Additional Current Sensors Research Articles

Novel Multi-Port Converter for Distributed MPPT Operation in Solar PV System

Solar photovoltaic (PV) systems continue to be the most prevalent renewable energy resource despite the presence of numerous limitations. A power discrepancy between PV modules on a large scale may result in power dissipation throughout the entire PV system. This particular paper proposes an efficient multi-port converter for distributed maximum power point tracking operation (D-MPPT) for a solar PV system. The operation details of the proposed multi-port converter along with analytical waveforms are presented in this paper. To implement the D-MPPT approach in the proposed multi-port converter, a detailed analysis of mathematical modeling of solar PV systems with a mismatch of PV power and voltage stabilization approach is done. In addition, the proposed approach eliminates the need for additional current sensors and semiconductor components to overcome the effect of mismatched power in the PV system. To validate this, the prototype has been built and integrated with the real environment of the solar PV system. To verify the operation, a detailed simulation study and experimental investigation have been carried out and presented in this paper. After a detailed investigation and discussion of measured results and analysis, it is concluded that the proposed multi-port DC-DC converter is the most suitable solution for solar PV applications.

A New Four-Step Commutation Method for Indirect Matrix Converter With Active-Voltage Vectors Being Applied

The existing two commutation methods of the rectifier stage for indirect matrix converter (IMC) are zero-current commutation and four-step commutation. The premise of zero-current commutation is that the inverter stage of IMC uses a zero-voltage vector, but when the inverter stage cannot use zero-voltage vectors (such as space overmodulation, common mode suppression modulation, etc.), the four-step commutation is adopted. The conventional four-step commutation method has a complex switching sequence and requires additional sensors. Based on the natural freewheeling characteristic of IMC and the switching sequence of zero-current commutation, a new four-step commutation method is proposed when active-voltage vectors are applied in the inverter stage, first turn off the two switches at 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> and 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> steps, and then turn on the two switches at 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> and 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> steps. The switching sequence of the new four-step commutation is not affected by the polarity of input voltage or output current direction, thus solving the complexity switching sequence problem of the conventional four-step commutation, and does not require additional voltage or current sensors, making the IMC commutation process safer and more reliable. Finally, this paper verifies the effectiveness of the new four-step commutation method of IMC through experiments.

A novel digital sensor-less synchronous rectification method for CLLLC resonant converters

With the rapid development of the renewable energy vehicles, pursuing the power converters with high efficiency and high reliability has caught more attention recently. In order to solve those problem with low cost, this paper proposes a sensor-less synchronous rectification method for the CLLLC resonant converters. The precise conduction time of the synchronous switches is obtained based on the analysis of the working principle of CLLLC resonant converter, and the relationship between the SRs switching time and the inverter switching time can be derived as well. To achieve the wide output voltage range, the converter requires wide working frequency. And the correct turn-on and turn-off time for the synchronous switches can be obtained respectively by calculation and piecewise linear function fitting methods within full working frequency range. Compared with traditional synchronous rectification control for CLLLC, which require additional high bandwidth voltage sensors or current sensors, the method proposed in this paper is realized by only one low-cost output voltage sensor. And the proposed method is suitable for high-power applications with a wide voltage and load variation. Moreover, because of the symmetrical topology, this method is valid in bidirectional power transfer. Additionally, the exist analog synchronous rectification control chips suffer from losing accuracy with wide bus voltage variation, however, this method can overcome this shortcoming. Thus, the proposed synchronous rectification method is a low-cost and suitable for high-power, high power density, high efficiency application which benefit from its simple algorithm. Finally, the proposed sensor-less synchronous rectification method is validated by the simulation results and experimental results. The results of simulation and experimental have shown the proposed method offers significant benefits which increases the efficiency of the whole CLLLC system by about 3%, and the reliability of the converter are greatly increased, due to the cooler SRs.

Virtual Admittance Reshaping Based Input Current Phase Shift Suppression Method for Totem-Pole Bridgeless PFC Converter

Grid-side current phase shift (GCPS) is an important issue in totem-pole bridgeless power factor correction (TBPFC) converters. In this article, a virtual admittance reshaping based GCPS suppression method is proposed based on the establishment of the admittance model of the TBPFC converter including the EMI filter. The virtual admittance reshaping does not need additional current and voltage sensors and can realize complex admittance through a control algorithm. Thus, the current phase error can be adjusted to zero with the optimal design. The inherent admittance of the system is analyzed from the perspective of system frequency characteristics to extract leading-phase admittance. Then, the parallel admittance is produced through the inductance current for canceling it. The current reference and the modulation voltage are combined to realize obtaining the equivalent virtual admittance and meanwhile reduce the burden of the current regulator. The sensitivity of the system parameters is analyzed, and the saturation effect of the inductor and the error of the EMI filter parameters have little effect on admittance reshaping. Besides, the research method does not need to adjust parameters according to the load. The effectiveness of the proposed method is verified by experiments on a TBPFC converter platform.

