Vector control of permanent magnet synchronous motor with variable DC-link voltage

As for the drive of control system in electric vehicles, if the inverter power is supplied by a constant DC-link voltage, there are some disadvantages in the system, such as small utilization of the voltage, big current harmonic distortion of the motor windings. A new strategy for vector control of permanent magnet synchronous motor (PMSM) with variable DC-link voltage is proposed, which is suitable for electric vehicles. According to the reference voltage amplitude of the inverter, the new system uses bidirectional DC/DC converter to adjust the DC-link voltage to improve the performance of the vector control system. At last, the whole system is simulated with MATLAB software. The simulation results show that the new strategy for vector control can increase voltage utilization, decrease torque ripple, improve current waveform effectively and decrease the total harmonic distortion of motor current. The results also verify the effectiveness and feasibility of the new strategy.     

The power-supply of X-ray machine adopting PID control and high-frequency inverter technology

To solve the problem of low control accuracy and low stability of current X-ray machines, a kind of digital power supply for X-ray machine is introduced. In the digital power supply, some key technologies are used to improve the output stability of the high frequency inverter, including improved BUCK circuit for voltage regulating circuit, high frequency inverter and soft switching technology for the high-voltage generator. The PWM control technology is used to control the switch transistor of voltage regulating circuit and inverter circuit, which makes the drive waveform output stable and easy to control. In order to improve the control accuracy, reduce the volume and change high voltage consecutively, the software PID of the microcomputer is used to control the feedback circuit. The high-accuracy power chip is used for the filament power supply to make the filament electric current stable. Through the analysis of the circuit, the parameters of the circuit are calculated and the circuit is simulated by PSPICE software. The results show that the theoretical analysis is consistent with the practical simulation results. The design can meet the requirement of the technology indices of the power supply of the X-ray machines.     

Research on a Novel Inverter of VSC

In order to improve waveform performance of light HVDC system, a lot of switches which operate in high frequency are used, which causes large switching losses and results high cost. A new Buck type voltage source converter(BVSC) is proposed. The new BVSC comprises a dual-buck converter and a three-phase inverter operating in grid frequency. Only two high frequency switches are used, which results good output waveform performance. In order to reduce the high frequency switching losses, a novel improved double-frequency Buck type voltage source converter(DBVSC) is also proposed. An additional dual-Buck converter is added to the BVSC, the added dual-Buck converter deals with the fundamental power that operates in low frequency, and BVSC only deals with harmonic power that operates in high frequency. The output waveform is enhanced and the switching losses are reduced in DBVSC, and the power rating is also increased. The DBVSC is very suitable for large power rating application. The one cycle control theory is adopted to control the proposed DBVSC with analog circuit, which is very simple. The proposed DBVSC and control method are verified by simulation.     

Utility Analysis of Reclosing in the Distributed Generation System

According to the type of the DG,the working situations of the reclosing are studied.The actual parameters of DG's rated capacity and transient reactance are adopted.According to the location and capacity of the DG, the possibility of auto-reclosing is analyzed,and the parallel feed inverter used in this system and its control method is presented.The system model and calculation results are given in MATLAB.It shows that the auto-reclosing technique is feasible in the distributed generation system and for some DGs connected to the net by inverters,the current instantaneous feedback control can realize the switching condition.     

Single-end Flyback High-frequency High-voltage Switching Power Supplies

Based on the research of a practical project of high frequency high voltage switching power supplies,the system design and experimental investigation of a single end flyback high frequency high voltage switching power supply are presented. In order to solve the problem of durable voltage of power MOSFETs that are used in the single end flyback high voltage switching power supply,an effective approach that adopts dual MOSFETs in series connected is proposed.The procedure of the designing and the parameter of each device is given in detail.A prototype of 220 Volt input and 2000V/3mA output is developed, and the validity of the scheme is demonstrated by the experiment.     

A Control Algorithm to Regulate the Active and Reactive Power and Simulation Research of Dual-frequency Dual-Buck Inverter

This paper deduceS the control algorithm ,which can both regulate the active and reactive power of the novel dual-frequency dual-Buck inverter, and the control function. The control function based on one cycle control can control the AC-side active and reactive power by simple circuit. The simulation is given and the results prove the validity of the theory analysis. This inverter is valuable for the research of grid-connected inverters.     

