Isolated Ac/Dc Converter Using Soft Switching Technique

This paper presents a high‐frequency isolated ac/dc converter using the soft switching technique. The ac/dc converter consists of a matrix converter for transforming three‐phase ac voltage to high‐frequency ac voltage, a high‐frequency transformer, and an ac/dc rectifier. In order to reduce the switching loss, soft switching at every commutation of the matrix converter and ac/dc converter is achieved. The effectiveness of the proposed converter and the control scheme was verified by experiments.     

Research on Maximizing Power Transfer Efficiency of Wireless In‐Wheel Motor by Primary and Load‐Side Voltage Control

The authors have developed a wireless power transfer (WPT) system for an in‐wheel motor (IWM). It is called a wireless in‐wheel motor (W‐IWM). This paper presents a method that enhances the WPT efficiency in this system. Some methods that maximize the power transfer efficiency by power converter control have been proposed in the past WPT research. In this research, a dc‐dc converter is inserted on the receiver side to vary the load state. However, the space on the receiver side is very small for the W‐IWM; therefore, it is preferable to make the secondary circuit small. Therefore, a full bridge converter is used instead of a dc‐dc converter in the W‐IWM. In this paper, the authors propose a theoretical formula for the transfer efficiency of the IW‐IWM. From an analysis of this formula, there is a combination of a primary voltage and load voltage that maximize the efficiency. The feasibility is validated by an experiment using a motor bench set.     

Extension of the variational equation to analog/digital circuits: numerical and experimental validation

Conventional shooting methods cannot be used to determine the steady‐state solution of circuits whose model is characterised by a vector field exhibiting zero order discontinuities. In the analysis of circuits working on a stable limit cycle, this limitation prevents the use of methods that exploit Floquet theory to compute the variational model and thus the properties of the fundamental matrix and, for example, phase noise in oscillators. In this paper, we use an improved shooting method that solves this drawback by resorting to saltation matrices and show how this method makes possible the correct computation of the first left eigenfunction (known as ppv ) of the fundamental matrix. ppv s are a key aspect in determining phase noise. The results obtained through numerical simulations are compared with measurements on a relaxation oscillator serving as a simple but significant comparison vehicle. Copyright © 2012 John Wiley & Sons, Ltd.     

Operation analysis of quasi‐resonant,high‐frequency transformer link dc–ac converters applied to phase‐shift PWM control on the secondary side

In recent years, the soft‐switching techniques have attracted attention for their peculiar advantages such as low switching loss, high power density, EMI/RFI noise reduction, and so on. The authors have previously reported on a quasi‐resonant dc–dc converter using new phase‐shift PWM control scheme. By using the proposed control scheme, circulating current is eliminated and ZVS (Zero Voltage Switching) is achieved with small commutating current. As a result, the conduction losses caused by their currents are substantially reduced. In this paper, the authors apply a proposed control scheme to a quasi‐resonant high‐frequency transformer link dc–ac converter. As a result, all switching devises in this dc–ac converter can achieve soft switching with small commutating current irrespective of inverter mode and rectifier mode. Its operating principle and unique features are described as compared with the symmetrical control scheme of dc–ac converter. Operating performance of this dc–ac converter in the steady state is illustrated by means of simulation results. © 1999 Scripta Technica, Electr Eng Jpn, 130(2): 88–98, 2000     

The Proposal of Isolated Single‐Stage AC‐DC Converter

An isolated ac‐dc converter has been used in various applications, such as power supply and as a battery charger for electric vehicle. In conventional converters, a loss in each conversion stage can be reduced by applying a soft switching method. However, a conventional converter has many conversion stages including the rectifier stage, power factor correction, and dc/dc converter stages; thus, it is difficult to reduce the total converter loss and size. In this paper, we propose a novel isolated‐type ac‐dc converter with only one conversion stage; it can realize a zero‐voltage switching operation in all switching devices.     

