Service manual

3 Internal Frequency Converter Operation
3.1 General
This section provides an operational overview of the main
assemblies and circuitry in the frequency converter.
3.2 Description of Operation
A frequency converter is an electronic controller that
supplies a regulated amount of AC power to a three-phase
induction motor to control the motor speed. By supplying
variable frequency and voltage to the motor, the frequency
converter controls the motor speed, also when the load on
the motor changes. The frequency converter can also stop
and start the motor without the mechanical stress
associated with the line start.
In its basic form, the frequency converter can be divided
into four main sections.
1. Rectifier
2. Intermediate Circuit
3. Inverter
4. Control and Regulation
The main frequency converter components are grouped
into three categories. They are:
1. Control Logic Section
2. Logic to Power Interface
3. Power Section
In 3.3 Sequence of Operation, these three sections are
covered in greater detail while describing how power and
control signals move throughout the frequency converter.
3.2.1
Logic section
The control card includes most of the logic section (see
Illustration 3.2). The primary logic element of the control
card is a microprocessor, which supervises and controls all
functions of frequency converter operation. In addition, a
separate PROM contains the parameters to provide the
user with programmable options. These parameters are
programmed to enable the frequency converter to meet
specific application requirements. This data is stored in an
EEPROM providing security during power-down and also
allows the flexibility to change the operational character-
istics of the frequency converter.
A custom integrated circuit generates a pulse width
modulation (PWM) waveform, which is then sent to the
interface circuitry located on the power card.
130BC343.10
Control Card
Power
MCP
Motor Control Processor
ACP
Application Control Processor
PWM
ADC
Standard I/O
LCP
RS485
Digital
Input
Analog
I/O
MCU
Supply
1 mbps
Processor
Interface
CAN
CAN
UART
UART
Illustration 3.1 Logic Section
The PWM waveform is improved through the Voltage
Vector Control Scheme, VVC
plus
. VVC
plus
provides variable
frequency and voltage to the motor matching the motor
requirements. Also available is the continuous pulsing
SFAVM PWM. The dynamic response of the system
changes to meet the variable requirements of the load.
Another part of the logic section is the removable LCP or
display mounted on the front of the frequency converter.
The LCP provides the interface between the internal digital
logic and the operator.
All programmable parameter settings can be uploaded into
the EEPROM of the LCP. This function helps in maintaining
a back-up frequency converter profile and parameter set.
Its download function can be used in programming other
frequency converters or restoring a program to a repaired
unit. The LCP is removable during operation to prevent
undesired program changes. With the addition of a remote
mounting kit, the LCP can be mounted in a remote
location.
Control terminals, with programmable functions, are
provided for input commands such as run, stop, forward,
reverse and speed reference. Additional output terminals
are provided to supply signals to run peripheral devices or
for monitoring and reporting status.
Internal Frequency Converte...
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®
HVAC Basic Drive Service Manual
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