Patent ID: 6771522
Filing Date: 2004-08-03
Classification: H02M,H02P

Abstract:
An inverter parallel operation system, comprising:a DC power supply circuit; a filter circuit: a plurality of AC output terminals; a PWM signal generator generating a PWM signal; an inverter circuit having a plurality of switching elements driven by the PWM signal; and a plurality of AC power supply units that switch an output of the DC power supply circuit, based on the switching elements, to deliver a high-frequency voltage via the filter circuit to the respective AC output terminals, the AC power supply units connected and configured to supply AC power via the respective output terminals to a common load, each AC power supply unit comprising: a power detector configured to detect an effective power at an AC output terminal side and an apparent power corresponding to the effective power; a phase angle calculator that calculates a phase angle of current relative to voltage from the detected effective power and apparent power; a phase angle detector that detects a leading or lagging state of the phase angle calculated by the phase angle calculator; and a frequency controller that controls the switching elements to (a) decrease a frequency of the output voltage of the inverter circuit when the phase angle detector detects a leading phase angle, and (b) increase the frequency of the output voltage of the inverter circuit when the phase angle detector detects a lagging phase angle.