Research and design of inverter power supply based on DSP deadbeat control

introduction

With the emergence of high-performance DSP controllers, UPS power supplies using digital control have become a hot topic of research. Digital dual closed-loop control based on DSP can effectively improve the anti-interference ability of the power supply system, reduce noise, improve efficiency and reliability, and further facilitate intelligent management, remote maintenance and diagnosis of power supplies. Among the various control strategies of the inverter, repetitive control technology can effectively eliminate waveform distortion caused by nonlinear loads and interference; sliding mode variable structure control method can make the system run in a sliding mode, which can ensure the robustness of the system; intelligent control such as fuzzy control and neural network control does not rely on the mathematical model of the control object and is suitable for nonlinear systems; deadbeat control can instantaneously control voltage, has strong adaptability to loads, and has the advantages of less output total harmonic distortion and less loss; PID control is simple and has good reliability; new digital PID control can achieve more satisfactory control effects. Various control strategies have their own advantages and disadvantages. If two or several control technologies can be combined and used, better output characteristics will be achieved. Based on this idea, a control strategy combining digital PID control and deadbeat control technology is proposed. Theory and practice have proved that this method has broad application prospects.

1 System structure design

The TMS320F2812 chip selected in this system is one of the TMS320C28x series of TI. Its instruction execution speed is fast, so complex control algorithms can be implemented on this basis to optimize the output characteristics of the system.

The block diagram of the inverter power system based on this chip is shown in Figure 1. The entire system consists of AC/DC, DC/DC, DC/AC, as well as filtering circuits and other auxiliary circuits. Among them, the DC/AC inverter part is an important component of the entire system. The inverter adopts a single-phase full-bridge inverter circuit to adapt to high-power occasions. The output voltage and current sampled by the sampling circuit are converted into digital signals through the A/D converter of the DSP as the feedback signal of the digital controller. After being compared with the given output signal, the SPWM wave is obtained by the control algorithm regulator and the pulse width modulator to control the on and off of the IGBT power tube, thereby changing the value of the output voltage to make it equal to the given input voltage. The given reference voltage is implemented by software, so the signal is stable without temperature drift and interference. This control method can still ensure that the output voltage is not distorted when the load changes rapidly.

2 Inverter control scheme and its parameter design

2.1 Research on inverter modeling and its control strategy

As shown in Figure 2, iL is the inductor current; iC is the capacitor current; io is the load current; uo is the output voltage; R is the inverter load resistance, VS1~VS4 are the inverter control switches; r is the circuit damping resistance; L and C form an LC filter; E is the inverter input DC power supply.

Taking x(t)=[uo(t)iL(t)]T as the state variable, the average voltage ui(￡) and the load current as the system input, the state equation of the main circuit is:

Where: TS is the sampling period; ω0 is the resonant angular frequency of the second-order LC filter. The voltage and current discretization state equation obtained is:

The control method designed and studied for this inverter: a dual closed-loop control algorithm is used to adjust the dynamic and static characteristics of the system. The inner loop adopts a deadbeat control method, which is an effective means of instantaneous voltage control and has a strong adaptability to loads, especially nonlinear loads. The output waveform distortion is small and can improve the dynamic response characteristics of the system. The outer loop adopts an instantaneous value digital PI algorithm. The instantaneous value signal of the output voltage is directly fed back and compared with the reference sinusoidal voltage to stabilize the output voltage at the set value and suppress the distortion of the output voltage. The two control algorithms can make up for each other's control deficiencies and enable the system to achieve better control effects.

2.2 Current inner loop

The inner loop adopts the interference deadbeat control strategy. Combining the discretized state equation and the analysis results of the system main circuit diagram, the deadbeat control implementation method can be obtained as follows:

The load current io(k+1) can be estimated by using a second-order estimation method:

And iref(k+1) can be obtained from the outer loop control algorithm.

2.3 Voltage outer loop

The voltage outer loop adopts the incremental PI algorithm, and its differential equation can be expressed as:

The performance of PI regulator depends on the selection of KP and KI. PI parameters can be calculated theoretically, but due to the disturbance of system parameters, it is more practical to use simulation debugging method to determine.

2.4 PWM wave generation

The sinusoidal reference current iref(k) is obtained by the estimation algorithm, and uI(k) can be calculated according to the inner loop control algorithm to obtain the switch control time, that is, the PWM pulse time. From the sampling interval of kTS to (k+1)TS, the IGBT conduction time is:

After obtaining the on-time, the value of the PWM output register in the DSP must be further determined, so that the DSP can control the on-off time of the IGBT.

3 Simulation study of inverter control circuit

The simulation model for the inverter control method study is as follows:

Main circuit parameters: inductance L=10 mH, capacitance C=20 μF, rated resistive load R=50 Ω, switching frequency fS=1/Ts=10 kHz, DC power supply voltage E=310 V, output voltage effective value uo=220 V, frequency f=50 Hz.

The main circuit of the inverter consists of a DC regulated power supply module, a full-bridge switch module, an LCR module, a voltage and current measurement module, a signal input module, etc. The voltage outer loop uses the PI discrete control module in the Simulink module library; the current inner loop uses the S function submodule. The simulation results are shown in Figures 3 and 4.

4 Conclusion

By analyzing the output voltage and current waveforms of the inverter circuit under different loads and different environments, the feasibility and superiority of the control method can be confirmed.