Pulse-width Modulated Current Source Converter Research Articles

New Adaptive Control Strategy for a Wind Turbine Permanent Magnet Synchronous Generator (PMSG)

Wind energy conversion systems have become a key technology to harvest wind energy worldwide. In permanent magnet synchronous generator-based wind turbine systems, the rotor position is needed for variable speed control and it uses an encoder or a speed sensor. However, these sensors lead to some obstacles, such as additional weight and cost, increased noise, complexity and reliability issues. For these reasons, the development of new sensorless control methods has become critically important for wind turbine generators. This paper aims to develop a new sensorless and adaptive control method for a surface-mounted permanent magnet synchronous generator. The proposed method includes a new model reference adaptive system, which is used to estimate the rotor position and speed as an observer. Adaptive control is implemented in the pulse-width modulated current source converter. In the conventional model reference adaptive system, the proportional-integral controller is used in the adaptation mechanism. Moreover, the proportional-integral controller is generally tuned by the trial and error method, which is tedious and inaccurate. In contrast, the proposed method is based on model predictive control which eliminates the use of speed and position sensors and also improves the performance of model reference adaptive control systems. In this paper, the proposed predictive controller is modelled in MATLAB/SIMULINK and validated experimentally on a 6-kW wind turbine generator. Test results prove the effectiveness of the control strategy in terms of energy efficiency and dynamical adaptation to the wind turbine operational conditions. The experimental results also show that the control method has good dynamic response to parameter variations and external disturbances. Therefore, the developed technique will help increase the uptake of permanent magnet synchronous generators and model predictive control methods in the wind power industry.

Modulation Schemes for Medium-Voltage PWM Current Source Converter-Based Drives: An Overview

Pulsewidth modulation current source converter (CSC)-based drive is one of the widely used drives in high-power (megawatt level) medium-voltage (MV) (2.3–6.6 kV) applications. The switching frequency of the MV CSC is limited to around 500 Hz to satisfy thermal requirement and reduce switching loss. Under such a condition, the overall performance of the used modulation scheme, especially its harmonics performance, is an important consideration for CSC-based drives. To date, a couple of modulation schemes have been proposed for MV CSCs, and this paper aims to present an overview of these modulation schemes. Traditional modulation schemes are reviewed, the recent advances are illustrated and analyzed, and the challenges and trends are discussed.

PBC Approach for SMES Devices in Electric Distribution Networks

This express brief presents a nonlinear active and reactive power control for a superconducting magnetic energy storage (SMES) system connected in three-phase distribution networks using pulse-width modulated current-source converter (PWM-CSC). The passivity-based control (PBC) theory is selected as a nonlinear control technique, since the open-loop dynamical model exhibits a port-Hamiltonian (pH) structure. The PBC theory exploits the pH structure of the open-loop dynamical system to design a general control law, which preserves the passive structure in closed-loop via interconnection and damping reassignment. Additionally, the PBC theory guarantees globally asymptotically stability in the sense of Lyapunov for the closed-loop dynamical system. Simulation results in a three-phase radial distribution network show the possibility to control the active and reactive power independently as well as the possibility to use the SMES system connected through a PWM-CSC as a dynamic power factor compensator for time-varying loads. All simulations are conducted in a MATLAB/ODE package.

Indirect IDA-PBC for active and reactive power support in distribution networks using SMES systems with PWM-CSC

Abstract In this paper an indirect interconnection and damping assignment passivity-based control (IDA-PBC) applied to the three-phase superconducting magnetic energy storage systems (SMES) is proposed to support active and reactive power in distribution systems. The SMES is connected to the distribution network using a pulse-width-modulated current source converter (PWM-CSC), due to its intrinsic current features that are more natural for controlling the current of a superconducting coil. A Hamiltonian function is selected as an hyperboloid representation taking into account the open loop dynamics of the system. The indirect control strategy is used to decouple the dynamical behavior between ac and dc side of the system, which allows to control active and reactive power independently in the ac side, while the dc side of the converter is employed as a supervisor controller for active power interchange. Simulation results demonstrate the efficiency and robustness of the proposed control methodology applied on a low-voltage distribution network under different operative conditions where the tracking errors were less than 6.2%.

A generalized passivity-based control approach for power compensation in distribution systems using electrical energy storage systems

This paper presents a generalized interconnection and damping assignment passivity-based control (IDA-PBC) for electric energy storage systems (EESS) such as: superconducting magnetic energy storage (SMES) and supercapacitor energy storage (SCES). A general framework is proposed to represent the dynamical behavior of EESS interconnected to the electrical distribution system through forced commutated power electronic converters. A voltage source converter (VSC) and a pulse-width modulated current source converter (PWM-CSC) are used to integrate SCES and SMES systems to the electrical power systems respectively. The proposed control strategy allows active and reactive power interchange between the EESS and electric distribution grids independently, guaranteeing globally asymptotically convergence in the sense of Lyapunov via Hamiltonian formulation. Simulation results show the effectiveness and robustness of the generalized IDA-PBC to operate EESS as active and reactive power compensator in order to improve operative conditions in power distribution grids under balanced and unbalanced conditions.