Single‐Inductor Dual‐Output DC–DC Converter Design Using RC Ripple Regulator Method

In this paper, we have proposed Single‐Inductor Dual‐Output (SIDO) buck–buck and boost–boost dc–dc converter using improved RC ripple regulator control. The proposed SIDO buck–buck converter has the characteristics of low‐ripple and high control frequency. RC ripple regulator control cannot be applied to SIDO boost–boost converter because RC ripple regulator undergoes self‐excited oscillation and two self‐excited oscillating controllers make the SIDO converter unstable. Thus we proposed the priority circuit for RC ripple regulator control. The proposed control circuit improves response characteristic and simplicity of the control circuit. Simulations are performed to verify the validity of the proposed SIDO converter. Simulation results indicate good performance of the proposed SIDO converter.     

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.     

Design of robust digitally controlled DC–DC converters in the presence of strong interference

One of the main advantages of digital control is the ability to design more sophisticated control strategies to enable high‐performance dc–dc converters. One such example is a buck converter operating with a digital state‐feedback controller. Previous works characterise the nonlinear dynamics of such systems under ideal operating conditions. However, in practical applications, these conditions cannot be guaranteed. The focus of this work is on the behaviour of such systems when they operate in the presence of strong interference signals. Previous works on the effect of noise have shown that intermittent operation is possible when the frequency of the noise signal is close to the switching frequency. Intermittent operation can be characterised by long periods of stable operation interspersed with periods of unstable or chaotic operation, which greatly downgrade the efficiency and performance of the converter and reduce its lifetime as for example increase the current ripple or add extra AC components at its output. Typically, such behaviour is avoided by modifying the circuit parameters. However, little or no work exists on developing design guidelines in order to effect its elimination. This is the focus of this research, that is, by utilising Filippov's theory on discontinuous differential equations, to set out a design procedure that can be applied to any dc–dc converter, to tune its controller in order to eliminate intermittent operation. As a case study, the digitally controlled buck converter with a state‐feedback control law is selected. Copyright © 2017 John Wiley & Sons, Ltd.     

基于模式切换的固态变压器多直流电压平衡控制方法

能源互联网通过固态变压器整合分布式可再生能源,但是容易出现不同H桥模块间电压失衡、直流变换效率低以及能耗高的问题。因此,研究基于模式切换的固态变压器多直流电压平衡控制方法,分析固态变压器中的负责能量传递的双移相桥隔离型双向直流变换器损耗分布情况,为直流变换器效率优化提供分析依据,通过移相控制模式和梯形电流控制模式间的合理切换控制,提高直流变换器效率,实现固态变压器中双向直流变换器全功率范围内的损耗最佳控制,在此基础上,通过单相任意单元数级联H桥固态变压器的SVPWM算法,解决变压器的模块级联H桥型固态变压器出现不同H桥模块间的均压问题,实现变压器多直流电压的平衡控制。结果表明,该方法对固态变压器多直流电压平衡后,使得变压器电网电流谐波小,固态变压器AC／DC的3H桥电容电压达到了平衡状态,固态变压器直流母线端口电压以及低压直流端口电压稳定,达到平衡状态。     

Control and protection scheme of HVDC system with self‐commutated converter in system fault conditions

For extending self‐commutated converter application to future trunk power systems, it is important to develop a stable operation scheme as well as to realize substantial cost reduction through coordinated system and control design. Suppression controls of converter overcurrent and dc overvoltage in various system fault conditions are essential in order to ensure stable operation and cost reduction of HVDC systems with voltage source type self‐commutated converters. Converter control and protection schemes which include such suppression controls have been developed, employing CRIEPI's ac/dc Power System Simulator test and EMTP analysis. This paper first discusses the cause of converter overcurrent at ac system faults, considering the effect of PWM pulse number and converter control speed. Continued operation has been achieved by adding a new overcurrent suppression scheme to the converter control. In the case of a dc line grounding fault, the selection of the grounding circuit constant and the adoption of a high‐speed converter control practically ensure the reduction of dc overvoltage while suppressing converter overcurrent. The converter block and restart sequence after a dc fault, which is coordinated with dc circuit breaker operation, enables stable recovery of HVDC transmission as fast as the usual line‐commutated HVDC system. © 2000 Scripta Technica, Electr Eng Jpn, 132(2): 6–18, 2000     

A convex optimization approach to adaptive stabilization of discrete‐time LTI systems with polytopic uncertainties

