A multilevel inverter system for an induction motor with open-end windings

In this paper, a multilevel inverter system for an open-end winding induction motor drive is described. Multilevel inversion is achieved by feeding an open-end winding induction motor with two two-level inverters in cascade (equivalent to a three-level inverter) from one end and a single two-level inverter from the other end of the motor. The combined inverter system with open-end winding induction motor produces voltage space-vector locations identical to a six-level inverter. A total of 512 space-vector combinations are available in the proposed scheme, distributed over 91 space-vector locations. The proposed inverter drive scheme is capable of producing a multilevel pulsewidth-modulation (PWM) waveform for the phase voltage ranging from a two-level waveform to a six-level waveform depending on the modulation range. A space-vector PWM scheme for the proposed drive is implemented using a 1.5-kW induction motor with open-end winding structure.     

A novel orthogonal-vectors-based topology of multilevel inverters

This paper presents a novel proposal of developing converter output voltage waveforms and novel converter topologies. The main idea is based on the assumption that the total converter output space vector is composed of two orthogonal space vectors. Two basic proposals are discussed. The first one is related to a converter built of two standard inverters: a main inverter (MI) and an auxiliary one. The converter output voltage space vector is composed of two orthogonal vectors generated by the respective inverters. The total power of the auxiliary inverter does not exceed 20% of the MI power. Thanks to the presented control method, the harmonic content of the output voltage is significantly reduced. The second proposal is related to a novel converter topology denoted as OVT-IHC. The converter is built of one two-level inverter and three isolated H-bridge circuit units. The structure and its performance are also discussed in the paper. The converter in question is able to generate 133 different output space vectors and permits achievement of a stepped adjustment of the RMS output voltage. Both topologies presented in the paper indicate some characteristics and advantages of multilevel inverters. The converters acting on the basis of the orthogonal vectors idea possess promising properties and are suitable to applications in medium-power converters. The paper presents main features and contribution to the theory.     

A generalized Undeland snubber for flying capacitor multilevel inverter and converter

This paper proposes a snubber circuit for a flying capacitor multilevel inverter and converter. It also explains the concept of constructing a snubber circuit for a multilevel inverter and converter. The proposed snubber circuit makes use of an Undeland snubber as a basic snubber unit, and thus can be regarded as a generalized Undeland snubber for a flying capacitor multilevel inverter and converter. It has such an advantage of Undeland snubber used in the two-level inverter. Compared with a conventional RLD/RCD snubber for multilevel inverter and converter, the proposed snubber keeps such good features as fewer number of components, reduction of voltage stress of main switching devices due to low overvoltage, and improved efficiency of system due to low snubber loss. In this paper, the proposed snubber is applied to a three-level flying capacitor inverter, and its features are in detail demonstrated by computer simulation and experimental result.     

Multilevel Multiphase Space Vector PWM Algorithm

In the last few years, interest in multiphase converter technology has increased due to the benefits of using more than three phases in drive applications. Besides, multilevel converter technology permits the achievement of high power ratings with voltage limited devices. Multilevel multiphase technology combines the benefits of both technologies, but new modulation techniques must be developed in order to take advantage of multilevel multiphase converters. In this paper, a novel space vector pulsewidth modulation (SVPWM) algorithm for multilevel multiphase voltage source converters is presented. This algorithm is the result of the two main contributions of this paper: the demonstration that a multilevel multiphase modulator can be realized from a two-level multiphase modulator, and the development of a new two-level multiphase SVPWM algorithm. The multiphase SVPWM algorithm presented in this paper can be applied to most multilevel topologies; it has low computational complexity and it is suitable for hardware implementations. Finally, the algorithm was implemented in a low-cost field-programmable gate array and it was tested in a laboratory with a real prototype using a five-level five-phase inverter.     

An efficient multilevel-synthesis approach and its application to a 27-level inverter

This paper presents an efficient multilevel-synthesis scheme and its application to a 27-level inverter. In the proposed multilevel scheme, this can be realized by an array of switching devices composing full-bridge inverter modules and proper mixing of each transformer terminal voltage. The most different aspect, compared to the conventional approach, in the synthesis of the multilevel output waveform is the utilization of a combination of transformers rather than the accumulation of capacitor voltage sources. A 27-level inverter consists of three full-bridge modules and their corresponding transformers. Quasi-sinusoidal voltage waves can be generated from a suitable selection of the turns ratio of the transformer. The validity of the proposed system is verified by computer-aided simulation and experimental results using a 500-W prototype, which can generate a 110-V ac output voltage from a 12-V dc input.     

