Energy Saving Technique By Using Inverter.pdf

Energy Saving Technique by Using Inverter Product Engineering Yaskawa PT Indoserako Sejahtera

Main Circuit and Control Circuit of Inverter DC

AC Voltage

Voltage

Current

Current Rectifier circuit (diodes)

Smoothing circuit or DC bus (capacitors)

AC Voltage Inverter conversion circuit (IGBTs)

Current

R S T

IM

Input terminals

FWD run REV run

Analog monitor

Multifunction input Sequence common

output

Analog input (speed setting) Pulse input Serial input

Multi-function analog output (output frequency, current, etc.) Fault

Digital Operator

train communication

Multi-function contact output (running, speed agree, etc.) Pulse train output

Output terminals

AC power supply

Advantages of Inverter Applications (1) No.

1

Advantage

Technical Details

Main Precautions

Can control speeds of the specified constant-speed type motors.

Number of revolutions changes when squirrel-cage-type motor terminal voltage and frequency are changed.

Since a standard motor has temperature rise that becomes greater at a low speed, torque must be reduced according to frequency.

Soft start/stop enabled.

Accel/decel time can be set freely from a low speed. (0.01 to 6000 seconds).

Set proper accel/decel time after performing load operation.

Little motor heat generation since smooth accel/decel is enabled with little current.

Motor or inverter capacity frame must be increased depending on the accel/decel capacity. Check the accel/decel time and load J.

Because of phase rotation changes by transistor, there are no moving parts like conventional contactors so that interlock operation can be assured.

When applying the inverter to an elevating unit, use a motor with a brake to hold mechanically for stand still.

f

2 t

Cushion Start

3

Cushion Stop

Highly frequent f start/stop enabled. t

FWD/REV run enabled without Inverter main circuit contactor.

4

FWD Run

REV Run

RUN Command FWD Run REV Run

Advantages of Inverter Applications (2) N o.

Advantage Can apply an electrical brake. f

5

t

Electrical Braking

6

7

Can control speeds of the motor under adverse atmosphere.

Technical Details

Main Precautions

Since mechanical energy is converted into electrical energy and absorbed in the inverter at decel, the motor can auto-matically provide braking force. DC current is applied to the motor around zero-speed so that it becomes dynamic braking, to completely stop the motor.

Braking force is approx. 20% when only the inverter is used. Attaching a braking resistor (optional) externally can increase the braking force. Pay attention to the capacity of the resistor.

Since the inverter drives squirrel-cage motors, it can be used easily for explosionproof, waterproof, outdoor or special types of motors.

An explosionproof motor in combination with an inverter is subject to explosionproof certification.

High-speed rotation enabled. Commercial power supply can provide up to 3600 min-1 (2-pole at 60Hz) or V 3000 min-1 (2-pole, at 50Hz). A general-purpose inverter can increase frequency up to 400 Hz (12000 min-1) while a high-frequency inverter can increase it up to 3000 Hz (180000 min-1). 60Hz

120Hz

400Hz

f

The speed of a general-purpose motor cannot be increased by simply increasing the frequency. (It can be applied without being changed if frequency is approx. 120 Hz.) Mechanical strength and dynamic balance must be examined.

Advantages of Inverter Applications (3) No.

Advantage

Technical Details

Main Precautions

The speeds of more than one motor can be controlled by one inverter.

The inverter is a power supply unit to the motor, therefore, as many motors as the capacity allows can be connected. These motors do not have to be the same capacity.

The number of motor revolutions differs depending on each motor characteristics or load ratio even at the same frequency. (Among general-purpose motors, speed deviation of 2 to 3% can be considered.) Synchronous motors have the same number of revolutions.

Power supply capacity can be small when the motor is started up.

Large current (5 or 6 times larger than the motor rating) does not flow as with a commercial power supply start. Current can be limited to at most 100 to 150% by low-frequency start.

Transformer capacity (kVA) = 1.5 × inverter output capacity

Number of revolutions becomes constant regardless of power supply frequency.

Output freq. can be set regardless of power supply freq. 50/60Hz.

IM

8

IM

Inverter IM

9

10

Concept of Energy Saving APPLICATION

Fans, blowers, pumps

Extruders, conveyors

Lifting cranes

HOW DRIVES SAVE ENERGY

Flow rate and Replacing with motors of better efficiency air flow quantity Collecting energy for excess facility capability (inverter constant application)

Flow rate and Recovering throttling loss of valves or dampers (inverter air flow quantity application) variable

Speed variable

Using an inverter drive makes an overall more efficient application (Eddy-current coupling drive → Inverter drive)

Speed constant

Replacing with motors of better efficiency

machines

such

as Inverter power supply regenerative function collects the regenerative energy at lowering.

