Development of Boost Inverter Using Single Phase Matrix Converter Topology

This paper presents the development of boost inverter using a single phase matrix converter (SPMC). A new switching algorithm was developed to control the SPMC circuit topology to operate as a boost inverter. The pulse width modulation (PWM) technique was used to calculate the switching duty ratio to synthesize the output. As part of boost inverter operation, a safe-commutation switching algorithm has been applied to avoid the voltage and current spikes due to the effect of inductive loads. The simulation of the proposed converter was carried out in MATLAB/SIMULINK. Selected simulation are presented to verify the proposed operation.


Introduction
DC-AC converter (also known as inverter) is used to change the input DC voltage into the output AC voltage. The inverter produces an AC voltage from DC power sources and is important for powering electronics and electrical equipment rated at the AC mains voltage. Direct current is very beneficial in daily life, but batteries can generally only provide low voltage DC power [1][2]. Nowadays, there are numerous devices that need more power to function properly more than what DC can provide. Mostly, the devices are designed to run on the 120V or 230V AC power [3]. Based on this situation, the inverter is very functional to generate the AC power from the DC source so that the power can being supplied to the AC load. The circuit topology of an inverter are divided into two types, which are inverter based upon frequency and inverter based upon output waveforms [4]. The inverter based upon frequency are based on high frequency and low frequency while the inverter based upon output waveform can be divide into three groups which are square wave, modified sine wave and the pure sine wave [5]. A boost inverter is a DC-AC converter that step up the voltage level and at the same time, reducing the current level that flows to the load [6]. The boost inverter is used as a step up the generated output voltage, so that it is able to provide the higher power into an AC load without the use of heavy and bulky transformer, thus reduces the cost and power loss [7]. In this paper, a new boost inverter circuit topology is proposed to solve the problem faced by conventional boost inverters in terms of power density and power loss [8]. The potential application of the proposed boost inverter are in photovoltaic system, uninterruptible power supply and also as a standalone boost inverter. Fig. 1 and Fig. 2 show the SPMC circuit topology required four bi-directional switches [14][15][16][17].

Principle DC To AC Operation Using SPMC
S2b S1b S1a  The design parameters of the proposed converter are as tabulated in Table 1. The switching strategy implemented in SPMC for basic inverter operation is as shown in Table 2. Fig. 3 shows the switching algorithm for basic inverter operation. During positive cycle operation, a PWM signal is controlled by switches S1a and S4a whilst during the negative cycle operation, the switch S2a and S3a acts as controller of PWM signal [8]. Fig. 4(a) and Fig. 4(b) show the illustration of the principle operation of DC-AC converter for positive cycle and negative cycle respectively.

Inverter Operation with Safe-Commutation Strategy
The proposed safe-commutation strategy is used to solve the spikes problem due to the used of inductive load [18] without additional snubber circuit [12]. An arrangement of the switching mode of operation for the safe-commutation strategy is as tabulated in Table 3. The PWM is function to control the power by the switching scheme with a fixed switching frequency. In this operation, three switches were used for every cycle as each switch will operates either as commutation switch or power controller. Fig. 5 shows the switching algorithm for inverter operation with safecommutation strategy. During the positive half cycle operation, the switch S1a is controlled by the PWM while switches S3b and S4a operated as commutation switches. During the negative half cycle operation, the switch S2a is controlled by the PWM signal. Then, both switches S3a and S4b were operated as commutation switches.

Boost DC to AC Operation
The operation of the boost inverter was designed to produce the output voltage higher than input. Thus, an additional inductor is used as an energy storage before this energy transferred to the load. Fig. 6 shows the switching algorithm for boost inverter operation. The proposed of switching algorithm for boost inverter is as shown in Table 4. The circuit operation for boost inverter using SPMC is proposed as below [11]: [1] Mode 1 (positive half cycle): The current from the positive DC supply will flow through switches S1a and S3a. Thus, the inductor, L will be charged. The switch S3a is controlled by PWM signals shown in Fig. 7(a). [2] Mode 2 (positive half cycle): The current flows through S1a and S4a. Hence, energy from the inductor will be transferred to the load as shown in Fig. 7(b). [3] Mode 3 (negative half cycle): The current flows through S1a and S4a. During this mode operation, the inductor, L will be charged. The switch S4a is controlled by PWM signal as shown in Fig. 7(c). [4] Mode 4 (negative half cycle): The current flows through S2a and S3a. During this mode operation, energy from the inductor will be transferred to the output as illustrated in Fig. 7(d).

Computer Simulation Model
The computer simulation model using MATLAB/Simulink was developed to investigate the operation of boost inverter circuit topology. In the main circuit of SPMC consists of eight IGBTs arranged in the common emitter configuration [16]. The boost inverter were operated with 12VDC supply and resistive and inductive load, 50Ohm and 10mH respectively including 10mH of additional boost inductor. The value of modulation index was fixed to 0.5 at 2kHz of switching frequency [16]. Fig. 8 to 12 show the computer simulation model of the inverter using SPMC. In order to produce clarity model of the inverter using SPMC, the subsystem is used to reduce the complexities of the main circuit model [13]. Fig. 9 shows the circuit topology of the SPMC. It consists four bidirectional switches. Fig. 10 shows the bidirectional switches connected with common emitter configuration. Fig. 11 and Fig. 12 show the model of controller circuit implemented for the operation of DC-AC converter with safe commutation strategy.

Principle DC-AC Operation with a Resistive Load
The simulation result of input voltage for basic inverter operation is as shown in Fig. 13. The waveform shows that the input source is from DC source which is 12V DC . After the operation of inverter using SPMC topology being applied, the results of the output voltage and current produced is in AC forms. Fig. 14 shows the simulation result of the output voltage. It is clearly show that the input voltage is in a DC form, whilst the output voltage is in an AC forms, hence proved the inverter operation.  Fig. 15 and Fig. 16 show the results for the operation of an inverter using SPMC without safe-commutation technique. The spikes occurs in the output voltage waveform and can affect the efficiency of electrical equipment [19]. The maximum voltage spikes that has been recorded from the simulation is about 12.38V. The result shows due to the presence of an inductive load, induces the voltage spikes. The results show that the voltage spikes has been successfully eliminated and prove that the proposed safe-commutation algorithm is affected.

Boost DC-AC Operation with Safe-Commutation Strategy
The results of boost inverter operation are shown in Fig. 19 and Fig. 20. From the simulation result, the output voltage increase from 12V DC to the 18.72V AC . The value of modulation index have been varied to study the effect on the output voltage. Table 5 shows the maximum output voltage can be produced with the maximum value of modulation index, while the value of inductance is fixed as 10mH. Fig. 21 shows the results of modulation index versus maximum output voltage. It is clearly shows that the output voltage increases by the increase of modulation index.

Conclusion
For the inverter operation without safe-commutation strategy, the result illustrates the effect of inductive load to the output waveform when the spikes occurs. While, with the proposed safecommutation strategy, the spikes was successfully eliminated and prove that the proposed safe-commutation algorithm is affected. For the boost inverter operation, the proposed new switching algorithm is successful when the result shows that the output voltage is greater than the input. The proposed boost inverter operation can simplify the conventional power electronics converter that use the transformer in order to step-up the AC voltage level, resulting in improved the power density, hence the reduction of the total power loss.