This article considers power transistor open-circuit fault in a two-level voltage-source inverter and proposes a highly accurate, robust, and simple diagnosis method based on seasonal–trend decomposition. First, the three-phase current signal is decomposed into the trend, seasonal, and remainder components through the simplified seasonal–trend decomposition algorithm. Then, two characteristics “seasonal index” and “trend index” are defined. The theoretical values of the two characteristic quantities under different conditions are derived through simplified current waveform analysis and approximate integral calculation. Finally, the thresholds of characteristic quantities are set, and the diagnosis algorithm is designed. Experiments verify the effectiveness and the merits of the proposed method.

The high-frequency (HF) signal injection method has been widely used in sensorless control for IPMSM drives. However, the audible noise caused by HF injection restricts the sensorless application. Moreover, the control bandwidth of systems based on sinusoidal multifrequency injection or variable-frequency injection for audible noise reduction is limited due to the need for filters. This article proposes a novel amplitude modulation multirandom frequency injection (AMMRI) method to improve control bandwidth and reduce audible noise. First, the detailed message signal modulation, error extraction, position tracking, and position estimation error compensation based on amplitude-modulated voltage signal are derived and analyzed. Because the filters for HF current and error extractions are removed, the control bandwidth is improved. Second, in order to reduce audible noise, the proposed AMMRI is derived by selecting the message signal according to equal-loudness contour. The proposed method improves the control bandwidth compared to conventional multifrequency injection and reduces audible noise compared to conventional square wave injection. Finally, experimental results verify the proposed method on a 1.5-kW IPMSM platform.

In the situations where multiple motors operate at the same speed, this article designs a dual-parallel induction motor (IM) system supplied by three-phase four-leg inverter for cost reduction and fault tolerance of the normal system. The dc offset and ac fluctuation of capacitor voltages exist in this system due to the motor phases connected to bus capacitors’ midpoint. It seriously affects voltage utilization and stable operational range. A novel synchronous control scheme with the ability of ac voltage fluctuation minimization (AVFM) and dc voltage offset elimination (DVOE) is proposed. The unified model of dual IMs is used to design the speed regulator, and the model predictive flux control method is combined with space vector modulation to realize torque and flux control of dual IMs. AVFM is realized by controlling the electrical angle difference of dual IMs as $\pi$ , which is first presented in this scheme. An angle regulator is proposed to control the electrical angle by adjusting stator flux amplitude. DVOE is realized by injecting a compensatory voltage vector, which is simplified in this scheme to avoid the voltage filter or additional coordinate transformation in the conventional method. Experiment results verify the effectiveness of the proposed scheme.

The four-wire T-type three-level rectifier(four-wire 3LT²R) has a wide range of applications because of its excellent performance. However, the open-circuit fault of transistors can lead to power loss, current harmonics, and even system crashes. A novel open-circuit fault diagnosis method for four-wire 3LT²R based on the three-phase currents and modulation voltages is proposed in this paper, considering power factor regulation. At first, the relationship between the power factor and the working interval of the transistor is deeply analyzed. Then, the diagnostic method is designed based on the analysis. The “zero current” in each phase current is used to detect the faults with the different features related to the size of working intervals. After the fault is detected, the fault transistor is located according to the polarities of the currents and the modulated voltages. No additional sensors are needed. Experiments are carried out, and the results show its high effectiveness, robustness, and applicability for different power factors.

A novel dual motor synchronous control system supplied by four-switch mono-inverter is proposed, where one phase of both motors is connected to the mid-point of dc bus capacitors, and other phases are connected to inverter leg. Since only four power switches are required, the installation space, weight, and cost can be further reduced than conventional mono-inverter. However, it presents control challenges due to the limited control freedom degree. An advanced vector control method is proposed for this problem. Based on predictive model, two motors' reference voltage vectors are calculated independently, and a self-adapting composite vector is selected as the output vector of inverter. The duty cycles of switching signals are obtained based on space vector modulation of the selected vector. The use of unified-model or master–slave strategies in conventional mono-inverter control methods is avoided. The control is simplified and computation is reduced, while a good performance is ensured. Experiment results verify the effectiveness of proposed method.

This paper presents a novel position and speed estimation method for low-speed sensorless control of interior permanent-magnet synchronous machines (IPMSMs). The parameter design of the position and speed estimator is based on the sampled current rather than the motor electrical parameters. The proposed method not only simplifies the parameter design, it enables the estimator to work normally even in the condition that the electrical parameters are uncertain or varied. The adaptive filters are adopted to extract the desired high frequency current. The structure and corresponding transfer function are analyzed. To address the shortage of insufficient stop-band attenuation, the structure of the adaptive filter is modified to provide suitable bandwidth and stop-band attenuation simultaneously. The effectiveness of the proposed sensorless control strategy has been verified by simulations and experiments.