Controlling multiple motors through single Variable Frequency Drive

Project Title

Controlling multiple motors through single Variable Frequency Drive

Project Area of Specialization Shared EconomyProject Summary

While controlling multiple motors through the single Variable Frequency Drive (VFD), there are numerous issues that need to be addressed for the advancement of the power industry.  After numbers of industrial surveys, we identify some problems, caused due to the negligence of technical parameters related to induction motor based industrial system. We have proposed a novel approach by choosing appropriate VFD, multiple motors and designed control box to tackle these problems. In the first step, VFD is programmed on scalar mode and all the initial parameters are set, according to the rating of motors. We aided VFD with a Direct On-line (DOL) starter to modify the current DOL systems since there is no in-rush current flow in the motor due to VFD internal protection. With the usage of DOL, our system becomes cost-effective and load can be connected and disconnected while operation with VFD; without cutting off power from primary circuit breakers. In case of short circuit or overloading in any motor, we implanted thermal relay in designing the DOL system that gets tripped and isolates the affected motor from the circuitry in case of any abnormal condition on the load side. Depending upon the requirement, the motor can be added back in the circuitry automatically or manually, after primary testing. To control the multiple motors at a different speed, we have added a double belt supported pulley on the shaft of motors. In the end, the variable load mechanism is installed on one belt that varies the speed of one motor without changing the frequency of the VFD and other motors remain at the same speed. The other belt is used to achieve the assigned task of the motor. In this way, we control multiple motors through single VFD and each motor running at its own speed without affecting the operation of other motors.  Due to individual protection, provided for each motor, the only malicious motor is isolated from the circuitry in case of any fault on load or motor while retaining the operation of the healthy part of the system. 

Our project not only saves the huge portion of power by reducing the harmonic losses caused by the VFD but also reduces the cost by a great number without any considerable changes.  Further improvement in the project can be made by controlling the load electrically and vary the speed of the connected motors.

Project Objectives

We proposed a solution of using single VFD for multiple motors. With the help of our project, there will be no chance of Motor or VFD to get damaged. This project can be used to run up to 12-13 Motors from a single VFD; highly beneficial for the power industry. Following are the objectives that we will achieve during our project are enlisted below;

Objective 1 - Simple electrical network:

Design a less complex and simple system that can effectively reduce multiple VFDs on the same system.

Objective 2 - Less technical fault:

With the installation of our project, it will be easy to find out fault and diagnose it since the electrical network will be simple and hence there will be less number of technical faults.

Objective 3 - Less harmonic losses due to single VFD:

We will reduce harmonics caused by VFD to improve efficiency that leads to a better system and outcome. Harmonics produced in VFD is one of the biggest problems and reducing it is one of the greatest successes of our project.

Objective 4 – Low Initial Cost:

By installation of our project initial cost is reduced a by a great figure. Since VFDs are one of the most expensive equipment used so reducing this quantity can help startups to save money from here and  invest it in a much better place which can be a better advertising or any other technical point in the industry.

Objective 5 - Cut cabinet size, complexity, and design costs:

To have a system that requires a small cabinet size. A small cabinet size system is simple and easy to handle and requires less space. So, indirectly our system is simple instead of being complex. A simple system requires a simple design which is cheap and efficient.

Objective 6 - Cuts maintenance time and cost:

Instead of having a number of VFDs, one VFD is used which saves the time during diagnosis of the problem. Similarly, maintenance cost is reduced as well because of fewer VFDs being used.

Objective 7 - Reduces inventory stocking requirements:

By the installation of our project inventory stocking requirements are reduced due to the small number of VFDs.

 Objective 8 - Reduces control system complexity:

Control system is one of the complex setups in any industry. By the installation of our project control system required for running VFD and motors become simple and easy to install. Diagnosis of the control system becomes easy. Installation of the control system can be done within little time.

Objective 9 – Power system protection:

Installation of our project guarantees separate protection for both motors and VFDs. Protection of the system remains a very weak point in the past. Our project assures the best quality protection by saving the motor and VFD and also it makes sure that in case of any failure the system remains in flow without any sort of interruption.

Project Implementation Method

Installation of Project:

Projects basic and most important module is VFD. It is installed at the start. 3 Phase supply is provided to input terminals of the VFD to power it up. After VFD installation, a DOL Contactor is designed and installed. DOL Contactor consists of a magnetic contactor and thermal relay along with the push buttons. Multiple three phase Induction motors are installed next to thermal relays. A pulley with the capability to support two belts is fixed on the shaft of the three-phase induction motor.

Working of Project:

Once the power is supplied through three phase connection to VFD, it is programmed according to desired situations. VFD is set to operate externally through the keypad. Input motor frequency rating and rated voltage of the motors are set. Torque boost required to start the motor is set along with the required motor direction. Once the start button is pressed motor starts to rotate. 
Next main component is Direct On-Line starter (DOL). Its purpose is to provide overload and short circuit protection. Since VFD contains Inrush current protection, so the only disadvantage of DOL starter is removed too, as DOL starter malfunctions due to inrush current. DOL starter not only provide protection to our motors but it is also used to connect and disconnect any motor from the system during the operation of the VFD without disturbing the whole mechanism. 
Next, to DOL Starter, three-phase induction motors are installed. A two belt supported pulley in fixed on the motor. One belt is attached with variable load. The functionality of the variable load is to vary the speed of the motor without changing the frequency of VFD, this method helps us to achieve the milestone which has never been achieved before. That is to control multiple motors through single VFD and each motor running at its own required different speed. Another belt of the pulley is used to perform work. 

