Z-Source AC–AC Converters Solving Commutation Problem

A new family of Z-source ac-ac converters with buck-boost ability are proposed, including four switches single-phase structure and six switches three-phase structure. New commutation strategies for these converters are proposed and safe commutation can be achieved without snubber circuit. The commutation strategies are easily to realize by sampling only voltage signals, and two switches are always turned on, so switching loss can be reduced. Analysis based on state-space averaging reveals the relationship between Z-source inductor current and filter inductor current as well as voltage ratio. The design considerations of voltage-fed single-phase topology are given as an example. Simulation results on the voltage-fed topologies and experimental results on voltage-fed single-phase topology verified the unique features of Z-source ac-ac converters and the proposed commutation strategies. These converters have merits such as less conduction and switching loss, less devices, therefore high efficiency and reliability can be achieved.     

Simple topologies of PWM AC-AC converters

This letter proposes a new family of simple topologies of PWM AC-AC converters with minimal switches. With extension from the basic DC-DC converters, a series of AC-AC converters such as buck, boost, buck-boost, Cuk, and isolated converters are obtained. By PWM duty ratio control, they become a "solid-state transformer" with a continuously variable turns ratio. All the proposed AC-AC converters in this paper employ only two switches. Compared to the existing circuits that use six switches or more, they can reduce cost and improve reliability. The operating principle and control method of the proposed topologies are presented. Analysis and simulation results are given using the Cuk AC-AC converter as an example. The analysis can be easily extended to other converters of the proposed family.     

三相电压型准阻抗源AC～AC变换器

摘要：为了克服传统三相斩控式交流调压器的不足,提出了一种三相电压型准阻抗源变换器电路拓扑。研究了其拓扑结构和工作原理,推导了输出电压与占空比的定量关系。运用matlab对电路进行了仿真,并根据仿真结果建立了实验电路,采用脉冲宽度调制法（PWM）对电路进行总体控制,得到占空比为0.2与0.8时的三相电压波形。实验结果验证了三相电压型准阻抗源电压调节的的可靠性和可行性。     

Z-Source-Converter-Based Energy-Recycling Zero-Voltage Electronic Loads

This paper proposes two high-efficiency energy-recycling zero-voltage electronic loads (ELs) based on a Z-source converter. ELs are a family of power converters which are used as variable impedance loads in several applications. Such applications include testing of photovoltaic (PV) cells, power converters, and power supplies or frequency control of stand-alone microgeneration. In PV-cell performance tests, the zero-voltage operation, near the short-circuit point of the PV cell's $I$– $V$ curve, creates a challenge for EL design. The converter that is suitable for this application must have the ideal current source behavior because the challenge is to draw a specific constant current from the source under test even during the zero-voltage condition. The energy recycling principle increases the efficiency and allows the construction of high-power ELs. The proposed topologies are based on the Z-source converter and achieve the ideal current source behavior of draining an adjustable current even when the source voltage is zero. These topologies also provide power recycling for energy saving and for developing high-power ELs. The first configuration is based on the traditional Z-source converter, and the second one is based on the recently proposed quasi Z-source converter. Two prototypes were analyzed and built. Experimental results are provided to verify the principle of operation.      

Zero-voltage-switching half-bridge DC-DC converter with modified PWM control method

Asymmetric control scheme is an approach to achieve zero-voltage switching (ZVS) for half-bridge isolated dc-dc converters. However, it is not suited for wide range of input voltage due to the uneven voltage and current components stresses. This paper presents a novel "duty-cycle-shifted pulse-width modulated" (DCS PWM) control scheme for half-bridge isolated dc-dc converters to achieve ZVS operation for one of the two switches without causing the asymmetric penalties in the asymmetric control and without adding additional components. Based on the DCS PWM control scheme, an active-clamp branch comprising an auxiliary switch and a diode is added across the isolation transformer primary winding in the half-bridge converter to achieve ZVS for the other main switch by utilizing energy stored in the transformer leakage inductance. Moreover, the auxiliary switch also operates at ZVS and zero-current switching (ZCS) conditions. Furthermore, during the off-time period, the ringing resulted from the oscillation between the transformer leakage inductance and the junction capacitance of two switches is eliminated owing to the active-clamp branch and DCS PWM control scheme. Hence, switching losses and leakage-inductance-related losses are significantly reduced, which provides the converter with the potential to operate at higher efficiencies and higher switching frequencies. The principle of operation and key features of the proposed DCS PWM control scheme and two ZVS half-bridge topologies are illustrated and experimentally verified.     

