Search

High-voltage direct-current (HVDC) power transmission is becoming increasingly important due to steadily rising need for bulk power delivery and interconnected power transmission and distribution systems. DC grids are vulnerable to dc faults, which lead to a rapid rise in dc fault currents. The dc faults must be cleared within the timeframe of milliseconds to avoid the collapse of the HVDC system. In the event of primary protection (PP) failure, back-up protection (BP) must be applied to clear the fault. In this paper, a novel algorithm based on a Naïve Bayes classifier is proposed to determine threshold levels and operational time frames for primary and back-up protection in multi-terminal voltage source converter-based HVDC. Local voltage and currents are measured to detect and identify the kind of fault. A four-terminal HVDC transmission system is developed in PSCAD/EMTDC and is subjected to line-line faults at different locations and time, to assess the designed protection schemes. Results show that a relaying algorithm effectively detects the fault and expedite the primary protection operation. On malfunctioning of PP, BP is accelerated in a short delay of 0.2 ms. Furthermore, the relaying algorithm provides faster protection compared with techniques available in the literature. The resulting reduced fault clearance time truncates the maximum fault current and, inevitably, leads to reduced power ratings required for dc grid equipment.

This paper deals with the power dispatch and direct voltage control in multiterminal high voltage direct current (MT-HVDC) systems. Generalized voltage droop (GVD) control is adopted for voltage source converters (VSC)s of a MT-HVDC system. A mechanism has been designed based on the power ratio within the GVD controlled stations to achieve flexible autonomous coordination control among VSC-HVDC stations, without need for communication. In this paper, several alternatives are considered to guarantee fault ride through of onshore converter stations. The performance of the proposed control strategy is analyzed with time-domain dynamic simulations, in an EMDTC/PSCAD platform, and experimentally validated. Results demonstrate the robust performance and capabilities of the proposed control strategy during changes in the power demand of the ac grids, unexpected change in wind power generation, and eventual permanent VSC-HVDC station disconnection.

To extend the lifetime, improve the power density and reduce the system cost, the film capacitor is applied to replace the large-volume electrolytic capacitor in motor drives. As the dc-link voltage fluctuates periodically, the rotor position estimation error and operation stability are necessary to be concerned in the position sensorless control methods. A cross-decoupling complex filtering-based position estimation method is investigated for the reduced capacitance interior permanent magnet synchronous motor drive system. Harmonic components of the extended back electromotive force (EEMF) caused by the dc-link voltage fluctuation are analyzed to evaluate the additional rotor position error. A cross-decoupling complex filter realized by the multiple first-order complex filters with different center frequencies is designed to improve the position estimation precision. Harmonics of the EEMF are suppressed and the position error can be eliminated. The estimation precision and operation ability are improved. Experimental results are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, a 2.5m five-stage inductive power transfer (IPT) system based on domino cylindrical solenoid coupler (CSC) compensated, respectively, in layers is proposed. The system is considered to be used as 220 kV post insulators application, transferring power for sensors and measuring instruments of smart grids. The distributed series compensation method is applied to double-layer CSC. Compared with the two types of parallel schemes, this method can significantly reduce the current of the main circuit. Compared with the concentrated series compensation method, this method can effectively reduce the resistance caused by the stray capacitance. The interaction between the post insulator and the magnetic coupling structure is analyzed. The circuit model of the system with constant voltage output characteristics is analyzed. A prototype with a maximum efficiency of 66.7% is built. When the power is transferred to a larger value of 77.8W, the efficiency can still reach 62%. Comparing with previous works, the wireless distance is extended while the efficiency is improved. [ABSTRACT FROM AUTHOR]

The overmodulation strategy plays an important role in the field weakening control for high-speed permanent magnet synchronous motor (PMSM) drives. However, the voltage jumps between the output voltage vectors (OVVs) in high overmodulation regions result in the deterioration of both current performance and loading capability. In order to solve this problem, a novel overmodulation strategy based on the voltage vector space division is proposed. The overmodulation regions are divided by the amplitude and the phase of reference voltage vectors to guarantee the continuity of OVVs. When the overmodulation region changes, the voltage jump can be efficiently suppressed, which contributes to eliminating current ripples. In addition, the proposed parallel projection replaces the traditional center projection to increase the modulation index, which can also improve the fundamental voltage amplitude, and make a reduction of the field weakening current and its current overshoot. By improving the utilization of the dc bus voltage, the higher capability of the output torque can be achieved in the field weakening region. Finally, the effectiveness of the proposed strategy is verified on a high-speed surface-mounted PMSM platform by the experimental results. [ABSTRACT FROM AUTHOR]

