Hussam Al-Atrash

Modeling and Control of Three-Port DC/DC Converter Interface for Satellite Applications

This paper presents the control strategy and power management for an integrated three-port converter, which interfaces one solar input port, one bidirectional battery port, and an isolated output port. Multimode operations and multiloop designs are vital for such multiport converters. However, control design is difficult for a multiport converter to achieve multifunctional power management because of various cross-coupled control loops. Since there are various modes of operation, it is challenging to define different modes and to further implement autonomous mode transition based on the energy state of the three power ports. A competitive method is used to realize smooth and seamless mode transition. Multiport converter has plenty of interacting control loops due to integrated power trains. It is difficult to design close-loop controls without proper decoupling method. A detailed approach is provided utilizing state-space averaging method to obtain the converter model under different modes of operation, and then a decoupling network is introduced to allow separate controller designs. Simulation and experimental results verify the converter control design and power management during various operational modes.

Tri-Modal Half-Bridge Converter Topology for Three-Port Interface

This letter proposes a novel converter topology that interfaces three power ports: a source, a bidirectional storage port, and an isolated load port. The proposed converter is based on a modified version of the isolated half-bridge converter topology that utilizes three basic modes of operation within a constant-frequency switching cycle to provide two independent control variables. This allows tight control over two of the converter ports, while the third port provides the power balance in the system. The switching sequence ensures a clamping path for the energy of the leakage inductance of the transformer at all times. This energy is further utilized to achieve zero-voltage switching for all primary switches for a wide range of source and load conditions. Basic steady-state analysis of the proposed converter is included, together with a suggested structure for feedback control. Key experimental results are presented that validate the converter operation and confirm its ability to achieve tight independent control over two power processing paths. This topology promises significant savings in component count and losses for power-harvesting systems. The proposed topology and control is particularly relevant to battery-backed power systems sourced by solar or fuel cells

Statistical modeling of DSP-based Hill-climbing MPPT algorithms in noisy environments

The effect of measurement noise on DSP-based maximum power point tracking (MPPT) algorithms is investigated in this paper. Based on the probabilistic characteristics of noise signals, a statistical model is constructed that allows quantitative analysis of the behavior of such algorithms both during transients and in steady-state. This model is then used to classify tracking problems into those presented by noise, and others resulting from other non-idealities such as measurement bias. It is then used to inspect different noise fighting techniques in order to predict their validity, and to suggest more relevant techniques. The results arrived at are then experimentally verified and confirm the predictions of the statistical model

Digital Controller Design for a Practicing Power Electronics Engineer

Practical digital controller design for switching power converters is addressed in this paper. A simplified direct-digital design approach is proposed where digital compensation tools are analyzed in the familiar analog frequency domain. The design is based on traditional concepts and tools such as Bode plots, zero/pole insertion, and gain/phase margins. In contrast to analog redesign methods, this approach is able to accurately account for loop parasitics such as zero-order holds and computational delays and predict the system response. It does not entail the creation of a discrete-time model of the controlled plant, necessary for other direct-digital design approaches. Families of compensation zeros/poles are presented. Notably powerful are two families of complex zero pairs, able to create a sharp phase boost of 180 degrees, specifically useful for converters with high-Q filters. A numbering system is introduced that enables simple -yet optimized-number representation within a fixed-point environment. This system is utilized to model different controller blocks, and to construct a blue-print of the controller code. A design example is then used to demonstrate the design methodology. Experimental results of a matching prototype are then presented that show close correspondence to theoretical and simulation predictions.

Boost-Integrated Phase-Shift Full-Bridge Converter for Three-Port Interface

Numerous modern systems require energy harvesting from multiple sources and the management of energy storage. The adoption of converter topologies specifically tailored for such applications offers great improvement potential over conventional systems. In this paper, two three-port converter topologies are proposed based on the integration of a boost stage into the popular phase-shift full-bridge converter. Each of the proposed converters is able to interface two bidirectional source/storage ports and an isolated loading port. They are specifically interesting due to their ability to achieve zero-voltage switching for a considerable range of operating conditions. Power flow control is performed using two degrees of freedom: duty-cycle and phase-shift of the two switching legs. Analysis of operating modes and component stresses is presented, leading to a discussion of design guidelines. A comparative study involving the proposed topologies and a conventional multi-converter system is conducted. This study formulates the constraints under which each of the three design choices is most profitable. It demonstrates the ability of the proposed converters to achieve significant savings in losses and/or costs for a range of multi-port applications. Experimental 1 kW prototypes are used to demonstrate the functionality of the proposed converters.

