DC-link Voltage Control Strategy Research Articles

Fast dynamic DC-link voltage control strategy for dual three-phase PM-assisted synchronous reluctance starter/generator system

Fast dynamic DC-link voltage control strategy for dual three-phase PM-assisted synchronous reluctance starter/generator system

A Phase-Shifting DC-Link Voltage Control Strategy for Parallel Inverters to Suppress Interharmonics in PV Systems

The large-scale installation of PV systems leads to interharmonic problems, which greatly affect the power quality of power system. It has been revealed that the DC-link voltage oscillation caused by the perturbation maximum power point tracking (MPPT) algorithm is one of the main causes of interharmonics. To address this issue, a phase-shifting DC-link voltage control strategy for parallel inverters to suppress interharmonics in PV systems is proposed. In this method, the relationship between interharmonic characteristics and reference DC-link voltage is the basis for suppressing interharmonics. The proposed system contains two parallel inverters whose reference DC-link voltages are antiphase. Therefore, the interharmonic current can be eliminated with each other. Simulations and experiments have been constructed to verify the effectiveness of the proposed interharmonic suppression strategy.

Dynamic control strategy for bi-directional DC/DC converters to suppress the dc-link voltage fluctuation in motor driver systems

This paper presents an improved dc-link voltage control strategy for bi-directional DC/DC converter to reduce the fluctuation of dc-link voltage. The bi-directional DC/DC converter is the top widely-adopted topology for machine drives. However, a wild dc-link voltage fluctuation may cause the overvoltage accident if the load is suddenly altered. Therefore, a novel energy-balanced dc-link voltage control scheme is presented. Through the analysis of the instantaneous energy balance of the whole system, this paper draws a conclusion that the energy stored in the dc-link capacitor will fluctuate in the dynamic process. Then, when the output power changes, the influence of the proposed control strategy on the dc-link voltage fluctuation is analyzed. Moreover, some deadbeat predictive control method has been applied within the current inner loop to improve systematically dynamic response ability. As the energy consumption can be compensated, the fluctuation of dc-link voltage is constrained in sudden load change. Small-signal model has been presented to analyze dynamic performances. As a result, experimental outcomes verify that above method is equipped with superior dc-link voltage fluctuation suppression capability, and the current overshoot is reduced and dynamic performance is improved. What is more, the controller design is simple to realize and has a bright application prospect.

A PV-DSTATCOM With Adaptive DC-Link Voltage for Grid Integration and PQ Enhancement

A photovoltaic based distribution static compensator (PV-DSTATCOM) is one of the leading approaches to deal with the energy demand shortage and power quality issues in the modern power system. This article achieves the improved performance of PV-DSTATCOM to establish the grid integration and power quality enhancement. In the proposed system, during the PV-DSTATCOM state, photovoltaic array power is used to maintain the dc-link voltage by extracting the maximum power based on the perturb and observe algorithm and supplying the excess power into the grid. During the DSTATCOM state, a reference dc-link voltage control scheme is proposed based on the connected load on the point of common coupling, which thus regulates the dc-link voltage and enhances the PV-DSTATCOM performance. The control signals for the voltage-source inverter are generated based on the modified synchronous reference frame control scheme. The effectuality of the proposed system is validated by the MATLAB simulation results. A hardware prototype is developed to verify the usefulness of the proposed system compared to the control technique in the literature. Finally, the results presented in this article convey how the improved performance of PV-DSTATCOM has been accomplished while guaranteeing power quality improvement and grid integration.

An improved fuzzy logic based DC-link voltage control strategy for smoothing output power of the PMSG-WECS

Direct power smoothing control methods relying on the wind turbine itself have been widely studied to improve wind turbines’ output power quality, and the DC-link voltage control based on the capacitor of the wind power converter is one of them. In this paper, the principle of DC-link capacitor voltage control is studied at first, then an improved time interval DC-link voltage control strategy on the basis of a low-pass filter (LPF) is proposed and compared with existing DC-link voltage power smoothing controls. To further improve the power smoothing effect, the fuzzy logic control is used to adjust the time constant of LPF, and the maximum time constant in the fuzzy logic control is determined through convolution calculation. For the sake of ensuring the system stability, the transfer function of proposed DC-link voltage control is derived to determine proper parameters of voltage loop. The proposed fuzzy logic-based DC-link power smoothing strategy is verified through effective simulation results of the permanent magnet synchronous generator wind energy conversion system (PMSG-WECS).

