Guopeng Zhao

A class of coupled inductors based on LTCC technology

Using coupled inductors in multi-phase point of load converters is an effective way to improve system steady state and dynamic performance. Thus, package of coupled inductors for system three-dimensional integration is attracting great interest of research. This paper explores design, fabrication and analysis of planar coupled inductors based on low temperature co-fired ceramic technology. Four structures classified by winding forms and their distribution in the core are introduced and compared firstly. Then, an analytical model for approximating inductance value is derived. Two LTCC coupled inductors are fabricated and their measurement results are provided. Finally, a 12V input, 1.8V/40A output two-phase interleaved buck converter is construed for testing a LTCC coupled inductor.

An analysis on the influence of interface inductor to STATCOM system with Phase and Amplitude Control and corresponding design considerations

Previous publications regarding the design and specification of interface inductor and DC side capacitor for STATCOM usually deal with the interface inductor and the DC side capacitor only, and seldom pay attention to the influences of interface inductor and DC side capacitor on STATCOM systems performance. Phase-shift Control and Phase and Amplitude Control (PAC) are two basic control methods. In this paper, the Phase and Amplitude Control is considered as the STATCOM control strategy. And, a detailed analysis on the influences of interface inductor and DC side capacitor on STATCOM systems and corresponding design consideration are presented. First, the models of the current loop and the voltage loop in STATCOM system by using two modeling methods are carried out. Second, the transfer functions of each control loop are presented. Through frequency domain methods, such as Bode plots, the influences of interface inductor and DC side capacitor on the STATCOM system stability are extensively investigated. Third, based on the analysis, the design considerations based on phase margin for interface inductor and DC side capacitor are discussed.

Analysis and specification of DC side voltage in parallel active power filter regarding compensation characteristics of generators

In this paper, an extensive analysis on the influence of DC side voltage to the performance of PAPF is carried out, and a specification of the DC side voltage rated value is presented. First, through equivalent circuit analysis and Fourier Transform analytical expressions, a required lowest value of DC side voltage for full compensation (a zero source current THD) is obtained for six-pulse converter harmonic current, where PAPF is providing six-pulse converter harmonic current. For the situation, of which the DC voltage is smaller than the above-obtained lowest value, the quantitative relationship between the DC voltage and the total harmonic distortion after compensation is also elaborated in the paper by using the diagram of curve relationship. Based on these analysis, the specification of DC voltage rated value for PAPF is quite straight forward. Simulation investigation results are finally provided to verify the analysis and specification.

Evaluation of LTCC capacitors and inductors in DC/DC converters

Low temperature co-fired ceramic (LTCC) technology has been proved to be an effective way to realize system integration. By using this technology, passive components in a DC/DC converter could be integrated into a passive substrate. This paper presents fabrication and evaluation of LTCC capacitors and inductors and summarizes challenges of applying LTCC technology to DC/DC converters. Four capacitors are made; two of them are made with single layer high permittivity thick film paste, and maximum 1.1µF capacitance is obtained; the other two are made with multilayer low permittivity LTCC tapes, maximum 30nF capacitance is obtained. A 70nH LTCC inductor is also fabricated with ferrite tapes. It is tested in a 1.2MHz buck converter and a 30MHz class Φ2 DC/DC converter. Finally, challenges of conductor resistance, capacitor tape permittivity, and shrinkage matching are discussed and summarized.

An analysis on the influence of interface inductor to STATCOM system with phase-shift control and corresponding design considerations

The design of the STATCOM interface inductor is very important. Previous publications regarding the design and specification of interface inductors for STATCOM usually deal with the interface inductor only, and seldom pay attention to the influence of interface inductor to STATCOM system performance. In this paper a detailed analysis on the interface inductor influence to STATCOM system and corresponding design consideration is presented. In STATCOM system, especially in high voltage and power situation, two basic control methods are used. One is phase-shift control, and the other is Phase and Amplitude Control (PAC). In this paper, the phase-shift control is considered as the STATCOM control strategy. First, the model of STATCOM is carried out. Second, the transfer functions are presented. Through frequency domain methods, such as transfer functions and Bode plots, the influence of interface inductor on the STATCOM system stability and filtering characteristics is extensively investigated. Third, based on the analysis, the design considerations for interface inductor are discussed, which leads to filter parameters different to traditional design. All the computer simulation results verified the validity of the above analysis and design.

