Voltage Utilization Rate Research Articles

New strategy for Mg-air battery voltage-efficiency synergy by engineering protective film with cation vacancies on Mg anode surface

Although the Mg-air battery with high theoretical energy density is desirable for the energy supply of marine engineering equipment, its applications remain limited due to the low actual discharge voltage and inferior Mg anode utilization rate. In addition to the microstructure of Mg alloy anodes, the properties of discharge product films are of great importance to the discharge performance. Herein, the discharge behaviors of Mg-Y-Zn alloys are first studied mainly from the perspective of film properties. Through contrastive analysis, it is found that the sufficient Y3+ produced during the discharge process can substitute Mg2+ in Mg(OH)2 to introduce effective cation vacancies. The Mg-Y-Zn anode with profuse cation vacancies in the product film shows a synergy of potential and efficiency, and this can be attributed to an increase in the migration pathway for Mg2+, reducing the diffusion over-potential caused by the protective product film. This study is expected to provide a new strategy from the perspective of cation vacancy design of discharge film for developing high-performance Mg-air batteries.

Active Power Allocation Strategy for a Novel Wireless Open-Winding Motor System With Improved Antimisalignment Capability

This paper proposes a wireless open-winding motor (WOWM) system, where noncontact operation can be achieved with the magnetic coupler. Thus, the flexibility and reliability of the WOWM system can be improved. Two isolated DC voltage ports for the open-winding motor can be obtained with only one DC voltage source, which facilitates the application of the system. The zero-sequence current in the motor winding can be suppressed and the DC link voltage utilization rate can be maximized owing to the isolated DC link structure. Besides, the operation characteristics of the WOWM system are analyzed in detail. The decoupled dual-receivers are designed, which ensures that the ratio of DC link voltages is load-independent. Moreover, the influences of misalignment on the WOWM system, including the overmodulation and increased phase current ripple are presented. The DC link voltage regulation (DVR) and active power allocation (APA) strategy are further proposed. The DC link voltage reference is identified based on the operating state of the motor for high performance operation. The allocation coefficient, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> is adjusted according to the extent of misalignment, which improves the anti-misalignment capability. The feasibility of the WOWM system and the effectiveness of the DVR and APA strategy are verified by experiments.

Super-twisting sliding mode control for neutral point voltage of three-phase four-wire inverter based on SiC/Si hybrid switch

The three-phase four-wire voltage source inverter (3P4W VSI) is widely used in applications like uninterrupted power supply (UPS) and bidirectional onboard charger. The increasing power density demand requires higher switching frequency and lower switching loss. To fulfill the conflicting objectives, two-fold methodology is proposed in this paper: 1) SiC/Si hybrid switches (HyS) together with recently reported gate trigger are reported for the first time in the 3P4W VSI; 2) the natural point voltage is controlled to track a sinusoidal voltage with the frequency equal to 3 times of fundamental frequency in order to achieve higher DC-bus voltage utilization rate, and further reduce the switching loss. The traditional PI controller is very hard to achieve desired performance due to both the nonlinearity and the variant reference of the natural point voltage control system. Thereby, the super-twisting sliding mode control (ST-SMC) is proposed in this paper to achieve desired tracking performance and fast dynamic response. The effectiveness and superiority of the system are verified by both simulation and experiment comparison with the existing methods using a 5 kW prototype.

Novel Active Snubbers for SSCBs to Improve Switch Voltage Utilization Rate

This paper proposes two novel active snubbers for direct current (dc) solid-state circuit breakers (SSCBs): metal-oxide-varistor with resistor-capacitor-switch (MOV-RCS) and active-MOV with resistor-capacitor-diode (AMOV-RCD). In the snubber branch, either half- or full-controlled switch can be applicable, leading to four novel topologies. There are two main contributions: 1) MOV is disconnected from the power line during SSCB OFF-state, which enhances reliability as neither voltage nor power appears on MOV; 2) voltage utilization rate η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>v</i></sub> of the main switch is remarkably increased, which improves efficiency and power density, and reduces design cost. Experiments of five prototypes are conducted including four proposed snubbers and a comparison with conventional MOV-RCD snubber. Results show that, for 1.2 kV MOSFETs as the main switch, new snubbers can enhance η <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>v</i></sub> from 37.5% to 60%, achieving 183 A dc current interruption under 720 V dc bus voltage within 2.4 μs. Meanwhile, the voltage peak is limited to 1.112 kV.

