The concepts of terminal voltage, phase voltage and line voltage in FOC vector control and BLDC control are still unclear

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One 、 Preface

In the process of teaching , It is found that some students have terminal voltage 、 Phase voltage 、 The concept of line voltage is vague , So this article intends to introduce these three concepts in detail , And use the actual waveform to show you the terminal voltage under different control modes 、 Phase voltage 、 What is the actual waveform of line voltage , In order to achieve the purpose of making these concepts no longer vague .

Figure 1 below shows three-phase inverter bridge and three-phase permanent magnet synchronous motor ( When interpreting the square wave control waveform, it is also equivalent to DC brushless motor ) Connection diagram , The concepts given later , Refer to the label definition in the figure .

Figure 1 ： Schematic diagram of connection between three-phase inverter bridge and three-phase permanent magnet synchronous motor

Two 、 terminal voltage 、 Phase voltage 、 Introduction to the concept of line voltage

On the Internet , There are a lot of data, and the concept description of terminal voltage and phase voltage is very vague , Even the concepts of terminal voltage and phase voltage are sometimes confused , The following is an introduction to the concept of three voltages , And show it in the form of pictures , To help you impress .

terminal voltage ： In the connection diagram of three-phase inverter bridge and three-phase permanent magnet synchronous motor , Three phase line (U,V,W) Relative to the reference point o The measured voltage is called terminal voltage .

In Figure 2 below ,Uao,Ubo,Uco It means three-phase terminal voltage .

 

Figure 2 ： Schematic diagram of three-phase terminal voltage measurement

Phase voltage ： In the connection diagram of three-phase inverter bridge and three-phase permanent magnet synchronous motor , Three phase line (U,V,W) Relative to the motor star connection point N The measured voltage is called phase voltage .

In Figure 3 below ,UaN,UbN,UcN It means three-phase voltage .

 

Figure 3 ： Schematic diagram of three-phase voltage measurement

But generally, the star connection point of motor N Will not lead out , Therefore, generally speaking, it is impossible to directly measure the phase voltage . If you want to see the phase voltage waveform , The star connection point can be simulated with a resistance much larger than the phase resistance of the motor , Measure the three-phase line U,V,W Relative to the simulated star connection point N1 The voltage of , It can also reflect the phase voltage equivalently . Therefore, figure 4 below is the schematic diagram of virtual Star point measuring equivalent phase voltage .

In Figure 4 below ,UaN1,UbN1,UcN1 It means three-phase equivalent phase voltage .

 

Figure 4 ： Schematic diagram of three-phase equivalent phase voltage measurement

Line voltage ： In the connection diagram of three-phase inverter bridge and three-phase permanent magnet synchronous motor , Three phase line (U,V,W) The voltage measured by taking any two phase lines is called line voltage .

In Figure 5 below ,Uab,Ubc,Uca It means the voltage of three lines .

 

Figure 5 ： Schematic diagram of three-phase equivalent line voltage measurement

3、 ... and 、 Terminal voltage measured under different control modes 、 Line voltage 、 Phase voltage waveform

1.  Square wave control , Measured terminal voltage waveform 、 Line voltage waveform 、 Phase voltage waveform

 

      Figure 6 ： Waveform measurement diagram of square wave control terminal voltage and line voltage

From the waveform , Before filtering , Because the switch tube is PWM The control of the , So the terminal voltage waveform 、 The waveform of phase voltage and line voltage contains switching chopper , After filtering , It can be seen that the terminal voltage is a trapezoidal wave , The filtered line voltage is also trapezoidal wave

Because there is no filter circuit in the measuring circuit , Therefore, only the phase voltage waveform before filtering is shown here .

2. SPWM Control time , Measured terminal voltage waveform 、 Line voltage waveform

Figure 7 ：SPWM Measurement diagram of voltage waveform at control terminal

Figure 8 ：SPWM Control line voltage waveform measurement diagram

SPWM In the control , From the measurement waveform , Terminal voltage and line voltage also contain switching chopper , Observe by expanding the waveform , The terminal voltage waveform is a pulse wave with gradually changing pulse width , The filtered terminal voltage and line voltage are sine waves , And because the phase voltage and line voltage are only different in amplitude , So we can also get SPWM The controlled phase voltage is also a sine wave .

therefore ,SPWM In the control , terminal voltage 、 Phase voltage 、 The line voltages are sine waves , However, observing these waveforms requires low-pass filtering of the original measured waveform .

3. SVPWM Control time , Measured terminal voltage waveform 、 Line voltage waveform

Figure nine ：svpwm Waveform measurement diagram of control terminal voltage and line voltage

SVPWM In the control , From the measurement waveform , Terminal voltage and line voltage also contain switching chopper , The filtered terminal voltage is a saddle wave , The line voltage is a sine wave , And because the phase voltage and line voltage are only different in amplitude , So we can also get SVPWM The controlled phase voltage is also a sine wave .

therefore ,SVPWM In the control , The terminal voltage is a saddle wave 、 Phase voltage 、 The line voltages are sine waves , However, observing these waveforms requires low-pass filtering of the original measured waveform .

Of course , The relationship between these waveforms , It can also be derived from relevant mathematical derivation , Those who are willing can deduce by themselves , You can also pay attention to Zhang Fei's actual combat Electronics FOC The motor drive line goes to work , There will be detailed explanations in the course .

Four 、 summary

This article , Through the terminal voltage 、 Phase voltage 、 Introduction of three concepts of line voltage , Try to make everyone not to confuse these three concepts . And there are also many engineers on the terminal voltage under different control modes 、 Phase voltage 、 The line voltage waveform is not very clear , This paper also passes the actual waveform test , The corresponding waveform diagrams of the three are shown for you .

I hope that after reading this article , We will encounter similar problems in the future , It is easy to say the test method of these waveforms and the corresponding waveform shape .

This article , Just share so much , Share more knowledge about the original motor drive , Welcome to continue to pay attention to Zhang Fei's actual combat Electronics ！

limit 300 name ,1.99 receive BLDC Motor drive control algorithm learning video （24-31 Ministry ）

limit 300 name , Scan the QR code below to add the customer service little sister （ Be sure to add a friend note STM）