Traditional sliding mode observers (SMOs) are prone to chattering, and existing improvement methods have limitations, such as increasing system complexity or suboptimal performance. To overcome these issues, this paper proposes an SMO based on the cooperative optimization of a sinusoidal saturation function and a dynamic gain, focusing on the switching function and observer gain. In this observer, the sign function is replaced with a sinusoidal saturation function, effectively suppressing chattering and improving estimation accuracy. Moreover, the need for a low-pass filter (LPF) is eliminated, thereby avoiding phase lag issues. Additionally, a variable gain function was designed, which is jointly controlled by the velocity error and state variables. This further reduces oscillations and errors, thereby improving the system's stability. Through Lyapunov stability analysis, the stability of the proposed observer is verified. Simulation results show that, compared to existing SMOs based on sign and saturation functions, the method proposed in this paper results in smaller speed chattering and position errors.

For the full-speed sensorless control of permanent magnet synchronous motors (PMSM) used in robotic joints, conventional methods adopt a combined strategy of zero-low-speed and medium-high-speed control methods. This requires switching between methods during motor operation, which reduces the reliability and stability, making it unable to be used in robotic joint motors. In this paper, a novel full-speed range sensorless control method is proposed. The method consists of two ranges: the zero-speed and the operation range. In the zero-speed range, a high-frequency square wave injection (HFSI) method with only 20 square-wave pulses (SWPs) is employed, resulting in a short injection duration, which ensures low noise. Leveraging the bidirectional convergence property of the linear time-invariant enhanced phase-locked loop (LTI-EPLL), the initial position and NS polarity can be determined without additional signal injection, ensuring smooth startup and rotor standstill. In the operation range, based on the eletrical properties of the PMSM, a sliding-mode speed observer (SMSO) is constructed to directly estimate the speed, and the position is obtained via integration. Thus, full-speed range operation is achieved without the need to switch between methods during operation range. Finally, the feasibility of this method is validated in MATLAB/Simulink.

The diagnosis and fault-tolerant control of open-phase faults in permanent magnet synchronous motor (PMSM) drive significantly rely on models describing post-fault behaviors of current and voltage. This paper aims to propose an improved current prediction model that can accurately estimate the post-fault current dynamics under the single open-phase fault. Firstly, in each switching state, the post-fault phase voltages are derived by considering the floating neutral voltage incurred by the back electromagnetic force (back-EMF). Furthermore, by incorporating the derived phase voltages as the activation sources in each switching cycle, the post-fault current prediction model is established. Moreover, the changes of inductances under the open-phase fault are taken into account by establishing the model in the independent phase model. Finally, experimental results validate the derived post-fault phase voltages and the post-fault current prediction model.

In this paper, aiming to systematically derive single-inductor multi-input multi-output (SI-MIMO) converters having favorable merits of high-density and low-cost, a basic model is firstly extracted from the working principle. Theoretically, by enumerating all possible connections of the basic model and one-by-one manually judging their effectiveness according to working criterions, multiple viable SI-MIMO topologies can be obtained, but with heavy workload. To simplify the topology derivation process, this paper also proposes a computer-aided method to replace the manual effort. By modelling the basic model and working criterions with graph theory, MATLAB codes can be developed to automatically screen out the effective topologies. With the proposed method, 8 three-port, 28 four-port and 115 five-port converters with single inductor are conveniently obtained, including both the existing and new topologies. Moreover, by configuring ports and switches in each derived topology, multiple specific converters can be further expanded. These converters can provide more options for practical engineering applications, and a new topology is also introduced and experimentally verified in the paper.