Input Voltage Feedforward Active Damping-Based Input Current Harmonic Suppression Method for Totem-Pole Bridgeless PFC Converter

Grid-side current harmonic (GCH) is an important issue in totem-pole bridgeless power factor correction (TBPFC) converters. In this article, a GCH suppression (GCHS) method based on input voltage feedforward active damping is proposed. First, an admittance model of the TBPFC converter considering the electromagnetic interference (EMI) filter and the time delay of the digital control system is established. The damping characteristics of the system are improved by constructing a virtual admittance, which does not require additional current and voltage sensors. Based on the admittance model analysis, the active damping can be matched and adapted to a wide power range. Through the extraction of harmonic information and the combination with current setting and modulation voltage information, the suppression of current harmonic under different loads can be realized. Besides, the sensitivity of the system parameters is analyzed. The system delay, load change, and system parameter change are considered in the design of active damping, so the current harmonics can be effectively suppressed in a wide power range. Finally, the effectiveness and feasibility of the proposed method are verified by experiments on a TBPFC converter platform.

Position Sensorless Control for PMSM Drives With Single Current Sensor

The aim of this article is an attempt to provide a more credible control mode or a fault-tolerant control strategy for permanent magnet synchronous motor (PMSM) drives when an unexpected failure occurs to the current or position sensor. Considering that, a position sensorless control method that uses only one current sensor is proposed. Different from a traditional position sensorless control scheme that utilizes additional current sensors to obtain information of multiple phase currents, only a single current sensor (SCS) arranged on one of the current branches is included among the whole control circuit. Three-phase currents are reconstructed by sequentially sampling the SCS under specific voltage vectors, and directly employed for motor position estimation. A nonlinear position observer established according to the gradient descent is adopted. Focusing on the special current-acquisition pattern in this article, a step-size optimization method based on golden section search is proposed to minimize position estimation error. The experimental results reveal that the method in this article is comparable to the traditional full-current-sensor method in terms of position estimation, which confirms the fault-tolerant capability as one certain sensor of the control structure malfunctions.

A 94% Peak Efficiency Dual Mode Buck Converter With Fully Integrated On-Time-Based Mode Control for Implantable Medical Devices

Fully integrated on-time-based mode control is utilized to achieve an efficient mode control of a PWM/PFM mode buck converter for implantable medical devices. The proposed method predicts load current from the on-time of the power switches of the buck converter and does not require an additional current sensor. Additional passive components for load current estimation are not required in this approach. Moreover, this method consumes less control power and requires a smaller area compared with other circuits used for load current prediction. The proposed dual mode buck converter is fabricated using TSMC <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~\mu \text{m}$ </tex-math></inline-formula> CMOS technology. The active chip area is 0.58 x 0.46 mm2. The input voltage range is 2.2–5.0 V, the output voltage is 1.8 V, and the load current range is 0.2–100 mA. The experimental results demonstrate the proper mode transition under step-up/down load current transient. The peak power conversion efficiency was approximately 94 % at 50 mA, and the minimum efficiency was approximately 77 % within the load current range.

An H∞ filter based active damping control strategy for grid-connected inverters with LCL filter applied to wind power system

Since the LCL filter has good performance to attenuate high frequency harmonics, it is widely used in wind power inverters. But it can cause high-frequency oscillations and instability, which limits its application in wind power system. For an LCL-type grid-connected inverter, the conventional capacitor-current-feedback type active damping control strategy can retain the high-frequency characteristics of LCL filter while suppressing the resonant peak effectively, with the drawback of requiring additional current sensors. Therefore, an H∞ filter based active damping strategy of LCL grid-connected inverter is proposed. The state space model and the process noise model of the LCL inverter are built, and then the general model of the standard H∞ control problem is derived, which helps to solve the H∞ filter. The H∞ filter can estimate the filter capacitor current according to sample values of the injected current and the voltage of the point of common coupling, and the estimation accuracy can be guaranteed even if parameter perturbations exist in the LCL filter. The proportional resonant controller is adopted to track the grid current. Therefore, the proposed control strategy can effectively suppress the resonance peak of the LCL filter without additional current sensors and be insensitivity to system parameter perturbations. The simulation and experimental results verify the feasibility and superiority of the proposed method.