High-frequency resonance (HFR) in the modular multilevel converter (MMC) has been reported in recent years frequently, yet, existing focuses on HFR are limited to the specific control strategy or grid condition, from which the conclusion may be not applicable if the control or grid changes. In this article, a unified MMC high-frequency impedance model (UHFIM) is proposed to fill this gap. By changing the gain of the model, UHFIM can reflect the high-frequency characteristics of the MMC under different control strategies in a unified form, which provides a theoretical basis for the general HFR suppression method. Analysis based on UHFIM reveals the worst cases of the HFR risk and the constraint of low-pass filter (LPF) order on the convergence of MMC high-frequency damping. In order to suppress HFR, this article proposes a joint design method for LPF and passive damper, which can completely remove the HFR risk from the entire high-frequency range without sacrificing too much dynamic performance of MMC, and it works no matter how the grid impedance varies. Besides, in the case that the damper cannot be installed, an alternative HFR suppression method based on delay time adjustment is also developed. Finally, the proposed unified model and the HFR suppression methods have been verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Communication links, as a part of coordinated control in dc microgrids (MGs), play an essential role in achieving high operational performance. In this article, a bipolar topology based on series modular structure of dc MG is designed, and a complementary dual-window dc bus interacting (CDBI) method which combines droop control with antidroop control is proposed to improve the robustness of system and against communication failure. In the proposed CDBI method, distributed generations regard dc buses as common communication channels for information exchange, and the coordinated control within the dc MGs can be realized through predesigned sequences of voltage pulses without extra communication links. Finally, the proposed symmetrical bipolar structure and communication-free coordinated control scheme have been verified in various cases through rapid control prototype. The experimental results show that the bipolar-type dc MG controlled by the proposed CDBI method can supply high-quality power for a long time even in the case of communication failure. [ABSTRACT FROM AUTHOR]

The power density can be improved and the system cost can be saved in the reduced dc-link capacitance motor drive system. The line inductance can also be diminished to reduce the system volume further. In previous research works, the active damping control methods mainly concentrated on the drive system equipped with a larger line inductor. In this article, a dc-link voltage estimation feedback-based active damping method is proposed to suppress the grid current harmonics and improve the drive system stability with low line inductance. The dc-link voltage ripple caused by the LC resonance is analyzed to evaluate the direct dc-link voltage feedback-based active damping control method. To improve the damping performance, the resonant component of the dc-link voltage caused by the LC resonance could be obtained through the grid current to establish the feedback control loop. The sampling delay should be compensated to improve the control performance. The stability of the drive system is evaluated by the Nyquist plots of the impedance model, and the grid current is also analyzed, which could satisfy the harmonic requirements of IEC-61000-3-2. Experimental results are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article proposes a coordinate impedance compression strategy for high frequency inverter systems. Based on a two parallel inverter structure, the strategy adopts two methodologies: 1) a passive LC network to adjust the current and voltage seen by each inverter module, and 2) an active modulation of the inverter input voltage and output voltage phase to adjust the load current distribution. For the proposed strategy, the resistance and reactance can be compressed coordinately, which can help the inverter to operate in high efficiency load range. The Half-Bridge Class D inverter is taken as an example to be analyzed. A 10-MHz prototype is built and the experimental results verify the correctness and feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

Electrolytic capacitorless Vienna rectifiers have many advantages, such as longer lifetime and higher power density. However, the reduced dc-link capacitance aggravates the voltage stress due to the neutral point (NP) fluctuation. In this article, a hybrid modulation strategy combining the modulations of redundant vector and compression vector is proposed, which can realize the NP voltage balance for electrolytic capacitorless Vienna rectifiers. On the basis of analyzing the limitation of NP-balance capability of conventional space vector pulsewidth modulation (PWM) strategy in the region of high modulation index, the negative influence of reduced capacitance on the NP fluctuation and the input current harmonics is revealed. To suppress the NP fluctuation, the compression coefficient is introduced to redistribute the duty cycles of voltage vector, which can reduce the negative effect of medium vector on the NP voltage. In addition, the phase voltage error is modeled to reduce the input current harmonics with the appropriate adjustment factor. The implementation of the proposed strategy is realized by the equivalent carrier-based PWM, which can avoid the sector judgment and angle calculation. By using the proposed strategy, the NP voltage balance and the input current harmonics reduction can be realized simultaneously. The effectiveness of the proposed strategy is verified on an electrolytic capacitorless Vienna rectifier platform. [ABSTRACT FROM AUTHOR]

Sharp LC resonance peak may enlarge inherent harmonics, dominant harmonics of the supply voltage generated by a three-phase diode rectifier, around the resonance frequency, which will intensify fluctuations of the dc-link voltage, and grid currents in motor drives with small dc-link capacitor. In this article, a novel resonance suppression strategy based on inherent harmonics impedance shaping is proposed specially for three-phase input permanent magnet synchronous motor (PMSM) drives with small dc-link capacitor. Instead of increasing the damping of the whole system for resonance suppression, the motor side power disturbance can be reduced by designing the impedance for inherent harmonics around LC resonance frequency based on the new model with the consideration of motor side characteristic. For damping current generation, the angle of the virtual admittance is modified to eliminate the influence of the dc-link voltage sampling delay. Experimental results show the effectiveness of the method on a prototype of electrolytic capacitorless PMSM drive. [ABSTRACT FROM AUTHOR]

It is important to improve the accuracy of rotor position estimation for the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To mitigate the position harmonic error caused by the nonideal factors in high-frequency signal injection based methods, an adaptive quasi-proportional-resonant rotor position observer (AQPRO) for sensorless PMSM drives is proposed in this article. The AQPRO can track the estimation error and generate the compensation value, which can realize online suppression for position error. By analyzing the stability and the influence of parameters of the proposed position observer on the suppression performance, a proportional-resonant gain self-tuning strategy is investigated to improve the suppression effect of the position harmonic error for different loads and speeds. The influence of self-tuning regulator parameters is modeled and analyzed in detail. The proposed method does not require offline detection and has a strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW PMSM drive platform. [ABSTRACT FROM AUTHOR]

