Yongsoon Park

Bio: Yongsoon Park is an academic researcher from Seoul National University. The author has contributed to research in topics: Inverter & Voltage. The author has an hindex of 11, co-authored 24 publications receiving 468 citations. Previous affiliations of Yongsoon Park include Gwangju Institute of Science and Technology.

A Novel Method Utilizing Trapezoidal Voltage to Compensate for Inverter Nonlinearity

Abstract: The nonlinearity of an inverter could be regarded as the output distortions of the inverter. In this paper, voltages in a trapezoidal form were utilized to compensate for the nonlinearity of an inverter. Undesirable harmonic distortions in the overall system were mitigated through the modulating shape of the trapezoidal voltage. For trapezoidal modulation, a dedicated modulator was designed to facilitate adaptive compensation for a wide operating range. The compensation effects from the proposed method were examined in a practical system, in which a permanent magnet synchronous motor (PMSM) was driven without any position sensor. Additionally, it was shown that the proposed method could enhance the sensorless control of the PMSM by reducing the output distortions of the inverter.

Asymmetric Control of DC-Link Voltages for Separate MPPTs in Three-Level Inverters

Abstract: It is important to improve the overall efficiency of a photovoltaic (PV) inverter when it is connected to the grid. Fundamentally, the conversion efficiency from dc to ac power of an inverter is important. However, in the presence of partial shading, maximum power point tracking (MPPT) on PV modules is more important than the conversion efficiency. In this paper, a new control method for a three-level inverter is proposed. With the proposed method, each dc-link voltage of the three-level inverter can be asymmetrically regulated. When PV modules are split into two and each split module is connected to the respective dc-link capacitors of the inverter, the asymmetric control can be helpful because separate MPPTs are possible. The effectiveness of the proposed method was examined through experiments with a T-type three-level inverter, where each dc-link capacitor was supplied by a PV simulator emulating two separate PV modules under different shading conditions.

Sensorless Control Method for PMSM Based on Frequency-Adaptive Disturbance Observer

Abstract: The rotor angle can be estimated from the stator flux in permanent magnet synchronous motor (PMSM). Although integrations are essential to estimate the stator flux from the voltages and currents in the stationary reference frame, disturbances can arise in the process of integrations due to practical reasons. In this paper, a frequency-adaptive disturbance observer has been proposed to remove the disturbances in estimating the stator flux and to enhance the accuracy of the rotor angle estimation. The design and utilization of the proposed observer are detailed under the consideration of its application to a practical system driving PMSM. The performance of the proposed sensorless method has been mainly assessed through experiments at low speed operations, where the sensorless drive of PMSM is regarded as being extremely difficult without the signal injection.

Phase-Locked Loop Based on an Observer for Grid Synchronization

Abstract: A grid synchronization technique is essential for grid-connected power converters. Phase-locked loop (PLL) has been widely exploited as an implementation technique, but additional efforts are required to deal with severely distorted grid voltages. In this paper, an observer is proposed to enhance the performance of PLL. A state equation is newly formulated to construct the observer, which extracts positive-sequence voltage from the distorted grid voltage. Additionally, guidelines are suggested to set the observer gains by considering its internal transfer functions. The PLL and proposed observer have been tested in simulations and experiments in contrast to dual second-order generalized integrator frequency-locked loop. The results have shown that the proposed method reveals a better phase-tracking performance for grid synchronization.

Implementation Schemes to Compensate for Inverter Nonlinearity Based on Trapezoidal Voltage

Abstract: Trapezoidal voltages can be used to compensate for the inverter nonlinearity. In particular, the modulating shape of these voltages facilitates the adaptation of the compensation to various operating conditions. In this paper, practical implementation schemes are proposed to improve the performance of the compensation method based on the trapezoidal voltage. After the implementation schemes are detailed, their effectiveness is discussed with experimental results. It has been proved that the proposed schemes are useful for the robust compensation.