Dynamic Analysis of Three-Port DC/DC Converter for Space Applications

This paper presents the control structure for a novel three-port converter topology. This topology has the advantage of low switch count, high power density, high efficiency, so it is a valuable choice for space applications. The three port converter for space application interfaces one solar panel input port, one bi-directional battery port and an isolated output port. Lithium-Ion battery charge control simulation is implemented. Maximum Power Point Tracking (MPPT) is adopted to maximize the solar energy input. Two of the three ports can be simultaneously regulated. However, the two control loops have interactions with each other due to the integrated power trains of the three ports. Therefore, implementing the closed loop control requires careful analysis of their dynamic behaviors. In this paper, the dynamic behavior of the converter during different operational modes is fully characterized and studied. Small signal models are derived based on state space equations, and experimental results verify the converter control structure.

Effect of Measurement Noise and Bias on Hill-Climbing MPPT Algorithms

Erroneous measurement of solar array voltage and current degrades the performance of hill-climbing, maximum power point tracking (MPPT) systems. This degradation is observed as a reduced climbing rate, erroneous settling point, and/or random operating point excursions. The effect of measurement bias and noise on MPPT performance is analyzed. Tracking problems are then classified according to their cause, which allows for easier debugging of a faulty tracker. The effectiveness of several error-mitigating techniques is then studied, and recommendations are given accordingly. Conclusions of the analysis are then experimentally verified.

A Zero-Voltage Switching Three-Port Isolated Full-Bridge Converter

This paper proposes an integrated single-stage three-port DC-DC converter. The proposed converter interfaces two bidirectional source/storage ports, and a galvanically isolated loading port. The power topology is based on the integration of a bi-phase boost pre-regulator stage into a phase-shift controlled full-bridge converter. The four bridge switches play the combined role of realizing synchronous boost conversion, and driving the transformer. The proposed topology is conditionally able to achieve zero-voltage switching of all bridge switches. Compared to the cascaded converter approach, this topology alleviates the cost overhead associated with introducing a switching leg for boost operation, and saves the switching loss it would exhibit. A constant-frequency switching scheme is adopted that presents two degrees of freedom necessary for proper control. The duty-cycle of the two phase-legs of the bridge is varied to control energy flow in the boost section, while the relative phase-shift between the legs is utilized to regulate the power pushed to the loading port. The operation of the topology is verified using an experimental 1 kW prototype, designed to handle a photovoltaic source, a storage battery bank, and a regulated DC load

A single-staged PV array-based high-frequency link inverter design with grid connection

This paper proposes an efficient control approach of photovoltaic (PV) array-based high-frequency link inverter architecture that tracks the maximum available power of a PV array source and synchronously supplies sinusoidal current into the utility grid by using only a single stage of power processing conversion. A feed-forward compensator eliminates the loop gain dependence on the utility grid and keep the input maximum power of PV array during variable grid voltage. Voltage seconds analysis shows that the transformer can be designed as the conventional high-frequency transformer of a DC/DC converter without any low frequency harmonics. Simulation and experimental results show that the full-bridge switches are turning on at zero voltage.

Tri-Modal Half-Bridge Converter for Three-Port Interface

This paper proposes a novel converter topology that interfaces three power ports: a source, a bidirectional storage port, and an isolated load port. The proposed converter is based on a modified version of the isolated half-bridge converter topology that utilizes three basic modes of operation within a constant-frequency switching cycle to provide two independent control variables. This allows tight control over two of the converter ports, while the third port provides the power balance in the system. The switching sequence ensures a clamping path for the energy of the leakage inductance of the transformer at all times. This energy is further utilized to achieve zero-voltage switching for all primary switches for a wide range of source and load conditions. Steady-state analysis of the proposed converter is included, together with a suggested structure for feedback control. Key experimental results are presented that validate the converter operation and confirm its ability to achieve tight independent control over two power processing paths. This topology promises significant savings in component count and losses for power-harvesting systems. The proposed topology and control is particularly relevant to battery-backed power systems sourced by solar or fuel cells.