This paper suggests a simple convex optimization approach to state‐feedback adaptive stabilization problem for a class of discrete‐time LTI systems subject to polytopic uncertainties. The proposed method relies on estimating the uncertain parameters by solving an online optimization at each time step, such as a linear or quadratic programming, and then, on tuning the control law with that information, which can be conceptually viewed as a kind of gain‐scheduling or indirect adaptive control. Specifically, an admissible domain of stabilizing state‐feedback gain matrices is designed offline by means of linear matrix inequality problems, and based on the online estimation of the uncertain parameters, the state‐feedback gain matrix is calculated over the set of stabilizing feedback gains. The proposed stabilization algorithm guarantees the asymptotic stability of the overall closed‐loop control system. An example is given to show the effectiveness of the proposed approach. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of High‐Power Density Interleaved dc/dc Converter with SiC Devices

We developed an interleaved dc/dc converter with SiC devices. We applied full‐SiC modules including MOSFETs and SBDs to the interleaved dc/dc converter to achieve a high‐power density. An SiC has a high temperature resistance, which facilitates an improvement in high‐frequency drives. We achieved a high‐power density by utilizing this high temperature resistance. We also fabricated a prototype and tested it with loads up to 65 kW.     

小波变换在变频机组定子故障诊断中的仿真研究

在变频机组运行过程中,定子突然出现故障是变频机常见故障之一,严重时会造成重大的经济损失和恶劣的社会影响。定子突然出现故障时,无论是外部故障还是内部匝间短路故障,它们的共同特征就是定子电流会产生突变信号。小波变换模的极值点常对应于信号突变点。利用Matlab/Simulink模块建立了变频机组定子的外部故障和内部故障模型。利用小波变换模极大值方法对两种故障模型进行了诊断,不但能够检测出故障,而且还能对故障发生的时刻进行准确的定位,实现了变频机组的实时诊断。     

Unified Pulse‐Width Modulation Scheme for Improved Digital‐Peak‐Voltage Control of Switching DC‐DC Converters

Contrast to conventional dependent double‐edge (DDE) pulse‐width modulation (PWM), independent double‐edge (IDE) PWM is investigated and applied to the control of switching dc‐dc converters, with improved digital‐peak‐voltage (IDPV) controlled buck converter in this paper. IDE modulation unifies all the PWM schemes reported up to now and is thus called as unified PWM. It is revealed that conventional trailing‐edge, leading‐edge, trailing‐triangle, and leading‐triangle modulations are special cases of IDE modulation. The control laws of IDPV controlled buck converter with IDE modulation are investigated and compared with those of IDPV with DDE modulation. Their stabilities and robustness are analyzed subsequently. Digital implementation of the unified PWM is also carried out. Steady‐state and transient performances of IDPV controlled buck converters with IDE modulation and DDE modulation are compared and verified by experimental results. It is concluded that steady‐state and transient performances of IDPV with IDE are better than those of IDPV with DDE modulation. Copyright © 2012 John Wiley & Sons, Ltd.     

含恒功率负荷直流微电网的状态反馈电压振荡控制技术

扰动发生后新能源发电和恒功率负荷侧换流器在现有功率控制模式下所表现出的负阻抗特性,会大幅增加直流电压振荡失稳的风险.为此,首先针对直流电压振荡失稳的问题,推导含恒功率负荷两端直流微电网的小扰动线性化状态方程.其次,结合各状态变量的参与因子,选取振荡电流、电压作为可调节控制参数,将其分别引入储能换流器与恒功率负荷换流器的占空比反馈环节中,提出基于状态反馈的多端直流电压振荡控制方法.然后,利用根轨迹、Bode图分析附加状态反馈电压振荡控制技术后的直流微电网稳定裕度的变化规律,为控制参数设计提供依据.最后,搭建时域仿真系统,验证了所提出的控制方法可有效抑制直流微电网的电压振荡,显著提高系统的动态稳定性.     

Fundamental Research on Control Method for Power Conversion Circuit of Wireless In‐Wheel Motor Using Magnetic Resonance Coupling

The in‐wheel motor (IWM) is the most preferred driving mechanism of electric vehicles for its advantages of vehicle motion control, energy efficiency, and vehicle design flexibility. One of the technical problems of the IWM is the reliability of power and the signal wires. Wireless power transfer technology is the best solution to this problem. In this paper, a bidirectional wireless power transfer circuit using a primary inverter and a secondary converter is proposed. We propose a control method for both the inverter and the converter to stabilize the secondary dc‐link voltage. The proposed method is verified by simulation and experiment using simulated test equipment.     

