Dongsen Sun

An Energy-Stored Quasi-Z-Source Inverter for Application to Photovoltaic Power System

The quasi-Z-source inverter (qZSI) with battery operation 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. This paper proposes a new topology of the energy-stored qZSI to overcome this disadvantage. The operating characteristic of the proposed solution is analyzed in detail and compared to that of the existing topology. Two strategies are proposed with the related design principles to control the new energy-stored qZSI when applied to the PV power system. They can control the inverter output power, track the PV panels maximum power point, and manage the battery power, simultaneously. The voltage boost and inversion, and energy storage are integrated in a single-stage inverter. An experimental prototype is built to test the proposed circuit and the two discussed control methods. The obtained results verify the theoretical analysis and prove the effectiveness of the proposed control of the inverters input and output powers and battery power regardless of the charging or discharging situation. A real PV panel is used in the grid-tie test of the proposed energy-stored qZSI, which demonstrates three operational modes suitable for application in the PV power system.

An Energy Stored Quasi-Z-Source Cascade Multilevel Inverter-Based Photovoltaic Power Generation System

This paper proposes an energy stored quasi-Z source (qZS) cascaded multilevel inverter (ES-qZS-CMI) based photovoltaic (PV) power generation system. The system combines advantages of both the qZS inverter and the cascaded multilevel inverter; moreover, the system uses a battery in each module to balance the stochastic fluctuations of PV power injected to the grid. This paper also proposes an effective control scheme for the ES-qZS-CMI based PV system, using which the system can achieve the distributed maximum power point track (MPPT) for each PV panel, balance the power between different modules, and provide the desired power for the grid. Simulation and experimental results verify the proposed system and the control scheme.

A new grid-connected PV system based on cascaded H-bridge quasi-Z source inverter

A new scheme for grid-connected photovoltaic (PV) interface by combination of a quasi-Z source inverter (qZSI) into cascaded H-bridge (CHB) is proposed in this paper. The proposed scheme enables PV string voltage boost to a higher level, and solves the imbalance problem of DC-link voltage in traditional CHB inverters. A multilevel voltage waveform of inverter output is generated by an improved phase shifted sinusoidal pulse width modulation (PS-SPWM) algorithm, which introduces shoot-through states into the conventional zero states to control qZS-CHB module. The effective control schemes are proposed to regulate the maximum power point tracking (MPPT) of each string, and control the DC-link voltage of each H-bridge, respectively. Grid injected power is controlled corresponding to the proportionality factors of each PV string output power. A 1.5 kW system is built in MATLAB/SIMULINK, and the simulation results verify the proposed novel multilevel PV interface inverter and its control principles.

Comprehensive Modeling of Single-Phase Quasi-Z-Source Photovoltaic Inverter to Investigate Low-Frequency Voltage and Current Ripple

The second harmonic (2ω) power ripple of single-phase quasi-Z-source (qZS) photovoltaic (PV) inverter highly affects the whole systems design and performance. The topologys 2ω ripple model is very important to analyze qZS PV inverters 2ω voltage and current ripple. The existing models did not consider the PV-panel dynamic and terminal capacitors, which causes the theoretical results apart from the truth. In this paper, a comprehensive modeling for single-phase qZS-PV inverter is proposed, where the 2ω ripple model of the qZS-PV inverter system with a real PV source is established and discussed without and with a PV terminal capacitor. The influences from qZS inductance and capacitance, and PV-panel terminal capacitance to the 2ω voltage and current ripple are investigated using the built model. The system parameter design method is proposed to mitigate this ripple. Simulation and experimental results validate the proposed 2ω ripple model and parameter design method.

Grid-connected wind farm power control using VRB-based energy storage system

To improve the power quality and stability of the grid-connected wind farm, and regulate the grid-connected power effectively, a new type of environmentally-friendly vanadium redox flow battery (VRB) based energy storage system (ESS) with many advantages are added at the exit of wind farm. A dynamic mathematic model of VRB based on the equivalent circuit is built. A bi-directional AC/DC converter is used to achieve the power conversion of VRB-based ESS and its corresponding control strategy is developed. The simulation model of the grid-connected wind farm with VRB-based ESS is established. The given wind speed in this paper is used for an example to validate the scheme, the simulated results show that the output active power of wind farm are effectively smoothed and a certain amount of reactive power support can be provided for the grid and the operating performance of grid-connected wind farm is well improved by the VRB-based ESS. The good charging-discharging performances of the VRB are also verified by simulated results.

