Peak Dc-link Voltage Research Articles

A Comprehensive Small-Signal Model Formulation and Analysis for the Quasi-Y Impedance-Source Inverter

This paper presents a detailed derivation of the small-signal model and components design considerations for the Quasi-Y-Source inverter. The design methodology is based on the converter steady-state operation, considering the impedance network inductor and capacitor voltage and charge balances, respectively. Moreover, the additional design criteria for component selection, considering control constraints and performance compromise, are given by parametric variation analysis based on converter dynamic response. The small-signal model and transfer functions are obtained using a state-space averaged model, including converter non-ideal characteristics given by equivalent-series resistances (ESR), which makes possible the proposition of different control strategies, using both single or multi-loop schemes. To demonstrate the usefulness of the proposed small-signal model, a DSP-based single-loop type-II PI control strategy is used in which the peak DC-link voltage is indirectly controlled through the measurement of the impedance network capacitor voltage. The controller and converter performances are verified with simulation and experimental results and successfully confirm the validity of the proposed dynamic model. Finally, the obtained results are validated with a built small-scale three-phase/three-wire inverter prototype.

Preview repetitive learning control for islanded microgrids based on equivalent input disturbance approach

Due to the rapid drop in peak dc-link voltage (PDV) caused by environmental changes, as well as the majority of loads being naturally nonlinear, the output voltage of the microgrid inverters is always distorted. To boost the PDV at a low cost and reduce the total harmonic distortion (THD) of output voltage, a strategy is proposed in this paper to synchronously control ac- and dc-sides voltage. A double closed-loop PI controller is used to indirectly control the PDV of Z-source inverter (ZSI). Sinusoidal reference voltage generated by the primary power layer is merged to construct an augmented dynamic system, and an integrated optimal controller on the ac-side is obtained. Preview repetitive control (PRC) and error compensation can improve output voltage tracking accuracy. The state feedback component effectively suppresses the resonance of the filter, lowering the system’s sensitivity to parameter perturbation. Combined with this, the equivalent input disturbance (EID) is used to eliminate the potential interference in microgrids, which can shorten the recovery time of the system. Both simulations and experiments are provided to demonstrate the better performance of the proposed approach in comparison to other different repetitive controllers.

Operation and Control of a Quasi Z-source Converter in a Renewable Hybrid Microgrid

The power sharing need and operational reliability of a renewable hybrid microgrid are addressed in this study. A hybrid microgrid allows for the flexible incorporation of renewable energy sources, overcoming the limitations of AC and DC microgrids in terms of conversion losses and efficiency. To ensure optimal system performance, an interlinking converter (IC) is necessary for the seamless transmission of electric power between the two subgrids while keeping a stable DC bus voltage and appropriate AC sub-grid frequency. In this study, a Quasi Zsource converter (qZSC) with integrated boost capability is introduced as an IC in a PV-Wind based hybrid microgrid. Also, an adaptive dual loop based-PI (ADL-PI) control is proposed which maintains a constant peak DC-link voltage and supports maximum power point tracking while improving the system's overall stability. The proposed system and control approach are assessed using MATLAB/Simulink, and the results indicate its efficacy under various scenarios.

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.

Indirect closed loop control of quasi-Z-source inverter for standalone solar PV-based energy conversion system

Nowadays impedance source inverter (ZSI) offers an attractive solution to renewable energy sources with low output, can buck/boost the output voltage by utilising shoot-through pulses. The presence of right half plane zero in control transfer function makes the closed loop control complex, an undershoot is visible in the capacitor voltage. This paper presents an indirect control method of peak dc link voltage for a quasi-Z-source (qZS) inverter connected system. Small signal model for dc and ac sides are elaborated, optimum parameters for impedance network and controller are designed by analysing various frequency and time responses. The control methodology uses a single loop PI controller at dc side, decoupled feed forward control at ac side and parasitic resistances are considered for dynamic analysis. Results depicts a fast reference tracking, without compromising stability, harmonic attenuation, and transient response. A stable controller response validates the presented design and control methodology.

Indirect closed loop control of quasi-Z-source inverter for standalone solar PV-based energy conversion system

Nowadays impedance source inverter (ZSI) offers an attractive solution to renewable energy sources with low output, can buck/boost the output voltage by utilising shoot-through pulses. The presence of right half plane zero in control transfer function makes the closed loop control complex, an undershoot is visible in the capacitor voltage. This paper presents an indirect control method of peak dc link voltage for a quasi-Z-source (qZS) inverter connected system. Small signal model for dc and ac sides are elaborated, optimum parameters for impedance network and controller are designed by analysing various frequency and time responses. The control methodology uses a single loop PI controller at dc side, decoupled feed forward control at ac side and parasitic resistances are considered for dynamic analysis. Results depicts a fast reference tracking, without compromising stability, harmonic attenuation, and transient response. A stable controller response validates the presented design and control methodology.

