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Wednesday, 27 June 2018

Single-Phase Active Power Filtering Method Using Diode-Rectifier-Fed Motor Drive


 This paper presents a single-phase high power factor motor drive system with active power filter function. Since most of electrical equipment connected to the grid must comply with regulations regarding grid current harmonics, motor drive systems are generally equipped with Power Factor Corrector (PFC) which is comprised of power switches and reactive components, e.g., inductor and capacitor. The reactive components are bulky and increase the system cost especially in low-cost applications such as electrical home appliances. In this paper, a new motor drive algorithm which is capable of both driving a permanent magnet motor and filtering the harmonic currents produced by other non-linear loads belong to the system is proposed. Since the input current of the drive system is directly controlled by manipulating not the motor current reference but the output voltage reference of the inverter, it is possible to achieve exact and immediate control of the grid current. The effectiveness of the proposed algorithms is validated by experiments with a permanent magnet motor drive system.
1.      Active damping
2.      Constant power load
3.       Dc-link capacitor
4.       Dc-link voltage stabilization
5.      Electrolytic capacitor
6.       Power factor corrector



Figure 1. Block diagram of the input current control and the active power filter function.


Figure 2. (a) Motor currents (a-phase current in the stationary frame and d-q axes currents in the syncronous reference frame) with the proposed input current control, and (b) grid current, dc-link voltage, speed error and estimated torque.

Figure 3. Experimental results : input current of non-linear load and motor drive, grid current, dc-link voltage of both diode-rectifier (a) with the input current control algorithm, (b) with both the input current control and the active harmonic filtering algorithms, (c) three-phase motor currents (ia, ib, ic), grid voltage and current.

Figure 4. (a) PFC operation at light motor load (15% motor load) , and (b) during load change from 15% to 100% motor load.

In motor drive systems supplied by a single-phase grid, the problems of input harmonic currents have been mitigated by a PFC, which makes the system bulk and expensive. In this paper, a power factor correction method for motor drive systems without PFC has been proposed. In the proposed system, the dc-link capacitor is reduced for continuous conduction of diode rectifier front end. And, the input current is controlled by directly manipulating the inverter output voltage according to the motor currents and the input current reference. Since the input current can be shaped into any waveforms using the proposed input current control method, it is also possible to eliminate the harmonics in the grid current that other electric loads generate by injecting the opposite harmonics. It was validated by experiments that the input current can be controlled using the proposed algorithm and the harmonic currents from other non-linear loads can be actively suppressed.
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