Three-phase voltage-fed type PWM power converter via power factor control

Recently, the voltage-fed type PWM converters have been investigated for their ideal and inherent properties as a dc power source. However, the current control system generally used may be somewhat complicated due to dc voltage detection. We propose here a simple control system of the PWM converter using the power factor control in which dc voltage detection is not always needed. In this system, the dc voltage is given by the line voltage and the modulating index of the PWM converter. The principle of the PWM control system is shown at first. From the simplified circuit model and its phasor diagrams, some basic relations of the PWM converter system are obtained and some fundamental characteristics are shown. From these investigations, it is seen that the phase control region is restricted to a certain angle, which depends on the setting power factor, the modulating bypass index of the PWM and the load. Under the operating condition of unity power factor, it is given by ±π/4 for both the converting and inverting operations. The system can be operated over the all-control range of the modulating index by restricting the angle to this critical value for the angle over this control range. The ideal operating characteristics as a dc power source can be verified by some experimental results, including the operating waveforms of line current, the steady state characteristics and the transient response between both operations of the converter and inverter. In this system it is simple to construct the control circuit; it also has some inherent and excellent characteristics as a voltage fed type dc power source. This control system may be applicable to any types of PWM converter used today.     

Fully parameterized fixed‐order controller design for H∞ loop shaping method using frequency responses—extension to MIMO systems

Robust control is often applied to systems with uncertainties and disturbances. Above all, the H∞ loop shaping method is known to achieve good control performance and robustness. In this method, the final controller consists of weighting functions and a stabilizing controller. The stabilizing controller is derived for the shaped plant to suppress the H∞ norm of the transfer matrix consisting of a sensitivity function, a complementary sensitivity function, and so on. In addition, the stabilizing controller improves robust stability margin while keeping gain characteristic of the shaped plant if weighting functions are suitable. As a result, the closed‐loop system is well‐balanced between good tracking and robustness. However, a final controller tends to be high‐order. For this problem, reduction techniques are often applied to the final controller. In this case, performance and stability is not always adequately evaluated due to errors by the controller reduction. This paper proposes a fully parameterized fixed‐order controller design method using frequency responses of the plant. We formulate a design problem for multi‐input–multi‐output systems as an optimization problem. Therefore, we can directly design a low‐order controller from frequency responses using the iterative LMI optimization. Accordingly, we can avoid to deteriorate the evaluation of performance and stability.     

A Hybrid DC Circuit Breaker Combining a Multilevel Converter and Mechanical Contactors: Verification of the Principles of Operation by Experiment and Simulation

This paper presents a new hybrid dc circuit breaker producing no conducting power loss under normal operating conditions and having the capability to interrupt a large amount of short‐circuiting current within several milliseconds. It consists of two reactors for current limiting and current control, two mechanical contactors, and a multilevel converter based on the cascade connection of multiple full‐bridge dc/dc converter cells. It is characterized by achieving current commutation from the main mechanical contactor to the multilevel converter with fast current control. This results in eliminating auxiliary power semiconductor switches that produce a nonnegligible conducting power loss under normal operating conditions. This paper discusses both principles of operation and control method of the new hybrid dc circuit breaker. Experimental verification is performed by a downscaled system rated at 300 V and 150 A, along with verification by computer simulation.     

SYNCHRONIZING TORQUE MATRICES AND STATIC BIFURCATIONS IN MULTIMACHINE POWER SYSTEMS

Abstract

The synchronizing torque matrices are used to characterize the transition from stability to instability in a multimachine power system. This transition is called a bifurcation. In this paper we concentrate on static bifurcations. Two representaions are used: the clssical and a detailed one. It is shown that steady state instabilty can be identified by checking the signs of the eigenvlues of the synchronizing matrix. This method has the advantage of applicability to any representation classical or detailed. It also provides a more convenient alternative to the identification of instability by the sign of the determinant of the Jacobian as suggested in the Russian literature. The method is checked using two systems: one with five machines and the other with ten.