Xu Dianguo

Development and application of wall-climbing robots

In this paper we introduce wall-climbing robots of two different absorption schemes: one with single suction cup and the other with permanent magnetic crawlers. The former adopts an omnidirectional vehicle and can perform remote-control inspection of nuclear storage tanks. Moreover, it is further developed for cleaning both the ceramic tile and glass surfaces of high-rise buildings. The latter consists of two types of robots: one is for maintenance automation of storage tanks in petrochemical enterprises, which can perform operations of sand-blasting, spray-painting and inspection; and the other is for monitoring the boiler wall water tubing.It is a challenge for mobile robots to climb a vertical wall primarily due to requirements for reliable locomotion, high manoeuvrability, and robust and efficient attachment and detachment. Such robots have immense potential to automate tasks which are currently accomplished manually, offering an extra degree of human safety in a cost effective manner. In contrast to vacuum suction, magnetic adhesion, and dry techniques used existing wall climbing robots, Canterburys research effort focuses on a novel approach which achieves attachment and detachment based on Bernoulli effect. The adhesion force is achieved on a variety of surfaces, independent on the material of the wall and surface conditions. Such ubiquitous mobility with a force/weight ratio as high as 5 is nearly impossible to be achieved by other adhesion methods.

A novel bridgeless buck-boost PFC converter

Conventional cascade buck-boost PFC (CBB-PFC) converter suffers from the high conduction loss in the input rectifier bridge. To resolve the above problem, a novel bridgeless buck-boost PFC topology is proposed in this paper. The proposed PFC converter which removes the input rectifier bridge has three conduction semiconductors at every moment. Comparing with CBB-PFC topology, the proposed topology reduces the conduction semiconductors, reduces conduction losses effectively, improves the efficiency of converter and is suitable for use in the wide input voltage range. In this paper, the average current mode control was implemented with UC3854, the theoretical analysis and design of detection circuits was presented. The experimental prototype with 400 V/600 W output and line input voltage range from 220 VAC to 380 VAC was built. Experimental results show that the proposed converter can improve 0.8% efficiency comparing CBB-PFC converter.

Unified power quality conditioner (UPQC): the principle, control and application

This paper deals with unified power quality conditioner (UPQC), which aims at the integration of series-active and shunt-active power filters. The main purpose of a UPQC is to compensate for voltage imbalance, reactive power, negative-sequence current and harmonics. This paper discusses the compensation principle and control strategy of the UPQC in detail. Experimental results obtained from a laboratory prototype of 20 kVA are shown to verify the viability and effectiveness of the UPQC.

Deadbeat Control Strategy of Circulating Currents in Parallel Connection System of Three-Phase PWM Converter

Module parallel connection for three-phase VSC can increase the system level effectively. However, the circulating currents problem will occur. The circulating currents will distort the three-phase currents, increase the power loss and decrease the system efficiency. A novel deadbeat circuiting currents control method is proposed in this paper. Based on the analysis of the average model of parallel system, a circuiting currents deadbeat controller is designed while presenting the design method. The control strategy is realized by adjusting the voltage zero vector of space-vector pulse-width modulation in each paralleled module. No additional hardware is needed through the method. Fast dynamic response can be achieved and the performance of circulating currents is better compared with conventional PI controller. This method can be applied to common dc-link double parallel three-phase voltage converters with communication line. The validity of proposed theory was verified by simulation and experimental results. It is shown that the parallel converters can operate with different line inductor or different line currents by using this novel control strategy.

Bandwidth Expansion Method for Circulating Current Control in Parallel Three-phase PWM Converter Connection System

The use of common dc-link parallel three-phase PWM converters without isolating transformers will cause zero-sequence circulating current problem. Previous works have proven that the circulating current is mainly affected by zero vectors employed in each PWM cycle. This paper proposes a novel method to suppress the circulating current. Detailed analysis is presented on the causes of zero-sequence circulating current based on a derived average model. A zero vectors feed-forward control strategy in combination with traditional PI control method is proposed to reject disturbances in zero-axis current system. In addition, a dual current sampling and dual PWM duty ratio update (DSDU) scheme is used to expand the bandwidth of zero-axis current loop. As a result, better circulating current suppression performance can be achieved in different filter inductance and converter output currents condition. Compared with the PI control method, the converters operated in parallel can be switched on and switched off separately with small current impact. Experimental results confirm the performance and effectiveness of the proposed method.