Winding design for pole-phase modulation of induction machines

Induction machines with pole-phase modulation (PPM) can extend speed / torque capabilities for applications in integrated starter/generator and hybrid electric vehicles. In this paper, a general winding design rule for the PPM of induction machines is proposed. A prototype is used to verify the proposed method and the feasibility of the designed pole-changing winding. Besides, the characteristics of three different structure machines — conventional winding machine, toroidal winding machine and dual-rotor torodial winding machine operated in the same mode are compared by using the finite element software JMAG-studio. The results show that both conventional winding machine and dual-rotor torodial winding machine present good performances. Moreover, conventional winding machine has many advantages such as a simple structure, so its experimental prototype is designed and manufactured for next control work.

Impedance design of quasi-Z source network to limit double fundamental frequency voltage and current ripples in single-phase quasi-Z source inverter

This paper proposes an analytic model to calculate the double fundamental frequency (2ω) voltage and current ripples for single-phase quasi-Z-source inverter (qZSI). The model enables the exact calculation of the 2 Ω components of the inductor current and the capacitor voltage, which is crucial for designing a single-phase qZSI system. A guideline for selecting the capacitance and inductance in quasi-Z-source (qZS) network to limit both the dc-link voltage and input current 2ω ripples within a tolerable range is presented. Three cases are tested to verify the proposed analytic model and the design method by using simulation and experimental results. The identical analytic calculation result, the simulation result, and the experimental result validate the analytic model and the design method.

Winding Design, Modeling, and Control for Pole-Phase Modulation Induction Motors

A general winding design rule for the pole-phase modulation (PPM) induction machine is proposed, and three different structures, such as conventional winding machine, toroidal winding machine, and dual-rotor toroidal winding machine, are compared. The results verify advantages of the conventional winding machine over the others in application to the PPM. A uniform model for the conventional winding-based PPM induction machine, including inductance matrices, voltages, flux linkages, mechanical dynamics, and torque equation, are deduced by employing the winding distributed function. A prototype validates the feasibility of the designed pole-changing winding and the built model, which is suitable for operation in different poles, separately; also, it illustrates effective operation in the pole-changing process, where both operating modes coexist. Double vector control algorithms are developed to control the PPM induction machine for different poles, respectively, with their different parameters and the given rotor flux linkages. Moreover, only four current sensors are required, even though there are nine winding currents; the torque share function ensures a constant torque during pole changing. The simulated and experimental results verify the proposed winding design, model, and control method of the PPM induction machine drive.

Quasi-Z source inverter with battery based PV power generation system

A new PV power generation topology, based on the quasi-Z source inverter (QZSI) with battery, is proposed in this paper. With a battery paralleled with one of the capacitors, this system can smooth the grid-injected/load power when the PV panel outputs a variable power with fluctuations. The battery can be charged or discharged without any extra circuit, because of the unique impedance network of QZSI. The operating principle and power flow of this system are analyzed. The closed-loop control strategy is used to achieve Maximum Power Point Tracking (MPPT) and keep the output voltage stable. Three operating modes of the proposed PV power generation system are simulated in the MATLAB/Simulink to verify its principle and theoretical analysis. A prototype is built in the lab, and the experimental results validate the whole system.

A hybrid modulation method for single-phase quasi-Z source inverter

Single-phase quasi-Z source inverter (qZSI) needs large capacitance, and its switching loss is high when controlled by traditional SPWM. In this paper, a new modulation method for single-phase qZSI is proposed, which combines SPWM and pulse-width-amplitude modulation (PWAM), as a result of hybrid modulation. SPWM is employed at low dc-link voltage to avoid shoot-through state and act switching at low voltage stress; PWAM is used at high dc-link voltage to reduce switching actions. With the proposed hybrid modulation, switching actions and loss are reduced, also the required capacitance is significantly reduced. The simulation and experimental results verify the proposed hybrid modulation method. The lower size and higher efficiency are confirmed in the hybrid modulation controlled single-phase qZSI when compared to that with traditional SPWM.