Three Phase AC Motor Speed Controller

What is an AC motor speed controller?

As the name implies, an AC motor speed controller is a device that controls the speed of the AC motors.

Why do we need speed controllers for AC Motors?

AC Motors, specifically induction motors, are the most pronounced motor in industrial as well as domestic applications. They are used to drive various industrial as well as domestic loads, which require different speeds to operate such as household fans, conveyor systems, HVAC systems, blowers etc. which operate on different speeds throughout the day. So, to full-fill these speed demands by various applications controlling the speed of AC Motors is essential.

Speed Control methods of Three-Phase AC motor

Generally, there are seven different methods to control the speed of AC motors. These are,

Voltage Control
Frequency Control
Pole Changing Method
Stator Resistance Control
Rotor Resistance Control
Slip Power Recovery
Cascading Tandem Connection

We have already discussed these methods in detail in “Speed Control Methods of Three Phase AC Motors”.

Out of these six methods, voltage control and frequency control are the most commonly used speed control methods now-a-days. These two methods are employed in around 80% of AC drives that are installed in industries as well as domestic applications.

How voltage and frequency control the speed of 3 phase AC motors?

We have already discussed the concept of variable-voltage variable-frequency method of speed control of AC Motors in detail in “Speed Control of Induction Motors. The main takeaway from this article is,

Ns = 120 F / P Synchronous speed of 3 phase AC Motor

N = Ns (1-s) Speed Equation of 3 phase AC motor

where,

Ns = Synchronous speed at which stator RMF rotates.
F = Frequency of given supply
P = number of poles
N = rotor’s speed
s = slip in induction motor
s = 1 at starting or under standstill condition.

From the above given equations, we can conclude that by changing the supply frequency, the synchronous speed of the AC motor will change, simultaneously the speed of the 3 phase AC motor will change.

However, changing the supply frequency also affects the flux density which is undesirable. So, in order to maintain the flux density constant, with changing frequency of supply the voltage applied has to be changed also.

ɸ α V/F

Extra:-

Er = 4.44 ɸ. F. T (EMF Equation of AC motor)

And Er is proportional to V

So, V = 4.44 ɸ. F. T

ɸ α V/F

Where,

F = frequency of supply voltage
V = Applied Voltage
ɸ = Flux
T = Number of Turns.

AC Motor Speed Controller Circuit

To change the voltage and frequency of the supply voltage, an ac motor speed controller typically employs a rectifier circuit and an inverter circuit, as shown in the given figure.

In AC motor speed controllers, the rectifier converts a constant frequency AC supply into a variable DC supply. This variable DC supply is then fed into the inverter by a DC link, where it is converted into a variable voltage variable frequency AC supply. This variable voltage AC supply is then delivered to three phase AC motors in order to control the speed of AC motors.

Technical factors to consider before choosing a speed controller for 3 phase ac motors

Supply Voltage :- Operating voltage of controller, check whether it is compatible with your power supply. Consider factors such as number of phases (either 1 phase or three phase), voltage range and supply frequency.

Output Voltage :- Output voltage of the controller or Operating voltage of the motor. Key parameters to check for compatibility; number of output phases (either 1 phase or three phase), output voltage range and output voltage frequency. These parameters must match the requirements of your three phase 3 AC motor, as they serve as the supply parameter of your three phase AC motor.

Power Rating :- Ensure that power rating of your three phase AC motor falls within the range of output power rating of the controller.

Range of Output Frequency :- The Range of output frequency gives you a broader idea about the range of speed control offered by the controller.

List of Some 3 Phase AC motor Speed controllers for different ratings

1) VFD-S-1-010-230V, 1 Phase 230V AC INPUT, 3 Phase 0 to 230V AC OUTPUT, 1 HP/0.75 kW, 5A By Selec

Specifications:-

4 pre-set V/f; 1 user-defined V/f program
Input: Single phase 230V AC, 50/60 Hz
Output: Three phase 230V AC, 0 to 400 Hz
Output power: 1HP /0.75kW
5 (PNP/NPN) Inputs, 1 POT Input, 1 Analog Input (0-10 V/0-20 mA/4-20 mA), 1 Relay output, 1 Analog Output (0-10 V/0-20 mA), and 1 Open Collector Output
Supports the RS485 Modbus Communication Protocol
Provides protection against Over current, Over Voltage, Under Voltage, Over Temperature, Overload and Under current
Suitable for applications like pumps, fans, conveyors, food and drink packaging machinery, industrial washing machines, and most general industries, etc.

2) DELTA MS Series VFDVFD5A5MS43ANSAA Three Phase 415V 2.2 KW By Delta

Specifications:-

Input: Single phase 230V AC, 50/60 Hz
Output: Three phase 230V AC, 0 to 400 Hz
Output power: 1HP /0.75k

3) CG Power and Industrial Solutions Nps - Crompton Greaves Emotron 1 Phase, 3Hp Solar Vfd For Ac Motors

Specifications:-

Input Supply (AC) - 200-240V
Output specification - 3Phase – 1100V
Output - AC 1PH & 3PH 220 V)
Output frequency - 0~600.00Hz (Default 0~50.00Hz)

4) XCFDP AC 220V/2.2kw 3HP Variable FrequencyDrive,12A VFD Inverter Single Phase to 3 Phase Frequency Converter for Spindle Motor Speed Control (Single-Phase Input, 3 Phase Output)

Specifications:-

Single phase vfd drive:
1 phase input : Input voltage: 220V(+/-15%)
3 phase output: Output voltage: 220V
Output Voltage Adjusting Method: PWM control
Input frequency: 50/60 Hz,
Output frequency: 0-400 Hz;
The power is 2.2KW 3HP 12A, AC 220V;
VFD Dimension: 4.61 x 4.96 x 6.89 inches (L x W x H).

Applications

This vfd inverter single to 3 phase is widely used in various types of automatic control equipment, such as: Spindle Motor, Speed Control, CNC, Drill, Press, HVAC, Lathe, Milling, Pumps, Conveyors, Mach3, Fan, Cooling, Compressor, Three-phase motor and other machines, etc...PLEASE NOTE: your motor power should not be more than twice the power of this vfd!!

Customer Service

Pre-Sale: Since our VFDs contain many models, welcome to consult our customer service to choose one of the vfd you need; After-Sale: This single phase vfd comes with a general user manual of multiple models, please refer to the part of AT1--Single-phase to three-phase. No matter what the problems before or during use, please feel free to contact our customer service in time. You will get WORRY-FREE 18-MONTHS WARRANTY & LIFELONG TECH SUPPORT.

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