TRIAC dimmable ballast with power equalization

A two-stage, two-wire TRIAC dimmable electronic ballast for fluorescent lamps is presented in this paper. It is constructed by using a flyback converter as the input power factor corrector to supply a half-bridge series-resonant parallel-loaded inverter to ballast the lamp. The flyback converter is operated in discontinuous conduction mode so that the filtered input current profile is the same as the TRIAC-controlled voltage waveform. The switches in the inverter are switched at a constant frequency slightly higher than the resonant frequency of the resonant tank. Based on the constant average input current characteristics of the inverter, the dimming operation is simply achieved by pulsewidth modulation control of the magnitude of the flyback converter output voltage. No synchronization network is required between the input and output stages. In addition, a linear power equalization scheme is developed so that the dc-link voltage (and hence the lamp power) is in a linear relationship with the firing angle of the TRIAC. The average output voltage of the dimmer controls the equalized flyback converter output voltage. Modeling, analysis, and design of the ballast will be described. A prototype was implemented to verify the experimental measurements with the theoretical predictions.     

Multilevel Diode-Clamped Converter for Photovoltaic Generators With Independent Voltage Control of Each Solar Array

In photovoltaic (PV) power systems where a set of series-connected PV arrays (PVAs) is connected to a conventional two-level inverter, the occurrence of partial shades and/or the mismatching of PVAs leads to a reduction of the power generated from its potential maximum. To overcome these problems, the connection of the PVAs to a multilevel diode-clamped converter is considered in this paper. A control and pulsewidth-modulation scheme is proposed, capable of independently controlling the operating voltage of each PVA. Compared to a conventional two-level inverter system, the proposed system configuration allows one to extract maximum power, to reduce the devices voltage rating (with the subsequent benefits in device-performance characteristics), to reduce the output-voltage distortion, and to increase the system efficiency. Simulation and experimental tests have been conducted with three PVAs connected to a four-level three-phase diode-clamped converter to verify the good performance of the proposed system configuration and control strategy.     

Zero-voltage-switching PWM hybrid full-bridge three-level converter

This paper proposes a zero-voltage-switching (ZVS) pulse-width modulation (PWM) hybrid full-bridge three-level converter, which has a three-level leg and a two-level leg. The switches of the three-level leg sustain only the half of the input voltage, and they can realize ZVS in a wide load range. The switches of the two-level leg sustain the input voltage, and they can realize ZVS with the use of the resonant inductance. The secondary rectified voltage is a three-level waveform having lower high-frequency content compared with that of the traditional full-bridge converters, which can reduce the output filter, and as a result, the dynamic response of the converter is improved. The voltage stress of the rectifier diode is reduced also. The input current of the converter has quite little ripple, so the input filter can also be significantly reduced. The operation principle of the proposed converter is analyzed and verified by the experimental results.     

Design of a Flexible Control Platform for Soft-Switching Multilevel Inverters

In modern high-power medium voltage drives, multilevel converters are increasingly used. Employing slight topological modifications, soft-switching technology can be applied to multilevel converters to reduce the switching losses. As a result, the switching frequency can be increased, thereby reducing the output filter size. However, common converter controls have to be modified. In this paper, a flexible control platform is presented that allows rapid prototyping of soft-switching topologies. An analysis of different auxiliary resonant commutated pole (ARCP) topologies shows that all switching commands can be synthesized with synchronized signals of two-level ARCP converters. Therefore, a flexible state-machine for two-level converters was developed first, which can also be used to build controls for multilevel topologies. It supports drivers with built-in intelligence as well as the control of additional switches that are required in some ARCP neutral-point-clamped (NPC) topologies. The switching commands for the state machines can be generated by standard multilevel modulation methods. Illegal switching states are filtered and multiple simultaneous commutations per phase are prevented for ARCP NPC converters. To verify the functionality, the control scheme was realized in a field programmable gate array and a completely modular test converter was developed. This test converter can be used to quickly implement all common multilevel topologies and test different modulation strategies. Experimental results are presented in this paper.     

