Hongtao Shan

A Novel Decoupled Current-Sharing Scheme Based on Circulating-Impedance in Parallel multi-Inverter System

Parallel multi-inverter systems can be designed to have the advantages of expandable output power, improved reliability, and easy N+X redundancy operation. However, a current-sharing control scheme has to be employed to enable the inverters to share the load current equally. The concept of circulating impedance is proposed in the paper, and introduced into current-sharing control scheme in parallel multi-inverter systems. The mathematical model of circulating impedance is set up. By introducing circulating-impedance control regulator, the characteristic of circulating-impedance is controlled to be similar to that of the pure resistance or inductance. Then the relationship between the circulating-current phasor and the amplitude, the phase of inverter modules output voltage reference is decoupled. Experimental 220 Vac/3 KVA inverter modules are built and parallel operated. The results of experiment verify that the current-sharing scheme based on circulating impedance is available and efficient.

Parallel Operation System of High Frequency modularized UPS Based on Distributed Logic Control

A parallel operation system of UPS based on distributed logic control has been studied in this paper. The mathematic model of the system was constructed and the parallel operation principle was analyzed. Real-time active and reactive power detecting method was given. A control scheme for circumfluence restraining was proposed herein. The parallel operation control technique was put forward and has been successfully applied in the power system where six modular high-frequency UPS operate in parallel. Experimental result was presented to verify the reliability and the feasibility of the parallel UPS system

The research on the digital controlled effect of performance on the PWM inverter

The traditional PID control strategy which is realized in digital method canpsilat achieve better performance than that in analog control. The reason was analyzed why the digital process influences the digital controlled PWM inverterpsilas performance in this paper. One is the process of the zero-order hold. Another one is one-step-delay control which is usually adopted in digital control. Three aspects were analyzed in which influence the digital controlled PWM inverterpsilas performance: (1) how the process of zero-order-hold effects the open-loop frequency property of the digital controlled inverter system (2) how the process of zero-order-hold effects the systempsilas stability (3) how the one-step-delay control effects the systempsilas stability. On the base of setting up discrete mathematical model of the digital controlled inverter system, theory deduction and simulations were done in the condition of P regulator Relevant experiments verify the rightness of the analysis and direction for the design of the digital controlled PWM inverter were given. Finally relevant experiments verify the theoretical analysis.

Research on one-step-delay effect of digital control PWM inverter

This paper focused on the research on one-step-delay effect of the stability of digital control PWM Inverter. Discrete stability criterion is used to research the stability of discrete system with/without one-step-delay control respectively. The research results are shown that the one-step-delay control degrades the stability system in the high sample frequency while it may increase the stability range compared with no one-step-delay control in some low frequency band. The unique phenomenon in the low sample frequency is explained by the analysis of frequency domain and root locus. So it is deduced that the introduction of predictive control can not improve the performance of inverter in any sampling frequency. Predictive control can upgrade the performance of inverter only in the high sample frequency.

The research for the stability of SPWM inverter affected by digital control

This paper focused on for the stability of spwm inverter affected by digital control. The stability of analog control inverter system, discrete system with no-step-delay control and discrete system with one-step-delay control are analyzed respectively so as to determine the relation of the inverters sampling period vs. controller parameters with critical stability. Then the essential reason was analyzed why the stability of digital control inverter was degraded compared with analog control inverter even if the sample frequency is ten times greater than the closed-loop bandwidth. The conclusion with realistic instructive significance had been drown clearly that one-step-delay control makes stable range of controller parameter larger than no-step-delay control in some low sample frequency.

The novel strategy of restraining circulating currents in distributed-logical-control on parallel inverter system

Distributed-logic-control is an independent parallel inverter control technique. The strategy to restrain circulating currents based on distributed-logical-control is researched in the paper. The conventional method by power regulation to restrain the circulating current is affected by the parallel impedance and has such disadvantages in the response speed and harmonic component of circulating current. The strategy to restrain circulating current based on tracing transient average current feedback was proposed in the paper. Its impedance characteristic and the current sharing principle are analyzed. This strategy can reduce the system output impedance, while increase the impedance between parallel inverters. The novel strategy of restraining circulating currents is adopted by the combination of tracing transient average current feedback control and power adjusting strategy. The relevant experiments on the novel strategy were made in parallel inverter with distributed-logical-control, and the validity of the novel strategy was verified.

Novel & Practical Digital Parallel UPS System Based on CAN_BUS

The novel & practical digital parallel UPS system has been introduced in this paper. The parallel UPS system bases on distributed logic paralleling control strategy used by TMS320F240 as main-control chip. Data communication is realized among all of parallel UPS units or between parallel UPS units and supervision device with application of CAN bus technology. This paper illustrates briefly relevant content such as the total frame of parallel UPS system, control principle based on DSP, the design of parallel supervision device, and so on. The design of the parallel UPS system has advantage of high practicality