The two-phase clamped modulation strategy has gained attention in industrial applications due to low switching losses. However, the reduced losses come at the cost of decreasing the controllable degrees of freedom, which poses a challenge for controller design. Aiming at a matrix-type back-to-back converter (MT-BBC) applied in a permanent magnet synchronous motor (PMSM) drive, this article presents a frequency-divided coordinated control. In this control scheme, a method for acquiring the input current reference of MT-BBC is proposed. An active damping method is proposed to suppress oscillations. A coordinated control is used to regulate the sixth harmonic component of the DC-link voltage to improve input current quality. The effectiveness of the frequency-divided control strategy is validated through simulation and experimental results.

In software-based resolver-to-digital converters, parameter deviations of detected envelope signals (amplitude imbalance, dc offset, and nonorthogonal phase shifts) can introduce periodic rotor position estimation errors, leading to significant degradation of control performance of a permanent magnet synchronous machine. To address this issue, an online self-calibration method is proposed in the article. First, a self-calibration framework based on certainty equivalence principle is designed, and the effect of resolver parameter deviations on the harmonic components of envelope signals is analyzed. Then, the correlated harmonic components are separated to estimate parameter deviations. The rotor position estimation error is self-calibrated in the parameter deviations estimation process. Finally, the effectiveness of the proposed method is verified by simulation and experimental results.

In single-phase voltage source rectifiers (VSRs) under weak grid conditions, asymmetric control dynamics induce complex frequency coupling, which complicates system modeling and stability analysis. To address this issue, this article proposes a symmetrical control framework for single-phase VSRs, consisting of a symmetrical DC-link voltage controller (Sym-DVC), a symmetrical phase-locked loop (Sym-PLL), and a modified alternating current controller (ACC). The Sym-DVC generates a symmetrical reference vector by normalized regulation of the average DC-link power and reactive power, where the d- and q-axis components correspond to the current reference amplitude and power factor angle, respectively. The modified ACC constructs an exponential-form reference, synthesized by both the outputs of Sym-DVC and Sym-PLL. The proposed symmetrical control scheme eliminates frequency-coupled components in the current reference, allowing the single-phase VSR to be accurately modeled as a single-input single-output (SISO) admittance model. On this basis, the stability boundaries, considering grid impedance and control bandwidth, are derived. Experimental results verify the effectiveness of the proposed symmetrical control strategy.

This article presents a three-phase AC-AC converter based on the unfolder topology, which consists of an unfolder rectifier and a T-type three-phase inverter connecting configuration. Since the converter inherits the features of the unfolder circuit such as ultra-low switching frequency and small DC-link capacitance, it exhibits high efficiency and high power density. Furthermore, it eliminates the additional balanced circuit or isolated DC-DC converters required in the conventional unfolder-based power converters, improving power density. To realize both power factor correction and output voltage regulation simultaneously, a special modulation scheme for the T-type three-phase inverter is proposed. The feasibility of the proposed converter is verified by theoretical derivation, simulation study, and experimental prototype testing.

Constant power loads (CPLs), LC filters, and digital modulators jointly render railway traction converters piecewise-smooth nonlinear time-periodic (NLTP) systems, posing challenges for small-signal stability analysis. Based on Filippov's analytical framework, this paper establishes a closed-form expression of the monodromy matrix for four-quadrant converters (4QCs), capturing the effects of switching dynamics and digital control on system behavior. Through eigenvalue analysis, the destabilizing impact of the LC filter is revealed for the first time. Additionally, the influence of key parameters, such as controller gains, load power, and grid impedance, on the stability boundaries is systematically assessed. The predicted stability regions and oscillation modes are validated against experimental data, showing excellent agreement and confirming the accuracy and effectiveness of the proposed method.

To overcome the hard-switching limitations of conventional inverter and to improve efficiency, this paper proposes a soft-switching topology for single-phase inverter based on auxiliary inductor. A zero voltage switching (ZVS) auxiliary circuit, comprising an auxiliary inductor and two auxiliary switches, is introduced: the auxiliary switches are connected in parallel with the main filter inductor, while the auxiliary inductor is placed in series with the AC output. Under the proposed modulation strategy, the auxiliary inductor current reverses during commutation, thereby discharging the parasitic capacitances of the main switches. As a result, ZVS is achieved for all high-frequency switches in the full bridge, and the added auxiliary switches exhibit excellent zero-current-switching (ZCS) performance. The operating principle, electrical characteristics, and parameter design of the proposed inverter are derived and analyzed in detail. Finally, a 600W prototype is built and tested. Experimental results show that the proposed inverter achieves a full-load efficiency of 95.17%, and compared with the hard-switching counterpart, the efficiency can be improved by 4.58% under light load.

In software-based resolver-to-digital converters (RDCs), parameter deviations of the detected envelope signals (amplitude imbalance, DC offset, and non-orthogonal phase shifts) can introduce periodic rotor position estimation errors. These errors will cause degradation in motor control performance. To address this issue, a parameter deviations estimation method is proposed for resolver self-calibration. Firstly, the detected envelope signal equations are parameterized to incorporate amplitude imbalance, phase shift, and DC offset as estimable parameters. A unified linear regression equation is then formulated. Second, to speed up parameter estimation, the dynamic regressor extension and mixing method (DREM) is employed. Finally, the effectiveness of the proposed method is verified by both simulation and experimental results.

