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To utilize the full potential of the direct matrix converter (DMC) and improve the output waveform quality, a three-level output strategy for conventional 3 × N ( N ≥3) DMCs is presented, where three-level output voltages are achieved without any changes in the topology. In this developed strategy, the DMC is treated as a two-stage converter that consists of a fictitious rectifier and a neutral-point clamped (NPC) three-level inverter. By applying a phase-shifted carrier modulation strategy to the rectifier and a modified carrier-based double-signal pulsewidth modulation strategy to the NPC inverter, sinusoidal input and output, reduced switching losses, and controllable input power factors are achieved in conventional 3 × N DMCs. The developed three-level output strategy improves output waveform quality while sacrificing input performance to some extent. Finally, the effectiveness of the developed strategy is verified by both simulations and experimental results.

In single-phase voltage source inverters (VSI) under a weak grid, the frequency coupling, caused by the asymmetrical system structure, poses a challenge to system modeling and controller design. In this article, a frequency coupling suppression control strategy is presented, where all the frequency coupling components in the current reference are eliminated. As a result, the single-phase grid-tied inverter is directly modeled as a simple single-input single-output (SISO) admittance rather than a complicated multiple-input multiple-output (MIMO) admittance matrix. The SISO admittance model is simple, compact, and accurate, which facilitates design-oriented analysis. The admittance characteristic analysis shows that the Sym-PLL has a critical impact on the system stability under weak grid conditions. To improve the system stability, a prefilter-based impedance-shaping control strategy is proposed by mitigating the negative resistor behavior of the Sym-PLL. Finally, simulations and experimental results validate the effectiveness of the frequency-coupling suppression control strategy.

For three-phase AC/DC converters, load disturbances and parameter uncertainties cause large fluctuations of the DC-link voltage, even resulting in system instability. In order to cope with this problem, the disturbance observer-based finite-time control (DOFTC) is put forward in this paper, where the finite-time disturbance observer (FTDO) is designed to fast and accurately estimate disturbances. Subsequently, the stability of the AC/DC converter closed-loop system is analyzed and theoretically proved. Finally, experimental results verify the effectiveness of the DOFTC strategy, where good dynamic and steady-state performance is achieved under load disturbance and parameter uncertainties. Compared with the enhanced state observer-based sliding mode control (ESO-SMC) and adaptive control method, the proposed DOFTC method not only reduced the fluctuations of the DC link voltage by at least 55% but also improved the transient response.

For the digitally controlled buck converters, the nonlinearity and time periodicity, caused by the pulsewidth modulator (PWM) and sample and hold, make the accurate frequency-domain analysis intractable. In this article, based on the harmonic transfer function (HTF) approach, a precise small-signal continuous-time modeling for the digitally controlled Buck converter operating in continuous-conduction mode (CCM) under constant-frequency voltage-mode control is presented. The sideband components on the closed-loop control are embedded in the model. Thus, this model is accurate within the full frequency domain region, which breaks the limit of Nyquist frequency. Furthermore, by overcoming the barrier of infinite series introduced by the sideband effects, the analytical loop gain expression is derived, which contributes to accurate stability assessment and reduction of computation burden. In addition, the proposed exact small-signal model has explained the reasons why different information injection points lead to different measured loop gains. Simulations and experimental results are conducted to verify the effectiveness of the proposed method.

High-frequency link matrix rectifier (HFLMR) is getting much interest in electric vehicle charger applications due to its high efficiency and compact volume. However, the inputs and outputs of HFLMR are highly coupled resulting in reduced system dynamic performance and robustness. This article proposes a dual closed-loop backstepping control (DCL-BSC) strategy to solve these problems, which consists of a dc output current outer-loop controller and a grid current inner-loop controller. First, the nonlinear mathematical model of HFLMR is established, and the six-segment space vector pulse width modulation scheme is used as the modulation method. Then, the DCL-BSC scheme is designed in detail based on the Lyapunov stability theory. And a compensation method based on the phase-shift angle is developed to realize the unity power factor. Compared with the conventional dual closed-loop PI control method, the proposed method has a better steady-state and dynamic performance, and robustness against system disturbances. Simulation and experimental results are used to verify the effectiveness of the proposed control scheme.