Unwinders

Re-use regenerative energy created by the unwinder.

Descaling pumps

Stores up energy for starting torque

Energy saving technique by using inverter Tehnik penghematan energi dengan inverter 1. Reduction of drive power by variable speed operation Mengurangi daya pada saat pemakaian kecepatan yang variatif Energy saving is realized by reducing the speed of fan, pump and blower drived at the constant speed Penghematan energi terjadi saat pengurangan kecepatan kipas, pompa dan blower dari kecepatan konstan. 2. Reduction of drive power by ON-OFF control Mengurangi daya awal dengan mengontrol ON-Off Energy saving is realized by the reduction of the operation time. To put it concretely, it applies a inverter to the start and stop of the motor. Penghematan energy dilakukan dengan mengurangi pemakaian daya pada saat awal dan akhir motor beroperasi.

3. High-efficiency operation by replacing drive system Efisiensi tinggi dengan menggantikan sistem kontrol manual. Energy saving is realized by substituting more high efficiency drive systems for the conventional systems which are used in the extrusion machine, conveyor and so on. Penghematan energi dengan efisiensi tinggi pada sistem kontrol untuk sistem biasa seperti extrusion mesin, konveyor dan lain-lain.

Energy saving technique by using inverter (2) Tehnik penghematan energi dengan inverter

4. Higy-efficiency operation by optimizing applied voltage to motors Energy saving is realized by adjusting the motor supply voltage for motor efficiency to be maximized when the efficiency of the motor declines with the load change. 5. Regeneration of mechanical energy such as inertia, etc. Energy saving is realized by putting back the regenerative energy to the power supply. The regenerative energy occurs in frequent reversible operation of the machine tool and descent of the elevator and crane .

Partial Load: Energy Saving

“At partial load” means operation at less than full load (rated air flow quantity). With a commercial power supply, “at partial load” indicates the status at which operation is performed when the air flow quantity is reduced by damper. There are mainly two types of dampers: a suction damper provided at the fan inlet, and a discharge damper provided at the fan outlet.

Fan

air flow tunnel

Air outlet

Air inlet Discharg e damper

Suction damper Air flow quantity adjusted by damper

Characteristic of Power Consumption for Air Flow Quantity When using an inverter, power consumption is either greater or equivalent to the inverter loss at 100% air flow quantity than when using damper control. However, as soon as the air flow quantity is reduced, the power consumption is rapidly reduced at inverter control.

Consumed power, shaft power (%)

100

50

0

50 Air flow quantity (rotational speed) (%)

100

Energy-saving Effect at Full Load When installing a fan, the fan capacity written in the fan specifications usually includes allowances for performance deterioration due to aging. In this case, the air flow quantity is set to the required value by installing the fixed throttle for the air tunnel. By removing this fixed throttle and setting so as to obtain required air flow quantity by using rotational speed control, the power indicated in the shaded section can be saved as well.

R1 A1

A2

Q1 0

Air flow quantity Q

R0 A0 N 0

H2

Air flow pressure H

1.0 (p.u.)

HO

1.0 (p.u.) Rated air flow quantity

N2 Ho: Fan characteristics at rotational speed No H2: Fan characteristics at rotational speed Q0N2

Rated air flow quantity exceeded

Energy Saving by Power Regeneration of Mechanical Energy How a load creates regeneration When a crane is lowering a load or when winder is unwinding a load, the motor acts like a generator, creating energy as the load pulls against the rotation of the motor. This is considered the regenerative status.

When crane is lowering

Winder

Motor

Weight W

Motor

Motor

Motor at rewinding side

Regenerative Energy Processing by Braking Resistor Regenerative energy flows into the inverter from the motor when the motor enters into regenerative status. This regenerative energy increases the voltage in the DC bus, and can trigger the overvoltage protection function (thus causing the drive to stop). In order to prevent this, a braking unit and a braking resistor are added in a general-purpose inverter drives to absorb regenerative energy and dissipate it as heat. Regenerative Energy Thermal energy Processing in Generalpurpose Inverter Drives

Diode converter section

Braking resistor

IGBT inverter section

AC power supply

DC bus bar voltage

Regenerative energy

Braking unit

IM

Using Regenerative Energy in an Inverter Drive Inverters with a power supply regenerative function can return the regenerative energy created by the motor using IGBTs for the converter section. This way, energy that was previously dissipated into the braking resistor can now be re-used. How regenerative energy is reused in an inverter drive

IGBT converter section

IGBT inverter section Regenerative power

AC power supply

IM

Operation Pattern 100%

Speed

Hoistin g

0 120.4%

Lowering 91.7%

Torque

63% 0

54kW

41.4 kW

40.7% 69.4%

Powe r

28.4 kW

98.1%

0 18.3kWEnergy saving 31.2kW

15 sec. 1.5 sec.

