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In this paper, a universal voltage clamping circuit for the T-type neutral-point-clamped (TNPC) converter is introduced. It is shown that, for any TNPC implementation, the proposed voltage clamping circuit can well suppress all voltage spikes of power devices at the switching transients. Therefore, the devices can operate in a much safer region.
This paper presents two different capacitors' voltage control schemes for modular multilevel converter (MMCs) with the application for back-to-back systems. Based on the derivation of the relationship between arm currents and active power of the MMCs in back-to-back system, the proposed scheme controls the currents of upper and lower arms independently in MMCs to achieve arm voltage balancing of capacitors...
Because of high cost of battery, BESS is not suitable for the situation when the demand of active power is less than that of reactive power. A novel STATCOM based on the hybrid cascaded multilevel converter is proposed to provide limited active power support. Meanwhile, this topology doesn't have the drawback of cascaded H-bridge BESS. The characteristic of output power for this topology is studied...
As the distributed generators are connected together through inverter interface in the microgrid, the control of the control of the interface inverter has an important influence on the operating performance of microgrid. In the paper, the study focuses on the control of the interfaced inverter, when microgrid operates in the islanded mode. In order to make the microgrid property similar to the utility...
The adoption of virtual synchronous generation (VSG) control can maintain the stability of voltage and frequency in power electronic interfaced mircogrid. In this paper virtual impedance is added to the VSG control strategy in order to improve the system control performance in resistive-inductive line impedance, the influence of virtual impedance on VSG system stability and dynamic performance is...
China Machinery Industry Standard (CMIS) GB/T 12326-2008 prescribed in the islanded operation mode, microgrid inverter (MGI) output voltage dynamic transient range is less than 10% when the resistive load is switched rapidly between 0% and 100%. The three-loop power virtual synchronous generator (VSG) control methods are commonly used in MGI units to share the loads among the parallel MGIs. However,...
The three-loop power virtual synchronous generator (VSG) control methods are commonly used in microgrid inverter (MGI) units to share the loads among the parallel MGI units. In order to achieve stable operation of the MGI units under paralleled or grid-connected mode, a droop synchronization controller is designed in this paper. The difference of phase and amplitude between different MGI units is...
To investigate the input impedance of digital-controlled bi-directional DC/DC converters, this paper develops a modeling method based on the sampled-data approach. Because the nonlinear pulse-width modulator generates sideband components, the sideband effect occurs in a closed-loop converter. And the sampling process of a digital controlled system can significantly influence the sideband components...
PWM converters have been widely applied for power processing and they are typically the stems of other types of converters, such as quasi-resonant and multi-resonant converters. Development of the PWM converters has been spanning over a century, starting from the buck converter. The well known PWM converters include buck, boost, buck-boost, Ćuk, SEPIC, Zeta, Z-source, quasi-Z source, etc. Many attempts...
In order to improve the output-regulation accuracy of the switching converter with conventional constant off-time (CCFT) modulation, dual-edge constant off-time (DCFT) modulation for switching converter is proposed in this paper. The principle of switching converter with DCFT modulation, including leading-triangle constant off-time (LT-CFT) modulation and trailing-triangle constant off-time (TT-CFT)...
This paper proposes a new modeling method for buck converter. The new modeling method, named bi-switching status method (BSM), for buck converter is obtained via the propositional calculus and linear constrain. Based on the mixed logical dynamical (MLD) model, BSM model of buck converter is obtained. Compared with other modeling methods, such as MLD method and state-space averaging method, streamlined...
The Boost converter with digital current-mode control and leading edge modulation is modeled in z-domain first in this paper. The influences of time delay and zero-order holder (ZOH) on digital controlled converters are taken into consideration. Then, the corresponding circuit model is established and simulations are performed to show the effectiveness of the z-model. It's shown by simulations based...
In this paper, an accurate small-signal model with peak current mode (PCM) control for the Active clamp forward converter under continuous inductor current condition is proposed. To obtain this model, the “Ridely Approach” is utilized to derive the accurate Modulation gain, feedback gain and feed-forward gain in which the magnetizing inductance is fully taken into account. Clamp capacitor and magnetizing...
Low-frequency oscillation occurs when the transmission lines equivalent impedance is small or negative. As the increase penetration of PV system, it plays an important role for system stability. A novel method for low-frequency oscillation suppression based on PV system is proposed. Model of PV accessed to power grid is established, which reveal the relationship between output power of PV system and...
This paper presents an on/off-grid integrated photovoltaic power generation system and its control strategy. The system consists of PV, lithium battery, public grid, converters and loads. The system can work on both on-grid condition and off-grid condition depending on the operation states of PV and lithium battery. The lithium battery works as an energy storage device coordinating with PV to realize...
The operating characteristics of photovoltaic (PV) cells are essential to the design of steady-state characteristics and control parameters of the interface converter in output voltage regulation (OVR) mode. From the perspective of output voltage closed-loop control stability, the effect of control loops form of the interface converter in OVR mode on the operating characteristics of PV cells is studied...
In recent years, there have been an increasing number of photovoltaic (PV) generators integrated into the modern distribution power network. However, the introduction of a large number of PV units could have a negative impact on the distributed PV grid-connected power generation systems, such as polluting the grid, and causing grid instability, even resulting in the voltage collapse if the relevant...
PR controller in stationary frame which is equivalent to PI controller in synchronous frame has been widely used in the application of PV inverters. While little attention has been devoted to VR(vector-resonant) controller in the application of PV inverters. VR controller in stationary frame is equivalent to VPI(vector PI) controller in synchronous frame, which takes decoupling into consideration...
In this paper, high-efficiency, extremely high step-up and step-down bi-directional DC-DC converter is proposed. The proposed converter consists of a flyback and an isolated switched-capacitor cell to achieve high cost competitiveness for the extreme operation. The output of the flyback converter and that of the isolated switched-capacitor is connected in series to obtain a high voltage step-up. In...
In this paper, we discuss the interleaved Flyback Micro-inverter with SiC device. The Micro-inverter is composed of front-end interleaved Flyback converter and a 50Hz switching MOSFET inverter. A loss model is used to compare the efficiency between using SiC devices and conventional device. Three solutions are compared: Micro-inverter with Si diode, Micro-inverter with SiC diode, and Micro-inverter...
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