Vladimir Yuhimenko

DC Active Power Filter-Based Hybrid Energy Source for Pulsed Power Loads

In this paper, design of a capacitor semiactive hybrid source for powering pulsed power loads based on dc power filter principle is presented. The system consists of an energy source connected directly to a load, supported by a bidirectional buck-boost dc-dc converter interfaced supercapacitor (SC). The converter is controlled such that the SC supplies the dynamic component of the load power, leaving the energy source to supply a near-constant power to satisfy average load demand. The control algorithm is adopted from the power filter theory, allowing to reduce the stress of an energy rich source despite operating under a high-power demanding load. Moreover, the SC-load voltage matching is not required and the control algorithm does not require load current sensing. Instead, energy source current of a much lower amplitude is necessary. The SC sizing methodology is proposed, and topology issues aiming to minimize the SC are discussed as well. Compared with a passive hybrid, the proposed system utilizes much lower capacitance at the expense of additional power electronics. Experimental results are presented to demonstrate the feasibility of the approach.

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

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.

Low-Frequency DC-Link Ripple Elimination in Power Converters With Reduced Capacitance by Multiresonant Direct Voltage Regulation

In this paper, a method for suppressing the low-frequency portion of dc-link ripple inevitably present in power conversion systems with reduced capacitance is proposed. The discussed active capacitance reduction circuitry (consisting of a feedback-controlled shunt-connected bidirectional buck-boost converter, terminated by a small auxiliary capacitance) directly regulates the dc-link voltage, utilizing a dual-loop control structure with parallel-connected multiresonant-bank-enhanced voltage loop stabilizing controller to achieve nearly constant, low-frequency-ripple-free steady-state dc-link voltage. Consequently, the proposed active capacitance reduction system may be perceived as a virtual infinite capacitor from the dc link point of view. The suggested circuitry is successfully applied to a single-phase commercial power factor correction front end in a nearly plug-and-play fashion. The control algorithm effectiveness is fully supported by simulations and experimental results.

Analysis and Control of Direct Voltage Regulated Active DC-Link Capacitance Reduction Circuit

The paper focuses on control analysis and operational issues of a recently proposed direct voltage regulated active capacitance reduction circuit, consisting of a small auxiliary capacitance interfaced to dc link by bidirectional dc–dc converter. The aim of such a system is replacing the bulk dc bus capacitor without escalating the ripple. While the hardware of the system under study is similar to some of the proposed active capacitance reduction solutions, the control structure is quite different. The primary goal of the controller is direct regulation of dc-link voltage rather than dc-link current, performed by most of existing solutions, thus avoiding the use of invasive dc-link current measurement/s. It is revealed that such an active capacitance reduction circuitry may be perceived as output-voltage regulated wide-input-range converter feeding a bidirectional power load. Such an arrangement was neither mentioned nor analyzed in the literature by far, requiring nontrivial and challenging control design. A dual-loop voltage-current arrangement widely used in typical power supplies is proposed to control the active capacitance reduction circuitry. It is shown that the control structure is sufficient to yield satisfactory performance even though the system possesses a slow unstable mode when absorbing power from the dc link. The revealed findings are fully supported by simulations and experimental results.

Infinite virtual capacitor realization for grid-connected power converters

An alternative approach to DC link capacitance reduction and ripple suppression of grid-connected converters was recently suggested. Instead of regulating the DC link current, the proposed system gains control over the ripple by replacing the grid-interfacing converter in the task of regulating the DC link voltage. This allows increasing the voltage control bandwidth (thus reducing the ripple) without sacrificing the input power factor. In this paper, a PI in conjunction with Multi-resonant voltage controller is introduced, allowing complete elimination the DC link voltage ripple thus realizing a virtual infinite capacitance.

Active voltage sensorless supercapacitor bank balancer with peak current protection

In this paper, average modeling 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. Dynamical equations of the system are developed in order to derive the switching-cycle-averaged model. Simulations support the presented findings.

Combining Diesel Generators With Ultracapacitors to Enhance Stability and Reliability

Diesel generator based auxiliary power units (DG-APU) are widely used in different civil and military applications. Fuel economy and service life are probably the most important issues concerning their operation. Controlling engine throttle position in accordance with the load power allows regulating fuel supply to the engine to optimize fuel consumption. Despite the advantage of the method, control stability is sacrificed in case of light load operation as follows. When the DG-APU is running with a light load, engine throttle position should be nearly closed in order to minimize fuel consumption. If a load step is applied in such situation, engine velocity may drop sharply until complete stop because of insufficient control system bandwidth. This is why velocity and throttle position of a DG-APU should not be decreased below some level even if load power is low to maintain reliability at the expense of increased specific fuel consumption. Moreover, for small diesel-generators the throttle position is usually fixed. Thereby, relatively wide range load power variations (typical for many of diesel-generator applications) cause excessive fuel consumption.The situation may be sufficiently improved by connecting ultracapacitors (UC) on the DG-APU output terminals, introducing additional inertia allowing smoothing engine velocity decrease during a sudden load increase thus providing more time to the control system to regulate throttle position. As a result, DG-APU would be operated much more efficiently at light loads without sacrificing stability. Moreover, the UC may be used at as starter motor power source, removing starting stress from electrochemical batteries. Present work investigates the improvements in UC-supported DG-APU fuel efficiency and stability compared to conventional technical solutions. The research is based on mathematical modeling of the entire system, verified by experiments. The results support the presented ideas and quantitatively demonstrate the improved fuel economy and reliability of small DG-APUs.Copyright