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The Cuk inverter operating in continuous conduction mode (CCM) is susceptible to grid disturbances and its transfer function has two right-half plane zeros, which cause a large phase lag. To improve the output-tracking precision in the grid-connected environment, a repetitive controller with linear phase-lead compensation has been developed for the Cuk inverter. However, this controller requires heavy computational burden and memory space; these problems become more severe as the converter operates at a higher switching frequency. This paper proposes to use a down-sampled repetitive controller (DRC) for Cuk CCM inverter to alleviate these problems. The down-sampling technique itself can significantly reduce the computational burden and memory space of RC. On the contrary, its control accuracy becomes very low, particularly for the Cuk CCM inverter. Unlike conventional module integrated inverters (MIIs), the Cuk CCM inverter must adopt a fractional-order phase-lead compensation algorithm to compensate for the effect of the large phase lag in the down-sampled environment. To clarify the inevitable usage of DRC with a fractional-order phase-lead compensation for Cuk CCM inverter, the DRC is classified into four types, this paper provides its detailed design guideline based on stability analysis of the overall control system and also presents design examples for representative MIIs. Experiments using a 300-W prototype Cuk inverter validate that the proposed control approach achieves acceptable output-tracking accuracy. The total computation time and memory space with the DRC decrease by 76.0% and 80.0% compared to those with the conventional RC while the output-tracking accuracy with the DRC decreases by 0.42%.

The Ćuk converters operating in continuous conduction mode (CCM) can be preferred in applications such as microprocessor power delivery and pulsed load because these circuits have advantages of being able to step up/down, a small number of power components, and low input/output current ripples. However, they show poor transient performance due to right‐half‐plane‐zeros (RHPZs) in the closed‐loop transfer function of the Ćuk CCM converter. To enhance the transient response, a combined feedback–feedforward control for the Ćuk CCM converter is proposed. The proposed control scheme comprises a feedback control signal based on a Lyapunov function and a duty‐ratio feedforward control signal. A Lyapunov‐function‐based controller (LBC) achieves fast dynamic response even under large‐signal variations from the operating point. The duty ratio feedforward controller (DFFC) is developed to predict the effect of the disturbances and compensate it, while alleviating the burden of LBC. The proposed control logic makes the closed‐loop system of the Ćuk CCM converter globally exponentially stable and thus provides a fast transient response even under large‐signal variations. To construct the proposed controller, the authors make use of the large‐signal averaged model of the Ćuk CCM converter, and consider the parasitic elements. To verify the proposed control scheme, numerical simulations and experimental tests are conducted.

In this article, we present a bridgeless hybrid-mode Zeta inverter for distributed energy systems. We integrate the secondary diode of the conventional unfolding-type Zeta inverter into one of diagonal pairs of the secondary-side switches in a bridgeless Zeta inverter. This structure decreases the number of active power components and provides naturally well distributed loss at the body diodes of the secondary-side switches over one cycle of grid voltage, and as a result, increases both output power transfer and reliability. To attain medium-high power capacity with appropriate size of magnetic components, the bridgeless Zeta inverter operates in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). However, control of the proposed inverter is difficult because of the distinct system dynamics caused by the operations in DCM and CCM. To deal with this control problem, we first identify the mode boundaries and, corresponding to each mode, develop a dynamic model to design a controller. Then, we propose to use a feedback controller plus a feedforward controller supplemented with a repetitive controller that uses a phase-lead compensator. Experimental results using a 300-W prototype demonstrate the feasibility and effectiveness of the proposed modeling and control approach.

This article introduces a highly efficient bidirectional resonant dc/dc converter over wide range of battery voltages for vehicle-to-grid (V2G) capable electric vehicles (EVs). It operates as a pulsewidth-modulation (PWM) full-bridge series-resonant converter in the forward direction and a half-bridge resonant boost converter in the backward direction. One advantage of the proposed converter is that it has a wide voltage gain range in the backward operation. Also, it requires only six active switches. To achieve high efficiency, SiC mosfet s are used for two bottom switches in the primary side, because only these switches suffer hard switching turn- off in both forward and backward directions. Since it operates with fixed-frequency and with PWM control, the magnetic components and passive filters can be optimally designed with respect to the volume and the loss. Thus, the proposed converter achieves low-cost, high-conversion ratio, and high efficiency over a wide range of battery voltages. Detailed analysis of the converter operation is presented along with the design procedure. A 3.3-kW/400-V prototype of the proposed converter has been built to operate for 250–415 V primary source voltages and tested to demonstrate its circuit design.

