Output Reference Voltage Research Articles

A Comprehensive Optimization Control of Dual-Active-Bridge DC–DC Converters Based on Unified-Phase-Shift and Power-Balancing Scheme

This paper presents a comprehensive optimization control scheme to improve efficiency and dynamic response of dual-active-bridge (DAB) dc-dc converters. Unified-phase-shift (UPS) control is widely used to increase the efficiency of DAB dc-dc converters by minimizing the peak current, but dynamic performance of the converters needs to be further enhanced. In this paper, to gain superior dynamic performance of DAB dc-dc converters, an equivalent power-balancing (PB) model is employed, which is capable of predicting dynamic behavior of converter output voltages due to input voltage fluctuation and load disturbance. And then, combining the UPS control and the PB control, a comprehensive UPS and PB (UPS-PB) scheme is proposed to improve the efficiency and dynamic performance simultaneously. This work also includes the detailed inductance parameter sensitivity of the proposed UPS-PB scheme and a zonal voltage control strategy to further improve dynamic responses of the output voltage under the start-up process or a large step change of the output voltage reference. Moreover, the variant of UPS-PB scheme for constant power load is analyzed in the experimental part. Finally, experimental results have verified the excellent performance of the proposed UPS-PB scheme and correctness of theoretical analysis in this work.

Performance Analysis of a Three-to-Five Phase Dual Matrix Converter Based on Space Vector Pulse Width Modulation

In this paper, space vector pulse width modulation (SVPWM)-based algorithms for a five-phase open-end load fed from dual matrix converter (DMC) have been proposed. In the presented modulation methods, the reference output voltage vector is synthesized from two three-to-five phase matrix converters at both the ends of the load. Depending on the power-sharing of the two MCs, two proposed modulation methods are defined as equal reference sharing (ERS) and unequal reference sharing (URS). The performance of ERS and URS for the three-to-five phase DMC drive is compared. Performance comparison is based on the total harmonic distortion in the output voltages and the percentage of the voltage transferred from the source to the load, for the full linear modulation index (MI) range. Common mode voltage and zero sequence current in the load are also discussed. The efficiency of the ERS and URS is compared. It has been observed that the proposed ERS scheme offers better performance compared with URS for most of the MI values. The suggested modulation techniques are implemented in MATLAB/Simulink. The hardware setup is developed and control algorithm is implemented using dSPACE working in conjunction with the FPGA interface board for practical validation.

Online Autotuning Technique of Switching Frequency for Resonant Converter Considering Resonant Components Tolerance and Variation

A simple online autotuning technique for a resonant converter to achieve output voltage regulation while tuning the switching frequency to the resonant frequency is proposed in this paper. The proposed method can deal with resonant frequency variation caused by the resonant components: tolerance and variation. The proposed technique is developed by detecting the zero-crossing point and peak point of resonant current. Moreover, the correction term of dc bus voltage reference is generated based upon the error between switching period (frequency) and resonant period (frequency). The voltage reference of power factor corrector output voltage is, thus, tuned to achieve both switching frequency tracking and output voltage regulation of resonant converter. The proposed method is simple and no knowledge of resonant frequency is required in prior. The proposed method is realized in software using DSP. Test results derived from a digital-controlled server power show that switching frequency can track the resonant frequency well even with large variation of resonant components. These measured results fully support the effectiveness of the proposed technique.

The Simplified Model of Back-To-Back PWM Converter

This paper proposes a simplified model of PWM converter, which is proved to be effective in saving simulation time. Take doubly-fed wind power system as an example, the PWM converter is simplified in two aspects: a) the AC side of converter precisely and flows the output voltage reference; b) ignore the power loss of converter, which means the AC side power equals to DC side. Based on the two assumptions, the voltage of AC side could be replaced by a voltage-controlled voltage source, and the DC side could be replaced a controlled current source. By this way, the complex IGBTs converter is simplified to an equivalent circuit. Simulation with specific model and simplified model then performed in PSCAD/EMTDC. By comparing their waveforms and simulation speed, the correctness and benefits of the proposed model are verified.