In this article, a shielding scheme based on ferrite magnetic antennas (SS-FMA) is proposed. The scheme can effectively provide a path for the magnetic field lines of three-dimensional couplers to be concentrated and conducted. The SS-FMA is considered to be applied for long range inductive power transfer (IPT) systems of post insulators to powering smart grid sensors and improve the efficiency under the influence of metal components. The negative influence of the aluminum flanges on the magnetic field distribution is analyzed. The suppression effects of the shielding scheme on the abovementioned influence have been analyzed. Parameters of the SS-FMA are optimized. The equivalent circuit model is established, and the abovementioned process is explained from the perspective of the circuit model. A prototype of a post insulator that includes IPT system and SS-FMA has been built. When the coils of the IPT system are attached to the flanges, the efficiency can still reach 47.8% under the influence of SS-FMA, which is an increase of 13.7% compared with no shielding scheme. When the coils are slightly away from the flanges, efficiency of the system including SS-FMA can be quickly improved to 54.3%. [ABSTRACT FROM AUTHOR]

Passive diode bridge rectifier with LC filter is widely used in wireless power transfer (WPT) system due to its simple structure and uncontrolled characteristics. However, as the load resistance decreases, its input phase angle will also decrease rapidly until it shows obvious capacitive. Therefore, a novel rectifier topology with an input-series inductor (hereafter called ISIR) is proposed in this article to solve this problem. What is more, the ISIR can avoid the duty cycle loss and improve the dc–dc efficiency. First, the mechanism of ISIR is analyzed in detail combined with the operating status of topology. Then, the inductance and compensation parameters are determined based on theoretical calculation and simulation results. Finally, a prototype with a maximum load of 7 Ω is built to validate the feasibility and effectiveness of ISIR, and 88% efficiency is achieved under this condition. Compared with the traditional method, it has increased by 1.05%. The maximum efficiency of WPT system is as high as 91.14% with the proposed ISIR. [ABSTRACT FROM AUTHOR]

Inductive power transmission has been applied in industries, such as electric vehicles, consumer electronics and biomedical fields. However, there is a long-term key problem in this field that has not been solved. This is the adverse effect of the parasitic capacitance of the coil, which will cause the change of the coil inductance, the reduction of the quality factor and the reduction of efficiency. Especially in the field of long-distance wireless power transmission. The existing technologies all adopt the scheme of sacrificing volume in exchange for the quality factor of the coil. As a result, the volume of the system is very large, and the quality factor of the coil is still not high enough because the influence of parasitic capacitance has not been completely eliminated. Here, we found the solution. Connect compensation capacitors in series to the coil sections to short-circuit the parasitic capacitance and reduce its loss. The designed system has a diameter of 502 mm and a thickness of 22 mm, which can transmit 115.2 W of power within a distance of two meters with an efficiency of 29%. [ABSTRACT FROM AUTHOR]

For the induction motor (IM) current loop, the supertwisting sliding-mode control (ST-SMC) has been considered as an effective approach to achieve chattering suppression and steady-state errorless control. However, due to the system disturbance, the conventional ST-SMC suffers from control delay in the convergence trajectory, resulting in decreased antidisturbance capability. To address this problem, this article proposed a ST-SMC with convergence trajectory optimization. First, a nonlinear sliding-mode manifold is designed to achieve the ideal ST-SMC convergence trajectory. Then, a disturbance compensation term is added into the control law to eliminate the system control delay. Compared with the conventional ST-SMC, the studied method can effectively enhance the antidisturbance capability of IM current loop, leading to improved transient performance. Finally, the superiority of the investigated method is verified by the experimental results from a 3.7 kW IM test bench. [ABSTRACT FROM AUTHOR]

This letter proposes a switched capacitor (SC)-based continuously adjustable modular bidirectional dc–dc converter. The structure of the proposed converter consists of three types of modules, series–parallel SC converter module, regulating module, and resonant SC converters module. A basic configuration of three modules working in buck operating mode is analyzed in detail. The boost mode operation is symmetrical to the buck mode. The regulation module provides all regulation capability, and the other two modules operate at fixed duty cycle and provide the main conversion ratio. A prototype of the basic configuration was built to verify the theory. The peak efficiency of the prototype is 97.15%. [ABSTRACT FROM AUTHOR]

In order to improve the performance of the traction permanent magnet motor drives without weight transducer for direct-drive elevator applications during starting operation, this article proposes a novel control method based on the high-gain nonlinear active disturbance rejection control (HNLADRC) strategy. First, the limitation of linear and nonlinear error decay function of active disturbance rejection control (ADRC) method is analyzed, which is not suitable for the complex situation at starting operation of the traction motor. A high-gain nonlinear error decay function based ADRC method is proposed, which can achieve better performance in the starting operation of the traction motor. Both the high-gain extended state observer (HNLESO) and the high-gain nonlinear error feedback law (HNLEFL) are constructed by the high-gain error decay function to improve the compensation accuracy of the starting torque and the dynamics of the speed loop. By analyzing the error decay performance of the HNLESO and the HNLEFL, it is proved that the HNLADRC method has a faster error decay rate. Experimental results show that the proposed method can obtain a shorter rollback distance and faster response capability. [ABSTRACT FROM AUTHOR]

