A high-performance vector control of an 11-level inverter

This paper presents a switching strategy for multilevel cascade inverters, based on the space-vector theory. The proposed high-performance strategy generates a voltage vector across the load with minimum error with respect to the sinusoidal reference. In addition, it generates very low harmonic distortion operating with reduced switching frequency, without the use of traditional sinusoidal pulsewidth modulation techniques or more sophisticated vector modulation methods.     

Analysis of Output Current Ripple rms in Multiphase Drives Using Space Vector Approach

Multiphase variable-speed drives, supplied from two-level voltage source inverters (VSIs), are nowadays considered for various industrial applications. Although numerous pulsewidth modulation (PWM) schemes for multiphase VSIs, aimed at sinusoidal output voltage generation, have been developed, no detailed analysis of the impact of these modulation schemes on the output current ripple has ever been reported. This paper presents a comprehensive analytical analysis and comparison of the output current ripple caused by the application of three different continuous PWM schemes, using a five-phase VSI as an example. Main properties of sinusoidal PWM, fifth harmonic injection PWM, and space vector PWM are elaborated and analyzed using the harmonic flux concept. Space vector theory is applied in the analysis. As a result, harmonic distortion factors are obtained for each PWM scheme. Theoretical considerations are verified by simulations and experimental investigation using a custom-designed five-phase VSI-fed induction motor drive.      

Real-Time Calculation of Switching Angles Minimizing THD for Multilevel Inverters With Step Modulation

Multilevel inverters have been widely applied in industries. A family of optimal pulsewidth modulation (PWM) methods for multilevel inverters, such as step modulation, can generate output voltage with less harmonic distortion than popular modulation strategies, such as the carrier-based sinusoidal PWM or the space vector PWM. However, some drawbacks limit the application of optimal PWM. One of such crucial drawback is that the optimal switching angles could not be calculated in real-time and one has to rely on lookup tables with precalculated angles. We propose a novel real-time algorithm for calculating switching angles that minimizes total harmonic distortion (THD) for step modulation. We give a mathematical proof that the output voltage has the minimum THD. We implemented the algorithm on a digital signal processor and provide experimental results that verify the performance of the proposed algorithm.      

Analysis and Design of a Novel Three-Phase AC–DC Buck-Boost Converter

This paper proposes a novel three-phase ac-dc buck-boost converter. The proposed converter uses four active switches, which are driven by only one control signal. This converter is operated in discontinuous conduction mode (DCM) by using the pulsewidth modulation (PWM) technique, and the control scheme very easily and simply achieves purely sinusoidal input current, high power factor, low total harmonic distortion of the input current and step-up/down output voltage. Also, the proposed converter provides a constant average current to the output capacitor and load in each switching period. Thus, the ripple component of sixth times line frequency will not appear in the output voltage. Therefore, a smaller output capacitor can be used in the proposed converter. Moreover, the steady-state analysis of voltage gain and boundary operating condition are presented. Also, the selections of inductor, output capacitor and input filter are depicted. Finally, a prototype circuit with simple control logic is implemented to illustrate the theoretical analysis.     

基于Buck-Boost逆变器的离散滑模控制仿真研究

为了获得比较理想的正弦输出电压，优化逆变器的动态性能，文中基于Buck—Boost逆变器．采用了离散滑模变结构的控制策略。Buck—Boost逆变器可以获得比直流输入电源高或低的交流输出电压，文中阐述了其工作原理．并结合状态方程，推导出滑模面的存在条件、到达条件和稳定条件，然后对电路参数、控制系数以及控制算法进行了设计。仿真结果表明采用离散滑模控制的Buck—Boost逆变器对系统扰动和负载变化具有很强的鲁棒性，系统具有良好的动态响应。     

Digital repetitive learning controller for three-phase CVCF PWMinverter

In this paper, a plug-in digital repetitive leaning control scheme is proposed for three-phase constant-voltage constant-frequency (CVCF) pulsewidth modulation inverters to achieve high-quality sinusoidal output voltages. In the proposed control scheme, the repetitive controller (RC) is plugged into the stable one-sampling-ahead-preview-controlled three-phase CVCF inverter system using only two voltage sensors. The RC is designed to eliminate periodic disturbance and/or track periodic reference signal with zero tracking error, The design theory of plug-in repetitive learning controller is described systematically and the stability analysis or overall system is discussed. The merits of the controlled systems include features of minimized total harmonic distortion, robustness to parameter uncertainties, fast response, and fewer sensors. Simulation and experimental results are provided to illustrate the effectiveness of the proposed scheme     

Line harmonics reduction in high-power systems using square-waveinverters-based dominant harmonic active filter