This paper presents a bridgeless Cuk-derived single power conversion inverter with reduced number of power components, which has reactive-power capability. The secondary diode of the conventional unfolding-type Cuk inverter is integrated into one of the secondary-side switches in the bridgeless Cuk-derived configuration, which reduces the number of active-power components. A modulation technique is developed to provide a current path during reverse power flow; this technique enables operations under unity and nonunity power factors. A repetitive controller coupled with a linear feedback controller and a feed-forward controller are used to achieve accurate output current tracking under the harsh control environment. Driving the diode-integrated switch in synchronous rectification mode provides higher power conversion efficiency than that under diode-based secondary side rectification. Circuit operation and design guidelines of the bridgeless Cuk inverter are presented in detail. A 500-VA prototype inverter was fabricated to demonstrate the desirable performance of the bridgeless Cuk-derived inverter.

A current-fed dual-half-bridge (CF-DHB) converter directly connected with a half-bridge (HB) inverter unit is proposed for residential photovoltaic power conversion systems. The proposed inverter requires only half as many switching devices as the full-bridge two-stage inverters and does not have to use a large dc-link capacitor. However, the converter unit suffers from 120-Hz dc-link voltage fluctuation and 60-Hz capacitor voltage unbalance, which degrade the control performance of the half-bridge inverter. To suppress both dc-link voltage fluctuation and capacitor voltage unbalance, we propose to use appropriate repetitive controllers, that are used to determine the nominal duty-ratio and the phase-shift. To make the proposed CF-DHB operate at the maximum power point (MPP), we use the incremental conductance method that offers smooth transition to MPP. Experimental results show that the proposed inverter system achieved high MPP tracking efficiency, low total harmonic distortion, high power conversion efficiency, and medium power capacity.

This paper presents a dual-mode Cuk inverter for photovoltaic/thermoelectric power applications. A dual-mode Cuk inverter operates in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM), and has the advantages of low ripples of voltage and current at the input and output, medium power density, and step-up/step-down ability, but is difficult to control because DCM and CCM have distinct system dynamics. To overcome this control problem, we propose to use a repetitive controller (RC) with a multiple phase-lead compensator for the dual-mode Cuk inverter. If the RC is applied by itself, the distinct system dynamics may severely degrade its system performance. Thus, in the proposed RC, we mainly use a multiple phase-lead compensator to compensate for the different phase lags of the dual-mode Cuk inverter. To reduce the burden from the RC, we use the dual-mode nominal duty ratio as feedforward control input. We also analyze the boundary of operation modes in the dual-mode Cuk inverter, then provide detailed and practical guidelines to design the control parameters. Experimental results obtained on a 500-W digitally controlled module integrated converter prototype confirmed the effectiveness of the control approach.

Conventional asymmetric half-bridge LLC converters have been attractive in on-board battery charger applications because of their simple control and structure. However, their usage with asymmetric PWM is limited due to the large dc-offset current and increased conduction loss. In this paper, we propose a bidirectional switch based half-bridge series-resonant converter. Proposed converter features a small number of power components, inherent zero voltage switching capability, and a zero dc-offset current. The combination of the half-bridge circuit and the bidirectional switch generates symmetric resonant current with the zero dc-offset current regardless of the duty cycle variation. When the output voltage is high, it operates in discontinuous conduction mode (DCM). When the output voltage becomes low and under heavy load condition, it naturally enters in continuous conduction mode (CCM), and so it provides low conduction loss. A 1.65-kW prototype of the proposed converter has been built and tested to demonstrate its circuit design.

This paper proposes a hybrid-mode Cuk inverter with low-voltage ride-through (LVRT) capability under grid-faults. It operates as an unfolding-type inverter during normal grid condition and two-stage inverter during abnormal grid condition. Thus, it normally transfers the energy to the utility grid highly efficiently, and also has the LVRT ability under grid-faults. Moreover, two types of inverters share the full-bridge circuit on the grid-side and so the proposed circuit can be developed with low cost and reduced size. This paper outlines operation principles and control methods for the proposed inverter. The prototype of the proposed converter was implemented and experimental tests were carried out to demonstrate its practical feasibility.

This article proposes an improved odd-harmonic repetitive controller (IORC) for a Cuk-derived inverter. The IORC is composed of a modified structure of an odd-harmonic repetitive controller (ORC) combined with a proportional-integral (PI) controller and a feedforward controller to achieve a zero steady-state error in the Cuk-derived inverter. The IORC features much larger gains at odd-harmonic frequencies by modification of an existing ORC, so both its convergence rate and transient response become much faster. The added benefit of using the IORC is that it has wider bandwidth at odd-harmonic frequencies, so it is more insensitive to the grid frequency fluctuation. The IORC also adopts a linear phase-lead compensator to compensate for the phase lag of the Cuk-derived inverter. Hence, the IORC can effectively eliminate the odd-harmonic components in the output current of the grid-connected Cuk-derived inverter while using less memory space. However, the distinctive structure of the IORC makes it difficult to guarantee the stability of the overall control system. Thus, in this article, a new stability analysis method is developed for the IORC system, and then a practical design guideline is also provided to obtain the optimal control parameters. Experimental results are presented to validate the proposed controller in the 300-W Cuk-derived inverter prototype.

