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In this paper, a novel filter structure is proposed based on the sequence of PWM voltage harmonics. At first, the phase of voltage harmonics is thoroughly analyzed. Based on the phase difference between three phases, it is shown that the sideband harmonics can be divided into positive-sequence, negative-sequence and zero-sequence components. Through 120° interleaving and three paralleled converters,...
In this paper, an asymmetric mixed MMC topology of multilevel converter for bipolar HVDC transmission systems is introduced. Among the existing MMC topologies for the bipolar HVDC systems, the asymmetric mixed MMC topology provides the benefits of: a lower number of submodule cells, fewer switching devices and lower conduction losses. Furthermore, the HVDC based on asymmetric mixed MMC can be flexibly...
This paper presents the theoretical analysis on the errors in voltage synthesis and position estimation due to the voltage distortion in position-sensorless operation. Especially, the pulsating square wave signal injection method into the estimated d-axis would be focused on, revealing the nature that the position estimation performance depends on the frequency of the injected signal. From the analysis,...
This paper proposes a compensation method for precise position-sensorless control using high-frequency pulsating voltage injection and the criterion for applicability of the proposed compensation method is discussed. Theoretical background of the proposed 3-dimensional compensation table as well as the implementation method is described and it is disclosed that the real rotor position and the convergent...
This paper analyzes the convergence of the rotor position tracking in signal-injection sensorless control especially for heavily saturated IPMSMs. In the analysis, it is revealed that the harmonic inductance and the operating current variation are critical factors determining the operation limit of signal-injection sensorless control. Considering this, the feasibility region of signal-injection sensorless...
In this paper, a guide for the admittance shaping is introduced for PWM converters tied to the grid using outer power control loop. To obtain intuitive tuning factor, the design method for the power control loop is proposed. The proposed design method could be applied to the power control of PWM converter regardless of system capacity and grid voltage. Instead of directly varying proportional or integral...
Nowadays, the Modular Multilevel Converter (MMC) based HVDC has been considered as a promising technology to meet the increasing electric power demand. However, constructing new transmission lines becomes more and more difficult because of environmental issues. Consequently, the newly constructed DC lines have to share the right of way with existing AC transmission in close proximity. Meanwhile, as...
This paper discusses the effect of current measurement error in angle estimation of permanent magnet AC motor for position sensorless control based on motor back EMF. The current measurement errors due to non-ideal elements in the system are classified into the scaling error, the offset error, and the discretization error. Those errors have been represented in the estimated synchronous reference frame...
In this paper, the suppression of the circulating current flowing between inverters in parallel with non-isolated dc-link is described. If the inverters are connected in parallel through sharing inductor, circulating current would follow between inverters. In early researches, the circulating current generally is considered as zero sequence component. However, circulating current is not confined as...
State-space control provides both high dynamic performance and sufficient stability margin to voltage source inverters with LC filter. In this paper, discrete state-space voltage controller is proposed by using direct pole-zero placement in rotating reference frame. Based on the discrete-time system model, the state feedback control with the reference feedforward path is designed in consideration...
In this paper, the characteristics of ripple current of multi-megawatt induction motor fed by a PWM inverter is investigated. And, based on the investigation a novel PWM scheme is devised to reduce the switching loss of the inverter under the same torque ripple of the induction motor. The proposed PWM is composed with two parts. One is Minimum Torque Ripple Pulse-Width Modulation (MTRPWM) which is...
This paper proposes a new maximum power point tracking (MPPT) scheme, based on perturb and observe concept, for a single stage PV water pump system working effectively under various environmental conditions. The selection of frequency step size is an important parameter for single stage solar water pump system. Larger step size may lead to a sudden drop in DC link voltage due to oscillations around...
This paper presents a power reference modifier for seamless transfer considering the power balance in the parallel operation. When the PCS (Power Conditioning System) is disconnected from the grid, the PCS should operate in the stand-alone mode to supply energy to the critical loads. If multiple PCSs work as one PCS, slave PCSs maintain the current control mode even if master PCS change its control...
A topology, so called, Double-Delta Sourced Winding (DDSW) has been proposed to improve harmonic properties in high-power conversion systems. In this paper, a pulse-width modulation method is proposed to further optimize the harmonic properties in DDSW-based systems. Specifically, it is described through mathematical analyses how to modify voltage references for reducing harmonics in combination with...
In this paper, a comprehensive control scheme for a delta-connected cascaded h-bridge (CHB) converter based static synchronous compensator(STATCOM) is presented, especially focusing on improving dynamic performance by novel feedforward control method. The method can conspicuously improve the dynamics of circulating current regulation of delta connected CHB STATCOM especially under grid fault condition...
This paper proposes a PWM method reducing harmonics of two interleaved converters at twice the switching frequency region. If harmonics at twice the switching frequency region can be reduced by the PWM method, the size of filter interfacing the grid and converter would be reduced. Based on Fourier series of phase voltage in every switching period, offset voltage for PWM minimizing harmonics at twice...
Cascaded H-Bridge (CHB) inverter is the most widely used topology for Medium Voltage (MV) drive system due to the high degree of modularity, easier implementation of medium output voltage, and ability to continuous operation under the cell fault condition. Because each power cell of CHB should have isolated DC source, multi-winding input transformer and three phase Active Front-End (AFE) are generally...
In this paper, it is described how the circulating current flows between inverters which have isolated DC-link such as Cascaded H Bridge (CHB) topology, when they operating in parallel. In this case, Zero Sequence Circulating Current (ZSCC) flowing through shared DC-link cannot flow between inverters in parallel. However, circulating current is provoked by asynchronous switching instant of devices...
With the conventional circuit configuration of DC microgrids, two power conversion stages are required to transfer the energy from the Energy Storage System to loads or sources: DC/DC and DC/AC conversions. This paper proposes a new circuit configuration which puts the battery directly to the lower DC-link of 3-level back-to-back converters. The proposed circuit reduces the two-step power conversion...
In this paper, new model-based sensorless control methods are proposed, including estimation methods for the position and speed errors and compatible position and speed estimators. In proposed methods, the speed error is estimated as well as the position error in the conventional model-based sensorless methods. By the proposed methods, unity transfer function from actual position to estimated position...
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