Load Current Detection Research Articles

Power Stability Control Strategy of the WPT System Based on Load Detection

The output power fluctuates when offset occurs between the receiving coil and the transmitting coil or load equivalent impedance changes in a wireless power transfer system (WPT). These two conditions will affect the safety of the system and the life of the battery load. Therefore, effective control methods are needed to ensure the stability of the load power. This paper analyzes the WPT system with LCC/S compensation topology and the secondary side containing DC/DC circuit. The relationship between mutual inductance and load voltage and current, mutual inductance and the system transmission efficiency, DC/DC circuit duty ratio and load voltage and current are deduced. The output power stability control strategy through load voltage and load current detection and control of DC/DC circuit is proposed. Finally, the WPT system with 1 kW output power is built through simulation and experiment, which verifies the effectiveness and correctness of theoretical analysis and control strategy in this paper.

Output power stabilization control strategy of WPT systems based on secondary side circuit

In the wireless power transfer (WPT) system, the output power is sensitive to the change of mutual inductance and load resistance. It is necessary to keep the output power stable quickly through effective control methods when the receiving coil and transmitting coil are offset or the load equivalent impedance changes. Based on the analysis of the WPT system with DC/DC converter on the secondary side, the relationship between mutual inductance and load voltage and load current, as well as the relationship between duty cycle of DC/DC converter and load demand power are given. A mutual inductance identification method based on load voltage and load current detection is proposed to monitor mutual inductance changes in real time. The output power stability control strategy based on DC/DC converter is also proposed. Finally, the effectiveness and correctness of the theoretical analysis and control strategy in this paper were verified by simulation and experiment.

A Shunt Active Power Filter for 12 Pulse Converter Using Source Current Detection Approach

A shunt Active Power Filter (APF) with current detection at the source side is considered as a closed-loop system from the view of the whole power distribution system, which is expected with better harmonics filtering performance compared with conventional current detection methods such as load current detection and open loop control. This paper introduces an efficient source current detection method (direct) control scheme to mitigate the grid current harmonics generated by the twelve pulse converter. The proposed system uses Control Rectifier (12 –pulse converter) which efficiently regulates the DC voltage by varying the angle of each 6 pulse converter. Moreover, the proposed system uses three winding transformer which eliminates the harmonics during equal angles switching at each six pulse converter which in turn simplifies the operation of the SAPF. The proposed system is simulated in MATLAB SIMULINK to evaluate the performance of the proposed system.

Analysis of the Control Strategies of Parallel Active Power Filter

Depending on detection points of harmonic current, the control strategies of parallel active power filter (PAPF) can be divided into two basic types. Load current detection is the simplest open loop control strategy, but the parallel resonant problem is an inherent defect of it. Source current detection forms an effective closed loop. However, a stability problem would be caused meanwhile. In this paper, firstly, typical system of PAPF was designed and analyzed, and different kinds of current control strategies were deeply discussed. In particular, a long time ignored problem (the amplification of the fundamental current after the compensation) associated with traditional source current detection was pointed out for the first time. Next, we proposed a new double-loop compound control strategy, which detects both the load current and the source current. Through the analysis of each part of the PAPF, the mathematics model of the system was put forward. Furthermore, we used this model to discuss the stability and compensation characteristics of the system, and found out the best working point through large amount of simulation. Finally, simulation results verified the validity of the proposed control strategy.

A Source-Current-Detected Shunt Active Power Filter Control Scheme Based on Vector Resonant Controller

A shunt active power filter (APF) with current detection at the source side is considered as a closed-loop system from the view of the whole power distribution system, which is expected with better harmonics filtering performance compared with the one with load current detection. The conventional source current detection control scheme can be mainly grouped into two types: 1) current-source-based (CS) scheme and 2) power-balance-based (PB) scheme. As introduced in this paper, the CS scheme has good dc-voltage regulation, but it bears inevitable conflict between filtering performance and system stability, whereas the PB scheme has excellent stable filtering performance, but it bears great influence on the dc voltage in the transient state. In this paper, a novel source current detection control scheme is proposed, which reserves the advantages of conventional schemes and, meanwhile, avoids their limitations. The proposed scheme employs a vector resonant controller, with which the shunt APF performs as an equivalent multiband rejection filter that series between nonlinear loads and the grid source, blocking selected harmonics components from the load side flowing into the source side. The proposed scheme is simple in structure, is needless of a harmonics extraction algorithm, and shows good stable and transient performance. Finally, the conclusions obtained in this paper are validated through experiments on the laboratory prototype.

Design criteria of a control strategy for hybrid power filters based on current and voltage detection

Summary A configuration consisting of a combination of a series active filter (APF) with a parallel passive filter has proven to be an efficient system for harmonic elimination of nonlinear loads. The most effective strategy for this configuration determines the APF reference voltage as the addition of two terms, the first proportional to the source current harmonics and the second opposite to the load voltage harmonics, current and voltage detection (CVD). To obtain the first term, an adequate adjustment of the proportionality constant ‘k’ is necessary for the implementation of the control algorithm. In this paper, design criteria to obtain the k values have been established, based on the system state model. Analysis of the resulting model provides the information needed to establish design criteria for the control strategy, both in terms of harmonic filtering and system stability. Finally, an experimental prototype was developed. The usefulness of the compensation equipment is experimentally confirmed in two contrasting situations: sinusoidal supply voltages and distorted supply voltages. Copyright © 2013 John Wiley & Sons, Ltd.

A Blend Control Scheme of Active Power Filter Based on Harmonic Voltage

This paper proposes a blend control scheme of APF based on harmonic voltage to solve the problem that load current detection APF cannot change the harmonic impedance in distribution system. In addition, based on the relationship between the rated volt-ampere of APF and the load volt-ampere, the conductance value could automatic adjustment. Computer simulation and laboratory system are designed and constructed to verify the validity and effectiveness of the shunt active filter equipped with the blend control. The shunt active filter with blend control not only can compensate the nonlinear load harmonic current but also can help to damp the harmonic voltage in distribution system.