Abstract
In this study, a Lyapunov energy function based control method with output voltage feedback loops is proposed for three-phase uninterruptible power supply (UPS) inverters. The presented paper demonstrates that the traditional Lyapunov-energy-function-based control method not only leads to considerable steady-state error in the output voltage, but also distorts the output voltage waveforms. Therefore, a modification has been performed on the traditional Lyapunov-energy-function-based control by incorporating the output voltage feedback loops in the control variables. The robustness of the proposed control method has been studied analytically through transfer functions which are expressed as the ratio of the output voltage to its reference. These analytical results are validated experimentally. In addition, the steady-state and dynamic performances of the proposed control method are also tested experimentally on a three-phase UPS inverter operating with linear (resistive) and nonlinear (diode-bridge rectifier) loads. As a consequence of incorporating output voltage feedback loops into the control variables, the proposed control method offers strong robustness against variations in LC filter parameters, high-quality sinusoidal output voltage along with acceptable total harmonic distortion (THD) values under linear and nonlinear loads, fast dynamic response under abrupt load changes, and negligibly small steady-state error in the output voltage.
Highlights
Critical loads such as communication systems, medical equipment and data centers are usually fed by uninterruptible power supply (UPS) systems in case of grid power failures [1], [2]
The model predictive control (MPC) with load current observer offers a simple implementation, but the obtained results do not show a remarkable performance in terms of steady-state error and total harmonic distortion (THD) [3]–[5]
The deadbeat (DB) control method exhibits rapid dynamic response, it is dependent on the system parameters which may cause unstable operation when the system parameter variations are large [6], [7]
Summary
Critical loads such as communication systems, medical equipment and data centers are usually fed by uninterruptible power supply (UPS) systems in case of grid power failures [1], [2]. S. Bayhan et al.: Lyapunov Energy Function-Based Control Method for Three-Phase UPS Inverters in the steady-state operation, its dynamic response is slow and performance is not satisfactory under non-periodic disturbance conditions [8]–[12]. The flatness-based control in [15] achieves a satisfactory THD level and exhibits good dynamic response, its design is complicated In addition to these control methods, various types of methodologies are proposed for the UPS inverters. It is revealed that the traditional Lyapunov-energy-function-based control causes considerable steady-state error and large distortion in the output voltage. Where Ud and Uq are the steady-state terms, ud and uq are the perturbed terms of the control variables
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