Selected paper. Voltage Controlled Single Phase Matrix Converter with Low Harmonics

Transcription

1 Noraliza Hamzah 1,*, M. F. M. Zin 1 and M. N. Seroji 1, J. Electrical Systems Special issue AMPE2015 Selected paper Voltage Controlled Single Phase Matrix Converter with Low Harmonics JES Journal of Electrical Systems This paper presents a closed-loop voltage controlled Single Phase Matrix Converter (SPMC) with the characteristic of unity voltage conversion ratio and low THD that comply with the IEEE Standard and The voltage controlled SPMC has a similar output voltage as compared to the input voltage which is 12Vrms. The THD at the input and the output of the SPMC is also reduced to below than 5%. The SPMC is controlled by a feedback control that measures the output voltage that has to be compared with the set point, Vref. The propose method is based on the simulation done using MATLAB/Simulink and experimentally verified. Keywords: AC-AC Converter, Single Phase Matrix Converter (SPMC), Total Harmonics Distortion (THD), Voltage Conversion Ratio 1. Introduction The single phase single phase matrix converter was first introduced by Zuckerberger [1]. Other SPMC topology have also been studied by S.H. Hoseini [2] and Abdullah Khoei [3]. Further studies on conventional matrix converter is continued ever since, Venturini M. and Alesina A [4] have discovered the improvement of the AC-AC matrix converter voltage conversion ratio from 0.5 to [5]. Later, another study has been carried out with the implementation of AC-AC SPMC topology operating as a boost converter with 3.77 and 3.98 of voltage conversion ratio. The switching frequencies applied are 6 khz and 10 khz [6]. A boost inductor is attached at the input of the AC-AC SPMC performing the openedloop operation. The switching pattern that is applied in this paper is based on the switching strategy used in [7]. Besides, the switching strategy is different as compared to [6]. Nevertheless, the utility system and the electricity distribution might be affected with the application of matrix converter since it contributes high harmonic distortion. On the other hand, harmonics could lead to many other negative effects for example, malfunctioning of devices and machineries. Recent development has made the power conversion issue becoming important on the aspect of energy efficacy. Hence, the single phase matrix converter that is applied in this paper has been improved for the sake of energy saving. The previous works have shown that the application of conventional SPMC would reduce the output production. The voltage conversion ratio of the conventional SPMC discovered was 0.5 to [5]. Thus, an attempt to get better voltage conversion ratio is carried out in this paper. However, with the use of IGBTs to be implemented as SPMC, high total harmonic distortion would probably exist. Thus, the total harmonic distortion produced has to be reduced to manipulate the advantage of the SPMC as a power supply conditioner. As a solution, an implementation of closed-loop voltage control is applied to the AC-AC SPMC to yield unity voltage conversion ratio as well as produces low total harmonic distortion by using Matlab/Simulink is done in this paper. An experimental verification has been carried out to prove the practicality of the proposed work. * Corresponding author: Noraliza Hamzah, Faculty of Electrical Engineering, Universiti Teknologi MARA, 40450, Shah Alam, Selangor, Malaysia, noralizah@salam.uitm.edu.my, 1 Faculty of Electrical Engineering, Universiti Teknologi MARA, 40450, Shah Alam, Selangor, Malaysia

