Voltage Ripple Research Articles

Enhancing System Stability: Robust Control Strategies for Modular Multilevel Converters in Weak Grid and Load Conditions

Abstract This paper focuses on operating a modular multilevel converter (MMC) under diverse operating conditions, particularly during weak grid scenarios. The system may approach instability as a result of changes in the resonance frequency and, subsequently, the grid impedance. To address the significant impedance variations between the converter and grid as outlined in IEEE standards 519 and DIN EN 61000-4-15, this paper proposes a novel hybrid damping approach to manage the converter under such conditions. This approach is used to reduce the extra power loss from passive damping and simultaneously increase the robustness of active damping. Various passive damping and hybrid damping methods are implemented to the proposed MMC model and their comparative analysis is presented in order to identify the stability attributes. Also, this paper provides a straightforward proportional resonant (PR) controller along with biquad filter-based approach that ensures system stability and improves system robustness. A detailed sensitivity evaluation of the cascaded control loops is conducted, with an emphasis on the effect of filter parameter variations on stability. Furthermore, the paper explores the contemporary circulating current references for MMCs. This approach offers a superior alternative approach to inject specific harmonics into circulating currents. Employing these schemes, this paper demonstrates the successful achievement of low voltage ripples. Simulation and experimental data are used to validate the proposed strategies' enhanced stability.

Power Quality Improvement in a Grid Connected Solar-PV System with Adaptive Neuro-Fuzzy Controller Based UPQC

Power quality (PQ) problems are frequently encountered in power grids, and these problems become more severe as the number of devices increases. Therefore, one of the primary responsibilities of utility systems remains to supply people with electricity by standard sinusoidal voltage and current configurations at appropriate amplitudes and frequencies adjoining the point of common connection (PCC). This research examines a solar-photovoltaic (PV) coordinated unified power quality controller (UPQC) to enhance the PQ in the distribution grid network. This paper proposes a UPQC control method relied on the Adaptive Leakage Least Mean Square (AL_LMS) algorithm. This approach uses both the Adaptive Neural Fuzzy Inference System (ANFIS) controller and Proportional-Integral (PI) controller to compare between the serial and shunted active converter switching of UPQC. The technique switches the UPQC's shunt and series voltage source converters (VSCs) to obtain a reference signal through iterative weight update. Through iterative weight update, the method obtains a reference signal by switching the shunted and serial VSCs of the UPQC. Therefore, the PQ disturbances such as load voltage drop and ripple and harmonic distortion of the grid’s current are abridged after the control technology is applied to the solar PV-UPQC. Conferring to the simulation results, the proposed ANFIS control AL_LMS algorithm stands the utmost operative in improving the PQ after applied to the solar-PV sourced UPQC, while complying with the IEEE-519 standards. The work was done in using MATLAB/Simulation software.

A reduced device symmetrical-asymmetrical multilevel inverter with self capacitor voltage balancing and reduced capacitor voltage ripple

ABSTRACT Multilevel Inverters (MLIs) have gained widespread acceptance in high-power conversion due to their distinctive features, including minimised harmonic distortion in the output and reduced voltage stress on power switches. Nevertheless, including numerous DC sources and switches in MLIs increases costs and system complexity. To address this challenge, this paper introduces a hybrid MLI topology featuring a reduced device count suitable for symmetrical and asymmetrical source configurations. The proposed hybrid MLI topology (PHMLIT) can produce a 9-level output voltage with a symmetrical configuration and 7- or 11-levels output voltage with an asymmetrical configuration. Moreover, the cascaded connection of the cells of the PHMLIT generates a broad range of voltage levels across the output. Additionally, a novel switching strategy is devised to minimise the size of the capacitor. The comparative analysis illustrates that the PHMLIT exhibits superior characteristics compared to conventional and recently developed topologies regarding the number of switches, DC sources, diodes, capacitors, and total blocking voltage (TBV). Finally, the feasibility of the PHMLIT is confirmed through various simulation and experimental tests.

