直流配电网多变流器纹波谐振问题研究

纹波是直流配电网中一种典型的电能质量问题。纹波谐振不仅影响直流配电网的电能质量,还会危及系统的安全稳定运行。探究了纹波在直流侧网络结构中的谐振现象;对接入端交流侧出现电压畸变和三相不平衡等情况引起的纹波从机理上进行了分析;建立了含变流器的直流配电网的等效电路,推导了变流器接入个数及接入位置对纹波谐振的影响关系;考虑各变流器间的耦合作用,推导了各变流器之间的耦合系数,研究了耦合作用对纹波谐振的影响。仿真结果验证了理论分析和所建模型的正确性。     

Reliability challenge for impedance network‐based DC‐DC boost converters

In this paper, reliability evaluation is proposed for some of the most famous impedance network‐based DC‐DC boost converters. Markov reliability approach is used to evaluate the reliability of the converters. Also, some other factors such as components' failure rates, reliability functions, and mean time to failures are introduced and evaluated. Detailed explanations for the evaluation methods of the mentioned factors are also provided in the context of the paper. In addition to the mathematical analysis, numerical calculations are also done through the simulation results of the converters. Simulations are done in PSCAD/EMTDC. Finally, a numerical and graphical reliability comparison is provided for the mentioned converters. The purpose of this paper is to give a comprehensive reliability evaluation and comparison for some of the most popular impedance network‐based DC‐DC converters. In addition, this paper gives a detailed reliability analysis that can be used in reliability assessment of all types of power electronic converters, so it can help the researchers to consider reliability calculations into their designing.     

A generalized geometrical piecewise‐affine model of DC‐DC power electronic converters

A generalized model of the dynamics (GMD) of DC‐DC power electronic converters (PECs) is discussed in this paper. It is a geometrical piecewise‐affine continuous‐time model. The general idea of the GMD is to determine the local dynamic behavior of trajectories on the faces of the PEC commutation structure, which is a geometrical model of its commutation. This allows us to establish the direction of PEC dynamics on these faces. It can be either ‘entering’ into specific regions in state space or ‘exiting’ from them. Therefore, the local PEC dynamics can be treated as logical (two‐state). In practice, the GMD can be used for the analysis of PEC practical stability, which is a completely different concept from the concept of PEC stability in the classical Lyapunov sense. An outline of the design‐oriented approach to PEC practical stability analysis, which is based on the GMD, has also been presented. As illustrative examples, the GMD of a boost converter under peak current‐mode control and its application are presented. These examples show that the Lyapunov stability of a given PEC does not imply its practical stability, and that the results of PEC Lyapunov stability analysis and practical stability analysis are complementary to each other. Copyright © 2013 John Wiley & Sons, Ltd.     

Graph‐theoretical approach to 2‐switch DC–DC converters

This paper presents a graph‐theoretic approach to analyse and synthesize switch mode DC–DC converters. The result is based on the state‐space averaging equation and the fundamental graph theory. Hence our proposed method is applied to various kinds of DC–DC converters with two switches and topological conditions for two‐switch DC–DC converters are obtained systematically. Copyright © 2005 John Wiley & Sons, Ltd.     

Non‐isolated single‐switch DC–DC converters with extended duty cycle for high step‐down voltage applications

Several new topologies of single‐switch non‐isolated DC–DC converters with wide conversion gain and reduced semiconductor voltage stress are proposed in this paper. Most of the proposed topologies are derived from the conventional inverse of SEPIC (Zeta) converter. The proposed topologies can operate with larger switch duty cycles compared with the existing single switch topologies, hence, making them well suitable for high step‐down voltage conversion applications. With extended duty cycle, the current stress in the active power switch is reduced, leading to a significant improvement of the system losses. Moreover, the active power switch in some of the proposed topologies is utilized much better compared to the conventional Zeta and quadratic‐buck converters. The principle of operation, theoretical analysis, and comparison of circuit performances with other step‐down converters are discussed regarding voltage and current stress and switch silicon utilization. Finally, simulation and experimental results for a design example of a 50 W/5 V at 42‐V input voltage operating at 50 kHz will be provided to evaluate the performance of the proposed converters. Copyright © 2014 John Wiley & Sons, Ltd.     