Control and Protection Scheme for DC-link of Solar PV based Microgrid

This paper presents the integrated DC-link voltage control and protection scheme for the DC-link of the microgrid. The proposed integrated scheme is designed to regulate the DC-link voltage during AC side faults or load switching conditions, and protect the DC-link when short-circuit fault occurs at DC-link. To test the proposed scheme, the microgrid test system is designed according to the IEEE 1547 standard in PSCAD/EMTDC software environment. Then the developed microgrid is tested under different fault conditions to verify the effectiveness of the proposed scheme. Results show that the proposed control and protection scheme is able to maintain the DC-link voltage under fault on AC or DC side in grid-connected and islanding modes of operation. The proposed scheme has the ability to ensure the voltage stability and protection of the DC-link of the microgrid under various operating conditions and faults.

Mpc Based Dc-Link Voltage Control Scheme with Improved Lvrt Ability in Grid Connected Pmsg System

Mpc Based Dc-Link Voltage Control Scheme with Improved Lvrt Ability in Grid Connected Pmsg System

Design of a GaN Totem-Pole PFC Converter Using DC-Link Voltage Control Strategy for Data Center Applications

In today’s power industry, a compact and highly efficient power converter is the main component for server power applications. The objective of this paper is to propose a totem-pole power factor correction (PFC) converter with DC-link voltage control strategies for data center applications. Gallium Nitride High Electron Mobility Transistors (GaN HEMTs) are also used to increase power density and conversion efficiency without the reverse recovery loss. With the derived equations of the converter loss, the dc-bus voltage control strategy is proposed to improve the conversion efficiency. Furthermore, this paper proposes the hold-up time extension method to increase the DC bus voltage under heavy load conditions. The reduction of the DC link capacitor capacitance is achievable, and the power factor can be improved in a wide range. A 2.9-kW GaN totem-pole PFC prototype is developed and fabricated to verify this paper’s theoretical analysis. As demonstrated in the prototype’s experimental results, the tested peak efficiency is 98.5% and the tested total harmonic distortion (THD) is less than 3%.

High voltage gain bi‐directional Z‐source inverters with dual‐loop feed‐forward peak DC‐link voltage compensation for fuel cell vehicles

High boost inverter is an essential part to interface the fuel cell stack and traction motor for fuel cell vehicles (FCVs). This paper proposes two novel high voltage gain bi-directional Quasi-ZSIs (QZSI) with new active switched inductor cells for FCVs application. The disadvantages of low voltage boost ratio, large start up current, unfavourable mode operations and unidirectional power flow in conventional Z-source inverter (ZSI) are eliminated. The proposed Z-source inverters are combined with active switched inductor cells to achieve a higher voltage gain and lower voltage stress over capacitors, which can be widely applied in energy storage systems. A small signal model is derived by dynamic analysis. In order to achieve a constant peak dc-link voltage, a dual-loop feed-forward peak dc-link voltage control strategy for the proposed QZSI is introduced in this paper. Simulation and experiment waveforms are presented to verify the theoretic analysis of the designed QZSIs and the proposed control strategy.

Generalized Predictive dc-Link Voltage Control for Grid-Connected Converter

The main function of the grid-connected converter in many applications is to control the dc-link voltage with high performance, i.e., strong disturbance rejection capability and good dynamic response. Take the grid-connected pulsewidth modulation (PWM) rectifier of a motor drive system as an example, good disturbance rejection capability is essential for the dc-link voltage control to address the varying loads on the motor side, and the dynamic process of the dc-link voltage control is preferred to be fast and overshoot-free, so as to adaptively adjust the dc-link voltage according to the motor speed and reduce the switching losses. However, the performance of the conventional proportional-integral (PI)-based dc-link voltage control is not always satisfying and can be further improved. In this article, the generalized predictive control (GPC) method is applied to the dc-link voltage control of a grid-connected converter for the first time, which can provide both good disturbance rejection capability and satisfying dynamic performance. Moreover, stability analysis of the proposed GPC-based dc-link voltage control strategy is theoretically studied, and a parameter tuning guideline is provided. The effectiveness and advantages of the proposed method are validated with experimental results.

A Comprehensive Review of Control Strategies to Overcome Challenges During LVRT in PV Systems

Due to the high penetration of grid-connected photovoltaic (GCPV) systems, the network operators are regularly updating the grid codes to ensure that the operation of GCPV systems will assist in maintaining grid stability. Among these, low-voltage-ride-through (LVRT) is an essential attribute of PV inverters that allows them to remain connected with the grid during short-term disturbances in the grid voltage. Hence, PV inverters are equipped with control strategies that secure their smooth operation through this ride-through period as per the specified grid code. However, during the injection of reactive power under LVRT condition, various challenges have been observed, such as inverter overcurrent, unbalance phase voltages at the point of common coupling (PCC), overvoltage in healthy phases, oscillations in active, reactive power and dc-link voltage, distortion in injected currents and poor dynamic response of the system. Several strategies are found in the literature to overcome these challenges associated with LVRT. This paper critically reviews the recent challenges and the associated strategies under LVRT conditions in GCPV inverters. The drawbacks associated with the conventional current control strategies are investigated in MATLAB/Simulink environment. The advanced LVRT control strategies are categorized and analyzed under different types of grid faults. The work categorizes the state-of-the-art LVRT techniques on the basis of the synchronization methods, current injection techniques and dc-link voltage control strategies. It is found that state-of-the-art control strategies like OVSS/OCCIDGS provides improved voltage support and current limitation, which results in smooth LVRT operation by injecting currents of enhanced power quality.

