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Freescale Semiconductor, Inc.
Application Note
AN2531/D Rev. 0, 5/2003 Standard Space Vector Modulation with Dead-Time Correction – XOR version TPU Function Set (svmStdDtXor)
By Milan Brejl, Ph.D.
Freescale Semiconductor, Inc...
Functional Overview
The Standard Space Vector Modulation with Dead-Time Correction – XOR version (svmStdDtXor) is a version of the Standard Space Vector Modulation with Dead-Time Correction (svmStdDt) function that uses two TPU channels to generate one PWM output channel. The TPU channel outputs are connected to an XOR gate whos output is the required PWM signal. See Figure 1. An advantage of this solution is the full range 0% to 100% of PWM duty-cycle ratios. There is no MPW (minimum pulse width) parameter to limit the edge duty-cycle ratios in this version, unlike in the svmStdDt. A disadvantage is that the number of assigned TPU channels is doubled.
AT1 XOR
Phase A - top
AT2 AB1 AB2
XOR
Phase A - bottom
BT1
XOR
Phase B - top
BT2 BB1
XOR
Phase B - bottom
BB2
CT1
XOR
Phase C - top
CT2 CB1
XOR
Phase C - bottom
CB2
Figure 1. Functionality of XOR version – illustration
© Motorola, Inc., 2003
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Freescale Semiconductor, Inc.
AN2531/D
The dead-time correction technique requires knowledge of the instantaneous direction of phase currents. In the case of positive phase current the top channel high-time is equal to the calculated high-time and the bottom channel has to control the dead-time. In case of negative phase current the bottom channel low-time is equal to the calculated high-time and the top channel has to control the dead-time. See Figure 2.
calculated high-time
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In case of positive current:
top channel bottom channel
DT
In case of negative current:
DT
top channel bottom channel
DT
DT
Figure 2. Dead-Time Correction Technique
The function set consists of 5 TPU functions: • • • • • Standard Space Vector Modulation with Dead-Time Correction – XOR version – R channels (svmStdDtXor_R) Standard Space Vector Modulation with Dead-Time Correction – XOR version – T channels (svmStdDtXor_T) Synchronization Signal for Standard Space Vector Modulation with Dead-Time Correction – XOR version (svmStdDtXor_sync) Resolver Reference Signal for Standard Space Vector Modulation with Dead-Time Correction – XOR version (svmStdDtXor_res) Fault Input for Standard Space Vector Modulation with Dead-Time Correction – XOR version (svmStdDtXor_fault)
The svmStdDtXor_R and svmStdDtXor_T TPU functions work together to generate 6 pairs of XOR gate inputs. The XOR gate outputs then produce a 6channel 3-phase center-aligned PWM signal with dead-time between the top and bottom channels. The Synchronization Signal for the svmStdDtXor
2
Standard SVM with Dead-Time Correction – XOR version (svmStdDtXor)
MOTOROLA
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Freescale Semiconductor, Inc.
AN2531/D Function Set Configuration
function can be used to generate one or more adjustable signals for a wide range of uses, that are synchronized to the PWM, and track changes in the PWM period. The Resolver Reference Signal for the svmStdDtXor function can be used to generate one or more 50% duty-cycle adjustable signals that are also synchronized to the PWM. The Fault Input for the svmStdDtXor function is a TPU input function that sets all XOR gate outputs low when the input signal goes low.
Function Set Configuration
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None of the TPU functions in the Standard Space Vector Modulation with Dead-Time Correction – XOR version TPU function set can be used separately. The svmStdDtXor_R and svmStdDtXor_T functions have to be used together. The svmStdDtXor_R runs on pins AB1, BB1, CB1 – see Figure 1. The svmStdDtXor_T runs on the other pins. One or more channels running Synchronization Signal for svmStdDtXor as well as Resolver Reference Signals for svmStdDtXor functions can be added to the svmStdDtXor_R and svmStdDtXor_T functions. They can run with different settings on each channel. The function Fault Input for svmStdDtXor can also be added to the svmStdDtXor_R and svmStdDtXor_T functions. It is recommended to use it on channel 15, and to set the hardware option that disables all TPU output pins when the channel 15 input signal is low (DTPU bit = 1). This ensures that the hardware reacts quickly to a pin fault state. Note that it is not only the PWM channels, but all TPU output channels, including the synchronization signals, that are disabled in this configuration. Table 1 shows the configuration options and restrictions.
Table 1. svmStdDtXor TPU function set configuration options and restrictions
TPU function svmStdDtXor_R svmStdDtXor_T svmStdDtXor_sync svmStdDtXor_res svmStdDtXor_fault Optional/ How many Mandatory channels mandatory 3 mandatory 9 optional 1 or more optional 1 or more optional 1 Assignable channels any 3 channels any 9 channels any chan.