Simplified SHE pulse‐amplitude modulation for multilevel inverters

In this study, a selective harmonic elimination (SHE)-pulse-amplitude modulation method is suggested for the cascaded multilevel inverters. This method is based on the balancing of the voltage-second area under the output voltage waveform and reference sinusoidal signal. The proposed method is free from the conventional transcendental SHE equations as it is based on a composite midpoint rule of numerical integration which works on linear equations. Reduced computational burden enables real-time implementation of the proposed method with great ease even for the inverter with a huge number of levels. The switching angles remain constant for an inverter while the output voltage is controlled by varying voltage of dc sources linearly. The proposed method eliminates more harmonics and offers reduced total harmonic distortion (THD) in comparison to the conventional SHE methods without amplifying the amplitude of higher order harmonics. THD of the output voltage remains constant with variation in modulation index. Performance analysis of the suggested method is validated with simulation and experimental studies on cascaded H-bridge inverter.

Model Predictive Control for DC–DC Boost Converters With Reduced-Prediction Horizon and Constant Switching Frequency

The implementation of multistep direct model predictive control (MPC) for dc–dc boost converters overcomes the well-known issue of nonminimum phase behavior. However, it can lead to a high computational burden depending on the prediction horizon length. In this paper, a simple and computationally efficient MPC method for dc–dc boost converters is proposed. The key novelty of the presented control strategy lies in the way dynamic references are handled. The control strategy is capable of providing suitable references for the inductor current and the output voltage, without requiring additional control loops. Moreover, this reference design allows the predictive controller to be implemented with a single-step prediction horizon. Thus, a significant reduction in the required real-time calculations executed in the control hardware is achieved. To obtain constant switching frequency, the power switch commutation instants within a sampling period are considered as control inputs. Therefore, the predictive controller is formulated as a continuous control set MPC. Additionally, the proposed formulation is able to deal with different operation modes of the converter without changing the controller structure. Finally, an observer is used to dynamically modify the reference to provide robustness to system parameter uncertainties. Simulation and experimental results show an accurate tracking of dynamic inductor current and output voltage references, while respecting the restrictions on maximum inductor current levels of the converter.

Hierarchical Distributed Balancing Control for Large-Scale Reconfigurable AC Battery Packs

This paper presents a hierarchical balancing algorithm for use in large-scale reconfigurable ac battery packs. Using a decentralized battery management system, the pack is organized in control layers with each layer controller responsible for a small number of slave controllers, thereby significantly reducing communication and centralized processing requirements. The hierarchical balancing algorithm uses all available voltage steps in the pack ensuring a high-quality sinusoidal output voltage while balancing the objects of different layers. Balancing priority can be swapped dynamically between layers according to the maximum state of charge (SoC) variation between the objects of each layer while also ensuring that the output voltage reference is always met even when a cell failure occurs, as long as there are an adequate number of cells available in the pack. An experimental demonstration of the proposed balancing algorithm is presented using an ac battery pack comprising 144 20-Ah lithium-titanate cells. Cell balancing to within 2 mV of the cell open-circuit voltage is achieved between cells with 20% initial SoC variation and 5% capacity difference.

Power Electronic Converter Based PMSG Emulator: A Testbed for Renewable Energy Experiments

This paper presents a converter-based permanent magnet synchronous generator (PMSG) emulator as a testbed for designing, analyzing, and testing of the generator's power electronic interface and its control system. The PMSG model is formulated in a real-time digital simulator. A voltage type ideal transformer model combined with a virtual impedance is presented as an interface algorithm. The design procedure and implementation of the virtual impedance in a simulation platform is discussed. A six-switch voltage source converter is used as a power amplifier to mimic the behavior of the PMSG supplying linear and nonlinear loads. A proportional–integral plus resonant controller is proposed as a voltage loop controller for tracking a distorted output voltage reference signal. The accuracy of the proposed emulator is investigated for the fundamental and low-order voltage harmonics. Technical challenges of the PMSG emulator are considered and proper solutions are suggested. The performance of the proposed emulator is compared with an actual PMSG.