Design of PID controllers using Filippov's method for stable operation of DC–DC converters

A lot of work has taken place into the design and control of DC–DC converters, and various methodologies have been proposed. While traditionally only P or PI controllers have been employed, recent applications that require a fast transient performance impose the usage of the derivative, D, term. As it is well known, using the D‐term can cause numerous problems in such converters that greatly downgrade their performance and lifetime. Having said that, in this paper, we first prove that by using the D‐term, it is possible to increase the stability margin (and hence keep a low current ripple), and then, we present a novel method to tune the PID controller that guarantees a fast and stable response over a wide range of parameter values without using an unreasonably high value of the derivative gain that magnifies the presence of noise in the system. The controller is designed utilising Filippov's method, and a simple and easy to implement strategy is proposed. Furthermore, an adaptive PID controller is designed whose gains are changed depending on the value of the supply voltage or output load. Another important contribution of this work is the derivation of the saltation matrix when the switching manifold is discontinuous, the complete proof is presented, and the results validated. Copyright © 2015 John Wiley & Sons, Ltd.     

Analytical multi‐parametric stability boundaries of DC‐DC buck converters under V1 control concept

Two main methods for controlling switching converters exist in the literature. The direct one is the voltage mode control, which suffers from some disadvantages such as slow response to load variations and an input voltage‐dependent total loop gain. The current mode control can overcome these problems but at the expense of extra cost and more complex control design. V¹ concept is a new promising control technique for designing voltage mode control of buck‐type converters with an optimal response similar to current mode control. In this paper, the dynamics and the stability of buck converters under V¹ control are studied. In particular, subharmonic oscillation limits in the parameter space are addressed. First, a closed‐loop state‐space model is derived and then used to formulate an analytical matrix‐form expression for predicting the stability limit of the system. Using this expression, multi‐parametric stability boundaries are obtained. It is shown that the equivalent series inductance of the output capacitor can narrow the stability region. It is also demonstrated that the integral action in the feedback loop of a V¹‐controlled buck converter has a negligible effect on the subharmonic oscillation boundary. The theoretical analysis is validated through numerical simulation of the circuit‐level switched model of the system. Copyright © 2017 John Wiley & Sons, Ltd.     

Fast switch fault diagnosis for PWM DC–DC low power converters

In this paper, a fast switching fault diagnostic scheme is proposed for low‐power pulse width modulation (PWM) DC–DC converters operating in different conduction modes. The outstanding feature of the proposed scheme is that no additional sensing circuits are needed. This is achieved by using the differential of output ripple voltage and the switch gate driver signal for diagnosis. Since the output voltage has to be normally measured for control purposes and the PWM signals are known to the controller, no additional sensors are needed in the proposed scheme. Moreover, based on the real‐time output voltage measurement and switch gate driver signal, the characteristics of switch open‐ and short‐circuit faults can be rapidly extracted, specifically, in less than one switching cycle. Besides, the fault detection scheme can be implemented by a low‐cost logical hardware circuit, which can be integrated into the control unit. The fault diagnosis principle, design considerations, and implementation of the detection scheme are discussed in this paper. Experimental results show that the fault detection system can detect the switching fault in four‐tenths of the switching period. Besides, the proposed method can be used in the applications where the output voltage ripple rate is more than 4%, which covers most situations. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A three‐vector‐based direct power control strategy for three‐phase voltage source PWM converters

For traditional direct power control strategy, there exist high steady‐state power ripples and large current harmonics. To solve this problem, this work proposes a novel three‐vector‐based direct power control strategy for three‐phase voltage source pulse‐width‐modulated (PWM) converters. Different from traditional predictive direct power control strategy, an improved vector table is presented and three voltage vectors are selected, which considers the impact of voltage vectors on the active and reactive power simultaneously. The performance of the three‐phase voltage source PWM converters with the proposed control strategy is investigated and compared with the predictive deadbeat direct power control strategy. Furthermore, the three‐phase voltage source PWM converters have also been tested in the condition of different loads and when voltage unbalance occurs. Simulation and experimental work are conducted. The results conclude that the proposed strategy is of simple structure and fast dynamic response. Besides, it can effectively reduce steady‐state power ripples and current harmonics, improving the performance of the three‐phase PWM converters. Copyright © 2016 John Wiley & Sons, Ltd.     

