Search

This paper addresses the low-frequency relative stability problem of the grid-connected voltage source inverter (VSI) based distributed generation (DG) unit in microgrid, in which the conventional active power-frequency (P-ω) and reactive power-voltage (Q-E) droop controllers are commonly used to share the loads. In the sense of the characteristic equation and eigenvalues, the relative stability and the transient response are remarkably affected by the change of the droop gains and/or stable operating points, resulting in the poor damping and eventually instability. An improved P-ω and Q-E droop scheme based on the static droop characteristics combined with a derivative term is presented to preserve the system stability and obtain an improved damping performance. Subsequently, the dynamic performance of the system can be adjusted without affecting the static droop gains to damp the oscillatory modes of the power sharing controllers. Finally, the desired transient and steady-state responses can be obtained.

DC injection suppression is crucial for the transformerless PV systems. IEEE Std.929-2000 specifies that the PV systems shall not inject the dc current greater than 0.5% of the full rated output current. DC injection measurement is not only useful for evaluating whether a transformerless PV system meets IEEE standards, but also for the effective dc suppression with injecting an equal but opposite dc component via a proper control scheme. In practice, however, it is difficult to extract the very low-level (0.5% I rated ) dc currents in the presence of high levels of ac currents in transformerless PV systems. In order to overcome the limitation, this paper presents a real-time dc injection measurement technique. Some major issues such as the basic operating principle, frequency excursion effect mitigation and discrete-domain implementation of the proposed method are discussed. Theoretical analysis and performance evaluation results verify the effectiveness of the proposed dc injection measurement technique.

Microgrid is an effective way to integrate the distributed energy resources into the utility networks. Conventionally, the voltage-source inverters in microgrid with sinusoidal current regulation are used in grid-connected mode. In this paper, a two-degree-of-freedom nonsinusoidal current regulation (NCR) is proposed for both the distributed power generation and power quality enhancement. The equivalent Thevenin-Norton circuit is provided to clarify the concept that NCR with virtual admittance leads to the power quality improvement. It is demonstrated that without any harmonic current sensor or additional compensating device, the harmonics of the voltages at the point of common coupling and currents in microgrid can be mitigated significantly. Time-domain performance evaluation results confirm the concept.

After the working principle and states of a new type of single-phase differential single-stage inverter based on classic BOOST DC/DC converters being analyzed, a topology family of single-phase and three-phase single-stage inverters are be concluded and be brought forward as a “BOOK” inverter name in the same differential working idea. The mathematical characteristics of single-phase and three-phase single-stage inverters are deduced. The experimental results of single-stage single-phase inverter with SPWM control are shown too. The computer simulations have been done through PSpice, and the results of “BOOK” inverter topology family are shown after that. The study shows that the “BOOK” inverter topology is feasible, and they can perform single phase or three phase invert function through single stage power conversation. The “BOOK” inverter could be widely used in the domains of distributed generation systems, UPS, motor control and drive and so on.

For acquiring of better quality and reducing the harmonic of the high frequency link matrix inverter-HFLMI output, a new envelope curve modulation method is discussed. The method can make the cycle duty of the front stage circuit of the HFLMI's driving signals variable and the HFLMI can gain better output voltage and current by working with de-re -coupling SPWM modulation. The carrier wave for front stage circuit is not a DC voltage but the envelope curve output voltage of the three-phase bridge rectifier without wave filter. The cycle duty of the driving signals of the HFLMI is changed with the envelope curve of the three-phase voltage. Some details of this circuit's operating principle and working states are analyzed, and the practicability and the feasibility of the envelope curve modulation method has been approved through PSpice simulation.

This paper discusses vector modulation and sliding mode control for a kind of high frequency link matrix inverter (HFLMC), and presents a kind of De-Re-couple analysis idea to the HFLMC. The De-Re-couple vector condition also has been induced. Especially aiming at its non-linear characteristic, this paper proposes a new control strategy called De-Re-couple vector modulation slide mode control and summarized the design steps of output voltage sliding mode controller. The accuracy is confirmed by closed loop simulation and Loop-locked experiment. The accordant results of MatLab simulation and experiment through DSP+CPLD controller confirm the feasibility of De-Re-couple analysis idea and validity of sliding mode control. And it provides the beneficial information for the further research.

Matrix rectifier is evolved from the traditional three phase to three phase matrix converter, and inherits merits of the traditional matrix converter, so it obtains more attention in recent years. According to transformer, matrix rectifier topology falls into the isolated and non-isolated topology. Now the existed modulation strategy mostly focuses on space vector modulation study and is realized difficultly. This paper adopts isolated matrix rectifier topology and proposes a novel SPWM modulation strategy based on absolute value logic, which can realize unit power factor and DC voltage output, and makes transformer keep voltage-second balance in a high frequency switching period. Experiments are done with DSP and CPLD based on the matrix rectifier platform. Simulations and experiments well prove the validity and feasibility of the proposed modulation strategy.