Investigation of three‐level NPC‐q Z S inverter‐based grid‐connected renewable energy system

The neutral point clamped quasi-Z-source (NPC-qZS) inverter is poised to become a potential candidate for renewable energy applications because it yields a continuous input current and voltage boost. In this study, the closed-loop control of grid-tied three-phase (3- ϕ ) NPC-qZS inverter, fed with renewable energy sources, is proposed for the first time. A dynamic model has been developed to accurately design the control strategy. The proposed strategy includes the control of grid-tied current and the peak dc-link voltage (PDV). The control of grid-tied current is achieved through a damped-second-order-generalised integrator. The PDV is estimated indirectly from the voltages of qZS network capacitors and is regulated by an integral-double-lead controller. Two modified modulation techniques based on phase-opposite disposition and in-phase disposition are proposed to yield shoot through by injecting 3rd harmonics for maximum constant boost control. A comparison is drawn between the performance of the proposed controller and sliding-mode controller on the dc side. The controller design and system performance are validated through real-time simulation and experimentation on a practical setup in the laboratory.

A novel strategy for indirect control of peak dc-link voltage of grid-connected qZS inverter fed through renewable energy sources

This paper presents a novel strategy to indirectly control the peak dc-link voltage (PDV) of grid-connected quasi-Z-source (qZS) inverter supplied with renewable energy sources (RES). The method is directed to indirectly determine and regulate the pulsating PDV through the qZS network capacitor voltages. The small signal model is developed by representing ac- and dc-sides separately. The ac-side control is designed with higher bandwidth to avoid interference from dc-side. The dc-side control utilizes shoot-through duty ratio to PDV transfer function and controller is designed to minimize the effect of its right-half-plane zero (RHPZ) characteristics. The gating signals are realized through maximum constant boost control in conjunction with one-sixth of third harmonic injection. The strategy is implemented through MATLAB/Simulink and is verified experimentally with real-time simulations (RTSs) in OPAL-RT.

Speed Control of Three Phase Induction Motor Using Universal Bridge and PID Controller

Speed control technique are generally essential in adjustable speed drive system. This system requires variable voltage and frequency supply which is obtained from a three phase voltage source inverter. This paper presents the speed control of induction motor fed by a three phase voltage source inverter using pulse width modulation method and universal bridge. To control the peak dc link voltage of voltage source inverter, a PID controller was designed. The performance analysis of open loop and closed loop speed control system is carried out in Matlab/Simulink. The simulation result shows that the speed controller has a good dynamic response and can control the induction motor successfully with a better performance.

TOIL and damped-SOGI control of quasi-Z-source inverter based grid-connected renewable-system

A strategy is proposed in this paper to indirectly control the peak dc-link voltage of quasi-Z-source (qZS) inverter fed grid-connected renewable-system by sensing the voltages of qZS network capacitors. The ac- and dc-sides are modeled separately and the crossover frequency of ac-side control loop is kept high to avoid clashes with the dc-side. A third-order-integral-lead (TOIL) controller is realized to regulate peak dc-link voltage and minimize the non-minimum phase characteristic effect of shoot-through duty-ratio to peak dc-link voltage transfer function. A damped-second-order-generalized-integrator (SOGI) offering high power frequency gain is used to control the ac-side current and attain zero steady-state error. The effect of time-delay in control is also analyzed. The performance of the proposed TOIL and damped-SOGI controllers is compared with other designed linear and sliding mode controllers. The system is investigated using MATLAB/Simulink and validated through hardware-in-the-loop (HIL) real-time simulations in OPAL-RT.

