Xiaomeng Cheng

A Novel PWM Technique With Two-Phase Modulation

In this paper, a new two-phase pulse width modulation (PWM) technique is proposed, in which the reference voltage is constructed by three space vectors. At any speed, the peak-to-peak value of the common-mode voltage (CMV) in one PWM cycle can be reduced to one third of the DC bus voltage, even despite of the dead-time effect. And in the low voltage region, not only the CMV but also the current ripple is restrained effectively. In the entire voltage range, the linear modulation region is not limited and the switching loss is reduced because of fewer switching actions. The validity of the proposed technique is verified through simulation and experimental results.

A Three-Phase Current Reconstruction Technique Using Single DC Current Sensor Based on TSPWM

Three-phase current reconstruction technique using dc current information in conventional two-level inverters can be used for the purpose of cost reduction and sensor fault tolerance. A novel phase current reconstruction scheme, with reduced immeasurable area and common mode voltage, is proposed in this paper. A tristate pulse-width modulation technique has been employed, in which three adjacent switching states are used to construct the reference voltage. The active switching states are arranged at the edge and the center of a PWM cycle. Fixed sampling and simultaneous three-phase currents can be easily achieved with very little hardware and software requirements. A detailed analysis of the effects of nonidealities leads to regional modifications of the switching sequence resulting in almost the whole hexagon as the feasible area. The usefulness of the proposed reconstruction algorithm has been verified by experimental results obtained from a 4-kW induction motor drive system. Smooth transitions between the redundant and fault-tolerant modes were observed.

Single current sensor operation with fixed sampling points based on TSPWM

The single current sensor operation (SCSO) is favorable for cost reduction and fault-tolerance purposes in three-phase inverter-driven systems. This paper addresses a SCSO method based on tri-state pulse-width modulation technique (TSPWM). It enables fixed sampling points with minimal hardware and software requirements. Simultaneous three phase currents can be easily computed due to symmetrical sampling. No change to TSPWM is needed for most working points, thus it maintains advantages in common-mode voltage (CMV), switching loss and DC current ripple reduction. Based on the detailed analysis of non-ideal factor effects, regional modifications enlarge the feasible voltage region to almost the whole hexagon. It works well in close-loop systems and enables seamless transition in fault-tolerance operation for current sensor. Experimental results on a 4-kW induction motor drive are presented to verify the above-mentioned conclusions.

Single current sensor operation with fixed sampling points using a common-mode voltage reduction PWM technique

A method is proposed for reconstructing AC currents with a single DC side current sensor in three-phase AC motor drive system. The method is based on a common-mode voltage (CMV) reduction PWM technique called LuPWM, which eliminates most of the invalid regions for current reconstruction both around zero voltage and near active-vectors. It realizes fixed-point sampling which is favorable for implementation. And the current prediction is also easier than traditional methods. Furthermore, it remains the good property of LuPWM that the peak-to-peak value of CMV, which leads to the premature deterioration of motor bearings, is reduced to 1/3 of the traditional three-phase PWM method in each sector. The additional computation load is minimal, and it can be widely applied. Experimental results are presented to fully support the above-mentioned claims.

An accurate rotor time constant estimation method for self-commissioning of multi-scale induction motor drives

This paper presents a novel strategy for accurate rotor time constant estimation while the induction motor keeps standstill. Based on the ‘Γ’ equivalent motor circuit model with all leakage located in the stator, the inertial first-order delay occurs in the mutual current relative to the stator current. Moreover, the delay time constant is only decided by the rotor time constant. Thus, an observer to estimate the mutual current by sample signal can be constructed. By changing the stator current at special moment according to the estimated mutual current, a significant transient response of stator voltage can be observed if estimated rotor time constant incorrect. Subsequently, a fast and robust close-loop null regulator is built to self-tune the rotor time constant. This method is completely independent of motor parameters and immune to the influence of dead time effect and voltage drop of semiconductor device. Experimental results on two different IMs are presented to prove the validity of the proposed method.

EMF Feedback Control Strategy of Induction Motor for Wide Speed Range

Variation of winding resistance, magnetic saturation and iron loss in the induction motor result in field angle estimation error, which causes detuning problems. Especially, in cases when the iron loss and change of inductance cannot be neglected, ordinary resistance identification methods may lead to incorrect results. To solve this problem, a new method to directly revise the observed field position is proposed in this paper. The position angle of rotor flux observed can be continuously revised by adding a feedback compensator of electro-magnetic force (EMF), which guarantees the correct direction of rotor flux. The principle of compensation is introduced, and in order to verify the validity of this method, various tests have been done on a 60 kW induction machine. The simulation and experimental results indicate that the flux orientation of an induction motor field oriented control (FOC) system with EMF feedback control strategy is more accurate than an ordinary FOC system, especially in high speed range.

Segment phase-shifted carrier PWM to reduce common-mode-voltage

In this paper, a segment phase-shifted carrier PWM method is proposed. According to the sector, the modulation wave can be discontinuous with different zero sequence signal injected and the carrier wave are phase shifted, which is different from conventional SVPWM. Using this technique, the peak-to-peak value of the common-mode voltage in one PWM cycle can be reduced to one third of the DC bus voltage at any speed, even despite of the dead-time effect. The good natural over modulation characteristic performance with high voltage utility is also researched. Furthermore, the technique can be generalized to obtain a series of PWM methods. Both theoretical and experimental results are presented to verify the validity of proposed technique.

An improved two-phase PWM strategy for inverters in electric vehicle

An improved pulse-width modulation (PWM) strategy with two-phase modulation is proposed for inverters in electric vehicle. By properly selecting the clamping phase in each PWM cycle, no switching occurs when the corresponding phase current is around its peak value, thus the switching loss will be significantly reduced. Meanwhile, the peak-to-peak value of the common-mode voltage (CMV), which leads to the premature deterioration of motor bearings, is reduced to 1/3 of the traditional three-phase PWM method in each sector. Furthermore, the harmonic distortion characteristic is also improved comparing with other PWM techniques for CMV reduction. Just a little software is needed for implementing the proposed strategy and the method can be widely applied. Experimental results are presented to fully support the above-mentioned claims.