what will be the output of the following formula?
=MAX(AC2:AC6)
Answers
Answer:
hope it will help you..
Explanation:
Main Content
Simulate an AC Motor Drive
To use the AC drive models of the Electric Drives library, you first specify the types of motors, converters, and controllers used in the six AC drive models of the library designated AC1 to AC6.
Dynamic Braking
When the DC bus is provided by a diode rectifier, the drive doesn't have a bidirectional power flow capability and therefore cannot perform regenerative braking. In the AC1, AC2, AC3, AC4, and AC6 models, a braking resistor in series with a chopper ensures the braking of the motor-load system. This braking scheme is called dynamic braking. It is placed in parallel with the DC bus in order to prevent its voltage from increasing when the motor decelerates. With dynamic braking, the kinetic energy of the motor-load system is converted into heat dissipated in the braking resistor.
Modulation Techniques
The VSI inverters used in the AC drive models of the library are based on two types of modulation, hysteresis modulation and space vector pulse width modulation (PWM).
The hysteresis modulation is a feedback current control method where the motor current tracks the reference current within a hysteresis band. The following figure shows the operation principle of the hysteresis modulation. The controller generates the sinusoidal reference current of desired magnitude and frequency that is compared with the actual motor line current. If the current exceeds the upper limit of the hysteresis band, the upper switch of the inverter arm is turned off and the lower switch is turned on. As a result, the current starts to decay. If the current crosses the lower limit of the hysteresis band, the lower switch of the inverter arm is turned off and the upper switch is turned on. As a result, the current gets back into the hysteresis band. Hence, the actual current is forced to track the reference current within the hysteresis band.
Next figure shows the hysteresis current control modulation scheme, consisting of three hysteresis comparators, one for each phase. This type of closed-loop PWM is used in AC3 and AC5 models.
The space vector modulation technique differs from the hysteresis modulation in that there are not separate comparators used for each of the three phases. Instead, a reference voltage space vector Vs is produced as a whole, sampled at a fixed frequency, and then constructed through adequate timing of adjacent nonzero inverter voltage space vectors V1 to V6 and the zero voltage space vectors V0, V7. A simplified diagram of a VSI inverter is shown below. In this diagram, the conduction state of the three legs of the inverter is represented by three logic variables, SA, SB, and SC. A logical 1 means that the upper switch is conducting and logical 0 means that the lower switch is conducting.
Simplified Diagram of a VSI PWM Inverter
In this diagram, the conduction state of the three legs of the inverter is represented by three logic variables, SA, SB, and SC. A logical 1 means that the upper switch is ON and logical 0 means that the lower switch is ON.
The switching of SA, SB, SC results in eight states for the inverter. The switching states and the corresponding phase to neutral voltages are summarized in the table that lists states, inverter operations, and space voltage vectors. The six active vectors are an angle of 60 degrees apart and describe a hexagon boundary. The two zero vectors are at the origin.
As an example, for the location of the Vs vector shown in the diagram of the inverter space-vector voltage, the way to generate the inverter output is to use the adjacent vectors V1 and V2 on a part-time basis to satisfy the average output demand. The voltage Vs can be resolved as:
V
b
=
2
G
3
V
s
⋅sinδ
V
a
=V
s
⋅cosδ−
1
2
V
b
Va and Vb are the components of Vs along V1 and V2, respectively. Considering the period Tc during which the average output must match the command, write the time durations of the two states 1 and 2 and the zero voltage state as:
t
a
=
3
2
⋅
V
a
V
d
⋅T
c
t
b
=
2
3
⋅
V
b
V
d
⋅T
c
t
z
=T
c
−(t
a
+t
b
)
State
SA
SB
SC
Inverter Operation
Space Voltage Vector
0
1
1
1
Freewheeling
V0
1
1
0
0
Active
V1
2
1
1
0
Active
V2
3
0
1
0
Active
V3
4
0
1
1
Active
V4
5
0
0
1
Active
V5
6
1
0
1
Active
V6
7
0
0
0
Freewheeling
V7
Open-Loop Volt/Hertz Control
The AC machine stator flux is equal to the stator voltage to frequency ratio because
φ(t)=v(t)dt
where
v(t)=G
2
⋅V⋅sin(ω⋅t)
therefore
φ(t)=
G
2
⋅V
ω
⋅cos(ω⋅t)
Because the motor is fed with a variable AC source voltage and frequency, it is important to maintain the V/Hz constant in the constant torque region if magnetic saturation is to be avoided. A typical V/Hz characteristic is shown below. Notice that the straight line has a small voltage boost in order to compensate for resistance drop at low frequency. Open-loop V/Hz control is used with low-dynamics applications such as pumps or fans where a small variation of motor speed with load is tolerable. The AC1 model is based on an open-loop V/Hz controller.