Zero-voltage and zero-current-switching PWM hybrid full-bridge three-level converter

This paper proposes a zero-voltage and zero-current-switching pulsewidth modulation hybrid full-bridge three-level (ZVZCS PWM H-FB TL) converter, which has a TL leg and a two-level leg. The voltage stress of the switches of the TL leg is half of the input voltage, and the switches can realize ZVS, so MOSFETs can be adopted; the voltage stress of the switches of the two-level leg is the input voltage, and the switches can realize ZCS, so IGBT can be adopted. The secondary rectified voltage is a TL waveform having lower high-frequency content compared with that of the traditional FB converters, which leads to the reduction of the output filter inductance. The input current of the converter has quite little ripple, so the input filter can also be significantly reduced. The operation principle of the proposed converter is analyzed and verified by the experimental results. Several ZVZCS PWM H-FB TL converters are also proposed in this paper.     

Cascaded Multilevel Inverter With Regeneration Capability and Reduced Number of Switches

Multilevel converters are a very interesting alternative for medium and high power drives. One of the more flexible topologies of this type is the cascaded multicell converter. This paper proposes the use of a single-phase reduced cell suitable for cascaded multilevel converters. This cell uses a reduced single-phase active rectifier at the input and an H-bridge inverter at the output side. This topology presents a very good performance, effectively controlling the waveform of the input current and of the output voltage and allowing operation in the motoring and regenerative mode. The results presented in this paper confirm that this medium voltage inverter effectively eliminates low frequency input current harmonics at the primary side of the transformer and operates without problems in regenerative mode.     

Three-Phase Low-Frequency Commutation Inverter for Renewable Energy Systems

The connection of distributed power sources with the utility grid generally needs an electronic power converter for processing the locally generated power and injecting current into the system. If the source provides a dc voltage, the converter must be able to produce a low-distortion high-power-factor ac current. The same aspects related with the voltage and current distortion produced by nonlinear loads can be considered for the injection of power into the grid. In the absence of a specific standard, this paper takes as a reference the limits for current harmonics given by international standards. The justification for this approach is that, from the resulting line voltage degradation, there is no difference between injected and absorbed currents. This paper presents a three-phase inverter using low-frequency commutation. An auxiliary circuit is added to the inverter topology to reduce the output voltage distortion, thus improving the current waveform. The main advantages of this approach are the minimization of the switching losses and the elimination of the electromagnetic interference, which avoids high-frequency filters necessary in high-frequency commutation inverters     

1.5kW户用光伏高频逆变器研制

分析了一种具有中间储能环节的高频隔离逆变拓扑结构,该电路能实现前后级解耦,适用于光伏发电系统。前级DC/DC高频升压电路基于有限双极性调制,实现升压功能;后级采用双极性SPWM逆变技术,结合电压平均值反馈使输出电压稳定。详细介绍了高频变压器和LC滤波电路的设计方法,最后搭建了1.5k W高频逆变实验平台,实验结果显示,逆变器具有输出电压稳定,波形畸变小等优点。     

Nonlinear Shaping SC Oscillator With Enhanced Linearity

A nonlinear shaping technique for a switched-capacitor (SC) bandpass filter (BPF) based oscillator yielding enhanced linearity is presented. Usually, for an SC oscillator consisting of a BPF and a two-level comparator, the linearity can only be improved by increasing the quality factor (-factor) of the BPF. This paper proposes an efficient way to improve the linearity of SC BPF-based oscillators. In particular, by replacing the conventional two-level comparator by a sound multilevel comparator, a nonlinear shaping of the signal at the output of the comparator causes a significant improvement in linearity. To illustrate the effectiveness of the proposed technique, one conventional SC BPF-based oscillator and the proposed oscillator have been designed and fabricated in a standard 0.35- CMOS technology. Each oscillator was designed to operate from a 1.65 V supply voltage and a master clock frequency of 80 MHz. The oscillation frequency is 10 MHz and the -factor of the BPF is 10. Experimental results demonstrate that the proposed scheme improves the third-order harmonic distortion by 20 dB with respect to the conventional SC BPF-based oscillator.     

A New Multilevel Conversion Structure for Grid-Connected PV Applications

A novel scheme for three-phase grid-connected photovoltaic (PV) generation systems is presented in this paper. The scheme is based on two insulated strings of PV panels, each one feeding the dc bus of a standard two-level three-phase voltage-source inverter (VSI). The inverters are connected to the grid by a three-phase transformer having open-end windings on the inverter side. The resulting conversion structure performs as a multilevel power active filter (equivalent to a three-level inverter), doubling the power capability of a single VSI with given voltage and current ratings. The multilevel voltage waveforms are generated by an improved space-vector-modulation algorithm, suitable for the implementation in industrial digital signal processors. An original control method has been introduced to regulate the dc-link voltages of each VSI, according to the voltage reference given by a single maximum power point tracking controller. The proposed regulation system has been verified by numerical simulations and experimental tests with reference to different operating conditions.     