The modular multilevel converter (MMC) becomes attractive in the medium- and high-power application with high modularity. In this paper, the MMC and cycloconverter based machine drive system is proposed. The six-phase MMC is used as the grid-side converter, which produces six-phase medium-frequency ac voltage for the machine side converter. The six-phase to three-phase cycloconverter is used as the machine-side converter, which converts the medium-frequency ac voltage to the low-frequency ac voltage to drive the machine. In addition, the corresponding control for the grid-side converter and the machine-side converter are also proposed. The proposed MMC and cycloconverter based machine drive system can effectively realize the control for the high-voltage, high-power and low-speed machine. What is more, the SM capacitance is significantly reduced owing to the medium-frequency ac output voltage of the MMC. The simulation studies of the proposed MMC and cycloconverter based machine drive system and control are conducted with a detailed PSCAD/EMTDC model, and the results show their effectiveness.

This article proposes a magnetic coupling multi-output (MCMO) buck converter which can work in a mixture of continuous conduction mode (CCM) and discontinuous conduction mode (DCM) to meet the demand for unbalanced loads including one heavy load and other light loads. For the output with heavy load, its current is equal to the continuous magnetizing current of coupled inductor, while the discontinuous leakage inductor current is distributed to the outputs with light loads. In comparison with the conventional single-inductor-multi-output (SIMO) converter working in CCM or DCM, the proposed converter can obtain small spike current and independent control simultaneously. In addition, only a magnetic core is utilized and thus the favorable advantage of reduced cost and volume is retained. In this article, in order to obtain a better understanding of the proposed converter, an example magnetic coupling dual-output (MCDO) one is thoroughly analyzed, and afterwards, experimental results are also demonstrated to verify the theoretical analysis.

Faults may be generated in power networks as a result of bad weather, human activities, or some other factors. The complex structure of power network adds to the difficulty of fault location (FL). This paper presents a novel FL scheme by utilizing the information of the time differences of arrival (TDOAs) of modal traveling waves (MTWs) asynchronously sampled in the network. First, the fault area is determined by searching the minimum TDOA of MTWs. Then, by applying the fictitious fault point method in the fault area, the minimum accumulated difference is used to detect the fault line. Finally, the accurate FL is estimated by solving the objective function of the absolute distance between the FL and multiple FL candidates. Various simulations are carried out in the IEEE 30-bus system. The calculation results demonstrate that the method is not affected by fault impedance, inception angle, location, and noises to a certain extent.

With the increasing demand of applications that have two different output voltages, the single-input dual-output (SIDO) converter with fewer components is becoming the cost-effective option instead of employing two single-input single-output converters. However, the cross-regulation of different outputs is still a challenge in SIDO converters design. To save cost and obtain improved cross-regulation performance, a novel SIDO converter consisting of three active switches is proposed in this article. Owing to the use of a voltage multiplier circuit, a high step-up voltage conversion ratio is achieved with relatively low voltage stress of switches. Thanks to the independent power flow and two control variables, the cross-regulation performance is improved, and simultaneous buck as well as boost output voltages is realized. Additionally, all switches can achieve zero-voltage switching operation, which contributes to a significant switching loss reduction. The operation characteristics, design considerations, and control strategy of the proposed converter are analyzed. To verify the theoretical analysis and measure the power efficiency, a prototype circuit with 48 V input and 24 V/2 A, 200 V/1 A outputs is built.

Targeting at reduce the difficulty of fault protection of a modern more-electric ship (MES), a doubly-fed induction motor (DFIM) based shipboard propulsion system (SPS) is proposed. The on-board electric power supply is provided by a synchronous generators (SG). Therefore, the accurate parameter setting is important for achieving the optimal system performance. In this paper, the effects of parameter deviations (PDs) in SG on the system performance are studied. The detailed models of a salient-pole SG and a type DC1A excitation system (EXS) are presented. Different degrees of PDs (DoPDs) are applied to 8 important parameters of SG to analyze the sensitivity of each parameter. Simulation studies are carried out in Matlab/Simulink to obtain data for investigating the PD effects. Three PD effect indicators (PDEIs) are defined to illustrate the effects on the SG terminal voltage and output active power. Meanwhile, when applying different DoPDs, the increasing rates of PDEIs are different, which are also investigated. Moreover, the two most critical SG parameters are determined, and the overall system performance is analyzed when applying different DoPDs on these two parameters.