Solid‐state transformer (SST) is an attractive concept, which provides galvanic isolation and voltage scaling by means of a medium‐frequency link. In this paper, a single‐stage alternative current (AC)‐AC SST solution without bulky energy storage elements is presented. The front‐end rectifier (FER) and rear‐end inverter (REI) of the SST works at line‐frequency, while the intermediate LLC series resonant converter (SRC) fulfils the tasks of galvanic isolating and regulating the output voltage. To achieve high efficiency and bidirectional power flow capability of the SST, the zero voltage switching (ZVS) condition of the LLC SRC is comprehensively analysed, and the parameters design method of the LLC SRC is developed, where the resonant currents are constructed by applying the same gating signals to the primary‐side and secondary‐side bridges and the dead‐time is properly selected. Consequently, the presented SST has the merits of high conversion efficiency, naturally bidirectional power flow capability, potentially high power density and high reliability. The experimental results on a 1.5 kW SST prototype show that sinusoidal input and output current, ZVS operation over the full load range are achieved, and the peak efficiency is 97.63%. The experimental results verify the functionality and effectiveness of the developed methods.

Aiming at fulfilling the desirable features of compact structure, high efficiency, high reliability, and multifunctionality for the solid state transformers (SSTs), a single-cell matrix-type SST as well as its control method is proposed as the interface between the medium-voltage (MV) and the low-voltage (LV) levels for direct MV AC to LV AC conversion. To achieve zero voltage switching (ZVS) at both the MV and LV sides, a modulation scheme to construct the special resonant currents during the dead time by actively controlling the MV and LV side gate signals is implemented. Furthermore, the ZVS conditions of the MV and LV side bridges are analyzed, and system parameters are properly designed to ensure full range ZVS operation. A 1-kW SST prototype is developed to verify the functionality and effectiveness of the proposed methods. The experiments show that sinusoidal input and output, bidirectional power flow capability, and ZVS at both sides over wide input voltage and load ranges are achieved with the nominal efficiency of 96.1%. The experimental results match the theoretical analysis and the simulation results well.

In this paper, possible coupling configurations of a four-plate capacitive power transfer system are studied by varying the combinations of its input and output ports. A voltage source is applied between two of the four plates, and a load is connected to the other two to form different circuit topologies. A mathematical model based on a 4 × 4 mutual capacitance matrix is established for equidistantly placed four identical metal plates. Based on the proposed model, four separate circuit topologies are identified and analysed in detail and described in a general form. The electric field distributions of the coupling configurations are simulated by ANSYS Maxwell. The theoretical modeling and analysis are then verified by a practical system, in which four aluminum plates of 300 mm × 300 mm are used and placed with a gap of 10 mm between adjacent plates. The experimental results show that the measured output voltage and power under the four coupling configurations are in good agreement with the theoretical results. It has found that the voltage gain is the highest when the two inner plates are connected to the source, and this coupling configuration also has the lowest leakage electric field.

In order to suppress the influences of disturbances, like parameter uncertainties and unknown load, a finite-time adaptive neural backstepping control (FTANBC) strategy is proposed for three-phase AC/DC converters in this paper, where the neural networks are designed to compensate uncertain disturbances. Furthermore, the finite-time Lyapunov stable theory is combined with the adaptive neural backstepping to achieve good dynamic performance and enhance the system robustness. In addition, the FTANBC controller is constructed in the αβ frame, which eliminates the use of the phase locked loop. Compared with the PI method, the proposed method has good disturbance rejection ability. The overshoot of the DC voltage under the FTANBC method is minimized by about 90% in the start-up period, the settling time has been minimized by about 95% with various disturbances. Simulation results verify the correctness of the developed method.

