Research on Topology and Control System of High Power Grid Simulator

Grid simulator can simulate the output of various types of power grid failure to test wind power grid-side equipment, in the design of high-power grid simulator, due to the switching frequency restrictions, will affect the control bandwidth, resulting in the power grid simulator system performance decline. Therefore, the modular multi-level converter (MMC) with higher equivalent switching frequency is used on the inverter side of the grid simulator, and the bridge arm circulation suppression strategy based on the second-order generalized integrator (SOGI) and vector scale integral (VPI) resonant controller is proposed for the internal bridge arm circulation of the converter. Finally, based on RT-LAB, the network simulator controller hardware in the ring (CHIL) experimental platform is built and experimented, the experimental results show that the design of high-power power grid simulator system can simulate the output to obtain the required grid failure.

Integrated Uncertainty/Disturbance Suppression Based on Improved Adaptive Sliding Mode Controller for PMSM Drives

Permanent magnet synchronous motors (PMSMs) have attracted great attention in the field of electric drive system. However, the disturbances caused by parameter mismatching, model uncertainty, external load and torque ripple seriously weaken the control accuracy. The traditional adaptive sliding mode control (ASMC) methodology can address slow-varying uncertainties/disturbances whose frequencies are located at the bandwidth of the filter used to design the adaptive law well; however, it has been barely discussed with respect to the periodic situation. In this paper, we extend the ASMC arrangement to periodic case to suppress the torque ripple by using a series-structure resonant controller. Firstly, a typical SMC is designed to force the tracking error of speed to converge to zero and obtain a certain capacity to disturbance. Then, the improved adaptive law is incorporated to estimate the lumped disturbance and torque ripple. The improved adaptive law is enhanced by embedding the resonant controller, which can obtain a better estimating result for torque ripple with repetitive feature. Finally, simulation and experimental results with PI, SMC and proposed methods are compared to verify the effectiveness of the developed controller.

Dual Active Bridge as a DC Link Current Pulsation Compensator in Energy Storage Applications

This paper presents a system for compensating DC link current pulsation in four-wire inverters with energy storage operating under unbalanced load conditions. This phenomenon occurs when an inverter with an independent power control in each of the phases attempts to locally balance the voltage imbalance in the grid. Such a condition creates a DC link current pulsation, which is destructive for energy storage connected to the DC link. The conditions when this situation appears are presented in detail in the paper. A solution to this problem is proposed in the form of a dual active bridge converter and a capacitor bank to actively compensate this pulsation. The control algorithm is proposed based on a proportional-resonant controller. This paper presents the technical background and method by which the controller parameters were calculated, implemented and tested in a real-time system. The test results are presented and discussed, concluding that the proposed solution is an attractive option for protecting the energy storage from DC link current pulsation. The dual active bridge converter combined with resonant controller can compensate the DC link current pulsation almost entirely.

Harmonics Reduction and Reactive Power Injection in Wind Generation Systems

In this work, methods are implemented to improve two aspects of energy quality in a wind generation system. First, the harmonic reduction is achieved by applying a linear control technique in the Grid Side Converter; and second, the power factor of the wind generation system using a Doubly Fed Induction Generator (DFIG) is adjusted by injecting reactive power. The reduction of the harmonic content is performed with a digital resonant controller, which tracks the periodic signals corresponding to the current harmonics of the Grid Side Converter (GSC), which is part of a “back to back” converter in a wind generation system. This technique allows implementing a current controller of the GSC with a high level of rejection of current harmonics, of frequencies with orders (1 + 6k) and (1 − 6k) (where k is an integer), when executed in the synchronous reference frame (dq). The purpose of this work is to inject currents to the grid with very low harmonic distortion and provide a method for tuning the resonant controller for a simple L filter; also, the GSC is used to generate reactive power. These two improvements achieve a unity power factor, and this is necessary to comply with the new codes where a leading power factor helps regulate the grid voltage.

Feedback control method to suppress stick-slip in drill-strings featuring delay and actuation constraints

In this work, performance of a modified-integral resonant controller with integral tracking is investigated numerically under the effects of actuator delay and actuation constraints. Actuation delay and constraints naturally limit controller performance, so much so that it can cause instabilities. A 2-DOF drill-string m with nonlinear bit–rock interactions is analysed. The aforementioned control scheme is implemented on this system and analysed under the effects of actuation delay and constraints and it is found to be highly effective at coping with these limitations. The scheme is then compared to sliding-mode control and shows to be superior in many regimes of operation. Lastly, the scheme is analysed in detail by varying its gains as well as varying system parameters, most notably that of actuation delay.