Discrete variable frequency soft starting on DSP-based voltage controller-fed IM drive

Thyristorized soft starters are being used as induction motor starters in fan or pump drives, etc, the principle of which is based on the control of variable voltage and constant frequency. One of the demerits of the soft starters is that a small reduction in voltage produces a considerable drop in electromagnetic torque, which may cause the motor with loads failure to start. A new control strategy is proposed to improve electromagnetic torque at starting. According to the relationship that the electromagnetic torque of the induction motors is inversely proportional to the ac power supply frequency, reducing the supply frequency can improve the starting torque. Based on the fixed main circuit of soft starters, the strategy defines the triggering instants of soft starter thyristors to include or omit partial half cycles of the ac power supply. Therefore, the discrete variable frequency voltage and current applied to the motor are obtained. In fact, the new discrete frequencies are the ones of the fundamental components of the generated voltage and current. For all the subharmonic frequencies, in order to obtain most positive torque, the system is properly unbalanced, using the method of symmetrical components to choose the most positive sequence of the initial phase angle combination of three phases. The strategy similar to variable voltage variable frequency inverters gets the motor to produce low impact of current and high torque. Applying this strategy combining with the method of soft start allows the induction motor to start with full loads. The proposed strategy has been verified experimentally on a laboratory machine using a 32-b DSP-based soft starter-fed induction motor drive system, and proved to have good starting torque and current performance.

Study on optimal design method for passive power filters set at high voltage bus considering many practical aspects

This paper proposes the optimal designs of passive power filter (PPF) using the advanced particle swarm optimization (PSO) method. In the PPF optimal design, the purposes are to minimize the total harmonic distortion (THD) and original investment cost, while maximize fundamental reactive power compensation. Several constraints of THD, individual harmonics, fundamental reactive power compensation, and parallel and series resonance with systems are considered comprehensively. Furthermore, the detuning effect is considered as a constraint during the optimal process, which improves the reliability and practicability of design results. And a novel optimal strategy is proposed in this paper to solve the multiobjectvie optimization problems for PPF, which can make a compromise among all the objectives. Finally, the optimal design results are compared with those designed by the conventional method, which shows the superiority and availability of the proposed design methods based on PSO.

An autonomous control scheme for DC micro-grid system

This paper presents an autonomous control scheme for DC micro-grid system both in grid-connected and islanding conditions. The proposed DC micro-grid architecture consists of a wind turbine generation unit, a photovoltaic generation unit, two battery stack units, a grid-connected inverter/rectifier and loads. Corresponding control strategy of each unit is presented. DC droop control method is adopted into voltage control loop to suppress the circulating current when two or more voltage sources are connected to DC bus. The energy that flows through each unit and different operating modes of the system both in grid-connected and islanding conditions are analyzed. Power management method to balance the energy of the system and stable the DC bus voltage is presented. Simulation results verify the effectiveness of the proposed control scheme in various operating conditions.

A 10KV shunt hybrid active filter for a power distribution system

This paper analyzes the compensation performance of a shunt hybrid active power filter. The hybrid active power filter, which combines passive filter and active power filter, has both respective merits, and is an important developing trend of filtering device. The hybrid active power filter can reduce the capacity of active power filter effectively and is more suitable for the engineering application for high voltage nonlinear loads. The compensation performance of hybrid active power filter is analyzed by estimating the effect of different active power filter gain and parameters change. Then, a conclusion has been obtained that the harmonic attenuation rate is insensitive to the variation of passive parameters when the active power filter with an enough feedback gain is combined. Finally, the feasibility and validity of proposed scheme is verified by simulation using Matlab and a hybrid shunt active power filter prototype.

Active voltage regulator based on novel synchronization method for unbalance and fluctuation compensation

Requirements on the power quality of AC sources are becoming more stringent as more voltage-sensitive equipments are being used. Among the power quality deterioration issues, voltage unbalance and voltage fluctuations are two serious ones. An active voltage regulator, which is used as a part of unified power quality conditioner (UPQC), is proposed to compensate for the voltage unbalance and fluctuations in this paper. It is composed of a voltage source inverter (VSI) coupled in series with the supply through transformers. The adopted topology guarantees that the energy can flow bi-directionally, thus it can regulate the load voltage to the expected value during long-drawn supply voltage fluctuation. Another aspect covered in this paper is the synchronization problem or the technique to get the phase angle of the reference signal, which is essential in voltage regulation. A software synchronization based on a new fundamental positive sequence (FPS) component extraction method is presented and proven in the paper. The active voltage regulator with the proposed topology and the synchronization method features in no hardware synchronization requirement, accurate and fast phase tracking and high dynamic performance. Experimental results performed on the prototype testify the validity of the proposed active voltage regulator in voltage unbalance and fluctuation compensation.