In this digest, the modulated model predictive control (MMPC) method for the three-phase third-harmonic injection two-stage matrix converter (3TSMC) is proposed, where the inverter and the current injection link are independently modulated. The sinusoidal input currents are achieved by the predictive control of the current injection link, simultaneously the output currents are obtained by the predictive control of the inverter. The proposed MMPC method guarantees good system performance at low switching frequency, and it eliminates the weight factor used to balance the input and output performance. The simulation results verify the correctness of the proposed method.

In this paper, two common-mode voltage (CMV) reduction methods are proposed for the three-to-five-phase indirect matrix converter. The effectiveness of the proposed CMV reduction methods is due to the reconfiguration of the zero vectors from the inversion stage to the rectification stage in modulation schemes. In theory, the proposed methods not only reduce the peak value of the CMV by up to 27.9% but also improve the differential-mode performance of the output voltage, thus benefiting the electromagnetic interference design. Moreover, the voltage transfer ratio, the spectrum of the resultant CMV, and the total harmonic distortions of the current and voltage are analyzed in this paper, where, thus, the pros and cons of the proposed modulation schemes are presented. Simulations and experimental tests are provided to verify the effectiveness of the proposed methods.

Brushless doubly fed induction machines (BDFIMs) feature some important advantages, such as high reliability and low maintenance cost, over alternative solutions for brushless machine applications. This paper proposes a modulated model predictive control (MPC) algorithm for BDFIMs, which achieves a fixed switching frequency and superior system performance. An improvement of power quality is shown in this paper when compared to the conventional finite-control set-MPC. This paper examines the design and implementation of the modulation technique as well as presenting the simulation and experimental results to verify the technique’s operation.

The relatively low-linear voltage transfer ratio (VTR) is considered an intrinsic drawback of the conventional two-stage matrix converter (TSMC). However, the studies demonstrate that the linear VTR of the third-harmonic injection TSMC (3TSMC) can push this limit. After reviewing the operating principles and modulation strategy of 3TSMC briefly, the VTR characteristic of 3TSMC is analysed and a control method to enhance the linear VTR is proposed. With the developed method, the maximum linear VTR can break through the intrinsic limit and VTR > 0.866 can be achieved by regulating the input reactive power under arbitrary output conditions theoretically. Finally, simulations and experimental results verify the correctness of the theoretical analysis, and the comparison of 3TSMC and other TSMCs with improved VTR demonstrates the effectiveness of the proposed method.

To increase the voltage transfer ratio of the matrix converter and improve the input/output current performance simultaneously, an over-modulation method based on predictive control is proposed in this paper, where the weighting factor is selected by an automatic adjusting mechanism, which is able to further enhance the system performance promptly. This method has advantages like the maximum voltage transfer ratio can reach 0.987 in the experiments; the total harmonic distortion of the input and output current are reduced, and the losses in the matrix converter are decreased. Moreover, the specific implementation of the proposed approach is developed in detail. Simulations and experiments verify the effectiveness of the proposed method.

The brushless doubly fed induction machine (BDFM) has great potential in the wind energy generation system because it offers the advantages of higher reliability and maintenance-free operation. In this paper, a mathematical model in the power windings stator flux orientation frame is discussed by taking the rotor flux as the disturbance. Consequently, the control of the BDFM system is implemented by generating suitable control winding currents. Moreover, in order to eliminate the speed error and compensate the system uncertainties caused by the rotor flux and parameter perturbations, an integral sliding mode variable structure controller for the rotor speed is developed, and the reactive power is adjusted by a proportional-integral (PI) controller in the outer-loop. Furthermore, the control winding currents are regulated by the PI control scheme in the inner-loop. The proposed control frame achieves a good static and satisfactory dynamic control performance. Finally, simulation and experimental results are used to verify the correctness and feasibility of the proposed method.