Improved Space Vector Modulation of Quasi Z-Source Inverter to Suppress DC-Link Voltage Sag

The three traditional strategies ZSVM1, ZSVM2, and ZSVM6 have been commonly used to control the quasi Z-source inverter (qZSI). However, there is a serious problem that the dc-link voltage of the qZSI drops under light load, leading to the distortion of the output voltage and current of the inverter. The peak dc-link voltage also becomes much higher than its reference value, endangering the safety of the inverter and load. This paper proposes an improved SVM, namely M-ZSVM1, to suppress the dc-link voltage sag under a light load. Through analyzing the reason, the harm, and the influence factors of the dc-link voltage sag, the diode current interruption is seen as the cause of the dc-link voltage sag. Therefore, an asymmetric shoot-through state distribution method is presented to achieve the minimum current ripple, which can increase the diode current. The qZSI can work properly without the dc-link voltage sag under wide load range, improving the safety and reliability of the qZSI. Moreover, other improved ZSI topologies can also be controlled by the proposed strategy to suppress the dc-link voltage sag.

A Novel Quasi-Z Source Cascaded Multilevel Photovoltaic Power System Applied to Smart Microgrid

A novel Quasi-Z source (QZS) cascaded multilevel inverter (CMI) (QZS-CMI) based photovoltaic (PV) power system applied to smart microgrid is proposed in this paper. The novel QZS impedance network has strong boost ability. Each PV panel connects to a QZS inverter (QZSI) to form a power generation module. By establishing an analytical model of each QZSI module to design reasonable parameters of the novel QZS impedance network, it can limit the second-harmonic (2) ripples. Each QZSI module has an independent DC-link peak voltage control with phase-shifted pulse-width-amplitude modulation (PS-PWAM), so the novel QZS-CMI’s power loss is reduced. The simulation results verify the feasibility of the control strategy. The proposed novel QZS-CMI provides an effective method for the realization of new energy generation.

Performance Metric of Z Source CHB Multilevel Inverter FED IM for Selective Harmonic Elimination and THD Reduction

This paper focuses on a Z source cascaded multilevel inverter which is designed to minimize harmonics in the output voltage. A balanced dc-link peak voltage can be achieved. The power generation module is built by PV panels which are connected to Z-Source Cascade H-bridge inverter. Cascaded multilevel inverter can achieve the distributed maximum power point tracking to increase the system efficiency and achieve high voltage/high power grid tie without a transformer. This paper analyzes the different PWM switching scheme and the operating states of a ZSI module and comparison is made with different PWM and total harmonic distortion of various PWM schemes.

Fuel Cell Fed Induction Motor Speed Control Through Z Source Inverter

This paper presents the Z- source inverter feeding to an Induction motor (IM). This Z-source inverter is also be used to boost up the available low voltage DC supply from the fuel cell. This paper has been proposed the speed control of fuel cell fed induction motor through z source inverter. The speed control of an induction motor is a highly efficient this can be used in numerous adjustable speed applications. To achieve transient performance, the peak DC link voltage is employed, which improves rejection of disturbance. SVPWM is used in switching algorithm. The closed loop SVPWM control technique of an induction motor is shown. This technique is widely used in industry. The performance of the proposed speed control method is verified through MATLAB/simulation. The simulation results of proposed scheme present good dynamic and steady state performance over the traditional voltage source inverter fed induction motor drive.

An Effective Control Method for Three-Phase Quasi-Z-Source Cascaded Multilevel Inverter Based Grid-Tie Photovoltaic Power System

The quasi-Z-source cascaded multilevel inverter (qZS-CMI) presented many advantages over conventional CMI when applied in photovoltaic (PV) power systems. For example, qZS-CMI provides the balanced dc-link voltage and voltage boost ability, saves one-third modules, etc. However, current research studies only disclosed control of single-phase qZS-CMI-based PV power systems, and there was no literature related to control of three-phase qZS-CMI-based PV power systems. In this paper, for the first time, three-phase qZS-CMI's control is proposed and demonstrated for application to PV power systems. The models of PV-panel-fed qZS H-bridge module and qZS-CMI-based PV power system are built to accurately design control algorithms for each module and the whole system. The proposed control method includes the distributed maximum power point tracking for each module, dc-link peak voltage balance control for all modules, and grid-tie control for the whole system; moreover, a new multilevel space vector modulation method is proposed for the three-phase qZS-CMI. Simulation and experimental results on a test bench with a three-phase seven-level qZS-CMI-based PV power system verify the proposed control and modulation methods.

