Why is a DC Link Capacitor Needed?
In power conversion, when AC is converted to low voltage DC, or AC from one frequency to another, the AC is usually rectified and smoothed. Once this is accomplished, the power is then routed to an inverter to obtain the final output. The DC that is fed into the inverter is called the DC link. As the name implies, the two sources are linked together with a filter capacitor.
In electric vehicle applications, the DC link capacitor is used as a load-balancing energy storage device. The DC link capacitor is placed between the DC (in this case, the battery) and the AC (which is the load side) of the voltage inverter. The capacitor is placed parallel to the battery, which maintains a solid voltage across the inverter. The device helps protect the inverter network from momentary voltage spikes, surges and EMI. The noise is the result of the pulsed inverter current and stray inductance on the DC bus.
The selection of the proper DC link capacitor is important to achieve the proper performance of the system. For example, an under- designed DC link capacitor can cause a premature failure, or will cause EMI interference resulting in problems with other electronic circuitry. An over-designed DC link capacitor is not as cost- or size-efficient.
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