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ABSTRACT: This paper presents a novel approach to the implementation of the
space vector modulation (SVM). The proposed technique takes advantage of
a modified Kohonen's competitive layer to calculate the on duration of
the adjacent switching state vectors. By using this technique: (a) the
hardware and software complexity of the system is reduced; (b) the
maximum attainable switching frequency and thus the bandwidth of the
control system is increased; and (c) the waveform degradation and
parasitic harmonics resulting from inaccurate calculations are avoided.
The proposed method is compared to the conventional implementations of
SVM techniques in terms of hardware/software requirements, switching
frequency, computation time, and harmonic spectra. The method is applied
to a DSP controlled 3 kVA unit (voltage source inverter) and
experimental results verify the validity of theoretical and simulation
results
Applied Power Electronics Conference and Exposition, 1997. APEC '97 Conference Proceedings 1997., Twelfth Annual; 03/1997
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ABSTRACT: Space vector modulation (SVM) in three-phase voltage source and
current source converters has become the preferred PWM method for
digital implementations. This paper presents an alternative SVM
implementation that is based on a neural network structure. The
technique reduces hardware and software complexity, and computation
time, and increases the accuracy of the positioning of the switching
instants. The technique exhibits the following features: (a) possibility
of higher switching frequencies, (b) higher bandwidth of the control
loops, (c) reduced hardware and software, and (d) reduction of parasitic
harmonics in all PWM waveforms. The proposed method is compared to
conventional implementations of SVM techniques in terms of
hardware/software requirements, switching frequencies, harmonic spectra,
and computation times. The method is applied to a 2 kVA unit and
experimental results confirm theoretical and simulation results
Industry Applications Conference, 1996. Thirty-First IAS Annual Meeting, IAS '96., Conference Record of the 1996 IEEE; 11/1996
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ABSTRACT: Current source converters are usually modulated using off-line
pattern generators, due to the complex requirements of the switch gating
signals. However, on-line patterns (carrier and space vector based)
offer a number of control advantages, such as: tracking error
minimization, zero steady state error, and potential implementation of
enhanced control strategies. With the ability of microprocessors and
DSP, the space vector modulation offers an interesting alternative to
standard carrier based modulation techniques. The paper addresses
practical issues such as switching frequency minimization, parasitic
harmonic reduction, and delay compensation. A unity power factor buck
rectifier is simulated to validate the proposed algorithm
Electrical and Computer Engineering, 1995. Canadian Conference on; 10/1995
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ABSTRACT: Current source inverter-based uninterruptible power supplies (UPS)
require sensing of two or more output voltages and synchronization with
the AC input voltage in addition to the DC voltage sensors used for
protection purposes. This paper proposes a DSP-based space vector
control scheme that requires only information provided by the DC bus
sensors. Output voltage estimation is based on AC line voltage
reconstruction by means of information available on the DC bus and
knowledge of the PWM pattern. In addition to providing low output
voltage harmonic distortion, the system minimizes the component count
and therefore increases ruggedness. The paper presents the DSP
algorithms required for the operation of the system, and experimental
results on a 208 V, 60 Hz, 5 kVA prototype inverter
Industrial Electronics, Control and Instrumentation, 1994. IECON '94., 20th International Conference on; 10/1994
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ABSTRACT: With the advent of powerful circuit simulation tools such as
Spice-based simulators, the simulation of a power converter system has
been reduced to the generation of an adequate electric circuit model of
the system. However, this approach often leads to large execution times
and uncertain results associated with convergence problems. Alternatives
are switched-circuit simulators, where the switches are idealized by
assuming zero on-resistance, infinite off-resistance and instantaneous
switching. Though these simulators overcome the long execution times and
convergence problems, both Spice-based and switched-circuit simulators
have execution times proportional to the number of power switches.