Sinusoidal signal integrator has the capability of controlling the ac current with zero steady-state error. However, their performances significantly degrade in case of the frequency variations with the steady-state error. So far, no literature has addressed the quantitative analysis of this steady-state error. Therefore, this paper reveals, for the first time, a theoretical guidance to get the accurate quantitative analysis for the error evaluation. Meanwhile, a frequency-adaptive sinusoidal signal integrator is proposed aiming at eliminating this steady-state error. The proposed strategy is suitable for grid-connected inverter applications in weak grids where the grid frequency may experience fluctuations. Detailed analysis and results verify the effectiveness of the proposed strategy.

Taking the high frequency link matrix style three-phase inverter as studying object, combining its topology and the work characteristic, this paper presented the de-re-couple analysis idea. The de-re-couple vector condition also has been induced. Aiming at its non-linear characteristic, this paper proposed a new control strategy called de-re-couple vector slide mode and summarized the design steps of output voltage sliding mode controller. The accuracy is confirmed by closed loop simulation and Loop-locked experiment. The accordant results of Matlab simulation and experiment of DSP+CPLD confirmed the feasibility of de-re-couple analysis idea and validity of sliding mode control. And it provides the beneficial information for the further research.

A novel topology family to realize sine-wave inversion is presented in this paper, and the main idea is using series resonant technology to afford zero-current switching (ZCS) state of the overall power switches. The proposed system consists of a full bridge LC series high frequency (HF) inverter which transforms the DC input into a HF sine-wave current source, an isolated HF transformer, a cycloconverter and a capacitor filter. Based on the one topology of family, the working principles are analyzed and the basic control thought is given. Finally, the experimental result proves the validity of the theoretical analysis

In this paper a novel ZVZCS FB-PWM DC/DC converter is analyzed. Comparing with the small signal models of the buck converter and the ZVS-FB PWM converter, the paper indicates that the characters of ZVZCS small signal model are significantly different from the latter. On the basis of small signal modeling, the compensation network is designed and verified by the simulation and experiment results

In this paper, a small signal model of a novel ZVZCS FB-PWM DC/DC converter is built and analyzed. A double closed loop controller is employed: the inner loop is a PI controller and the outer loop is a fuzzy logic with integrator controller. The novel control strategy improves the performance of the converter greatly, such as stability, control precision and dynamic response. The dramatic feature of topology and the superiority of control strategy are proved by experiment results on a 3 kW prototype

A data fusion method for single-phase inverter fault diagnosis based on D-S evidential theory and fuzzy logical theory is presented. By measuring the output voltage the two bridge-arms voltage and the temperature of MOSFET, the belief function assignment is obtained, and the fusion belief function assignment is obtained by using D-S rule and fuzzy logic, and fault component is found. By comparing the diagnosis results based on separate original data and fused data respectively, it is shown that the latter is more accurate than the former in the fault recognition

a novel method for islanding detection of a grid-connected photovoltaic system is proposed in this paper. Islanding can be more effectively detected through adding periodical disturbing current to the output current of the inverter. Compared with the active frequency drift method, the method has the many merits that it does no harm to utility, doesn't affect the utility frequency and also it does not generate harmonic current and voltage. In addition to, it has the least NDZ (non detection zone). This method has been proved by simulations and experiments.

In this paper, a high performance circuit topology and control techniques are developed. The proposed bidirectional quasi-single-stage push-pull forward high frequency link inverter consists of a push-pull forward converter, a bidirectional active rectifier, an active clamp branch and a SPWM inverter bridge. In particular, a two-degree-of-freedom PID digital controller is applied to achieve high performance in both the command tracking and the load disturbance regulation. The modulation and control strategy are realized by using the TMS320LF2407A DSP and EPM7128 CPLD. The principles of circuit operation are also discussed in this paper. Theoretical analysis and experimental results indicate that the proposed topology and control scheme are promising for the applications of DC/AC power supply.

The objective of this paper is to establish the industrial design procedure of the resonant tank components and HF transformer in series-resonant converter or inverter. Based on the analysis of the main operation principles of the resonant tank and HF transformer, an industrial design process of these components is given by considering the design requirements which is acquired via the simulation; utilizing the aforementioned components, a 1 KW series-resonant inverter prototype has been constructed, and the validity of the design procedure has been proved via the experimental results.

