Abstract
To reduce the cost of the inverter system in home appliances, a method using a shunt resistor at the DC-link can be substituted for a method using two current sensors at the inverter output. However, the minimum time of the active vector is required to sample the accurate current using a 1-shunt resistor. Therefore, many studies have been conducted investigating current reconstruction methods in the unmeasurable region of the current. The conventional methods using voltage injection have some problems such as high THD (Total Harmonic Distortion) and acoustic noise, because the PWM pattern is shifted. In addition, the current reconstruction is inaccurate in a low modulation region. In this paper, the cause of the noise in conventional methods is analyzed and a simple current reconstruction method based on an average current estimation and a current reference is utilized for reducing acoustic noise. In an immeasurable area, especially a low modulation region, an intermittent PWM shift method is proposed to enhance the accuracy of the reconstructed current. Therefore, a control strategy that combines all of the mentioned methods is implemented for the entire operating range. The effectiveness of the proposed methods is verified through the experimental results and the results of sound measurement in an anechoic chamber are included to compare with the acoustic noise.
Highlights
Phase current information is required to control the torque and speed of an AC motor
Since two different active vectors are applied in a switching period, two phase currents can be sampled from the shunt resistor and the other phase current is calculated using the following equation: ia + ib + ic = 0
In order to verify the proposed method, the experimental setup is implemented for a washing machine drive system with a DC link shunt resistor
Summary
Phase current information is required to control the torque and speed of an AC motor. Most appliances use shunt resistors for measuring the phase current to reduce costs [1,2,3]. The current measurement method using one shunt resister (shown in Figure 1) further reduces the cost because the information of two phase currents can be acquired in one switching period through the DC link shunt resistor, Rshunt [4,5]. Since two different active vectors are applied in a switching period, two phase currents can be sampled from the shunt resistor and the other phase current is calculated using the following equation: ia + ib + ic = 0
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