Accurate rotor time constant (RTC) is the key to achieving high-performance induction motor (IM) drives. To obtain an accurate RTC, a new robust online RTC estimation method based on harmonic current injection is presented. In the proposed method, the RTC is estimated from the speed response corresponding to the injected harmonic current. Compared with the existing schemes, the parameter mismatches will not influence the steady-state identification results of RTC. Thus, it has stronger robustness to parametric uncertainties. Finally, the effectiveness and correction of the proposed method are verified by simulations and experiments.

Vector current control (VCC) is widely used in grid-connected voltage source inverters (VSIs) but suffers from stability issues under weak grid conditions due to phase-locked loop (PLL) limitations. To address this, this paper proposes a voltage-modulated dead-beat direct power control (VM-DB-DPC) strategy, eliminating the PLL and enhancing system robustness. By leveraging grid voltage modulation for phase synchronization, the proposed method ensures accurate power tracking without relying on conventional PLLs. Additionally, a band-pass filter extracts the fundamental voltage component to mitigate harmonic disturbances, while a dead-beat control algorithm improves the power response speed. Compared to traditional VCC, the proposed method achieves a 38

Most existing back-electromotive-force (EMF) observer necessitates a phase-locked loop (PLL) for real-time observer parameter updating, i.e., the rotor's angular speed. However, the observer-PLL coupling effect complicates the back-EMF observer design and poses challenges in ensuring stability. In this article, a filtered transformation-based adaptive back-EMF observer (FT-AO) for surface-mounted permanent magnet synchronous motors is presented. The FT-AO enables direct estimation of back-EMF without relying on a PLL, avoiding the observer-PLL coupling and thus simplifying the control parameter design. Additionally, the asymptotic stability of the FT-AO is rigorously proven using Lyapunov's theorem. Experimental results confirm the superiority of the FT-AO in terms of dynamic/steady-state performance.

This article proposes an adaptive observer-based control scheme for the monoinverter dual parallel (MIDP) surface-mounted permanent magnet synchronous motors (SPMSMs) system, equipped with two phase-current sensors and a rotor position sensor. An auxiliary vector input is introduced to ensure that the observation error system is strictly positive real, which is necessary for the design of adaptive observers. The observer gain is adjusted online using the adaptive term, ensuring that the observer poles remain unaffected by motor speed variations. Furthermore, the stability of the adaptive observer is proved via the Lyapunov theorem. Finally, the feasibility of the proposed adaptive observer-based control scheme is validated by experiments.

Frequency coupling effect (FCE) commonly exists in single-phase converters, introducing complexity to the analysis and synthesis of single-phase inverter systems. Although the band-pass filter (BPF) has been widely used in controllers for filtering harmonic and damping improvement, this article rethinks the effect of the BPF on FCE in single-phase inverters. The article reveals that the output impedance of the inverter equipped with a BPF remains almost unchanged, whether accounting for FCE or not, even under weak grid conditions. That is to say, when the BPF is applied, the output impedance without considering FCE can be used for accurate stability analysis and controller design. Furthermore, it is identified that a significant expansion in the stability regions of the single-phase inverter compared to control schemes without the BPF. Both simulations and experiments verify the effectiveness of the theoretical analysis results.

The modulator-injected zero-sequence signal (MI-ZSS) technique has found widespread application in modulating three-phase power converters, contributing to enhancements in efficiency, modulation range, and power quality. However, little attention has been given to its effect on system stability, mainly due to the neglect of modulator dynamics in traditional averaged models. This article bridges this gap by investigating the influence of MI-ZSS under carrier-based pulse-width modulation (CB-PWM) on the stability of three-phase voltage source converters (VSCs). A unified multifrequency small-signal model of the three-phase VSC is developed, taking into account CB-PWM dynamics under various MI-ZSS conditions. The model facilitates the analysis of the effects of MI-ZSSs on the system stability. The findings reveal that different MI-ZSSs result in distinct stability regions. Finally, experimental results verify the feasibility and correctness of the theoretical analysis presented above.

Filippov's method has been extensively used to evaluate stability in dc-dc converters. However, its application to dc-ac converters, which operate at both the switching frequency and the grid frequency, has rarely been studied. In this article, the stability of a digitally controlled single-phase grid-tied inverter (GTI) is investigated via extended Filippov's method, which fully accounts for multifrequency dynamics and digitization effects. The closed-form expression of the monodromy matrix for the digitally controlled single-phase GTI is established. Using the obtained monodromy matrix, the stability boundary concerning various control bandwidths and grid impedances is assessed, and the oscillation frequency in unstable cases is predicted. Finally, experiments are carried out to validate the theoretical analysis.

