Multi-port dc-dc converters find significance in applications such as renewable integration, and hybrid- source systems. Power flow control and its management is one of the major challenges associated with multi-port converters. This work proposes a hybrid model predictive controller for control of power within the integrated dual dc boost converter topology. This topology is a three-port converter with one bidirectional port (suitable for an energy buffer, eg. battery). Due to sharing of control duty ratio using the same set of controllable switches, using separate controllers for each control objective results in cross-regulation within the different ports. This work presents the model predictive controller which can simplify control design for the multi-port system and hence provide robustness to the regulated system. The design of the controller and its evaluation is presented in this work.

Neutral-point ( NP) voltage balancing is a well-known challenge associated with Neutral Point Clamped (NPC) multi-level voltage source converters. Most of the literature on multilevel NPC converters discusses on multiple balancing techniques that are used to nullify dc or ac unbalance and claims the adaptability of these techniques over wide range of modulation indices and power factors. This paper details out the analysis for estimating the maximum balancing ability of an optimized neutral point balancing technique applied on a grid connected 3-Level Active-NPC (ANPC) converter with supporting simulation and experimental results. Also, a simplified analysis to study the impact of grid harmonics on the neutral point potential is presented and validated with the help of simulation results.

Operation of Doubly fed induction generator (DFIG) based wind turbine with 3-Level back-to-back converter has been discussed. Converter operation and loss analysis on a 3.2 MW-60Hz turbine shows that classical NPC converter is suitable for line side converter, while Active-NPC (ANPC) converter is optimal for rotor side converter realization.

This paper presents impedance-based analysis, mitigation, and power-hardware-in-the-loop (PHIL) demonstration of reactive power oscillations in a wind power plant using a 4-MW Type III wind turbine drivetrain. Because such low-frequency oscillations result from interactions among slower control loops of wind turbines regulating phasor quantities-active and reactive power output of the wind turbine and the magnitude of voltages at the point of interconnection (POI)-a new type of admittance is defined in terms of phasor quantities for their analysis. The so-called power-domain admittance of a wind turbine is defined as the transfer function from the frequency and magnitude of voltages at the POI to the active and reactive power output of the turbine. The power-domain admittance responses of the 4-MW wind turbine are measured using a 7-MVA grid simulator to identify the source of the reactive power oscillations. Power-domain impedance analysis and PHIL experiments are performed to explain how a resonant mode manifests as turbine-to-turbine and plant-to-grid reactive power oscillations. It is discovered that weaker grids exhibiting high inductive impedance mitigate oscillations in the reactive power output of wind power plants; however, a higher grid impedance does not help in damping turbine-to-turbine reactive power oscillations. This paper presents a simple droop-based solution to eliminate both turbine-to-turbine and plant-to-grid reactive power oscillations.

Large-signal impedance of grid-connected converters can be used to predict resonance-generated distortions in converter-grid systems. Note that the large-signal impedance of a network represents its impedance response for different magnitudes of perturbation injected at its terminals. This paper presents large-signal impedance-based modeling and mitigation of resonance of grid-connected voltage source converters. Challenges of large-signal modeling because of the inapplicability of the small-signal approximation are addressed by leveraging the dominating influence of hard nonlinearities (such as pulsewidth modulation saturation and limiters) over soft nonlinearities (such as Park's transformations and phase-locked loop (PLL)) in shaping the large-signal behavior of the converter. The paper develops large-signal gains of hard nonlinearities using different types of describing functions. The paper shows that the large-signal impedance of a voltage source converter (VSC) can be shaped to reduce resonance-generated distortions by inserting limiters in the control system of the VSC. Developed large-signal impedance models are validated using numerical simulations of a VSC with dq current control and PLL. Large-signal impedance measurements of a commercial 1 MW VSC-based inverter and a medium-voltage doubly-fed induction generator with approximate 4 MW rating are presented to experimentally demonstrate the influence of the injected perturbation magnitude on the impedance response.