A novel boost self-balanced thirteen-level inverter based on switched-capacitor H-bridge units

ABSTRACT This paper proposes a new switched-capacitor thirteen-level inverter with a voltage gain of six and reduced device counts. It involves two switched-capacitor H-bridge (SCHB) units and one back-end H-bridge (BEHB) unit, which generally includes one input DC source, twelve switches, two diodes, and three capacitors. In the SCHB units, the capacitors can be charged as self-balanced by turning on a few switches at most output voltage levels. The switching algorithm, optimal capacitor determinations, and efficiency calculation have been brought. The proposed inverter has multiple advantages, such as the low number of device counts per level, low-cost function (CF), low capacitor voltage ripple, and 94% efficiency. To assess the proposed topology, simulations, and experimental results have been performed by MATLAB and Arduino controller board ARM cortex-M3, respectively, in both steady-state and transient conditions.

A two‐channel data and power synchronous transmission method for SRG‐integrated power networks through piecewise composite modulation

AbstractReliable communication is key to achieving remote control, status monitoring, and early fault detection in SRG‐integrated power networks. This paper proposes a novel piecewise composite modulation method to simultaneously modulate data and power during the excitation and power generation stages in each phase of an SRG system. By adopting a frequency‐shift keying modulation strategy, two‐channel data can be modulated and injected into the bus voltage as voltage ripples, allowing for more efficient use of the bus voltage frequency band. Welch's algorithm‐based power spectrum method is innovatively employed to demodulate the transmitted data on the SRG's output bus. Experimental results confirm the feasibility of the proposed data and power synchronous transmission (DPST) strategy, which shows significant potential in SRG‐integrated power networks.

Robust Adaptive Control of Dual Active Bridge DC-DC Converter with Constant Power Loading

Abstract The standard model reference adaptive control (MRAC) application to the Dual Active Bridge (DAB) converter has proven to achieve excellent dynamic and tracking responses under parametric uncertainty. However, it is sensitive to bounded non-parametric uncertainty caused by measurement noise and ripples in the output voltage produced in the electronic device. When left unchecked, it affects the system’s performance and may lead to instability. This paper investigates two robust modifications to the standard MRAC, namely the projection operator and dead zone techniques, to tackle the issue of the bounded noise to the dual active bridge with constant power loading (CPL). It further develops an improved form of the dead zone-based MRAC, which ensures better transient and steady-state output voltage when compared with the traditional dead-zone-based MRAC.

A Three-Phase Four-Leg Neutral Point Clamped Photovoltaic Inverter With Decoupled Active & Reactive Power Control and DC Link Voltage Ripple Minimization Under Unbalanced Grid Operation

A Three-Phase Four-Leg Neutral Point Clamped Photovoltaic Inverter With Decoupled Active & Reactive Power Control and DC Link Voltage Ripple Minimization Under Unbalanced Grid Operation

Sensitivity Analysis of the High-Frequency-link MMC to DC link voltage ripples in a Back-to-Back Connected MMC-based Power Electronic Transformer

Sensitivity Analysis of the High-Frequency-link MMC to DC link voltage ripples in a Back-to-Back Connected MMC-based Power Electronic Transformer

Analytical computation of arm inductor for minimizing MMC circulating current using passive method

The study of circulating currents in modular multilevel converters is vital for improving their efficiency and reliability. The circulating current may arise from capacitor voltage unbalancing, modulation imperfections, load variations, and transient conditions. Such currents typically induce distortions in arm currents, exhibiting second-order harmonics that lead to power losses and negatively impact the ratings of converter components as well as the amplitudes of capacitor voltage ripples. Despite ongoing research, effective strategies to mitigate circulating currents are limited. This paper aims to systematically address this issue by selecting key design parameters specifically arm inductance and capacitor values, to suppress circulating currents. The methodology incorporates harmonic analysis and instantaneous power theory to derive expressions for arm inductance. Initial modelling includes common mode and differential mode analyses, leading to an examination of harmonic content. Analysis reveals that the selection of the arm inductor value is mainly influenced by the second-order harmonic component, whereas the capacitor value is determined by the fundamental harmonic component. By adopting this methodology, the boundary limit for arm inductor selection can be determined. This article proposes a novel expression for arm inductor selection. The proposed expression mainly depends on factors such as load, submodule capacitor voltages, submodule capacitor, and differential current. By selecting an appropriate inductor value based on converter-rated parameters, circulating current within the system can be effectively suppressed. The methodology offers a practical framework for arm inductor selection. Simulation results validation shows strong alignment with analytical results with the error margin of less than 1%, hereby the MMC parameter can be determined with better accuracy through analytic method.

