Small DC-link Capacitor Research Articles

Beatless Control Strategy Based on Impedance Reshaping for PMSM Drives With Small DC-Link Capacitors

Beatless Control Strategy Based on Impedance Reshaping for PMSM Drives With Small DC-Link Capacitors

Improved Extended EMF-Based Sensorless Control for IPMSMs With Small DC-Link Capacitor Considering DC-Link Voltage Measurement Error

Improved Extended EMF-Based Sensorless Control for IPMSMs With Small DC-Link Capacitor Considering DC-Link Voltage Measurement Error

Overvoltage Avoidance Control Strategy for Braking Process of Brushless DC Motor Drives with Small DC-Link Capacitance

Single-phase input rectifier brushless DC motor drives with a small film capacitor have many advantages, such as high power density and high reliability. However, when the motor system operates in regenerative braking mode, the dc-link capacitor with reduced capacitance may suffer from overvoltage without adding additional hardware circuits. At the same time, the braking torque control of the motor will be affected by speed variations. In order to ensure smooth and reliable operation of the motor system, an anti-overvoltage braking torque control method is proposed in this article. The relationship among the dc-link capacitance, the dc-link capacitor voltage, and the speed during regenerative braking is analyzed quantitatively, and the speed at which the regenerative braking is switched to the plug braking is obtained, which in turn consumes the capacitor energy to avoid dc-link overvoltage. Additionally, based on the relationship between the controllability of the braking torque and the speed, a reference value of the braking current that matches the speed is designed. The proposed method makes use of the capacitor’s energy storage during regenerative braking. Meanwhile, it mitigates the impact of motor speed on braking torque. Finally, the effectiveness of the proposed method is verified on a motor platform equipped with the dc-link film capacitor.

Adaptive Virtual Admittance Reshaping-Based Resonance Suppression Strategy for PMSM Drives With Small DC-Link Capacitor

Adaptive Virtual Admittance Reshaping-Based Resonance Suppression Strategy for PMSM Drives With Small DC-Link Capacitor

Series IGBT Chopping Strategy Based on SVPWM for PMSM Drives with Small DC-Link Capacitance

Series IGBT Chopping Strategy Based on SVPWM for PMSM Drives with Small DC-Link Capacitance

Revolutionary building approach for maximal photovoltaic system results to improve maximum power point tracking in solar inverter

Due to the inherent frequency ripple in single-phase photovoltaic (PV) grid-connected solar inverters, the Maximum Power Point Tracking (MPPT) will inevitably be affected. To improve the MPPT performances, a passive LC power decoupling circuit with a Robust Sliding-Mode Control (RSMC) is proposed in this article. The frequency pulsation on the DC link is effectively canceled with the passive LC decoupling path. Thus, the MPPT accuracy is significantly enhanced, and the utilization of a small DC-link capacitor becomes possible. The resonance between the LC circuit and the main DC-link capacitor appears, which can be damped through an active damping method. The proposed RSMC offers good steady-state, dynamic performance (voltage fluctuation and settling time), and the robustness of the DC-link voltage, which is also beneficial to MPPT control in terms of high accuracy and fast dynamics. The systematic design of RSMC is presented, and a detailed parameter optimization design of the LC decoupling circuit is discussed. Experimental tests are performed on a 2.5-kW single-phase grid-connected solar inverter, and the results validate the effectiveness of the proposed strategy.

Linear Modulation Region Expansion Strategy Based on Voltage Vector Angle Regulation for PMSM Drives With Small DC-Link Capacitor

Modulation fluctuations will decrease the linear operation range and cause the reduction of DC-link utilization for reduced DC-link capacitance motor drives. In this paper, a novel strategy for expanding the linear modulation region based on voltage vector angle regulation is proposed. The phase relationship between the voltage reference and the DC-link voltage fluctuation is carried out creatively to clarify the reduction of linear modulation margin. Based on the impedance matching method, the linear modulation region can be expanded by reducing the phase differences with the regulation of voltage vector angle. According to parameter and performance analysis of the proposed method, the DC-link utilization can be improved by 13.2%. Experimental results validate that the effectiveness of the proposed method.