In this paper, a doubly-fed induction motor (DFIM) based shipboard propulsion system (SPS) is proposed for more-electric ships (MESs). Two power flow paths are presented, which are based on direct AC power transmission and power decoupling with back-to-back converter (BTBC). This type of SPS minimizes unnecessary power conversion and increases the system robustness to power converter faults. The synchronous generator (SG) and DFIM are the main power components in the proposed DFIM-SPS. An emulated stator voltage orientated vector control (ESVO-VC) strategy without using phase-locked loop (PLL) is proposed. The simulation study is carried out in Matlab/Simulink to verify the performance of the proposed DFIM-SPS, with frequent load variations taken into consideration. By employing the proposed ESVO-VC scheme, high quality of input three-phase currents, high power factor, and superior torque tracking performance are presented. Furthermore, a control-hardware-in-the-loop (CHIL) setup is used to implement the proposed ESVO-VC with the power circuits of SG and BTBC simulated in a realtime digital simulator (RTDS) to verify the system control performance in the almost practical environment.

Interior permanent magnet synchronous machines (IPMSM) often work under flux weakening state in electrical vehicles for higher speed. But unavoidable faults might occur during that process, after which the power transistors are switched off immediately and the battery packs are charged through the three-phase uncontrolled rectifier composed of six flywheel diodes. That is also renowned as uncontrolled generation (UCG) operation which needs to be well understood to avoid damage to either inverter or battery. In order to achieve more accurate analytical results, this paper proposes an improved steady-state model of the drive system for UCG analysis. On the basis of the model, the parameter dependencies are detailed. The voltage and current characteristics of UCG and the effectiveness of the proposed steady-state model are verified by experimental results.

When an emergency happens to electric vehicles, the voltage of the dc-bus capacitor, which is an important part of the permanent magnet synchronous machine (PMSM) drive system, requires to be reduced as quickly as possible. Recently, a new idea of directly using the windings to discharge the capacitor has come forth. This paper proposes a physical energy flow model (EFM) to explain explicitly the winding-based discharge mechanism first. In the EFM, the performance characteristics of the classical winding-based discharge scheme are evaluated, but it is found that the discharge time will not be qualified when the machine rotor inertia is large and the system safe current is small. In order to reject intense voltage surge, a current control algorithm is proposed to bleed the capacitor voltage. Moreover, the proposed current control method shortens the discharge period to below 3 s for the system studied. The proposed discharge algorithm is verified by the experiment that is conducted on a three-phase PMSM drive system.

This paper introduces an isolated high voltage gain DC-DC converter, which can achieve high output voltage and large power level with hybrid connection of modular active-clamping current-fed push-pull(CFPP) converters. Thanks to the modularity, the voltage stress of semiconductor devices and the power rating of magnetic components are low. In addition, zero-voltage-switching operation is achieved for all switches and thus low EMI noise can be obtained. Furthermore, the secondary current of different CFPP converters in the same column is auto-balanced, contributing to reduced control complexity. With redundant rows and columns, the converter can remain normal operation under fault state. In the paper, the operation and analysis of the converter are illustrated in detail and the simulation results are demonstrated to verify its advantages.

Flux-switching permanent magnet (FSPM) machine is consist of a salient rotor and a salient stator with windings and magnets. Adding stator lamination bridge in segmented stator can simplify stator assembly significantly, which will be beneficial to manufacture and popularize the FSPM machine. Due to the doubly salient structure, the cogging torque in FSPM is larger than other traditional PM motors. In this paper, cogging torque of FSPM with stator lamination bridge is analyzed, and a novel short magnet (SM) structure is proposed to reduce the cogging torque by shortening the magnets. The simulation results indicate that shortening magnets reasonably can reduce the cogging torque at the cost of little output torque loss.