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| 9 | Figure 1: The system input requirements from the AC network are for a 16A mains input PFC system that scales to 11.5kW. (Source: Bourns, Inc.) For a PFC of near unity power factor (resistive load), the input current is required to be in phase with the input voltage and have low distortion. The switch S1 shown in Figure 1 is connected to a controller, which monitors the input voltage. The switch will be turned "on" and "off" (or duty cycle modulated) at 200kHz as the instantaneous input voltage changes relatively slowly during the 100Hz period. The average current in Lboost will track the input voltage signal in relative shape and phase during the cycle. Current waveform distortion will be reduced from capacitive and inductive loads. From the AC mains side, the load is made to look resistive. The amplitude of the mean current in Lboost is also adjusted over time to compensate for line and load changes. Inductor Material Powder iron material is normally used as the magnetic material for this type of inductor. Powder iron has a distributed gap inherent in the magnetic material due to the non-magnetic binder used in its manufacture. The permeability (µ) is typically on the order of 20-200. Because of the very strict constraint on the volume of the inductor plus the inductance requirement (greater than 150µH at a full load), the power losses would be excessive with a powder core and would overheat the inductor in this application. Instead, another approach was needed. To optimize our boost inductor design for PFC, Bourns used a conventional split- core consisting of low loss manganese zinc (MnZn) ferrite material. We found that the MnZn ferrite material has much lower losses and much higher permeability than powder iron. To prevent the ferrite core from saturating, an air gap should be added in the magnetic path. Adding the air gap also lowers the permeability in the material. Through testing and simulation, we discovered that by using a distributed multi-gap approach to minimize flux fringing, copper losses are greatly reduced when compared with a single-gap inductor. Air Gap Calculation The air gap part of the inductor design held the key to unlocking maximum efficiency and the ability to reduce AC losses. This design direction was based on the assumption that all the reluctance in the magnetic circuit will be in the air gap. The first stage of the design was to verify the number of turns the boost inductor should have to ensure the core does not saturate at peak current at a given inductance. The number of turns was calculated first, followed by the calculation of the magnetomotive force (MMF). Bourns determined that in this application, the operating flux density needed to be limited to 0.3T. It was also important to figure out the level of magnetic reluctance (R) needed to limit the flux to 0.3T at peak current. Limiting the core to 0.3T will ensure that the magnetic core doesn't saturate. Once the reluctance that was required to limit the flux density to 0.3T was known, then the gap size could then be calculated. Bourns found that the copper losses in a single gap inductor of this type can be significantly reduced by reducing the gap size and increasing the number of gaps in the center leg of the inductor. We also were able to reduce the AC resistance from 5.5Ω with one gap to finally 0.616Ω with three gaps distributed in the core center leg. ELECTRIC VEHICLES: Let's go for ZERO Emissions! The electric car revolution is here, and Amelia Dalton from EE Journal and Cathal Sheehan from Bourns talk about Bourns' battery management systems (BMS), voltage isolation, and circuit protection to meet the challenge. CHALK TALK: ELECTRIC VEHICLES CATHAL SHEEHAN - 2019

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