Motors for TPE
pump
s
TPE E-circulators
11
22
Grundfos variable frequency drive
The variable frequency drive in the MLE motor of the
TPE-pump is a highly integrated electronic unit. It is
based on an integrated hybrid module developed by
Grundfos.
The functional blocks of the single-phase MLE motor
variable frequency drive with PFC-circuit (Power Fac-
tor Correction) are shown in figure 10. Components of
Power electronics are;
• RFI filter (Radio Frequency Interference)
• Rectifier, PFC-circuit and intermediate circuit (1 ph)
• Inrush circuit
• Inverter
EMC (electromagnetic compatibility)
The Grundfos MLE motors fulfill the EMC directive
89/336/EEC and are tested according to standard EN
61 800-3. All Grundfos MLE motors are equipped with
radio interference filter and varistors in the mains
supply input to protect the electronics against voltage
peaks and noise present in the mains supply
(immunity). All inputs included in the electronic unit are
protected against peaks and noise which can damage
or disturb the function of the unit.
Grundfos MLE motors are designed to operate under a
radiated electromagnetic disturbance well above
requirements in EN61 800-3. MLE motors can be used
in both residential areas and industrial areas.
Integrated RFI filter
The integrated radio interference filter (RFI) limits the
amount of electrical noise which the MLE motor emits
to the mains supply network (emission). At the same
time the filter ensures that noise signals in the mains
generated by other equipment do not enter the
electronic devices of the variable frequency drive
causing damage or disturbances.
Rectifier, PFC-circuit and intermediate circuit,
single-phase E-pumps
Single-phase MLE motors are equipped with
PFC-circuit (Power Factor Correction). The purpose of
this circuit is to ensure that the current input from the
mains is sinusoidal and the power factor is close to 1.
The single phase MLE motor range is not covered by
EMC directive and not required to comply with it.
Grundfos chose to include the PFC -circuit with the
variable frequency drive design in order to comply with
the EMC directive standard EN 61000-3-2 stipulating
the limits for harmonic current emissions.
The purpose of PFC is to ensure that the mains are not
"contaminated" by non-sinusoidal loads which have a
tendency to distort the waveform of the mains voltage
and furthermore cause unnecessarily high peak
currents in the mains.
Benefits of PFC circuit:
• Low reactive load on power supply
• the current will have 40-50% lower RMS
• smaller fuses are required in the installation
• when connecting several pumps supplied by
different phases in parallel, the current in the
common neutral lead will be balanced so that the
neutral lead current will never exceed the current in
any one of the mains phases.
• the pump is less sensitive to variations in the mains
voltage.
Inrush circuit
When the variable frequency drive is connected to the
mains voltage, the intermediate circuit capacitor is
charged to achieve its normal operating voltage. A
series resistor ensures that the charging happens
slowly to avoid large charge spike in supply power and
intermediate capacitors.
Inverter
The inverter consists of six transistors which are
"switched on/off" by control signals from the control
electronics. The transistors have a diode placed in
parallel and are arranged in three branches each
consisting of a series connection comprising two
transistors.
Fig. 10
Block diagram showing the functional blocks of the
frequency converter of a single-phase MLE motor
TM
02
12
03
06
01
M
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E-circulator.book Page 22 Friday, October 7, 2011 4:01 PM
