UG0468: Space Vector Modulation IP User Guide

Space Vector Modulation IP
UG0468 User Guide
Table of Contents
Table of Contents...........................................................................................................2
Introduction ....................................................................................................................3
Min-Max Method ............................................................................................................................................ 4
Hardware Implementation .............................................................................................5
Inputs and Outputs ........................................................................................................................................ 6
Configuration Parameters .............................................................................................................................. 6
Timing Diagram ............................................................................................................................................. 7
Resource Utilization ....................................................................................................................................... 7
List of Changes ..............................................................................................................8
Product Support.............................................................................................................9
Customer Service .......................................................................................................................................... 9
Customer Technical Support Center ............................................................................................................. 9
Technical Support .......................................................................................................................................... 9
Website .......................................................................................................................................................... 9
Contacting the Customer Technical Support Center ..................................................................................... 9
ITAR Technical Support .............................................................................................................................. 10
2
UG0468: Space Vector Modulation IP User Guide
Introduction
Space Vector Modulation (SVM) is an improved technique for generating a fundamental sine wave that provides a
higher voltage to the motor in a 3 phase system, lower total harmonic distortion, and controls the number of short
pulses in the PWM waveform.
A sinusoidal PWM drive cannot provide a line-line output voltage as high as the line supply.
Carrier wave
Sinusoidal modulating
wave
PWM wave
Figure 1 · Sinusoidal PWM Waveform
SVM is a technique that is used to increase the output voltage of PWM drive and reduce the number of short pulses.
The strategy used in SVM technique is to modify the modulation of sine waves (input phase voltages) to increase the
inverter voltage gain and also to reduce inverter losses.
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UG0468: Space Vector Modulation IP User Guide
Min-Max Method
Min-Max Method
There are many techniques to implement SVM out of which Min-Max method requires least computation and is used
in the IP block. The third harmonic voltage is generated from min and max values of instantaneous 3-phase reference
voltages.
𝑣𝑣3𝐻𝐻 =
𝑚𝑚𝑚𝑚𝑚𝑚(𝑉𝑉𝑎𝑎 , 𝑉𝑉𝑏𝑏 , 𝑉𝑉𝑐𝑐 ) + 𝑚𝑚𝑚𝑚𝑚𝑚(𝑉𝑉𝑎𝑎 , 𝑉𝑉𝑏𝑏 , 𝑉𝑉𝑐𝑐 )
2
The computed third harmonic voltage is added to each phase voltage to get space vector modulated reference.
𝑉𝑉𝑆𝑆𝑆𝑆 = (𝑉𝑉𝐴𝐴 − 𝑉𝑉3𝐻𝐻 )
𝑉𝑉𝑆𝑆𝑆𝑆 = (𝑉𝑉𝐵𝐵 − 𝑉𝑉3𝐻𝐻 )
𝑉𝑉𝑆𝑆𝑆𝑆 = (𝑉𝑉𝐶𝐶 − 𝑉𝑉3𝐻𝐻 )
The addition of third harmonic reduces the peak of the reference signal by 15% and hence allows more fundamental
without reaching over-modulation. Even though third harmonic is added in phase voltages, it does not appear in line
voltages because it is common mode voltage. As a result, there is no third harmonic current but only fundamental
current. For a given modulation index, the peak modulation voltage is farther from the peak carrier voltage. Thus, the
number of short pulses is minimized. To utilize the DC bus fully, the voltages must be scaled up by 15% in one of the
blocks that follow the SVM in the FOC loop.
1
0.866
Sine PWM
SVM
Common mode
voltage (Vcm)
or
OFFSET
- 0.866
-1
Figure 2 · SVM MIN-MAX Method
If the output should be a unity peak value and the reduction in peak introduced by the block is 0.866, the factor k
must be 1.155 (k * 0.866 = 1, k=1/0.866).This implies that there is a 15.5 percent boost introduced in the phase
voltage, which results in better utilization of the DC bus.