Multistep Model Predictive Control for Cascaded H-Bridge Inverters: Formulation and Analysis

In this paper, a suitable long prediction horizon (multistep) model predictive control (MPC) formulation for cascaded H-bridge inverters is proposed. The MPC is formulated to include the full steady-state system information in terms of output current and output voltage references. Generally, basic single-step predictive controllers only track the current references. As a distinctive feature, the proposed MPC also tracks the control input references, which in this case is designed to minimize the common-mode voltage (CMV). This allows the controller to address both output current and CMV targets in a single optimization. To reduce the computational effort introduced by a long prediction horizon implementation, the proposed MPC formulation is transformed into an equivalent optimization problem that can be solved by a fast sphere decoding algorithm. Moreover, the benefits of including the control input references in the proposed formulation are analyzed based on this equivalent optimization problem. This analysis is key to understand how the proposed MPC formulation can handle both control targets. Experimental results show that the proposal provides an improved steady-state performance in terms of current distortion, inverter voltages symmetry, and CMV.

GA-BASED FUZZY LOGIC CONTROLLER WITH BOOSTER TYPE DC-DC CONVERTER

In this study, a booster–type DC-DC converter is designed by Matlab/Simulink Environment and an output voltage control has been analyzed for different load conditions. The designed DC-DC converter is controlled for different scenarios such as variable input-constant output voltage and constant input-variable output voltage references. The converter controller performance is observed with using classical Proportional+Integral (PI) controller and Fuzzy Logic Controller (FLC). On the other hand, the controller parameters are determined by employing Genetic Algorithm (GA) according to Integral of the Time weighted Absolute Error (ITAE) to improve the controller performance. Thus, more efficient and intelligent controllers are obtained for the DC-DC converter system. The system simulation is realized by the Matlab/Simulink and results are compared with each other.

Novel high PSRR high-order temperature-compensated subthreshold MOS bandgap reference

Novel high power supply rejection ratio (PSRR) high-order temperature-compensated subthreshold metal-oxide-semiconductor (MOS) bandgap reference (BGR) is proposed in Semiconductor Manufacturing International Corporation (SMIC) 0.13 μm complementary MOS (CMOS) process. By adopting subthreshold MOS field-effect transistors (MOSFETs) and the piecewise-curvature temperature-compensated technique, the output reference voltage's temperature performance of the subthreshold MOS BGR is effectively improved. The subthreshold MOS BGR achieves high PSRR performance by adopting the technique of pre-regulator. Simulation results show that the temperature coefficient (TC) of the subthreshold MOS BGR is 1.38×10−6/°C when temperature is changed from −40 °C to 125 °C with a power supply voltage of 1.2 V. The subthreshold MOS BGR achieves the PSRR of −104.54 dB, −104.54 dB, −104.5 dB, −101.82 dB and −79.92 dB at 10 Hz, 100 Hz, 1 kHz, 10 kHz and 100 kHz respectively.

A Sub-1V Full CMOS Bandgap Voltage Reference with a Body Bias

In this paper, a low-power sub-1V bandgap voltage reference(sub-BGR) without any resistors and BJTs is presented. To reduce process variations without bipolar junction transistors(BJTs), a weighted Vgs structure is modified with a body bias for the generation of both complementary-to-absolutetemperature(CTAT) voltage and proportional-toabsolute-temperature(PTAT) voltage. Moreover, the proposed sub-BGR is operated in subthreshold region to minimize the power consumption. The proposed sub-BGR is implemented with a 0.18 μm deep N-well (DNW) CMOS technology. The measured results show that the temperature variation of 55ppm/°C is obtained with a temperature range from -40°C to 80°C. The power supply rejection ratio(PSRR) of -44 dB at 100 Hz is achieved while consuming total power of 38 nW at the supply voltage of 0.8 V. Measured output reference voltage is 435 mV and the active area is 150 μm by 49 μm.