Dual active bridge (DAB) converters have been gaining increasing popularity in the context of high-frequency solid state transformers. However, modeling of a DAB converter remains a challenge to retain the ripple information for the design of high performance stable digital control under uniform sampling. This paper proposes a discrete-time framework using approximate discrete-time models considering various practical parasitics. These models are used to derive various discrete-time small-signal transfer functions under phase shift modulation using both voltage mode and current mode control techniques. The accuracy of the proposed models is verified through SIMPLIS simulation as well as experimentation in time-domain and in the frequency domain using SIMPLIS simulation. Finally, a design case-study using digital voltage-mode control is considered for a prototype DAB converter under phase-shift modulation with a power rating of 50 W and switching frequency of 500 kHz. The digital controller is implemented using an FPGA device, and the test results are demonstrated. The proposed framework can be extended to different modulation techniques as well as other isolated DC-DC converter topologies to design high frequency digital control.

Buck-converter-based topologies are used to generate high-frequency sinusoidal outputs. Buck-based inversion circuits such as voltage source inverters or class-D amplifiers have inherent control-to-output linearity in large-signal sense. However, in these topologies, the instantaneous output is always smaller than the dc-input during linear modulation. A differential boost inverter (DBI) is a boost-based topology that is used to generate a sinusoidal output. In DBI, the instantaneous output can be higher or lower than the dc-input voltage. DBI exhibits nonlinear control-to-output behavior in large-signal dynamic sense. Therefore, generating a high-frequency sinusoidal output using this topology is a challenge. The issues associated with a DBI for high-frequency sine wave generation are characterized in this paper. Conventional linear and nonlinear control techniques fail to produce a high-quality sine wave output at higher operating frequency. A nonlinear feedback linearization technique is proposed, which forces the output to be linear with respect to the reference even at higher operating frequency. This leads to a high-frequency high-quality sine wave generation using a DBI. The proposed modulator is verified using a laboratory prototype to generate a sine wave up to 2 kHz. A triangular wave of 100-Hz frequency is also generated by the proposed technique. Superior dynamic responses of a dynamic linearizing modulator controlled DBI for a step change in frequency, load current, input voltage, and reference are also experimentally verified.

In Power-hardware-in-the-loop (PHIL) simulations, one part of a whole network is simulated inside the Real-Time (RT) simulator and another part is in the form of actual hardware. Therefore, operation of a power Hardware-Under-Test (HUT) can be observed and analyzed when it is integrated to a larger network, without building the whole system beforehand. In this paper, a MATLAB/Simulink based toolbox is used as RT simulator for PHIL simulations. The power amplifier, another major constituent of a PHIL simulator, is constructed using boost-based topology, viz., Differential-Boost-Inverter (DBI). DBI has an advantage of generating higher output voltage compared to the applied dc-input. However, a conventional DBI exhibits nonlinear control-to-output behavior, therefore, a Dynamic-Linearizing-Modulator (DLM) is used to linearize it in large signal and dynamic sense. The linearized DLM-controlled-DBI is a suitable power amplifier for PHIL applications. The constructed PHIL simulator is used to analyze the operation of a Distributed-Generation (DG) system tied to the utility-grid. The grid network is simulated inside the RT simulator and DG is in the form of actual hardware. A proportional + resonant controller is used to control the current being injected to the grid. Experimental results in a PHIL environment show that by controlling magnitude and phase of the reference current, real and reactive power supplied to the utility-grid can be controlled.

Power-hardware-in-the-loop (PHIL) simulations are used to test power hardware with the help of computer-based real-time simulations. Generally, buck-based power amplifiers that have good dynamic performance are used to construct a PHIL simulator because of their linear large signal control-to-output characteristics. However, their output voltage peak is limited to the applied dc input in the linear region of modulation. In this paper, a differential boost converter (DBC)-based power amplifier is proposed for PHIL simulations, which does not suffer from the aforementioned limitations of a buck-based amplifier. A conventional DBC exhibits highly nonlinear control-to-output behavior. A feedback linearization technique is used to linearize the DBC in a large signal and dynamic sense, which makes it suitable for PHIL applications. Using this power amplifier and a MATLAB/Simulink toolbox for real-time simulations, the PHIL simulator is constructed. Experimental results under various operating conditions of source voltages, such as unipolar, bipolar, transients in frequency, and the dc step, and various load conditions, such as reactive, nonlinear, and transient faults, are provided to confirm the effmicacy of the proposed PHIL simulator.