44.1 kW 15 sec.

20 sec. 1.5 sec.

1.5 sec. 76 sec.

20 sec. 1.5 sec.

New Motor and Inverter Technologies

New motor technology Motor loss must be reduced in order to improve the motor efficiency. There are 4 types of motor loss: ① stator copper loss, ② rotor copper loss, ③ iron loss, and ④ mechanical loss. Reducing these four types of loss improves motor efficiency.

① Stator copper loss Motor loss

Better efficiency

② Rotor copper loss ③ Iron loss ④ Mechanical loss Reduction

New Motor and Inverter Technologies (Continued)Motors called “high-efficiency motors” or “power-saving motors” are designed to minimize loss types ① and ③. To reduce stator copper loss (①), increase the size of copper wire used in the motor windings. For ③, iron core material is upgraded to minimize the loss. Unlike induction motors, synchronous motors use permanent magnets for the rotors, and consequently have hardly any rotor copper loss. This makes synchronous motors capable of even greater efficiency.

① Stator copper loss

Increase the size of copper wire.

② Rotor copper loss

Apply permanent magnets.

③ Iron loss

Upgrade the iron core material. Improve bearing and cooling structure.

④ loss

Mechanical

New Inverter Technology The diagram below illustrates five steps that can be taken to improve motor control and inverter drive performance: ① Reducing the loss generated in the inverter unit; ② and ③ concern circuitry and the control method used for high-efficiency performance; ④ covers improvements to drive’s power supply side; ⑤ involves a new approach to power conversion. How to improve inverter efficiency

New power conversion method

① Reducing loss ② Improving PWM control ③ Improving inverter output voltage waveform ④ Improving the drive’s input power factor

⑤ New power conversion method

Reducing component losses Drive section

AC power supply

Motor

Speed sensor

Improving input power factor Improving PWM control

Improving output voltage

Processing section

Reducing Inverter Component Loss One way to improve inverter efficiency is to reduce loss from various components. The circle graphs below show the amount of loss generated from each component in the drive. About 10 years ago, the loss generated from IGBT (Insulated Gate Bipolar Transistor) switching in the main circuit exceeded 60% of all loss. Recent improvements in switching technology have now minimized loss from IGBTs down to 40%. 8.1% 1.0% 0.8% 0.2%

BEFORE

NOW

15.3%

8.6%

22.0% 12.4%

11.6%

5.3% 1.5%

60.8% Rectifier diode

IGBTs

Main circuit fuse

Discharge resistance

Smoothing capacitors ＭＣ Control Others power supply

1.1% 0.2% 7.6%

43.6%

Rectifier diode

IGBTs

Smoothing capacitor

ＭＣ

Main circuit fuse

Discharge resistance

Control power supply

Others

Improving the switching characteristics of the IGBT device has reduced the power loss to the half of what it was 10 years ago. In addition to reducing power consumption for the control power supply and control circuit, inverter efficiency is 9o% better than in the past.

Improvements with PWM Control The high carrier frequency used in PWM (pulse width modulation) increases the amount of IGBT switching loss. Yaskawa has created a 2-phase modulation method to minimize this switching loss. As shown below, the 2-phase modulation method stops switching when current is large. This way, one of the 3 phases is always in the stopped status. Using this 2phase PWM control method can reduce the switching loss by approx. 30%.

High-efficiency PWM control: 2-phase modulation Output voltage

Output current

Switching loss is not generated in the 2phase modulation method since IGBT switching does not occur in this area.

Output voltage

Output current

(b) 3-phase modulation

(a) 2-phase modulation Employing 2-phase modulation can reduce IBGT switching loss by approximately 30%.

Improving the Output Voltage Waveform Although high carrier PWM control makes the output current waveform very close to sinusoidal, the actual voltage waveform created is still a group of square waves. The surge voltage generated at rising and falling edges of this square waves causes trouble. A surge suppression filter is normally attached between the inverter and the motor in order to prevent the motor insulation from being damaged by surge voltage. This filter is called RLC filter, and is is composed of a resistor, reactor, and a capacitor. A large filter is not needed if the inverter and motor are close together. If they are far apart, however, a large capacity filter is needed. For example, with the motor capacity of 75 kW, the filter consumed power is 0.3 kW, 1.4 kW and 12.6 kW when the wiring length is 30 m, 100 m and 300 m, respectively. As the distance gets longer, the required capacity is sharply increased. Additionally, the size of the filter also becomes larger, it will be necessary to examine where to install. To omit this filter, 3-level control inverters have been devised. Using these inverters can solve the problem of ①. Furthermore, this control method can reduce the remaining 3 failures (②, ③ and ④) at the same time.