This paper proposes a memory space adjustable repetitive controller (RC) for an unfolding-type isolated Cuk inverter operating in the continuous conduction mode (CCM). To achieve acceptable tracking performance with reduced computation burden and memory space, we use the memory space adjustable RC in addition to the proportional-integral (PI) controller and the feedforward controller. Two right-half plane (RHP) zeros in the transfer function of the Cuk CCM inverter cause phase lag of the closed-loop control system. To compensate for the phase lag accurately under the low-sampled environment, we develop a fractional-order phase-lead compensator in the memory space adjustable RC. Simulation and experimental tests using a 300-W unfolding-type Cuk CCM inverter have verified the proposed controller achieves desirable performance.

Conventional bidirectional resonant converters can transfer the power in both forward and backward directions, but their usage is limited due to a narrow input voltage range. In this paper, we propose a new modulation strategy to operate the bidirectional resonant converter under the extended input voltage range. In the forward direction, the converter operates as a PWM resonant boost converter. In the backward direction, it operates as a pulse-width-modulation (PWM) resonant buck converter. The use of bidirectional switch enables the circuit operate in both the PWM resonant boost converter and the PWM resonant buck converter. The proposed converter achieves the wide input voltage range with a small number of power components. At 250-415 V, 1.65 kW/400 V prototype of the proposed converter has been built and tested to demonstrate its circuit design.

We propose an iterative learning controller (ILC) with hybrid learning scheme for a flyback inverter operating in continuous conduction mode (CCM). The flyback CCM inverter has advantages such as buck-boost capability, small number of circuit components and high power conversion efficiency, making it suitable for the distributed renewable energy systems. But the conventional proportional-integral (PI) controller for the flyback CCM inverter exhibits poor steady-state response because it suffers from control problems caused by right-half-plane (RHP) zero in closed-loop transfer function and time-varying grid-voltage disturbances. Phase-lead ILC is one of the candidates to solve these problems, but it requires massive amounts of memory. To overcome this problem, we use a sampled-data iterative learning controller with phase-lead compensation, in which sampled-data technique reduces the memory space needed. The proposed ILC is also computationally simple and easy to implement. The stability of the closed-loop system is derived and the zero tracking error is achieved. Experimental tests demonstrate the proposed control approach.

A high step up converter having rippleless input current is proposed for a fuel-cell power conditioning system. The proposed converter consists of a double current-fed half-bridge circuit at the primary side and a bridgeless rectifier with series-resonant circuit at the secondary side. Interleaving scheme and fixed 0.5 duty-cycle operation at the primary-side make the input current ripple become zero. A high step-up capability of the proposed converter can be achieved by secondary switching operation. The steady-state operation for the proposed converter is analyzed. A 600-W prototype converter was built and used to validate the performance of the proposed converter.

This paper proposes a repetitive controller to be used for capacitor-less current-fed dual-half-bridge (CF-DHB) converters under the grid-connected environment. When the dc-link capacitor is very small, the dc-link current fluctuation can distort the input current severely. Compared with the previous controllers introduced to reduce the input current ripples, the proposed repetitive controller can reduce them more significantly. In developing the proposed controller, we derived the dynamic model of the capacitor-less CF-DHB in the grid-connected environment, and used it to implement the repetitive controller. Experimental results verify that the proposed control scheme achieves desirable performance.

This paper proposes a PWM based integral sliding mode controller (ISMC) for the single-stage Cuk inverter. The fourth-order model of the Cuk inverter is derived first and it is simplified to use ISMC. Based on the simplified system model, the ISMC that consists of the equivalent control part plus the switching control part is designed and applied to the single-stage Cuk inverter. Comparing to conventional controller, the ISMC can accurately control the output current of the single-stage Cuk inverter. Simulation and experimental tests using the prototype of the single-state Cuk inverter were performed to validate the proposed control approach.

A integral sliding mode controller (ISMC) for a fixed-frequency PWM is proposed for the Cuk converter. The fourth-order model of the Cuk converter is derived first and it is simplified to use ISMC. Based on the simplified system model, the ISMC that consists of the equivalent control part plus the switching control part is designed and applied to the Cuk converter in the presence of uncertain variations and unknown disturbances. The closed-loop system is also proved to be exponentially stable. Simulation and experimental tests using the prototype of digitally controlled DC-DC converter were performed to validate the proposed control approach.