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UG0468: Space Vector Modulation IP User Guide
Hardware Implementation
The block diagram of the SVM block implemented is shown in Figure 3.
reset_i
va3h_o
sys_clk_i
vb3h_o
start_i
va_i
vb_i
SVM
vc3h_o
done_o
vc_i
Figure 3 · SVM Hardware Block Diagram
The SVM block is a control unit which implements the MIN-MAX method discussed in the Min-Max Method on page
4. The computations involved in the MIN-MAX method are performed within the block.
The entire system is synchronized with a system clock given to sys_clk_i and controlled by a finite state machine
(FSM) and then implemented in the SVM block.
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UG0468: Space Vector Modulation IP User Guide
Inputs and Outputs
Inputs and Outputs
Table 1 gives the description of the input and output ports of the SVM block.
Table 1 · Inputs and Outputs of SVM
Signal Name
Direction
Description
sys_clk_i
Input
System clock
reset_i
Input
Active Low asynchronous reset signal to design.
start_i
Input
A single bit signal whose rising edge must be detected in
order to start the FSM and also when new input is to be
accepted.
va_i
Input
Input phase voltage(va)
vb_i
Input
Input phase voltage(vb)
vc_i
Input
Input phase voltage(vc)
va3h_o
Output
Output voltage signal corresponding to input phase voltage
va_i, with the third harmonic component.
vb3h_o
Output
Output voltage signal corresponding to input phase voltage
vb_i, with the third harmonic component.
vc3h_o
Output
Output voltage signal corresponding to input phase voltage
vc_i, with the third harmonic component.
done_o
Output
A single bit signal which goes High for one clock cycle to
indicate that all the computations are done and output
corresponding to given inputs is obtained.
Configuration Parameters
Table 2 gives the description of the configuration parameters used in the hardware implementation of SVM. These
are generic parameters that vary as per the application requirements.
Table 2 · Configuration Parameters
Name
g_STD_IO_WIDTH
g_RESET_STATE
Description
Defines the bit length of data ports.
When 0, supports active Low reset
When 1, supports active High reset
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UG0468: Space Vector Modulation IP User Guide
Timing Diagram
Timing Diagram
Figure 4 shows the timing diagram of the SVM block.
sys_clk_i
start_i
va_i
va_in1
va_in2
vb_i
vb_in1
vb_in2
vc_i
vc_in1
vc_in2
done_o
va3h_o
va3h_out_1
va3h_out_2
vb3h_o
vb3h_out_1
vb3h_out_2
vc3h_o
vc3h_out_1
vc3h_out_2
Figure 4 · SVM Timing Diagram
Resource Utilization
Table 3 shows the resource utilization report of the SVM with g_STD_IO_WIDTH equal to 18 in the SmartFusion2
device.
Table 3 · SVM Resource Utilization
Resource
Usage
SLE (Sequential)
93
CFG
78
ARI1
126
BUFFER
0
MACC
0
RAM1kx18
0
RAM64x18
0
UG0468: Space Vector Modulation IP User Guide
7
List of Changes
The following table shows important changes made in this document for each revision.
Date
Page
Revision 4
(August 2015)
Removed FSM related information from SVM
Configuration Parameters sections (SAR 69654).
Revision 3
(February 2015)
Changed the block name from SVPWM to SVM throughout the document (SAR 64768).
Revision 2
(December 2014)
Updated the title of the user guide (SAR 63243).
1
Updated Min-Max Method section and removed Direct Injection of Third Harmonic section
(SAR 63243).
4
Revision 1
(February 2014)
8
Change
Hardware
Implementation
and
Updated Table 1, Table 2, and Table 3 (SAR 64768).
NA
NA
6, 6, and 7
Updated Table 1 and Table 2 (SAR 63243).
6, 6
Removed Appendix (SAR 63243).
NA
Initial release.
NA
UG0468: Space Vector Modulation IP User Guide
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UG0468: Space Vector Modulation IP User Guide
ITAR Technical Support
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10
UG0468: Space Vector Modulation IP User Guide
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