Adjustable Speed Electrical Power Drive Systems—
Part 8: Specification of Voltage on the Power Interface
1 Scope
This part of GB/T 12668 gives the methods for the determination of voltage on the power interface of power drive systems (PDS's).
Note: The power interface, as defined in the GB/T 12668 series, is the electrical connection used for the transmission of the electrical power between the converter and the motor(s) of the PDS.
This part is applicable to for the determination of the phase to phase voltages (line voltage) and the phase to ground voltages (phase voltage) at the converter and at the motor terminals.
These guidelines are limited in the first issue of this document to the following topologies with three phase output:
—indirect converter of the voltage source type, with single phase diode rectifier as line side converter;
—indirect converter of the voltage source type, with three phase diode rectifier as line side converter;
—indirect converter of the voltage source type, with three phase active line side converter.
All specified inverters in this part are of the pulse width modulation type, where the individual output voltage pulses are varied according to the actual demand of voltage versus time integral.
Other topologies are excluded of the scope of this part.
Safety aspects are excluded from this part and are stated in GB/T 12668.5 series. EMC aspects are excluded from this part and are stated in GB/T 12668.3.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 61000-2-4 Electromagnetic compatibility (EMC)—Part 2-4: Environment —Compatibility levels in industrial plants for low-frequency conducted disturbances
3 Overview and Terms and Definitions
3.1 Overview of the System
A power drive system (PDS) consists of a motor and a complete drive module (CDM). It does not include the equipment driven by the motor. The CDM consists of a basic drive module (BDM) and its possible extensions such as the feeding section or some auxiliaries (e.g. ventilation). The BDM contains converter, control and self-protection functions. Figure 1 shows the boundary between the PDS and the rest of the installation and/or manufacturing process. If the PDS has its own dedicated transformer, this transformer is included as a part of the CDM.
In this part, the following agreement for all symbols is set, that:
—the index "head" means the peak value;
—the index "star" means bipolar value.
For a given drive topology, the voltage waveform patterns between the later defined sections are in principal constant as shape (including peak values), while their amplitudes depend on the suited operating voltages, assumed as reference values in each section.
Depending on the considered section interface and on the nature of the examined voltages (differential or common mode quantities), the reference voltages between sections are average DC or RMS fundamental AC quantities.
The actual voltage values shown between sections in the differential mode model and in the common mode model are evaluated as peak values: they are obtained starting from the corresponding reference values, multiplied by suited factors including the effect of the overvoltage phenomena.
Figure 1 Definition of the Installation and Its Content
3.2 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
3.2.1 Power interface
Connections needed for the distribution of electrical power within the PDS.
[GB/T 12668.3-2012, 3.3.11]
3.2.2 Two-port network
Two-port network (or four-terminal network, or quadripole) is an electrical circuit or device with two pairs of terminals.
3.2.3 Converter reference point; NP
NP is the reference point of the converter (Vd++Vd-)/2. The converter reference point can be dedicated for the different topologies. The voltage from NP to ground is generally a common mode voltage.
3.2.4 DC link
Power DC circuit linking the input converter and the output converter of an indirect converter, consisting of capacitors and/or reactors to reduce DC voltage and/or DC current ripple.
3.2.5 DC link voltage
Ud, Vd+, Vd-
DC link voltage of the converter section. Vd+ means the positive potential; Vd- means the negative potential.
3.2.6 f0
Filter resonance frequency.
3.2.7 f1
Fundamental frequency of the inverter output voltage.
3.2.8 fp
Pulse frequency of the phase.
3.2.9 fs
Fundamental frequency of the supply voltage system.
3.2.10 fsw
Switching frequency of each semiconductor active device.
3.2.11 Ideal ground
Ideal ground is the earth reference point of the installation.
3.2.12 kcμ
Amplifying factors of the related section in the common mode model (peak values).
3.2.13 kDv
Amplifying factors of the related section in the common mode model (peak values).
3.2.14 Number of levels
N
Number of levels N is equal to the number of possible voltages of the output phase to NP-Potential.
3.2.15 ndcmult
Number of DC links per phase of the multi DC link inverter topology.
3.2.16 System star point; SP
SP is the reference point of the inverter output. The system star point can be dedicated at different system points. It is used to define the common mode voltage of a three phase system against ideal ground.
3.2.17 Rise time
tr
Rise time of the voltage is defined between 10% to 90% of the voltage transient peak equal to t90-t10 (see Figure 2)
Figure 2 Voltage Impulse Wave Shape Parameters in Case of the Two Level Inverter. Where, Rise Time Tr=T90-T10
3.2.18 Overshoot voltage
UB
Amount of voltage that exceeds the steady state value of a voltage step "Ustep" (see Figure 2).
3.2.19 Grounding potential
VGi
Reference potential to ground at the individual Section i sometimes the phrase "earth potential" or "earthing" may be used in the same content.
3.2.20 UPP
Phase to phase voltage (line voltage).
3.2.21 UPNP
Phase to NP voltage at the inverter output.
3.2.22 UPSP
Phase to star point voltage at the inverter output.
3.2.23 UPG, motor
Phase to ground voltage at the motor terminals.
3.2.24 UPP, motor
Phase to phase voltage at the motor terminals.
