Low-frequency Current Ripple Research Articles

Analysis of DC-Link Low-Frequency Current Harmonics in Multi-Source Multi-Three-Phase Electric Drives

In a multi-source permanent magnet synchronous motor (PMSM) drive, three distinct winding structures can be implemented: multi-sector, multi-three-phase, and highly coupled. However, due to variations in the magnetic coupling between windings, their low-frequency DC-link current ripple components differ. This paper presents a method to identify the phenomena associated with each low-frequency harmonic content. Three analytical models are developed for the DC current ripple induced by unbalanced winding, counter-electromotive force (back-EMF) harmonics and aliasing effects, respectively, with the results validated through simulations. Experimental validation is conducted for highly coupled winding drives, demonstrating agreement with the analytical models and simulations. The maximum DC current ripple ratio found in the analytical model, the simulation and the experiments is less than 15%, which is deemed acceptable for motor drive applications.

Universal Input Single-Stage High-Power-Factor LED Driver with Active Low-Frequency Current Ripple Suppressed

In this paper, a light-emitting diode (LED) driver with a high power factor (PF) and low-frequency current ripple suppression over a wide input range is presented, and a flyback converter is designed to operate in the discontinuous conduction mode (DCM), with a digital controller used to keep the duty cycle constant for half of the utility cycle under a fixed load and input voltage. This method ensures that the input current is in phase with the universal input voltage, thus achieving a high power factor without utilizing feedforward control. Furthermore, on the secondary side, the time of the zero point of the utility voltage can be attained so that the duty cycle can be updated at this time. In addition, a simple auxiliary circuit is connected parallel to the output side to absorb the excess output current of the flyback converter or to release the current to the load to make up for the shortage of the output current of the flyback converter so that the low-frequency ripple of the output current can be inhibited. There are only two current-detecting resistors used in this study: one is the output current-sensing resistor of the flyback converter, and the other is the output current-sensing resistor of the auxiliary circuit.

Low-Frequency Current Ripple Minimization of Single-Star Bridge Cells-Based Battery Energy Storage System Using Optimal Third Harmonic Voltage Injection

Single-star bridge cell (SSBC) based multilevel converters are a promising solution for constructing high-voltage and large-capacity battery energy storage systems (BESSs) in power systems. Nevertheless, an undesirable second harmonic current (SHC) will be generated in the battery units since the single-phase instantaneous power of the SSBC pulsates at twice the line frequency. Such SHC-dominated low-frequency current ripple not only shortens the lifespan of the BUs but also degrades the system's efficiency. However, this intrinsic issue is overlooked in recent studies. To this end, an SHC suppression scheme that makes full use of the residual modulation index of the system to inject an optimal third harmonic voltage (THV) is proposed. The phase of the THV is determined first, followed by a closed-loop control strategy to regulate its magnitude dynamically for achieving a minimum SHC within the modulation constraints. The scheme is implemented with the variables that already existed in the main control system, resulting in a low increase in cost. The adverse impact of the technique on the AC-side output characteristics is investigated quantitatively, and a modified design procedure for the DC filter network is presented to address this issue. Hardware-in-the-loop experiments are carried out to validate the technique.

Performance Enhancement of Single-Phase Two-Stage AC-DC Converter With Reduced DC-Link Capacitance

Single-phase two-stage AC-DC converters employed in electric vehicle (EV) chargers have the tendency to produce low frequency ripple due to input/ output power mismatch, making it necessary to use bulky DC-link capacitors. High voltage ripple at DC-link due to reduced capacitance, prompts poor input power quality and high low-line frequency ripple at the output of secondary-stage. In state-of-art, input power quality in converters with low DC-link capacitance is enhanced by using a digital low-pass filter (LPF). However, employing LPF to sensed DC-link voltage results in a non-optimum dynamic response and deteriorated stability margins. With the objective to improve input power quality, enhance dynamic performance and reduce secondary-side ripple for low valued DC-link capacitance AC-DC converters, a modified unit-template based model predictive (MUT-MPC) and a DC-link feedforward (DFF) controls are presented in this paper. The current feed-forward for the unit-template is controlled by predictive voltage error through an optimization process of cost function to improve input power quality and dynamic performance for primary AC-DC converter. Furthermore, a DC-link feedforward (DFF) control is implemented for secondary DC-DC stage, which reduces the low-frequency current ripple at the load. Finally, to verify the effectiveness of presented multi-objective control method in comparison with traditional controls, MATLAB simulations and experimental results are provided.

