On-line uninterrupted power supply (UPS) is used to guarantee stable power supply in case of grid faults. It is widely applied in industry, commerce, medical and transportation. In many application scenarios, several on-line UPSs are required to work in parallel due to high load demand. However, high-frequency resonance might occur in the output current of paralleled UPSs. This paper provides impedance model analysis of the resonance and proposes a mitigation method based on digital notch filter. Through this method, the resonance can be mitigated significantly, and voltage dynamic performance is not deteriorated. The effectiveness of the proposed method is verified through experimental tests.
The rank deficiency of conventional model reference adaptive system(MRAS)multi-parameter identification method leads to the parameter identification error.To address this problem,an MRAS multi-parameter identification method based on permanent magnet synchronous motor(PMSM)current incremental state equation is proposed.Taking advantage of the fact that the motor electrical time constant is much smaller than the mechanical time constant,the current incremental state equation is constructed and used as the adjustable model of MRAS.Thus,the resistance and inductance parameter accurate identification can be realized in the case of the flux parameter is completely unknown,and the identification error caused by the rank deficiency issue is avoided.The proposed method does not need to in-ject additional excitation signal.Finally,experimental validation demonstrates that the proposed method can accurately identify motor parameters.
A novel voltage-frequency response control strategy for MMC-HVDC systems is introduced,leveraging ener-gy storage to enhance grid-side voltage regulation and system stability.By integrating a coupling coefficient between voltage and frequency deviations,this approach incorporates grid frequency variations during oscillations into the con-trol loop of the grid-side converter.This modulation of the MMC-HVDC impedance not only suppresses oscillations but also supports frequency inertia,enhancing the overall system resilience.The efficacy of this strategy in mitigating wide-frequency oscillations is demonstrated using the Typhoon HIL 404 experimental platform.
The turn-off capability of integrated gate commutated thyristor(IGCT)is highly dependent on the commu-tation capability of its gate drive unit.In order to improve its commutation capability,limiting stray inductance is the key.The main factors affecting the stray inductance in the turn-off circuit are analyzed,and a method to suppress and reduce the stray inductance of the circuit is proposed.By using this method,the total stray inductance of the turn-off circuit is reduced from 13.6 nH to 4.7 nH,and finally reaches 3.5 nH,so that the peak and rise rate of gate current reach-6 120 A and-5 720 A/μs,respectively,which meets the requirements of the turn-off ability of the drive cir-cuit of 4 500 V/4 000 A IGCT.The stray inductance of the surrounding turn-off circuit is divided and measured in de-tail,and the inductance distribution of each part is analyzed.The results have important reference value for the design of IGCT drive circuit board with higher current capacity.
An adaptive negative sequence control strategy based on virtual synchronous generator(VSG)under three-phase unbalanced load is proposed because the output voltage of the inverter is too unbalanced.Firstly,the mathe-matical model of the inverter is established to analyze the reasons why the output voltage imbalance is too large.Sec-ondly,positive sequence VSG controls the positive sequence voltage amplitude and phase angle to realize load power control,and adaptively negative sequence VSG suppresses the negative sequence component of output voltage.Then,by establishing VSG small signal model for stability analysis,the value range of moment of inertia and damping of posi-tive and negative sequence VSG is obtained.Finally,the experimental results show that the voltage unbalance is re-duced to 0.05％,and the peak value of transient voltage unbalance is reduced to 1.8％,indicating that the proposed control strategy can effectively suppress the three-phase voltage unbalance caused by the unbalanced load.
Due to the increase in frequency and voltage level of switching devices,the impact of impulse voltage caused by stray inductance in the power loop is becoming more and more of a concern.In order to solve the pheno-menon of excessive impulse voltage caused by busbar stray inductance under high-frequency devices,the analytical modeling and partial element equivalent methods are combined in previous studies to establish a comprehensive indu-ctance model that can reflect the mechanism of structural parameters and the influence of each part inductance on the impulse voltage.Based on the model,a multilayer busbar for three-phase interleaved parallel DC/DC converter is desi-gned according to the three steps of stacked design,basic size design and device layout design.For the structural para-meters with complex influencing effects,the mathematical model is substituted into the double-layer programming algori-thm,and the parameter optimization is carried out.Finally,a low stray inductance and low impulse voltage busbar is designed,and the effectiveness of the design and the accuracy of the model are verified by double pulse experiments.
The field of motor drive makes extensive use of electronic power modeling and simulation of three-phase IGBT full-bridge inverter circuits. The accuracy and computational efficiency of these models have a direct impact on the dependability of the motor control system. The majority of earlier research focused solely on static processes of turning on and off in IGBTs, disregarding the transient proesses that occur when three-phase IGBT full-bridge inverter circuits are switched at high frequencies. This has an impact on the circuits' accuracy in real-time simulation. Therefore, this paper proposes and builds a field-programmable logic gate array (FPGA)-based steady-state and transient dual-phase three-phase IGBT full-bridge inverter circuit model for the static and transient characteristics of the insulated gate bipolar transistor (IGBT) element in the circuit. Depending on whether or not the switching states of the six IGBTs in the three-phase IGBT full-bridge inverter circuit are altered, the simulation process is split into steady state and transient phases. In the steady state phase with large step size, the circuit is discretized using the binary L/C approach. In the transient phase, the transient process is divided into several small-step-long time domains. Real-time simulation waveforms are generated by interleaving and combining the multistage fitting method's solution of the circuit's transient waveforms at tiny step lengths with the steady state phase. Finally, in order to demonstrate the accuracy of the circuit model in this work, the simulation results of the two-stage three-phase IGBT full-bridge inverter circuit model based on FPGA are compared with those of the conventional ideal model for waveform comparison and data analysis.
