Qiubo Ye

New control strategy based on model predictions and PI for three-phase off-grid inverter

When the problem of the model predictive control cannot be solved, the control system will not work properly. A control strategy based on model predictive control and PI is proposed in this paper. The control strategy of the model predictive control and PI is applied to the three-phase off-grid inverter. Adaptability of the PI controller to the operating mode is improved and the dynamic performance is improved. Simulation and experimental results are provided to verify the effectiveness of the proposed control strategy.

Design of PLL based on FPGA under unbalanced conditions

This paper proposes a new way based on FPGA to realize decoupled double synchronous reference frame software phase locked loop (DDSRF-SPLL) under unbalanced conditions. DDSRF-SPLL can lock in unbalanced grid voltage accurately as well as overcome the impact of the phase-locked loop on frequency performance in adopting the positive and negative sequence decoupling algorithm. When the frequency of three-phase voltage under unbalanced conditions fluctuates, the frequency will be fed back to the AD sampling module through the PI regulator. Thus the sampling period is adjusted and the accuracy of phase-locked loop is improved. Simulation by ModelSim shows that the proposed three-phase PLL has strong anti-interference ability and good adaptability to frequency fluctuations.

Comparison of two different modulations and conduction loss analysis for single-phase two-level rectifier

The operating theory of single-phase two-level pulse width modulation (PWM) rectifiers is analyzed and the mathematical model is established. In order to reduce switching losses, a single-phase two-level space vector pulse width modulation (SVPWM) strategy and a single-phase two-level carrier PWM strategy with zero-sequence voltage injection are presented in this paper. Their design methods are given in detail. Through theoretical analysis and calculation, the SVPWM and PWM with zero-sequence voltage injection are found to be the same type of pulse width modulation method essentially. And then this paper analyzes and compares the conduction losses for two-level rectifier for the SVPWM and sinusoidal pulse width modulation (SPWM) with zero-sequence voltage injection. Finally, simulation results and conduction loss calculation verify the consistency of the two PWM strategies.

Effect on harmonic performance for three-level ANPC converter with small change in SHEPWM switch angles

The effect on harmonic performance for a three-level active neutral point clamp (ANPC) converter with small change in Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) switch angles is researched. A small change in the SHEPWM switching angles is used to balance the neutral point voltage for the three-level ANPC converter. But this strategy may result in bad harmonic performance of the three-level ANPC converter. In this paper, the equation of the selective low-order harmonics after a small change in the SHEPWM switching angles is deduced. When the change of the SHEPWM switching angles becomes bigger, the converter harmonic performance would be worse and the natural balancing of neutral point voltage would be enhanced. The simulation and experimental results are provided to verify the effectiveness of the equation and to draw conclusions.

Research on effect of temperature on performance and temperature compensation of interior permanent magnet motor

Temperature of windings increases because of the heat generated during motor running process, therefore motor parameters will be changed. The effects of temperature on external characteristics of the motor were analyzed as the rising temperature causes demagnetization of the permanent magnet. A new control strategy is designed to reduce the influence of the temperature. The simulation results show the validity of the compensation method.

Research on rotor magnet loss in fractional-slot concentrated-windings permanent magnet motor

Eddy current loss in rotor permanent magnet can cause magnet heating and even demagnetization. It is much worse in machines equipped with fractional-slot concentrated-windings (FSCW). The paper analyzes harmonics of magnetic flux in airgap, slot harmonics, spatial harmonics and temporal harmonics of the magneto-motive-force (MMF). The relationship between the rotor magnet loss and air-gap size is investigated by finite element method (FEM). The effects on magnet loss with different magnet segmentations are analyzed in detail.

Vector control strategy for PMSM using rotor kinetic energy

An energy exchange relation of the permanent magnet synchronous motor control system is analyzed firstly. Then a novel control strategy using the rotor kinetic energy is proposed. A load estimation method is put forward for the load and inertia ripple. The simulation and experiment results demonstrate the effectiveness of the proposed control strategy and the method.

Sensorless vector control system of induction motor by nonlinear full-order observer

A novel design of a nonlinear full-order observer for sensorless vector controlled induction motors is proposed in this paper. It is known that the speed-sensorless vector control drive system of induction motors does not perform satisfactorily at the low speed, which is caused by the voltage model and its emf calculation of motors. The nonlinear full-order observer system abandons the voltage model and its emf calculation of motors, makes use of the motor as a reference model and the stator model together with the current model as an adjustable model. In this paper, the model reference adaptive system (MRAS) is proposed, and then the nonlinear full-order observer system is presented based on the MRAS. Finally, several simulations verify feasibility of the proposed strategy.

A neutral-point potential balancing method for three-level inverters based on improved virtual space vector modulation

A new modulation method is proposed to solve the unbalancing problem of neutral-point potential in the DC side in three-level (3L) three-phase neutral-point-clamped (NPC) voltage source inverters. Based on properties of current balancing of three phases and redundant short vectors, different short vectors have different time distribution factors, which can be used to improve the control of the neutral-point current. The neutral-point voltage is under control by adjusting the time of the virtual vector, therefore the distortion of the output voltage waveform and the voltage across switch devices will be reduced. Simulation results show the validity of the method.