Power-hardware-in-the-loop (PHIL) simulation technique allows part of the simulation circuit to be realized using a physical hardware. It has a real-time software component and a hardware component which work like one unit. A power amplifier is one of the most fundamental interface blocks in a PHIL simulation. It converts a low power signals received from the software simulator to a high power signal. This high power signal drives the hardware component of the simulation and is called hardware under test (HUT). Generally, power amplifiers are constructed using buck based topology due to their large signal linear control-to-output characteristics. However, their major drawback is that the output voltage amplitude is always smaller than the applied dc-input in linear modulation region. In this paper, a boost converter based topology known as differential boost inverter (DBI), which does not suffer from the aforementioned limitations of a buck based amplifier, is used as power amplifier for PHIL simulations. However, the DBI exhibits non-linear control-to-output characteristic and cannot be used for PHIL simulations as such. A feedback linearization technique known as dynamic linearizing modulator is used to linearize the control-to-output behavior of a DBI. Experimental result verifies that the proposed power amplifier exhibits superior dynamic performance and it is used in PHIL simulations for various power HUTs.

Differential Boost Inverter (DBI) can generate an amplified bipolar output voltage from a DC-input in a single power stage. However, traditional contol techinque limits a DBI's power bandwidth. Dynamic linearizing modulation (DLM) was used to lineazie an uni-polar boost converter to improve its power bandwidth. In this paper, DLM principle is applied to DBI topology to construct a variable amplitude, and frequency source. Implementation aspects, analysis, and operational challenges of this realization are presented. An experimental prototype was used to realize a variable amplitude and frequency source based on the proposed concept. An output of 62.4 V (peak-to-peak), 100 Hz sine wave was generated from a 20 V DC-input. The technique is also extended to generate a 200 Hz, and 500 Hz sine wave outputs.

A traditional Boost Inverter generates output more than the applied DC-input. However, boost converter exhibits highly nonlinear control to output response. A Dynamic linearizing modulator (DLM) was used to control a boost converter which improves the large signal linearity of the converter at higher operating frequency. The DLM controlled boost converter has a conversion ratio which is highly dependent on the design of the modulator. These design limitations are described in this paper. Methods to overcome these limitations are proposed. Based on these proposals, an improved control strategy is validated using simulation and experiments.

Various methods to linearize the control-to-output behavior of a boost converter are discussed. Most of the previously reported linearizing techniques are not suitable when the reference input amplitude or frequency is large. In this paper, a dynamic linearizing modulator for the boost converter is proposed, which transforms the open-loop converter into a linear amplifier with an operating frequency as high as one-fifth the switching frequency. The modulator generates a duty ratio by comparing the nonlinear part of the boost converter dynamic equation with a sine wave reference voltage on a cycle-to-cycle basis. The technique exhibits superior audio susceptibility due to the feedforward of input voltage. The formulation, implementation, and verification of this technique are discussed. Experimental results show the validity of the technique for a reference input frequency up to one-fifth the switching frequency.

Various methods to linearize the large-signal control-to-output behavior of a boost converter are discussed. Most of the previously reported linearizing techniques are not suitable when the reference input amplitude or operating frequency is large. In this paper, a dynamic linearizing modulator (DLM) for the boost converter is proposed, which transforms the open-loop converter into a linear amplifier with an operating frequency as high as one-fifth of the switching frequency. The modulator generates the duty by comparing the non-linear part of a boost converter dynamic equation with a sine wave reference voltage on a cycle-to-cycle basis. The technique exhibits superior audio-susceptibility due to the feed-forward of input voltage. The formulation, implementation, and verification of this technique are discussed. Experimental results show that the output voltage is able to track a large-signal reference input upto one-fifth the switching frequency.