Question

BDC(Bidirectional Converter) works as a boost converter in discharge mode for microgrid energy storage. How find transfer function of the system to control voltage - current in plecs simulation, so find the transfer function of it step by step ?

Answer 1

In orbit, the structure of a power supply system incorporating a bidirectional DC-DC converter . The system consists of a storage battery or a power supply network, a bidirectional DC-DC converter, a super capacitor set, an inverter and a He Yongci synchronous machine. In the process of vehicle braking charging, the average charging current is determined according to the regenerative braking power and the capacitor voltage of the locomotive, and the charging process can be automatically ended when the super capacitor voltage reaches the highest charging voltage. In the discharge process, the discharge current is determined according to the starting power of the vehicle and the voltage of the super capacitor, and the bidirectional DC-DC converter is turned off when the voltage of the ultracapacitor is reduced to the minimum operating voltage.Whether the converter operating condition is the charging state or the discharging state, It is determined by the conditions of the vehicle operation, the voltage of the power supply network and the super capacitor voltage. In the case of running conditions, controling the control signal of the main circuit of the corresponding contactor controlchip and a certain duty cycle PWM pulse,which were sent by high-speed output port of control chip , and by the drive circuit to isolate the signal after the drive, the main circuit switching device IGBT Work according to the required The bidirectional DC/DC converter consists of a three-phase three chopper circuit, the difference of control pulse is 120 degrees, and its working principle is as follows: (1) when the vehicles brake again , resulting the power grid voltage increased, bidirectional DC/DC converter circuit in Buck circuit model, and the super capacitor energy storage system connected, for charging. The ultracapacitor group absorbs regenerative braking energy while reducing the voltage of the power supply network. (2) when the vehicle is accelerating or starting, power supply network voltage will be lower, then the controller of bi-directional DC/DC converter working in Boost circuit mode, super capacitor energy feedback through duty cycle. thus achieve the recovery of braking energy and reuse. bidirectional converter. Under this condition, the super capacitor energy storage system is put into use, which reduces the requirement of the peak power of the power supply system, and makes the voltage drop of the power supply network be eased. (3) when the running vehicle is idle, the controller can control the energy storage state of the super capacitor set by the main circuit of the bidirectional DC/DC converter according to the capacitance of the super capacitor group. To sum up the analysis can be seen, according to the different operation condition of the vehicle and power supply voltage, the controller control bidirectional DC/DC converter to achieve super capacitor energy storage system and inverter energy exchange, and achieve energy storage utilization.