Influence Of Inverter Nonlinearity Research Articles

Improved High-Frequency Voltage Injection Based Permanent Magnet Temperature Estimation for PMSM Condition Monitoring for EV Applications

Permanent magnet (PM) temperature is critical to ensure high-performance and reliable control of permanent magnet synchronous machines (PMSMs) for electric vehicle (EV) applications. High-frequency (HF) voltage injection based approach has been shown to be capable of PM temperature estimation under all-speed range with simple implementation. This paper improves existing HF voltage injection based PM temperature estimation approach by considering the cross-coupling effect. The key to PM temperature estimation is the temperature-dependent HF resistance estimated from the injected HF voltage and the current response. It is found that the cross-coupling effect has a great influence on the HF resistance estimation. This paper firstly improves the HF voltage injection model by considering the cross-coupling effect. Then, a comparative numerical investigation is conducted to analyze the estimation errors induced by the cross-coupling effect. A novel HF resistance estimation approach is derived from the proposed improved model and the PM temperature is calculated from the HF resistance with a linear thermal model. The influence of inverter nonlinearity is also analyzed. Experimental investigations demonstrate that the proposed approach is able to improve the performance of PM temperature estimation.

Enhancement of voltage quality in a passive network supplied by a VSC-HVDC transmission under disturbances

When a VSC-HVDC transmission is connected to a passive network, the receiving AC system is weak and is subject to power quality problems such as voltage sag and swell. Dynamic performance of voltage control would affect the voltage quality in the receiving AC system directly. The direct voltage control (DVC) method is simple but fails to quickly eliminate voltage fluctuation caused by load current change. One solution is to add a feed-forward controller to the DVC. The inverter nonlinearities, however, degrade the performance of the feed-forward controller. This paper presents a modified direct voltage control to enhance control dynamics in the receiving AC system by overcoming the effect of inverter nonlinearities. In the proposed control scheme, the influence of inverter nonlinearities on the performance of the feed-forward controller is first discussed. A compensation method for nonlinearities of the inverter is then designed in the d–q rotating axis. Moreover, to overcome parameter sensitivity of the feed-forward controller, a feed-back loop with a PI controller is implemented. Simulation results from PSCAD/EMTDC showed that the VSC-HVDC system using the proposed control scheme, as compared to that with the conventional control methods, has a better capability to mitigate voltage fluctuation during system disturbances.