Grid codes require wind turbines to have capability to withstand a certain grid voltage unbalance without tripping. However, existing controls for brushless doubly-fed induction generator (BDFIG) based wind turbine under grid unbalance have many problems such as difficulty in realizing decoupling control, involvement with flux or current estimations, and complex control structure. Moreover, the existing studies only focused on the control of machine side converter (MSC), but the coordinated control between MSC and grid side converter (GSC) and the control objectives of overall BDFIG wind turbine system have not yet been addressed so far. To overcome these problems and improve the control capability, this paper proposes a coordinated control strategy by considering MSC and GSC together. First, the enhanced control objectives for overall BDFIG wind turbine system are determined. Second, the simple single current closed-loop controllers without involving with any flux or current estimations are designed for MSC and GSC, respectively. Meanwhile, in current loops, all the disturbances and cross-coupling terms on dq axes are derived and used for feedforward control so as to achieve decoupling control and improve system dynamic response. Further, a fast sequence decomposition approach is employed to enhance the control characteristics of the whole system. Finally, the effectiveness of proposed control is validated through case studies for a 2 MW BDFIG based wind generation system. The results demonstrate that the proposed control can effectively achieve the control objectives of overall wind turbine system under grid voltage unbalance and provide excellent dynamic and stable performance.

/pdf/modeling-and-coordinated-control-design-for-brushless-doubly-3z4o6um33c.pdf

Modeling and Coordinated Control Design for Brushless Doubly-Fed Induction Generator-Based Wind Turbine to Withstand Grid Voltage Unbalance

Fuel cells guarantee ecological ways of electricity production by promising zero emissions. Proton exchange membrane fuel cells (PEMFCs) are considered one of the safest methods, with a low operating temperature and maximum conversion efficiency. In order to harness the full potential of PEMFC, it is imperative to ensure the membrane’s safety through appropriate control strategies. However, most of the strategies focus on fuel economy along with viable fuel cell life, but they do not assure constant output voltage characteristics. A comprehensive design to regulate and boost the output voltages of PEMFC under varying load conditions is addressed with dynamic integral sliding mode control (DISMC) by combining the properties of both the dynamic and integral SMC. The proposed system outperforms in robustness against parametric uncertainties and eliminates the reaching phase along with assured stability. A hardware test rig consisting of a portable PEMFC is connected to the power converter using the proposed technique that regulates voltage for varying loads and power conditions. The results are compared with a proportional integral (PI) based system. Both simulation and hardware results are provided to validate the proposed technique. The experimental results show improvements of 35.4%, 34% and 50% in the rise time, settling time and robustness, respectively.

/pdf/fuel-cell-voltage-regulation-using-dynamic-integral-sliding-2a4m4a0r.pdf

Fuel Cell Voltage Regulation Using Dynamic Integral Sliding Mode Control

In the standalone power generation system based on brushle doubly fed induction generator (BDFIG), the special loads such as unbalanced loads and nonlinear loads will cause negative sequence, fifth and seventh harmonic components in power winding (PW) and the corresponding harmonic components in control winding, which will cause some torque ripple so as to make the machine unable to output stable active power, increase the vibration and noise, and so on. This article will first analyze the harmonic components of the torque in details, and then propose an optimized torque ripple suppression method. Through the low frequency harmonic control method of the line side converter without additional sensors, the negative sequence, and fifth harmonic components of PW voltage are controlled to achieve the suppression of the second and sixth harmonic components of the torque. Compared with traditional active filtration method, the proposed method in this article needs to satisfy fewer constraints and tune fewer parameters, and can be utilized more flexibly. Comprehensive experimental results based on a 5-kVA BDFIG demonstrate the effectiveness of the proposed method. 

Optimized Torque Ripple Suppression Method for Standalone Brushless Doubly-Fed Induction Generator with Special Loads

The current control and mode control of permanent magnet synchronous motor in the P2.5 hybrid system is analyzed to achieve good stability and robustness. The current control which includes the current vector control, the MTPA, flux weakening control, PI current control and SVPWM control. The motor mode contains the initialization mode, the normal mode, the fault mode, the active discharge mode, and the power down mode. To minimize the jerk in the vehicle that arises when motor torque is going from negative to positive or vice versa, the motor anti-jerk control is introduced. The anti-shuffle is defined to minimize the driveline oscillations that occurs in an electric vehicle due to the low stiffness between the wheels and the electric machine. Finally, the real vehicle test is performed and the motor control design is proved successfully. 

Research on Motor Control of P2.5 Hybrid Vehicle

Brushless doubly fed motor (BDFM) can obtain excitation indirectly through rotor pole pairs conversion, without slip rings and brushes. Besides, the power winding (PW) of BDFM can be connected to the high voltage gird, and the control winding (CW) can be connected to a conventional-voltage partial-power inverter for partial-range speed regulation. This reduces the cost of the motor drive system, making the BDFM ideal for industrial fan and pump loads. In the actual application process, it is necessary to solve the motor starting problem, so this paper analyzes the application of starting control technology on BDFM. And according to the startup requirements under common working conditions, the corresponding low-cost series resistor control strategy is proposed. In addition, the operability of the control strategy is verified through simulation, and it operates reliably under actual conditions. This provides an important reference for the subsequent industry promotion of BDFM. 

Application of Starting Control Technology on Brushless Doubly Fed Motor with Fan and Pump Loads

The brushless doubly fed machine (BDFM) drive system based on a fractional unidirectional converter is a promising low-cost variable-speed drive system, which shows great potential in applications of driving fans and pumps. However, the harmonic current generated by a diode rectifier can flow into the machine and the grid under a weak grid, which will cause a 6th-order frequency torque ripple and lead to voltage distortion. A steady equivalent circuit considering the uncontrolled rectifier and the grid impedance is built firstly to study the harmonic distribution characteristics. To eliminate the influence of harmonic currents, the harmonic equivalent impedance of the machine system should be regulated to change the harmonic distribution characteristics. This paper improves the conventional control method through adding a harmonic control loop to prevent harmonic currents from being injected into the machine or the grid, which is then applied in the fundamental synchronous frame. Two indirect parameters are selected to realize the two control targets. Afterwards, the influence of the control system on the harmonic equivalent impedance of the machine system under the conventional method and the proposed method are compared. Finally, experimental results obtained from a 30 kW BDFM prototype verify the proposed method.

/pdf/bidirectional-harmonic-current-control-of-brushless-doubly-4k25sumjbh.pdf

Bidirectional Harmonic Current Control of Brushless Doubly Fed Motor Drive System Based on a Fractional Unidirectional Converter Under a Weak Grid

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Bidirectional Harmonic Current Control of Brushless Doubly Fed Motor Drive System Based on a Fractional Unidirectional Converter Under a Weak Grid