One-cycle Technique Based Adjustable Ac Source

By using one-cycle control theory, a novel voltage source inverter is proposed. The conventional one-cycle control technique needs that the integrator is reset instantaneously. But it is very difficult to realize with hardware due to the finite time constant of the reset circuitry. Therefore, based on the one-cycle technique, the paper gives a new control scheme to resolve the problem with dual switched integrator, and the performance of the integrators is close to ideal. The paper also uses the dc offset to implement the voltage measurement. Furthermore, the amplitude and frequency of the output voltage are effectively adjustable. The one-cycle control technique not only provides fast dynamic response, but also can admirably suppress the perturbation yielded by dc source and abate the undesired harmonic contents. Simulation studies were performed to prove the proposed scheme. The results show that the one-cycle control based voltage source inverter makes good use of dc source that is 92.8% and THD is only O. 255 9%.     

Hierarchical control method of low voltage looped microgrid

The low voltage (LV) looped microgrid has high reliability of power supply and good accessibility of the DG. The medium voltage distribution network with single loop network and multi sectioned & multi linked is studied to analyze the wiring mode of the LV looped microgrid. A research on the two hierarchical control scheme of the looped microgrid is conducted, and the sub microgrid, which meets island operation requirements, is divided according to their segments. Then the incidence matrix is formed based on the connection relation of different segments and components, and the plan for switching the microgrid operation status is concluded from the reform of incidence matrix on the basis of the judgment of island and reconnection segments. A resynchronization strategy using microgrid central controller is proposed. The MATLAB/SIMULINK simulation software is used to analyze the dynamic characteristics of different operation status switching and synchronizing, and the results verify the effectiveness and correctness of the proposed control method.     

Commutation Failure Factors Analysis In HVDC Transmission System

Commutation failure is one of the most common faults in HVDC transmission system, which is affected by many factors. This paper analyzes the effects of some major factors, such as voltage of commutation bus, DC current, advance firing angle, short circuit impedance and ratio of converter transformer, on the commutation failure in the inverter in HVDC transmission system. The obtained general rule of commutation failure in the inverter in HVDC transmission system is helpful to practical operation.     

Comparative study of aircraft three-phase power factor corrections

This paper summarizes the requirements of standards for aircraft power supply firstly,and then points out that the input current harmonic and output DC voltage ripple should be considered seriously when designing three-phase power factor correction (PFC)for aircraft under variable line frequency and unbalanced line supply. Based on reviewing the topologies for aircraft three-phase PFC,three typical topologies,i.e. three-phase pulse width modulation (PWM)rectifier,traditional shunt active power filter (APF)and generalized APF,are picked up. A unified single-phase equivalent model is developed for comparing the harmonic suppression performance of the three active PFC schemes. And the switching stress is also calculated for evaluating their efficiency and power density. Three 5 kW PFC are designed by employing each of the three selected schemes. Simulation is carried out to verify the correctness of the theoretical analysis. The theory and simulation results indicate that the generalized APF topology shows the most technical merit for aircraft three-phase PFC. Future research works on generalized APF are also pointed out,which are solving the uncontrollability of its DC output voltage and optimal designing the filter inductors.     

含旋转电机接口和逆变器接口的微网小信号稳定性分析

提出了一种包含了逆变器接口（voltage source inverter,VSI）、同步电机接口（synchronous generator,SG）的独立微网控制策略,并分析了其小信号稳定性。VSI接口和SG接口的分布式电源均采用下垂控制策略,二者之间无需实时通信,可实现负荷功率共享。建立了系统的小信号状态空间模型,主要包括：同步发电机及其控制器的小信号模型、逆变器及其控制器的小信号模型、电网络及负荷小信号模型。计算了下垂增益变化时的根轨迹,得到了系统主特征值随参数变化的根轨迹,计算了不同状态变量对特征值的参与因子。稳定性分析结果表明：当所有分布式电源采用下垂控制时,引入同步发电机接口的分布式电源,系统频率小信号稳定性大大增强。PSCAD时域仿真验证了特征值计算的正确性。     

Improvement and simulation on direct torque control system of permanent magnet synchronous motor

To solve the problems of large flux, torque ripple and inconstant inverter switching frequency in conventional direct torque control (DTC), a space vector modulation (SVM) technique is introduced to the conventional PMSM-DTC system and analyzed thoroughly based on the mathematical model. This novel control method which enjoys the advantages of VC and DTC has only one easy adjustable PI regulator and is easy to realize. The simulation verifies that this control system is capable of effectively improving the steady state performance and keeping the excellent dynamic performance of the PMSM-DTC system simultaneously and remain the switching frequency constant.     

