Discrete-time sliding mode control based on disturbance observer applied to current control of permanent magnet synchronous motor

This paper proposes a robust current control technique based on a discrete-time sliding mode controller and a disturbance observer for high-performance permanent magnet synchronous motor (PMSM) drives. This scheme is applied in the PMSM current control loops to enable the decoupling between the dq current axes, rejection of disturbances caused by mechanical load changes and robustness under parametric uncertainties. In order to ensure the discrete-time sliding mode properties, which make the system cross the sliding surface at each sampling period, the PMSM model is extended, including the digital implementation delay resulting from the discrete-time algorithm execution. The development of this method allows direct implementation in microcontrollers and digital signal processors. Stability and convergence analysis are developed in the discrete-time domain. Simulation and experimental results demonstrate the effectiveness and good performance of the proposed current control approach

Performance comparison of discrete-time robust adaptive controllers for grid-tied power converters under unbalanced grids

Renewable energy generation systems largely use grid-tied power converters with LCL filters. A well-known issue in this kind of system is the resonance of the LCL filter, whose frequency is straightforwardly affected by grid condition. Variations on grid impedance tends to make the controller performance poor and until turn the closed-loop unstable. Therefore, some controllers are designed for specific operation ranges to ensure performance and global stability. However, a deep study of Model Reference Adaptive-based Controllers for this kind of issue was not conducted yet. The aim of this paper is to fit this research gap. Thus, this paper presents a performance comparison of feasible discrete-time robust adaptive controllers, based on reduced order reference model, for grid-tied power converters with LCL filter under unbalanced grid conditions, providing an assessment of the benefits and drawbacks of each considered control strategy. The evaluated control laws are: Robust Model Reference Adaptive Controller, Robust Model Reference-based Adaptive Super-Twisting Sliding Mode Controller, Robust Adaptive One Sample Ahead Preview Controller, and Robust Adaptive Proportional-Integral Controller. Through performance comparison, it can be defined what controller is more adequate in face of grid condition, taking into consideration grid-injected currents quality and design complexity of controller. Experimental results of grid-injected current control of a grid-tied 5.8 kW Voltage-Source Inverter with LCL filter considering relevant grid voltage unbalance are presented to corroborate the controllers’ performance and discuss their reference tracking response, robustness to the parametric variation, exogenous disturbance rejection, parameters adaptability, and global stability. In evaluated scenarios, Robust Adaptive Proportional-Integral controller presented slower regulation dynamics between compared adaptive structures, but reduced tracking error, as well as lower total harmonics distortion, while Robust Model Reference-based Adaptive Super-Twisting Sliding Mode Controller has the smaller overshoot in the initial transient regime, as well as the shorter transient regime

Abordagem geométrica para modulação de conversores três braços no acionamento de máquinas de indução bifásicas simétricas e assimétricas

Este trabalho apresenta uma abordagem geométrica para modulação PWM de inversores a três braços acionando máquinas de indução bifásicas. A principal característica do esquema proposto é o número reduzido de cálculos numéricos na modulação de tensões equilibradas e desequilibradas. Na modulação de tensões equilibradas é demonstrado que as amplitudes de linha das mesmas podem variar de zero até 0,707 pu da tensão do barramento CC, enquanto que na modulação de tensões de linha desequilibradas a amplitude da uma destas pode ultrapassar o valor de 0,707 pu do barramento CC. Os resultados obtidos com a técnica proposta são semelhantes aos resultados obtidos com modulação space vector, porém, a implementação da técnica geométrica proposta neste trabalho é realizada com menor esforço computacional comparado a modulação space vector. Resultados experimentais são apresentados para validação da análise teórica, e estes confirmam o bom desempenho do método de modulação proposto.This paper presents a geometric approach for PWM modulation of three-leg inverters driving two-phase induction machines (TPIM). The main contribution of proposed scheme is the low computational effort to obtain symmetrical and asymmetrical line voltages suitable to fed two-phase induction machines. It is demonstrated that the amplitudes of line voltages can to vary from zero until 0.707 pu of DC-link for symmetrical output, while one of the voltages can overcome 0.707 pu of DC-link voltage in the asymmetrical case. The results obtained with the proposed modulation technique are similar to those obtained with space vector modulation, however, the implementation of the proposed modulation technique is much more simpler than the implementation of space vector modulation. Experimental results that validate the theoretical analysis are presented and they demonstrate the good performance and simplicity of the proposed modulation method