Design of Two Phase DC-AC Interleaved Boost Inverter with Voltage Control System using PI Controller

DC-DC Interleaved Boost Converter (DC-DC IBC) topology was developed through the interleaving technique since conventional DC-DC Boost Converter has many problems related to complex circuit control, harmonics, and output power. In this research, DC-DC IBC was developed into a Two-Phase AC-AC Interleaved Boost Converter (TP AC-AC IBC), then combined with a Two-Phase Full Bridge Inverter to become a Two-Phase DC-AC Interleaved Boost Inverter (TP DC-AC IBI). TP DC-AC IBI has several advantages, including minimal current and voltage ripples and greater output power because it consists of two AC-AC IBCs. This research aims to meet highly regulated AC voltage needs with the renewable energy source input using the proposed topology, by implementing Proportional Integral (PI) close loop control system. The output voltage is detected using a voltage transducer LV-25P, then compared with a reference voltage and controlled using a PI controller to keep the output voltage consistently stable. The switching signal setting uses the Sinusoidal Pulse Width Modulation (SPWM) technique by modulating the control output with a high frequency. As a verification step, testing was carried out using Power Simulator (PSIM) software and then validated by hardware testing in the laboratory. Testing was carried out using several test signals, and it was found that the proposed method worked well. System efficiency and Total Harmonic Distortion (THD) tests carried out using various load values, and a maximum efficiency of 93.87% and a minimum THD of 2.46% were obtained.

Design of Multi-Time Programmable Intellectual Property with Built-In Error Correction Code Function Based on Bipolar–CMOS–DMOS Process

The coupling capacitor of the MTP cell used in this paper is an NCAP-type capacitor that has only a source contact, and the layout size of the unit cell is 6.184 μm × 6.295 μm (=38.93 μm2), which is 0.44% smaller than the MTP cell that uses the coupling capacitor of the conventional NMOS transistor type that has both a source contact and a drain contact. In addition, a 4 Kb MTP IP with a built-in ECC function using an extended Hamming code capable of single-error correction and double-error detection was designed for safety considerations. In this paper, a new test algorithm is proposed to test whether the ECC function operates normally in the MTP IP with a built-in ECC function, and it is confirmed through a test using logic tester equipment that the output data DOUT[7:0] and the error flag ERROR_FLAG[1:0] are exactly the same in the cases of no error, a single-bit error, and a double-bit error. In addition, by sharing a current-controlled ring oscillator circuit that uses a current-starved inverter in the VPP, VNN, and VNNL charge pumping circuits that share a single ring oscillator in the erase and program operation modes of the MTP IP and using the regulated VPVR as power, the pumping capacitor size is reduced, and a new technology to reduce ripple voltage variation is proposed. Meanwhile, in the VNN level detector circuit that detects whether the VNN has reached the target voltage, a folded-cascode CMOS OP-AMP whose output swing voltage is almost VDD is used instead of a differential amplifier circuit with a PMOS differential input pair to ensure that normal VNN level detection operation occurs.

Carbon Nanostructures Derived from In Situ Grown ZIF Nanocages within Bacterial Cellulose for AC-Filtering Electrochemical Capacitors.

Electrochemical capacitors (ECs) offer superior specific capacitance for energy storage compared to traditional electrolytic capacitors but face limitations in alternating current (AC) filtering due to the need for balancing fast response and high capacitance. This study addresses these challenges by developing a freestanding nanostructured carbon electrode, derived from the rapid carbonization of bacterial cellulose (BC) embedded with zeolitic imidazolate framework 8 (ZIF-8) and in situ formed carbon nanotubes (CNTs). The electrode exhibits an exceptionally low area resistance of 9.8 mΩ cm2 and a high specific capacitance of 2.1 mF cm-2 at 120Hz, maintaining performance even at high frequencies. Stacking these electrodes enhances the capacitance to 5.3 mF cm-2, with the phase angle degrading to -74.4° at 120Hz; however, they retain a phase angle below -45° up to ≈50kHz, demonstrating excellent high-frequency performance. Furthermore, connecting three aqueous units in series as an integrated cell or utilizing organic electrolytes extends the voltage window to 2.4V, enhancing their suitability for high-voltage applications. Ripple voltage analysis under various loads and frequencies indicates effective filtering capabilities, highlighting the potential of these nanostructured ECs for next-generation electronic applications.

