![]() For example, if the switches S1 and S4 are turned ON for 0.5 second and S2 and S3 for 0.5 second and this operation is repeated, the AC with one alternation per second, i.e., the AC with a frequency of 1 is created. The frequency changes by changing the period to turn ON and OFF the switches S1 to S4. If these operations are repeated by a certain period, the AC is created since the direction of the current flowing in the lamp alters. When the switches S2 and S3 are turned ON, the current flows in the lamp in the direction of B. When the switches S1 and S4 are turned ON, the current flows in the lamp in the direction of A. When four switches, S1 to S4, are connected to the DC power supply, S1 and S4 and also S2 and S4 are respectively paired and the pairs are alternatively turned ON and OFF, the AC flows as shown in Fig 11. 10 shows the example of the method to convert the DC to the AC by utilizing a lamp for the load in place of a motor. See the basic principle with the single-phase DC as the simplest example. The smoothing circuit creates the DC voltage E 2 with little pulsation from the rectified DC voltage E 1 using a smoothing capacitor.Īn inverter is a device to create the AC from the DC power supply. This circuit is called an inrush current control circuit. After that, short the both ends of these resistors with a magnetic switch to configure a resistor-bypassed circuit. To prevent rectifying diodes from being damaged by this large inrush current, make a forcible series connection to capacitors for approximately 0.05 second from the power on to control the inrush current value. At the moment when the voltage is applied, a large inrush current flows for charging a capacitor. A capacitor has a nature to store electricity. However, a smoothing capacitor is actually used for the load. The basic principle of rectification is explained with a resistor. 7 since the AC voltage flows only when it surpasses the DC voltage. If a smoothing capacitor is used, the input current waveforms become not sine waveforms but distorted waveforms shown in Fig. However, a smoothing capacity or is actually used for the load. ![]() ![]() The principle of rectification is explained with a resistor. Input current waveform when capacitor is used as load 5 (Continuous waveforms of the ones in Table 1)įor the three-phase AC input, combining six diodes to rectify all the waves of the AC power supply allows the output voltage as shown in Fig. (To convert the AC to the DC is generally called rectification.)įig. That is to say, the AC is converted to the DC. 3, the voltage is always applied to the load in the same direction shown in Table 1. This diode nature allows the following: When the AC voltage is applied between A and B of the circuit shown in Fig. These diodes let the current flow or not flow depending on the direction to which the voltage is applied as Fig. 3 shows the example of the method to convert the AC to the DC by utilizing a resistor for the load in place of a smoothing capacitor.ĭiodes are used for the elements. See the basic principle with the single-phase AC as the simplest example. Method to create DC from AC (commercial) power supplyĪ converter is a device to create the DC from the AC power supply. The converter part consists of the following parts as following figure shows: Inverter: Circuit to change the DC to the AC with variable frequencyĬontrol circuit: Circuit to mainly control the inverter part Smoothing circuit: Circuit to smooth the pulsation included in the DC 1 Basic configuration of variable frequency driveĮach part of a variable frequency drive has the following function.Ĭonverter: Circuit to change the commercial AC power supply to the DC The basic configuration of a variable frequency drive is as follows.įig. Variable Frequency Drive (VFD) Basic Configuration
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