A 1 MHz active-clamp flyback converter for solar street-lighting applications, featuring a partial power processing, is proposed in this article. The secondary-side resonance between the output capacitor and transformer leakage inductor is utilized to reduce rms current and conduction losses. In comparison with the traditional light-emitting diode drivers based on full power converters (FPCs), the proposed approach that uses partial power converters (PPCs) can significantly improve the overall system efficiency by eliminating the redundant power handling process. The universal schemes are discussed and the optimal solution is eventually determined by the partial power ratio. The advantages of PPC compared with FPC in device stress, losses, and regulation capability are demonstrated by simulation. With GaN devices, a 100 W/1 MHz prototype was built to verify the analysis. The experimental results show that the proposed topology can reduce the power rating of the converter by up to about 80% while increasing the system efficiency by up to 95.8%. [ABSTRACT FROM AUTHOR]

Accurate rotor position estimation is important to ensure the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To suppress the estimated rotor position harmonic error (ERPHE) caused by inverter nonlinearities, flux spatial harmonics, and the current measurement error in high-frequency signal injection-based schemes, an adaptive iterative learning control-based online suppression method is proposed in this article. This method constructs a P-type iterative learning rotor position observer with the forgetting factor to obtain the tracking error and generate the compensation value in real time. The stability, the convergence, and the parameter sensitivity of this observer are analyzed in detail. To improve the suppression effect of the ERPHE for different loads and speeds, an iterative learning gain self-tuning strategy is investigated. The proposed method does not require the offline detection and the discrimination of harmonic frequencies, which has strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW interior PMSM drive platform. [ABSTRACT FROM AUTHOR]

In this article, a high-performance modified Y-source dc–dc converter is proposed. Comparing with traditional Y-source dc–dc converter, the proposed converter can achieve soft switching characteristics. Due to the discontinuous conduction mode operation of one of the coupled inductor windings and the resonant cell constructed by switch parasitic capacitor, the switch can operate in zero voltage switching (ZVS) and diodes realize zero current switching. Also, the voltage gain of the proposed converter is greatly improved. Meanwhile, the control strategy of hybrid pulsewidth modulation and PFM is adopted to guarantee the ZVS operation within a wide range. A 160 W experimental prototype based on planar coupled inductor is built to verify theoretical analysis and efficiency is up to 94.45% under full load condition. [ABSTRACT FROM AUTHOR]

In meshed high-voltage direct current (HVdc) grid, the current flows through the lines cannot be controlled with sufficient freedom without additional power electronics-based devices, namely current flow controller (CFC). In this article, a novel hybrid modular interline CFC is proposed based on H-bridge submodules and thyristor valves. Due to its modularity, the proposed CFC is particularly suitable for applications requiring high voltage and large power capacity. The circuit structure, operation principle, and parameter design are presented. In addition, a control strategy is developed for the proposed CFC. Simulations are carried out using a four-terminal meshed HVdc grid to verify the effectiveness of the topology and its control strategy. A downscaled prototype is built, which further validates the proposed CFC. [ABSTRACT FROM AUTHOR]

Active disturbance rejection controller (ADRC) possesses the considerable capability of improving the robustness of the permanent magnet synchronous motor (PMSM) drives. Nevertheless, the traditional linear ADRC (LADRC) and nonlinear ADRC (NLADRC) have their specific characteristic disturbance range of application. To further expand the disturbance range so as to improve the robustness against the disturbances, a novel NLADRC is proposed, which replaces the traditional linear function with a nonlinear function (NLF). And it is applied as the speed regulator for PMSM drives. Considering the accuracy and the dynamic performance of the disturbance estimation at the same time, an NLF is developed, and its describing function is established accordingly. Based on the above analysis, the NLADRC employing a cascaded nonlinear extended state observer is constructed to guarantee the relatively rapid and accurate disturbances estimation and compensation. Then, via the describing function technique, the theoretical frequency-domain analysis for the stability, the disturbance estimation performance, and the stiffness of the proposed NLADRC-based sensorless PMSM drive is given. Finally, the validity of the proposed scheme is verified experimentally on a 2.2-kW PMSM drive platform. [ABSTRACT FROM AUTHOR]

The nonlinearity of the voltage source inverter (VSI) leads to the error between output voltage and reference voltage, and causes the phase current harmonics. It is necessary to compensate its influence in the fields such as parameter identification, sensorless control, and servo drives. In this article, an industrial solution for VSI nonlinear compensation method based on lookup table (LUT) is introduced. The characteristics of semiconductor devices, equivalent dead-time and influence of parasitic capacitance effects are calculated quantitatively though injecting increase and decrease current during self-commissioning process. The critical current value for parasitic capacitor and the variation of equivalent dead time are verified through different distorted voltage curves. Considering dc-link voltage variation is irresistible for industrial products, 3-D linear interpolation is adopted to compensate the variation of VSI nonlinearity under different voltage conditions. Proposed LUT method does not require VSI datasheet and complicated calculation formula during implementation. Experiments are carried out on a commercial permanent magnet synchronous motor drive system to verify the proposed LUT method. [ABSTRACT FROM AUTHOR]

