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A simple third-order equivalent circuit model of series resonant converter (SRC) is proposed in this paper. Up to now, the most successful equivalent circuit model of SRC is based on extended describing function concept, which is proposed by Dr. E. Yang [30]. However, the equivalent circuit is a complicated fifth-order circuit with the cross-coupling effect and no analytical solution is provided for...
Resonant converters have gained popularity for a variety of applications due to their ability to provide soft switching conditions and high power density. Controlling these converters is complex because of their non-linear behavior and high frequency resonant tank. Controllers are often designed by using small-signal models, which are limited to operating around a quiescent point. However, the small-signal...
The grid-feeding voltage controlled inverter (GF-VCI) based on droop control is vulnerable to the harmonic voltages of the utility grid. Because of the equivalent impedance of system is small, the slight distorted grid voltage will result in the harmonic component increasing of GF-VCI output currents. Therefore, the reason of generation of distorted grid-feeding current of GF-VCI under the distorted...
An effective output voltage regulation method using harmonic burst mode control strategy is presented. By using this strategy, the operating performance of the full-bridge series resonant dc-dc converter (SRC) applied to electric vehicle (EV) battery charging is improved. The proposed control strategy not only performs load regulation, but it also achieves soft switch both at turn-on and turn-off...
This paper presents the design procedures of an unity-power-factor AC-DC power converter for wireless power transfer application. This newly proposed AC-DC converter consists of two stages: the PFC front stage uses LC series resonant circuit to perform power factor conditioning and the second stage uses a DC-DC converter to regulate the output voltage. New equations to describe the input impedance...
An improved buck-boost + LLC (IBB LLC) cascaded converter appropriate for wide input voltage situation is presented in this paper, which can be used as a constant voltage source or a constant current source charger for battery. The control strategy of dual frequency PWM (DFPWM) is introduced. For the LLC converter, ZVS for MOSFETs and ZCS for diode are achieved. As a result, the switching loss is...
This paper points out the low accuracy of the traditional fundamental harmonic approximation (FHA) in predicting the gain characteristics and resonant behaviors of the full-bridge isolated bidirectional CLLC resonant converter, which results in great impediments in optimally designing the resonant tank parameters. Given these drawbacks of FHA for CLLC converter, this paper proposes a novel operation...
This paper proposes control of 3-level inverter with small DC-link capacitance and grid filter inductance for high speed motor drive system where regeneration and hold-up time are unnecessary. The controller consists of three simultaneously operating sub-controllers; High speed motor controller for flux weakening and maximum torque per ampere (MTPA) control, neutral voltage controller for DC-link...
The following two types of resonant controllers are mainly employed in stationary reference frame to obtain high performance in voltage-source converters: 1) proportional + resonant (PR) and 2) complex vector proportional + integral (cVPI). The performance analysis and parameter design of these two controllers has been researched in many papers. In this paper, these two groups of resonant controllers...
The light load efficiency has drawn more and more attention for the LLC resonant converters. And the high frequency LLC converters are emerging in recent years. The conventional burst mode control cannot fix to the efficiency-optimal state during the burst-on time. Optimal Trajectory Control (OTC) for burst mode can solve this problem by using fixed 3-pulse pattern; however, the burst operation range...
With increasing penetration of grid-connected photovoltaic (PV) power generation in distribution network, the equivalent impedance of the distribution network and the distribution capacitance of the interconnection cables are changed. The changed impedance network may be excited by the harmonic current of inverters or the harmonics of the grid voltage, which will affect the power quality and stable...
This paper illustrates the assessment between the multiloop control strategies that aim to damp the resonance hazard of LCL-filters and expanding the available stability margins. The establishment of the multiloop control is sustained in a sensorless manner with the reconstruction of the state variables using the Kalman observer, thus enhancing the cost measures and reliability of the distributed...
This paper presents a novel prototype of a timesharing frequency doubler principle-based current-fed zero current soft-switching (ZCS) high frequency resonant (HF-R) inverter for inductive power transfer (IPT) systems. The newly-proposed ZCS HF-R inverter is suitable for producing a higher frequency resonant current with switching power loss reduction by using a middle-class switching frequency insulated-gate-bipolar-power...
This paper investigates the stability regions of current control for LCL-filtered grid-connected converters, where no active or passive damping is required to stabilize the closed-loop control system. It is already identified in the literature that if the LCL resonance frequency is placed within 1/6 to 1/2 of the system sampling frequency, the grid current control can be directly used without damping...
This paper proposes Multi-step Simplified Optimal Trajectory Control (SOTC) for the high frequency LLC converters. SOTC can improve the transient performance of the LLC converters by immediately changing the pulse width of the primary driving signal during the load transient. However, the implementation of SOTC requires high-performance digital controllers. The proposed Multi-step SOTC calculates...
Previous work reveals that the magnetically coupled resonant (MCR) wireless power transfer (WPT) technology is efficient and practical for mid-range wireless energy transmission, able to handle nontrivial amount of power. This paper presented an equivalent analytical model for MCR WPT system to incorporate spatial misalignments between the transmitting coils and receiving coils. The mutual inductance...
In this paper, a hierarchical control system based on a novel autonomous current sharing controller for grid-connected microgrids (MGs) is presented. A three-level hierarchical control system is implemented to guarantee the power sharing performance among voltage controlled parallel inverters, while providing the required active and reactive power to the utility grid. A communication link is used...
Instabilities due to mutual interactions among converters and inverters are sometimes observed. The Lyapunov-based, or an energy-based control is useful to assure stability of parallel-connected power converters. This paper investigates why the Lyapunov-based method can stabilize the system even when linear methods fail in stabilization due to a large line impedance. The analysis is based on the impedance...
By utilizing next-gen wide band-gap (WBG) devices, such as GaN and SiC, at high switching frequency in a single-phase Quasi-Z-Source PV inverter (qZSI), the impedance network can be significantly reduced. Although, the reduced qZS impedance network will decrease cost and improved power density, it will also result in frequency resonance that will introduce oscillations in the capacitor voltage and...
Active damping of LCL-filter resonance based on single-state feedback control is widely used with voltage source converters. Its robustness against grid impedance variation has always been a major concern with its controller design. To deal with this issue, this paper begins by developing a generalized impedance-based model of grid current control with feedback-type active damping. Then, a controller...
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