This paper presents a novel modulation and digital controller based on a bi-directional voltage mode high frequency link inverter with active clamp to achieve fast dynamic response and high static performance. The inverter consists of a full-bridge converter, a bi-directional active rectifier, an active clamp branch and a pulse width modulation (SPWM) inverter bridge. A novel modulation strategy is applied by modulating the triangle carrier wave and two inverse sinusoidal modulation waves, it is no need of checking the pole of the output voltage to switch the modulated signals, and it is able to weaken the distortion of the output waveform on zero passage. Double closed-loop digital control with load current feed-forward is applied to achieve good dynamic response. The modulation and control strategy is realized by using the TMS320LF2407A DSP and EPM7128 CPLD. Theoretical analysis and experimental results referring to a laboratory prototype (3 KVA) indicate that the proposed modulation and control scheme are promising for the applications of DC/AC power supply.

The paper present an optimal robust waveform controller using H/sub /spl infin// optimization theory for three phase converter. In general D-Q axis synchronous frame to realizing a decoupling current control, the input net voltage must be measured. To decrease the cost and control the system at ease, a new scheme for three phase PWM converter without net voltage sensor is present in this paper. The input voltages in the system are treated as a disturbance variable. H/sub /spl infin// optimization theory is suitable to design the waveform controller with disturbance noises of the three-phase converter. The stability and performance requirements for the converter can be expressed in terms of ||/spl middot/|| norm of closed loop transfer and sensitivity functions and appropriate weighting functions, the controller achieves stability and performance robustness in the presence of input voltage sensorless control with H/sub /spl infin// optimal arithmetic. The feasibility and advantage of the control scheme is verified by simulation and experimental results.

This paper presents a novel modulation and a two-degree-of-freedom (2-DOF) PI digital controller based on a bi-directional voltage mode high frequency link inverter with active clamp. A novel modulation strategy is applied by modulating the triangle carrier wave and two inverse sinusoidal modulation waves. It is no need of checking the pole of the output voltage to switch the drive signals, and it is able to weaken the distortion of the output on zero passage. This 2-DOF PI controller has two parameters to be designed separately and can obtain good dynamic responses both in the command tracking and load disturbance regulation characteristic. In this paper, the 2-DOF PI digital controller for the inverter system is designed and implemented to obtain high dynamic and static performance. The parameters of the controller are found by model building, theoretical deduction according to the desired specifications. The simulation and experimental results are provided to verify the proposed modulation and digital control strategy

This paper analyzes the influence of the amplitude and phase of the inverters output voltage on the power of the parallel system. A no-master-slave control strategy for paralleling inverter based on an interactive following method is proposed, which controls the amplitude of reference voltage and synchronize the phase of the reference voltage to share the active and reactive power by synchronization bus and CAN bus. The DSP (TMS320LF2407) is adopted to realize full digital control in this system. The experimental results demonstrate that the function of N+1 redundancy can be realized and the active and reactive powers are greatly shared

A novel bi-directional series resonant inverter is present in this paper, which all switch can work in a ZCS condition with fixed frequency. A bilateral switch is connected to primary side of transformer which will control the energy following more perfectly. With the bi-directional switch k degree of current control was improved. Power flow with different switch combination was analyzed and its waveform library was used to control the energy following. The topology has a bright prospect in low THD inverter and special inverter. Experimental result proves the validity of the theoretical analysis

A new control approach based on unified constant-frequency integration control (UCI) for current tracing is presented for photovoltaic grid-connected inverters. The working theory is analyzed and the control equation is deduced. The control approach is realized by a digital controller DSP. Different from the normal SPWM and PLL (phase locked loop) control approach in grid-connected inverters interface control, this control approach has the merit of automatic phase tracking capability, simplified control and high output power factor. And it can regulate the output in accordance with the dc voltage and grid voltage automatically

Switch mode DC to AC inverters using DC-to-DC converter topology has many advantages over the traditional bridge-type inverter. One cycle control is proposed to form a high performance inverter, but high performance ability was need for the magnify integrated chip. In this paper the control circuit error near the zero crossing point was magnified and steady state point of the magnifier was changed from zero to a positive number to minimized the distortion near the zero crossing point. Because one cycle control method was not acute to the load changed, a proportional loop was used and voltage feedback archived from the filter end. And the experimental results are given out.

A back propagation neural network is used in this paper to control the three phase converter input current with state vector PWM (SVPWM) performance. The paper presents some characters of the current modulator. To improve the performance in response of current, robustness and insensitivity to system parameters, a online training neural networks proportional integrate modulator is used. Simulation and experimental results are given out.

In the paper, the soft-switched technique is used in the AC/DC rectifier. A new voltage-fed AC/DC high power factor rectifier with bridge-mode parallel resonant-DC-link is proposed and ZVZC switching can be realized for bridge devices. The two kinds of operating states for the rectifying and inverting are analyzed in normalization with the phase-plane method and the phase-plane figure is given. On this basis, the critical conditions which guarantee all switch devices to realize soft-switching, are discussed and the main parameter design is made. The results of simulations and experiments are presented.