Variable Frequency Drive

A variable frequency drive, which is also called VFD, is used for controlling the frequency of the electrical power supplied to AC electric motor, thus controlling the rotational speed of the motor. Variable frequency drives are also known as adjustable frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter drives. These drives are sometimes also called variable voltage variable frequency (VVVF) drives, for the voltage is varied along with frequency. A variable frequency drive system generally consists of an AC motor, a controller and an operator interface.

Definition of HARSVERT Variable Frequency Drive model
Model is explained as follows:

Note:
1 Rated output current is □□□A, including 3 digital bits.
2 Rated output voltage: 03－3kV; 03.3－3.3kV; 04.16－4.16kV; 06－6kV; 06.6－6.6kV; 10－10kV; 11－11kV.
3 Control mode: A- asynchronous motor; S-synchronous motor; VA-asynchronous motor vector control; VS- synchronous motor vector control; FVA-asynchronous motor, regenerative drive; FVS-synchronous motor, regenerative drive;

For example:

HARSVERT Variable Frequency Drive parameters

Item	Parameter
Standard	IEC61800-4:2002 Q/CP BLH003-2007
	Input
Phase, frequency	Three phase, 50/60Hz
Allowable range of frequency fluctuation	±10%
Allowable range of voltage fluctuation	±10%
Input power factor	>0.95 (at more than 20% load)
	Output
Output voltage range	3kV~11kV
Output current range	25A~600A
VFD capacity	280kW~8000kW
Over-load capacity	120% of rated current for 60 seconds per 10minutes; 150% of rated current for 3s; 200% immediately
Output frequency	0.5-120Hz
	Basic performance
Efficiency	≥96% (including phase-shifting transformer)
Harmonics	Comply with IEEE 519 standard
Frequency resolution	0.01Hz
Touch screen HMI	Output frequency, voltage, current, power; input voltage, current, power, power factor; failure/alarm; log; parameter setup; waveform display, etc.
	Control
Control mode	V/F control; Vector control
Acceleration/deceleration time	0~3200s, Adjustable
Digital I/O	5/5channels digital inputs/outputs; extendable
Communication port and protocols	RS485; Modbus-RTU[OPTIONAL Protocols: Profibus-DP, TCP/IP, DeviceNet, GPRS wireless transmission]
Control signal between Power cell and Controller	Connected by optical fibre
Auxiliary power supply	Single phase AC110V/ AC220V/ AC230V; or DC220V Capacity: 3kVA
PID function	Embedded PID regulator
Control function	Auto re-start after the recovery of main medium voltage; Torque booster; Frequency-skip; Self-diagnosis; Fly-start; Synchronous transfer[OPTIONAL]; Cell bypass[OPTIONAL]
	Operation
Operation mode	Local/Remote; Open loop/Close loop
Frequency given	Manually setting in the interface/Analog signal
Status output of VFD	analog output and digital output
	Ambience
Work field	Inside without corrosive and explosive gas and without dust, Altitude of below 1000m.
Temperature/humidity	Temperature: 0~+45oC; Humidity: below 90%, no condensation
Storage condition	-25~+55℃
	Others
Protection	Over current, Short circuit, Earth fault, Over voltage, Low voltage, Over load, Over heat, Phase loss.
Enclose	IP20~IP41
Cooling	Air cooling/Hot air to Chiller water heater exchanger cooling

Application Of Variable Frequency Drive
HARSVERT- series of medium voltage VFD can usually be applied in these fields:
Power generation:induced draft fans, forced draft fans, condensate exhausting pump, boiler feed water pumps, primary fan, secondary fan, circulating pump, mill fan, slurry pump, mill .

System Principle of Variable Frequency Drive
Principle of Variable Frequency Drive
System configuration
Multi-level voltage source Variable Frequency Drive with the technology of cascade-connected power cells can directly output medium voltage, i.e. 3kV, 3.3kV, 4.16kV, 6kV, 6.6kV, 10kV and 11kV. Variable Frequency Drive is composed of phase-shifting transformer, power cells and controller.

Main Features of Variable Frequency Drive
At soft start status, Variable Frequency Drive will start and accelerate to the frequency of power grid regardless of the given frequency. When the output frequency of Variable Frequency Drive reaches the frequency of power grid (set in main interface), then the output of VFD will become 0, at the same time VFD sends ' transfer to power grid' command. This command can make the control circuit to transfer the power supply of the motor from VFD to the power grid. During the transient transfer, there is a big inrush current.

Technical Data of Variable Frequency Drive
1 Rated output current is □□□A, including 3 digital bits.
2 Rated output voltage: 03－3kV; 03.3－3.3kV; 04.16－4.16kV; 06－6kV; 06.6－6.6kV; 10－10kV; 11－11kV.
3 Control mode: A- asynchronous motor; S-synchronous motor; VA-asynchronous motor vector control; VS- synchronous motor vector control; FVA-asynchronous motor, regenerative drive, vector control; FVS-synchronous motor, regenerative drive, vector control

Technical Certification of Variable Frequency Drive