Research On Improved Double Loop Control Of Inverter System With State Observer

Uninterruptible power supplies(UPSs)are widely used for the sensitive loads which require clean and uninterruptible power.Inverter is the core component in a UPS system,which is generally required for excellent output voltage even with non-linear loads.To realize the high performance,a great number techniques to control waveform have been proposed.This paper is focused on voltage and current double loop digital control inverter,for it can realize high stability,fast dynamic response and nice output voltage.And a feedforward controller is introduced in the inner loop to improve the tracking accuracy,as the conventional double loop controller's dynamic response is limited by the inner loop's bandwidth.Then it is discussed that how the controller is designed with the influence of digital delay by sampling,calculation,and PWM delay.Further,in order to avoid one-time step delay caused by time consumption in sampling and digital processors' calculation,a state observer to calculate state variables of next step is brought in.Due to the ripples in DC voltage and dead time effect,there is negligible prediction error of state observer.To overcome the prediction error,a repetitive compensator is proposed.The experimental results in a 3kW,single-phase diode clamped three-level inverter show that a double loop controller with feedforward controller improves the output voltage,and the state observer with repetitive compensation manages to solve the problem of one-time step delay,increase the control bandwidth and enhance the system's steady-state and dynamic performance.