Why electric cars in the future to be used to control the Variable Speed Drive ?

      Why Will Future Automobiles Be Electric? How to Make a Variable Speed Drive For Your Electric Car
In the previous article in this series we saw that the most suitable motor for an electric car is a 400Hz three-phase induction motor. Operated on a fixed frequency supply this type is essentially a constant speed motor. To be able to vary the speed of our car we need to vary the frequency of the supply. The speed of the motor will then be proportional to the frequency. To avoid damaging the motor the voltage of the supply should be varied in the same proportion as the frequency. The device for achieving this is called a Variable Speed Drive (VSD). There are various types but the most suitable for our purpose is the type that uses Insulated Gate Bipolar Transistors (IGBT's) to form a three-phase inverter with Pulse Width Modulation (PWM). The easiest will be to purchase a VSD with the motor. These are usually designed to operate on a 200 volt or 208 volt three-phase AC supply. If you are planning to use a battery for your car, you will need to remove, or bypass, the rectifier on the input side. If you are electronically inclined, you may prefer to build your own. On my website you will find references to a number of useful papers on the subject.

If you are not electronically inclined, your best bet may be to buy a 200 volt 60Hz motor complete with matching VSD. It will be considerably heavier than a 400Hz outfit, but still acceptable for a local runabout. There are several manufacturers in the far east that can supply good units at a reasonable price. If you are able to connect to a Talbot Electric grid system, these will be suitable. If you have to use a battery, you will need a 200 volt lithium-ion battery. Typically, these lose storage capacity by about 20% per year and will need to be replaced at three to four year intervals. The cost will be comparable with the use of gasoline. For those east of the Atlantic where the standard 3-phase mains voltage is 400 or 415, there is a wide selection of 50Hz motors and VSD's ranging from 60 watts up to 350kW. These are ideal for heavy vehicles. Operating these from a battery is not recommended as the battery will need to be huge.

Several useful articles are to be found in the Wikipedia under the heading Variable Frequency Drives.

Energy Saving Using Variable Frequency Drive - Explanation of How to Energy Saving Using VFD

 

Energy Saving - An introduction

Many systems use constant speed motors and control process flow rates or pressures by mechanically regulation using throttling valves, dampers, fluid couplings or variable inlet vanes etc. These devices generally do not control flow or pressure efficiently because energy is dissipated across the throttling device.

Running a motor at full speed while throttling the input or output is like driving a car with one foot on the accelerator and the other on the brake; a part of the produced output immediately goes to waste.

A variable speed drive can save over 60% of the energy. This is possible as it controls the energy at source, only using as much as is necessary to run the motor with the required speed and torque - much in the same way as the accelerator in the car controls the engine revs and without the foot on the brake. Types of loads - which are suitable for energy saving?

Drive applications are categorized with respect to power and torque changes in response to the motors speed. It is important to understand the type of load for a particular application because not all are equally good energy saving opportunities for the application of a variable speed drive. In fact, if a variable speed drive is used on some loads there will be little or no energy savings.

Variable speed drives and the loads they are applied to can generally be divided into 3 groups:

- Constant power
- Constant torque
- Variable torque

Constant Power Loads

In constant power applications, the power requirement remains constant at all speeds, and the torque requirement varies inversely with speed. One example of this type of load would be a lathe. At low speeds, the machinist takes heavy cuts, using high levels of torque. At high speeds, the operator makes finishing passes that require much less torque. Other examples are drilling and milling machines.

Typically, these applications offer no energy savings at reduced speeds.

Constant Torque Loads

In constant torque loads, the power is directly proportional to the operating speed. Since torque is not a function of speed, it remains constant while the power and speed vary proportionately. Typical examples of constant torque applications include conveyors, extruders, mixers and positive displacement pumps. Usually these applications result in moderate energy savings at lower speeds.

In variable torque load applications, both torque and power change with speed. Torque varies with speed squared, and power varies with speed cubed. This means that at half speed, the power required is approximately one eighth of rated maximum. Common examples of variable torque loads are centrifugal fans, blowers and variable discharge pressure pumps.