Different type of work can be done from the multiple motors installed next to single VFD and any motor can be stopped or start at its own speed without disturbing the operation of other motors and VFD.

Benefits of the Project

In the 21st century where countries are moving rapidly in the field of technology, third world countries like Pakistan need revolutionary ideas for its industry advancement in order to catch developed countries. Improvement of industry guarantees better basic life needs and boost in economic conditions along with advancement in the health sector

1. Taking a look at cost, this method reduces the production cost up to 90 percent so it makes sure that the cost of the end product will be decreased as well which benefits the common people.

2. It can be implemented without changing any infrastructure or technology of current running setups so indirectly it boosts the economy without any further investment. 

3. Many startups related to power industry do not step-in because of the high cost of V.F.Ds. So it will encourage industrialists to invest in V.F.D related setups since our project decreases the cost and requires no extra addition in the previous setup. 

4. After installation of the project, it removes the extra V.F.Ds from previously running setup. So, the spared V.F.Ds can be utilized for the expansion of the current setup and it will increase the production too.

5. In Pakistan, VFDs is being used for irrigation purpose on a large scale. The reduction in the number of VFDs will help the farmer to afford VFD-motor combo which will result in better irrigation system having optimal power usage.

6. It reduces harmonic losses generated due to VFD. 

7. It removes the negative effect of Inrush current on the Direct on-line starter, making it the perfect device to use.

8. Any motor can be connected and disconnected from the system without disturbing the operation of the system

9. It provides overvoltage, under voltage, over current, short current, inrush current protection without making the circuit of the system complex.

Technical Details of Final Deliverable

Variable Frequency Drive

The VFD can also refer as variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, Microdrive, and inverter. It is a system which gets used to control the speed of the electric motor by controlling the frequency and voltage. Frequency is directly proportional to the speed of the electric motor. By adjusting the frequency, speed can be varied according to requirements or applications. VFD makes the process reliable and the output variable is easily controlled. It has different types as Voltage source inversion (VSI), Current source inversion (CSI), Pulse width modulation (PWM). Mainly PWM based VFD used in industries as CSI required large inductor while constructing and VSI has a poor power factor. 

VFD has three stages as input converter, DC bus, and Output inverter. Input converter is consisting of Diode Bridge. DC bus consists of inductor and capacitor. Output converter consists of the IGBT. Output inverter is connected to the motor. The working of the VFD is based on three stages that are converter converts AC into DC with the help of rectifier that is compromised of 6 diodes. Then the DC bus is installed to remove ripples and acts as a linkage between converter and inverter. At the output of the rectifier circuit, we get a DC signal. The output of rectifiers contains a large number of ripples so DC bus removes ripples from the output. It also provides protection for the drive. At the output of DC bus ripple free DC is present. In the last stage of VFD, inverters that are made up of Insulated Gate Bipolar Transistor (IGBT); a switching component is added. An inverter is a unit where filtered DC supply is being converted to AC Supply with different frequency from the input, which is supplied to the electric motor connected to it.

Induction Motor:

 One of the most widely used AC motors is an induction motor. Its name shows that it works on the principle of induction (Faraday’s law). When an external AC current is only applied on the windings of a stator in an induction motor and no current is provided to the rotor windings. Then required AC currents that are needed for torque production in the rotor is obtained due to the mechanism of electromagnetic induction from the magnetic field of the stator winding (Steinmetz, 1897) and the rotor starts to rotate.

Thermal Relay:

Thermal motor protection relays contain three bi-metal strips together with a trip mechanism in a housing made of insulating material. The bi-metal strips are heated by the motor current, causing them to bend and activating the trip mechanism after a certain interval which depends on the current setting of the relay.

Magnetic Contactors:

Magnetic Contactor is a switching device used along with the relay. Its function is to break down the connection when the current exceeds the limit and isolates faulty part of the system from the healthy one. 

Final Deliverable of the Project Hardware SystemType of Industry Energy , Manufacturing Technologies Shared Economy, OthersSustainable Development Goals Decent Work and Economic Growth, Industry, Innovation and Infrastructure, Sustainable Cities and CommunitiesRequired Resources

Item Name	Type	No. of Units	Per Unit Cost (in Rs)	Total (in Rs)
			Total in (Rs)	63800
Variable Frequency Drive	Equipment	1	30000	30000
Induction Motor	Equipment	3	7000	21000
Thermal Relay	Equipment	3	500	1500
Magnetic Contactor	Equipment	3	600	1800
Project Frame	Equipment	1	8000	8000
Power Cables	Miscellaneous	1	1200	1200
Thimbles	Miscellaneous	30	10	300