A Low Frequency Ripple Current Suppression Strategy for Single-Phase Photovoltaic Grid-Connected Inverter

Due to the absence of the insulated transformer, the non-insulated photovoltaic (PV) inverter possesses excellent properties such as small size, light weight, etc. However, the inherent parasitic capacitance between the PV panels and the ground brings serious leakage current problem, which has been the focus of researchers. Since the instantaneous power of the single-phase inverter results in a ripple current at a double-frequency ripple(100Hz), according to the theorem of conservation of power, the fluctuation of PV panels output voltage leads to a double frequency ripple of input current, which will have a negative influence on the maximum power point tracking in terms of PV panels and reduce the utilization efficiency of solar energy. This paper aims to investigate the suppression of the leakage current of PV single-phase inverters and the double-frequency ripple, the circuit proposed in this paper substitutes a bridge arm of the conventional PV grid-connected inverter with a Boost converter, which can eliminate the leakage current directly. The suppression strategy of double-frequency ripple for the proposed topology is provided as well. By transferring the double-frequency ripple in the DC-link capacitor of the inverter to another capacitor that has no connection to loads, it can suppress the low-frequency ripple current of the input side effectively. The paper verifies the feasibility of the proposed topology and the corresponding control strategy through simulation and experimental results.

Low Frequency Current Ripple Suppression for Two-Stage Single-Phase Inverter Based on Impedance Editing

The instantaneous output power of the two-stage single-phase inverter pulsates at double-line frequency, generating a large amount of second harmonic current (SHC) in the front-end dc-dc converter and input dc source. The SHC is harmful to the system performance. To address the issue, a control strategy based on port-impedance editing, where inductor current feedforward (ICFF) and bus voltage feedforward paths are employed, is proposed to reduce the low frequency ripple in the article. Due to only bandpass filter employed in each feedforward path, the proposed control scheme is relatively easy to be implemented. Under the control strategy, the dc-bus port-impedance of dc-dc converter is increased rapidly at double-line frequency, while staying low impedance for other frequencies. What is more, different ICFF paths are taken into insight to obtain optimized path. Meanwhile, the small signal model of front-end dc-dc converter is established and the design principle of key parameters is provided for the derived control strategy. Furthermore, the dynamic response with bandwidth limitation is also discussed in this article. Finally, a two-stage single-phase inverter prototype was fabricated and tested. The experimental results verify the performance of the proposed strategy with SHC reduction.

A novel low frequency current ripple suppression method for energy storage system in DC microgrid

• A novel control method is proposed for NF, QPR and LPF based on dual-loop control. • This method improves the suppression effect of secondary harmonic current (SHC). • This method also improves anti-load mutation ability. • SHC suppression effect and dynamic response of four control methods are analyzed. The instantaneous output power of the energy storage system pulsates at twice the output voltage frequency, generating a large amount of secondary harmonic current (SHC) in the switching tubes and batteries. The SHC is harmful to the system performance and battery life. Firstly, through the analysis of traditional dual-loop (DL) control method, it is concluded that SHC is not suppressed obviously and the dynamic characteristics of the system is inferior when load hopping. To address these two questions, a novel control method is proposed for introducing notch filter (NF), quasi-proportional resonator (QPR) and load power feedforward (LPF) based on DL control (it can be abbreviated as NQLDL). This method increases the amplitude of the inductor branch equivalent impedance (IBEI) at twice the output frequency without changing the frequency adaptability, improves the suppression effect of SHC, reduces the amplitude of the IBEI outside of twice the output frequency and also improves anti-load mutation ability. Furthermore, the SHC suppression effect and dynamic response are also discussed under four control methods. Finally, the validity of proposed control methods are demonstrated by experimental results.