The use of a variable speed drive with a variable torque load often returns significant energy savings. In these applications the drive can be used to maintain various process flows or pressures while minimizing power consumption. In addition, a drive also offers the benefits of increased process control, which often improves product quality and reduces scrap.

Effective speed ranges are from 50% to 100% of maximum speed and can result in substantial energy savings.

How do variable speed drives achieve energy saving with variable torque loads?

Variable speed drives regulate the speed of motors and in turn the speed of the fan or pump by controlling the energy that goes into the motor rather than restricting the flow of a process running constantly at full speed.

A variable speed drive can save over 60% of the energy as it controls the energy at source, only using as much as is necessary to run the motor with the minimum speed and torque.

Large amounts of energy can be saved on fan and pump systems, because of the affinity laws for pressure and flow rates.

The Affinity laws state -Flow is directly proportional to speed Torque is directly proportional to speed squared Power required is proportional to speed cubed Therefore, this means that if 100% flow requires full power 75% flow requires 0.753= 42% of full power 50% flow requires 0.53= 12.5% of the power

Mechanical control methods such as inlet guide vanes, throttling valves, discharge dampers do not take advantage of the affinity laws.

With mechanical flow control methods the motor always runs at full speed and the flow is mechanically restricted.

A variable speed drive saves energy by reducing the actual speed of the motor when full flow is not required.

Example A fan is running at fixed speed (50Hz) and the output from the fan is restricted by a discharge damper to restrict airflow to the correct level for the process. The input power is typically 95% of full load power.

A variable speed drive is fitted to the system and the discharge damper removed so there is no restriction to airflow. The speed of the motor is reduced to 40Hz which gives the same airflow as before when the motor was run at full speed and a discharge damper used. Now the input power is typically 50% of full load power.

Therefore by using a variable speed drive, the power being consumed is reduced by typically 45%.

Centrifugal Fans Massive potential energy savings using a variable speed drive compared to the two most common methods of flow control for fans: - Inlet guide vanes require about 60% power to give a flow rate of 50% - A discharge damper requires a huge 90% power to give 50% flow

Centrifugal Pumps - Operating at 75% flow requires less than 50% power, whilst the throttling valve requires around 90% power.

Centrifugal fan - Typical input powers

The following table shows the typical input power to a motor when run at full speed with flow rate is restricted by an outlet damper compared to the typical input power when the same motor is run at reduced speed from a variable speed drive, achieving the same air flow rate as with the outlet damper. It can be seen that if an outlet damper reducing the air flow rate to 80% uses 95% input power, a variable speed drive achieving the same air flow rate uses 50% input power.

Other advantages of variable speed drives

o A variable speed drive can also make it possible to stop a motor completely when it is not required as re-starting with a variable speed drive causes far less stress than starting direct on line - soft start is an inherent feature of the drive.
o Regulating the motor speed has the added benefit of easily accommodating capacity rises without extra investment, as speed increases of 5-20% is no problem with an AC variable speed drive as long as there is enough spare capacity in the system.
o Reduced maintenance compared to DC systems (brushes and commutators)
o Reduced motor/application noise levels.
o If the variable speed drive has an internal PID loop, it will be possible to automatically control flow or pressure based on feedback from a sensor within the system. This can make further energy savings as the motor can slow right down if very little flow or pressure is required.

Another method of saving energy

Most companies forget about the motors when considering energy saving. As well as saving money by installing a variable speed drive, installing high efficiency motors can also save energy and money. Please see the enclosed document for further details on high efficiency motors. Motor Control Warehouse can supply EFF1 accredited motors. Please take a look at our website for further details.

Example of energy saving using a variable speed drive

A 30kW pump operating for 16 hours during weekdays and 12 hours during week ends, total of hours per week = 92 hours.

Energy Cost at constant speed Energy consumption per week - 30kW x 92hours = 2760kWh Assume electricity rate is 10p per kWh Energy cost per year - 2760kWh x £0.10 x 52 weeks = £14352

Energy Cost at variable speed Assume average speed is 75% which corresponds to 42% power consumption Energy consumption per week - 0.42 x 30kW x 92 hours = 1159.2kWh Energy cost per year - 1159.2kWh x £0.10 x 52 = £6027.84 Value of energy saved per annum by using a variable speed drive £14352 - £6027.84 = £8324.16

NOTE: This calculation is just an example using a figure of 10p/kWh but gives a good guide as to what can be saved by using variable speed drives. For a more accurate value of possible energy savings, a full survey including tests would be required

Variable Frequency Drives VFD

 

      Variable Frequency Drives (AC) help to save electrical energy in mechanical machines. The drive allows to reduce the power consumption using Insulated Gate Bipolar Transistors (IGBT) as switch to control the frequency and voltage of the output power. VFDs are available in the market for variety of mechanical machines. Typically the variable frequency drives are useful in lifts, stamping machines, hoists, cranes, and automation applications in the industries.

LGIS (LG Industrial Systems) is a renowned manufacturer of the VFDs. The LG 1ph Starvert IG series drives suits the industrial and commercial lifts. The drives are compact, have easy installation mounts. Also the drives are suitable for low budget applications where the control panel uses micro-controllers as the processing units.

The drives also give a flexible interface to a number of programmable logic controllers (PLCs) in the market. All you need is a programmed PLC and the communication cable that connects the two electronic devices. Usually the cable is RS485 compatible.

The drive helps to reduce the mechanical jerks because of acceleration at the start and stop of the lift. The change in acceleration is spread over two speeds: low and high. Two proximity sensors limit the physical travel of the lift between the start point and stop point near the halts in this travel. At start,the speed of the lift is slow for about 30% of the travel near the stop point of the lift. The high speed covers the remaining 70% travel.The lift mechanic installs these sensors near the door of the lift.

The interfacing of the drive with the control panel of the lift is easy, three connections for slow speed, fast speed, and brake operation are necessary.Also a common electronic earth connects the drive and the control panel.

The drive connects between the 1ph 220V electrical power supply and the 1ph electrical motor. The drive acts as an electrical switch to control the power supply to machine to achieve different speeds. The drive varies the frequency and voltage of the power supply to the electrical machine, thus increases the torque at starts of the motor. The modified torque gives additional advantage at start of the motor with increased load capacity.

Use aspects of Appling Variable Frequency Drive (VFD)

Today Frequency Inverters are widely used in a variety of applications for various reasons. And in pump and fan application, variable frequency drives (VFDs, variable speed drives, VSDs) are the most effective energy savers.
A thorough understanding is essential while appling frequency inverters.
The output voltage of a Pulse Width Modulation (PWM) variable frequency drive (VFD) consists of a train of pulses switched at the carrier frequency. Because of the rapid rise time of these pulses, transmission line effects of the cable between frequency inverter (vfd) and the motor must be considered. Since the transmission-line impedance of the cable and motor are different, pulses tend to reflect back from the motor terminals into the cable. The resulting voltages can produce up to twice the rated line voltage for lone cable runs, putting high stress on the cable and motor winding and eventual insulation failure.
Increasing the cable or motor size/type for long runs and 480v or 600v motors will help offset the stresses imposed upon the equipment due to the VFD (modern 230v single phase motors not effected). At 460 V, the maximum recommended cable distances between VFDs and motors can vary by a factor of 2.5:1. The longer cables distances are allowed at the lower Carrier Switching FrequencY (CSF) of 2.5 kHz. The lower Carrier Switching FrequencY (CSF) can produce audible noise at the motors.
For applications requiring long motor cables, variable frequency drive (VFD, variable speed drive, VSD) manufacturers usually offer du/dt filters that decrease the steepness of the pulses. For very long cables or old motors with insufficient winding insulation more efficient sinus filter is recommended. Expect the older motor's life to shorten. Purchase VFD rated motors for the application.

