design flaws can be discovered earlier, and the development cycle can be shortened. Second, the HVS system and its components are simulated as a whole instead of using unified test benches for each component. The location of each single component within the car is considered by using exact models of the cable harness which correspond to the length and the used cable type.
One test defined by the norm VW80300 is the maximum voltage dynamic and the maximum voltage ripple. Fig. 4 shows the simulation results of the performed test and the simulated voltage gradient and voltage ripple at the DCDC converter. In this test, the machine was operated with maximum torque. It can be seen that the maximum voltage gradient does not exceed -16.9 V/ms and the voltage ripple is below 10 Vpkpk and therefore the VW80300 test is passed. (In addition, the filters and sample rate of the DCDC voltage measurement was added as well, to evaluate the effect of the voltage ripples on the measured input voltage of the DCDC.)
Fig. 4: Simulated voltage gradients and ripple
As a result of the voltage ripple, the filter components of the HV components, e.g. the interlink capacitor, are stressed by an additional load current. This load current has to be considered during the design of the component and is important for the lifetime of the component. Especially during high load driving profiles, e.g. race start, high load currents occur in the HV filters, and it has to be guaranteed that the thermal operating area of the component is not exceeded. Since the digital HVS twin contains each single electric component, the electric stress can be calculated for dedicated components. Fig. 5 shows the simulated load current which occurs during the lifetime of a car over dedicated operating points (torque and speed of the electric drive). For a holistic system analysis, it is not only important to know how high the occurring load currents are, but also, how often and how long they occur. More detailed analysis of the load currents and load profiles for specific drive scenarios will be presented in the final paper.
Fig. 5: Simulated load current of interlink capacitor

REFERENCES
[1] VW80300 Electrical and Electronic High-Voltage Components in Motor Vehicles – Electrical Requirements, Test Conditions, and Tests, 2021-02
[2] T. Velic et al., „Efficiency Optimization of Electric Drives with Full Variable Switching Frequency and Optimal Modulation Methods,“ 2021 17th Conference on Electrical Machines, Drives and Power Systems (ELMA), Sofia, Bulgaria, 2021, pp. 1-6, doi: 10.1109/ELMA52514.2021.9503056.

Eduard Specht received the Ph.D. degree in electrical engineering in 2023 from the Karlsruhe Institute of Technology (KIT). His main research interests include modeling and control of power electronic systems. In 2017, he joined Porsche Engineering Services GmbH (PES) where he is currently working as a specialist engineer with the focus on electric drivetrains and power electronic systems.

Sascha Bahl-Fritz received the master’s degree in electrical engineering from KIT in 2022. Since 2022, he has been with PES where he is currently working as a development engineer with a focus on control and simulation of power electronics and electric drivetrains.

Volker Reber received the master’s degree in civil engineering from the George-Washington-University in 2004 and the diploma in mechanical engineering from the University of Stuttgart in 2005. He joined PES in 2013 working in several responsible positions in the area of e-mobility.