Characteristics Of Rectifier Circuit And Generated Harmonics - Mitsubishi Electric FATEC FR-A800 Manual

7
REVIEW OF INSTALLATION ENVIRONMENT
Item
Frequency
Source
Cause
Environment
Quantitative
understanding
Generated
amount
Affected
equipment
immunity
Countermeasure
7.1.2

Characteristics of rectifier circuit and generated harmonics

Harmonics are generated by a rectifier, an AC power adjuster, etc. The converter circuit of a general-
purpose inverter consists of a rectifier circuit, and generates a large amount of harmonic current.
There are various types of rectifier circuits depending on the main circuit method. The three-phase
bridge method is most widely adopted in the general-purpose inverter.
The ordinal number "n" of the generated harmonic current is theoretically equal to PK ± 1 (P =
number of pulses, K = 1, 2, 3......). The general-purpose inverter using the three-phase bridge
method (P = 6, as 6-pulse converter is used) generates harmonic current of 6K ± 1st (5, 7, 11,
13th.....). The magnitude of the harmonic current (harmonic content) is 1/n, and as the ordinal
number of harmonic current increases, the generated amount decreases. The inverter using the
single-phase power supply input generates harmonic current of 4K ± 1st (3, 5, 7, 9th.....).
7.1 Power supply of inverter (harmonics and instantaneous power failure)
90
Table 7.1 Differences between harmonics and noise
Harmonics
Normally 40th to 50th degrees or
less (3 kHz or less).
Converter section
Rectifier circuit commutation
To-electric channel, power
impedance
Theoretical calculation is possible.
Nearly proportional to the load
capacity
Specified by standards per
equipment.
Provide a reactor (L).
Three-phase power supply
Fig. 7.3 Inverter input current waveform (harmonic current)
High frequency (several 10 kHz to MHz order)
Inverter section
Transistor switching
To-space, distance, wiring path
Due to random occurrence, quantitative grasping is
difficult.
Changes with the current variation ratio. (Gets
larger as switching speed increases.)
Different depending on maker's equipment
specifications.
Increase distance ( ).
Single-phase power supply
Noise