Hybrid Inverter and Control Strategy for Enabling the PV Generation Dispatch Using Extra-Low-Voltage Batteries

This paper proposes a dispatchable photovoltaic (PV) hybrid inverter for output power tracking without any dependency on the converter’s efficiency and with no power closed loop. The system uses an extra-low-voltage battery energy storage system (BEES) based on a Li-ion battery pack to be applicable for use inside homes and other installations close to the end-user. A bidirectional isolated current-fed dual-active bridge (CF-DAB) converter associated with the batteries provides a wide conversion voltage ratio and ensures safety for the users. The proposed control system shares the DC bus voltage controller between the ac grid interfacing converter (AC-DC) and CF-DAB (DC-DC), eliminating the converter’s efficiency in the reference equations. When dispatchable power is not required, or according to the user’s request, the battery’s charge/discharge current can be specified. A disturbance rejection technique avoids low-frequency current ripple on the battery side. It contributes to the battery’s lifespan. Experimental results presenting the dc bus voltage control, current disturbance rejection, and power dispatching are included to validate the proposal.

DC and AC Power Quality Control for Single-Phase Grid-Tied PEMFC Systems With Low DC-Link Capacitance by Solution-Space-Reduced MPC

The low-frequency current ripple, which is inherent in the two-stage single-phase grid-tied fuel cell power system, gives harmful effects on fuel cell stack itself and causes a reduction in the lifetime, efficiency, and operating performance of system. This article first presents a direct current control scheme to improve the dc and ac power quality with a dc-link voltage notch filer and a proposed improved model predictive control (MPC) method. However, since the number of the switching states is low, the fuel cell dc current and grid current may suffer contaminated and distorted, when the conventional MPC algorithm implementation is straightforward. With the aid of feedforward duty ratio and the rotation angle of reference grid current, the optimization space can be reduced in real time, avoiding evaluating all the feasible virtual-vectors, and then the improved MPC has been proposed. Finally, the correctness and effectiveness is verified by the simulation and experiment results.

Bandwidth-Increased Ripple-Mitigating Scheduling Algorithm for Dynamically Reconfigurable Batteries

Modular cascaded circuits offer attractive qualities in reconfigurable battery applications, including improved fault tolerance and flexibility. In contrast to conventional hard-wired dc battery packs, however, cascaded topologies, such as modular multilevel circuits (MMC) with serial or serial and parallel connectivity, load modules with substantial low-frequency current ripple, which generates additional loss and can accelerate battery aging. Recent studies reveal that low-frequency ripple can cause noticeable battery aging, whereas high frequencies are insignificant, presumably mainly as they can be absorbed by the dielectric electrode capacitance, and reduce heating associated with lower high-frequency battery impedance. Previous MMC–battery control methods solely focus on state-of-charge and thermal balancing of individual modules, while the few existing methods for suppressing ripple tend to form low-frequency patterns in the modules’ load, which increase battery cycling as well as loss. This paper presents a ripple-oriented high-bandwidth control technique that minimizes low-frequency components in the module load spectrum and improves battery treatment, while maintaining the average switching frequency. The control method takes limitations related to module data acquisition into account and enhances the feedback bandwidth using observers. It works with a wide range of topologies including modules with series connectivity only as well as series/parallel. The measurements in the laboratory verify the shift of the module load from the 10 – 100 Hz range to ~5 kHz and a reduction of battery losses by up to 20 %.

