Zhao Qinglin

A Single-Phase Grid-Connected Inverter System With Zero Steady-State Error

A single-phase grid-connected inverter system with a novel current control strategy is presented in this paper. The controller consists of a proportional regulator and a new type of resonant regulator. Compared with traditional PI control methods, the P+resonant (PR) control can introduce an infinite gain at the fundamental frequency and hence can achieve zero steady-state error. A more practical quasi-PR controller is used based on theoretical analysis. In this paper, a step by step procedure for designing the quasi-PR controller is proposed and verified by experiments. Theoretical analysis and experimental results of an experimental prototype verified the high performance of the proposed system in both the sinusoidal reference tracking and the disturbance rejection

A Single-stage Boost-Flyback PFC Converter

This paper presents a novel single-stage single-switch power factor correction (PFC) converter. The proposed topology is derived by combining a boost cell and a flyback cell into one power stage. In this converter, the transformer in the flyback cell has two-coupling primary windings, which have the same turns. Two bulk storage capacitors are used to store the power energy from the input source, and then feed one primary winding of the transformer respectively. In addition, the two capacitors can absorb the leakage inductances energy and clamp the voltage of power switch. Compared with using one bulk capacitor, the voltage across each capacitor here is lower, only half of the line voltage. This converter will potentially have low switch voltage stress, good regulation capability and high efficiency. To verify the performance of the proposed converter, a design example is given with its experimental results

Improved Control for Parallel Inverter with Current-Sharing Control Scheme

A novel current-sharing control scheme is presented for redundant parallel inverters. The control scheme employs the share bus which interconnects all the parallel inverters to transfer synchronous signal and average current signal. Current-sharing of all the parallel modules is realized through distributed average circuit. Average current is subtracted from the output current of each parallel inverter module and the subtraction result provides the instantaneous current deviation. The average current deviation of half line cycle is used to revise the voltage reference of next line cycle, which can achieve current-sharing and improve overall reliability. The instantaneous current deviation of switching period is fed back to the current-loop to improve the system dynamic response. Theoretical analysis and experimental results indicate that the control scheme performs a precise current sharing in dynamic state and steady state

DSP-based closed-loop control of bi-directional voltage mode high frequency link inverter with active clamp

This paper presents a novel modulation and digital controller based on a bi-directional voltage mode high frequency link inverter with active clamp to achieve fast dynamic response and high static performance. The inverter consists of a full-bridge converter, a bi-directional active rectifier, an active clamp branch and a pulse width modulation (SPWM) inverter bridge. A novel modulation strategy is applied by modulating the triangle carrier wave and two inverse sinusoidal modulation waves, it is no need of checking the pole of the output voltage to switch the modulated signals, and it is able to weaken the distortion of the output waveform on zero passage. Double closed-loop digital control with load current feed-forward is applied to achieve good dynamic response. The modulation and control strategy is realized by using the TMS320LF2407A DSP and EPM7128 CPLD. Theoretical analysis and experimental results referring to a laboratory prototype (3 KVA) indicate that the proposed modulation and control scheme are promising for the applications of DC/AC power supply.

An interactive following current-sharing control strategy for paralleled inverters in full digital

This paper analyzes the influence of the amplitude and phase of the inverters output voltage on the power of the parallel system. A no-master-slave control strategy for paralleling inverter based on an interactive following method is proposed, which controls the amplitude of reference voltage and synchronize the phase of the reference voltage to share the active and reactive power by synchronization bus and CAN bus. The DSP (TMS320LF2407) is adopted to realize full digital control in this system. The experimental results demonstrate that the function of N+1 redundancy can be realized and the active and reactive powers are greatly shared

Frequency-adaptive sinusoidal signal integrator for grid-connected inverters in weak grids

Sinusoidal signal integrator has the capability of controlling the ac current with zero steady-state error. However, their performances significantly degrade in case of the frequency variations with the steady-state error. So far, no literature has addressed the quantitative analysis of this steady-state error. Therefore, this paper reveals, for the first time, a theoretical guidance to get the accurate quantitative analysis for the error evaluation. Meanwhile, a frequency-adaptive sinusoidal signal integrator is proposed aiming at eliminating this steady-state error. The proposed strategy is suitable for grid-connected inverter applications in weak grids where the grid frequency may experience fluctuations. Detailed analysis and results verify the effectiveness of the proposed strategy.

Two-degree-of-freedom PID digital control of a bidirectional quasi-single-stage push-pull forward high frequency link inverter

In this paper, a high performance circuit topology and control techniques are developed. The proposed bidirectional quasi-single-stage push-pull forward high frequency link inverter consists of a push-pull forward converter, a bidirectional active rectifier, an active clamp branch and a SPWM inverter bridge. In particular, a two-degree-of-freedom PID digital controller is applied to achieve high performance in both the command tracking and the load disturbance regulation. The modulation and control strategy are realized by using the TMS320LF2407A DSP and EPM7128 CPLD. The principles of circuit operation are also discussed in this paper. Theoretical analysis and experimental results indicate that the proposed topology and control scheme are promising for the applications of DC/AC power supply.

Two-degree-of-freedom PI digital control of bi-directional voltage mode high frequency link inverter with active clamp

This paper presents a novel modulation and a two-degree-of-freedom (2-DOF) PI digital controller based on a bi-directional voltage mode high frequency link inverter with active clamp. A novel modulation strategy is applied by modulating the triangle carrier wave and two inverse sinusoidal modulation waves. It is no need of checking the pole of the output voltage to switch the drive signals, and it is able to weaken the distortion of the output on zero passage. This 2-DOF PI controller has two parameters to be designed separately and can obtain good dynamic responses both in the command tracking and load disturbance regulation characteristic. In this paper, the 2-DOF PI digital controller for the inverter system is designed and implemented to obtain high dynamic and static performance. The parameters of the controller are found by model building, theoretical deduction according to the desired specifications. The simulation and experimental results are provided to verify the proposed modulation and digital control strategy