应用STATCOM的DFIG风力发电机低电压穿越能力分析

针对DFIG（double fed induction generator）风电机组低电压穿越能力（LVRT,low voltage ride through）问题,笔者基于STATCOM研究了一种电压外环与电流内环相结合的双闭环反馈控制策略,并仿真验证了所提出方法的有效性。将STATCOM分别安装风电机组机端、并网点高压侧和低压侧,且设置不同电压跌落深度,比较其补偿效果。实验结果表明,安装在风电机组机端时补偿效果最好。在电网电压跌落时,STATCOM能快速为电网输入无功,抬高风力机的机端电压,从而提高风电场的LVRT能力,从STATCOM输出无功大小和风电场机端电压被抬升的比例两方面分析,对于不同深度的电压跌落,STATCOM补偿效果都较为显著。     

Dual mode AC DC AC converter for contactless power transfer system

A new type AC DC AC converter which can work in Buck or Boost mode is proposed in order to overcome the deficiencies of the primary circuit of the traditional contactless power transfer system. Through switching this two modes and turning the duty cycles of the switches, not only the resonant current amplitude of the primary resonant current can be controlled to be constant against a wide range variation of input voltage, but also the problems, such as surge current, high cost, complex control etc., caused by the DC filter and DC/DC converter in a traditional CPT system are effectively eliminated. The topology and operation principle of the proposed converter have been analyzed. The corresponding control strategy has been presented and verified by simulation results.     

Modelling and Analysis of Multi-terminal Unified Power Flow Controller

To control the complex powers emanating from a bus in power system, there are two solutions. The obvious solution is to equip each of the n lines radiating from the node with its own UPFC. The next evolution of the idea is to equip with a multi-terminal UPFC. First, the configuration and the principle of the Two-terminal UPFC (when n=2) are presented. In consideration of the existing shortages of output model-constructing method and topological model-constructing method for T-UPFC, a switching function mathematical model of this device is constructed by introducing the concept of switching function. It has more generality than the output and the topological model with the consideration of the internal switching character and the physical course of the T-UPFC.     

EQUAL ARA ALGORITHM OF PWW WAVEFORM

This paper presents the equal theory of the sine wave voltage and PWM waveform in the integration of time. Using the graphic method as well as the comparison method of sequential integration the PWM control pattern is calculated. Depending on an example for PWM circuit inverter the microcomputer is investi-gated. The method is simple and effective. It is specially adeguate to the engineering control.     

Modeling and control of An LCL bi-directional inductive power transfer system

Since there exist high-frequency switching networks and complicated operating modes in bi-directional inductive power transfer (IPT) system, it is easy to result in high harmonics and EMI interference. An LCL filter network is introduced to effectively filter out the unwanted harmonics in track current and reduce EMI interference. Based on a mathematical model of the power transmission established by complex analysis of the AC variables, under the condition of maximum transmission efficiency, the phase angle differences between the primary input voltage and secondary output voltage U·so are ±90° and the energy is respectively transferred in forward or backward direction. Moreover, the power magnitude can be controlled by adjusting the modulus of U·pi and U·so. In addition, to keep the track current constant, different phase-shifting control strategies are designed in the primary and secondary parts. Simulation and experimental results show that these strategies can not only adjust track current to keep constant but also dynamically change the direction and magnitude of power transmission according to the working conditions and actual needs of the system load to improve the system operating efficiency.     

Full bridge LLC series resonant converter for X-Ray high voltage DC power supply

To prevent the duty cycle loss of full-bridge converter controlled by the phase-shifting method, a high frequency high voltage X-ray power supply is proposed. It combines full bridge LLC(FB-LLC) series resonant converter with bipolar single-phase symmetrical voltage multiplier. FB-LLC series resonant, high voltage transformer and bipolar single-phase symmetrical voltage multiplier are used in the main circuit. The LLC series resonant circuit and working conditions of soft switch are analyzed. The fundamental harmonic approximation model is established. The parameters of the main circuit are designed. The simulation results show that the output voltage adjusted continuously within 40~120 kV and without duty cycle loss. The X-ray power supply is proposed to achieve a quick rise and low ripple of output voltage. According to the simulation results, the proposed topology is correct and reliable.     

A Review on Class D Audio Power Amplifier Control Techniques

Although class D amplifier has high efficiency, its distortion is larger than linear counterparts due to switching behaviour of power transistors. It is the hotspot of power electronics and audio power amplifier that researching new control technique to improve fidelity of class D amplifier. In this paper, a few novel control techniques in class D audio power amplifier are reviewed.     

One-cycle Control Three-phase Four-wire Active Power Filter with Four-arm

This paper presents a three-phase four - wire active power filter based on one-cycle control. This method need not sense the three phase load currents or the three phase voltages, need not use any multipliers. It has simplified circuit , and the controller is composed of four integrators with reset along with several flip-flops, comparators and some analog components. The main circuit switching frequency is constant, which is desirable for industrial applications. Analysis and simulation are carried out with the four-arm inverter, the simulation results verify that the APF with one-cycle control can dynamically and effectually compensate the harmonics, reactive current and zero sequence current.