A robust cascaded controller for DC-DC Boost and Cuk converters

PurposeThis paper aims to propose a robust cascaded controller based on proportional-integral (PI) and continuous sliding mode control.Design/methodology/approachCascaded control structure is an attractive control scheme for DC-DC power converters. It has a two-loop structure where the outer loop contains PI controller and the inner loop uses sliding mode control (SMC). This structure thus combines the merits of both the control schemes. However, there are some issues that have prohibited its adoption in industry, the discontinuous nature of SMC which leads to variable switching frequency operation and is hard to realize practically. This paper attempts to overcome this issue by changing the discontinuous functionality of SMC to continuous by utilizing the concept of equivalent control.FindingsThe robustness of the controller designed is verified by considering various cases, namely, ideal case with no uncertainties, sudden variation of input supply voltage, load resistance, reference voltage, circuit-parameters and for noise disturbance. The controller effectiveness is validated by simulating the DC-DC boost and Cuk converters in SimPowerSystems toolbox of MATLAB/Simulink. It is shown that the performance of the proposed controller is satisfactory, and both reference output voltage and inductor current are tracked with little or no sensitivity to disturbances.Originality/valueThe results for various scenarios are interesting and show that the controller works quite satisfactorily for all the simulated uncertainties.

Implementación del Algoritmo Sünter-Clare en un Convertidor Matricial 3x3

This paper presents the direct and easy way to implement digitally a Sünter-Clare modulation algorithm for a 7.5 KVA, three-wires, matrix converter. This modulation algorithm is used to calculate 3x3 matrix converter duty cycles to produce constant output voltage and frequency signals. The Sünter-Clare modulation algorithm recalculates switching patterns and switching times every sampling period in order to compensate the input voltage and frequency variations. This algorithm is defined in terms of the three-phase input and the output reference voltages at each sampling instant and is convenient for closed loop operations when the input voltage and frequency are variable in time as in the variable speed wind generation system. The experimental control setup is comprised of a field programmable gate array board, a digital signal processor and a graphics interface board.

Model predictive control for pre‐compensated voltage mode controlled DC–DC converters

This study introduces the use of model predictive control (MPC) to improve the performance of pre-compensated power supplies, and in particular of DC-DC converters, by dynamically modifying their output voltage reference. The importance of developing controllers for pre-compensated converters is twofold. First, the hierarchical structure is particularly useful when the primal controller is already coded, or hardware based, and cannot be changed. Second, the double-loop and, possible, multi-rate structure represents a computationally cheaper alternative to a direct MPC that would replace the primal controller and would require a much higher sampling frequency. In this study a MPC controller has been applied for the regulation of a pre-compensated synchronous DC-DC buck converter. The aim is to improve the performance of standard voltage mode control (VMC), without replacing the linear controller and without drastically affecting the computational burden. The algorithm has been tested both in simulation and experimentally, on commercially available hardware. The results show the performance improvement with respect to the standard VMC, as well as the feasibility of the proposed approach in an embedded platform. Tests with different primal controller tunings, and unknown varying loads, confirm the advantages of the method.