一种改进的二极管箝位型多电平变换器拓扑

多电平电路在高压大功率领域的拓展受到其复杂电路拓扑的制约,因此近年来不断有新型多电平电路结构被提出。本文在传统多电平逆变器拓扑结构的基础上,提出了一种新型单相七电平电压源逆变器拓扑。新型电路拓扑是在传统的单相全桥五电平箝位二极管电路基础上,增加了两个开关器件,利用10个开关器件以及4个箝位二极管产生了7种不同的电平输出。详细分析了该逆变器的拓扑结构,给出了PWM控制策略。最后通过仿真实验验证了这种拓扑的可行性。该逆变器对传统箝位二极管逆变器在结构上做出了优化。     

Control of DC-DC converters with linear optimal feedback andnonlinear feedforward

This paper describes a new control design procedure for PWM DC-DC converters. The control action has two components: a linear feedback, designed via the LQ approach, and a nonlinear feedforward. The proposed control scheme guarantees excellent regulation of the output voltage, even in the presence of large variations of the input reference signal, as pointed out by numerous simulations carried out on different converter topologies. Good performances are also achievable when a suitably designed estimator is inserted into the control loop to reconstruct internal variables and input voltage disturbances from output voltage measurements     

Soft-switching PWM three-level converters

This paper proposes a family of modulation strategies for PWM three-level (TL) converters. The modulation strategies can be classified into two kinds according to the turn-off sequence of the two switches of the pair of switches. The concept of the leading switches and the lagging switches is introduced to realize soft-switching for PWM TL converters. The realization of soft-switching for both the leading switches and the lagging switches is proposed, based on which, soft-switching PWM TL converters can be classified into two kinds: zero-voltage-switching (ZVS) and zero-voltage and zero-current-switching (ZVZCS), for which the suitable modulation strategies are pointed out respectively from the family of modulation strategies. A novel ZVZCS TL converter is proposed, its operation principle and parameter design are analyzed, and the experimental results are also included     

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.     

Family of Soft-Switching PWM Converters With Current Sharing in Switches

In this paper, a new family of soft-switching pulsewidth modulation (PWM) converters is introduced. In this family of converters, two switches operate out of phase and share the output current while providing soft-switching condition for each other. A buck converter, from this family of converters, is analyzed and its operating modes are discussed. The adoption of regular PWM control circuit to the proposed converters is presented. A prototype converter is implemented and its experimental results are illustrated.     

A DC to DC PWM series resonant converter operated at resonantfrequency

Resonant DC-DC converters that are usually operated using frequency modulation to achieve regulation have the disadvantage of wideband frequency modulation. An alternate regulation scheme that uses fixed-frequency pulse width modulation (PWM) is proposed. This control scheme is applied to a series-loaded, series-resonant converter. When operated in a full-bridge configuration and with a variation of PWM that can be described as a phase shift modulation between the two sets of switches, the converter presents low switching stresses. Analytical results presented include VA rating and stresses on critical active and passive components as a function of input voltage variation. A 200 kHz, 700 W, 48 V output offline converter was realized using this concept, and some experimental results are presented to corroborate the analysis     

Novel zero-current-transition PWM converters

A new family of zero-current-transition (ZCT) pulsewidth-modulated (PWM) converters is proposed. The new family of converters implements zero-current turn-off for power transistor(s) without increasing voltage/current stresses and operates at a fixed frequency. The proposed converters are deemed most suitable for high-power applications where the minority-carrier semiconductor devices (such as IGBTs, BJTs, and MCTs) are predominantly used as the power switches. Theoretical analysis is verified on a 100 kHz, 1 kW ZCT-PWM boost converter using an IGBT     

Novel Three-Phase AC–AC Sparse Matrix Converters

A novel three-phase ac-ac sparse matrix converter having no energy storage elements and employing only 15 IGBTs, as opposed to 18 IGBTs of a functionally equivalent conventional ac-ac matrix converter, is proposed. It is shown that the realization effort could be further reduced to only nine IGBTs in an ultra sparse matrix converter (USMC) in the case where only unidirectional power flow is required and the fundamental phase displacement at the input and at the output is limited to plusmnpi/6. The dependency of the voltage and current transfer ratios of the sparse matrix converters on the operating parameters is analyzed and a space vector modulation scheme is described in combination with a zero current commutation method. Finally, the sparse matrix concept is verified by simulation and experimentally using a 6.8-kW/400-V very sparse matrix converter, which is implemented with 12 IGBT switches, and USMC prototypes.     