A Current‐Fed Switched Capacitor Inverter With Voltage Boosting, Reduced Harmonic Distortion, and Minimal Device Count

ABSTRACTDC–AC inverters are an important set of power converters when it comes to integration of the renewable energy resources in to the AC grid or to local AC loads. The multilevel inverters (MLIs) are a common and popular choice for such applications. However, MLIs require many switching devices for higher number of voltage levels, multiple isolated DC sources, need for additional charge‐balancing circuits for the DC‐link capacitor, and unequal voltage stress in the devices at higher power levels. Switched capacitor–based inverters are emerging as a popular alternative to the conventional MLIs that do provide inherent charge balancing, reduced device stress, output voltage–boosting capability, and highly compact converters. This work proposes such a current‐fed DC–AC switched capacitor converter (SCC). This converter offers advantages such as reduced count of switched capacitors and power devices, elimination of load‐side filtering elements, reduced switching ripple in output voltage due to inherent interleaving, reduced voltage and current total harmonic distortion (THD), and lower ratings of the switched capacitors. An adaptive hysteresis control scheme is used to track the voltage across the switched capacitors to a desired sinusoidal reference. The overall control architecture is straightforward to implement, and the switching architecture uses overlapping logic to prevent interrupting the input current. The work includes a complete analysis and design procedure. A 500‐W laboratory prototype of the proposed converter is built, with the control architecture implemented using the TMS320F28379D microcontroller. Simulation results are verified with experimental outcomes.

Ultrahigh Step-Up DC-DC Converter Utilizing a Three-Winding Coupled Inductor and a Switched Capacitor Network With Reduced Input Current Ripple and Low Voltage Stress on the Power Switch

Ultrahigh Step-Up DC-DC Converter Utilizing a Three-Winding Coupled Inductor and a Switched Capacitor Network With Reduced Input Current Ripple and Low Voltage Stress on the Power Switch

Speed control analysis of voltage source inverter fed brushless DC motor

The brushless DC (BLDC) motor requires to be controlled at the preferred speed in order to operate. A brushless DC motor's speed can be adjusted by adjusting the input voltage. In general, speed increases with voltage. The application of a Luo converter is made to satisfy the load demand, get rid of output voltage ripples, and reduce parasitic effects. The magnitude of stator input voltage to BLDC motor is controlled through the pulses applied by ATMEGA 328P micro controller to voltage source Inverter which in turn controls the magnitude of speed of BLDC motor. The position of the brushless DC (BLDC) motor is continually monitored by infrared sensors, which are then processed by a PIC16F872 microcontroller to produce the necessary pulses for BLDC motor speed regulation. The BLDC motor speed can be regulated by the pulses applied to voltage source inverter through the IR sensors placed at the motor. The outcomes of controlling the speed of a BLDC motor using voltage variation values have been shown.

Improved direct ripple power predictive control of single-phase rectifier based on ripple separation

Voltage ripple is introduced to the DC link when a single-phase rectifier operates, which affects the energy balance of both the DC and AC sides. Accurate acquisition and fast, precise tracking of the decoupling capacitor voltage and decoupling inductor current reference values are challenges in the design of active power decoupling controllers. This article employs instantaneous ripple power control, shifting the focus from the accuracy of the decoupling capacitor voltage and decoupling inductor current reference values to the accuracy of the ripple power reference value. A ripple separation-based active power decoupling control strategy is proposed. By designing a time-varying observer, the amplitude feedback signal of the output voltage’s second-harmonic ripple is extracted in real time to generate the ripple power reference, enhancing its accuracy and reliability. The endpoint equivalent modulation method is adopted to track the instantaneous ripple power. Compared with traditional finite control set model predictive control, it achieves better tracking performance at the same control frequency, with a fixed switching frequency. Additionally, measures are proposed to address input current distortion caused by output voltage ripple entering the rectifier’s grid-side current control loop. This avoids the pollution of the input current by the output ripple voltage. Simulations and experimentations are performed to test the proposed control strategy.

