Compensation of Dead Time Effects Based on the New Switching Strategy

The dead-time inserted into the switching signals of inverters case the dead-time effect of output voltage distortion. The influence of dead-time on output voltage in inverters is analyzed in detail, Then, a new switching strategy, which can provide excellent inverter output voltage distortion correction, is proposed. At last, the experiment results of inverter are presented to demonstrate the practicability and validity of the control strategy.     

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.     

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.     

Theoretical Analysis and Design of Resonant DC Base High Frequency Inverter

A theoretical analysis of the Resonant DC Base High Frequency Inverter is given. A optimal control scheme for the short circuit current of the resonant inductor is proposed. The system parameters,output current,output voltage and characteristics of the Resonant DC Base in this scheme are analysed. In the theoretical analysis the load is supposed as a resistor to void the calculating error while the load is treated as a constant current source. The analysis and test result have proved that the optimal parameters of the Resonant DC are only determined by the load resistance and the output frequency.     

Parameter Simulation on the Control Strategy for a Parallel Hybrid Electric Vehicle by CRUISE

The purpose of a parallel hybrid electric vehicle(PHEV) is for the best energy distribution between internal-combustion engine(ICE) and electric motor though the appropriate control strategy.It can not only keep the advantage of the ultra-low emission of electric vehicles(EV),but also take advantages of the hyperbaric energy of ICE.Simulation model for PHEV is built based on CRUISE,an auxiliary control strategy is designed,and then parameter simulation study on the control strategy is performed.The simulation results show that according to the different control requirements,the vehicle performance can be improved by adjusting!the corresponding control parameters.     

simulation of a brushless direct current motor based on finite state machine theory

A novel method simulating a brushless direct current(DC) motor was presented, based on principles of hybrid system modeling and finite state machine theory. Brushless DC motor control mainly focuses on controlling the on/off condition and power switch duration. Modes of control therefore can be defined by corresponding states, and the states can be combined as a finite state machine. This approach uses the popular Simulink/Stateflow simulation method to control brushless DC motor loops. A three phase brushless DC motor was analyzed to illustrate the process of model building with Simulink/Stateflow. The analysis demonstrates the feasibility and validity of the proposed method.     

Simulation of The Torque Control System of Motor for Hybrid Vehicle

A strategy for induction motor control based on the grade of errors is developed to improve the performance of hybrid vehicle drive system. The stator flux error, electric magnetic torque error and flux position angle are used as control variables, and rules for the switching states are chosen according to the errors and the principle of the Direct Torquc Control. This strategy improves efficiently the electric magnetic torque response of the system. The result of simulation shows that this strategy is an ideal control strategy of hybrid vehicle, which can make the motor generate the electric magnetic torque efficiently, steadily and quickly.     

The efficiency of a Ni MH battery used in hybrid vehicles

The efficiency of the 60QNY6.5 battery is studied by testing and theoretical analysis in order to improve the control precision of hybrid electric vehicles (HEVs) and the battery useful life. A rig for testing the Ni MH batteries of HEVs is established. The data from experiments performed on the Ni MH battery are analyzed. Based on the experimental results and the temperature of the batteries, internal resistance and electromotance models of Ni MH batteries are proposed by function fitting methods. The theoretic formula for battery efficiency is deduced by the operational principle of the battery and motor, which provides theoretical basis for dynamic optimizing technology of HEV system controlling strategy.     

Two quadrant Current Chopper Control for Brushless DC Motor

In order to decrease the current ripple and improve the operating performances of the rare earth permanent magnetic brushless DC motor system,a two quadrant current chopper is used in the system and its operating principles are analyzed in this paper.The results of digital simulation and system experiment are presented and confirm that the system based on the two quadrant current chopper has attractive performances.     

A NEW DISCONTINUOUS CURRENT MODEL FOR SCR DC MOTOR SPEED CONTROL SYSTEM AND CURRENT ADAPTIVE CONTROL

The paper presents a new approximative model suitable to discontinuous current and continuons current in the three-phase controlled bridge rectifier DC motor control system. This model offers a new approach for discontinuous current adaptive control.As an example of application of the model, digital simulation results of discontinuous current adaptive control in a double-closed-loop control system are presented.     

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.     

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.     

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%.     

An asymmetric fault ride-through control strategy for PMSG wind turbine

In order to improve the asymmetric fault ride-through capability of PMSG wind turbine, a novel control method is proposed. This method can reduce the negative sequence current component in the grid side converter and eliminate the 2 nd order voltage fluctuation in the DC link capacitor voltage of the AC-DC-AC converter. The proposed control method employs the grid voltage feed forward to reduce the grid side negative sequence current component, while a novel power control concept, output power of generator tracking the grid side power, is applied to control the electro-magnetic power of the PMSG to eliminate the 2 nd order voltage ripple in the DC link. Simulation results for a 1 MW case study show that the control method can eliminate the grid side negative sequence current component and the 2 nd order voltage ripple in the DC link at the same time.     