Optimal switching Lyapunov‐based control of power electronic converters

This paper presents new ideas and insights towards a novel optimal control approach for power electronic converters. The so‐called stabilizing or Lyapunov‐based control paradigm is adopted, which is well known in the area of energy‐based control of power electronic converters, in which the control law takes a nonlinear state‐feedback form parameterized by a positive scalar λ . The first contribution is the extension to an optimal Lyapunov‐based control paradigm involving the specification of the optimal value for the parameter λ in a typical optimal control setting. The second contribution is the extension to more flexible optimal switching‐gain control laws, where the optimal switching surfaces are parameterized by a number of positive scalars λ _j . Systematic derivation of gradient information to apply gradient‐descent algorithms is provided. The proposed techniques are numerically evaluated using the exact switched model of a DC–DC boost converter. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamic modeling of DC–DC converters with peak current control in double‐stage photovoltaic grid‐connected inverters

In photovoltaic (PV) double‐stage grid‐connected inverters a high‐frequency DC–DC isolation and voltage step‐up stage is commonly used between the panel and the grid‐connected inverter. This paper is focused on the modeling and control design of DC–DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. In the proposed overall control structure the output voltage of the DC–DC converter is regulated by the grid‐connected inverter. Therefore, the inverter may be considered as a constant voltage load for the development of the small‐signal model of the DC–DC converter, whereas the PV panel is considered as a negative resistance. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. The theoretical analysis is corroborated by frequency response measurements on a 230 W experimental inverter working from a single PV panel. The inverter is based on a Flyback DC–DC converter operating in discontinuous conduction mode (DCM) followed by a PWM full‐bridge single‐phase inverter. The time response of the whole system (DC–DC + inverter) is also shown to validate the concept. Copyright © 2011 John Wiley & Sons, Ltd.     

A new method of damping harmonic resonance at the DC link in a large‐capacity rectifier‐inverter system

This paper proposes a new method of damping harmonic resonance in the DC link of a large‐capacity rectifier‐inverter system, such as in rapid‐transit railways. A voltage‐source PWM converter is connected in series to the DC capacitor of the rectifier through a matching transformer, acting as a damping resistor to the DC capacitor current. No filters are needed to extract harmonic components from the DC capacitor current. This results in a quick response and highly stable damping. The relationship between the control gain of the PWM converter and the required rating is theoretically discussed. We show that the required rating is less than one‐thousandth of that previously proposed. In particular, regenerating the power consumed by the PWM converter is very important because of the large power in practical systems. Normally, an additional PWM inverter is connected to the DC bus of the PWM converter to regenerate the consumed power. The additional inverter regenerates the DC power to the AC source through a transformer. This method, however, makes the damping circuit complex, thus the proposed method for the DC‐link harmonic resonance is less practicable. In this paper, a simple and novel scheme that utilizes the DC‐link voltage of the rectifier as a DC source for the PWM converter is proposed. The excellent practicability of the proposed damping method with the novel regenerating scheme is confirmed using digital computer simulation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 53–62, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10172     

Nonaveraged control‐oriented modeling and relative stability analysis of DC‐DC switching converters

This paper presents a unified and exact nonaveraged approach to derive a frequency‐domain control‐oriented model for accurate prediction of the fast timescale dynamics and performances of switching converters with fixed frequency naturally sampled pulse width modulation and integrating feedback loop. Because the approach avoids averaging and approximations related to this process, a very good accuracy of the derived model is obtained. The main difference between the presented approach and the existing methodology for accurately predicting the behavior of switching converters is that, here, we break the feedback loop and we focus on analyzing the open‐loop gain and the effect of the system parameters on relative stability. This results in an approach much similar to control systems techniques rather than nonlinear dynamical system approaches. Consequently, the relative stability is tackled easily in the frequency domain. In particular, by treating the modulator as a gain depending on the operating point, the new model is formulated in such a way that standard control‐oriented tools such as Bode diagrams and root‐loci can be easily used. Therefore, the proposed approach gives some important issues like gain and phase margins that are highly useful in controller design. It is noticed that the crossover frequency, gain, and phase margins predicted by using the averaged model may deviate significantly from the actual values given by the proposed approach. The paper points out the sources of discrepancies and the theoretical results are validated by simulations using a circuit‐level switched model.     

