[Simulation Model] 06-Controlled source and three-phase power supply

Lichuang EDA Simulation Classroom--Controlled Source and Three-Phase Power Supply

1. Controlled source

      The characteristic of a controlled source is that its output terminal is a voltage source or current source, and the output voltage or current is controlled by the voltage or current at the input terminal. In practical applications, the collector current of the bipolar transistor is controlled by the base current, and the output voltage of the operational amplifier is controlled by the input voltage. According to the control amount of the control branch, the controlled source is divided into four categories:

      Voltage controlled voltage source (VCVS), voltage controlled current source (VCCS)

      Current controlled current source (CCCS), current controlled voltage source (CCVS)

(1) Voltage controlled voltage source (VCVS)

      The voltage-controlled voltage source can be understood as a simple voltage amplification or reduction, that is, Vout=Vin*μ, where μ is the voltage gain, also known as the voltage transfer ratio. Draw the simulation circuit as follows:

      The input voltage U1 is provided by the DC power supply with a voltage of 1V. After passing through the voltage control voltage source, the voltage at both ends of the output load is measured with a multimeter to be 2V. Modifying the voltage gain of the voltage control voltage source can change the output voltage. The voltage gain can be set to integer, decimal and negative number.

(2) Voltage controlled current source (VCCS)

      After understanding the voltage-controlled voltage source, it will be very clear to look at the voltage-controlled current source. The usage is the same, except that what is controlled here is the output of the current. The output formula is Iout=Vin*gm, where gm is the transfer conductance, also known as transconductance. The simulation circuit is drawn as follows:

      The input terminal of the voltage-controlled current source is provided by a 2V DC power supply. Since the transconductance of VCCS is 2, the current flowing through the load resistor after passing through the controlled source is 4A. It is necessary to pay attention to the current direction of the voltage-controlled current source. A multimeter can Flip the positive and negative directions by pressing the X key on the keyboard after selecting it.

(3) Current controlled voltage source (CCVS)

      Current controlled voltage sources are calculated somewhat similarly to Ohm's law, where voltage equals current multiplied by resistance. Here the output voltage is equal to the product of the input circuit and the transfer resistance. The calculation formula is: Vout=Iin*rm, where rm is the transfer resistance, also called mutual resistance. The simulation diagram is as follows:

      Use a DC current source as the input. Note that the direction of the current is consistent with the direction of the controlled source. The output voltage is measured directly with a multimeter. Since the mutual resistance is 10 and the input current is 1A, the output voltage is 10V, which is consistent with the theoretical calculation results.

(4) Current controlled current source (CCCS)

      The same is true for current-controlled current sources. The output current is controlled by the input current and the controlled source. The output formula is Iout=Iin*β, where β is the current gain, also known as the transfer current ratio. The simulation circuit is as follows:

      The input DC current source is 1mA. After passing through the current control current source with a current gain of 10, the output current is 0.01A, which is 10mA, which meets the theoretical calculation value.

      The introduction to the four controlled sources ends here. During the course of the circuit analysis course, you will also be exposed to the use of operational amplifiers to form four controlled source models and the corresponding load characteristics and transfer characteristics. If you want to learn more about them, you can find some related books to read.

Two and three-phase power supply

      Three-phase power is also widely used in actual production and application. For example, three-phase power is generally used when generating and transmitting electricity. Three-phase power is also often used in AC motors. Since it is three-phase, it must have three interfaces. In Easy EDA simulation, two different three-phase electrical connection methods are provided: Y-shaped connection and delta connection. Let’s explain them one by one:

(1) Y-type connection

      When using Y-type connection, an external GND network needs to be connected. The three output circuits of V1, V2 and V3 are AC networks with the same amplitude and frequency and a phase difference of 120°. Take the common 380V AC three-phase network as an example. Use a multimeter to output the three-channel voltage. The effective value read should be 220V, and the voltage difference between any two circuits is 380V. This involves the concepts of phase voltage and line voltage. The line voltage refers to the voltage of the output branch to the ground, and the phase voltage refers to the voltage of any two circuits. For the voltage between branches, a diagram can be used to specifically describe the relationship between the three branches:

      The above schematic diagram can be drawn based on the relationship between the three-phase voltage output of the three-phase power supply. Each line is 220 in length, connect the three vertices, and make a vertical line downward from the intersection of the three lines. Then the distance from V2 to V3 can be calculated according to Pythagorean The theorem calculation can be found to be 380, so the voltage of any two branches is equal to the total voltage of the three-phase power supply. The simulation diagram created in Lichuang EDA is as follows:

      Place a Y-shaped three-phase power supply and set it to 380V. Use voltage probes to measure the three output circuits. Name the voltage probes V1, V2 and V3 respectively, and use two multimeters to test the output voltage of V1 and the two circuits V2 and V3. voltage, the simulation waveform results are as follows:

      Based on the waveform analysis of the three branches of the three-phase electrical output, we can draw the following conclusions:

• • The sum of the instantaneous values ​​of the three-phase symmetrical sinusoidal voltages is 0
  • The sum of the phasors of the three-phase symmetric sinusoidal voltage is 0
  • The phase difference of the three-phase symmetrical sinusoidal voltage is 120°

(2) Triangular connection

      The only difference between the delta connection and the Y-type connection is that the delta connection does not have an input GND interface, but the loads that output three voltages can be connected together as the common terminal. The circuit connection is as shown in the figure below: