Development of Space Vector Pulse Width Modulation Algorithm for Voltage Source Inverter
Using dsPIC Controller 30F4011
S. Allirani1 and V. B. Thurai Raaj2
1Department of EEE, Sri Ramakrishna Engineering
College,Coimbatore - 641022, Tamilnadu, India.
2Department of EEE, Madanapalle Institute of Technology and
Science Madanapalle - 641022, AndraPradash, India.
Abstract
The Main focus of this paper is to design and develop a highly effective Space Vector Modulation (SVM) algorithmic rule by using dsPIC Microcontroller. SVM methodology is reduces the harmonic distortion and it terrifically path to implement a control circuitry for a drive. This Practice has found its applications recently in voltage source inverters, AC/DC converters, resonant converter, multilevel converters, matrix converters etc. This paper discusses the implementation of this SVM technique using low cost, versatile dsPIC controller 30F4011 for VSI along with experimental results.
Keywords Sinusoidal Pulse Width Modulation, Space vector modulation, Voltage source inverter, dsPIC controller.
1. INTRODUCTION
Initially, sinusoidal PWM was a one of the most familiar technique for AC
drives control applications [9]. In this method a triangular wave acts as a carrier
signal, sine wave act as a reference signal the points of intersection determine the
switching instants of the power devices constituting the inverter. This method was
found to suffer from the following disadvantages:
1. It is not able to make full use of DC bus voltage of the inverter and
2. This method produces relatively high harmonic distortion in the inverter
outputs.
In comparison, Space Vector PWM (SVPWM) is a sophisticated/multifaceted
technique capable of generating higher sine wave voltage from the inverter for given
DC bus voltage.
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SVM offers several additional advantages like, less harmonic distortion when
compared to SPWM. Reduced switching losses, which will become significant for
inverters of high power rating. This technique is extendable to multilevel inverters
by the addition of switching states. It is compatible for digital implementation
In papers [1] and [2], the basic principle of SVM was presented and realized in
MATLAB/ Simulink environment. In paper [3], a new SVM technique was used to
control PWM rectifier to achieve unity power factor and for reducing the harmonic
currents of non linear loads. The proposed control technique has the advantage of
reducing switching frequency and losses by applying the zero voltage vectors [3]. The
control structure was developed and implemented on a DSP controller,
TMS320LF2407.
In paper [4], space-vector based Pulse Width Modulation (PWM) strategy was
discussed highlighting selective harmonic elimination. In paper [5], SVM was shown
to reduce the inverter losses. Several modulation techniques such as Sinus PWM
(SPWM), Square Wave PWM, Carrier Based PWM and Space Vector PWM
(SVPWM) techniques were implemented using dsPIC30F2010 controller (a DSP
controller developed for motor control applications) in paper [6] and it was shown
experimentally, SVPWM produce minimum current harmonics. SVM technique for
multilevel inverter was discussed in [7]. Simulation results of SVM controlled IM for
both open loop and closed loop conditions are given in paper [8], [10].
This paper proposes a simple and compact controller, dsPIC30F4011, suitable for IM
drive. The voltage source inverter is designed and implemented using power
MOSFETs with sophisticated driver IC IR240. The SVPWM algorithm is
implemented in dsPIC controller 30F4011 which is featured with specific motor
control PWM module.
The paper is organized as follows: Section II describes SVM algorithm and section III
presents digital signal controller dsPIC30F4011. Section IV discusses the
experimental setup and results. The paper is concluded in section V.
2. SPACE VECTOR PULSE WIDTH
MODULATION
Induction motors have many advantages like simple construction, reliability,
ruggedness and low cost. Initially DC drives are popular in the field of adjustable
speed drives due to their better dynamic performance and simple control techniques.
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Fig. 1. VSI fed Induction Motor Drive
After the arrival of powerful switching components and efficient control
techniques, IM drives have gained popularity. Mostly, in IM drives, IM is fed by
voltage source inverter controlled by SVM technique.
Fig.1 shows VSI fed IM drive controlled with SVM technique. A VSI consists of
six power switches in three arms. Each arms have two switches one at top another at
lower, the top side switches are S1, S3 & S5 lower side switches are S4, S6 & S2 to
drive three phase IM.
Fig.2. Eight switching state topologies of three phase inverter.
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Fig.3. Voltage vectors and sectors
The on and off states of upper arm switches S1, S3, S5 can be used to
determine the output voltage. The relationship between the switching variable
corresponding to upper arm switches [a b c]t as in fig. 2 and the line to line voltage
vector [Vab Vbc Vca]t is given by equation [1]
Table I Sector selection table
Voltage
Vectors
Switching
Vectors
Line to neutral
Voltage Line to Line Voltage
a b c Van Vbn Vcn Vab Vbc Vca
V0 0 0 0 0 0 0 0 0 0
V1 1 0 0 2/3Vdc -1/3
Vdc
-1/3
Vdc Vdc 0 - Vdc
V2 1 1 0 1/3
Vdc
1/3
Vdc
-2/3
Vdc 0 Vdc - Vdc
V3 0 1 0 -1/3
Vdc
2/3
Vdc
-1/3
Vdc - Vdc Vdc 0
V4 0 1 1 -2/3
Vdc 1/3Vdc
1/3
Vdc - Vdc 0 Vdc
V5 0 0 1 -1/3
Vdc
-1/3
Vdc
2/3
Vdc 0 - Vdc Vdc
V6 1 0 1 1/3
Vdc
-2/3
Vdc
1/3
Vdc Vdc - Vdc 0
V7 1 1 1 0 0 0 0 0 0
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[
] = [
] [ ] [1]
Similarly, the relationship between switching variable [a b c]t and
phase voltages can be expressed as in equation [2]
[
] =
[
] [ ] [2]
These line to line voltages and line to neutral voltages in terms of
DC link voltage Vdc are given in Table I.