Range of industrial variable frequency drives (VFD)

Control

         Technology has evolved. The electrical system or unit (Unit) has evolved rapidly. Engine. Rotates at a constant speed. Variable speed. Fast and accurate. Magnetic torque and speed, if necessary. Therefore, the drive system or unit (s) function and a good job. It is justified in this field is very important. More efficient production system.

variable frequency drives (VFD)  features they need.

            The air conditioning is available in a variety of industrial sectors. It should contribute to the role of working to improve quality. It also saves energy. 

Torque.

           Accelerate choice of units of torque. Motor control the flow. And low-end torque. It can control the ratio of the load. Download speed is suddenly changed. Loaded everything. And running torque. If the increase or decrease the torque. What activities. 

Process Control 

      You have the ability to output back in control, show that the feedback system. There are methods that require deviations from the requirements, a response to the IP-and software equipment for the starting point. Advantage of using the power supply. Get to "Auto / Manual" open the possibility that repeated. In addition, the installation, configuration and installation in the factory. Lead to completely manage the complex. Inverter is set according to the requirements of good reviews.

Slip Compensating

     Torque and speed. Or a slip of the tongue, which is related the velocity of the stator automotive industry here. The relationship between the slip of the motor load is very important because the device will automatically increase the output frequency is still active. Without the need to reduce the speed to compensate for the amount of slippage in relation to the height of the load increases. Maximizing the value of the load of the leaves is an appropriate and effective improvement of economic conditions. Speed. Improve the performance of the torque.

Speed ​​and direction 

        Speed ​​control function, he added. I am slow to react to the series. The motor rotates in the direction corresponding to the flow. I have the ability to run the engine speed to determine the direction and speed of the engine. He compares the engine. There are programs to improve the speed and direction to determine the motor. I have the best start. Desire to continue in control.

       You can also change the number of motors is controlled by a single team or put a new motor was installed in the system. Motor controls to work with others, especially if the Motor does not have the same type and size the same.

Overload Protection

    Improved design protects the engine. Overload as well as the standard. If the congestion of the heat. Temperatures motor. When operating under full load. The costs are higher in about 70-80% of the control (travel costs). 

Auto Economize
     This is to control the flow of the stator with a model of energy. This allows you to save energy costs. The monitor automatically to save energy. Compare to support the current position of power while working. Protection against overload. 

Braking
      Is the use of "brake" to stop the motor during operation. Invented, and how the level of DC and the time to develop the engine torque to stop, take the "Off Ramp" you as soon as possible to stop the engine. Input voltage DC motor. To determine when the engine stops instead. If you are not braking to the outside. You can stop in an emergency. 


Frequencies 
      Control of mechanical resonance frequencies are usually published. I caused by "fluctuations in the frequency and the rapidly changing case of a continuous oscillation. This can cause mechanical damage to the site. Therefore, development programs, turns on the windshield constantly in the process of resonance. You can increase or decrease the frequency. frequency changes rapidly.


Fault
      There are programs that record of failure and the role of what is happening. In addition, you can tell what the package with aluminum foil. The analysis of the parameters to determine the parameters in groups. And when the blade in the position, the motor will start automatically. Each time, the role that becomes very long. This saves time and increases productivity.

Variable frequency drive (VFD) service

    Variable frequency drive (VFD) maintenance includes three essential steps that should be monitored at regular intervals.

     Cleanliness Variable frequency drive (VFD). Most of the standard NEMA1 (standard with side vents air flow in and out), or NEMA12 standards (dust) must be paid NEMA1 dust. Dust. Variable frequency drive (VFD) to cause the air flow is not easy. Degrade the heat sink and the cooling fan (circulating fan) Figure 1, the dust formed on the electronic device Knicks can cause the error. The dust absorbs the moisture, which encourages corruption as well.

 

Figure 1 shows the dust when the fan is blown Variable frequency drive (VFD).

 

 

         Air rifle, and the fan means to get good protection upright. The release of air pressure transducer. This option is available, under certain conditions. Air space structure consists of oil and water. 

