Application of a bus-type measurement and control technology in high-frequency switching combined power supply

Abstract: In view of the need for efficient, low-pollution green power design, a highly reliable, easy-to-maintain, fully functional, and compact power monitoring system is very necessary. This paper introduces the design principle of a bus-based measurement and control technology in an intelligent power monitoring system, and provides the hardware circuit and software design of the bus measurement and control interface.

Keywords: power supply; bus-type measurement and control; single-chip microcomputer

How to measure and control power products reliably and conveniently is the core issue of intelligent high-frequency switching power supplies. Power supply measurement and control involves data measurement, control, communication, and human-computer dialogue. The rationality of the measurement and control scheme is the key to the reliability of the power supply system. In view of this, this article focuses on the specific application of a bus-type measurement and control scheme in intelligent high-frequency switching combination power supplies.

Intelligent high-frequency switching combined power supply generally uses dual-circuit mains as AC input through electrical interlocking, and provides lightning protection measures and user AC shunts. The input AC is rectified by the high-frequency switching rectifier module to generate the DC power required by the user (usually 12V, 24V, 48V, 110V, 220V and other voltage levels), and then the output DC is connected to the battery pack and the user DC shunt. This is the basic principle of the intelligent high-frequency switching combined power supply, as shown in Figure 1.

2 Design Principles

The power supply monitoring system needs to accurately measure various analog quantities and switch quantities of the power supply, including: the voltage, current, frequency of the AC unit, the working status of the lightning protection module and the AC branch; the system closing bus voltage, control bus voltage, and the current and working status of each control bus branch of the DC unit; the battery pack voltage and current, single battery voltage, battery temperature, and charging and switch quantity (door and window switches, air conditioning switches, fire alarms, water alarms, smoke alarms, and unattended) of the battery unit; the insulation status of each bus branch of the insulation detection unit; the transient changes in the operating parameters of each rectifier module; and real-time control of the mains switching, step-down silicon stack voltage regulation, battery management (equalizing charge, floating charge, current limiting, steady current, discharge test, battery temperature compensation, feeder resistance compensation), multi-stage battery deep discharge protection, user alarm nodes, etc.; classify and set various operating parameters to respond to various requirements of centralized monitoring of remote users in a timely manner; at the same time, the rationality of the system electrical design, the operability of assembly and commissioning, and the maintainability of engineering services must also be considered. According to the above functional conditions, the following measurement and control scheme is proposed, as shown in Figure 2.

Figure 1 Schematic diagram of intelligent high-frequency switching power supply

Figure 2 Schematic diagram of bus measurement and control principle of power supply monitoring system

The obvious feature of this power monitoring test solution is that AC detection board, DC detection board, battery detection board, insulation detection board, environment detection board and electrical control board are externally mounted on the measurement and control bus BUS. These 6 boards can be selected according to user needs, and in the electrical design of the whole machine, these boards can be arbitrarily arranged according to the needs of designers, overcoming the disadvantage of connecting all signal lines to various interfaces on the back of the monitor, thereby greatly improving the work efficiency of assembly and debugging and engineering service personnel, and at the same time overcoming the weakness that the real-time and reliability of measurement and control are greatly reduced due to data exchange between various detection and control boards and monitors in a communication manner.

3 Hardware Design

3.1 Measurement and control main board

The measurement and control main board is based on PCF80C552, and the INS8250A universal asynchronous receiver and transmitter UART chip is expanded as the communication interface for centralized monitoring or remote monitoring of the power supply system. In Figure 3, PWM0 and PWM1 of PCF80C552 are used as the control signal interface of the internal feedback link of the rectifier module, MAX813 is used as the automatic reset circuit of the microcontroller, ATMEL93C66 is used as the EEPROM to save the system operation parameters, and a 4×4 row-column keyboard interface and a 240×128 dot-matrix LCD display interface are expanded on the 8-bit data bus of the P0 port. In addition, the 8-bit data drive interface composed of D flip-flop SN74HC574, inverter SN74HC04, and Schmitt trigger SN74HC14 is expanded as the 8-bit input control signal (DC0-DC7) of the bus measurement and control interface (pins 9-16 of socket X1). Pins 1, 3, and 5 of the bus measurement and control interface socket X1 are respectively +15V, GND, and -15V of the detection board, and pins 7 and 8 are respectively the digital signal Digital and the analog signal Analog output by the detection board. The switch quantity Digital from each detection board is sent to the P1.0 port of the microcontroller in a time-sharing manner. The 12-bit parallel output high-speed A/D converter MAX120 accurately, quickly, and time-sharingly converts the Analog signal of each detection board into a 12-bit Digital signal and sends it to the P5 (low 8 bits) and P4 ports (high 4 bits) of the 80C552, and the 8-bit input control signal (DC0-DC7) of the bus measurement and control interface can be used to drive and trigger the electrical control board. Therefore, the bus measurement and control interface has the dual functions of the forward channel and the backward channel of the microcontroller, realizing the detection and electrical control of analog signals and digital signals.

3.2 Bus measurement and control interface circuit

As shown in Figure 4, 8 detection and control boards are externally mounted on the measurement and control bus (special users need multiple sets of batteries, so 3 battery detection boards are designed), and the hardware circuits of the control signal (DC0-DC7) and the sampling signal (Analog, Digital) are shared channels of each detection board. This requires the single-chip microcomputer to automatically identify the 8 detection boards. Therefore, the 8-bit control signal (DC0-DC7) must be decoded. The board selection address circuit of the 8 detection boards is composed of the analog conversion switch U5 (SN74HC4051) and the address switch X2. DC5, DC6, and DC7 are respectively sent to the A, B, and C ports of U5, and X0-X7 are selected with 000-111. During debugging, only one of the X2 address switches on each detection board needs to be turned on to play the board selection function (see Table 1). Then, the board selection signal is sent to the NAND gate U8A, U8B, U8C (SN74HC10) unit, and at the same time sent to the OR gate U7A (SN74HC4075) unit through the Schmitt trigger U6B (SN74HC14) unit. If the board selection signal is low level (L), the output signals of U7A, U8A, U8B, U8C are high level (H), and the INH ports of the analog switches U1, U2, U3, and U4 are blocked respectively, and the detection board has no signal output or input; if the board selection signal is high level (H), the outputs of U7A and U8A, U8B, and U8C only depend on DC3 and DC4. When DC4 and DC3 are 00, only U7A outputs a low level to select U1, and U8A, U8B, and U8C output H to lock U2, U3, and U4; when DC4 and DC3 are 01, only U8A outputs L to select U2; when DC4 and DC3 are 10, U8B selects U3; when DC4 and DC3 are 11, U8C selects U4 (see Table 2). DC3 and DC4 pass through a small or-not gate (composed of U7B, U6E, and V4) and a large or-not gate (composed of V1, V2, U6A, and R2) to achieve the selection control of U5. When one of U1 to U4 is selected, it is sent to its A, B, and C ports respectively through DC0, DC1, and DC2, thereby controlling the analog conversion switch to sample the values ​​of the input signals X0 to X7, or to control the output signals X0 to X7 (see Table 3). U1 and U2 collect 16 digital signals DIG1 to DIG16 (such as lightning protection status, AC branch and DC branch switch status, bus insulation status, etc.). The selected digital signals (Digital) are input to P1.0 of CPU (PCF80C552) through pin 7 of bus measurement and control interface in time-sharing manner.

Figure 4 Bus measurement and control interface circuit

Figure 5 Inspection flow chart of DC, AC and environmental detection boards

Figure 6 Inspection flow chart of insulation and battery detection board

Table 1 DC5～DC7 decoding table

DC7	DC6	DC5	U5	X2(on)	Selected test panels
L	L	L	X0	1	comminicate
L	L	H	X1	2	DC
L	H	L	X2	3	insulation
L	H	H	X3	4	electric
H	L	L	X4	5	environment
H	L	H	X5	6	Battery 1
H	H	L	X6	7	Battery 2
H	H	H	X7	8	Battery 3

Table 2 DC3, DC4 decoding table

DC4	DC3	The 74HC4051 is selected
L	L	U1
L	H	U2
H	L	U3
H	H	U4

Table 3 DC0～DC2 decoding table

C	B	A	Detection quantity of U1～U4
DC2	DC1	DC0
L	L	L	X0
L	L	H	X1
L	H	L	X2
L	H	H	X3
H	L	L	X4
H	L	H	X5
H	H	L	X6
H	H	H	X7

U3 and U4 collect 16 analog signals AN1~AN16 (such as voltage, current, temperature, frequency, etc.). The selected analog signals are input to the AIN port of the 12-bit A/D converter MAX120 through the pin 8 of the bus measurement and control interface in time-sharing. After high-speed and accurate conversion by MAX120, the 12-bit Digital signals output in parallel are sent to the P5 (low 8 bits) and P4 (high 4 bits) ports of the CPU. In short, DC7, DC6, and DC5 can select 8 detection boards, DC4 and DC3 can select 4 analog conversion switches, and DC2, DC1, and DC0 can select 8 signals of each analog conversion switch. According to the multiplication principle, the bus measurement and control interface can detect 8×4×8 or 256 signals through DC0-DC7. Table 4 lists the signal access addresses of the 8 detection boards. In fact, DIG1~DIG16 of the insulation and battery detection boards are analog quantities, and AN1~AN16 of the electrical control board are triggered digital quantities.