3.2.25 ?PP
Peak value of the phase to phase voltage (line voltage) ?PP=Ustep+UB (example for the two level case)
3.2.26 ?PP*
Peak value between two bipolar peak voltages.
Figure 3 Relation Between Typical Voltage Curve and Parameters and Time at Motor Terminal (Line Voltage) When Two-Level Inverter Supplies Power
3.2.27 ?PP_fp*
Peak value of the phase to phase voltage including two times the over voltage spike
3.2.28 US
Phase to phase supply voltage (feeding voltage) of the converter This voltage is used in this part to normalize the peak voltages and the DC link voltage as “per unit values” and includes all tolerances according to IEC 61000-2-4
3.2.29 USN
Nominal phase to phase supply voltage (feeding voltage) of the converter, the secondary voltage of the input transformer without tolerances
3.2.30 Ustep
Difference between steady state voltage values before and after a switching transition (see Figure 2)
Figure 4 Relation Between Typical Voltage Curve and Parameters and Time at Motor Terminal (Line Voltage) When Three-Level Inverter Supplies Power
3.2.31 Ustep_PP
Ustep of the phase to phase voltage (line voltage) UPP
3.2.32 Ustep_PNP
Ustep of NP Vstep of the phase to NP voltage UPNP
3.2.33 Ustep_PSP
Ustep of the phase to SP voltage UPSP
3.2.34 Ustep_Gi
Ustep of the common mode voltage UGi
4 System Approach
4.1 General
The voltage source type drive system (see Figure 5) essentially consists of the following elements: line section, line side filter (if needed), line-side rectifier, DC reactor (if needed), DC capacitor bank in the DC link, self commutated motor-side converter output filter (if needed), cable system between converter and motor and finally a motor.
Figure 5 Voltage Source Inverter (VSI) Drive System with Motor
4.2 High Frequency Grounding Performance and Topology
The PE connection using cables belongs to the so called low frequency based grounding. To specify the dynamic voltage behavior in the system approach, the high frequency grounding performance and topology is of interest.
The grounding potentials VG0 to VG4 of the different sections in a real installation are shown in Figure 5. They may be different as far as the grounding impedances are different and they are expected to be high frequency based potentials (if earthing wiring is of poor performance), although they might be of the same value in respect to low frequency based grounding.
—Single point grounding topology provides poor high frequency grounding performance. The high frequency based grounding potentials VG0 to VG4 may contain additional parasitic voltage fractions.
—Multi point or mesh type grounding topology provides excellent high frequency grounding performance. The high frequency based grounding potentials VG0 to VG4 will not contain additional parasitic voltage fractions.
4.3 Two-port Approach
For the description of the resulting voltage waveforms at the motor terminals the two-port approach is of advantage.
There are basically two kinds of two-port elements which allow separating the system into two superposing parts:
—The amplifying elements in the differential mode model
—The adding elements in the common mode model
4.3.1 Amplifying element
In Figure 6, an amplifying element is shown. In this case, the output voltage of the two port can be calculated as follows:
Foreword i
1 Scope
2 Normative References
3 Overview and Terms and Definitions
3.1 Overview of the System
3.2 Terms and Definitions
4 System Approach
4.1 General
4.2 High Frequency Grounding Performance and Topology
4.3 Two-port Approach
4.4 Differential Mode and Common Mode Systems
5 Line Section
5.1 General
5.2 TN-Type of Power Supply System
5.3 IT-Type of Power Supply System
5.4 Resulting Amplification Factors in the Differential Mode Model of the Line Section
5.5 Resulting Amplification Factors in the Differential Mode Model of the Line Section
6 Input Converter Section
6.1 Analysis of Voltages Origins
6.2 Indirect Converter of the Voltage Source Type, with Single Phase Diode Rectifier as Line Side Converter
6.3 Indirect Converter of the Voltage Source type, with Three Phase Diode Rectifier as Line Side Converter
6.4 Indirect Converter of the Voltage Source Type, with three Phase Diode Rectifier as Line Side Converter
6.5 Resulting Input Converter Section Voltage Reference Potential
6.6 Grounding
6.7 Multipulse Application
6.8 Resulting Amplification Factors in the Differential Mode Model of the Line Section
6.9 Resulting Amplification Factors in the Common Mode Model of the Rectifier Section
7 Output Converter Section (Inverter Section)
7.1 General
7.2 Input Value for the Inverter Section
7.3 Description of Different Inverter Topologies
8 Filter Section
8.1 General Purpose of Filtering
8.2 Differential Mode and Common Mode Voltage System
8.3 Filter Topologies
8.4 Resulting Amplification Effect in the Differential Mode Model after the Filter Section
8.5 Resulting Additive Effect in the Common Mode Model after the Filter Section
9 Cabling Section Between Converter Output Terminals and Motor Terminals
9.1 General
9.2 Cabling
9.3 Resulting Parameters after Cabling Section
10 Calculation Guidelines for the Voltages on the Power Interface According to the Section Models
11 Installation and Example
11.1 General
11.2 Example
Appendix A (Informative) Different Types of Power Supply Systems
Appendix B (Informative) Inverter Voltages
Appendix C (Informative) Output Filter Performance:
