An electron cyclotron resonance ion thruster must emit an electron current equivalent to its ion beam current to prevent the thruster system from being electrically charged. This operation is defined as neutralization...An electron cyclotron resonance ion thruster must emit an electron current equivalent to its ion beam current to prevent the thruster system from being electrically charged. This operation is defined as neutralization. The factors which influence neutralization are categorized into the ion beam current parameters, the neutralizer input parameters, and the neutralizer position. To understand the mechanism of neutralization, an experiment and a calculation study on how these factors influence thruster neutralization are presented. The experiment results show that the minimum bias voltage of the neutralizer was -60 V at the ion beam current of 80 mA for the argon propellant, and a critical gas flow rate existed, below which the coupling voltage increased sharply. Based on the experiment, the neutralization was analyzed by means of a onedimensional calculation model. The computation results show that the coupling voltage was influenced by the beam divergence and the negative potential zone near the grids.展开更多
An analytical evaluation method for output waveform quality of space vector pulse width modulation(PWM)strategies applied in neutral⁃point⁃clamped three⁃level converter(3L⁃NPC)is proposed in this paper.Low frequency e...An analytical evaluation method for output waveform quality of space vector pulse width modulation(PWM)strategies applied in neutral⁃point⁃clamped three⁃level converter(3L⁃NPC)is proposed in this paper.Low frequency error caused by neutral point voltage ripple and high frequency error introduced by space vector synthesis were both taken into account,and the unified error model of output current ripple was established.By taking continuous and discontinuous modulation strategies as examples,the unified error model was validated through Fourier analysis of the experimental results.The proposed evaluation method will be helpful for the switching sequence optimization and the modulation strategy selection.展开更多
Carrier-based pulse width modulation (CBPWM) and virtual space vector pulse width modulation (VSVPWM) are briefly reviewed for neutral-point-clamped three-level inverters (NPC TLI). A new modulation strategy referred ...Carrier-based pulse width modulation (CBPWM) and virtual space vector pulse width modulation (VSVPWM) are briefly reviewed for neutral-point-clamped three-level inverters (NPC TLI). A new modulation strategy referred to as N3S_CBPWM is then proposed to simultaneously consider multiple goals, such as the-neutral-point voltage (NPV) balance, switching loss, and common-mode voltage (CMV) reduction. For N3S_CBPWM in each switching cycle, the three-phase switching actions are zero, one, and two. In addition, the constraint conditions of the modulation waves are provided based on the reduction of the CMV. Subsequently, N3S_CBPWM, CBPWM, and VSVPWM are compared in terms of the NPV balance capability, switching loss, and CMV reduction. Finally, the feasibility and superiority of the proposed N3S_CBPWM are verified experimentally.展开更多
With the acceleration of agricultural electrification,a lot of nonlinear and shock loads appear in the rural power grid,and the resulting harmonic and reactive currents pollute the rural power grid more and more serio...With the acceleration of agricultural electrification,a lot of nonlinear and shock loads appear in the rural power grid,and the resulting harmonic and reactive currents pollute the rural power grid more and more seriously.To solve the above problem,three-level neutral point clamped(NPC)inverters have been widely used,but their development is greatly restricted by the defect of neutral point voltage imbalance.In this paper,an improved virtual space vector pulse width modulation(VSVPWM)was proposed.Firstly,the mathematical models of various space vectors were established,and the influence of various space vectors on neutral point voltage was analyzed.The sum of the vector current at the neutral point was zero and the voltage control at the neutral point was completed by.introducing the time offset into different switching times of the redundant small vector.This method was simple in design and avoided the redundant calculation of the traditional VSVPWM method and tedious switch sequence design.This balancing control strategy could greatly reduce the influence of virtual vectors on neutral point voltage and effectively control the low-frequency oscillation of neutral point voltage.The validity of the method was verified by establishing a matlab simulation model.展开更多
基金support from National Natural Science Foundation of China (Grant No. 11475137)
文摘An electron cyclotron resonance ion thruster must emit an electron current equivalent to its ion beam current to prevent the thruster system from being electrically charged. This operation is defined as neutralization. The factors which influence neutralization are categorized into the ion beam current parameters, the neutralizer input parameters, and the neutralizer position. To understand the mechanism of neutralization, an experiment and a calculation study on how these factors influence thruster neutralization are presented. The experiment results show that the minimum bias voltage of the neutralizer was -60 V at the ion beam current of 80 mA for the argon propellant, and a critical gas flow rate existed, below which the coupling voltage increased sharply. Based on the experiment, the neutralization was analyzed by means of a onedimensional calculation model. The computation results show that the coupling voltage was influenced by the beam divergence and the negative potential zone near the grids.
基金National Natural Science Foundation of China(Grant Nos.51807140 and 51690183).
文摘An analytical evaluation method for output waveform quality of space vector pulse width modulation(PWM)strategies applied in neutral⁃point⁃clamped three⁃level converter(3L⁃NPC)is proposed in this paper.Low frequency error caused by neutral point voltage ripple and high frequency error introduced by space vector synthesis were both taken into account,and the unified error model of output current ripple was established.By taking continuous and discontinuous modulation strategies as examples,the unified error model was validated through Fourier analysis of the experimental results.The proposed evaluation method will be helpful for the switching sequence optimization and the modulation strategy selection.
文摘Carrier-based pulse width modulation (CBPWM) and virtual space vector pulse width modulation (VSVPWM) are briefly reviewed for neutral-point-clamped three-level inverters (NPC TLI). A new modulation strategy referred to as N3S_CBPWM is then proposed to simultaneously consider multiple goals, such as the-neutral-point voltage (NPV) balance, switching loss, and common-mode voltage (CMV) reduction. For N3S_CBPWM in each switching cycle, the three-phase switching actions are zero, one, and two. In addition, the constraint conditions of the modulation waves are provided based on the reduction of the CMV. Subsequently, N3S_CBPWM, CBPWM, and VSVPWM are compared in terms of the NPV balance capability, switching loss, and CMV reduction. Finally, the feasibility and superiority of the proposed N3S_CBPWM are verified experimentally.
基金Supported by Application Technology Research and Development of Harbin City(2017RAXXJ075)。
文摘With the acceleration of agricultural electrification,a lot of nonlinear and shock loads appear in the rural power grid,and the resulting harmonic and reactive currents pollute the rural power grid more and more seriously.To solve the above problem,three-level neutral point clamped(NPC)inverters have been widely used,but their development is greatly restricted by the defect of neutral point voltage imbalance.In this paper,an improved virtual space vector pulse width modulation(VSVPWM)was proposed.Firstly,the mathematical models of various space vectors were established,and the influence of various space vectors on neutral point voltage was analyzed.The sum of the vector current at the neutral point was zero and the voltage control at the neutral point was completed by.introducing the time offset into different switching times of the redundant small vector.This method was simple in design and avoided the redundant calculation of the traditional VSVPWM method and tedious switch sequence design.This balancing control strategy could greatly reduce the influence of virtual vectors on neutral point voltage and effectively control the low-frequency oscillation of neutral point voltage.The validity of the method was verified by establishing a matlab simulation model.