Fast Y-Type Thyristor-Based DC SSCB Using Complementary Commutation in a Capacitor–Capacitor Pair Structure

This article proposes a new thyristor-based dc solid-state circuit breaker (SSCB) named Y-type. Main contributions focus on a new complementary commutation circuit including a capacitor–capacitor pair, which features three remarkable advantages. First, a fast commutation is achieved using a countercurrent pulse injection by the capacitor–capacitor pair structure. Second, metal-oxide varistors (MOVs) are disconnected from the power line when SSCB is <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> , which solves the reliability issue due to the MOV degradation and enhances the voltage utilization rate of the main switch. Third, benefiting from the capacitor–capacitor pair structure, reliable reclosing and rebreaking are obtained for practical applications. Experiments are conducted on a 400 V/120 A prototype to validate the proposed Y-SSCB. The peak voltage on the main and auxiliary thyristors reaches 773 and 400 V, respectively. Also, the peak voltage on the auxiliary capacitors pair reaches 740 and 400 V. The Y-SSCB achieves a fast reaction time of 80 μs in interrupting 120 A short-circuit fault current.

Design of a Two-phase Brushless DC Motor Control System

With the depletion of petrochemical resources in the whole region, reducing the dependence on petrochemical energy, and reducing environmental pollution and carbon emissions have become the common goal of the world. Pure electric vehicles are a kind of new energy vehicle. Compared with fuel vehicles and other types of electric vehicles, they have high energy utilization efficiency, low price, and less pollution emission. Therefore, this paper will discuss the structure, working principle, and control system of the two-phase brushless DC motor and put forward the two-phase four-bridge arm drive scheme to improve the voltage utilization rate and achieve more environmentally friendly and efficient electric energy application.

3-레그형 2상 인버터에서의 전류 복원 영역 확장

For measuring phase currents of two-phase motors driven by the three-leg inverters, the leg shunt resistors inserted between the lower switch of each inverter leg and the negative DC rail can be used instead of the expensive Hall-effect sensors. The two-leg shunt method using shunt resistors located on the two-phase legs has a limited current measurement range. In addition to this method, the three-leg shunt method can reconstruct the immeasurable phase currents by using an additional shunt resistor on a neutral leg. Therefore, the current measurement range can be wider than that in the two-leg shunt method. However, this method cannot properly reconstruct the currents in the specific areas where the voltage modulation index of the inverter is high, thereby decreasing the DC voltage utilization rate, and increasing the torque ripple of the motors. To improve this problem, this paper analyzed the current reconstruction areas of a three-leg type two-phase inverter applied CPWM(Continuous Pulse Width Modulation) method, and proposed a simple technique to expand the areas. The proposed technique can expand the current reconstruction areas by securing the turn-on time of the inverter lower switches utilizing the DPWM(Discontinuous PWM) method, which results in the improvement of DC voltage utilization rate.

Power Compensation-Oriented SVM-DPC Strategy for a Fault-Tolerant Back-to-Back Power Converter Based DFIM Shipboard Propulsion System

For safety critical transportation applications like all-electric ship propulsion systems (SPS), the reliable system operation is definitely the primary concern. In this paper, a fault-tolerant back-to-back power converter based on the four-switch three-phase (FSTP) topology is applied to a doubly-fed induction machine (DFIM) based all-electric SPS. A power compensation-oriented space vector modulation direct power control (PCSVM-DPC) strategy with dc-bus voltage unbalance elimination is proposed to ride through the single bridge arm open-circuit fault in the source-side converter (SSC) and improve the system dynamic performance simultaneously. Besides, the DFIM-SPS is endowed with excellent steady-state performance by applying the proposed control strategy. The dc-bus voltage deviation is suppressed based on the calculation of active and reactive power compensation terms to increase the dc-bus voltage utilization rate. Moreover, good post-fault system operation performance can be achieved with fast active power and electromagnetic torque tracking speeds. The proposed PCSVM-DPC strategy for the fault-tolerant FSTP SSC based DFIM-SPS is easy to implement without high computational burden. The SVM-DPC method is also presented for the load-side converter. The proposed control strategy is verified by experiments on a 1.5 kW DFIM-SPS experimental platform.