The matrix converter is a direct ac–ac power conversion topology. To improve the output waveform quality of the conventional matrix converter and overcome the drawbacks of the neutral-point clamped matrix converters such as the neutral-point voltage balancing issue, the limited control range of the input reactive power and the need for strict synchronization in the modulations of the rectification and inversion stages, a three-level third-harmonic injection indirect matrix converter, and a neutral-point voltage balancing algorithm are proposed. The topology consists of a line-commutated input voltage selector, a three-level inverter and a third-harmonic injection circuit, where the split dc source voltage of the inverter is formed by two input line–line voltages. Furthermore, by adopting the active power filtering technique and utilizing the third-harmonic injection circuit to compensate the neutral-point current, the neutral-point potential is balanced without extra control effort. In addition, except the advantages such as bidirectional power flow, sinusoidal input–output currents, and multilevel output voltages, the synchronization in modulations is eliminated, and the control range of the input reactive power is extended significantly. Finally, the functionality and effectiveness of the proposed methods are verified by simulations and experimental results.

In respect to a Doubly-Fed Induction Generator (DFIG) system, its corresponding time scale varies from microsecond level of power semiconductor switching to second level of the mechanical response. In order to map annual thermal profile of the power semiconductors, different approaches have been adopted to handle the fundamental-frequency thermal cycles and load-varying thermal cycles. Their effects on lifetime estimation of the power device in the Back-to-Back (BTB) power converter are evaluated.

With the continuous increase of battery capacity in the power battery charging and discharging system(PBCDS), the charging and discharging equipment of power battery also needs to output large power or energy, so the multi-DC-DC parallel-connected structure on the battery side becomes the first choice. In addition, considering the traditional PI control method have a complex parameter adjustment process and the complexity of parameter adjustment increases sharply with the parallel-connected of multi-DC-DC, but also it cannot meet the special requirements of high dynamic response speed and non-overshoot in the power battery charging and discharging process(PBCDP). Therefore, this paper innovatively proposed a model predictive control method for the parallel-connected system with n DC-DC converters, which does not require complicated parameter tuning, but also achieves the special requirements of high dynamic response speed and non-overshoot in the PBCDP. The method has strong universality and high flexibility, and can be applied to power battery charge and discharge conditions with any level of power. Finally, the simulation is conducted to validate the feasibility and correctness of the proposed MPC control method.

This study proposes a decentralized coordination control scheme for series-connected H-bridge rectifiers. Each rectifier module is controlled as a voltage-controlled source by a local controller, which needs only individual information. The local controller is composed of an active power-frequency (P-ω) control and a fixed voltage amplitude control. Compared to the conventional methods based multi-level phase-shifting modulation where centralized controller is needed, the proposed control strategy allows indefinite modular expansion without increasing the computational load of the local controller. Therefore, it has decreased cost and increased scalability. The synchronization mechanism of series modules is analyzed and the stability of the system is proved. The feasibility of the proposed strategy is verified by experimental results.

In order to realize sensorless control for brushless doubly fed induction machine (BDFIM), this paper presents a model reference adaptive system (MRAS) observer, designed based on the error of the control winding current. Furthermore, a phase-locked loop is employed to estimate the current winding position and rotor speed. Consequently, a detailed theoretical derivation proves that the MRAS observer is stable and the dynamic performance is good. Thus, it does not cause any estimated speed error in steady state. Moreover, the estimated position error is bounded and trivial, thus its effects on the sensorless control of the BDFIM are neglected. The correctness, feasibility, and robustness of the proposed sensorless control method are verified by means of experimental validation on a 30 kW test rig.