Analytical DC-side stabilizing conditions for hybrid HVDC links based on dominant frequency model reduction

Incorporating the advantages of line commutated converters (LCCs) and voltage-source converters (VSCs), hybrid high voltage DC (HVDC) links have bright prospects in bulk power transmission. For this new technique, however, there is a risk of oscillatory instability in the DC link, and the mechanism behind the instability is still unclear. This paper derives analytical DC-side stabilizing conditions for hybrid HVDC links by using dominant frequency model reduction. The small-signal model of the LCC-VSC link is first truncated by reserving only the state variables highly relevant to the dominant mode so that the expression of the dominant oscillation frequency can be obtained. Dynamics of other state variables are reintroduced and then simplified while leaving their properties nearby the dominant frequency intact. Based on the reduced model, an analytical stability criterion is obtained, which reveals that the DC-side stability of hybrid HVDC links will deteriorate with reduced DC voltage operation, a heavy load, a small DC-link capacitor, slow inner loop dynamics, a small proportional and a large integral gain of the DC voltage regulator. In addition, simplified sufficient stabilizing conditions of hybrid HVDC links are further derived for control parameter design. Case studies validate the accuracy of dominant frequency model reduction and the derived stabilizing conditions.

Single-Phase Grid-Forming Strategy with Power Decoupling Implementation for Electrolytic-Capacitor-Free EV Smart Battery Charger

Smart Battery Chargers (SBCs) implementing grid-forming (GFM) control strategies are a promising solution to provide voltage and frequency support, increasing the grid reliability. Typically, GFM studies consider inverters with high DC-link capacitance. Therefore, there is a research gap in two-stage DC-AC converters with small DC-link capacitance implementing GFM strategies. This article proposes a novel approach to implement a GFM control strategy along with active power decoupling (APD) in an isolated, single-phase, electrolytic-capacitor-free two-stage DC-AC structure. The structure is composed of a voltage source inverter (VSI), DC-linked by film capacitors, with a dual-active-bridge series-resonant (DABSR) DC-DC converter. High DC-link ripple is allowed and managed by the APD. Hence, electrolytic capacitors are avoided, increasing the converter lifetime. In the proposed approach, the VSI implements the GFM strategy, operating in the four quadrants of the active and reactive power plane. However, the DABSR allows galvanic isolation, average DC-link voltage control, and suppression of the low-frequency ripple on the battery current, minimizing the impact in the battery lifetime. Design criteria are given for the DC-link voltage controller, active-reactive power controllers, inner inverter controllers, and APD technique. The control strategy is validated for vehicle-to-grid and stand-alone vehicle-to-home applications, using hardware-in-the-loop for a 2kW test setup.

Impedance Reshaping for Inherent Harmonics in PMSM Drives With Small DC-Link Capacitor

Sharp <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance peak may enlarge inherent harmonics, dominant harmonics of the supply voltage generated by a three-phase diode rectifier, around the resonance frequency, which will intensify fluctuations of the dc-link voltage, and grid currents in motor drives with small dc-link capacitor. In this article, a novel resonance suppression strategy based on inherent harmonics impedance shaping is proposed specially for three-phase input permanent magnet synchronous motor (PMSM) drives with small dc-link capacitor. Instead of increasing the damping of the whole system for resonance suppression, the motor side power disturbance can be reduced by designing the impedance for inherent harmonics around <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance frequency based on the new model with the consideration of motor side characteristic. For damping current generation, the angle of the virtual admittance is modified to eliminate the influence of the dc-link voltage sampling delay. Experimental results show the effectiveness of the method on a prototype of electrolytic capacitorless PMSM drive.

Grid Current Quality Improvement for Three-Phase Diode Rectifier-Fed Small DC-Link Capacitance IPMSM Drives

In order to improve the grid current quality of the small dc-link capacitance (SDC) motor drives fed by three-phase diode rectifier, a grid current control method based on regulation of the rectifier current sixth harmonic is proposed in this paper. Considering the 120° maximum conduction angle of the rectifier diodes, a 120° rectangular waveform with low total harmonic distortion (THD) is selected as the grid current reference. Based on the relationship between the grid current and the rectifier current, the proposed scheme shapes the grid current into the selected 120° rectangular waveform by regulating the rectifier current sixth harmonic. In this way, the grid current THD of the SDC system is significantly reduced. Since the regulation of the rectifier current harmonic is independent of the speed and motor current control loops, the proposed method avoids the complicated controller and the cumbersome parameter tuning in the grid current control process. The experimental results demonstrate the effectiveness of the proposed method.