A Novel Low-Frequency Virtual Space Vector Modulation With the Improved Continuity of Output Average-Voltage and Bus Voltage Utilization for Single-Phase Neutral Point Clamped Three-Level Inverter

In the high-power superconducting fusion converter, the single-phase neutral point clamped (NPC) three-level converter is applied to replace the traditional thyristor converter using an integrated gate-commutated thyristor (IGCT) as a power device. The operating frequency of IGCT is usually lower, only a few hundred Hz. An optimized hybrid space vector pulsewidth modulation (SVPWM)-8H is proposed to solve the problems of discontinuous output average voltage, low dc bus voltage utilization rate, dead time compensation, and neutral point potential balance. The new sectors are inserted to make the range of output average voltage of adjacent sectors intersect, which improves the continuity of output average voltage. Furthermore, some sectors are composed of four vectors to reduce the minimum working time of redundant small vectors, improving the dc bus voltage utilization ratio and the converter’s performance. Moreover, by analyzing the influence of dead time on redundant small vectors, redundant vectors are rearranged to make redundant small vectors’ working time synchronously in sector and sector switching, which reduces the influence of dead time on neutral point potential balance. Finally, by analyzing the influence of dead time on the output average voltage, dead time compensation is applied, which reduces the difficulty of compensation implementation. Simulations and experiments verify the rationality of the optimized hybrid SVPWM-8H.

An optimal grid-connected strategy for improving the DC voltage utilization rate by increasing the number of PV modules connected in series in the string

The further reduction of the cost can improve the competitiveness of PV power generation in practice. This work proposes a low-cost hardware circuit integrated in the PV module junction box, which can increase the DC voltage utilization rate and capacity ratio of the system by limiting the voltage of the PV modules to increase the number of modules in series. According to the I-V characteristics, the theoretical optimal proportion of short-circuited cells in the PV module is analyzed. Based on the structure of the actual PV modules, a strategy of limiting the voltage of a single PV substring in the module is implemented. In order to avoid the power loss caused by the voltage-limited substrings that may not be released by mismatch, a control strategy combining the inverter MPPT to lower the voltage of the PV string is proposed for ensuring that all the modules in the string are released. The results of actual test verifications show that the proposed strategy can effectively reduce the voltage of PV modules and strings. The number of PV modules in each string of 1000 V and 1500 V systems can be increased by 5 and 8, respectively, and the capacity of each string can be increased by more than 20%, such that great practical application and potential for reducing the cost of PV system can be achieved.

An Over-Modulated Model Predictive Current Control for Permanent Magnet Synchronous Motors

To improve the voltage utilization rate of DC bus and reduce the voltage vector tracking error, a finite-control-set modulated model predictive control (FCS-M2PC) with overmodulation capacity for permanent magnet synchronous motor (PMSM) incorporating penalty function is proposed in this paper. Firstly, three modulation regions are determined according to the combined action of dead-beat control and model predictive control (MPC). Secondly, three, two and one voltage vectors are applied to linear modulation region (LMR), overmodulation region I (OMR-I) and overmodulation region II (OMR-II), respectively, to synthesize the reference voltage vector. Thirdly, to obtain better steady-state performance in the whole modulation region, the optimal vector dwell-times can be obtained from the uniform penalty function defined by a set of mode parameters to minimize the error between the current references and the current predictions, rather than applying a single voltage vector in the conventional finite-control-set model predictive control (FCS-MPC). The effectiveness and superiority of the proposed method are validated experimentally.

Cascade Model Predictive Current Control for Five-Phase Permanent Magnet Synchronous Motor

As to the model predictive control for five-phase permanent magnet synchronous motor (PMSM), it is difficult to ensure the optimal control performance by using calculation method to obtain the weighting factor. To solve this problem, a cascade model predictive current control based on the idea of sequential model predictive control is proposed for five-phase PMSM for the first time. Firstly, the principle of selecting the optimal voltage vector by the proposed method is analyzed in detail. Then, combined with the characteristics of five-phase PMSM, the control priority of controlled variables is set for designing two cost function schemes without weight factor. The maximum torque scheme can generate a trapezoidal stator voltage, improving the DC bus voltage utilization rate and the system loading capacity. The minimum harmonic current scheme can reduce the harmonic of stator current, obtaining small system noise and vibration. The experimental results indicate that the proposed method can ensure the optimality of the voltage vector applied. Therefore, the five-phase PMSM obtains good performance under different working operation, such as small torque ripple, fast dynamic response, and small harmonic current.