This study presents an active third-harmonic injection indirect matrix converter (3HI2MC) topology with dual three-phase outputs. The presented 3HI2MC has the advantages of sinusoidal input and output currents, bi-directional power flow, and can provide two sets of three-phase outputs, whose frequencies and amplitudes can be regulated independently. Compared with the conventional indirect matrix converter (IMC), the input reactive power control range is extended significantly, and the converter can even work as a static compensator. Moreover, a maximal voltage transfer ratio of 0.866 is achievable under all operation conditions. Furthermore, operations of the rectifier and inverters are independent. Thus, for a 3HI2MC system containing multiple voltage-source-type inverters (VSIs), modulation and control task can be implemented flexibly by a separate controller for each VSI, while it is difficult for the conventional IMCs to achieve such a goal. All of the features above make 3HI2MC competitive for the applications that require multiple three-phase outputs such as multiple drives. After describing the topology structure, operating principles and control algorithm in detail, simulation and experimental results are presented to demonstrate the validity and effectiveness of the proposed topology.

Due to the merits of sinusoidal input currents and excellent conversion efficiency, buck-type active third-harmonic injection converters have received increasing attention in recent years. However, three major problems of these converters still exist in theory and practice. First, the existence of the dc-link capacitor, utilized by early researchers, causes inrush transient and distorts the input currents. Second, in some specific situations, such as wind energy conversion system and flexible ac transmission system, these converters' capabilities of generating input reactive power need sufficient improvements. Third, proper selection of the third-harmonic injection inductor is the key challenge to implement these converters, since the inductor affects not only the current ripple but also the tracking performance of the third-harmonic current. To solve these problems, this paper studies the two-stage matrix converter with third harmonics injection and demonstrates that the dc-link capacitor can be removed by bidirectional implementation and proper control of the rectifier. Then, an algorithm enhancing the input reactive power capability is developed. Thus, sinusoidal input currents are achieved and the reactive power control range is extended significantly. Moreover, the design criteria of the third-harmonic injection inductor are discussed. Finally, the proposed method is verified by simulation and experimental results.

In the wind energy generation system, the brushless doubly-fed induction machine (BDFIM) has shown significant application potential, since it eliminates the electric brush and slip ring. However, the complicated rotor structure increases the control difficulty, especially resulting in complicated coupled terms in the current sub-system, which deteriorates the dynamic performance and reduces the system robustness. In order to address the problems caused by complex coupled terms, an internal model current control strategy is presented for the BDFIM, and an active damping term is designed for suppressing the disturbance caused by the total resistance. The proposed method simplifies the controller parameters design, and it achieves the fast-dynamic response and the good tracking performance, as well as good robustness. On the other hand, the feedforward term composed by the grid voltage is added to the internal model controller in order to suppress the disturbance when the symmetrical grid voltage sag happens. Finally, the simulation and experimental results verify the feasibility and effectiveness of the proposed method.

With the increasing penetration of wind power, reliable and cost-effective wind energy production is of more and more importance. As one of the common configurations, the doubly fed induction generator based partial-scale wind power converter is still dominating in the existing wind farms, and its reliability assessment is studied considering the annual wind profile. According to an electro-thermal stress evaluation, the time-to-failure of the key power semiconductors is predicted by using lifetime models and Monte Carlo based variation analysis. Aiming for the system-level reliability analysis, a reliability block diagram can be used based on Weibull distributed component-level reliability. A case study of a 2 MW wind power converter shows that the optimal selection of power module may be different seen from the reliability perspective compared to the electrical stress margin. It can also be seen that the B1 lifetimes of the grid-side converter and the rotor-side converter deviate a lot by considering the electrical stresses, while they become more balanced by using an optimized design strategies. Thus, the system-level lifetime increases significantly with an appropriate design of the back-to-back power converters.

To improve the input and output waveform quality in terms of total harmonic distortion (THD) for the three-level diode-clamped matrix converter topology, the phase disposition carrier-based modulation method is a good option. However, it is difficult to implement because of the loss of zero-current commutations. Aiming at addressing the problem above, a hybrid switching sequence for the phase disposition method is presented to realise the safe commutation, and a prediction-based method is used to alternate the switching sequences. The current direction information of the switches in cascaded rectifier for commutations is obtained by a current reconstruction method. As demonstrated by experimental results, the phase disposition method contributes to lower input and output waveforms THD values compared with the phase opposition disposition method.

