The device uses an asynchronous sampling method to ensure that the sampling value of the voltage current is more accurate, and the system is more stable. In order to reduce the noise when the battery charge and discharge system is steady state, improve the dynamic response, introduce the hysteresis PI regulator, relative to the PI regulator without the hysteresis, and improve the stability of the system. In this paper, the full digital controlling battery charge and discharge circuit and control method are introduced as an example.
1 system main circuit
BUCK-BOOST main circuit and TMS320LF2407 control target board are shown in Figure 1. The current of the circuit can flow two-way flow: When the current flows from the UDC to UBA, S1 and D1 are turned off (S2 and D2 blocking), and the battery is charged; when the current flows from UDE to UDE, S2 and D2 Tutan work (S1 and D1 resistance ) Battery discharge, At this time, UDE turns into load. UDE, UBA, and IL are sampled in DSP with sensors to perform AD conversion. When the program determines that the circuit is working properly, the circuit start signal IOPB4 is sent. The previous circuit is in a closed non-operating state.
2 system control principle
2.1 Introduction to Control Method
As shown in FIG. 1, the UDC, UBA, and IL three-way sampling signals sent by the sensor are converted through the AD module inside the DSP. By comparing the size of the UDE and the UBA voltage to operate in the charging state or the discharge state. When UDE "UBA, the circuit operates in BUCK (battery charging) mode. Depending on the size of the UBA, it is determined that the battery is operating in trickle charging, constant current charging or constant voltage charging. The 12V battery is actually connected in series by six monomer batteries, so ubal = 1.75 V6 = 10.5 V; UBA_H = 2.256 = 13.5V. When the battery voltage is too low, lower than UBA_L, in order to extend the battery life, the battery is charged, the charging current is, ILL = O.0L C. When the battery voltage rises to UBAL, it turns into constant current charging, the charging current is, IL_H = O.1 C. When the battery voltage rises to UBA_H (13.5V), it turns to constant pressure charging, the charging voltage is 13.5V, and the charging current should continue to decrease. Here is the battery of 12V, 100A.H. C = 100A. When UDC "UBA, the circuit operates in the Boost mode.
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2.2 Three-level charging mode
Traditional battery is mostly two-stage charging mode, which is insufficient for depth discharge storage (battery monomer voltage below 1.75V). The device increases the trickle charging mode before constant current and constant voltage charging mode, as shown in Figure 2. Trickle charging mode is essential to the battery of the depth discharge.
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2.3 Non-synchronous sampling method
The synchronous sampling method is to voltage when the switch is started, and the current sample is sampled because the switching pipe action causes a voltage, current spike, and the number of samples is large, resulting in system unstable, so use non-synchronous sampling method control accuracy higher. As shown in FIG. 3, the PWM switching frequency of the device is 20 kHz, and by delaying 5μs in the period interrupt program, it can avoid the switching tube action to generate an effect on the sampling value, and achieve non-synchronous sampling.
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2.4 PI regulator with hysteresis
Dynamic and steady state adjustment targets for DC / DC converters. Dynamically requires the system to be fast and smaller, and the regulator can effectively control the system oscillation and quickly enter the steady state. When steady state is required, the system is stable and the stable range is wide. In response to these two states, the PI adjustment of the battery charges is adjusted to the hysteresis regulation.
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Where: f [e (k)] is the PI adjustment function.
When the absolute value of the output error E (K) is relatively small, the lag ring is used to adjust the PI adjustment when e (k) is outside the hysteresis (the absolute value of the error) is adjusted. This will adjust the battery charge and discharge quickly and smoothly. Technology area
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