Extensive Application And Research On The Key Technology Of Four-Quadrant Converter

Different from the conventional ac/dc/ac converter, the four-quadrant converter (FQC) has been widely applied in the field of electric power drive systems, the distributed power generation using renewable energy, the flywheel energy storage, the brushless doubly-fed generator (BDFG) control and the high-voltage converters etc. Along with the continuous renewal of power electronic devices, the voltage level and the switching frequency have been significantly improved meanwhile the advance of the modern control theory provides the FQC with the broad application prospects and development space. The core topological structures of the FQC are introduced in detail and their operating principles are also analyzed. On this basis, the extensive applications of the FQC are conducted, such as the motor control of the oil pumping unit, the cascaded multi-level high voltage inverter and the ship shaft synchronous generator (SSG) converter. In the field of these applications and on the basis of application characteristics, the analysis and validation of the key technology are conducted. The main contents are as follows:(1) The pulse width modulation (PWM) strategy is decided by the main circuit topology of converter. The sinusoidal PWM (SPWM) and the space vector PWM (SVPWM) are the common modes in the traditional two-level converters. In order to improve the utilization factor of the dc voltage, the SVPWM is selected in the rectifier and the inverter control systems. In the case of the neutral point clamped (NPC) three-level topology and the T-type three-level topology, the neutral-point voltage balance control should be added into the SVPWM strategy. It makes rational utilization of the positive/negative small vector and the middle vector in each sector. According to the deviation of upper/lower capacitor voltage and the mid-point current caused by small vector, the syntagmatic relations can be confirmed. Then, a varying virtual voltage middle vector is constructed to participate in SVPWM. Through this method, the fluctuation of the mid-voltage can be well suppressed. In the case of the cascaded multilevel structure, a sample-time-staggered (STS) SVPWM is simplified by analoging the carrier phase shifting (CPS) SPWM. The differences and similarities between these two modes are analyzed and their digital realizing method with simulation is carried out.(2) The current control technique as the core technique in a voltage-current double-loop control system determines the dynamic-static performance of the PWM rectifier. The conventional current loop is realized by the active and reactive current decoupling PI control in the d-q coordinate. The precision of a rotational transform angle and the thoroughness of an inductance decoupling determine the PI control effect. In some special cases, such as the unbalanced source voltage, the grid voltage with harmonics, and the SSG converter application, the accuracy of the voltage phase angle and the line inductance parameters are hard to be guaranteed. According to these conditions, a no inductance parameter current decoupling control based on a complex vector PI controller is proposed, and then a quasi-direct power control based on a self-adaptive PR controller and a variable frequency resonance PLL is designed in this dissertation. The correctness and feasibility are verified by the simulations and the experimental results.(3) The inverter side of FQC is generally used to control the ac motor or as an inverter power supply.A good control performance can be obtained in both application fields. In the modern ac drive system, the vector control has become a mainstream for its better static and dynamic performance. However, the induction motor vector control is a multi-loop control system which is hard to design. The complete decoupling control of an induction motor is realized by analyzing the dynamic mathematical models of an induction motor and the parameters tuning method in each loop is also studied in depth. Sliding mode adaptive speed estimation method is proposed based on the rotor flux field-oriented vector control, and then applied on a FQC prototype and a regenerative cascaded multilevel inverter. When the inverter side is used as an ac power supply, a double-loop stand-alone control mode based on an ac voltage outter-loop and a current limt-loop is proposed. In order to realize the grid-connected operation with a diesel generator, the inverter connection control scheme is designed based on the drooping characteristics of a synchronous generator, which can smooth switches to the stand-alone control mode.(4) In order to improve the power response of the FQC, the load current feed forward scheme is studied and a load current observer is also designed. For further suppression of the dc voltage fluctuation and minimization of the dc capacitance, an integrated current feed forward control scheme is proposed based on a small-signal model analysis of the FQC. This mothod calculates the integrated current given value by using the information about the inverter side current and voltage within one switching period, without the dc current sensors. As a result, the anti-disturbance performance is well promoted. The correctness and feasibility are verified by the experimental results on a FQC prototype.