Three-Phase PLLs: A Review of Recent Advances

Abstract: A phase-locked loop (PLL) is a nonlinear negative-feedback control system that synchronizes its output in frequency as well as in phase with its input PLLs are now widely used for the synchronization of power-electronics-based converters and also for monitoring and control purposes in different engineering fields In recent years, there have been many attempts to design more advanced PLLs for three-phase applications The aim of this paper is to provide overviews of these attempts, which can be very useful for engineers and academic researchers

Adaptive Compensation Method for High-Speed Surface PMSM Sensorless Drives of EMF-Based Position Estimation Error

Abstract: To improve the performance of the surface permanent magnet synchronous motor drives, a sensorless control scheme based on the sliding-mode observer with an orthogonal phase-locked loop (PLL) incorporating two synchronous frequency-extract filters (SFFs) is proposed. The rotor position estimation errors are analyzed. The analysis results show that the harmonic errors of the estimated signal are hard to eliminate completely. Therefore, an improved adaptive notch filter - The SFF is proposed to extract the fundamental wave of the rotor position estimation before applying to the PLL. This method of the PLL combined SFFs can compensate the estimated back electromotive force harmonic error efficiently and adaptively. An experimental driveline system used for testing the electrical performance of the developed magnetically suspended motor is built. The effectiveness and the feasibility of the proposed method are validated with the experimental results.

Adaptive Second-Order Sliding-Mode Observer for PMSM Sensorless Control Considering VSI Nonlinearity

Abstract: This paper proposes an adaptive super-twisting algorithm based sliding-mode observer (STA-SMO) for surface-mounted permanent magnet synchronous machine (PMSM) sensorless control, in which voltage source inverter (VSI) nonlinearity is taken into consideration. An adaptive algorithm for online tuning the sliding-mode coefficients of STA-SMO is proposed based on the existing stable conditions. Thus, position estimation error can be reduced by the proposed adaptive algorithm in wide-speed range. Furthermore, voltage distortion due to VSI nonlinearity is online compensated to improve the accuracy of PMSM model. Because mismatch between reference and actual voltage due to VSI nonlinearity may bring large rotor position and speed estimation error, especially in low-speed range where distorted voltages may become dominant compared to actual voltages. Thus, a STA-SMO with adaptive sliding-mode coefficients and accurate voltage value could be obtained. Finally, the effectiveness of the proposed adaptive STA-SMO with online VSI nonlinearity compensation is verified on a surface-mounted PMSM by experiments.

Single-Phase T-Type Inverter Performance Benchmark Using Si IGBTs, SiC MOSFETs, and GaN HEMTs

Abstract: In this paper, benchmark of Si IGBT, SiC MOSFET, and Gallium nitride (GaN) HEMT power switches at 600-V class is conducted in single-phase T-type inverter. Gate driver requirements, switching performance, inverter efficiency performance, heat sink volume, output filter volume, and dead-time effect for each technology is evaluated. Gate driver study shows that GaN has the lowest gate driver losses above 100 kHz and below 100 kHz, SiC has lowest gate losses. GaN has the best switching performance among three technologies that allows high efficiency at high-frequency applications. GaN-based inverter operated at 160-kHz switching frequency with 97.3% efficiency at 2.5-kW output power. Performance of three device technologies at different temperature, switching frequency, and load conditions shows that heat sink volume of the converter can be reduced by 2.5 times by switching from Si to GaN solution at 60 $^{\circ }$ C case temperature, and for SiC and GaN, heat sink volume can be reduced by 2.36 and 4.92 times, respectively, by increasing heat sink temperature to 100 $^{\circ }$ C. Output filter volume can be reduced by 43% with 24, 26, and 61 W increase in device power loss for GaN-, SiC-, and Si-based converters, respectively. WBG devices allow reduction of harmonic distortion at output current from 3.5% to 1.5% at 100 kHz.

Online Estimation of the Rotor Flux Linkage and Voltage-Source Inverter Nonlinearity in Permanent Magnet Synchronous Machine Drives

Abstract: This paper proposes a method for online estimating the rotor flux linkage and voltage-source inverter (VSI) nonlinearity of permanent magnet synchronous machine (PMSM) drives. Thermocouples are employed for measuring the temperature variation of the stator winding in order to obtain the actual value of stator winding resistance. An Adaline estimator is used for online estimation of distorted voltage Vdead due to VSI nonlinearity. Both are subsequently used for the estimation of the rotor flux linkage. The proposed method is experimentally validated on a PMSM drive system and shows good performance in tracking the variation of the rotor flux linkage and compensating the VSI nonlinearity.