DC-Link Voltage Research of Photovoltaic Grid-Connected Inverter Using Improved Active Disturbance Rejection Control

In this paper, a robust DC-link voltage control scheme is proposed to improve the tolerance of photovoltaic (PV) grid-connected inverter to disturbances. The sensitive characteristic of the DC-link voltage complicates the dynamics of the inverter control system and limits its overall performance, especially when uncertain disturbances are considered. To cope with this issue, a voltage controller based on the linear active disturbance rejection control (LADRC) is designed. By exploring the principle of deviation regulation, an improved linear extended state observer (LESO) is established to ensure that the total disturbance can be estimated in a relatively timely manner. The linear state error feedback (LSEF) control law is generated to compensate for the total disturbance, which reduces the plant to approximate the canonical cascaded double integrator. The stability and disturbance rejection capability of the improved LADRC are further analyzed in frequency domain. Finally, theoretical analysis and experimental results confirm the feasibility of the proposed control scheme.

MPC-based DC-link voltage control for enhanced high-voltage ride-through of offshore DFIG wind turbine

To deal with the DC-link overvoltage during high-voltage ride-through (HVRT) of the wind turbine, a coordinated DC-link voltage control (CDVC) scheme is proposed for enhancing the HVRT performance of offshore doubly-fed induction generator (DFIG) wind turbines equipped with the supercapacitor energy storage system (SESS). This scheme is formulated as a two-stage control problem depending on the depth of grid voltage swell, which can prevent damaging the converter resulting from the insufficient reactive support in the first stage, and achieve efficient coordinated control under various magnitude and timescale of grid voltage swell. In the first stage, considering the dynamic behavior of the DFIG during HVRT, a voltage-dependent reactive current control (VRCC) scheme is designed to regulate the current reference of the wind turbine. The first stage aims to supply fast reactive current support without the DC chopper. In the second stage, once the DC-link voltage exceeds the predefined threshold, a coordinated control scheme considering the SESS and the wind turbine operation is implemented using model predictive control (MPC), aiming to regulate the excessive active power by tracking the current reference from the first stage. The proposed control scheme is validated in PSCAD/EMTDC under various operational scenarios. Case study results show that the proposed scheme can effectively mitigate the DC-link overvoltage and enhance HVRT capability under asymmetrical and symmetrical voltage swells.

DC‐link voltage control strategy of Z‐source inverter for high‐speed permanent magnet motor

In order to widen the flux-weakening range of motors, this study proposed a DC-link voltage control strategy for high-speed permanent magnet motor drive systems powered by Z-source inverter. In this strategy, the DC-link voltage, also known as the output voltage of the impedance network, varies with the inverter output voltage and remains optimal at all times, whether in steady state or transient state. As for the shoot-through duty ratio and the modulation index, the two main control variables in the Z-source inverter are under unified control to ensure the stability of the system, while achieving fast tracking and reducing the loss. In addition, a new sliding mode control system based on the indirect control of the capacitor voltage is used to control the DC-link voltage to suppress the system fluctuation caused by the change of the given value or the motor load. Besides, various conventional voltage Z-source inverter pulse width modulation strategies can be applied to this technology. Simulations and experiments verified the effectiveness of the proposed strategy.

A Single Stage Common Ground Three-Level PV Inverter With Integrated Power Decoupling

In this paper, a T-type common ground transformer-less single phase inverter with dynamic swing of the dc-link voltage is presented for photovoltaic (PV) application. The topology is a combination of a bi-directional, partial-power-processing boost stage and an asymmetric half-bridge inverter stage along with a T-branch. It takes advantage of the three-level switching states with reduced voltage stress on the main switches to achieve lower switching loss and almost one-half the inductor current ripple w.r.t. two level implementation. The double line frequency power decoupling is addressed by a dynamic dc-link approach, which allows a large swing of the dc-link to reduce the decoupling capacitor requirement, enabling an all-film capacitor implementation. This topology also significantly reduces the high-frequency capacitive coupled ground current by directly connecting the PV negative terminal to the grid neutral. Moreover, an adaptive dc-link voltage control scheme that optimally changes the average value of the dc-link voltage as the operating conditions (load and power factor) vary, has been proposed and thoroughly investigated from the perspective of better utilization of passive components and further reduction of switching losses. A SiC MOSFETs-based 1 kVA laboratory prototype has been built to validate the converter's operation at 200 V dc nominal input and 120 V/60 Hz ac nominal output with a wide range of power factor and load operations. Extensive experimental results validate the superior performance of the topology with the adaptive dc-link voltage control implementation showing a peak efficiency of 98.22% and a CEC efficiency of 98.03% at 50 kHz switching frequency.