2 J. Electrical Systems Special issue AMPE Voltage Control SPMC There are four bidirectional switches connecting the single-phase input to the singlephase output in a conventional single phase matrix converter [1],[7]. The four ideal switches S1, S2, S3 and S4 have the capability of switching between states without any delays, blocking forward and reverse voltages (symmetrical devices) as well as conducting current in bidirectional condition [5],[8]. This proposed work presents the application of a closed-loop voltage-controlled SPMC circuit with attached passive filter. The close loop operation that is applied is based on the studies done in [9-12]. However, the studies in [9-12] are only applied to a rectifier applying the single phase matrix converter topology in order to compensate the supply current. In previous studies on AC-AC SPMC in [13-15], are focused on the closed-loop current control using an active current wave shaping technique to obtain a higher output voltage with low harmonics. Meanwhile in this proposed voltage-controlled SPMC, AC-AC single phase matrix converter topology is utilized by using the closed-loop voltage control operation to reduce the THD. Figure 1 shows the block sets of the main model of the proposed voltage controlled SPMC simulation using Matlab/ Simulink. Subsystems are used in the simulation in order to optimize the large model by breaking into smaller subsystem for ease in implementation. The proposed study consists of a single phase matrix converter block or subsystem, a closed-loop voltage control subsystem and also the signal separator that separates the signal for each of the switch involved. At the input side, a low pass RL filter, R 10Ω, L 0.1mH is connected, together with the closed-loop voltage control circuit in order to mitigate the ripple of the supply current. While at the output side, a low pass LC filter is utilized to help reducing the presence of ripples of the waveform produced. The LC filter parameters are L 100mH and C 100 µf and Rload 50Ω. The proposed work is applying the AC-AC SPMC switching strategy as in [13-15]. Figure1a shows the switching strategy for positive cycle where S1a and S2b are turned on while the S4a acts as the controlling switch synthesized by the SPWM. When the voltage supply is enabled, the input current flows from the input voltage supply to S1a since the switch is turned on simultaneously. Then, the current flows to the output load of 50Ω and continues to flow to the other switch involved; S4a. In order to maintain the simultaneous and continuous flow of the current, a free-wheeling path is created whenever S4a is turned off by turning on S2b. It is due to the IGBT collector current tailing-off which may create a short circuit with the next switch turned on. Then, after the current flow through S4a, it completes the cycle by returning to the supply voltage. Figure 1b shows the operation of the SPMC during negative cycle, the S1b and S2a switches are turned on while S4b acts as the controlling switch controlled by the SPWM signal produced by the closed-loop voltage control. Once the current completes the positive cycle, the current then flows backward from the supply voltage to S4b and flows through the output load. The current flows to S1b and a free-wheeling path is created by turning on S2a to avoid a short circuit produced by the IGBT collector current. Then, the current flows back to the supply voltage completing the whole cycle. The switching strategy involves in this work is shown in Table I. The output voltage from the output side of the single phase matrix converter is being controlled by comparing it with the sinusoidal reference voltage of 12Vrms as the set point 19

3 International Conference on Advanced Mechanics, Power and Energy 2015 (AMPE2015), 5-6 December 2015, Kuala Lumpur, Malaysia to generate the sinusoidal pulse width modulation (SPWM). The operation is done in the closed-loop voltage controller subsystem as shown in Fig.2. The sinusoidal pulse width modulation (SPWM) signal is generated by 6 khz of switching frequency. This switching strategy is applied as referred in [5] and [7]. The switching pattern for AC-AC SPMC as in [5] and [7] also has been utilized in [13-15] applied using a closed-loop current control method. As in previous studies, a controlled rectifier using SPMC topology incorporating active power filter were done to ensure that the supply current is continuous, sinusoidal and in phase with the voltage [9-12]. In classical rectifier with DC capacitor filter, a discontinuous supply current is drawn which contains high harmonic distortion level affecting the quality of the power supply system. Fig.1a) Switching Strategy (Positive Cycle) Fig.1b) Switching Strategy (Negative Cycle) Table I: The Switching Strategy Operation Switches Positive cycle (State 1) Negative cycle (State 2) S1a ON OFF S1b OFF ON S2a OFF ON S2b ON OFF S3a OFF OFF S3b OFF OFF S4a SPWM OFF S4b OFF SPWM 20

4 J. Electrical Systems Special issue AMPE2015 Fig.2: The Closed-loop Voltage Controller Fig.3: Simulation Configuration of Proposed Voltage-Controlled SPMC 3. Experimental Works The experimental works have been carried out as in Fig.4 in order to verify the simulation operation of the proposed work. It consists of a main configuration circuit of the SPMC topology which has four IGBT driver circuits mounted on PCB boards. Each driver circuit contains two IXGH40N120B2D1 IGBTs. The closed-loop voltage control operation is realized by adapting a programming installed in two peripheral integrated circuit (PIC) which are Chipkit Digilent Max32 and PIC16F84A. Those are for the signal processing and the generation of the sinusoidal pulse width modulation (SPWM). Besides that, a phase detector circuit, an absolute circuit, voltage transducer circuit, dc supply, function generator and transformers are used. The parameters that are applied in the experimental work similar to the simulation work done. The experiment is supplied by a 12Vrms with 50Hz frequency transformer. The 6 khz switching frequency is applied using a function generator. Then, it is compared with the output voltage of the SPMC circuit using the Chipkit Digilent Max32 microcontroller to produce the SPWM signal. The phase detector circuit is connected to the PIC16F84A to separate the different phase of the positive and negative cycle before it is connected to the switches involved. The output voltage is forced to follow the reference voltage that is set as 12Vrms. The results obtained in the 21