The modular multilevel matrix converter can provide frequency control support for remote AC power grids and has good application prospects in high-voltage low-frequency AC transmission systems. However, the dynamic performance of the traditional outer-loop PI controller is susceptible to changes in its own parameters and external conditions, which in turn influences the control effect. Therefore, a variable universe fuzzy proportional-integral (PI) adaptive outer-loop control strategy is proposed in this paper. Using the automatic sensing and self-adaptive capability of variable universe fuzzy control, the self-adaptation and self-adjustment of the size of the input error of the outer loop is achieved. Meanwhile, a function-based scaling factor approach is utilized to develop scaling factors for the input and output domains to enhance the control accuracy. Simulation and experimental findings demonstrate that this control strategy advances system stability and reinforces the self-adaptive adjustment capability of outer-loop control when compared to preexisting approaches.
Aiming at the single-phase full-bridge active neutral-point clamped (ANPC) converter, the traditional space vector modulation (SVPWM) method has the problem of unbalanced loss of internal and external switching devices. Based on the analysis of the switching process, a loss model is established, and a loss-balanced space vector modulation is proposed. When the output voltage of the bridge leg is clamped to the neutral point, the chosen switching states are used to synthesise the reference space vector, therefore the current is freewheeled through the dual commutation loops, thus effectively making the switching loss between the inner switching devices more balanced. Compared with the traditional modulation method, the proposed method can balance the loss while taking into account its operating efficiency, and fully exploit the advantages of the ANPC converter. Finally, simulation and experiment results show that the method is simple to implement, and can effectively balance the loss of switching devices.
The control system of new energy electric vehicles generally uses low-voltage batteries for power supply, including contactors that control the on-off of power lines. For this reason, contactors in cars are usually driven step up-down converters. This article compares and analyzes the driving schemes between constant-type current, stepped-type current, and curved-type current by modeling and simulating the electromagnetic mechanism of the contactor. The simulation results show that the contactor driven by the curve current has better dynamic characteristics. A prototype of contactor driver with $9\sim 18\mathrm{V}$ input was constructed based on the buck-boost converter. The experimental results showed that compared with the traditional constant-type current or voltage drive scheme, the curved-type current scheme reduced the number of bounces by 67%, the bounce time by 60%, and the closing time was only extended by 2ms. At the same time, the contactor holding power consumption was only 8.3% of the original, effectively optimizing the working performance of the contactor.
Nowadays, AC charging piles are widely used, and with the increasing number of charging piles, the harmonic pollution generated by them becomes more serious and affects the power quality of the grid. Aiming at the problem of harmonic control of the single-phase AC charging pile, it is decided to apply the active filter technology. The single-phase parallel active filter (PAPF) is selected according to the characteristics of the charging pile. The single harmonic detection method is studied based on instantaneous reactive power theory, and a new adaptive low-pass filter with fixed-step size is proposed to improve the performance of harmonic detection by combining the least mean square (LMS) and the least fourth-order moment (LMF) adaptive algorithms. The PAPF control part adopts the composite control strategy of inner and outer loop combined with repetitive control to complete the voltage stabilization control, harmonic tracking, and compensation. Based on MATLAB/SIMULINK, the output waveforms of the low-pass filter link are simulated and analyzed, and the prototype experiment is carried out. The results verify that the algorithm can improve the performance of harmonic detection. Finally, the single-phase PAPF system simulation is established and the harmonic compensation capability of system is analyzed by the Fast Fourier Transform (FFT). The results demonstrate that single-phase PAPF can effectively manage harmonics and the total harmonic distortion (THD) is reduced to less than 5%.
Aiming at the problem that the model control strategy of quasi-Z-source inverter has large error and low output voltage and power quality, a multi-vector model predictive control method based on pre-judging operation mode is proposed. In order to reduce the calculation amount and the burden of the system, the predictive working state is proposed. At the same time, in order to reduce the THD value of the output waveform, two basic vectors in the same sector are combined with zero vectors to increase the number of original alternative vectors, reduce the approximation error between the expected output vector and the actual output vector, and thus reduce the ripple of the current. Finally, the algorithm is verified by simulation and experiment. The proposed algorithm not only reduces the total harmonic distortion of output current, but also shorths the time required for iterative calculation.