A Generalized Model and Control forSupermagnetic and Supercapacitor EnergyStorage

This paper presents a generalized linear model based on LMI state-feedbackwith integral action, applicable to the control of Electric Energy Stora-ge Systems (EESS) such as Superconducting Magnetic Energy Storage(SMES) and Supercapacitor Energy Storage (SCES). A Voltage SourceConverter (VSC) and a Pulse-Width modulated Current Source Converter(PWM-CSC) are respectively used to integrate the SCES and the SMESsystems to the electrical distribution system. To represent the dynamicsbetween the EESS and the power distribution system a reduced generallinear model in the state-space representation is introduced. The proposedcontrol scheme regulates independently the active and reactive power flowbetween the EESS and ac the grid. Three case scenarios comparing a con-ventional PI controller and the proposed technique are conducted conside-ring grid voltage fluctuations. Extensive time-domain simulations demons-trate the robustness and proper performance of the proposed controller to operate the EESS as power compensator, in order to improve the operativeconditions of electrical distribution systems.

An Adaptive Control Strategy for a Wind Energy Conversion System Based on PWM-CSC and PMSG

This paper proposes a new adaptive control strategy for a wind energy conversion system based on a permanent magnet synchronous generator and a pulse-width modulated current source converter. Most of the studies on wind farms are based on double fed induction technology. Nevertheless, the proposed conversion system is a good alternative due to its high efficiency and reliability. Electrolytic capacitors are not required in this type of converter and the voltage in the DC-link as well as the generated reactive power can be dynamically modified according to the wind velocity, being even negative if required. However, it is challenging from the control and stability standpoint. Capacitive filters placed on the AC side, which are required for safe commutation, can create resonances with the power grid. Reactive power is generated according to the capacity of the converter, the wind velocity and the load profile. The adaptive control strategy uses an adaptive PI which is self-tuned based on a linear approximation of the power system calculated at each sample time. A model reference is also proposed in order to reduce the post-fault voltages. Simulation results demonstrate the advantages of the proposed control.

Control Strategies for Balanced Three-phase Output in PWM Current Source Converter with Single-phase Input

This paper deals with a pulse width modulated (PWM) current source converter with single-phase input and three-phase output, and proposes control strategies for it. The converter circuit is a three-phase bridge circuit with three legs. The three-phase PWM method is used to obtain sinusoidal input and output. The single-phase-to-three-phase conversion can be achieved by using the phase-shifted PWM pattern. Moreover, to obtain a balanced three-phase output, the phase-angle control strategies of two PWM patterns are employed. The angle is determined with the feedback of the positive phase sequence component of the output currents. The paper describes in detail the circuit operation and the control method for balanced sinusoidal output. The RL static loads are used as three-phase loads to examine the performance of the converter. The experimental results prove that the three-leg converter with single-phase input can generate balanced three-phase output and includes sinusoidal waves in the input/output sides.

Integration of Offshore Wind Farm Using a Hybrid HVDC Transmission Composed by the PWM Current-Source Converter and Line-Commutated Converter

This paper investigates the feasibility of the application of a hybrid HVDC transmission system for the grid integration of offshore wind farms. The proposed hybrid HVDC consists of a pulse width modulated current source converter (PWM-CSC) and a line-commutated converter (LCC). The PWM-CSC is connected to the offshore wind farm and the LCC connects the onshore grid. The hybrid topology takes advantages from self-commutated converters as well as LCCs. On the one hand, LCC-based HVdc is the most mature technology with the lowest power losses and lowest cost. On the other hand, PWM-CSC has the same features that a voltage source converter for offshore applications, i.e., the ability to operate without an external commutation voltage, reactive power control capability, and a relative small footprint. Moreover, both the PWM-CSC and the LCC are current source converters and hence the coupling can be effortlessly done. The control design for the entire system is presented and verified using numerical simulations. Simulations are performed using PSCAD/EMTDC under different conditions including changes in the wind speed and ac and dc faults.

A Simple Method for Suppression of Resonance Oscillation in PWM Current Source Converter

This paper deals with a suppression method for the resonance oscillation in the ac side of a pulse-width modulation (PWM) current source converter. The converter is operated with the PWM switching pattern which is generated by the full digital control of computer software. The resonance current, caused by the LC low pass filter at the step change of the pattern, can be effectively suppressed by one pulse control of the pattern. The proposed method does not need to have the feedback loop of the current/voltage and does not offer the switching stress of the devices. The switching timing of the control is determined by pre-calculation of the off-line in consideration of the circuit constants. The experimental and the simulated results in the single-phase and the three-phase PWM converters are given, compared with those without the control, and show good response of the supply current.