In the wind energy generation system, mission profiles are complicated, which range from seconds to years. In order to estimate the consumed lifetime of the power converter, wind speed profiles with the time resolution of 1 hour, 1 second and 0.5 millisecond are studied in this paper, and the corresponding thermal modeling of power semiconductors are discussed. Accordingly, effects of different mission profiles on the consumed lifetime of the power converter are evaluated. In the above three thermal cycles, the IGBT of the grid-side converter and the diode of the rotor-side converter are more fragile, and the total consumed lifetimes are higher. Moreover, the short-term thermal cycles with milliseconds resolution induce the unbalance of the lifetime between the diode and IGBT of the grid-side converter, while thermal cycles with hour, second, and millisecond resolution consumes the similar lifetime of the power components in the rotor-side converter. Furthermore, it is concluded that the lifetime of power components reduces with the increased time resolution, especially for the rotor-side converter.

With the increasing penetration of wind power, reliable and cost-effective wind energy production are of more and more importance. As one of the promising configurations, the doubly-fed induction generator based partial-scale wind power converter is still dominating in the existing wind farms, and its reliability assessment is studied considering the annual wind profile. According to an electro-thermal stress evaluation, by using lifetime models and Monte Carlo based variation analysis, the time-to-failure distribution of the key power semiconductors is predicted. Aiming for the system-level reliability analysis, a Weibull distribution based component-level model is applied by using a reliability block diagram. A case study of a 2 MW wind power converter shows that the optimal selection of power module may be different viewed from the reliability perspective compared to the electrical stress margin. It can be seen that the B 1 lifetime of the grid-side converter and the rotor-side converter deviates a lot by considering the electrical stresses, while they become more balanced by using an optimized reliable design. The system-level lifetime significantly increases with an appropriate design of the back-to-back power converters.

In order to reduce the Common-Mode Voltage (CMV) in three-to-five phase indirect matrix converters, three improved Space Vector Pulse Width Modulation (SVPWM) methods are proposed and discussed. The improved modulation schemes are achieved by reorganizing zero vectors from the inversion stage to the rectification stage. The proposed methods can not only theoretically reduce the CMV peak value by up to 47.1%, but also decrease the switching losses of the power devices. Moreover, comparisons show that a superior CMV reduction performance is achieved when only two large active voltage vectors (AVVs) in the inversion stage, which results in a large amount of third-order harmonics in output currents. In addition, the method that utilizes two adjacent active current vectors (ACVs) and the method that uses two non-adjacent ACVs in the rectification stage have the same CMV peak value. By contrast, the latter achieves a lower Total Harmonic Distortion (THD) level of the output currents. Simulation results verify the effectiveness of the proposed methods.

This paper proposes a modulated model predictive control (MMPC) algorithm for a brushless double-fed induction machine. The Brushless Doubly-Fed Induction Machine has some important advantages over alternative solutions for brushless machine applications. The proposed modulation technique achieves a fixed switching frequency, which gives good system performance. The paper examines the design and implementation of the modulation technique and shows the comparison of finite control set-model predictive control (FCS-MPC) and MMPC. Simulation results verify the operation of the proposed modulation technique.

This paper proposes a sample model predictive current control strategy for the third-harmonic injection two-stage matrix converter (3TSMC). The discrete-time model of 3TSMC is used to predict the future behavior for every feasible switching state. The control method chooses the optimal switching state that minimizes the cost functions, for rectifier and inverter. The model predictive current control consists of two parts. One is to produce sinusoidal three-phase input currents, and the other is to obtain high quality output currents. Besides, this control strategy guaranty good dynamic performance. Compared with the conventional PI current control method, the current quality has significantly improved by applying proposed approach. The feasibility of the proposed method is verified through simulation.