Inthis article, a two-phase series capacitor dual-path hybrid dc–dc converter with the step-down ratio of less than 1/6 is proposed for the first time. In this converter, the output current is divided into capacitance- and inductance-path, so the average value and ripple of inductance current are reduced. On the same time, the conduction loss caused by inductance equivalent series resistance (ESR) is also reduced. The addition of series capacitor leads to desirable characteristics, including lower switching stress, switching loss, parasitic output capacitance loss on mosfet, automatic phase current balancing, duty ratio extension, etc. A 120 W prototype has been designed to demonstrate theoretical analysis. Obtained efficiency was up to 93.18% at full load. Experimental results show good agreement with theoretical analysis and high feasibility of proposed converters. [ABSTRACT FROM AUTHOR]

To overcome the challenges of large reactive energy transmission loss and high current stress, which ocurr during the operation of auxiliary commutated circuit (ACC) of novel parallel resonant dc-link inverter (PRDCLI), an improved modulation strategy for reactive energy transmission loss is herein proposed based on the discontinuous pulsewidth modulation (DPWM), which adopts sawtooth carrier wave with alternating positive and negative slopes and shunt dead zone. Compared with the original modulation strategy, based on minimizing the ACC operation frequency, the proposed modulation strategy is able to realize all switches soft-switching, and avoid the superposition of resonant current and load current during the operation of ACC, thus, effectively reducing the reactive energy transmission loss and the current stress of auxiliary switches of the ACC. Under the proposed modulation strategy, the equivalent circuits in different operation modes are divided, and the operation principle, voltage/current stress, loss distribution, and optimal parameter design method of novel PRDCLI are researched. Eventually, the proposed modulation strategy is verified by experiments on a 5-kW/40-kHz prototype made by SiC mosfet. [ABSTRACT FROM AUTHOR]

An integrated zero common-mode voltage (ZCMV) modulation algorithm is developed in this article for dual-parallel neutral-point-clamped (NPC) inverters treated as an integrated system. While the conventional methods achieve CMV elimination with the cost of worse harmonic performance, the proposed method guarantees a ZCMV and better current quality simultaneously by taking advantage of the extra space vectors provided by paralleling. Specially designed switching sequences are developed to maintain a balanced neutral point of dc bus and keep the averaged value of the circulating current to be zero, ensuring the normal function of parallel NPC inverters. In addition, although the switching sequence design is complicated, a simple approach is proposed and implemented on a commonly used digital signal processor. A laboratory prototype is developed to test the system performance under steady-state conditions and dynamic process in grid-connected operation. Compared with the conventional ZCMV modulation, experimental results verify the effectiveness of the integrated modulation in eliminating the CMV, in addition to the dramatically reduced output current distortion. [ABSTRACT FROM AUTHOR]

Nowadays, the dual closed loop proportional-integral-lead (PI-Lead) controller is widely used, especially for the servo systems where high performance is required for motion control, like lithography machines and vehicle-used Lidars. Considering complex industrial applications and working conditions, more comprehensive and systematic research about the structure and potential problem of the PI-Lead controller is necessary for enhancing its performance and robustness. In this article, the failure mechanism of the classic antiwindup methods in the PI-Lead controller is analyzed. By adjusting the location of control blocks, a novel reversed structure based PI-Lead controller is proposed as a complement to the traditional antiwindup methods for effective operation and to make the system stable under severe impact disturbances. Then, a self-commissioning strategy is designed based on a fast root mean square error (FRMSE) index and without additional manual tuning factors. Compared with classic indicators, the proposed FRMSE index can achieve faster instability detection and accelerate the tuning process to protect the equipment. [ABSTRACT FROM AUTHOR]

In the existing offline inductance identification methods of permanent magnet synchronous machines (PMSMs), dq-axis voltage equations are generally adopted and the inverter nonlinearity compensation is necessary, which complicates the identification process and restricts the generality. In order to solve the problem, an offline inverter-nonlinearity-immune inductance identification method is proposed in this article based on the PMSM equivalent impedance model. The method can identify the dq-axis inductances by injecting both dc and high frequency signals, where the magnetic saturation and the cross saturation are considered. Besides, an inductance surface forming algorithm is introduced based on the bilinear interpolation. The continuous dq-axis inductance surfaces can be then obtained by only a few identified data, so that the time of data sampling and processing is greatly shorten compared with the existing methods. To enhance the accuracy of the identification method, the digital delay error and the sampling error in zero current zone are investigated and compensated. The effectiveness of the proposed method is validated on three different test machines. [ABSTRACT FROM AUTHOR]

The extensive application of vector phase shift modulation method in permanent magnet synchronous motor drive systems with single dc-link current sensor results in obvious current ripple in the low-speed region. The patterns of these ripples vary greatly in different sectors, leading to nonnegligible phase current reconstruction errors. In this article, an estimation of the local average current change rate (ELAC2R) based reconstruction error suppression method within the switching cycle is proposed to resolve this problem. By comparing the actual and the ideal sampling points, the increase of current ripple and the reconstruction error caused by the combination of the vector phase shift and the single current sensor sampling in the low-speed region are modelled and analyzed. Then according to equivalent modelling of the current ripple between the ideal and the actual sampling points, the more accurate phase current information can be quickly obtained based on the sampling value. The compensation process is significantly simplified and the computation burden of the processor is reduced. Experimental results show that the performance of current reconstruction can be improved effectively with less harmonic content with the proposed method. [ABSTRACT FROM AUTHOR]