Furthermore, modern control techniques are difficult to implement. A
practical and efficient solution that allows use of the discrete state
approach is available today in the form of powerful and user friendly
high level language compilers, such as C and BASIC. This paper
illustrates the clear advantages of combining this approach with BASIC
to simulate power converter systems. Moreover, the use of discrete
states, instead of ideal switches, to model static power converters
reduces execution time and introduces high flexibility in implementing
complex PWM pattern generation algorithms, such as space vector or
predictive control techniques, regardless of the power and control
circuit structure and/or complexity
Computers in Power Electronics, 1994., IEEE 4th Workshop on; 09/1994
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ABSTRACT: Shunt type static VAr compensators are an effective means of
increasing the transmission capability of power systems and of
increasing the power factor of industrial loads. This paper presents an
alternative in the form of a series-connected transformer coupled PWM
inverter. The scheme consists of a current source inverter connected to
a self controlled DC bus. It presents the following features: (a)
instantaneous series injected voltage control through online modulation
index control; and (b) steady state modulation index control to a value
near unity. The first feature results in fast dynamic response, while
the second feature ensures that the harmonic distortion of the injected
voltage under steady state operation is kept to a minimum, independently
of the operating conditions. Operation of the compensator and of the two
loop control scheme are presented. Simulation and experimental results
on a prototype unit confirm the feasibility of the proposed structure
Power Electronics Specialists Conference, PESC '94 Record., 25th Annual IEEE; 07/1994
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ABSTRACT: AC adjustable speed drives employ mostly a voltage source inverter
(VSI) to control the motor armature, despite the inherent advantages of
the current source inverter (CSI) topology. This is partly due to the
current source nature of the topology and the complexity of the controls
required, the voltage source being a more universal power supply and
being easier to control. This paper demonstrates that a
voltage-regulated CSI offers the same features as its VSI counterpart,
together with the added advantages inherent in the CSI topology, namely
suppression of high dv/dt across motor windings, built-in short-circuit
protection, natural power reversibility and high reliability. A constant
V/f scalar speed controller is implemented in this paper to illustrate
the high steady state and dynamic performances offered by the topology.
Its flexibility also allows for increased system efficiency and output
voltage quality. Simulation results are given for a 5 kW induction motor
drive
Applied Power Electronics Conference and Exposition, 1994. APEC '94. Conference Proceedings 1994., Ninth Annual; 03/1994
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ABSTRACT: Force commutated current source rectifiers are mostly controlled
using PWM patterns generated offline. This procedure simplifies the
inclusion of special requirements associated with unidirectional power
switches. This paper shows that online techniques developed for voltage
source inverters can be readily adapted to current source rectifiers,
thus taking advantage of features such as reduced switching frequency
and increased gain. Implementation and performance of the proposed
carrier-based and space vector techniques are presented. Finally, the
proposed carrier-based techniques are verified an a 5 kVA experimental
unit
Industrial Electronics, Control, and Instrumentation, 1993. Proceedings of the IECON '93., International Conference on; 12/1993
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ABSTRACT: PWM current source inverters (CSI's) are usually operated with a fixed pattern and fed from a thyristor rectifier controlled current source. Transient response of the output current is slow and input power factor is low. This paper proposes a symmetrical PWM CSI topology with a two loop control structure. A voltage regulated current source inverter ensures instantaneous output voltage control through on-line PWM current generation. The PWM rectifier maintains unity displacement power factor, thus improving the power factor. Furthermore, it maintains the DC link current to a value such that the inverter modulation index remains high at all times; this results in reduced voltage harmonic distortion at the output. The topology is particularly well suited for fast fluctuating loads. It also has regenerative capabilities, inherent short circuit protection and increased reliability. The paper describes the power circuit topology and the two control loop structure and presents controller design considerations and procedures. The complete topology is implemented on a 2 kVA unit and experimental results confirm theoretical and simulation results.
Industrial Electronics, 1993. Conference Proceedings, ISIE'93 - Budapest., IEEE International Symposium on; 02/1993
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ABSTRACT: PWM rectifiers and current source inverters (CSI's) are usually gated using optimized patterns stored in EPROMs. Patterns are therefore mostly of fixed modulation index, since variable modulation index requires storing patterns for a finite numbr of indices. Furthermore, the modulation index can only be changed once per cycle, thus reducing the dynamic response of the system. This paper proposes a technique of generating gating patterns online for CSI topologies based on carrier PWM techniques (PWM rectifiers or inverters). The proposed technique is designed and implemented for the standard three-phase six-switch configuration. It delivers the appropriate gating signals for all switching patterns and modulation indices including overmodulation. It is therefore possible to extend the concept of duality in the power circuit topology between VSI's and CSI's to carrier PWM modulation techniques. In the proposed approach, the requirements imposed on gating signals are satisfied by the appropriate combinations of single phase switching patterns and the introduction of the required complementary and overlap pulses. Implementation in a mixed analog/digital circuit is described and experimental results obtained on a 2 kVA voltage-controlled current source inverter unit are given.
Industrial Electronics, 1993. Conference Proceedings, ISIE'93 - Budapest., IEEE International Symposium on; 02/1993
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ABSTRACT: The authors present a fully functional voltage controlled current
source inverter (VC-CSI) three-phase inverter that can closely track a
given voltage reference signal and also provide various performance
improvements. The adaptive SPWM control method has been used to force
the output voltage to track the respective sinusoidal reference signals.
The combination yields a general-purpose three-phase balanced voltage
supply with precise frequency and voltage amplitude control. Moreover,
it has the inherent regeneration and short circuit protection features
associated with current source inverters. Key analysis/design results
and performance features are verified on a 2 kVA experimental
inverter-load prototype system
Industrial Electronics, Control, Instrumentation, and Automation, 1992. Power Electronics and Motion Control., Proceedings of the 1992 International Conference on; 12/1992
