A novel energy saving method for use with variable frequency drives

Many Variable Frequency Drives use low pass passive filters that have wye connected capacitors for performing filtering action. While the passive filters in Active Front End (AFE) PWM drives and in matrix converters are primarily used for filtering PWM frequency components, they are also a major source of power loss as their configuration allows for the flow of circulating currents even when the main power converter is OFF. This standby power loss can become an important part of the overall grid power wastage when numerous active front end converters in the form of wind power generating units or solar power inverters or other overhauling loads like oil beam pumps, form a major part of the power system. In this paper, a new filter topology which allows for actively opening the neutral point of the filter capacitor during standby is proposed. The proposed topology can also be used to protect the capacitor banks in AFE LCL filters from overload due to a grid fault. LCL or LC filters used in input passive harmonic filters and in output sine wave filters in Uninterruptible Power Supply (UPS) systems can also benefit from the proposed topology. A damping resistor can be added to the proposed electronic switch to provide a means of damping. Such a scheme is also proposed in this paper. Test results with active front end rectifier are provided to prove the concept.