October / November 2021

22 INDUSTRY NEWS Issue 4 2021 Power Electronics Europe www.power-mag.com High-voltage (HV) switches are an indispensable link within an HV architecture of modern Battery Electric Vehicles (BEV). They are used to safely and unambiguously separate auxiliary units from the rest of the vehicle‘s electrical architecture on the high-voltage side (400/800V side) - depending on the platform architecture - and thus prevent major damage. Next-generation electric vehicles will have up to three different voltage levels: 12V electrical system for small actuators and all control units 48V electrical system for larger power consumers such as water pumps, EPS or radiator fans 400 to 800V electrical system containing the battery pack and the largest consumers such as the inverter, the high-voltage heater, the OBC, the HV/LV DCDC and the HVAC. Especially the latter requires a maximum of safety and reliability for all installed components. BEV of the future In terms of circuitry, the HV disconnector consists of an isolated 800 V power stage with 12 V measurement and evaluation electronics and an AURIX TC375 Lite Kit. The concept of the HV isolator switch is realized in the switching stage with SiC MOSFETs from ROHM, galvanic isolation of the measuring channels, high-precision shunts, new optocouplers and all protective components from Vishay. In addition, a second-generation AURIX microcontroller from Infineon controls the device. With the 1200V SiC MOSFETs of the fourth generation in SMD housing and a precisely tuned control via a SiC gate driver, the HV disconnector is able to switch powers of up to 40 kW. The resulting power loss reaches approx. 16 W. The resulting heat can be passively dissipated at room temperature (25°C). The HV circuit breaker has a pre-charge path that allows capacitive loads to be pre-charged via a SiC MOSFET, series-connected pre-charge resistors and two implemented pre-charge modes (13 ms and 130 ms respectively), thus preventing a possible over-current at switch-on. The control of the main MOSFETs is realized via a galvanically isolated SiC driver, which is buffered via a new polymer tantalum capacitor (T51 series from Vishay). The pre-charge MOSFET is driven via a galvanically isolated optocoupler with phototransistor output (VOMA617A). The maximum load current of the disconnector can be set either via the microcontroller or individually via a potentiometer in stand-alone mode. The Powerstage features high-precision shunts from Vishay, which are characterized by their accurate bi-directional measurement of the battery current. The current and voltage measurement signals are transmitted galvanically isolated (floating measurement), processed by measurement signal amplifiers and passed on to the microcontroller. The newly developed Smart Automotive High-Voltage Circuit Breakers The cooperation between the e-mobility specialists of Rutronik‘s Automotive Business Unit (ABU) and Vishay‘s Automotive Division realised a new reference design for a high-voltage (HV) circuit breaker with a maximum breaking capacity of 40 kW. This replaces previous options that used mechanical relays with a resettable and low-loss semiconductor solution. VOA300 linear optocouplers from Vishay provide galvanic isolation from the 12 V side. Two series-connected high-voltage MLCCs from Vishay provide the galvanically isolated supply of the op-amps. This supply includes a push-pull driver stage with 50 kHz. The AURIX board is connected via a cable connection and, after successful connection, can output the processed measured values via an already implemented software. The configuration and readout of measured values of the eFuse with AURIX control is done via an existing CAN interface. Precise measurements, diagnostic function and protective measures In addition to the precise current and voltage measurements, the concept also has a diagnostic function and further protective measures, such as over- current detection with adjustable threshold, in- & output transient protection as well as additional TVS diodes for power supply protection. The input and output voltage is monitored via ratiometric thresholds, which thus also enables use for 400 V systems. In addition, the reference design has a status display with LEDs as well as two push buttons for manual control. Equipped with a housing that allows access to all measuring points, protection against accidental contact is also guaranteed. Rutronik makes the reference design available to selected customers with above-average requirements, thus enabling fast and high-quality implementation of a state-of-the-art circuit concept in future projects. www.rutronik.com Reference design PCB for a high-voltage circuit breaker with a maximum breaking capacity of 40 kW top side Reference design PCB for a high- voltage circuit breaker with a maximum breaking capacity of 40 kW bottom side