Parallel Operation of Inverters With Isolated DC Link for Minimizing Sharing Inductor

In this paper, it is described how the circulating current flows between inverters that have isolated dc link such as cascaded H-bridge (CHB) topology when they are operating in parallel. In this case, zero sequence circulating current, which normally flows through shared dc link, cannot flow between inverters in parallel. However, circulating current is provoked by asynchronous switching instant of devices, difference of dc-link voltages of parallel inverters, and unbalanced impedance. The circulating current should be suppressed by a sharing inductor that is inserted between inverters. Generally, all of the inverters should synthesize the same output voltage reference for load current control to minimize the size of this sharing reactor. However, this conventional method cannot guarantee diminishing circulating current in the transient state and even in the steady state. In this paper, in order to reduce sharing reactance, after deriving circulating current model from general case of n-parallel operation, circulating current control method is devised based on the model. This proposed algorithm is applied to active front end five-level-CHB inverter system for medium voltage drive. Simulation and experimental results are provided to verify the effectiveness of the proposed control scheme.

Sub-1 V, pico-watt subthreshold CMOS voltage reference circuit with dual temperature compensation

A pico-watt CMOS voltage reference is developed using an SK Hynix 0.18µm CMOS process. The proposed architecture is resistorless and consists of MOSFET circuits operated in the subthreshold region. A dual temperature compensation technique is utilized to produce a near-zero temperature coefficient reference output voltage. Experimental results demonstrate an average reference voltage of 250.7mV, with a temperature coefficient as low as 3.2ppm/°C for 0 to 125°C range, while the power consumption is 545pW under a 420mV power supply at 27°C. The power supply rejection ratio and output noise without any filtering capacitor at 100Hz are −54.5dB and 2.88µV/Hz1/2, respectively. The active area of the fabricated chip is 0.00332mm2.

Nonlinear and vector closed-loop control methods for flying-capacitor power converters

ABSTRACTIn this paper, the design and implementation of two different, nonlinear and vector, closed-loop control methods for flying-capacitor power converters are proposed and evaluated. Specific focus has been given to the decoupling problem, the influence of the balancing compensator on the output voltage reference tracking controller. In the first method, the coupling between the internal voltage balancing dynamics and the external load dynamics is solved in the pulse-width modulator by means of vector modulation. In the second method, input–output decoupling is achieved by feedback linearization to resolve the nonlinearity caused by switching the flying-capacitor voltage state. For both methods, classical linear control theory is applied in the design of a feedback control law. The theoretic evaluation is supported by simulation and experimental results.

Hybrid Modular Multilevel DSCC Inverter for Open-End Winding Induction Motor Drives

This paper proposes a hybrid modular multilevel drive system based on a modular multilevel cascade inverter (MMCI) with double-star chopper cells (DSCC) and a two-level (2L) inverter to feed three-phase induction motors with open-end windings (OEWs). The proposed system is an alternative for high-speed motor drives based on a small-scale DSCC topology. A voltage reference technique is presented based on the analysis of the degrees of freedom of the system for generating the output voltage references, considering any voltage ratios of the dc links. The proposed system is evaluated in a symmetric scenario, in which the dc-link voltages are equal. Thus, the 2L inverter is set up to operate at the fundamental frequency, while the DSCC inverter synthesizes the output voltage references from high-quality waveform with a significant number of voltage levels. Experimental results obtained from a downscaled 10-kVA 380-V prototype driving a full loaded 3.7-kW OEW induction motor are provided to verify the viability of the proposed system.

A Hybrid Modulation Scheme for Dual-Output Five-Leg Indirect Matrix Converter

This paper proposes a hybrid modulation method for a dual-output five-leg indirect matrix converter topology. The proposed control technique combines a space vector modulation scheme (SVPWM) applied to the rectifier stage so as to control the input currents and a new digital scalar modulation scheme (DSPWM) designed to control the two loads output voltages. A generalized expression of the output voltage references is also developed showing the capability of the proposed method to control more than two independent loads without requiring additional mathematical development. Furthermore, a new modified expression of the output voltages references is proposed to enable the correct operation of the converter under unbalanced grid voltages. Also, this paper proposes a detailed mathematical analysis that allows evaluating the effect of output loads unbalances on the input current harmonic content. Simulation and experimental results are provided to show the effectiveness of the proposed theoretical investigations and confirm the capability of the proposed method to control multiple drive systems as well as ac input currents.