In this paper, a novel single-phase unified power quality controller (UPQC) is proposed, which can compensate for various power quality problems from grid side and load side. Firstly, the paper introduces the topological structure and basic working principle of the new single-phase unified power quality controller, and then introduces the topological structure and voltage stability control algorithm of the load side and the grid side in detail. This paper uses MATLAB/Simulink to model and simulate the system. The results show that the proposed topology and the corresponding control algorithm are effective.
In this paper, a new single-phase UPQC topology is proposed, which does not need transformer. It has the advantages of simple structure and low cost. The corresponding control algorithm is also proposed for this topology. Firstly, the paper introduces the topology and basic working principle of the new single-phase UPQC. Then, it introduces the new single-phase UPQC load side’s topology and corresponding control algorithm in detail. Then, it introduces the structure and control algorithm of the new single-phase UPQC grid side, thermostatic element and carries out modeling and Simulation on the load side and the grid side respectively. The results show that the proposed topology combined with the corresponding control algorithm has better compensation characteristics and can simultaneously solve the typical power quality problems in the distribution system. In the topology shown in Fig.
1, the DC side of two half-bridge inverters is connected by common bus capacitors, and the grid side is connected to the grid side through input filters, which are mainly used to compensate for current quality problems. In the load side, the inverters and switch K1 work in coordination, and the output filters are connected to the load side to modulate voltage. Typical voltage and power quality problems such as sag and sag. Operating mode 1: Input is rated voltage (pure sine wave), K1 is closed, inverter bridge K2, K3 is disconnected, the input directly supplies power to the load, and the output is pure sine wave. Mode 2: When the input voltage is lower than the rated voltage, the K3 tube of the inverting bridge is disconnected in positive half cycle, the K2 tube and K1 complementary opening, and the K2 tube of the inverting bridge is disconnected in negative half cycle, and the K3 tube and K1 complementary opening. Mode 3: When the input voltage is higher than the rated voltage, the K2 tube of the inverting bridge is disconnected, the K3 tube and the K1 complementary opening, and the K3 tube of the inverting bridge is disconnected and the K2 tube and the K1 complementary opening at the negative half cycle. This part has the functions of eliminating voltage sag and rise.
The modulation waveforms of the load part inverters and the switch K1 can be obtained from the analysis of the above working principle as shown in Figure 3. In a period, the fundamental component of the grid voltage is obtained by filtering the sum of the actual grid voltage and the output voltage of the inverter. The duty cycle of switch K1 is D, because the inverters and K1 are complementary, then the duty cycle of the inverters is 1-D. The fundamental wave of the coordinated modulation of K1 and inverters should be equal to the standard sinusoidal voltage. The waveform of the coordinated modulation of switch K1 and inverters is shown in Figure 3. After the duty cycle D of the switch K1 is obtained, the PWM wave of the switch K1 can be obtained by comparing with the triangular wave, and the PWM wave of the inverter can be obtained by inversing the PWM wave of the switch K1. From this, the control block diagram of the load side can be obtained as shown in Figure 4. According to the control principle block diagram, the control principle diagram of the load side is obtained as shown in Fig. 5. The working principle of the grid side part is shown in Fig.
6 (b). Active power filter detects the harmonic component of the load current through the detection circuit and uses it as an instruction signal. The compensation current IC generated by the compensation current generating circuit is equal to the harmonic component in the load current, and the direction is opposite, so the two cancel each other, making the power supply electricity.
There is only fundamental wave in the current, but no harmonic [5-8]. For the new single-phase UPQC grid side, the paper first uses the fundamental active component method of load current (detection principle as shown in Figure 7), extracts the harmonic current as an instruction signal, and then controls the output compensation signal of the inverter through hysteresis comparison control (as shown in Figure 8). A new single-phase UPQC topology is proposed in this paper. It does not need transformer. A switch is added to the main circuit. It has simple structure and low cost.
According to the proposed topology, the corresponding control algorithm is also proposed in this paper. Through the simulation of the load side of the new single-phase UPQC, the results show that the proposed topology and the corresponding control algorithm have good modulation effect for the voltage sag of the power grid. As expected, the proposed topology and control algorithm are effective. The simulation of the new single-phase UPQC power grid side proves the validity of the proposed topology and control algorithm. The grid side can well compensate for typical current quality problems.