Design Analysis of SSD Optimized Speed Controller for BLDC Motor

Brushless Direct Current (BLDC) motor is widely applied for both domestic and industrial applications especially in computer peripheral devices and electric vehicles. This paper introduces BLDC motor design using Social Ski Driver (SSD) optimized speed controller. Better efficiency, high power density, good reliability, less noise &amp; maintenance, and the use of simpler control mechanisms are major benefits of the BLDC motor. Proposed work mainly focuses on torque ripple compensation with speed control at low cost. The use of a small DC link capacitor instead of a bulkier capacitor helps to reduce ripples by using Social-Ski Driver optimized controllers. However, torque reduction with reasonable speed control has not been achieved in existing works. So, the proposed work planned to design an advanced controller with the recent bio-inspired algorithm to control the PWM signal. The proposed work will be implemented in MATLAB Simulink working environment for research analysis. From the implementation result, the proposed work achieves 422 (rad/sec) speed, 0.03(Nm/A) torque constant, and 25 (MW) rated power.

Active Damping Stability Control Method Based on Voltage Compensation for IPMSM Drives with Small DC-Link Capacitor

Active Damping Stability Control Method Based on Voltage Compensation for IPMSM Drives with Small DC-Link Capacitor

A mitigation technique for torque ripple in a brushless DC motor by controlled switching of small DC link capacitor

High performance applications are now days utilizing the brushless DC motor (BLDC) drives due to its ruggedness, compactness, high torque to weight ratio, high dynamic response etc. the feature of square-wave current excitation waveforms in BLDC motor drives allows some major system simplifications for trapezoidal BLDC motors. The developed torque is constant in ideal conditions in this motor when its back emf waveform is of trapezoidal type. Despite this, due to the physical construction of the motor and its settings, torque ripple exists in the output torque and is an undesired phenomenon in the BLDC motor drives and are also linked to the motor's control and driver sides. This paper provides a new way for reducing torque ripple and is simple, compact and cost effective. To prove the correctness of the compensation technique, circuit is modelled and simulations are carried to examine the theoretical performance of the BLDC motor drive. Experiments on a prototype drive were conducted to further validate the theoretical analysis as well as the utility of the proposed technique.

Capacitors Voltage Ripple Complementary Control on Three-Level Boost Fed Single-Phase VSI With Enhanced Power Decoupling Capability

Power decoupling is always a strong desire for single-phase voltage source inverter (VSI) due to the inherent double-line (2ω) frequency ripple caused by the instantaneous power unbalance between dc- and ac-side. The existing solutions either apply a large capacitor or employ a small power converter to compensate it, which inevitably increases the system cost and control complexity. To overcome these drawbacks, this article performs the transient modeling analysis and it reveals that 2ω frequency power component in the converter achieves minimum value when the inductor current ripple is minimized. A novel capacitors' voltage ripple complementary control algorithm based on three-level boost fed single-phase VSI is proposed. By mitigating the 2ω power component from the inductor and redistributing the stored energy between two intermediate series-connected capacitors, the oscillating power is absorbed with notably eliminated input current ripple and significantly reduced dc-link voltage ripple. Thus, the good power quality of both dc- and ac-side is guaranteed. Furthermore, the total capacitance requirement is minimized under the given dc-link ripple tolerance without any more electric stress increment and lifetime reduction. Simulation and experiment results verify the theoretical analysis and proposed control method. It is promising in applications, where both input current ripple is strictly limited and ac output voltage quality is highly required with small dc-link capacitance.

Optimization Design and Control of Single-Stage Single-Phase PV Inverters for MPPT Improvement

Due to the inherent double-frequency (2 f 0) ripple in single-stage single-phase photovoltaic grid-connected inverters, the maximum power point tracking (MPPT) will inevitably be affected. To improve the MPPT performances, a passive LC power decoupling circuit with a robust second-order sliding-mode control (SOSMC) is thus proposed in this article. With the passive LC decoupling path, the double-frequency pulsation on the dc link is effectively cancelled out. Thus, the MPPT accuracy is significantly enhanced, and the utilization of a small dc-link capacitor becomes possible. However, resonance between the LC circuit and the main dc-link capacitor may appear, which can be damped through an active damping method. Additionally, the proposed SOSMC ensures good steady-state, dynamic performance (voltage fluctuation and settling time), and the robustness of the dc-link voltage, which is also beneficial to MPPT control in terms of high accuracy and fast dynamics. The systematic design of SOSMC is presented, and a detailed parameter optimization design of LC decoupling circuit is discussed. Experimental tests are performed on a 2.5-kW single-stage single-phase grid-connected inverter, and the results validate the effectiveness of the proposed strategy.