Although the impedance/admittance model of modular multilevel converter (MMC) considering internal harmonic is discussed extensively in the literature, few attentions have been focused on how to determine the number of harmonics to be included in the model. This article fills this gap by developing the MMC signal-flow graph (SFG), providing the analytical transfer function to quantitatively estimate the attenuation degree of MMC harmonics, so as to guide the model truncation. Besides, SFG offers an intuitive understanding on the mathematical characteristic of MMC, including the conjugate symmetry and the effect of phase reference on admittance, which helps to reduce the modeling calculation. Moreover, conversion formula of MMC multiple input multiple output and single input single output admittance is derived based on the truncated model to further simplify the stability analysis. The correctness of this article has been verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

The overmodulation-based nonlinear voltage extension could increase the maximum output torque of the induction motor (IM) in the field-weakening (FW) region. Since the voltage distortion increases with the deepening of overmodulation degree, the extreme nonlinear voltage extension (six-step voltage) is only worthwhile in maximum torque demand conditions. However, the conventional overmodulation-FW scheme always adopts the six-step voltage regardless of torque demand, leading to severe torque ripple. To solve this problem, the minimum-nonlinear-voltage (MNV) method is proposed to satisfy the torque demand with minimum overmodulation-voltage nonlinearity. The difference between the limiting and the feedback values of the torque current is used for suppressing the nonlinear voltage extension during a nonmaximum torque demand state. The quantitative relation between the torque ripple and torque demand of the MNV method is calculated and compared with that of the conventional six-step-FW method. Analysis shows that the MNV method can eliminate the torque ripples of low and medium torque demand conditions completely and partially, respectively. The effectiveness of the proposed method is verified experimentally on a 3.7 kW IM platform. [ABSTRACT FROM AUTHOR]

Wireless power transmission technology is used to transmit energy without contact in the field of electric vehicles, consumer electronics, and other industries. Among them, there are some applications with very low coupling coefficient where multilayer coil needs to be wound. Influenced by the parasitic capacitor between layers, the loss of the multilayer coil increases. The improved coil winding method and compensation method are proposed in this letter. Winding coils following the same sequence from outside to inside in each layer and connecting capacitors in series between layers of the coil can significantly reduce the voltage of the layers’ parasitic capacitor, which will decrease the coil loss. Compared with traditional method, the improved method increases the system efficiency at heavy load and light load by 0.74% and 2.48%, respectively. A 1-kW prototype was built with the maximum efficiency of 93.58%. [ABSTRACT FROM AUTHOR]

The capability of misalignment tolerance is vital for an inductive power transfer (IPT) system. In this article, a new loosely coupled transformer (LCT) structure with series solenoid and DD pads (SDDP) is proposed to improve the misalignment tolerance of the IPT system. The designed LCT not only has strong misalignment-tolerant capability in the X-direction but also has strong misalignment-tolerant capability in the Y-direction. The fluctuation of mutual inductance is 3.15% within 67.0% misalignment distance of the largest size of the SDDP in the X-direction and 44% misalignment distance of the largest size of the SDDP in the Y-direction. Finally, an LCC/S compensated IPT system with 300 W power is built as an example to demonstrate the performance of the proposed LCT. The output voltage fluctuates with the rated load, which is less than 3.2%, and the efficiency is 90.2–91.3%. [ABSTRACT FROM AUTHOR]

Simultaneous wireless power and data transfer (SWPDT) is widely investigated because of the increasing requirement for real-time communication between the primary and secondary sides in wireless power transfer systems. This article classifies SWPDT systems into four categories according to the type and number of data channels and data carrier generation method. They are power carrier-based SWPDT system, high-frequency data carrier-based SWPDT system, multiple inductive channels SWPDT system, and inductive–capacitive hybrid channels SWPDT system, respectively. Four key issues, including cross-talk minimization, improvement of signal-to-noise ratio, modulation method for high data rate and low bit error rate, and special design to achieve full-duplex communication and improve misalignment tolerance, are discussed. The advantages, disadvantages, and applications of the four types of SWPDT systems are summarized. Finally, conclusions and outlook of the SWPDT system are given. [ABSTRACT FROM AUTHOR]

A three-stage-five-coil inductive power transfer (IPT) system which is based on cylindrical solenoid coupler (CSC) is proposed in this article. The shape and parameters of the CSC are optimized. The five litz coils compensated by series capacitors are considered to form an IPT system based on equivalent CLC/S/CLC compensation topology with constant voltage characteristics. The mutual inductance between compensation auxiliary coil (CAC) and power transfer coil could be changed by moving the position of CAC, and the freedom of parameter design is enhanced. Mathematical model and loss model of the system are established, and power transfer characteristics of the system are analyzed. The system is considered to be used as a power source for state detection equipment of high-voltage (HV) device to achieve long-distance IPT, the effect of the coupler on the HV electric field is verified. Finally, a prototype with a length of 1.54 m was built. Based on the platform, output voltage and dc–dc power transfer efficiency curves with changed input voltage and load are obtained. The maximum efficiency of the dc–dc system can reach about 60%. [ABSTRACT FROM AUTHOR]

