Measuring the small-signal response of diode rectifier loads using a DSP controlled switching converter system

The assumption that nonlinear rectifier loads contribute only to the steady state of a power system is commonly made in the design and analysis of power conditioners such as the shunt active filter. This tacitly assumes that the nonlinear rectifier load is less sensitive than the AC system. This paper presents experimental measurements of the sensitivity of nonlinear rectifiers made by injecting a perturbing current into the point of coupling of the rectifier. The perturbing current is generated with a DSP controlled switching power converter typically used in shunt active filters. The DSP system also measures the change in the load current. Results are presented for both single-phase and three-phase rectifiers. These show that both these rectifiers are sensitive to the perturbing current, that the response is measurable with relatively unsophisticated hardware and that the response has a well defined pattern in the frequencies that occur.