To implement the SVPWM, the voltage equations in the abc reference
frame can be transformed into stationary dq reference frame as in equation [3]
[
] =
[
] [
] [3]
(
) [4]
‖ ‖ √
[5]
The conduction time for the upper and lower arms are calculated by
using the adjoining voltage space vectors and two null vectors. Assume the
reference voltage space vector Vref is located in sector 1 as shown in fig. 4.
Then the switching time duration at sector 1 is calculated as in equations (6) &
(7)
Fig.4. Expanded view of sector 1
∫ ∫ ∫ ∫
[6]
[7]
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Similarly for the remaining five sectors the equations for switching time
calculations are given in table II. Fig.5 presents the switching patterns of S1, S3,
and S5 in sector 1. The reference voltage space vector Vref is assumed to be
located 7at null vector V0 (000) at T0 time and then switched to first space vector
V1 (100). It is held at V1 for time T1, then the reference voltage vector switched to
V2 (110) and remains there for T2 time. Finally, the reference voltage vector
moved to V7 (111).
Table II Equations for switching time
At this time all upper arms are turned on and all lower arms are turned off.
Fig.5. Switching state timing diagram
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3. dsPIC CONTROLLER The dsPIC30F motor control family is specifically designed to control the motor.
dsPICs are processing the data at much higher rate than the normal PIC
controllers. It has motor control pulse width modulation (MCPWM) module and
high speed analog to digital converters. The MCPWM modulator has eight output
pins and six PWM generators. The DSP engine of dsPIC30F4011 supports the
necessary mathematical operations. It has 10 bit, 1 MSPS analog to digital
converter. Fig.6 shows schmatic diagram of dsPIC30F4011 controller [11].
Fig.6. Schmatic of dsPIC 30F4011 controller
The controller is inbuilt with DSP Engine which is featured with [11]
Dual data fetch
Accumulator write –back for DSP operations
Modulo and Bit-Reversed Addressing modes
Two, 40-bit wide accumulators with optional saturation logic
All DSP instructions are single cycle
17-bit × 17-bit single-cycle hardware fractional/integer multiplier
The controller has specific Motor Control PWM Module whose features are [11]
6 PWM output channels
Complementary or independent output modes
Edge and center aligned modes
3 duty cycle generators
Dedicated time base
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Programmable output polarity
Dead-time control for Complementary mode
Manual output control
Trigger for A/D conversions
4. EXPERIMENTAL SET UP AND
RESULTS The block diagram of experimental set up of the proposed digital signal controller
based IM drive is shown in fig.7. The IM is fed by MOSFET based VSI. The switching
pulses for inverter switches are generated using digital signal controller
dsPIC30F4011.
Fig.7. Block diagram of dsPIC controller based IM drive
Fig. 8 (a) dsPIC Controller section
Fig. 8 (b) Inverter Section
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The PWM pulses are given to MOSFETs through MOFET driver IC IR240. The duty
cycle is controlled using dsPIC controller. Fig. 8(a) and 8(b) show the photographs of
controller section and three phase inverter section, respectively.
4.1. Results and Discussions Fig. 9 shows switching pulses obtained in SVM based inverter with dc link voltage of
400 V, fundamental frequency of 50 Hz and PWM carrier frequency of 20 kHz.
Fig. 9(a) MOSFET driver output signal Fig. 9(b) Gate pulses generated for Phase
A (S1 &S4)
Fig. 9(c) Gate pulses generated for
Phase B (S5 & S6)
Fig. 9(d) Gate pulses generated for
Phase C (S3 & S2)
Fig. 9(a) shows the MOSFET driver output signal of 12V, raised from 5V. As
the magnitude of 5V generated by controller is not sufficient to drive the MOSFET in
VSI, the sophisticated MOSFET driver IC IRF240 is used to increase the voltage
level from 5V to 12V. Fig. 9(b) to Fig. 9(d) show the gate pulses applied to each of the
three arms of three phase bridge inverter.
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Fig. 9 (e) Switching pulses for
the switches (S1 & S3)
Fig. 9(f) Switching pulses for the
switches
(S3 & S5)
Fig. 9(g) Switching pulses for the
switches (S5 & S1)
Fig. 9 (h) Dead time between upper
and lower switches of same leg
Fig. 9(i) PWM carrier frequency of
20 kHz
Fig. 9(j) Inverter output voltage
(Phase voltage)
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The gate pulses of switches in conduction are shown in figs 9(e) to 9(g). Fig.
9(h) shows that there is sufficient time delay between off time and on time of the
switches on the same leg in order to avoid dead short of the source. Fig. 9(i) shows
the PWM carrier signal of frequency 20 kHz generated using dsPIC controller and
fig. 9(j) represents the output phase voltage of VSI.
5. CONCLUSION This paper presented a design and implementation of the space vector
modulation algorithm for calculating switching times in three phase voltage source
inverter. This SVM algorithm was implemented using a dsPIC controller
dsPIC30F4011. The voltage source inverter was implemented using MOSFET
IRF840 which is fed by sophisticated MOSFET driver IC IR240. The experimental
results proved that this compact and efficient algorithm allowing high switching
rates with relatively low cost dsPIC controllers.
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[7]. Wenxi Yao, Haibing Hu, Zhengyu Lu, “Comparisons of space vector
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