Beat phenomenon is an important issue for the practical application of electrolytic capacitorless motor drives. In this study, the characteristics of stator current harmonics caused by the voltage sampling delay are analyzed. Further, the beat phenomenon generated from the interaction between the harmonics and the fundamental currents is investigated, and the envelope feature of the stator current is derived mathematically. For the purpose of suppressing the beat phenomenon, a voltage reconstruction strategy is proposed to reduce the influence of dc-link voltage sampling delay at the six times of grid frequency. By utilizing the reconstructed dc-link voltage for calculation of PWM duty ratio, the beat phenomenon can be attenuated significantly. The proposed method can be integrated into motor control system easily. Experimental results show the effectiveness of the proposed strategy in a prototype of electrolytic capacitorless permanent magnet synchronous motor drive. [ABSTRACT FROM AUTHOR]

In this letter, a high-power step-up dc/dc converter dedicated to dc offshore wind farms is proposed, with the combination of half-bridge submodules, thyristors, diodes, and transformer. Compared with the other promising dc/dc topologies, the device numbers, costs, losses, and energy storage requirement are greatly reduced. The operation principle is introduced. The effectiveness and validity are confirmed by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this article, an optimal design for mid-range wireless power transfer system based on multiple repeaters is proposed, which aims at powering high-voltage side sense module in HVdc applications. The mathematical model of the system is established. The characteristics of current distribution and impedance angle are analyzed under equally spaced situations. To further optimize the system, the optimized spaced structure with different distances is investigated, which can improve transferring efficiency under same distance requirement. The effect of load is also analyzed. A 1.5 m prototype with eight repeaters is built and the experimental results verify the feasibility of optimized coil arrangement, which can effectively improve efficiency, especially under light load situations. [ABSTRACT FROM AUTHOR]

This article proposes a kind of cubic-magnetic coupler (CMC) for inductive power transfer (IPT) system, which has huge application potential in the charging field of moving targets. The CMC can still maintain sufficient coupling coefficient when used for long-distance wireless power transfer, it also has great capability of misalignment tolerance. Distance-to-diameter ratio (DDR) is defined to eliminate the impact of coil size and make the comparison between different couplers fairer and easier. This article optimizes the parameters and shape of the CMC. Then, the proposed coupler is compared with several existing couplers employed in long-distance IPT systems. Double-sided LCC compensation topology is chosen to limit the current flowing through the coupling coils. A CMC with an outer size of 180×180×180 mm3 was made, based on which an IPT prototype was built. The superiorities of the proposed coupler were verified by a series of experiments. When the DDR equals 3, the coupling coefficient of the CMC is 0.00985, and the maximum dc–dc and ac–ac efficiencies are 64.9% and 72.8%, respectively. [ABSTRACT FROM AUTHOR]

In the voltage source inverter applications, inverter nonlinearities would affect the parameter identification process in many ways. Hence, this article proposes an offline identification method for resistance and dq-axis inductance surface by considering the inverter nonlinearity characteristics. A variable amplitude square-wave injection (VASI) scheme is proposed for the dq-axis inductance identification. The VASI method achieves the inductance identification with a novel data sampling strategy. Meanwhile, it can also establish the inductance surfaces by only a few identified data points with a polynomial fitting algorithm, which greatly reduces the identification time compared with the existing methods. The resistance identification is realized by a slope signal injection method, in which the effect of IGBT voltage drop is analyzed. In order to improve the identification accuracy, the inverter nonlinearities are compensated by a self-learning method considering the zero-axis voltage at different rotor positions. At the same time, the sampling error in zero current zones of abc-phases is researched. In order to verify the effectiveness and generality, the proposed method is carried out on two different test machines and confirmed by finite element analysis. [ABSTRACT FROM AUTHOR]

In this article, a 10 MHz dc/dc converter based on three-dimensional air core transformer with zero-phase difference synchronous driving signals is designed. By using the characteristics of no leakage inductance in the inner winding of the nested toroidal air core transformer, the phase difference between the output voltage of the inverter and the input voltage of the rectifier can be regarded as zero, so that the rectifier and the inverter can use the same driving signal, which simplifies the control of the synchronous rectifier switches, and realizes the reliable and efficient synchronous rectification control at 10 MHz. The prototypes with primary and secondary compensation are proposed and the experimental results verify the feasibility of the proposed control method and numerical design method. [ABSTRACT FROM AUTHOR]

The overmodulation canimprove the utilization of dc-link voltage in the induction motor (IM) field-weakening (FW) control, thereby extending the maximum output torque. Nevertheless, the high modulation index (MI) will cause severe torque ripple. To figure out the relation between the torque ripple and MI, the amplitude of torque ripple with different MI is calculated quantitatively. Then, a torque quality evaluation function (TQEF) is designed to evaluate the torque quality in overmodulation-FW region by considering both fundamental torque extension and torque ripple suppression. On this basis, a modulation index optimization module is proposed for the maximum TQEF value realization. The analysis shows that the studied method could achieve the optimal trade-off between the fundamental torque extension and the torque ripple suppression. The TQEF value of the studied method is higher than that of the conventional six-step voltage method and the inscribed circle voltage method, meaning that the torque quality is optimized. Finally, the effectiveness of the studied method is verified experimentally on an advanced RISC machines (ARM)-based 3.7 kW IM platform. [ABSTRACT FROM AUTHOR]