Grid Connection Using a Structure That Combines a Buck Converter and a Push-Pull Converter to Reduce the Low-Frequency Current Ripple of the Fuel-Cell

Grid Connection Using a Structure That Combines a Buck Converter and a Push-Pull Converter to Reduce the Low-Frequency Current Ripple of the Fuel-Cell

Multilevel Fixed Pulse Pattern Control for Medium-Voltage High-Frequency Inverter

To satisfy the demand for more compact medium-voltage motor drive systems, it is desirable to increase the frequency of the cascaded H-bridge inverters used in high-speed motor systems. However, in asynchronous pulse width modulation (PWM) systems, as the output frequency increases, the command voltage and triangular wave carrier frequencies get closer, making it impossible to accurately output the command voltage. This manifest itself as increased current harmonics, increased surge voltage at the motor terminals, and increased low-frequency ripple current due to the asynchronous nature of the system. In this study, we adopt a fixed pulse pattern modulation method to address these problems. In our method, a low-distortion output voltage is compiled in advance into a table, and subsequently output in synchronization with the fundamental voltage phase. We were able to confirm the effectiveness of the proposed method in simulations at fundamental wave frequencies of 700 Hz and 1000 Hz.

Control of a Single Stage Boost Inverter Based on Dynamic Sliding Mode Control with Power Decoupling

In this paper, the problem of control a single-stage boost inverter is studied. The goal is to achieve a system with robustness against variations in parameters, fast response, high-quality AC voltage, and smooth DC current. To this end, a new type of dynamic sliding mode control is proposed to apply to various scenarios such as parameter uncertainties and DC input voltages. In comparison with the conventional double-loop controllers, the proposed sliding mode controller utilizes only a single loop in its design, while having attractive features such as robustness against parametric uncertainties. In addition, a methodology is proposed for the decoupling of double-frequency power ripples based on proportional-resonant (PR) control to remove the low-frequency current ripples without using additional power components. Compared to conventional controllers, the proposed controller provides several features such as fast and chattering-free response, robustness against uncertainty in the parameters, smooth control, proper steady-state error, decoupled power and good total harmonic distortion (THD) over the output voltage and input currents, and simple implementation. In a fair comparison with classical sliding mode control, simulation results demonstrate more satisfactory performance and effectiveness of the proposed control method.

AC–DC Flyback Dimmable LED Driver with Low-Frequency Current Ripple Reduced and Power Dissipation in BJT Linearly Proportional to LED Current

In this paper, a dimmable light-emitting diode (LED) driver, along with the low-frequency current ripple decreased and the bipolar junction transistor (BJT) power dissipation reduced, is developed. This driver is designed based on a single-stage flyback converter. On the one hand, the low-frequency output current ripple reduction is based on the physical behavior of the linear current regulator. On the other hand, when the voltage across the LED string is decreased/increased due to dimming or temperature, the output voltage of the flyback converter will be automatically regulated down/up, thereby making the power dissipation in the BJT linearly proportional to the LED current. By doing so, not only the power loss in the linear current regulator will be decreased as the LED current is decreased or the LED temperature rises, but also the output current ripple can be reduced. Furthermore, the corresponding power factor (PF) is almost not changed, and the total harmonic distortion (THD) is improved slightly. In addition, the LED dimming is based on voltage division. Eventually, a 30 W LED driver, with an input voltage range from 85 to 295 Vrms and with 24 LEDs in series used as a load, is developed, and accordingly, the feasibility of the proposed LED driver is validated by experimental results.

Control System Development for the Three-Ports ANPC Converter

This paper proposes a control system for the single-phase Three-Ports Active Neutral- Point-Clamped (ANPC-3P) converter, which can inject a sinusoidal current into the grid, balance the neutral point voltage, and regulate the energy storage system (ESS) current with reduced low-frequency ripple. Despite other applications, ANPC-3P inverter can be used in grid-tied renewable generation to allow the simultaneous connection of a photovoltaic (PV) energy source and an ESS to the AC grid. The ESS is connected directly to the inverter circuit without any auxiliary DC-DC converter, but due to the DC bus pulsed power, it can be subjected to low-frequency current ripple. This undesired current ripple is difficult to filter and can lead to shorter battery life. A control system based on well-known controllers is analyzed and designed. Theoretical analysis is validated experimentally using a single-phase 1-kW prototype.