A compare research on third harmonic current control for five-phase permanent magnet synchronous motor

The injection of a third harmonic current can improve the electromagnetic torque output of the five-phase permanent magnet synchronous motor. In this paper, constant copper consumption and constant maximum current are used as constraints, and the influence of the ratio between the third harmonic current and the fundamental current on the electromagnetic torque under the two constraints is analyzed. The electromagnetic torque is the largest when the third harmonic current reference value is equal to the fundamental current reference value of ψf3/ψf times under the premise of the constant copper loss. On the premise that the maximum current is constant, the electromagnetic torque is the largest when the third harmonic current reference value is equal to the fundamental current reference value of kw/(6kw-kw3/3) times. On this basis, according to the vector amplitude, phase and action time, the changing trends of maximum voltage utilization rate with Vref3/Vref1 under three different kinds of methods are given. Finally, through the experimental platform, the control effects of the three kinds of SVPWM are compared under two constraint conditions.

Discharge characteristics of Hall thruster with large height-radius ratio

Using a permanent magnet to realize a design with a large height-radius ratio can effectively reduce the radial size of the thruster. The experimental results show that a Hall thruster with a large height-radius ratio also has significant advantages in its discharge performance. Taking the 1.35 kW Hall thruster HEP-1350PM, which has a large height-radius ratio, as an example, the thrust, specific impulse, and efficiency of HEP-1350PM are increased by up to 4.3%, 10.4%, and 7%, respectively, as compared to SPT-100, while its weight is only 56% of that of SPT-100. Numerical simulations were performed to understand the discharge characteristics of a Hall thruster with a large height-radius ratio and the internal mechanism of its performance improvement. The results show that the small middle diameter and wide channel structure concentrate the distribution of the neutral gas in the channel, accelerate the decrease of the propellant density along the axial direction, and move the main ionization zone closer to the channel upstream. These factors increase the ionization concentration, ionization rate peak, working medium utilization rate, and voltage utilization rate. They also reduce the ion loss on the wall surface and plume divergence, thereby improving the comprehensive discharge performance. This study verifies the feasibility of a large height-radius ratio in the design of a Hall thruster, and demonstrates that the design would not only be valuable for reducing the volume and weight of the thruster, but also has the advantages of enhancing its discharge performance and prolonging its working life.

Wide Speed Range Operation Strategy of Indirect Matrix Converter–Surface Mounted Permanent Magnet Synchronous Motor Drive

In order to expand the speed range for an indirect matrix converter–surface mounted permanent magnet synchronous motor drive (IMC-SPMSM), a wide speed range operation control strategy based on a flux-weakening control and an over-modulation method is proposed in this paper. In the stage of the inverter, an IMC over-modulation method is designed, which increases the fundamental voltage transmission ratio (VTR) to 1. In addition, considering the variation of the voltage limit boundary of the IMC with motor speed, flux-weakening control is implemented based on the voltage error feedback method, which maximizes the voltage utilization rate by setting the endpoint of the output voltage vector on the voltage boundary during the flux-weakening operation. In the stage of the rectifier, over-modulation is automatically switched on or off according to operation requirements by a modulation depth controller. Finally, experimental results show that the proposed strategy increases the maximum speed of the IMC-SPMSM by nearly 35% compared to the maximum torque per ampere (MTPA) method. Besides, the enlarged voltage margin by the rectifier stage over-modulation effectively shortens the setting time.

Switching-Table-Based Direct Torque Control of Dual Three-Phase PMSMs With Closed-Loop Current Harmonics Compensation

In this article, the new closed-loop current harmonics compensation strategy is introduced in the switching-table-based direct torque control (ST-DTC) of dual three-phase permanent magnet synchronous machines. The harmonic current distortion is the major problem of ST-DTC of multiphase machines and is typically caused by the lack of control in the auxiliary x-y subspace under the vector space decomposition model. The synthetic vectors to obtain average zero voltage in the x-y subspace can be a solution. However, this cannot compensate for current harmonics; for example, due to dead-time and back-electromotive force distortion, which is also mapped into the x-y subspace. Therefore, in this article, the x-y voltage references are obtained by the closed control loop that controls x-y currents to zero. To modulate the nonzero x-y voltage reference, the new modulation approach employing voltage vector groups in the x-y subspace together with the new switching table is developed and incorporated into ST-DTC. Meanwhile, the analysis of the two available sets of 12 voltage vector groups illustrates a tradeoff between linear range in the x-y subspace and the dc-link voltage utilization rate. Finally, the effectiveness of the proposed ST-DTC strategy is verified through experiments and simulation.

