Control system of inverter excitation device for l

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At present, the three-phase excitation device of the pump station is large, the cost of synchronous control device is low, and most of the synchronous control devices of the three-phase excitation system are low. Therefore, it is very necessary to carry out technical transformation on the excitation device of large and medium-sized synchronous motor. Taking the excitation power supply of large and medium-sized synchronous motor in pump station as the object, this paper discusses the design of inverter excitation device control system. Because the switching power supply technology has the remarkable characteristics of energy saving and material saving, the introduction of switching power supply technology into the excitation device is expected to reduce the volume and weight, improve the efficiency and have good dynamic response characteristics. Firstly, this paper introduces the block diagram of the main circuit of the system. On this basis, the structure of the control system is discussed, and the hardware and software design are introduced respectively. Finally, the experimental results of the excitation device are given and analyzed. 2. The system structure is as mentioned above. The technical transformation of the excitation device first focuses on the transformation of the main circuit. The topology of the main circuit of the device is introduced below. As shown in Figure 1, the circuit adopts the form of ac-dc-ac-dc. The first conversion link - rectifier circuit uses three-phase uncontrollable rectifier bridge to obtain uncontrollable DC output. The second conversion link - inverter circuit is the core part of the main circuit. It adopts half bridge circuit. Its anti DC bias ability is stronger than the full bridge circuit widely used in high-power inverter. Among them, the switching device adopts a new fully controlled switching device - IGBT. The output of the inverter circuit is transformed and isolated by a high-frequency transformer and then sent to the last conversion link - diode full wave rectifier circuit, so as to obtain an adjustable DC output. In this system, the synchronous motor is started by asynchronous starting method, so it is connected to the rotor winding after a de excitation link. The device uses the power module parallel technology and is composed of four power modules in parallel. The three-phase rectifier bridge in the device is a common part. The inverter circuit and full wave rectifier circuit constitute the power module. The inverter circuit input and full wave rectifier circuit output of each power module are connected in parallel. In this way, it not only increases the power capacity and improves the reliability of the device, but also reduces the manufacturing difficulty of the inverter circuit. 3 the control circuit design takes into account the parallel form of power modules in the main circuit structure, and the control circuit adopts a hierarchical structure - the main control circuit and four auxiliary control drive circuits. Each power module contains an auxiliary control driving circuit. Its tasks are as follows: 1. Drive the full control switching device IGBT of the power module. 2 control the current output of the power module according to the given value of the main control circuit. 3. Protect the power module. The main control circuit controls the output current of the whole device, completes the protection of the whole device, cycle back detection and display of user keys, etc. 3.1 the excitation device of current controlled synchronous motor is actually an adjustable DC current source. Its current output control is an important function to be realized by the control circuit, which is completed by the auxiliary control drive circuit and the main control circuit

Figure 1 overall structure of excitation device

the total output current of excitation device is the sum of the output currents of four power modules. Therefore, the current control is completed in layers - the current output control of each power module and the total current control of the device. The current output of each power module is completed by the hardware circuit in the auxiliary control driving circuit of the power module, taking into account the vision, touch, hearing and taste of the passengers. The main control circuit gives the current setting value of each power module, so as to control the current output of the whole device. Since the requirement for device loss is not too high, the switching mode of all control devices in the main circuit is hard switching pulse width modulation (PWM). Therefore, the hard switching PWM controller SG3525 produced by American general company is selected in the auxiliary control circuit [document 3]. The given value of the main control circuit is connected from the in-phase input pin of SG3525, the detection value of the output current of the power module is connected from its inverting input pin, and then the amplifier in SG3525 is used to form a PID regulator. The current control closed loop formed in this way adjusts the PWM waveform pulse width output by SG3525, so as to control the output current of the power supply module. For SG3525, the frequency and dead time of PWM waveform can be designed independently. The switching frequency of the device is designed to be about 35kHz and the dead time is about 3 μ S。 The main control circuit divides the current value set by the user's key by 4 as the current setting value of each power module. Since the device is actually a current source, the parallel connection of the power supply can be completed by using the above simple method, and the total output of the current of the pneumatic units t, kg, N, kn, G and LB can also be controlled. When the power module or the whole device fails, a blocking signal is generated inside the power module, or when the whole device fails, the main control circuit also sends a blocking signal, which will block the PWM pulse and protect the main circuit. Next, the control principle of current is explained with frame figure 2. 3.2 driving circuit and module protection circuit the other two functions of the auxiliary control driving circuit are the driving of the fully controlled switching device in the power module and the protection of the module. We use the special integrated driver EXB840 produced by Fuji company of Japan to drive IGBT. The protection of power module includes IGBT fault protection, overheating protection and overcurrent protection. 3.3 the prospect of main control is very decadent. The main control circuit adopts 80C196KC [document 1] and psd813f1 [document 2] to form a powerful dual chip system. In terms of selecting the main control chip, at present, 8-bit CPU is mostly used in the design of microcomputer excitation system in China, which is limited in terms of running speed and control accuracy. In order to overcome the above shortcomings, the main control circuit of the system plans to adopt the 16 bit single chip microcomputer 80C196KC introduced by Intel company as the main control chip. It adopts CHMOS technology, so it has higher operation speed, lower power consumption, and enhances the functions of interrupt, a/D and DMA. Using this single chip microcomputer, it can form a data acquisition system with high integration and high performance. The system also plans to use advanced peripheral programmable system device psd813f1 to realize ram and Epro

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