Pseudo-resonant full bridge DC/DC converter

A DC-DC power converter topology that combines the ease of control and wide range of conventional DC-DC converters, with low switching losses, low dv/dt and low electromagnetic interference that is typical of zero voltage switched resonant converters is proposed. Consequently, the ratings of these components are substantially lower than for similarly rated resonant topologies. While resonant elements are used to ensure zero voltage switching of all devices, they have little or no role in the actual power transfer and can thus be reasonably sized. As the resonant elements are not involved in the primary power transfer, the converter is referred to as a pseudo-resonant converter. It is shown that the converter offers significantly higher levels of performance than either the pulse width-modulated (PWM) or typical resonant converters. Operation at very high frequencies is possible and is shown with the fabrication of a 200 W 1 MHz DC-DC converter     

Novel zero-voltage and zero-current-switching (ZVZCS) full-bridge PWM converter using coupled output inductor

A novel zero-voltage and zero-current-switching (ZVZCS) full-bridge pulse-width-modulated (PWM) converter is proposed to improve the previously proposed ZVZCS full-bridge PWM converters. By employing a simple auxiliary circuit with neither lossy components nor active switches, soft-switching of the primary switches is achieved. The proposed converter has many advantages such as simple auxiliary circuit, high efficiency, low voltage stress of the rectifier diode and self-adjustment of the circulating current, which make the proposed converter attractive for the high voltage and high power applications. The principles of operation and design considerations are presented and verified on the 4 kW experimental converter operating at 80 kHz.     

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.     

Single-phase single-stage power-factor-corrected converter topologies

Single-phase single-stage power-factor-corrected converter topologies are reviewed in this paper. The topologies discussed in the paper are related to ac-dc and ac-ac converters that are classified on the basis of the frequency of the input ac source, the presence of a dc-link capacitor, and the type of control used (resonant or pulsewidth modulation). The general operating principles and strengths and weaknesses of the converters, which the authors have investigated over the last decade, are discussed in detail, and their suitability in practical applications is stated. Considering practical design constraints, it is possible to effectively employ many single-stage converter topologies in a wide range of applications.     

Soft-switched DC/DC converter with PWM control

In this paper, a new power converter with two variations is proposed. A novel asymmetrical pulse-width-modulation (PWM) control scheme is used to control the power converter under constant switching frequency operation. The modes of operation for both variations are discussed. The DC characteristics, which can be used in the design of the power converters, are also presented. Two 50 W power converters were built to verify the characteristics of the converters. Due to the zero-voltage-switching (ZVS) operation of the switches and low device voltage and current stresses, these power converters have high full- and partial-load efficiencies. They are, therefore, potential candidates for high-efficiency high-density power supply applications     

An improved ZCS-PWM commutation cell for IGBT's application

An improved zero-current-switching pulsewidth-modulation (ZCS-PWM) commutation cell is proposed, which is suitable for high-power applications using insulated gate bipolar transistors (IGBTs) as the power switches. It provides ZCS operation for active switches with low-current stress without voltage stress and PWM operating at constant frequency. The main advantage of this cell is a substantial reduction of the resonant current peak through the main switch during the commutation process. Therefore, the RMS current through it is very close to that observed in the hard-switching PWM converters. Also, small ratings auxiliary components can be used. To demonstrate the feasibility of the proposed ZCS-PWM commutation cell, it was applied to a boost converter. Operating principles, theoretical analysis, design guidelines and a design example are described and verified by experimental results obtained from a prototype operating at 40 kHz, with an input voltage rated at 155 V and 1 kW output power. The measured efficiency of the improved ZCS-PWM boost converter is presented and compared with that of hard-switching boost converter and with some ZCS-PWM boost converters presented in the literature. Finally, this paper presents the application of the proposed soft-switching technique in DC-DC nonisolated power converters     

An improved family of ZVS-PWM active-clamping DC-to-DC converters

A new family of DC-to-DC converters featuring clamping action, PWM modulation and soft-switching (ZVS) in both active and passive switches, is proposed to overcome the limitations of clamped mode DC-to-DC converters. The new family of converters is generated and the new circuits are presented. As the resonant circuits absorb all parasitic reactances, including transistor output capacitance and diode junction capacitance, these converters are suitable for high-frequency operation. Principle of operation of the boost converter, theoretical analysis, simulation and experimental results are presented, taken from a laboratory prototype rated at 1600 W, input voltage of 300 V, output voltage of 400 V, and operating at 100 kHz. The measured efficiency at full load was 98%