Integrated High- and Low-Frequency Current Ripple Suppressions in a Single-Phase Onboard Charger for EVs

Current ripples produced in single-phase onboard charging systems of electric vehicles (EVs) impact the lifetime of their batteries. In this article, an isolated multifunctional charger topology is proposed. The charging system can be used to charge the auxiliary batteries or serve as an active filter (AF) for the power battery charger. By time-sharing multiplexing it, the high-frequency (HF) and low-frequency (LF/second harmonic) current ripple can be suppressed in driving and parking charging modes, respectively. The proposed topology can also achieve zero voltage switching for all power switches under a full-load range in the driving charging mode. In addition, the integration and the power density of the charging system can be improved due to the reconstruction of the capacitive energy storage AF in the parking charging mode. Finally, a 400-W experimental prototype is developed and the experimental results are presented to validate the performance and feasibility of the proposed topology.

LLC Resonant Tank based Converter for EV Charging Application

The aim of the article is to maximize the battery life using LLC resonant tank. LLC tank designing methodology and also the practical designing examination is introduced in LLC multi converter. Designed dc- dc converter increases the battery life by eliminating low and high frequency current ripples. In addition, bridgeless cuk converter is used for power factor improvement. To achieve the better power factor and to reduce the conduction losses the cuk converter is aimed to function in discontinuous mode of conduction (DCM). DC output voltage ranging 42-24 V for 650 W is obtained from the modelling for battery charging application.

Research on low input current ripple two‐stage converter for low frequency pulsed‐power applications

In this study, a two-stage cascaded pulsed power converter based on the proposed optimised control scheme has been presented. In order to eliminate the low-frequency input current ripple, the front-stage converter only needs to provide average power and the second-stage converter provides pulsed power. Meanwhile, the isolation of energy transfer mode combines with the proposed optimised control method based on the input current AC signal feedback control guarantee smooth input power with low repeat frequency pulsed load. To demonstrated the effectiveness of the proposed low-frequency input current ripple cancellation technique, a 1 kW peak pulsed power prototype is built and tested. The experimental results verify the validity and reliability of the two-stage isolated pulsed power converter with proposed optimised control method, and the proposed methods and concepts in this study can also be applied to all kinds of pulsed power applications.

Fuel Cell High Efficiency Power Converter for Suppressing Low Frequency Current Ripple

Abstract For the generation of proton exchange membrane fuel cells, the problem of low frequency current ripple, battery efficiency and lifetime is reduced. This paper presents an efficient fuel cell power converter that suppresses low frequency current ripple. The front-end DC/DC boost circuit uses an active clamp push-pull circuit to reduce low-frequency current ripple; the downstream DC/AC inverter circuit uses a half-bridge inverter circuit to implement the DC inverter. First, the generation mechanism of low-frequency current pulsation and its influence on proton exchange membrane fuel cells are discussed. Secondly, the topology of high-efficiency power converter is analyzed in detail. Finally, a closed loop for suppressing low-frequency current ripple is proposed. Control method.

Closed Loop Control of a Series Class-E Voltage-Clamped Resonant Converter for LED Supply with Dimming Capability

In this work, a new closed-loop control system is applied to a class-E resonant DC–DC converter with voltage clamp used for light-emitting diode (LED) supply. The proposed power topology was first described by Ribas et al. in a recent work. In the present paper, the LED current is sensed and used to implement a feedback control loop instead of the simplified feedforward scheme used in this previous reference. To design the control, a novel, simplified small-signal model is presented. This model is used to analyze the converter behavior as a function of the output power. The proposed approximation is significantly simpler than the multifrequency averaging technique normally used to analyze resonant converters. The feedback control loop is designed to reduce the LED low frequency current ripple while providing dimming control. Both the model and the control are verified by simulation and laboratory experimentation and the results obtained are in good accordance with the expected values.