Overmodulation Strategy for Electrolytic Capacitorless PMSM Drives: Voltage Distortion Analysis and Boundary Optimization

Permanent magnet synchronous motor (PMSM) drives equipped with slim film capacitors have many advantages, including longer lifetime, smaller volume, and lower cost. However, improving the dc-link voltage utilization rate by the typical overmodulation strategy will cause the distortion of the stator voltage and current due to the dc-link voltage fluctuation. In this article, the influence of the dual-mode overmodulation strategy used in the small dc-link capacitor PMSM drive, including the stator voltage distortion and uncontrollable time for entering the six-step operation, is analyzed. A novel overmodulation strategy named as the optimized voltage boundary-based overmodulation strategy is proposed to reduce the distortion of the stator voltage and current. By switching between the actual dc-link voltage and the fixed dc-link voltage used for space vector pulse width modulation (SVPWM), the performance can be improved in the overmodulation region if the value of the dc-link voltage for SVPWM is selected appropriately. Experimental results on a PMSM drive platform are provided to verify the effectiveness of the proposed strategy.

Enhanced Flux-Weakening Control Method for Reduced DC-Link Capacitance IPMSM Drives

Reduced dc-link capacitance interior permanent magnet synchronous motor (IPMSM) drives have many advantages, such as longer lifetime, reduced cost, and higher power density. However, due to the dc-link voltage fluctuation, the dc-link voltage utilization rate and the torque ripples are two major issues in flux-weakening operation region. It is important to consider these two issues comprehensively when a flux-weakening control method is adopted. In this paper, the IPMSM torque ripples caused by the dc-link voltage fluctuation and the overmodulation are analyzed in depth. In order to reduce the torque ripples and increase the utilization rate of the dc-link voltage, a novel adjustable maximum voltage based voltage closed-loop flux-weakening method is proposed. By switching between the minimum dc-link voltage control mode and the extended dc-link voltage control mode, the torque ripples can be reduced effectively and a nearly maximum utilization of the dc-link voltage can be realized. The proposed flux-weakening control method only depends on the dc-link voltage and the stator current vector reference. Experimental results on a 2.2-kW IPMSM drive platform are provided to verify the effectiveness of the proposed method.

Fault-Tolerant Operation of DFIG-WT With Four-Switch Three-Phase Grid-Side Converter by Using Simplified SVPWM Technique and Compensation Schemes

In this paper, in response to the open-circuit fault scenario in the grid-side converter (GSC) of doubly fed induction generator-based wind turbines (DFIG-WTs), a fault-tolerant four-switch three-phase (FSTP) topology-based GSC is studied. Compared with other switch-level fault-tolerant converter topologies, fewer switches, less switching and conduction losses, and simpler converter structure are derived. A simplified space vector pulse width modulation (SVPWM) technique is proposed to improve the output current quality and reduce the computational complexity in the control process. Unified expressions of duty ratios for the two remaining healthy bridge arms are obtained. In addition, the three-phase unbalance phenomenon caused by the capacitive impedance in the faulty phase is analyzed from the ac point of view, and a current distortion compensation scheme is illustrated. Furthermore, a dc-bus voltage deviation suppression strategy is proposed to maximize the dc-bus voltage utilization rate and mitigate the damage to the dc-link capacitors. Simulations are carried out in MATLAB/Simulink2017a to demonstrate the validity of the proposed SVPWM technique and compensation schemes in FSTP GSC for a 1.5-MW grid-connected DFIG-WT when different working conditions are considered.

Sensorless Control of Late-Stage Offshore DFIG-WT with FSTP Converters by Using EKF to Ride through Hybrid Faults

A hybrid fault scenario in a late-stage offshore doubly-fed induction generator (DFIG)-based wind turbine (DFIG-WT) with converter open-circuit fault and position sensor failure is investigated in this paper. An extended Kalman filter (EKF)-based sensorless control strategy is utilized to eliminate the encoder. Based on the detailed analysis of the seventh-order dynamic state space model of DFIG, along with the input voltage signals and measured current signals, the EKF algorithm for DFIG is designed to estimate the rotor speed and position. In addition, the bridge arm open circuit in the back-to-back (BTB) power converter of DFIG is taken as a commonly-encountered fault due to the fragility of semiconductor switches. Four-switch three-phase (FSTP) topology-based fault-tolerant converters are employed for post-fault operation by considering the minimization of switching losses and reducing the circuit complexity. Moreover, a simplified space vector pulse width modulation (SVPWM) technique is proposed to reduce the computational burden, and a voltage balancing scheme is put forward to increase the DC-bus voltage utilization rate. Simulation studies are carried out in MATLAB/Simulink2017a (MathWorks, Natick, MA, USA) to demonstrate the validity of the proposed hybrid fault-tolerant strategy for DFIG-WT, with the wind speed fluctuation, measurement noises and grid voltage sag taken into consideration.