Modelling and controller design of quasi‐Z‐source cascaded multilevel inverter‐based three‐phase grid‐tie photovoltaic power system

Quasi-Z source cascaded multilevel inverter (qZS-CMI) is an emerging topology applied to photovoltaic (PV) power system. It can overcome disadvantages of conventional CMI-based PV power system, because of achieving the balanced dc-link voltage through using its boost ability, and saving one-third modules. At present, there was not literature to disclose the modelling and controller design for qZS-CMI-based three-phase grid-tie PV power system. In this study, a control scheme for three-phase qZS-CMI-based grid-tie PV power system is proposed, where distributed maximum power point tracking (MPPT) and constant dc-link peak voltage are achieved for all qZS H-bridge inverter (qZS-HBI)-based PV modules, with grid-injected power in unity power factor. The detailed controller parameter design is demonstrated by using Bode plots and the built models of qZS-HBI-based PV module and whole system. A test bench of 7-level three-phase qZS-CMI-based PV power system is built. Simulation and experimental results validate the proposed control scheme and design method.

Modeling, Impedance Design, and Efficiency Analysis of Quasi- <inline-formula> <tex-math notation="TeX">$Z$</tex-math></inline-formula> Source Module in Cascaded Multilevel Photovoltaic Power System

The quasi-Z source (qZS) cascaded multilevel inverter (CMI) (qZS-CMI) presents attractive advantages in application to photovoltaic (PV) power system. Each PV panel connects to an H-bridge qZS inverter (qZSI) to form a power generation module. The distributed maximum power point tracking and all modules' dc-link peak voltage balance can be achieved. However, it is the same with the conventional CMI that the second-harmonic (2ω) voltage and current ripples exist in each qZSI module. It is crucial for a qZS-CMI to design the reasonable qZS network parameters to limit the ripples within a desired range. This paper proposes an analytic model to accurately calculate the 2ω voltage and current ripples of each qZSI module. A qZS impedance design method based on the built model is proposed to limit the 2ω ripples of dc-link voltage and inductor current. Simulated and experimental results through using the designed 1.5-kW prototype validate the proposed analytic model and the design method. Furthermore, this paper analyzes all of the operating states for a qZSI module and calculates the power loss. The measured efficiency from the prototype verifies the theoretical calculation, and the qZS-CMI-based grid-tie PV power system is tested in practical.

System design of series Z‐source inverter with feedforward and space vector pulse‐width modulation control strategy

For Z-source inverter (ZSI), the peak DC-link voltage is the actual voltage fed to the inversion stage. Controlling the peak DC-link voltage at the constant level can effectively decrease the voltage stress and simplify the design process of the inversion stage. By adopting input feedforward control, the constant peak DC-link voltage can be achieved. The feedback control of the peak output voltage is utilised to obtain the constant output without steady-stage error under load variation. Both the peak DC-link voltage and ac output is controlled to a desired level under different input and load condition. A prototype is built in the lab, and detailed design procedure of the ZSI with space vector pulse-width modulation scheme is given. Simulation and experimental results are presented to demonstrate the feasibility of the proposed control strategy and parameters design method.

Novel Energy Stored Single-Stage Photovoltaic Power System With Constant DC-Link Peak Voltage

The quasi-Z source inverter (qZSI) with battery can balance the stochastic fluctuations of photovoltaic (PV) power injected to the grid/load, but its existing topology has a power limitation due to the wide range of discontinuous conduction mode during battery discharge. For an energy stored qZSI, traditional control methods cannot ensure a constant dc-link peak voltage because of battery's voltage clamp. This paper proposes a novel energy stored qZSI-based PV power system with constant dc-link peak voltage to overcome the above demerits. The new topology of energy stored qZSI is employed to improve the power compensation ability of existing topology, new constant dc-link peak voltage control and load related maximum power point tracking are proposed, and the whole system is analyzed in detail. Experimental results verify the theoretical analysis and the proposed energy stored qZSI-based PV power system.

A Comparative Study of Control Methods for Induction Motor and High Performance Z-source Inverter

Design studies of the most suitable controller for the speed of induction motor (SIM) and peak DC-link voltage (PDV) of high performance z-source inverter (HP-ZSI) greatly affects performance of hybrid electric vehicles. This paper is to give comprehensive analyses comparison and evaluations of the different control techniques as PI controller, self-tuning fuzzy PI controller (SFP) and genetic algorithms optimal tuning gains of the PI controller for controlling the SIM based on criteria of the integral of the absolute value of speed error. With control PDV, this paper also presents comparisons of the different techniques as PI controller, fuzzy logic controller, SFP based on observation of its response and total harmonic distortion of current. All methods are applied to the closed loop of the SIM which relies on direct torque control combined with modified space vector modulation and closed loop of PDV in HP-ZSI. These methods are verified by Matlab software. DOI: http://dx.doi.org/10.11591/telkomnika.v11i6.2445 Full Text: PDF