直流微网双向DC/DC变换器虚拟惯量和阻尼系数自适应控制策略

在高新能源渗透率下的直流微网系统中,电力电子器件比例不断提高,导致系统存在低惯性问题,降低系统运行稳定性。为此提出了一种改进的虚拟惯量和阻尼系数自适应控制策略。该方法通过类比交流系统逆变器的虚拟直流发电机控制,分析直流微网系统在虚拟惯量和阻尼系数控制下负荷扰动量与输出电压扰动量的关系特性,将自适应控制策略引入虚拟惯量和阻尼系数。通过建立小信号模型,利用系统输出阻抗结合阻抗比判据给出虚拟惯量和阻尼系数的变化范围和边界,分析虚拟惯量和阻尼系数自适应选取下系统惯性变化及母线电压响应效果,该方法提高了直流微网系统惯性,同时改善了直流母线的动态响应。最后通过Matlab/Simulink仿真和RT-LAB半实物实验,验证了所提控制策略的有效性。     

一种直流微电网多光伏变换器新型功率分配策略

为了解决光伏单元在运行过程中因工作模式切换造成的母线电压波动问题,提出一种新型平滑切换控制策略。根据光伏电池的输出特性曲线,将输出功率对输出电流的微分作为控制变量。通过跟踪不同的dp/di指令值来实现光伏单元最大功率点跟踪模式、恒压下垂模式的控制以及两种模式间的平滑切换。在此基础上,针对多光伏变换器工作在恒压下垂控制时因线路阻抗差异造成功率分配精度较低的问题,提出一种基于二次调节的自适应下垂控制策略。此外,构建相邻光伏单元间的稀疏通信网络,并采用动态一致性算法实现相关平均信息的全局稳定收敛。仿真和实验结果表明,所提控制策略可以实现光伏单元工作模式切换过程平滑过渡和负荷功率的精确分配。     

A ZVS‐ZCS phase shift full bridge DC‐DC converter with secondary‐side control for battery charging applications

The output power requirement of battery charging circuits can vary in a wide range, hence making the use of conventional phase shift full bridge DC‐DC converters infeasible because of poor light load efficiency. In this paper, a new ZVS‐ZCS phase shift full bridge topology with secondary‐side active control has been presented for battery charging applications. The proposed circuit uses 2 extra switches in series with the secondary‐side rectifier diodes, operating with phase shift PWM. With the assistance of transformer's magnetizing inductance, the proposed converter maintains zero voltage switching (ZVS) of the primary‐side switches over the entire load range. The secondary‐side switches regulate the output voltage/current and perform zero current switching (ZCS) independent of the amount of load current. The proposed converter exhibits a significantly better light load efficiency as compared with the conventional phase shift full bridge DC‐DC converter. The performance of the proposed converter has been analyzed on a 1‐kW hardware prototype, and experimental results have been included.     

Two‐switch flyback PWM DC‐DC converter in continuous‐conduction mode

The two‐switch flyback DC‐DC converter is an extended version of the conventional single‐switch flyback converter. An additional switch and two clamping diodes serve as a simple, but an effective way to limit the switch overvoltages, which occur in the conventional single‐switch flyback converter due to the ringing of the resonant circuit formed by the transformer leakage inductance and the transistor output capacitance. The clamping diodes in the two‐switch flyback topology clamp the maximum voltage across each switch equal to the DC input voltage. This paper presents a detailed steady‐state analysis and design procedure of the diode‐clamped two‐switch flyback converter operated in continuous‐conduction mode (CCM). The power loss in each component of the two‐switch flyback converter is compared with those of the single‐switch flyback converters with and without RCD clamp, and is presented in a tabular form. The two‐switch flyback converter was bread‐boarded to validate the theoretical analysis. Experimental results from a 10 V/30 W, 100 kHz laboratory prototype verified that the maximum switch voltage is limited to the DC input voltage. Copyright © 2010 John Wiley & Sons, Ltd.     

Power Flow Analysis and DC‐Capacitor Voltage Regulation for the MMCC‐DSCC

This paper discusses power flow analysis and DC capacitor voltage regulation of a modular multilevel cascaded converter (MMCC) based on double‐star chopper cells (DSCC). This analysis reveals the relationship between the circulating current through the DC link and the average power flowing out of or into each chopper cell. The DC component of the circulating current supplies half the active output power to the upper and lower strings of the chopper cells, while in contrast the fundamental frequency component transfers an amount of power between the upper and lower strings. Thus, the MDCC–DSCC can balance the capacitor voltages among the cells by controlling the amplitude of the fundamental frequency component of the circulating current. A new control method based on power flow analysis is employed, and its effectiveness is verified by circuit simulation.     

电力电子开关变换器的滑模控制

以电力电子开关变换器为对象,分析带有开关元件系统的数学模型,应用变结构控制方法,调制电力电子元件的开关模式,以获得预期的电压、电流波形和动态性能。为减少抖振,引入了模糊控制,对传统变结构控制加以改进,综合二者优点,使系统既具有变结构控制的优良性能,又能最大限度地减少抖振。最后仿真结果验证了文中控制算法的有效性。