Under weak grid condition, negative influence is brought in on system stability because the grid impedance and the grid-connected converter control system are coupled to each other. The key factor affecting the stability of the system is the perturbation of the voltage fluctuation at the point of common coupling (PCC) to the phase-locked loop (PLL) and the dc-link voltage loop. In this article, the impedance model of a three-phase grid-connected converter, including the current loop, PLL, and dc-link voltage loop in the dq frame, is adopted, because it includes coupling information of the converter and reflects the transferring relationship among grid-connected system variables. Based on the transferring relationship, this article analyzes the perturbation paths of PCC voltage and proposes the corresponding compensation methods, i.e., the PLL and dc-link voltage loop compensation terms, which are inserted into the q and d axes of the current loop controller, respectively. The impedance analysis results show that the proposed method can effectively improve the system stability. In addition, the experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

For speed-sensorless induction motor (IM) drives, the observability of rotor speed is still a challenging problem under steady-state operations at low synchronous frequencies. To cope with this problem, an enhanced magnetizing current-oriented low-frequency ride-through method is proposed for adaptive full-order observers to ensure the observability of rotor speed. The adaptive changes of magnetizing current reference are generated to maintain the speed observable margin near zero synchronous frequency. Compared with existing methods, it avoids the noises caused by direct rotor flux reference calculation. In addition, the feedback matrix is employed to narrow the unstable regenerating region, and enlarge the observable margin. Addressing the detailed implementation, the analyses are provided with respect to output torque constraint, magnetizing current selection, and observability. Finally, the effectiveness of proposed method is validated on a 2.2 kW IM experimental bench during low-frequency ride-through. [ABSTRACT FROM AUTHOR]

Power hardware-in-the-loop (PHIL) simulation combines the advantages of digital simulation and physical experiment, which provides great convenience for research and verification of a complex electric system, such as the high-voltage direct current (HVdc) system. The digital interface algorithm realizes interconnection of the digital and physical system, but it is also the main factor to affect stability and accuracy of the PHIL results. In this article, the damping impedance interface algorithm is adopted to test the performance of a modular multilevel converter (MMC) connected into an HVdc system. Instead of online acquiring the exact MMC dc impedance, a simple RLC damping impedance is proposed to ensure stability and particularly, low-frequency accuracy for the PHIL system. Moreover, as testing in the laboratory does not allow hundreds of MVA-rated physical MMC, suitable scaling factors are proposed to design a scaled-down MMC prototype which presents identical dynamic characteristic with a full-scale MMC. A PHIL setup including RT-LAB real-time simulator, power amplifier, and a scaled-down MMC prototype is built and the experiments confirm the effectiveness of the proposed interface algorithm. [ABSTRACT FROM AUTHOR]

Many reduced common mode voltage (CMV) modulation methods have been proposed for three-level inverters. However, most of them suffer from large current distortion because only part of the available base vectors is utilized. The interleaved paralleling can reduce both CMV and the output current distortion, though the CMV reduction is limited and large zero-sequence circulating current (ZSCC) is inevitably caused by the phase-shifted carriers. To further reduce the CMV while maintaining smaller current distortion and ZSCC, a five-level reduced CMV (RCMV) modulation method is proposed in this article, which treats the parallel inverters as a whole. Theoretical analysis reveals that the integrated modulation provides additional base vectors that contribute to smaller total harmonic distortion (THD) of the current, and the selected vectors ensure the nearest-three-vector synthesis and half-reduced CMV. The switching sequences design and neutral point balancing strategy are also developed for dual-parallel three-level inverters, ensuring that the average circulating current is zero and the neutral point voltage is balanced, which are both critical to the proper operation of parallel inverters. Superior performance in terms of CMV, THD, and ZSCC provided by the proposed method in comparison with conventional modulation is verified by comprehensive simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this article, a 10-MHz low-profile converter for bendable equipment based on aircore inductor is proposed. The mathematical model and inductance calculation method of the bendable planar circular spiral coil under different bending situations is analyzed. An optimal design method of the T type matching network is depicted in detail which helps to guarantee soft-switching characteristics and high efficiency within the whole bending range by realizing weak inductive equivalent input impedance. A 32 V input, 9V/6.3 W output prototype is proposed in the laboratory and the experimental results verify the feasibility of the proposed optimal design methodology, the system efficiency can be improved by 4% than the traditional method. [ABSTRACT FROM AUTHOR]

This article presents a simultaneous wireless power and data transfer (SWPDT) system based on double-sided inductor–capacitor–capacitor compensation topology and frequency-shift keying. A simplified method to analyze the power transfer, data transfer, and interference between them is proposed. To obtain higher data transfer gain and lower bit error rate, the data injection and extraction transformers are optimized. A laboratory prototype was built to verify the correctness of the analysis and the methodology. The proposed SWPDT system is less susceptible to interference between the power and data transfer. This is experimentally proven by high signal-to-noise ratio of 47 dB in the worst case. The power transfer efficiency is 90.5% under nominal conditions, and the data rate is 150 kb/s. The proposed system is robust against coupling variations, with effective data transfer even though the coupling coefficient is decreased by 95.3%. [ABSTRACT FROM AUTHOR]