5 International Conference on Advanced Mechanics, Power and Energy 2015 (AMPE2015), 5-6 December 2015, Kuala Lumpur, Malaysia oscilloscope are recorded in an external storage and plotted in Matlab/Simulink in order to perform the analysis on the harmonics of the signals. Fig.4: Experimental Work Fig.5: Supply Voltage 4.0 Result and Discussion The results of the proposed voltage control and passive filter incorporated in SPMC is presented in this section. Both of the simulation and experimental SPMC operation are done using AC single phase supply of 12Vrms, Vp with 50Hz frequency as shown in Fig.5 and is loaded by 50Ω of R load. At the first stage, the simulation is carried out together with the closed-loop voltage control circuit and a low pass LC filter is connected at the output side. Then, the proposed voltage-controlled SPMC is implemented experimentally. The experimental procedure is carried out using the parameters similarly as in the simulation work. Fig.6a shows the input current waveform and its THD obtained in the simulation operation. The Input current is measured as 2.255A (peak) or A (rms). The THD is recorded as 2.72%. On the other hand, Fig.6b shows the input current of 2.292A (peak) or A (rms) and the THD of 3.75% obtained from the experimental work. The results shown in Fig.6 shows that the input current has a difference of A (rms) and the THD obtained in the experimental work is higher with 1.03%. Fig.7a shows the output current measured from the simulation as A (peak) or 0.240A (rms) with THD of 3.29%. Fig.7b shows the output current of A (peak) or A (rms) with 3.70% of its THD. Figure 8a shows the output voltage amplitude is recorded as 16.96V (peak) or Vrms and as for the experimental work in Fig.8b shows the output voltage of 16.95Vp or Vrms. The output voltage obtained in the simulation work is verified experimentally. The THD of the output voltage of the simulation is 3.29% while the THD obtained experimentally is 3.62%. From the result obtained in Figure 8, the voltage conversion ratio is calculated and tabulated in Table II. Table II shows that the voltage conversion ratio obtained from the simulation works is The result is verified experimentally with the voltage conversion ratio of Both figures calculated from the simulation and experiment are approaching 1.0. Hence, the voltage conversion ratio of the proposed work is unity. 22

6 J. Electrical Systems Special issue AMPE2015 Fig. 6: Input Current and THD a) Simulation b) Experimental Fig. 7 Output Current and THD a) Simulation b) Experimental Figure 8: Output Voltage and THD; a) Simulation, b) Experimental 23

7 International Conference on Advanced Mechanics, Power and Energy 2015 (AMPE2015), 5-6 December 2015, Kuala Lumpur, Malaysia 14 RMS Output Voltage vs Time 14 RMS Output Voltage vs Time R M S O u t p u t V o l t a g e ( v ) R M S O u t p u t V o l t a g e ( v ) Time (s) Time (s) Figure 9: RMS Output Voltage; a) Simulation, b) Experimental Table II: Voltage Conversion Ratio Simulation Experimental Voltage Conversion Ratio V o V i Vrms 12Vrms 16.96V 12V ~ 1.0 Voltage Conversion Ratio V o V i Vrms 12Vrms 16.95V 12V ~ Conclusion The proposed voltage-controlled SPMC operating as a direct AC converter has been realized. The results obtained in both of the simulation operation and its experimental verification prove that the implementation of the closed-loop voltage control and passive filter operation itself could improve the THD of the supply current and also the output voltage of the AC-AC SPMC. The total harmonic distortions obtained comply with the IEEE Standard [16] and [17] that requires the THD to be below 5%[9-10]. The proposed SPMC has proven to perform a unity voltage conversion ratio. Acknowledgment Financial support from Research Management Institute (RMI), Universiti Teknologi MARA (UiTM) Excellence Grant No: 600-RMI/ST/DANA 5/3/Dst(402/2011), is gratefully acknowledged for implementation of this project. Financial assistance from Ministry of Higher Education (MOHE) is also highly acknowledged. 24

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