Distributed generation (DG) is expected to play a vital role in the future to improve the quality of human life. DG and its integration to the local AC grid provide options for economical, continuous, and bidirectional power flow (utility interface). In addition, it provides a back-up to support during grid failure or blackouts. Extensive promotion of the DC grid is also proposed for the future to facilitate easy integration of renewable resources. Low-voltage DC grid derived from DG is safe and may cover a significant portion of residential load, which is mostly DC load avoiding inefficient AC/DC power supply. Vehicles in the smart grid have introduced a concept of living and mobility, i.e., sustainable living and low carbon mobility and are foreseen as a part of future microgrid. Research is needed to push and commercialize these technologies to make the environment clean by replacing conventional generation systems. This “Special Section on Power Converters, Control, and Energy Management for Distribution Generation” of the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, is a step forward to promote and encourage extensive investigations in the areas associated with DG. In all, 16 papers were selected, which have one or more very unique features for the proposed applications. The topics range from new high gain DC/DC converters to inverters for solar PV integration on one side and development of effective test bed to brushless generation systems for potential DG applications on the other. To facilitate an in-depth survey of the published papers, the Guest Editors will now examine one by one the different contributions by highlighting the most noteworthy developments and findings.

Power Converters, Control, and Energy Management for Distributed Generation

In this paper the stability and sensitivity function of three basic dc-dc converter with the consideration of circuit parasitics has been analyzed for analog and digital controller implementation. The steady state and small-signal analysis has been used to derive the mathematical expressions for uniformly sampled voltage-mode controlled converters. The effect of digital controller using the ratio of sampling to carrier frequency has been analyzed. The sampling frequency limits the voltage gain in the stepped manner and also affects the stability of the digitally controlled converter. The sensitivity function has been defined for voltage gain with respect to various system parameters. The maximum affected regions on duty ratio scale with corresponding parasitic variable have been discussed. The detailed stability analysis has been carried out for digitally implemented three basic dc-dc converters, i.e., buck, boost, and buck-boost circuits. The analytical results are verified with the simulations performed in PSCAD/EMTDC. An FPGA controller is considered as digital controller for the dc-dc converter and verification of the results through experiment.

Stability and Sensitivity Analysis of Uniformly Sampled DC-DC Converter With Circuit Parasitics

In this paper, average modeling and analysis of a dual-supercapacitor bank, actively balanced by a bidirectional buck–boost converter, is presented. In such a system, natural balancing is achieved when the converter is operated in open loop with 50% duty cycle, eliminating the need for measuring the voltage of each storage device. Nevertheless, excessive currents arise even for slight voltage misbalance because of the highly underdamped nature of the system. In order to remedy this drawback, bidirectional pulse-by-pulse inductor current limitation is introduced, which is equivalent to adding a peak-current-mode-like control loop to the system. Since the duty cycle never exceeds 50%, compensation ramp is not required to maintain stability. On the other hand, while the uncontrolled system dynamics is linear, introducing the current limit mechanism turns the closed-loop dynamics into a nonlinear one, burdening the analysis task and thus calling for suitable average model to perform fast simulations for system analysis. Therefore, dynamical equations of the system are developed in order to derive the switching-cycle-averaged model and reveal the tradeoff between current limit level, balancing time and efficiency for the worst case of imbalance. Simulations and experiments support the presented findings.

Average Modeling and Performance Analysis of Voltage Sensorless Active Supercapacitor Balancer With Peak Current Protection

A unified observer for robust sensorless control of DC–DC converters

Primary-side regulation (PSR) flyback converters operating in discontinuous conduction mode (DCM) are widely used in low-power applications. In DCM, the peak current control method for PSR flyback is generally adopted to achieve constant current (CC) output. However, there are few effective schemes suitable for DCM and continuous conduction mode (CCM) operation of PSR flyback converters due to the difficulty in estimating the output information correctly, especially in the case of analog circuit control. In this article, a control scheme based on midpoint sampling method is proposed to achieve a high-precision CC control, which operates seamlessly as the operating mode switched between DCM and CCM. In order to verify the feasibility and performance of the proposed control, a control IC with the proposed CC control scheme has been implemented in 0.18  μ m 5 V/40 V BCD process. The experimental results show that the deviation of the output current is within ±1.93% under different input and load conditions.

A Constant Current Control Scheme for Primary-Side Controlled Flyback Controller Operating in DCM and CCM

While current-mode control of dc–dc converters provides numerous benefits over voltage-mode control, previous models of the control strategy have been limited to the form of classical control models. Through the use of a state-space averaged (SSA) model of current-mode control, both the open-loop and closed-loop circuit parameters of open-loop control-to-output frequency response, conducted susceptibility, input admittance, output impedance, and any other desired response can be easily obtained. In this paper, SSA models of current-mode-controlled converters are derived and presented for buck, boost, and flyback topologies operating in continuous conduction mode. The new model allows for simpler and more accurate modeling than possible with previous methods, facilitates the modeling of cascaded converters, and allows for the use of state-variable feedback and other modern control methods in applications that use current-mode control.

Sean C. Smithson

Papers

A Unified State-Space Model of Constant-Frequency Current-Mode-Controlled Power Converters in Continuous Conduction Mode