In view of the performance degradation and safety degradation of lithium-ion battery at low temperature, a capacitor based self-heating method for low temperature lithium-ion battery discharge was proposed. By turning on and off the MOSFET, a group of batteries can charge the capacitor in turn, realizing the internal circulating heating of the battery. Under the condition of low frequency, capacitors and inductors are connected in series, which not only limits the peak current, but also ensures the effective value of the current, thus improving the heating efficiency. At the same time, the low-temperature heating of high-voltage and high-capacity lithium battery pack can also be realized through the cascade of heating circuits. The feasibility of the scheme proposed in this paper is verified by simulation and comparison.
级联H桥多电平逆变器可以实现光伏阵列在非均匀照射下,各个光伏组件的输出电压单独被控制并实现最大功率点跟踪(MPPT).为进一步深入研究,此处提出了一种级联H桥光伏逆变器的倒置去耦MPPT控制方案,首先使用具有占空比前馈补偿的比例积分(PI)电流控制器实现单位功率因数,同时借助直流电压控制器实现每个光伏组件的MPPT,并在此基础上提出一种双输入双输出系统的倒置去耦环路增益设计方法,从而有效地将两个H桥环路的相互影响降到最低,最终借助仿真和样机实验的手段对该方案进行了验证.实验结果表明该级联H桥光伏逆变器系统可以在实现单位功率因数的前提下,实现每个光伏组件的MPPT,并且两个H桥环路相互不影响.
针对传统无位置传感器高速直流无刷电机(BLDCM)驱动硬件电路复杂,高速换相效率低等问题,提出了一种组合时机的模数采样非导通相反电动势,进行软件过零点判定换相的方法.该方法依赖于可靠的采样机制,并配合三段式启动策略和超前角度补偿,降低了硬件电路复杂度,有效提高了控制性能,保证了换相的稳定性.实验结果给出了电气转速达到100 kr·min-1的BLDCM运行波形,表明了该控制策略的可行性与正确性.
孤岛运行微电网存在因线路阻抗不一致引起的分布式电源(DG)输出功率无法按其容量比例分配问题.针对上述问题,利用电压-电流(U-I)下垂特性对各DG输出电压幅值进行控制,通过卫星授时技术产生相位相同、频率固定的输出电压.进一步利用同步定频微电网中的同步信息,对不同测点电压电流同步测量,实现对线路阻抗的主动辨识.在此基础上,提出基于虚拟负阻抗的改进下垂控制策略,可实现线路阻抗的完全补偿,各DG按其容量比例精确分配功率.此外,为提高系统稳定性,通过奈奎斯特曲线分析虚拟负阻抗的参数对系统稳定性的影响,为参数设计提供依据.最后通过仿真和实验结果验证了所提方法可使DG输出有功功率及无功功率按其容量比例精确分配.
针对采用开环控制方式的数字磁通门线性度差、分辨率低等问题,提出了一种基于反馈控制的数字磁通门系统设计.通过利用该反馈控制系统,实现了对原磁场信号的有效反馈补偿并拓宽了信号带宽.采用数字磁通门反馈控制系统改善了开环控制方式下数字磁通门系统所带来的线性度差、分辨率低及稳定性差的问题.通过实验测试,结果显示:系统测量范围为±60 000 nT,线性度为0.04％,分辨率为3 nT,与高性能磁通门的相关系数为0.872,验证了该方法的可行性.
针对电力系统缺乏无功导致电压跌落的问题,通常采用静止无功发生装置(STATCOM)对电网无功综合补偿,而级联H桥STATCOM以易模块化、谐波含量小等特点广泛应用于电力系统无功补偿中,且使用过程中通常搭配LCL滤波器消除高频谐波.为应对级联H桥STATCOM并网过程中与LCL滤波器交互引起的高频谐振,此处提出一种阻抗重塑方法,针对级联H桥STATCOM与LCL滤波器交互的高频谐振机理建立序阻抗模型,并制定了基于序阻抗模型的阻抗重塑控制策略,有效抑制了高频谐振,并基于5 kvar样机试验验证了阻抗模型的正确性及阻抗重塑策略的有效性.
基于Rogowski线圈原理建立了高频电流传感器(HFCT)等值电路,研究了 HFCT的工作原理,在Matlab等平台对影响传感器灵敏度的因素进行了分析,结合电缆中间接头局部放电的特性,对接头的局部放电在线监测设计了一种小型便携HFCT.实验结果表明,所设计的传感器一致性良好,在100 kHz～5 MHz通频带内具有较高的增益和高度拟合的线性度,在工程上具有较强的实际应用价值.
太阳能具有清洁、可持续等优势,被广泛应用于光伏发电,而最大功率点追踪(MPPT)是光伏发电的关键技术.针对基于LLC变换器脉冲频率调制(PFM)控制的中心点迭代MPPT法迭代次数过多,导致追踪速度较慢的问题,此处提出一种变权重直接频率控制(DFC)光伏MPPT算法,通过对比中心点迭代法和不同权值迭代法的光伏功率和开关频率曲线,在中心点迭代法的基础上增加了每次迭代的权重因子,根据划分的区域及对应点的dP/df,确定每次迭代的权重因子的值,实现快速MPPT控制.试验结果表明,所提变权重DFC法较传统中心点迭代法在进入最大功率点范围过程中迭代次数少,提高了追踪速度和稳态精度.