A boost DC-AC converter: analysis, design, and experimentation

This paper proposes a new voltage source inverter (VSI) referred to as a boost inverter or boost DC-AC converter. The main attribute of the new inverter topology is the fact that it generates an AC output voltage larger than the DC input one, depending on the instantaneous duty cycle. This property is not found in the classical VSI, which produces an AC output instantaneous voltage always lower than the DC input one. For the purpose of optimizing the boost inverter dynamics, while ensuring correct operation in any working condition, a sliding mode controller is proposed. The main advantage of the sliding mode control over the classical control schemes is its robustness for plant parameter variations, which leads to invariant dynamics and steady-state response in the ideal case. Operation, analysis, control strategy, and experimental results are included in this paper. The new inverter is intended to be used in uninterruptible power supply (UPS) and AC driver systems design whenever an AC voltage larger than the DC link voltage is needed, with no need of a second power conversion stage     

A novel switch-mode DC-to-AC inverter with nonlinear robust control

A switch-mode DC-to-AC inverter based on a DC-to-DC converter topology using a novel nonlinear robust control to generate a sinusoidal output waveform is presented. The control scheme is based on simultaneous feedback of the output voltage and feedforward of the input voltage and inductor voltage. As a result, the output voltage remains dynamically unchanged when there are large disturbances in input voltage or load current. The nature of the control law is explained. Computer simulation results show the robustness and fast dynamical response of the control system. The experimental results are presented to verify the analysis and demonstrate the feasibility of the control strategy     

Three-Level AC–DC–AC Z-Source Converter Using Reduced Passive Component Count

This paper presents a three-level AC-DC-AC Z-source converter with output voltage buck-boost capability. The converter is implemented by connecting a low-cost front-end diode rectifier to a neutral-point-clamped inverter through a single X-shaped LC impedance network. The inverter is controlled to switch with a three-level output voltage, where the middle neutral potential is uniquely tapped from the star-point of a wye-connected capacitive filter placed before the front-end diode rectifier for input current filtering. Through careful control, the resulting converter can produce the correct volt-second average at its output, while simultaneously achieving inductive voltage boosting by shooting through either an appropriately selected inverter phase-leg or two phase-legs being commanded simultaneously. More interestingly, these performance features are achieved with no increase in the number of semiconductor commutations, and hence, no increase in switching losses. The proposed converter therefore offers a low-cost alternative to applications that need to ride through frequent input voltage sags. For confirming the converter performance, experimental testing using a constructed laboratory prototype is performed with its captured results presented in a later section of the paper.     

Development of a new adaptive sigma-delta modulator scheme applied to multilevel inverter control

Interest in multilevel inverters is increasing in recent years, especially in high voltage applications. Traditional pulse width modulation (PWM) techniques can be applied to control this type of switched converter. However, it is necessary to adapt these techniques to the particularities of multilevel operation. As an alternative, other modulation techniques, such as sigma-delta modulation (SDM) can be used. In this case, it is possible to use advanced modulation techniques, such as adaptive modulation, to adapt the SDM to the multilevel operation. This article presents a new adaptive sigma-delta modulator that controls a five levels multilevel inverter. The algorithm that generates the sigma-delta signal is implemented in a field-programmable gate array (FPGA). This allows a very fast operation independent of the overall control circuit operation response. In addition, the FPGA can generate the control signals necessary to drive the power semiconductors in the power stage. The resulting modulator is simpler than the PWM version.     

高频反激变压器绕组模型优化设计

反激变换器中高频变压器是核心部件,其效率直接关系到变换器的效率,因此优化设计高频变压器就成为提高效率的关键。通过对反激变压器绕组采用不同结构时所带来不同的涡流损耗和漏感进行分析,得到本文所设计绕组结构二维模型。利用有限元分析软件进行数值仿真,获得的数据证明此模型是可行的。制作出实验样机对其进行实验比较,验证了所设计的高频变压器绕组结构合理,漏感小,效率高,输出的电压的谐波含量低。