Realizing parallel-connectable inverter power supply based on DSP (Part 2)

feifei

Realizing parallel-connectable inverter power supply based on DSP (Part 2) [Copy link]

Continued from the previous article 4 System Software 4.1 Software Principle The main task of the system software is to realize digital sinusoidal signals, stabilize the output signal voltage, manage various devices, and complete the coordination of parallel machines. The system software sends the digital signal to the pulse width modulation circuit to form a sinusoidal signal Us by looking up the table, obtains Uf by sampling and feedback of the output signal, and corrects the amplitude of the output sinusoidal signal to achieve the purpose of stable output. Its structure diagram is shown in Figure 5. 300)this.width=300" border=0 ncpop="Click to view the original image in a new window"> Considering the damage of inductive load to the inverter operation, this machine adopts capacitor compensation. After intensive sampling of the output voltage and current, the apparent power S, active power P and reactive power Q are calculated. 300)this.width=300" border=0> According to the size of reactive power and the characteristic parameters of this machine, the reactive power allowable window is set, and the appropriate capacitor combination is invested by using the table lookup method to achieve the purpose of compensation. 4.2 Software module structure This system software adopts modular design and can be divided into 7 modules according to the task: system initialization module, digital sinusoidal signal generation and output stabilization module, compensation module, parallel current sharing module, fault detection and processing module, display module, and communication module. The process is shown in Figure 6. 300)this.width=300" border=0> 4.2.1 System initialization module The system initialization module includes: interrupt and priority setting, PWM setting, timing setting, A/D setting, general input and output port setting, communication port setting, etc. The system initialization module is the beginning of DSP work, and the program is placed in the DSP_init() subroutine and appcofig.h program. 4.2.2 Digital sinusoidal signal generation and output stability module The digital sinusoidal signal generation and output stability module is divided into three submodules: signal sampling and processing module, output stability module, and PWM reload interrupt service module. Among them, the signal sampling and processing module is further divided into: A/D sampling, active power calculation, reactive power calculation, power factor calculation, output voltage effective value calculation, output current effective value calculation, etc. The main task of the output signal stability module is to use fuzzy algorithm based on the difference between the given standard signal (output 220V) and the output feedback signal to adjust the output voltage to the standard value at the fastest speed. The PWM reload interrupt has the highest priority. In order to ensure that the PWM reload work is completed at the fastest speed, this program uses assembly language and the fast 16-bit multiplication of DSP56F805 to complete the reload calculation work in about 3μs. 4.2.3 Compensation module When the inverter is loaded with inductive load, on the one hand, the power factor is reduced, which reduces the active power of the inverter. On the other hand, the lagging current will cause harm to the inverter. The function of the compensation module is to compensate the inductive load by inserting appropriate capacitors when carrying inductive loads. According to the signal sampling module, the reactive power Q and the maximum allowable reactive power ΔQ of the machine are calculated, and the fuzzy algorithm is used to adjust the reactive power to the allowable range at the fastest speed. 4.2.4 Parallel current sharing module The parallel current sharing module is used for parallel output of multiple units. It not only ensures that the amplitude, frequency and phase of the output voltage of each unit are consistent, but also requires the output load of each unit to share the current. The current of each unit participating in the parallel operation is analyzed and calculated through the CAN bus, so that the current of this unit is 1/N of the total current, so as to achieve the purpose of current sharing. The timing phase-locked circuit is used to detect the phase and frequency, so that the phase and frequency of the digital sine signal generator output are consistent. 4.2.5 Fault detection and processing module The fault detection and processing module detects input voltage too high or too low, output voltage too high or too low, output overload, PWM circuit fault, machine temperature, and switch tube status. The detected faults are divided into two categories and handled in different situations: for non-fatal faults, fault display and alarm are used; for fatal faults, in addition to fault display and alarm, PWM work is also turned off to prevent further damage to other devices. 4.2.6 Display module The display module is used to display the working status and parameters of the inverter power supply. The displayed parameters mainly include Vin , Iin , Vout , Iout , Pout , θ, etc. Due to the use of 16X2 LCD, only Vout and another parameter can be displayed at a time . Other parameters can be displayed by pressing the S2 key cyclically . 4.2.7 Communication module The communication module works independently of other modules and performs multi-unit communication through CAN bus management. Each unit running in parallel uses data packets to communicate with each other. The data packet contains a data packet flag and several data blocks. Each data contains the identification number of the unit participating in the parallel connection, the output current value and other information. The communication module is responsible for managing the sending and receiving of data packets, and it works independently. It and the parallel current sharing module use communication to transmit data. The parallel current sharing module calculates the output current of the local machine and puts it in the buffer, and notifies the communication module to send a signal. When the communication module receives the signal sent by the parallel current sharing module, it waits until the data packet arrives at the local machine, and then the local state is added to the data packet and sent out. At the same time, it also sends a valid data packet signal to the parallel current sharing module. After receiving the signal sent by the communication module, the parallel current sharing module takes the data from the buffer. This system uses Motorola's MSCAN software for programming CAN communication software, which is convenient and fast. 4.3 Main program list 300)this.width=300" border=0> 300)this.width=300" border=0> 300)this.width=300" border=0> 300)this.width=300" border=0> 300)this.width=300" border=0> 300)this.width=300" border=0> 4.3 Special software algorithm description The quantities that need to be adjusted in this machine include: output voltage amplitude, frequency, phase, power factor, current sharing, etc. All algorithms use fuzzy algorithms. The input variables for output voltage adjustment are voltage deviation E and change rate ΔE, and the output control quantity is pulse width Z c . Therefore, two languages are defined for the input variables: voltage deviation and change rate. There are 5 fuzzy values for voltage deviation, namely low, lower, medium, higher, and high. There are 3 fuzzy values for change rate, namely decrease, unchanged, and increase. Make corresponding fuzzy judgments based on the above definitions. The input variable for power factor compensation is active power deviation (i.e., the difference between feedback reactive power and allowed reactive power), and there are 3 fuzzy values, namely negative, just right, and too large. Its output control quantity is the capacity of the input capacitor. There are 8 combinations of capacitor capacity, which can be determined based on the active power deviation. 5 Experimental results We used DSP56F805 to make two inverter power prototypes, and the test results were satisfactory. Figure 8 is a 50Hz drive waveform, Figure 9 is a 100Hz half-wave waveform, and Figures 10 and 11 are SPWM waveforms. The main technical parameters are as follows: Input voltage DC40~60V Output voltage AC220 (1±1%) V Output frequency 50Hz±0.001Hz Output power 2000VA Current sharing deviation ≤2% Overall efficiency ≥89% 300)this.width=300" border=0> 300)this.width=300" border=0> 300)this.width=300" border=0> 300)this.width=300" border=0> 6 Conclusion This paper introduces the principle of the inverter power supply that can be paralleled based on DSP56F805 digital control, and proposes the process of generating control signals. The experimental results prove the correctness of the digital implementation and achieve good results. The inverter power supply that can be paralleled based on DSP56F805 control has the advantages of good real-time performance, high control accuracy, convenient development and low cost.