This paper presents a dominant harmonic active filter (DHAF) scheme using small-rated square-wave inverters for supply line harmonic current reduction for high-power nonlinear loads in the range of 10 MW and above to meet IEEE 519 harmonic standard. The active filter inverters are connected in series with the fifth and seventh L-C tuned filters, respectively. A synchronous reference frame-based controller which achieves harmonic isolation for the dominant fifth and seventh harmonic load currents in the presence of supply voltage harmonic distortion is presented. Impact of mistuned passive filters on the operation and rating of the square-wave active filter inverters is examined. Simulation results validate the proposed harmonic isolation controller under mistuned fifth and seventh L-C tuned filter conditions and supply voltage harmonic distortion. The proposed scheme is general and applicable for high-power 6- or 12-pulse rectifier loads. The use of small-rated square-wave inverters (approximately 2% of load kilovoltampere rating) increases the cost effectiveness of the DHAF system for high-power applications     

Nonlinear-controlled strategy for soft-switched series-resonant DC/AC inverter without auxiliary switches

A nonlinear control for soft-switched series-resonant DC/AC inverter without auxiliary switches is presented. The inverter is configured by a full-bridge series-resonant inversion (FB-SRI) without cycloconversion and auxiliary switches. The inverter is a series resonator with four main switches to configure adaptively the output current suitable for impedance load. The output sinusoidal voltage is synthesized by a series of equal-amplitude quasisinusoidal pulses (QSPs) and the corresponding current is formed by unequal QSPs and adaptively phase-shifts to the impedance load. The nonlinear control strategy is designed against the input DC perturbation and achieves good dynamic regulation. The presented FB-SRI is operated by frequency modulation with a constant-on time control. Waveform syntheses for the output sinusoidal voltage and its current are clearly derived. A typical design example of a 500W FB-SRI inverter is examined to assess the system performance. The power efficiency is over 90% when the inverter output is above 200 W. The total harmonic distortions (THDs) for various impedance loads are all within 6%.     

“Dead-band” PWM switching patterns

Reference/modulating waveform continuity is not a necessary condition for the implementation of switching patterns for three-phase pulse-width modulated (PWM) converters if the load or the source are Y-connected. This is based on the fact that the converter phase-voltages do not need to be sinusoidal and switching pattern discontinuities-“dead-bands”-do not degrade the quality of output/input voltage/current waveforms by introducing low-order harmonics if certain parameters are optimized. This paper discusses general characteristics of various discontinuous switching patterns for PWM converters and shows that they can yield better performance than their continuous counterparts in some operating regions. Performance is defined as harmonic distortion normalized with respect to effective switching frequency and serves as a measure of comparison with continuous PWM techniques, The applications considered include general purpose and application specific solid-state power supplies using voltage source inverters and PWM rectifiers. Theoretical considerations are verified on an experimental unit     

Decoupling Control Strategy for Single Phase SPWM Parallel Inverters

A deconpling control strategy of inverter parallel system is proposed based on the equivalent output impedance of single phase voltage source SPWM （sinusoidal pulse width modulation） inverter. The active power and reactive power are calculated in terms of output voltage and current of the inverter, and sent to the other inverters in the parallel system via controller area network （CAN） bus. By calculating and decoupling the circumfluence of the active power and reactive power, the inverters can share load current via the regulation of the reference-signal phase and amplitude. Experimental results of an 110V/2kVA inverter parallel system show the feasibility of the decoupling control strategy.     

Elimination of common-mode voltage in three-phase sinusoidal powerconverters

This paper presents an active solution to a common-mode voltage created by typical three-phase inverters. It is shown that the addition of a fourth leg to the bridge of a three-phase inverter eliminates the common-mode voltage to ground created by the modulation of the inverter. An appropriate four-phase LC filter is inserted between the inverter and the load in order to create sinusoidal output line-to-line voltage. A simple modification of the modulation strategy is implemented for the four-phase inverter to achieve a three-phase wye-output neutral-to-ground voltage which is equal to zero at all times for an ideal inverter. The modulation strategy thereby completely eliminates the common-mode potential produced by traditional modulation techniques with traditional three-phase inverter topologies     

A Unity Power Factor Correction Preregulator With Fast Dynamic Response Based on a Low-Cost Microcontroller

Low cost passive power factor correction (PFC) and single-stage PFC converters cannot draw a sinusoidal input current and are only suitable solutions to supply low power levels. PFC preregulators based on the use of a multiplier solve such drawbacks, but a second stage dc-dc converter is needed to obtain fast output voltage dynamics. The output voltage response of PFC preregulators can be improved by increasing the corner frequency of the output voltage feedback loop. The main drawback to obtaining a faster converter output response is the distortion of the input current. This paper describes a simple control strategy to obtain a sinusoidal input current. Based on the static analysis of output voltage ripple, a modified sinusoidal reference is created using a low cost microcontroller in order to obtain an input sinusoidal current. This reference replaces the traditional rectified sinusoidal input voltage reference in PFC preregulators with multiplier control. Using this circuitry, PFC preregulator topologies with galvanic isolation are suitable solutions to design a power supply with fast output voltage response (10 or 8.33 ms) and low line current distortion. Finally, theoretical and simulated results are validated using a 500 W prototype.     