Design of a Univariate Dual‐Loop Voltage System Based on the Multisampling Method

ABSTRACTThis study presents an innovative control framework designed for voltage source inverters (VSIs) equipped with LC output filters. The objective of this control framework is to reduce delay and suppress aliasing effects by employing multisampling techniques and implementing repetitive filtering methods. The multisampling approach can significantly reduce control delays, thereby enhancing both the bandwidth and stability margins of the system. The implementation of multisampling techniques for inverter voltage can enhance dynamic performance. However, it may introduce high‐frequency ripples in the control loop, resulting in low‐order aliasing harmonics and ultimately leading to output voltage distortion. To address this issue, a multiple notch filter with minimal phase delay is employed suppress aliasing. The optimal parameters of the system are determined by evaluating the filter specifications, filtering effectiveness, output voltage ripple, and overall system performance, while also considering the actual filtering requirements and circuit size. Its effectiveness and performance are carefully verified by experimental results.

A decoupling strategy for average value control and ripple suppression of capacitor voltages in modular multilevel converters based on notch filters

AbstractModular multilevel converters (MMC) have become an emerging hotspot in the field of medium‐voltage drives. A major challenge is the large voltage ripple of sub‐module capacitors at low rotor speeds with high torque. Therefore, it is necessary to achieve ripple suppression while maintaining the average values of the capacitor voltages at their reference. However, the average value control and ripple suppression of the capacitor voltages have a coupling effect during the circulating current control loop, which reduces the performance. This paper proposes a decoupling strategy based on notch filters (NF). First, the coupling problem existing in the traditional control strategy is analysed by theoretical analysis and simulation. Then, the principle and parameter design method of the improved decoupling strategy are introduced. Finally, the performance of the decoupling strategy is experimentally verified using a small prototype.

A Simple 18‐Pulse Uncontrolled Star Rectifier by Adopting Dual Passive Injection Circuits at DC Side

ABSTRACTThis research introduces a simple 18‐pulse star rectifier, which is a combination of a conventional double‐star rectifier and two new passive injection circuits. The proposed passive injection circuits are constituted with a specially tapped interphase transformer (STIPT) and four diodes. The proposed passive injection circuits can simultaneously increase the step number of the input line current and the pulse number of the load voltage. The first passive injection circuit (FPIC) doubles the pulse number of the traditional double‐star rectifier converting it into an asymmetrical 12‐pulse star rectifier while the second passive injection circuit (SPIC) further converts the 12‐pulse star rectifier into 18‐pulse star rectifier. For tripling the pulse number of the double‐star rectifier, the STIPT requires to be designed optimally. For designing purpose, the proper tap ratios of the STIPT are determined depending on the minimum total harmonic distortion (THD) of the input line current. When designed optimally, the proposed rectifier simultaneously reduces the THD of the input line current and ripple of the output voltage with increasing pulses. In order to provide experimental validation for the theoretical evaluation, a laboratory prototype is constructed. The theoretical THD of the input line current is about 10.1%, whereas the experimental THD is about 5.42%.

Design of a Feedforward Decoupled Current Controller and an Optimized Voltage‐Oriented Control for Bi‐Directional Power Flow for V2G Application

ABSTRACTBi‐directional power exchange between the lithium‐ion battery and the grid can be achieved using vehicle‐to‐grid (V2G) technology. Bi‐directional battery chargers for V2G applications present opportunities and challenges, as the rapid growth of active components can compromise system reliability. This paper proposes an adaptive control mechanism for a three‐phase bi‐directional battery charging system to address this. The system integrates a bi‐directional active front‐end (AFE) converter (BAC) with an interleaved buck‐boost converter to enable adaptive constant current/constant voltage (CC/CV) mode operation and bi‐directional power flow. A feedforward decoupled current controller and pulse width modulation scheme optimize battery charging, while an optimized voltage‐oriented control (OVOC) model‐based controller ensures stable bi‐directional power exchange between the electric vehicle (EV) and the utility. Experimental results validate the effectiveness of the proposed approach, with findings demonstrating low total harmonic distortion (THD), unity power factor (UPF), and minimal DC voltage ripple. A 12.5 kW prototype further confirms the practical viability of the design, offering a promising solution for enhanced reliability and performance in V2G battery chargers.