Decouple control for symmetrical six-phase PMSM series-connects three-phase PMSM system based on harmonics couple

Symmetrical six-phase series-connected three-phase PMSM driven by single inverter is a novel multi-machines system. To research EMF harmonics influence on the decouple control of series-connected system, the series-connected system mathematic models with 2nd harmonic of symmetrical six-phase PMSM under d-q coordinates are deduced. The torque ripple amplitude and frequency influenced by harmonic are discussed. The decouple control strategy based on harmonic effect compensating is presented. And the simulations with variable operating states are proposed to validate the feasibility.     

A new control design for grid integration ofDFIG wind farm with VSC-HVDC

This paper proposes a control scheme for a doubly-fed induction generator (DFIG) wind farm with VSC-HVDC grid integration to ensure secure and reliable operation of power system with fluctuated wind power penetration. The whole system dynamic models are respectively described. Based on vector control system with a virtual voltage orientation, a steady-state voltage control block and a dynamic voltage control block with a cross-product term of d-q currents are separately designed for WFVSC to control the corresponding parts of the wind farm voltage. Meanwhile, with the consideration of AC and DC side parameter variation and external disturbance, an improved backstepping control scheme with Lyapunov stability provement is also proposed for the GSVSC. The combination of the two schemes makes up the new control design of this study. Besides, to verify the performance of the proposed new control design, three different cases are suggested which contain the AC and DC side parameter variation and external disturbance such as local load cut off-in, grid voltage harmonics. Finally, numerical simulations using MATLAB/Simulink are presented for a 200MW DFIG wind farm with VSC-HVDC grid integration to validate the proposed control scheme and demonstrate the improved system operation performance. Moreover, the corresponding discussions are also presented for further illustrations.     

A SELF-TUNING CONTROL FOR A PARALLEL AC/DC POWER SYSTEM

Based on a non-linear system model, an adaptive control methodology is presented for a parallel AC/DC power system by means of on-line recursive parameter identifications. Taking the advantage of rapid power regulatiing ability of the DC power system and combining with the generalized minimum variance self-tuning control principles, the dynamic qualities of the controlled system has been greatly improved. Using SISO form makes the control system very simple to implement. Through the design, simulation and analysis of the self-tuning control system for a practical example, it shows that the self-tuning control strategy is very promising for AC/DC power systems.     

Model predictive control strategy of a medium hybrid electric vehicle

The intense coupled and nonlinear behaviors were observed on the tall long span tower line systems which were under the icing and wind loads in heavy icing areas. A set of stiffness equations of insulator, conductor and boundary conditions was deduced. Taking the ±800 kV UHV DC transmission line from Xiangjiaba to Shanghai as an example, the simplified numerical model of transmission tower, conductor, insulator and constraint was developed. The long span transmission tower line system models under seven loads conditions were analyzed by static nonlinear methods. It was found that the P Δ effect of tower components was small when the covered ice was uniformly distributed. The unbalanced wire loads on the tower would lead to twist effect when the covered ice was uneven distributed. The axial forces, moments at restraint nodes and the longest cantilever member were greatly affected by the P Δ effect, under which the unfavorable effect on the structure should be considered.     

A dual-boost three-phase DC link active power filter based on coupled impedance

A three-phase DC link active power filter (APF)based on coupled impedance and its control strategy are proposed in order to eliminate the input current harmonics of the three-phase diode rectifier. The presented APF is composed of impedance network and two asymmetric dual Boost converters. Average current control is adopted to control the DC link APF. The switch signals of the two asymmetric Boost converters are obtained respectively by leading and trailing edge modulation methods. Compared with the normal DC link active power filter,this topology reduces an active switch and a capacitance. So it can reduce costs,and there is no voltage imbalance in the DC link. Simulation results verify the correctness of the proposed topology and the corresponding control method.     

Theoretical analysis on the protection properties against electric shock of low voltage DC distribution system with different grounding types

The low voltage direct current(LVDC)distribution system has great potential and advantage to be applied to conventional areas, such as residential house, due to its characteristics of energy conservation and being eco-friendly, but there is no existing standard specifications to guide its application in practice to ensure the electrical safety of this system. The protection against electric shock is a key indicator of electric safety, but the effect of electric shocks on AC and DC are different. Refer to the international standard IEC60479-1 and analytical method in AC system, the protection against electric shock between DC 750, 400, 300, 220 V and AC 220 V systems are compared and analyzed based on ideal DC source model. It demonstrates that the negative grounded TT & TN DC distribution system has significant advantages over the traditional AC system, and the safety voltages are given, which could be a reference to develop the normative guidance for the application of LVDC in practical application.