Single-Phase Voltage Source Inverter With a Bidirectional Buck–Boost Stage for Harmonic Injection and Distributed Generation

A transformerless single-phase inverter topology is proposed that can operate over a wide dc input voltage range and has the ability to track reference signals with fast dynamics, making it suitable for harmonic elimination and distributed generation applications. The necessary capacitor and inductor are easier to design than those for filtering the output of traditional inverters. Unlike traditional inverters, no output filter stage is required. Analysis of inverter operating mechanisms is carried out for two control schemes, which are confirmed by simulation and practical results.      

An accurate approach of nonlinearity compensation for VSI inverter output voltage

An accurate nonlinearity compensation technique for voltage source inverter (VSI) inverters is presented in this paper. Because of the nonlinearity introduced by the dead time, turn-on/off delay, snubber circuit and voltage drop across power devices, the output voltage of VSI inverters is distorted seriously in the low output voltage region. This distortion influences the output torque of IM motors for constant V/f drives. The nonlinearity of the inverter also causes 5th and 7th harmonic distortion in the line current when the distributed energy system operates in the grid-connected mode, i.e., when the distributed energy system is parallel to a large power system through the VSI inverter. Therefore, the exact compensation of this nonlinearity in the VSI inverter over the entire range of output voltage is desirable. In this paper, the nonlinearity of VSI inverter output voltage and the harmonic distortion in the line current are analyzed based on an open-loop system and a L-R load. By minimizing the harmonic component of the current in a d-axis and q-axis synchronous rotating reference frame, the exact compensation factor was obtained. Simulations and experimental results in the low frequency and low output voltage region are presented.     

Harmonics in voltage-source PWM inverters

The performance of an induction motor fed by PWM inverters is mainly determined by the harmonic contents of the output voltage. This paper presents a method of numerically calculating the harmonics in the output voltage waveform. Equal pulse-width modulation and siunsoidal PWM are studied. Analysis has been done for single-phase and three-phase bridge inverters. A systematic procedure is given for computing the harmonics and the results are. tabulated.     

矩阵变换器在不平衡输入电压下的控制策略

通过检测矩阵变换器的瞬时输入电压并实时调节输出电压调制矢量,采用空间矢量调制策略的矩阵变换器能够在不平衡且非正弦的输入电压下得到正弦平衡的输出电压。在非平衡输入电压下,若输入功率因数角不变,矩阵变换器的输入电流将不再正弦。本文给出了输入电流与输出功率及输入功率因数角之间的关系,通过调节输入电流调制矢量的方向,可得到正弦但不平衡的输入电流。仿真证明了理论的正确性。     

Comparison of two current modulation strategies for matrixconverters under unbalanced input voltage conditions

In this paper, the input current performance of matrix converters is analyzed, especially with reference to the operating conditions determined by unbalanced supply voltages. The space-vector modulation (SVM) technique is utilized to calculate the duty cycles of the active voltage vectors that must be applied, in each switching cycle period, in order to satisfy the input and output requirements. A detailed theoretical analysis of the input current harmonic content under unbalanced input voltage conditions is presented for two different current modulation strategies. On the basis of numerical simulations as well as measurements on a laboratory prototype setup, the strategies' performance are compared and the validity of the theoretical investigation confirmed. It is concluded that, when the input voltages are unbalanced to a significant extent, a dynamic input current modulation strategy has to be preferred, since a lower harmonic line current distortion will appear     

The uni-polarity phase-shifted controlled voltage mode AC-AC converters with high frequency AC link

A circuit configuration and circuit topological family of voltage mode ac-ac converters with high frequency ac links, which are based on forward converters, and a uni-polarity phase-shifted control strategy are proposed and deeply investigated. These kinds of converters consist of a input cycloconverter, a high frequency transformer, an output cycloconverter, input and output filters, and can transfer an unsteady ac voltage with a high harmonic into steady same-frequency ac sinusoidal voltage with a low harmonic. By using uni-polarity phase-shifted control strategy, output filtering inductance current is naturally commutated, and zero voltage switching of the output cycloconverter is realized. The converters' averaging model, the output characteristic curve, and design criteria for the key circuit parameters are given. The theoretical analysis and test result of 1kVA 220V /spl plusmn/ 10% 50Hzac/110V 50Hz ac prototype have shown that the converters have such advantages as high frequency electrical isolation, simple topology, two-stage power conversion (LFAC/HFAC/LFAC), bidirectional power flow, uni-polarity synchronized pulsewidth modulation waveform, high efficiency, high power density, high steady precision, low total harmonic distortion of the output voltage, strong adaptability to various loads, high line power factor, and low audio noise etc.     

Application of Pulse Ratio Modulation to Fixed-Frequency Sinusoidal Tracking Inverters

The application of pulse ratio modulation techniques in the field of fixed-frequency inverters with sinusoidal output waveforms is discussed. In particular, the criteria for choosing the parameters of the output filter and of the compensation network are analyzed, and a comparison is effected between the results obtained by employing either the aforementioned modulation technique or a fixed-frequency pulsewidth modulation technique. The comparison, effected by simulation, has also taken into account a nonlinear load, and it has shown that the employment of the pulse ratio modulation technique allows a remarkable reduction of the inverter supply overvoltage necessary to use tracking control techniques with high modulation frequencies. Lastly, the results obtained by simulation have been confirmed by a prototype.