Calibration Method of Equivalent Series Resistance Parameter for Nonintrusive Current Sensors Used in DC–DC Power Electronic Converters

Nonintrusive current sensors process indirect measurements (e.g., voltage) in order to estimate the current flow through an electrical element. Within dc–dc power electronic converters, instead of using an additional current sensor(s), high-frequency inductor currents within the topology can be estimated by measuring inductor terminal voltages using simple low-cost comparators used with digital postprocessing circuits. The figure of merit for such sensors depends upon the accurate identification of sensor transfer function. This transfer function relates inductor terminal voltage to estimated current, and consists of two major parameters, i.e., inductance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> ) and equivalent series resistance (ESR), of the element. Both the parameters vary with changes in operating conditions, e.g., temperature, and additional trace resistances. Variation of ESR parameter introduces dc offset within the estimated current measurement, and hence an accurate knowledge of ESR is essential for closed-loop stability of dc–dc converters. This letter presents a calibration method of ESR parameter for nonintrusive current sensors used in dc–dc power electronic converter applications. The theory behind the proposed approach, its implementation aspects, and verification are presented in this letter.

Weighting Factor Free Model Predictive Control for a Flying Capacitor Converter in a DC Microgrid

This paper presents a single-objective model predictive control for a bidirectional DC-DC flying capacitor (FC) converter, which integrates a battery to the microgrid. The presence of multiple FCs facilitates the converter to interface a low-voltage battery to a high-voltage DC bus at reduced voltage stress on its power switches. However, such converter requires a controller that fulfils multiple objectives, namely DC bus and FC voltage regulations, and bidirectional power flow. The key feature of the proposed controller is that it utilizes a model predictive control with a single-objective cost function based on battery current and a redundant state selection scheme to attain these multiple objectives. Adopting such a strategy not only reduces computational burden but also eliminates the need for weighting factors and requirement of complex numerical models for its estimation. Another notable aspect is that the controller employs an improved dynamic reference model to generate appropriate battery current reference for the DC bus voltage regulation, without necessitating a secondary control loop and additional current sensors. Finally, experimental results of the proposed system for a step-response of the DC bus voltage, varying PV power, and loads are validated and compared against finite control set model predictive control.

Rotor Position Error Compensation in Sensorless Synchronous Reluctance Motor Drives

A new approach to compensate rotor position errors caused by parameter mismatching in model-based sensorless synchronous reluctance (SynchRel) motor drives is presented in this article. According to the proposed approach, the error in estimating the rotor position is detected by injecting some low-frequency current signals and adjusting the estimated rotor angular position through a gradient descent algorithm until minimizing the ripple generated on the estimated rotational speed. A rotor position correction can be fully online accomplished coping with saturation and cross saturation effects, as well as with unmodeled phenomena and unpredictable variations of the stator resistance with the temperature. The correction procedure can be accelerated by starting from an approximated correction table, which can be offline built using the same technique. The proposed approach neither needs additional current or voltage sensors nor motor design modifications, thus providing an inexpensive mean to improve the control performance and robustness. Although originally conceived to deal with back EMF-based sensorless control techniques, the correction procedure can be extended to other model-based sensorless SynchRel motor drives.

Aging Condition Monitoring for Aluminum Electrolytic Capacitor in Variable Speed Drives

In this article, an aging condition monitoring method for the aluminum electrolytic capacitor (AEC) is presented. The target AEC is used in an ac–dc–ac variable speed drive (VSD), which usually contains an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCR</i> network composed of a dc choke, an AEC, and a braking branch. The condition of the AEC is monitored through the capacitance value and the equivalent series resistor (ESR) value. The capacitance value and the ESR value are identified by the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCR</i> network response, i.e., magnitude gain and phase shift of the network. The existing components of the VSD are fully utilized instead of adding additional current sensors and active devices. Some potential disturbances in field application, such as three-phase voltage unbalances, are also considered. Experiments are carried out in a 10-kW general-purpose VSD with different AECs. The maximum errors of capacitance value and ESR values identifications are 1.1% and 5.48%, respectively.