Discrete-Time DC-Link Voltage and Current Control of a Grid-Connected Inverter with LCL-Filter and Very Small DC-Link Capacitance

The paper presents a controller design for grid-connected inverters (GCI) with very small dc-link capacitance that are coupled to the grid via an LCL filter. The usual controller designs would fail and result in instability. The proposed controller has a cascaded structure with a current controller as inner control loop and an outer dc-link voltage controller. The controller design is performed in discrete time and it is based on a detailed stability analysis of the dc-link voltage controller to determine the controller parameters which guarantee stability for all operating points. The inner loop is a state-feedback current controller that is designed based on the discrete linear-quadratic regulator (DLQR) theory. An additional integral error feedback assures steady-state accuracy of the current control loop. The simulation and experimental results validate performance and stability of proposed controller design.

A Novel SiC-Based Multifunctional Onboard Battery Charger for Plug-In Electric Vehicles

This article proposes a simple and effective method to reduce the bulky capacitor in onboard battery charger (OBC) where low-voltage (LV) battery charging circuit is utilized as an active power decoupling (APD) circuit to filter out the second-order ripple power. When the OBC is connected to the grid to charge the high-voltage (HV) battery, the switches on the primary side of the LV charging circuit are operated as those of an ac-dc converter with APD function. Consequently, small dc-link capacitors can be used instead of large capacitor banks. In the proposed OBC, the switching devices are shared for the ac-dc converter, APD circuit, and primary-side of the LV charger. For a simultaneous charging of the LV and HV batteries, a dc-dc converter is added, which shares the same transformer core and secondary side with the LV charging circuit. So the functions of the OBC are maintained in the proposed topology whereas the volume and cost are decreased by 52.3% and 46.9% compared with the conventional nonisolated OBC, respectively. A 2-kW SiC-based prototype has been designed and tested to verify the validity of the proposed system. The peak efficiencies of the OBC and LV charger are 96.1% and 95.3%, respectively.

Overmodulation Strategy for Electrolytic Capacitorless PMSM Drives: Voltage Distortion Analysis and Boundary Optimization

Permanent magnet synchronous motor (PMSM) drives equipped with slim film capacitors have many advantages, including longer lifetime, smaller volume, and lower cost. However, improving the dc-link voltage utilization rate by the typical overmodulation strategy will cause the distortion of the stator voltage and current due to the dc-link voltage fluctuation. In this article, the influence of the dual-mode overmodulation strategy used in the small dc-link capacitor PMSM drive, including the stator voltage distortion and uncontrollable time for entering the six-step operation, is analyzed. A novel overmodulation strategy named as the optimized voltage boundary-based overmodulation strategy is proposed to reduce the distortion of the stator voltage and current. By switching between the actual dc-link voltage and the fixed dc-link voltage used for space vector pulse width modulation (SVPWM), the performance can be improved in the overmodulation region if the value of the dc-link voltage for SVPWM is selected appropriately. Experimental results on a PMSM drive platform are provided to verify the effectiveness of the proposed strategy.

An Improved DC-Link Series IGBT Chopping Strategy for Brushless DC Motor Drive With Small DC-Link Capacitance

This article proposes an improved DC-link series IGBT chopping strategy for the brushless DC motor (BLDCM) drive equipped with a small DC-link capacitor fed by single-phase AC source. In this strategy, different vector sets are established according to the switching state of the DC-link IGBT and the operation mode of BLDCM. By analyzing the effect of each vector on phase current change rate, a vector selection-based current control scheme is presented. In particular, when the rectifier output voltage is less than the average line voltage of BLDCM, the combined action of vectors with only DC-link IGBT chopping is designed, in order to decrease the converter switching times and reduce the DC-link capacitance at the same time. In addition, the constraint of the DC-link capacitor voltage is analyzed to satisfy the reliable regulation of the motor phase currents, and the calculation method of the DC-link capacitance is given furthermore. The proposed strategy can achieve the smooth operation of the motor with small DC-link capacitance. Meanwhile, the total switching times of the converter are reduced, thereby improving the converter efficiency. The contrastive experimental results verify the correctness of the theories and the effectiveness of the proposed strategy.