Table 4 Detection board signal address

Detection board	Digital quantity (DIG1～DIG16)	Analog (AN1～AN16)
comminicate	00～0F	10～1F
DC	20～2F	30～3F
insulation	40～4F	50～5F
electric	60～6F	70～7F
environment	80～8F	90～9F
Battery Pack 1	A0～AF	B0～BF
Battery Pack 2	C0～CF	D0～DF
Battery Pack 3	E0～EF	F0～FF

It should be noted that the bus measurement and control interface circuit shown in Figure 4 is only applicable to DC, AC, and environmental detection boards. The bus measurement and control interface circuits of other detection boards need to be adjusted appropriately. For the electrical control board, as long as the X pins of U1~U4 are grounded, X0~X7 are connected to the pull-up resistor and then connected to the relay through the Schmitt trigger, the control of 32 relays can be realized. For the insulation detection board, as long as the X pins of U1~U4 are connected, and then connected to the pin 8 of X1, the insulation detection of 32 bus branches can be realized. For the battery detection board, since each battery voltage needs to be processed by differential proportional operation, a dual 8-way analog conversion switch MAX397 can select 8 batteries, and the control signals of U7A, U8A, U8B, and U8C can be expanded to 4 MAX397s, so that 32 batteries can be inspected. After the voltage of each battery is processed by time-sharing, the generated battery polarity signal and battery correction voltage signal are respectively input into the Digital and Analog pins of the bus measurement and control interface. Moreover, after the three battery test boards are linked in the software, a maximum of 96 batteries can be measured. Of course, according to user needs, other test boards can be replaced with battery test boards, thereby increasing the scale of battery testing.

4. Software Design

Faced with complex measurement data and electrical control, after bus decoding and addressing, the software design has obvious regularity. Due to space limitations, this article lists the process of the inspection subroutine RdAux1 applicable to the DC, AC, and environmental detection board in Figure 4, as shown in Figure 5, and the process of the inspection subroutine RdAux2 applicable to the insulation and battery detection board, as shown in Figure 6. The program of the electrical control board is relatively simple. As long as it is programmed according to the functional conditions and the relay address in Table 4, the corresponding relay can be controlled.

The RdAux1 assembly program listing is as follows:

;Internal RAM register definitions

FLAG EQU 20H; detection board installation flag

ACB BIT 0 ; AC board enable

DCB BIT 1 ; DC board enable

AMIB BIT 4 ;Enable environmental board

;Definition of storage area of ​​external RAM

AUXAD EQU 1000H ; Inspection buffer first address

ACBUF EQU AUXAD; AC board buffer

DCBUF EQU ACBUF＋ 48 ; DC board buffer

AMBUF EQU DCBUF＋ 48 ;Environmental board buffer

IOBUF EQU EC00; Inspection entry address, used to input the detection quantity address

;======Inspection subroutine======

RdAux1: MOV A,FLAG

JB A.0,AC

JB A.1,DC

JB A.4,AMI

SJMP EndAux

AC: MOV R6, # HIGH (ACBUF); temporarily store the buffer address of the detection board in R6, R7

MOV R7,＃LOW(ACBUF)

SJMP RDAX

DC: MOV R6,＃HIGH(DCBUF)

MOV R7,#LOW(DCBUF)

SJMP RDAX

AMI: MOV R6,＃HIGH(AMBUF)

MOV R7,＃LOW(AMBUF)

RDAX:MOV R2,＃16; 16-way detection

MOV R4,＃ 0; R4 stores the starting address of the detection value

Digit: LCALL RdAux0; Patrol 16-channel digital quantity

MOV A,#0

MOV C,P1.0

RLC A

MOV DPH,R6

MOV DPL,R7

MOVX @DPTR,A

INC DPTR

INC R4

DJNZ R2,Digit

MOV R2,#16

Analog:LCALL RdAux0; Patrol 16 analog quantities

LCALL ADCVER ; MAX120 A/D conversion

MOV A,P5

MOVX @DPTR,A ; Save the lower 8 bits of A/D

INC DPTR

MOV A,P4

ANL A,#0FH

MOVX @DPTR,A ; Save A/D high 4 bits

INC DPTR

INC R4

DJNZ R2,Analog

RET

RdAux0:MOV DPTR,＃IOBUF; Get the inspection value

MOV A,R4

MOVX @DPTR,A

LCALL DELAY; Delay subroutine

EndAux:RET

5 Conclusion

Bus-type measurement and control technology is the basis for intelligent high-frequency switch combination power supply to achieve high reliability, intelligence and maintainability. It is also one of the intelligent core technologies for efficient, reliable, low-pollution green power supply with few or no personnel on duty. Its notable features are:

1) Meet the requirements of different monitoring solutions for various types of power supplies;

2) The modularization of software and hardware greatly facilitates the development of new products;

3) Enhanced the flexibility of the overall machine layout for electrical designers;

4) Improved the maintenance efficiency of engineering services.