Jian Chen

Maximal Power Point Tracking under Speed-Mode Control for Wind Energy Generation System with Doubly Fed Introduction Generator

The Doubly Fed Induction Generator (DFIG) with back-to-back four-quadrant converters between its rotor winding and the grid can realize the maximal wind energy capture in variable-speed wind energy generation system. Based on the stator flux-oriented excitation vector control strategy, this paper presents that the system dynamic characteristics under speed-mode control are superior to the dynamic characteristics under current-mode control in the process of Maximum Power Point Tracking (MPPT) and brings forward the explanation based on state space theory. And it designs the gains of two typical PI controllers in the current inner loop and the speed outer loop under speed-mode control based on Internal Model Control (IMC) theory and pole assignment method, respectively. At last, simulation results in MATLAB/SIMULINK are put forward to verify the good static and dynamic performance of the designed closed-loop control system.

Practical approaches and novel control schemes for a three-phase three-wire series-parallel compensated universal power quality conditioner

Three-phase three-wire series-parallel compensated universal power quality conditioner based on two voltage-source converters controlled separately by two digital signal processors is discussed at length. Different from those popular active power filters, the series voltage-source converter is controlled as a fundamental sinusoidal current source in phase with the utility, while the parallel voltage-source converter is controlled as a fundamental sinusoidal voltage source with constant voltage and constant frequency. These novel control schemes and some practical approaches are both verified by detailed experiment results. It is shown that the total harmonic distortion values of input current and output voltage are both less than 5% with almost unity input power factor, even in the case of distorted utility and feeding reactive and nonlinear loads.

Study on dual-DSP-controlled three-phase series-parallel compensated line-interactive UPS system (delta-conversion UPS)

A three-phase series-parallel compensated line-interactive UPS system consisting of two voltage-source inverters controlled separately by two digital signal processors is studied in this paper. According to international IEEE standards, AC UPS system can be classified into three of a kind, i.e. passive-standby, line-interactive and double-conversion. Why this kind of UPS system is often called delta-conversion, which is a member of the line-interactive UPS family in nature, may lie in a little power bandied by both inverters in standby mode and the quasi-feedback PWM technique it adopted. Delta-inverter can be controlled either as AC fundamental sinusoidal current source or as nonsinusoidal voltage source to compensate harmonic voltage at the utility, while main-inverter can be controlled either as AC constant-voltage constant-frequency fundamental sinusoidal voltage source or as nonsinusoidal current source to compensate reactive and harmonic currents deriving from inductive and nonlinear loads. Compared to double-conversion counterpart, delta-inverter is of a small kilo-volt-ampere rating in any modes, while a little reactive and harmonic currents flow through main-inverter in standby mode. Thus, the efficiency and reliability of this kind of UPS are both increased with reduced cost. Some simulation waveforms and partial experimental oscillograms are shown in detail to verify the theoretic analysis.

The power conversion system performance of a superconducting magnetic energy storage unit

A superconducting magnetic energy storage (SMES) unit consisting of a voltage source converter (VSC) and a chopper is used to damp the oscillation of a synchronous generator. The state feedforward decoupling method based on synchronous frame is used to improve the dynamic response of the VSC. The work modes of the chopper are discussed, and a small signal model of the chopper is established for the regulator design. Simulations and experimental results demonstrate the dynamic performance of the SMES unit.

Improve direct torque control performance of induction motor with duty ratio modulation

Since 1980s Direct Torque Control has get more and more attentions, but there still are many problems need to be solved in this field. One of these is how to minimize the torque ripple and current harmonics. As we all know the out put voltage in DTC contains much harmonics for applying hysteresis band in this kind of system. In this paper the torque ripple in DTC is analyzed in detail with little signal model. And it is found that the torque ripple can be divided into two parts, one is only related to the motor parameter and the other is related to not only the applied voltage but also the rotor angular velocity. Based on the analysis, a duty ratio modulation method is proposed that only sends the voltage vector in part of the sampling period, while in the rest time of the sampling period zero voltage vector is sent. The duty ratio modulation algorithm, which is induced from the torque ripple analysis, allocates the sampling period. Simulation results indicate the effectiveness of the proposed torque ripple minimizing method.

Series of two transistors forward ZVZCS converter with phase-shifted control for high input voltage

This paper presents a soft switching series two transistor forward converter (STTFC) in interleaving for high input voltage. Two identical two transistor forward converters are connected in series. The voltage stress of switching device and freewheeling diode is only half the input voltage. In control method, phase-shifted control is applied. All the switches are turned off with zero voltage switching (ZVS), leading switches are turned on with a zero voltage and and zero current switching (ZVZCS), lagging switches are turned on with zero voltage switching (ZCS). The advantages of the proposed topology is high reliability, high efficiency and low cost. The circuit prototype, theoretical analyses and the experimental results of the converter for input voltage 600-1200V, output 24 V/20 A, 20 kHz are presented. The principle balancing voltage automatically is discussed. The effect factors of the efficiency are analyzed. The design is suitable for high input voltage and high power application.

A new control scheme for series-parallel compensated UPS system

This paper describes a new control scheme using synchronous reference frame (SRF) of a three-phase series-parallel compensated UPS system in detail. By controlling the series converter as a sinusoidal current source in phase with the input voltage and the parallel converter as a sinusoidal voltage source in phase with the input voltage, the proposed control scheme can make this kind of UPS carry out all of the control goals: sinusoidal input current with cos /spl phi/=1 and sinusoidal output voltage with normal value in the case of nonsinusoidal, nonnormal supply voltage and nonlinear load. Digital simulation results are presented to verify the good performance of the UPS system and the effectiveness of the new control scheme.

Analysis and design of the DSP-based fully digital-controlled UPS

This paper proposes a new control scheme based on two parallel controllers to improve both the steady and transient state responses of close-loop regulated pulse-width-modulated (PWM) inverter for UPS. The controller consists of the repetitive and instantaneous controllers. The repetitive controller is designed to eliminate periodic disturbance and the instantaneous controller is synthesized for transient state response improvement. Design procedure is given for synthesizing the repetitive and instantaneous controllers. The proposed control scheme has been realized using a single-chip digital signal processor (DSP) TMS320F240 from Texas instruments. A 7.5 kVA UPS has been constructed to verify the proposed control scheme. Simulation and experimental results show that the DSP-based fully digital-controlled UPS can achieve both low total harmonics distortion and good dynamic response.

Enhancement of generator transient stability using superconducting magnetic energy storage (SMES) in dynamic simulation test of power system

A prototype, double-DSPs controlled power conditioning system (PCS) for super-conducting magnetic energy storage (SMES), is used for experimental study in dynamic simulation test of power system. The function of SMES is to improve the dynamic performance of a single-machine infinite bus for power system. The experimental results show that the transfer of SMES energy is done almost immediately depending on the system requirement, and SMES is able to restore system stability for short circuit. The control algorithms for the SMES are simple and implementation has required very a little hardware.

Improvement of generator damping through superconducting magnetic energy storage (SMES) in dynamic simulation test of power system

A prototype, double-DSPs controlled power conditioning system (PCs) for superconducting magnetic energy storage (SMES), is used for experimental study in dynamic simulation test of a power system. The function of the SMES is to improve the dynamic performance of a single-machine infinite bus for power system. The experimental results show that the transfer of SMES energy is done almost immediately depending on the system requirement, and SMES is able to restore system stability for short circuit. The control algorithms for the SMES are simple and implementation has required very little hardware.