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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 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...
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...
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...
The Zero Sequence Circulating Current (ZSCC) flows inevitably in parallel converters sharing common DC and AC sources. The currents flowing commonly in all converters increase losses and decrease the overall capacity of parallel converters. This paper proposes a simple and effective ZSCC suppression method based on the Space Vector PWM (SVPWM) method with the ZSCC controller. The zero sequence voltage...
This paper analyzes and compares position estimation performances of fundamental-model-based sensorless control methods considering the effects of inverter nonlinearities and parameter estimation errors. Based on the investigation of four conventional sensorless control algorithms, estimated position error from each algorithm is represented in a quantitative manner. This representation is helpful...
The AC side Single Line to Ground (SLG) fault is one of the most frequent faults in power systems. And, in an HVDC system based on modular multilevel converter it calls for the fault ride through strategy to transmit maximum possible electricity during the fault to secure power system stability. It presents different characteristics of SLG faults at the voltage regulator side and the power dispatcher...
This paper presents the techniques for regulation of system balancing in modular multilevel converter (MMC) based HVDC system under the AC grid double line fault condition. Due to the special structure of MMC, the balancing of the cell capacitor voltage is crucial for any operating circumstance of the system. Also, the responses against the grid faults of HVDC system based on MMC are different to...
This paper proposes an active damping method for LCL filters of grid-connected converters. LCL filters are mainly utilized for the interface of distributed generation systems to the grid due to their small size and effectiveness of current harmonics attenuation. However, owing to the resonance of LCL filters, bandwidth of the current controller of the converters is usually limited far to the resonant...
In this paper, a bilateral reactive power injection method is proposed for islanding detection of grid-connected converters in distributed generation units. The proposed method injects capacitive and inductive reactive power periodically with half of the grid frequency to perturb the frequency of point of common coupling (PCC). The magnitude of the injected reactive power is derived in order to remove...
Natural capacitor voltage balancing of six arms of a direct modulated Modular Multilevel Converter (MMC) has been observed by several articles both by experiments and simulations. However, its principles have not been revealed clearly and its dynamics have not been analyzed analytically. In this paper it's shown that a DC component and a line frequency circulating current would be induced inside the...
In the conventional control strategy of the VSC-HVDC system based on the MMC, direct modulation was employed and the terminal behavior of the MMC was similar to that of the two-level converter. The DC bus voltage of the power dispatcher side was regulated indirectly by controlling voltage regulator side DC bus voltage, and the transmission line current was determined passively by the power flow. Fluctuation...
Nowadays, a Line Commutated Converter (LCC)-HVDC is a mature technology with decades industry experience. Even though it's with several advantages such as higher reliability, lower cost, and higher efficiency, it presents some drawbacks such as large converter station size and lack of black starting capability. So the LCC-HVDC is not suitable for some applications in which black starting capability...
A MIMO antenna with decoupling network for LTE mobile application is proposed. To improve the isolation between the two radiating elements of MIMO antenna, decoupling network is added. The decoupling network consists of two sections of transmission line, a shunt reactive component and quarter-wavelength jointed shorting structure. The isolation is improved by approximately 25 dB at the center frequency...
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