Chong Zhu

Modeling, Modulation, and Control of the Three-Phase Four-Switch PWM Rectifier Under Balanced Voltage

The modeling, modulation, and control of the three-phase four-switch (TPFS) PWM rectifier are investigated in this paper. Three space vector pulse width modulation methods using different equivalent zero vectors are developed, where sector identification and the trigonometric function are not required. Then, the high-frequency model for the current ripple analysis is proposed, and the effects of three SVM approaches on the ac current ripple are investigated. According to the analytical results, the method introducing the smallest current ripple is selected. With the optimized SVM approach, a control-oriented model, considering the capacitor voltage oscillation and deviation, is built in the dq synchronous frame to facilitate the controller design. Furthermore, a control strategy implementing the proportional controller is developed to eliminate the capacitor voltage deviation. Meanwhile, the dual-loop control of the TPFS is not affected by the proposed strategy as the capacitor voltage deviation is eliminated. Finally, a novel linear modulation index function is defined to reject the low-frequency harmonic current introduced by the overmodulation. Experimental results demonstrate that excellent current performance is achieved with comprehensive considerations of the modeling, modulation, and control strategy.

The Comprehensive Design and Optimization of the Post-Fault Grid-Connected Three-Phase PWM Rectifier

The comprehensive design and optimization, including the optimized modulation approach, detailed modeling, and reliable control algorithm, is presented in this paper to guarantee the stable operation of the postfault three-phase pulsewidth modulation (PWM) rectifier. The effects of the space vector modulation approaches on the capacitor current are investigated. Based on the analytical results, the method introducing the smaller capacitor current is selected as the optimized modulation approach, which is of paramount importance to avoid the permanent failure of the dc-link capacitors. Then, with the optimized modulation approach, a control-oriented model for the post-fault PWM rectifiers is derived based on the α - β stationary frame, where the capacitor voltage oscillation and deviation are taken into account. The proposed model-based controllers do not require the phase-locked loop (PLL), and the elimination of the PLL means that the post-fault rectifiers can never lose synchronization with the grid. Furthermore, an equation of the required dc voltage for linear modulation is proposed, and using the proposed equation, a correct dc voltage is selected to reject the overmodulation. The experimental results validate the effectiveness of the proposed comprehensive design and optimization. Finally, a conclusion can be drawn from the experimental results-that the dc-link capacitor current and the linear modulation should be taken into account when selecting the dc voltage in the post-fault operation.

Hybrid Space Vector Modulation Strategy for Torque Ripple Minimization in Three-Phase Four-Switch Inverter-Fed PMSM Drives

Three-phase four-switch (TPFS) inverters are generally applied as cost-reduction topologies for permanent-magnet synchronous motor (PMSM) drives because of their reduced number of switching devices. However, undesirable torque ripples are produced by the inverter-fed PMSMs due to the application of nonsinusoidal voltages. Because the torque ripples are strongly influenced by the employed pulse width modulation (PWM) strategy, two commonly used switching sequences in TPFS inverter-fed PMSM drives are fully investigated based on the root mean square value of the torque ripples, in which the effects of the different equivalent zero vectors on the torque ripples are presented. Then, a hybrid space vector modulation (SVM) strategy is proposed to minimize the torque ripples by alternatively using the two equivalent zero vector synthesis approaches during a fundamental period. The sector division of the proposed hybrid SVM strategy is determined by the location of the stator current vector, which is quite different from the methods used in other SVM methods. Then, a simplified sector identification method is proposed to reduce the computational burden. The experimental results demonstrate that the proposed hybrid PWM strategy can effectively reduce torque ripples in TPFS inverter-fed PMSM drives.

Comprehensive Analysis and Reduction of Torque Ripples in Three-Phase Four-Switch Inverter-Fed PMSM Drives Using Space Vector Pulse-Width Modulation

As a result of their reduced number of switches, three-phase four-switch (TPFS) inverters are generally applied as cost-reduction topologies for permanent magnet synchronous motor (PMSM) drives. However, the torque ripples of PMSM severely deteriorate the performance and reliability of the entire system. Hence, comprehensive considerations for torque ripple reduction, including high- and low-frequency torque ripples, are elaborated considering TPFS inverter-fed PMSM drives. The second-order torque harmonics produced by dc-capacitor voltage fluctuations are first demonstrated, and a very simple compensation method is presented by introducing a novel nonorthogonal coordinate transformation. Then, to evaluate the effects on the high-frequency torque ripples of space vector modulation (SVM) schemes, three SVM schemes for TPFS inverter-fed PMSM drives are assessed based on the torque ripple root-mean-square value. Consequently, the preferred SVM scheme is obtained for high-frequency torque ripple minimization. Moreover, the linear modulation range of the TPFS inverter-fed PMSM drive is derived considering capacitor voltage fluctuations, therein avoiding the low-frequency torque ripples caused by overmodulation. Meanwhile, an adaptive capacitor voltage offset suppression method is proposed to fully exploit the dc-link voltage. The experimental results demonstrate the validation and effectiveness of the proposed analysis and methods for torque ripple reduction.

Improved voltage vector control for a stand-alone DFIG system based on predictive current regulation algorithm

This study proposed an improved voltage vector control strategy based on predictive current control (PCC) for stand-alone doubly fed induction generator (DFIG) systems. The proposed control scheme implements close-loop control of both d-axis and q-axis stator voltage in a synchronously rotating reference frame, which regulates the magnitude and the phase of stator voltage precisely. Compared with previous voltage control schemes, this method provides fast and accurate tracking ability of stator voltage, resulting in excellent steady-state and dynamic performance of the system. Moreover, complex delay time compensation in PCC is no longer needed with the recommended strategy, intensely reducing the calculation burden. Simulation results for a 160kW stand-alone DFIG system are presented to validate the effectiveness of the proposed method.

An optimized algorithm for SVPWM based on three-phase stationary frame

The conventional space vector pulse width modulation (SVPWM), including coordinate transformation, sector identification, and active time calculations of voltage vectors, needs lots of complex irrational number operations such as trigonometric function calculations, which introduces challenges for real-time digital control chips. Considering the shortcomings of traditional algorithm, this paper presents an optimized algorithm based on three-phase stationary frame. In the proposed algorithm, the reference voltage vector is projected onto the three-phase stationary frame firstly, then a unified formula is obtained by utilizing the principle of symmetric, where only normal mathematical operations of modulation wave is required. With the unified formula, the duty ratios of three bridge-arms will be calculated directly. Comparing with conventional algorithm, the proposed algorithm is more suitable for digital system owing to the characteristic of easier programming, faster operating speed, and higher real-time ability. The simulation and experimental results show the validity and feasibility of the proposed algorithm.

Modeling, control and modulation strategy of a three-phase four-switch PWM voltage-source rectifier based on novel non-orthogonal coordinate

Modeling and controller design principles for six-switch PWM voltage-source rectifiers have been covered thoroughly in recent studies. In contrast, the control strategies for four-switch PWM VSRs are rarely reported. In order to achieve a high performance control, this paper develops a control oriented dual single-input-single-output model for 4-switch PWM VSRs in a novel non-orthogonal frame. Using given DSISO model, the controller design becomes much easier than ever before, and basic guidelines are provided in this paper. To suppress the DC voltage offset inherited in 4-switch PWM VSRs, a split capacitor voltage balancing method is analyzed in details. Then, a very simple modulation strategy is proposed based on the non-orthogonal coordinate system, which exhibit the merits of less computation and higher accuracy compared with traditional methods. The resultant zero voltage vector of 4-switch PWM VSRs is synthesized by a pair of opposite vectors, thus two switching sequences derived from alternative selection of zero vector synthesis schemes are introduced in this paper. For lower harmonic distortion injected to the grid currents, performances of two applied switching sequences are fully evaluated when the RMS value of current ripple is chosen as the standard. Experimental results are presented to demonstrate the feasibility and validity of the proposed methods.