Multi-vector-based model predictive direct speed control (MV-MPDSC) suffers from outer loop disturbance, inner loop disturbance, and weighting factor tuning. To solve these problems, a multi-vector-based model-free predictive speed control (MV-MFPSC) is proposed for the surface-mounted permanent magnet synchronous motors (SPMSMs). First, a reduced-order ultra-local model is established by introducing an equivalent speed-tracking error as a state variable, which derives the outer and inner loop disturbances as a lumped disturbance while compensating for differences between mechanical and electromagnetic time constants. It reduces the number of observers and the speed overshoot/oscillation. Theoretical analysis indicates that the nonlinear extended state observer (NESO) exhibits a poor estimation performance facing the lumping disturbance of large-scale changes. Thus, a modified NESO (MNESO) is introduced to achieve a faster and more accurate lumped disturbance estimation, which significantly improves the dynamic performance. Moreover, its parameter design principles are proposed to enhance the practicality. Then, an algebraic minimizing approach is introduced to directly calculate the duty cycle of the selected voltage vectors, and the weighting factors can be eliminated through clever mathematical operation. It avoids the duty cycle calculation error caused by imperfect weighting factors and improves the steady-state performance. The effectiveness of the MV-MFPSC was demonstrated through experiments.

The design of the back electromotive force (EMF) observer is important in sensorless speed control of surface-mounted permanent magnet synchronous motors. However, many existing back EMF observers are coupled with the phase-locked loop (PLL), which not only complicates observer design but also poses challenges in ensuring global asymptotic stability. To address this challenge, this article introduces a reduced-order adaptive observer (ROAO) characterized by PLL-independent, which greatly simplifies the parameter design of the observer. In addition, the proposed ROAO is globally asymptotically stable with rigorous proof via the Lyapunov theorem. Finally, the effectiveness of the proposed observer is verified by simulation and experiment.

Carrier phase shift (CPS) and switching signal phase shift (SSPS) are two commonly used switching delay methods for modulation in series capacitor buck converters (SCBCs). This article studies the nonlinear behavior of the SCBC under CPS and SSPS using the Filippov-based stability analysis method. Closed-form monodromy matrices of the SCBC are developed, incorporating the phase shift effects. Both fast and slow timescale stability are studied through eigenvalue analysis of the monodromy matrix. The findings reveal that different phase shift strategies result in the same steady-state behavior but different stability regions and even distinct bifurcation instability behaviors. Finally, experimental results confirm the correctness of the theoretical analysis.

This paper proposes a two-stage current limiting control strategy for DC Solid-State Power Controllers (SSPCs), aimed at addressing the challenges posed by inrush current and thermal stress during the rapid switching of large capacitive loads. In the resistor-based current limiting stage, a current-limiting resistor is utilized to suppress the inrush current, thereby protecting the system from instantaneous high current damage. In the gate voltage clamping current limiting stage, the gate voltage of the main-branch MOSFET is clamped to a given value, enabling rapid charging of the load capacitor. Throughout the limiting process, natural commutation occurs between the main branch and the current-limiting branch, resulting in a continuous variation of the SSPC's equivalent resistance. This effectively reduces secondary inrush current and fully utilizes the thermal capacity of the power devices. Experimental results show that the SSPC employing this strategy can switch on a 3300 mu F capacitive load within 10.1ms, with an initial inrush current of 191A and a secondary inrush current of less than 76A, verifying the effectiveness and reliability of the proposed strategy.

Resistance-emulating control is a cost-effective control scheme for grid-connected converters. However, it is not suitable for the case in which bidirectional power flow is required. To overcome this limitation, a new resistance-emulating control scheme is presented in this article. The emulated resistance is composed of a notch filter and a band-pass filter. Compared with the conventional resistance-emulating control, two extra degrees of freedom are introduced into the proposed one. By choosing the degrees of freedom properly, both the steady and dynamic performance of the system can be enhanced. In addition, the operating range of the grid-connected converter is extended greatly. Meanwhile, the advantages of no grid voltage sensor and phase-locked loop are retained in the proposed method. Experimental results verify the effectiveness and correctness of the proposed method.

For three-phase grid-tied voltage-source converters (VSCs), the presence of unbalanced grids (unbalanced grid voltages, asymmetric line impedances, etc.) tends to excite the frequency coupling effect (FCE), posing a challenge to system modeling and stability analysis. In this article, a frequency coupling suppression control strategy is developed for three-phase grid-tied VSCs to deal with FCEs caused by unbalanced grids. The proposed control strategy consists of a dual second-order generalized integrator-based symmetric phase-locked loop (DSOGI-SPLL) and an inductance-emulating control loop. The DSOGI-SPLL suppresses the FCE induced by unbalanced grid voltages, while the inductance-emulating control loop is responsible for addressing the FCE arising from asymmetric line impedances. The presented control strategy allows the derivation of a concise single-input single-output complex vector model, facilitating a stability-oriented design. Furthermore, a phase-locked loop (PLL) correction method is introduced to enhance system stability under weak grid conditions. The effectiveness of the proposed control strategies is verified through simulation and experiments.