A New Single-Phase Controlled Rectifier Using - IEEE Xplore

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Abstract :- This paper presents the applications of single-phase matrix converter (SPMC) as an AC-DC controlled rectifier. For basic operation the multiple-PWM ...
First International Power and Energy Coference PECon 2006 November 28-29, 2006, Putrajaya, Malaysia

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A New Single-Phase Controlled Rectifier Using Single-Phase Matrix Converter R. Baharom, A.S. A. Hasim, M. K. Hamzah, Member, IEEE, M. F. Omar Abstract :- This paper presents the applications of single-phase matrix converter (SPMC) as an AC-DC controlled rectifier. For basic operation the multiple-PWM technique was used to calculate the switch duty ratio to synthesize the output. Safe commutation strategy was developed to avoid voltage spikes due to inductive load. Active current wave-shaping technique are also proposed to ensure that the supply current waveform is continuous, sinusoidal and in phase with the supply voltage. This approach utilizes boost rectifier technique for compensation. Selected experimental results are presented to verify the concept. Keywords: Pulse Width Modulation, Matrix Converter, Controlled Rectifier, Insulated Gate Bipolar Transistor

1. INTRODUCTION Many theoretical studies have been investigated on Matrix Converter (MC) but have found limited practical applications in power electronics. Nevertheless, MC has been described to offer an "all silicon" solution for AC-AC conversion, removing the need for reactive energy storage components used in conventional rectifier-inverter based system [1] and hence an attractive alternative converter. The topology was first proposed by Gyugyi [2] in 1976. Previous reported works mainly dealt with three-phase circuit topologies [3-5]. The Single-phase matrix converter (SPMC) was first realised by Zuckerberger [6] which was followed by subsequent works on direct AC-AC single-phase converter [7] and DC chopper [8] but none on rectifier operation.

In this work the SPMC topology are presented to operate as a controlled rectifier by suitable switching schemes, where IGBTs are used for the main power switching devices. Apart from converting AC input supply to a DC type, investigations are also carried out to maintain a unity power factor operation of the supply. Inherent commutation problems that lead to switching spikes are also discussed with safe commutation algorithm being proposed. Results of simulations and selected experimental results are also presented to verify that the proposed technique is feasible. Simple resistive load is initially used to reduce the complexities of the circuit. This is followed by investigations on the introduction of simple inductive load. Satisfactory agreement between simulated and laboratory results was observed. Further investigations are then carried-out to implement rectifier boost technique to ensure that the supply current waveform is continuous, sinusoidal and in phase with the supply voltage.

2. SPMC The SPMC requires 4 bi-directional switches as shown in Fig. 1, capable of blocking voltage and conducting current in both directions [9]. Unfortunately there is no discrete semiconductor device currently that could fulfil the needs [10, 11] and hence the use of common emitter anti-parallel IGBT, diode pair as shown in Fig. 2. The SPMC has four switching state is illustrated by Fig. 3 to 6.

Sla

S2b

Slb DIODE

Current Flow S4b

Figure 1: AC-AC single-phase matrix converter topology Sla

Sib

S3b

Load S3a S4a

Vi(f) ~

S2b

Figure 3: State 1 AC Input (Positive cycle)

1-4244-0273-5/06/$20.00 C2006 IEEE

Current

DIODE

IGBT

Flow

Figure 2: Bi-directional switch

S2a Vi(t)

S4b

Figure 4: State 2 AC Input (Negative Cycle)

454

S2a

S2a Vi()

S4b

iS4b

Figure 6: State 4 AC Input (Negative Cycle)

Figure 5: State 3 AC Input (Positive Cycle)

3. CONTROLLED RECTIFIER The classical rectifier normally uses a bridge-diode in implementation without affording any control function. The simplicity makes it universal for rectification of low-power application and some common high-power applications but are major contributors to power factor and current distortion problems. Sensitive equipments are less tolerable to nuisances caused by harmonics penetration into the supply system. Associated problems such as poor overall power factor, heating effects, device malfunction and destruction of other equipment caused by nonlinear loads such as bridge diode rectifier with capacitor filter have been recorded [12]. Therefore the demand for high quality power supply has shown an upward increase in recent years. This trend reflects in the increase use of provision of unity supply power factor [13]. To implement SPMC as a controlled rectifier, only State 1 and 4 described in the previous section are used, making State 2 and State 3 redundant. However, these redundant switches could be used to add features to the controlled rectifier operation that may include, amongst others; safecommutation and unity power factor operation particularly when RL load are used. Figure 7 and 8 illustrates operation that includes safe commutation arrangements as indicated by the dotted-line and will be discussed in subsequent section.

4. COMMUTATION PROBLEM The use of Sinusoidal Pulse Width Modulation SPWM as in Fig.9 as the switching algorithm in this converter, results with possible reversal current if inductive loads are used, during switch turn-off. Detailed treatment on safecommutation problem can be obtained in reference [14] restated here briefly for completeness. Theoretically the switching sequence in the SPMC must be instantaneous and simultaneous; unfortunately impossible for practical realization due to the turn-off IGBT

characteristic, where the tailing-off of the collector current will create a short circuit with the next switch turn-on. This problem occurs when inductive loads are used. A change in current due to PWM switching will result in current and voltage spikes being generated resulting in the occurrence of a dual situation. First current spikes will be generated in the short-circuit path and secondly voltage spikes will be induced as a result of change in current direction across the inductance. Both will destroy the switches in use due to stress. A systematic switching sequence is required that allows for the energy flowing in the IGBTs to decay. In conventional controlled rectifier, free-wheeling diodes are used for this purpose. In SPMC this does not exist, hence the need to develop a switching sequence to allow energy dissipation. This is to protect the converter from being damaged as a result of voltage and current spikes as described.

5. UNITY POWER FACTOR OPERATION Investigations in the rectifier operation are generalised for any types of DC load filtered by a capacitor as illustrated in Figures 12 & 13 with further details from Figures 14 -16, where the dotted line represents current wave-shaping

routes.

Classical rectifier with DC capacitor filter has a setback in that it draws discontinuous supply current waveform with high harmonics content. As a result it contributes to high total harmonic distortion (THD) level and low total effective supply power factor affecting the quality of the power supply system. Traditionally, the rectifier circuit incorporates supply current wave shaping technique to provide for unity power factor operation [15]. This socalled boost rectifier unit must have the blocking diode to function properly during the stored energy transfer operation. However as shown in Fig.13 the need for the blocking diode is eliminated due to controllable switching function inherent in the SPMC.

455

IL

Sla

S2b

1S3i

S4b

AC

AC

S3

L

I

Figure 7: Positive Cycle with Commutation (State 1)

Figure 8 : Negative Cycle with Commutation (State 3)

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AC INPUT

ASYNTHESIZED a

T

T

I

L

"

1-l 1 ILl

0

b

S2b

} SEQUENCE

COMMUTATION

SWITCH

S3b & S4aF Os

20ms

40ms

60ms

80ms

Table 1: Switching State

td_

S4a

state 1

S2b

state 3

Sla&&SS2b

1

Figure 1 0: Switching Pattern Commutation Strategy

Figure 9: PWM waveform _td