Bin Duan

Design of three-phase PWM converter in the battery pack testing system using fractional-order control

The rapid development of power battery technology puts forward more strict requirements of testing systems, particularly the transient performance for the charge and discharge processes. The three-phase PWM converter is mostly used in the front of the battery testing system to ensure the stability of input voltage for DC/DC converter. However, conventional PI (Proportional, Integral) controller has limited control gain at the frequency of interest and its tuning parameters are sensitive to the changes of system parameters. Therefore, in this paper, the fractional order control algorithm is studied and applied to the three-phase PWM converter. First, a mathematical model of converter with an inductive filter is established. An optimized fractional order PI (FOPI) controller is designed by evaluating accurate performance index. The controller design procedures are given in detail. The analysis and simulation results show that the system response using fractional order control has better dynamic performance and stronger robustness fairly compared with using conventional integer order controllers, and is adaptive to model uncertainties.

Variable-order fractional equivalent circuit model for lithium-ion batteries

Battery models play important roles in battery manufacturing, design, safe operation, and many of its applications, such as in providing power sources of electric vehicles due to the high energy density, long life, and high cell voltage. Unlike the detection of impedance spectrum in a short linear interval, the I-V characteristic of lithium-ion batteries presents strongly nonlinearity such as the serious polarization in both ends of charging /discharging. To modeling the nonlinear characteristic of real battery accurately, this paper proposes a variable-order fractional equivalent circuit model that provides a novel and effective trade-off of model accuracy and simplicity. The proposed method is verified under the working conditions of pulse and constant current charging /discharging, where the maximum model error is less than 1.8%.

Independent voltage outputs control for VIENNA rectifier considering multiple loads situations

The VIENNA rectifiers have advantages of high efficiency as well as low output harmonics and are widely utilized in power conversion system when dc power sources are needed for supplying dc loads. VIENNA rectifiers based on three-phase/level can provide two voltage outputs with a neutral line at relatively low costs. However, total harmonic distortion (THD) of input current deteriorates seriously when unbalanced voltages occur. In addition, voltage outputs depend on system parameters, especially multiple loads. Therefore, unbalance output voltage controller and modified carrier-based pulse-width modulation (CBPWM) are proposed in this paper to solve the above problems. Unbalanced output voltage controller is designed based on average model considering independent output voltage and loads conditions. Meanwhile, reference voltages are modified according to different neutral point voltage conditions. The simulation and experimental results are presented to verify the proposed method.

Neutral-point voltage balance control and oscillation suppression for VIENNA rectifier

In view of a three-phase/level boost rectifier, the performance of VIENNA rectifier is affected by the neutral-point (NP) voltage unbalance and oscillation. A novel strategy of zero-sequence component injection to balance the neutral-point voltage and suppress oscillation for VIENNA rectifier is proposed in this paper. Based on the mathematical expressions of neutral-point voltage, a simplified carrier-based PWM based on the equivalence of SVM is implemented to balance the neutral-point voltage. Analyzing mathematical relationship between the fluctuation of neutral-point voltage and the zero-sequence component, an optimized zero-sequence component is proposed to suppress neutral-point voltage oscillation. The validity of the theoretical analysis and feasibility of the proposed strategy are verified by simulation and experimental results.

Voltage independence control of split-DC bus for a three-phase/level T-type converter with unbalanced loads

Three-phase/level T-type converter has advantages of high efficiency and low current harmonics, which is utilized in power conversion systems for supplying dc loads widely. Three-phase/level T-type converter provides bipolar dc buses with a neutral line at relatively low cost. In order to extend applications for bipolar dc bus structure, voltage independence control of split-dc bus proposed in this paper plays a key role in the flexibility of converter. However, the coupling relationship between asymmetric capacitor voltages and unbalanced dc loads gives rise to the inherent operational limit of three-level T-type converter. Therefore, the serious grid current distortion and attenuation of neutral point voltage regulation appears when system is driven out of operational limit. To overcome these issues, a novel architecture consisting of a three-phase/level T-type converter and a neutral leg is proposed to deal with asymmetric capacitor voltages with any unbalanced dc loads. Voltage independence control of split-dc bus and modified carrier based pulse width modulation (CBPWM) of novel architecture are presented, correspondingly. The simulation and experimental results are presented to validate the proposed architecture and control strategy.