Power capacitor in HVDC converter substation has strong power frequency and rich harmonic frequency component at actual operation condition. For simulating actual condition

a kind of bridge full condition current injection circuit for noise test of capacitor unit is designed on the basis of studying existing current injection circuit. Two bridge ends of circuit is used to load power frequency current and power frequency supply current is reduced by the use of shunt resonance compensation inductance; the other two bridge ends of the circuit is used to inject harmonic current. The harmonic current power supply is composed of harmonic signal generator and power amplifier

which can apply simultaneously any harmonic combination of harmonic under 48 times to simulate various application places of actual operating conditions. It is shown by the test that such test as simultaneously injecting into capacitor unit of power frequency and 12 harmonic current is achieved. The test result complies completely with simulating audible noise requirement of capacitor unit in HVDC converter station.