In order to reduce the common-mode voltage (CMV) for three-to-five-phase indirect matrix converter (IMC), the CMV with the conventional modulation strategy is analyzed. A novel carrier-based PWM (CBPWM) method is proposed in this paper. The zero vectors in the inverter stage are assigned to the rectifier stage, equivalently, which are not considered in the inverter stage. The zero vectors are selected appropriately to ensure that the dc-link is connected to an input phase with the minimum absolute value, so that the larger CMV can be avoided. Then, the modulation signals are derived by the duty ratios, which are used to compare with the only one carrier signal and generate the gate pulses of switches. With the proposed method, the CMV is reduced effectively compared with the conventional modulation strategy. This method is analyzed and researched with a simulation model established by Matlab/Simulink. Simulation results are provided in detail to verify the feasibility and validity of the proposed method.
With the rapid development of the power electronic converter, the drive system gradually gets rid of the bound of the phase number. Multiphase drive system has received more and more attention [
The topology of three-to-five-phase IMC.
However, the CMV between the motor neutral point and the ground is caused inevitably when the SVPWM strategy is applied to MC. Due to the switches operating at high switching frequencies, the CMV, with a high value of
At present, the research on control strategy to reduce CMV of the three-to-three-phase MC is relatively mature [
However, the research on CMV of the multiphase MC is relatively few. The zero vectors in the inverter stage are reselected based on SVPWM strategy in [
In view of the above problems, a carrier-based PWM (CBPWM) method is proposed in this paper to reduce the CMV of three-to-five-phase IMC. This method focuses on the reasonable distribution of the zero vectors in both stages, so that the value of CMV is reduced. And the switching losses of the inverter stage are decreased.
The topology of three-to-five-phase IMC is shown in Figure
For the rectifier stage, suppose the three input voltages are described by
Segment partition for input voltages.
Input three-phase voltages
Input three line voltages
In each segment, to obtain the maximum dc-link voltage
Combining (
Thus,
According to the above analysis, the switching states in each segment and the corresponding duty ratios are shown in Table
The switching state and corresponding duty ratio in each segment.
Segment | ON switch | Modulated switches and duty ratios | |||
---|---|---|---|---|---|
| | ||||
1, 12 | | | | | |
2, 3 | | | | | |
4, 5 | | | | | |
6, 7 | | | | | |
8, 9 | | | | | |
10, 11 | | | | | |
For the five-leg inverter stage, assume the expected output voltages are described by
The distribution of output voltage space vector is shown in Figure
Distribution and Generation of output voltage space vector.
Distribution of output voltage space vector
Generation of output reference voltage
There are six adjacent vectors in each sector that can be used to synthesize the reference output voltage vector. However, in order to obtain the maximum output reference voltage, only two adjacent maximum vectors
The reference output voltage vector
Suppose the output voltage is in sector I (
From (
On the left of (
From (
To obtain the sinusoidal input and output waveforms, the switching pattern should produce an effective combination of the rectifier and inverter switching states. The input voltages in segment 1 and output voltages in sector I are taken as an example; the duty ratios of switching states within one sampling period are obtained by (
According to Figure
The switching sequence of conventional modulation strategy.
The principle of the transition from one segment to the other adjacent segment is to ensure the least switching number.
In the rectifier stage, The states of six switches in rectifier stage are represented by the set (
In the inverter stage, the switching sequence in sector I is
The principle of CMV when a five-phase AC motor is driven by the three-to-five-phase IMC is shown in Figure
Distribution and variation of the CMV.
| Vector | | Ranges | Peak value of |
---|---|---|---|---|
| | | [ | |
| ( | [ | | |
| ( | [ | | |
| ( | [ | | |
| ( | [ | | |
| | [ | | |
| ||||
| | | [ | |
| ( | [ | | |
| ( | [ | | |
| ( | [ | | |
| ( | [ | | |
| | [ | |
Generation of CMV and leakage current.
From Table
By analyzing the switching sequence in Figure
The switching sequence and generation of gate pulses by using the improved modulation strategy.
In terms of the change rate of CMV, the CMV is changed 16 times within one sampling period by using the improved modulation strategy. While it is 22 times and 18 times when using two zero vectors and one zero vector, respectively, under conventional modulation strategies.
According to (
In the rectifier stage, when the switching states are switched, the active vectors are used in the inverter stage. Thus, the commutation mode should be applied appropriately to ensure the safe commutation of switches in the rectifier stage.
According to the above analysis and Table
The modulation strategy is realized by complex division and combination of sectors, which is similar to the SVPWM strategy. In order to simplify the process, only one symmetrical triangular carrier signal is applied in this paper, which is described as
Figure
From Figures
Combining (
In other segments, the two modulation signals are similar to (
In Figure
The switching sequence for output phase “E” is obtained by (
From Figures
Combining (
The two modulation signals of other phases are similar to (
In the inverter stage, the gate pulse of the lower switch of each phase has a complementary relationship with that of the upper switch. However, in the different sectors, the switches which keep ON state or OFF state continuously are different. Thus, the different modulation signals are needed, as shown in Table
Switching states and modulation signals in each sector.
Sector | ON state switches | OFF state switches | Modulation signals |
---|---|---|---|
I | | | |
II | | | |
III | | | |
IV | | | |
V | | | |
VI | | | |
VII | | | |
VIII | | | |
IX | | | |
X | | | |
In order to verify the feasibility of the proposed CBPWM method, the simulation model of three-to-five-phase IMC is established based on Matlab/Simulink. The parameters of the simulation model are shown in Table
The simulation parameters for the simulation model.
Parameters | Value |
---|---|
Input voltage (line-to-line RMS) | 220 |
Input frequency | 50 Hz |
Input filter | |
Switching frequency | 10 kHz ( |
Output frequency | 25 Hz |
Voltage transfer ratio | VTR = 0.75 |
Five-phase | |
Input and output waveforms and FFT analysis.
Input voltage and current of phase “a”
Output adjacent line-to-line voltage
FFT analysis of
Output five-phase current
Waveforms of CMV.
The CMV of conventional modulation strategy
The CMV of the proposed CBPWM method
Figure
Figure
In this paper, a CBPWM method to reduce CMV of three-to-five-phase IMC is proposed. To ensure the dc-link is connected to an input phase with the minimum absolute value, the zero vectors are selected and arranged reasonably. Thus, the peak value of CMV can be reduced effectively, which is
The authors declare that there is no conflict of interests regarding the publication of this paper.