An internal power angle control strategy for high-speed sensorless brushless DC motors

High-speed Brushless DC Motors (BLDCMs) usually adopt a sensorless control strategy and operate in three-phase six-state drive mode. However, the sampling errors of the rotor position and the driving method increase the Internal Power Angle (IPA), resulting in a decrease in the efficiency of the system. Conventional IPA reduction strategies are either sensitive to motor parameters, or ignore diode freewheeling during the commutation process, or require additional current sensors. In this paper, a new strategy to reduce the IPA is proposed. Firstly, a Zero-Crossing Point (ZCP) detection method for the back-EMF without filter is proposed to reduce the sampling errors of the rotor position. Secondly, the relationship between the non-energized terminal voltage and the ZCP of the corresponding back-EMF is analyzed. The non-energized terminal voltage that has completed the diode freewheeling is divided into two triangles by half of the bus voltage. When the IPA is suppressed, the areas of the two triangles are equal. Thirdly, an advanced angle for reducing the IPA is obtained through a PI regulator which can eliminate the deviation between the two areas. Finally, both a simulation model and an experimental circuit are built to verify the proposed control strategy.

Enhanced Direct Torque Control for a Three-Level T-Type Inverter

Direct torque control (DTC) is a widely used approach for motor drives due to its distinctive advantages, e.g., fast dynamic response and highly robust against motor parameters uncertainties and external disturbances. To achieve a lower torque ripple, a higher switching frequency is usually required, which, however, can reduce the drive efficiency. Using the emerging silicon carbide (SiC) devices, which can operate efficiently at a much higher switching frequency than their silicon counterparts, thus, it could be feasible to achieve high efficiency and low torque ripple simultaneously. In this work, a novel multilevel DTC for a SiC T-type inverter is proposed to significantly reduce the torque and flux ripples while retaining the fast-dynamic response. The unbalanced dc-link is a common issue of the T-type inverter, which may also lead to a higher torque ripple. To address this issue, the proposed DTC algorithm only uses the real voltage space vectors and virtual space vectors (VSVs) that do not contribute to the neutral point current such that an inherent dc-link capacitor voltage balancing can be achieved without using any active dc-link voltage controls or additional dc-link voltage and/or current sensors. The feasibility and effectiveness of proposed methods are verified by using both simulation and experimental studies.

A Theoretical Concept of Decoupled Current Control Scheme for Grid-Connected Inverter with L-C-L Filter

This paper proposes a nonlinear decoupled current control scheme for a grid-connected inverter with LCL filter. Decoupling the active and reactive current control channels is one of the main demands in the control of inverters. For inverters with an L filter, the decoupling can be achieved by a proper feed-forward of grid voltages. However, the coupling of channels is a complex issue for converters with LCL filters. The resonance mode of the LCL filter may cause instability, which adds more complexity to the analysis. In this paper, state equations of the system are provided, which highlight the coupling between active and reactive currents injected into the grid. Accordingly, a non-linear control scheme is proposed which effectively decouples the channels and dampens the resonant modes of the LCL filter. The stability of the proposed control method is verified by the Lyapunov criterion. Independency of the system stability to the grid-impedance is another feature of the proposed approach. Moreover, only grid-side currents are needed for implementation of the proposed scheme, avoiding the need for additional current sensors for the output capacitor and grid-side inductor. For accurate modelling of the inverter, the computation and PWM sampling delays are included in the controller design. Finally, various case studies are provided that verify the performance of the proposed approach and the stability of the system.

Observer-based neural network dynamic surface control of single-phase LCL-filtered grid-connected inverters under parametric uncertainties and weak grid condition

This paper focuses on the current control of single-phase LCL-filtered grid-connected inverters in the presence of parametric uncertainties and weak grid condition. Therefore, a novel neural network dynamic surface control (NNDSC) method is proposed by overcoming the problem of ‘explosion of complexity’. In addition, radial basis function neural networks (RBFNNs) are employed to approximate the system parametric uncertainties. Furthermore, by considering practical considerations, a novel state observer (SO) is designed to estimate the inverter-side current and capacitor voltage. As a result, additional current and voltage sensors are not required, which makes the implementation of the proposed approach straightforward and reliable. The origin neighbourhood convergence of estimated and tracking errors is assured through Lyapunov stability theorem and Young’s inequality. The effectiveness and performance of the proposed NNDSC+SO approach is demonstrated through MATLAB/Simpower simulations in view of the reference current changes, LCL filter parametric uncertainties and weak grid condition.

Direct Parallel and Hybrid Power Control Scheme of a Low-Power PV and Piezoelectric Energy Harvesting Module

This paper presents a novel direct parallel power control scheme with independent current paths for the proposed hybrid energy-harvesting system that consists of a low-power photovoltaic panel, a piezoelectric harvesting module, and an energy storage system. A battery is connected to store the generated power from the two renewable power sources to provide a continuous power supply for the users. The designed power converter controls both battery state and power supply without any power conditioning system. To achieve this, a low-power DC–DC converter with battery charging function and control algorithm is designed for the hybrid power source. Therefore, in the proposed system, no additional battery charge controller is required. To control the battery, however, an additional current sensor to detect the battery power is simply added to each DC–DC converter. In the proposed power control scheme and controller, each power input, output, and the combined power flow are connected with neither communication protocols nor additional controller. Moreover, the converters can adjust the supplied power for parallel power-sharing. For maximum output current protection in each converter and constant current control for the battery, a hybrid power connection and its related current path are also proposed in this paper. The effectiveness of the proposed hybrid power system and the direct parallel power control scheme was verified through experiments.

Series DC Arc Fault Detection Method for PV Systems Employing Differential Power Processing Structure

Arc fault detection is an important process for ensuring the safety of PV and grid-connected inverters and is essential for producing PV systems in real applications. However, it is difficult to detect series dc arc faults using conventional fuses because these faults produce only small current variations. In addition, the arc fault detection devices have limited performance, because they focused on arc fault detection between PV arrays and inverter. Moreover, they require the additional current and voltage sensors to implement the arc fault detection algorithm. This article proposes an arc fault detection algorithm employing differential power processing (DPP) structure. The proposed algorithm only uses intrinsic voltage sensors of DPP and inverter, which can improve the cost-effectiveness of PV systems. In addition, the proposed algorithm can integrate the functionality of maximum power processing for each PV panel and arc fault detection. The voltage relationship between DPP and inverter is analyzed to detect the arc fault condition according to the DPP voltage sensing type. The performance of DPP units and its voltage relationship are verified with the control hardware-in-the-loop system. The arc fault detection performance is verified with the prototype PV system.

Accelerated Life Testing Method of Metallized Film Capacitors for Inverter Applications

DC-link capacitors are one kind of reliability-critical component in traction inverters. As such, it is essential to evaluate the degradation characteristics of dc-link capacitors. Accelerated life testing is an effective and standard method to evaluate the capacitors’ lifetime and degradation mechanisms. Therefore, an accelerated life testing method for dc-link capacitors in three-phase inverter applications is proposed in this article. In order to reproduce the same encountered stress, exactly reflecting the real condition for the capacitor under test, a three-phase inverter with the capacitor under test and a three-phase balanced inductor load are used as the evaluation circuit. Due to the employment of the inductor load, the power consumption of the inverter can be reduced, while the full-scale current rating can be maintained so that the capacitor under test is subjected to the practical ripple current stress. In order to estimate a capacitor’s capacitance with high accuracy, an effective and direct condition monitoring method, which is based on the proposed evaluation circuit, is also proposed in this article. By injecting an ac voltage into the dc link, the ac current and voltage components in the dc-link capacitor are generated. Then, the capacitance mathematical model can be developed by analyzing the injected voltage component and the resultant current component. As the proposed method only requires estimating the parameters from the input voltage and current, there is no need to install additional capacitor current sensors, which are usually difficult to install. Moreover, the amount of monitored and processed data can be reduced. Thus, the proposed method is easy to implement for accelerated life testing in practice. In addition, experiments are carried out to verify the analysis and effectiveness of the proposed solution.

A 7.4-MHz Tri-Mode DC-DC Buck Converter With Load Current Prediction Scheme and Seamless Mode Transition for IoT Applications

The growth of IoT applications requires DC-DC converters to have small printed circuit board (PCB) areas and high efficiency over a wide load range. A multi-mode operation of DC-DC converters, therefore, is often necessary to achieve this high efficiency over a wide load range. This paper introduces a tri-mode DC-DC buck converter for IoT applications. The tri-mode operation with PWM, PFM, and multiple-sawtooth PWM (MSPWM) modes helps to retain the high efficiency over the wide load range. The MSPWM mode also enhances a noise margin of the converter, ensuring a regular switching operation at an ultra-light load condition. With a load current prediction scheme, the proposed tri-mode converter requires neither additional load current sensor nor multiple mode controllers. In addition, a soft-start operation is employed to prevent an in-rush current. The proposed tri-mode buck converter has been fabricated through a 0.18- $\mu \text{m}$ CMOS process with a chip area of 0.97 mm $\times0.88$ mm. A load-dependent seamless mode transition is realized, and a maximum converter efficiency of 91% has been measured with a 7.4-MHz switching frequency.