Analysis and Design of Fully Digital and Direct Current Controlled Voltage Source Converters Connected to the Grid

Direct current control has been used in many voltage source power converters connected to utility grid, such as Static Var Generators (SVGs) and parallel Active Power Filters (APFs). In their stationary coordinates control systems, there are usually two closed control loops. One is the current loop and the other is the voltage loop. In practical applications, because the voltage source converters are connected to the grid, the output current will be affected and very often a command-tracking error exists in the current control loop. In this paper, a detailed analysis and design considerations are carried out to investigate this command-tracking error caused by the source voltage. Based on the obtained current loop transfer function and block diagram of the system, analytical expressions of the current control error are derived. The variables that affect the current control errors are then identified. The relationship between the circuit/control parameters and the current control errors are extensively explored. The command-tracking error affects the peak value of the modulation wave. When we design a fully digital control system, the peak value of the modulation wave is smaller than the peak value of the carrier wave. Then, according to choosing the values of the variables that affect the command-tracking error, the methods to design a fully digital direct current controlled voltage source converters connected to the grid are presented. The computer simulation investigations and hardware experimental results verify the analysis and design considerations.

Simulation study of parameter influence on Dynamic Voltage Rise Control

High power IGBTs are widely used in wind power generation systems. An advanced IGBT gate driver with Dynamic Voltage Rise Control (DVRC) is used to suppress the turn-off over-voltage of the IGBT. Mass simulations are done to evaluate the performance, showing influence of the DVRC parameters, in order to select the right parameters for applications.

A Transformerless 2-Level Inverter Based Static Var Generator with Multiple Functions in Medium Voltage Application

This paper proposes a transformerless 2-level inverter based static var generator (SVG), which employs 20 series-connected IGBTs in each leg of the bridge for medium voltage blocking capability. The multifunctional SVG is used to compensate reactive power, negative sequence current, current harmonics and unbalanced utility voltages. Especially, a voltage controlled current source (VCCS) strategy is introduced and analyzed to mitigate grid voltage unbalance. Furthermore, the approaches to generating the reference signal for the SVG control circuit is presented according to different compensation objectives. Successful field installation and test results under 6kV voltage level showed satisfactory performance of the proposed SVG

Control and optimization of VCVS static var generators for voltage unbalance mitigation

Reactive power control through static var generator (SVG) has been gaining wide attentions due to its outstanding performance. But for a SVG with traditional control strategies, unbalanced utility voltages have greatly affect the performance of the SVG and in severe case may even cause shut-down of the SVG for overcurrent protection. This paper proposes a voltage controlled voltage source (VCVS) strategy to assure normal operation of SVG with series-connected IGBTs when severe system voltage unbalance happens, and furthermore to mitigate voltage unbalance at the point of common coupling (PCC) whether it is caused by utility or load. The control law, operation principle, compensation characteristics and parameter optimization of the proposed control strategy are analyzed in detail. Based on the VCVS control, a modified VCVS strategy is proposed and the difference between them is presented. Finally, the simulation and experimental investigations were carried out respectively for resistive and rectifier load conditions. The results verified that the current passes through the SVG is under control and the voltage at PCC is much more balanced than that before compensation. The compensation performance of the SVG is thus proved satisfactory

Analysis and Specification of Switching Frequency in Parallel Active Power Filter Regarding Compensation Characteristics of Generators

The choice of switching frequency is a very important issue for the development of Parallel Active Power Filter (PAPF), but so far is lack of discussion in a quantitative manner from previous publications. In this paper, an extensive analysis on the switching frequency to the performance of PAPF is carried out, and a specification of the switching frequency values with different compensation results is presented. First, the approximate models are presented. The PAPF are considered as a first-order inertia element and a second-order oscillation element respectively. The magnitude and phase of each order harmonic current are obtained at different switching frequency. The relationship between the output current and the reference current is shown. Second, with different types of system loads which are rectifier with resistance and inductance load and rectifier with resistance, inductance and capacitance load, the total output current is carried out with different switching frequencies, and the THD is proposed, that is, the compensation characteristic is analyzed. Third, the influence of source impedance and load impedance on the compensation characteristic is discussed when the switching frequency is different. Based on these analyses, the specification of compensation characteristics with different switching frequencies is quite straight forward. Both simulation investigations and hardware experimental results are finally provided to verify the analysis and specification.