Common Problems ① Motor insulation damaged by surge voltage ② Peripheral devices malfunctioning due to noise generated by the inverter ③ Earth leakage breaker malfunctioning due to leakage current ④ Motor bearings corroded by shaft current

Solved with 3-level control!

What Is 3-Level Control?

Ｎ

U

V

A EB

０ VPN

FC D

Ｎ W

U

V

W

＋

＋ Phase voltage

VPN －

Line voltag e

Ｐ

Voltage control by 12 transistors

VPN

Varispeed G7: 3-level control

０ －

VPN

VPN /2

Voltage fluctuation reduced to half of conventional model

Circui t config uration

Voltage control by 6 transistors

Conventional Drives: 2-level control Ｐ

VPN /2

VPN : DC bus bar voltage = AC input voltage × √２

Principle of 3-Level Control Method In conventional 2-level control, 2 transistors are used for each phase, making a total of 6 transistors for 3 phases to switch DC bus bar voltage VPN. Phase voltage turns ON and OFF depending on the size of VPN, and changes according to it. In the 3-level control, 4 transistors are used per phase, for a total of 12 transistors for 3 phases. The illustrations below shows how transistors switching works during one phase. In this figure, voltage P appears in phase U when transistors A and B turn ON. Then O appears in phase U through diodes E and F when transistors B and C turn ON. N appears when transistors C and D turn ON. It means that phase U can take three states: P, N, and O. This is how 3-level control was named. While voltage fluctuates between P and N in 2-level control, it fluctuates between P & O, and between O & N in 3-level control. Therefore, phase voltage turns ON and OFF depending on the size of VPN/2, which is half of VPN during 2-level control. This creates an output waveform very close to a perfect sine wave. Surge voltage is cut in half when voltage fluctuation becomes half, which means that noise and leakage current is also cut in half, resulting in reduction of shaft current.

(a) Circuit configuration during for one phase (phase U appears below)

P

VP N ２ VP N

A E

B Phase U

F

C

O VPN ２

Motor

D N

(b) Switching patterns

VPN : DC bus bar voltage

A

B

C

D

Potential

ＯＮ

ＯＮ

ＯＦＦ

ＯＦＦ

Level P

ＯＦＦ

ＯＦＦ

ＯＮ

ＯＮ

Level N

ＯＦＦ

ＯＮ

ＯＮ

ＯＦＦ

Level O

P O

N

VPN 2

Comparison of Surge Voltage Waveform in 3-level Control Method The following figures show the output voltage waveforms of 400 V class inverter 2-level control and 3-level control, respectively. In the 2-level control method, the peak value of the waveform is almost 1200 V, while it is limited to 770 V in the 3-level control method. Since this value is lower than the insulation voltage of the 400 V class motor, the existing motors can be driven by an inverter without using surge suppression filters. Suppression effect 770 V peak

1200 V peak VPN

0

VPN

0

(a) 2-level control surge voltage waveform

(b) 3-level control surge voltage waveform

Comparison of Radiation Noise in 3-level Control Method These graphs show noise levels. In the frequency bandwidth between 30 MHz and 300 MHz, the noise level is limited to 20 dB at the maximum. This reduces the effects on surrounding peripheral devices caused by noise. 100 Level dBμV/m

Level dBμV/m

100 80

6 0 4 0 2 0 0 30

80

50

70 100 200 300 Frequency Max. 20 (MHz) down

6 0 4 0 2 0 0 30 dB

50

70

100 200 300 Frequency (MHz)

Crushing the Competition with Energy Saving Drives for All Voltage Levels The packaged combination of drive and motor

High Performance Vector Control Drive

Compact Vector Control Drive

Compact V/f Control Drive

Compact and Energy Efficiency

Super Compact and Environmentally

A1000

V1000

J1000

ECOiPM Drive

V1000pico Drive

Three-Level Control Environment Friendly Motor Drive General-Purpose Inverter with Matrix Converter Advanced Vector Control U1000

Varispeed G7

FSDrive-MV1000

Low-voltage Super Energy-Saving Medium Voltage Matrix Converter inverter drive for systems FSDrive-MX1S

(3 kV, 6 kV, 11 kV)

(3 kV, 6 kV)

Super Energy Saving Medium Voltage Inverter

FSDriveLV1H