Adaptive dc-link voltage control strategy to increase PV inverter lifetime

This work proposes an adaptive dc-link voltage strategy applied to a double-stage three-phase grid-connected PV inverter, in order to decrease the power devices and capacitors thermal stress, and increase the system-level reliability as a consequence. The objective is to reduce the dc-link voltage to the minimum value required to inject power into the grid. A system reliability analysis is made based on mission profiles from Brazil. The results show that the proposed technique has a positive impact on the system reliability, increasing the estimated lifetime by 75% when compared to the traditional fixed dc-link voltage strategy.

The combination of two control strategies for series hybrid electric vehicles

With most countries paying attention to the environment protection, hybrid electric vehicles have become a focus of automobile research and development due to the characteristics of energy saving and low emission. Power follower control strategy &#x0028 PFCS &#x0029 and DC-link voltage control strategy are two sorts of control strategies for series hybrid electric vehicles &#x0028 HEVs &#x0029. Combining those two control strategies is a new idea for control strategy of series hybrid electric vehicles. By tuning essential parameters which are the defined constants under DClink voltage control and under PFCS, the points of minimum mass of equivalent fuel consumption &#x0028 EFC &#x0029 corresponding to a series of variables are marked for worldwide harmonized light vehicles test procedure &#x0028 WLTP &#x0029. The fuel economy of series HEVs with the combination control schemes performs better compared with individual control scheme. The results show the effects of the combination control schemes for series HEVs driving in an urban environment.

DC-Link Voltage Disturbance Rejection Strategy of PWM Rectifiers Based on Reduced-Order LESO

In applications of pulse-width modulation (PWM) rectifiers, the high quality of the DC power is required. The fluctuation of grid voltage and the switching of equipment connected to the DC supply are likely to cause a sudden change in the DC-link voltage, resulting in equipment instability or even damage. Considering the bandwidth of the closed-loop current dynamic, this paper presents a novel DC-link voltage control strategy of PWM rectifiers based on the reduced-order linear extended state observer (RLESO). Using a first-order RLESO to observe and even compensate the model variations caused by grid voltage and DC-link voltage fluctuations or load transients, the proposed method can effectively improve the dynamic performance against grid and load disturbances, as well as for sudden changes in DC-link reference voltage. Combined with frequency domain analysis, this paper theoretically analyzes the sensitivity, stability, and tracking performance of the proposed method, providing a basis for the selection of controller parameters. And finally, simulation and experimental results are presented to demonstrate its validity and the superiority over the traditional PI control strategy.

A 1-MHz Series Resonant DC–DC Converter With a Dual-Mode Rectifier for PV Microinverters

The photovoltaic (PV) output voltage varies over a wide range depending on operating conditions. Thus, the PV-connected converters should be capable of handling a wide input voltage range while maintaining high efficiencies. This paper proposes a new series resonant dc–dc converter for PV microinverter applications. Compared with the conventional series resonant converter, a dual-mode rectifier is configured on the secondary side, which enables a twofold voltage gain range for the proposed converter with a fixed-frequency phase-shift modulation scheme. The zero-voltage switching turn- on and zero-current switching turn- off can be achieved for active switches and diodes, thereby, minimizing the switching losses. Moreover, a variable dc-link voltage control scheme is introduced to the proposed converter, leading to a further efficiency improvement and input-voltage-range extension. The operation principle and essential characteristics (e.g., voltage gain, soft-switching, and root-mean-square current) of the proposed converter are detailed in this paper, and the power loss modeling and design optimization of components are also presented. A 1-MHz 250-W converter prototype with an input voltage range of 17–43 V is built and tested to verify the feasibility of the proposed converter.

A Simplified Minimum DC-Link Voltage Control Strategy for Shunt Active Power Filters

The active power filter (APF) is a popular electrical device to eliminate harmonics in power systems. The rational design and effective control of DC-link capacitor voltage are important for implementing APF functions. In this study, the influences from the DC-link voltage on the APF compensating current characteristic and compensation performance are analyzed, and the reason to maintain DC-link voltage at a minimum value is investigated. On this basis, a simplified minimum DC-link voltage control strategy for APF is proposed. Compared with the existing DC-link voltage control strategies, the minimum DC-link voltage value in proposed strategy is only determined by the grid voltage and modulation ratio, reducing the calculation burden and the implementation difficulty in application, avoiding the interference from external parameters on the compensation effect. Additionally, the reference DC-link voltage varies at different values according to the grid voltage and modulation ratio. A shunt APF prototype is established and the experimental results verify the correctness and effectiveness of the analysis and proposed strategy.