       To be cooled with compressed air. We have to use oil, dry air. Alternatively, you can sometimes do more harm than good. This requires a special kind of strength in the air. Remains sensitive to static electricity. Spraying is not a static vacuum, or move to EDS has managed to reduce the buildup of static electricity. 

        The plastic begins to static electricity. EDS empty boxes and fan material. Plastic is not caused by static electricity. Cylindrical cans of compressed air, vacuum and pressure are not static. They can easily be by a company with experience in Static Control Components (static control device) purchased. 

         Check the moisture. Install the Variable frequency drive (VFD) on the wall is clean and dry storage, so that the water damage to components from moisture, dust, and the Variable frequency drive (VFD). What makes the system corrosion. As shown in Figure 2

Figure 2 shows the arrangement of the corrosion caused by moisture.

        To prevent condensation of water droplets, which radiates the heat, the heat (radiators) and can take up blocker. If an Variable frequency drive (VFD) is not used all day and installed in environments where condensation. You can change the default NEMA12 default view, and bake in a position to check the temperature. To determine the benchmark for the protection of Variable frequency drive (VFD).

      Check the joints tightly. Heating and vibrations occur. You can make calls. We were on the maintenance. This combination does not create an arch. Arc, UPS. September overload of stress. Thus, the fuse is to prevent damage to the equipment. Arch output of the Variable frequency drive (VFD). Overcurrent, or the dangers of electrical appliances.

Figure 3 shows the damage, loose connections at the input of the

Variable frequency drive (VFD).  is tight.

          Check the box. Since the process of monitoring mechanisms. Do not forget, the different components. UPS. The fan must be in compliance with the bearings are damaged or not be verified. This property is a fan or not connected. Unusual noises, and the hearts of rock fans and the move in Figure 4 and includes screws. To release or not. 

Figure 4 shows an object that is stuck in the fan.

 

              Check the capacitor.  Then check the voltage of the capacitor is also buses. They are filled with a solution. Loss or less. Two cases are caused by stress factors, electrical components and applying the wrong method. And at the same potential. When using the variable frequency drive (VFD). Increase the voltage drop across the circuit and it can be shown that the deterioration of the capacitor. This document is one of the capacitors. It acts as a filter gas-record energy provider in the home. Abnormal AC voltage of the capacitor voltage is always a problem.

Rules of fine motor speed (VFD Variable frequency drive) for pumps and fans.

      In theory, the power of the water pump and fan controllers, valves can restrict flow to the right, but it turned out that energy loss only slightly, since reduced. The system also caused most of the valves, Figure 1, the speed reduction, to reduce the engine power to pump water and to respect the laws of affinity.

 

Figure 1 compares the performance of pumps, valves and cooling of the regulator to control the speed.

The rules for controlling the motor speed to regulate the flow.

 

          All electrical appliances are all energy needs. But when properly organized and controlled energy. To reduce energy consumption and energy efficiency. In this case, the electric motor control system. When comparing the use of motors, which is a nearly constant speed, the speed of the motor under load can rotate, the power consumption is lower than the normal fans (see affinity ..)  

1. The flow rate will vary according to speed.

                               

 2. The pressure will vary the speed squared.

3. The power used to vary the speed Example three.

       If the previous report shows that, if the flow is reduced by reducing the speed, power, a reduction of 50% to 8 times the voltage (in theory). If a transfer. What seems to be more efficient. If it is moving at a constant speed, the speed of the additional space. By reducing the engine speed can be used to control the drive according to the equation.

If 

n = speed.

f = Frequency
P = number of poles.

       Lower than all previous ones. You can see that you self-manage their use of electricity and its practical application and can be used in automatic control.

       Variable frequency drive (VFD) applications can work on multiple tasks. Please use this equipment cooling water for cooling water. We need to know the proper flow of this model the flow of water and electricity. If it seems that the value is greater than the norm, we consider the cooling capacity of the pump. Evaluate the potential energy in the system.