Abstract: This paper introduces the application of ABB ACS-510 frequency converter in thermal network and provides a method to control frequency converter using Modbus. Keywords: Inverter square load 1 Introduction Heating network with heating effect, pollution-free and so on, the thermal station as a major part of the heat network, the level of the heat station directly affects the user's control of the heating situation, thermal station energy saving is also the main part of the heat network, so the thermal station Energy conservation, safe operation, of great significance. 2 Engineering Overview Harbin Airport Development Zone, a total of 120 central heating station thermal stations, heating area of ​​about 5.7 million mm2, the total load of 10000J / H, a network of water temperature design 130 ℃ ~ 70 ℃, heating mode for hot water heating , Heat station functions mainly for residents and factories heating, heat station for the first network and the second network for heat and secondary pressure, two pressurized and circulating pump inverter control, the project thermal station ABB ACS510 series Frequency changer circulates the pump as well as complements the transmission part of the water pump to raise the automatic control level of the heat station, has realized the energy conservation. 3 Process Profile The composition of the thermal station [1]: mainly by the heat exchanger, self-control screen, circulating pump, make-up pump, communication line, as shown in the figure. The self-control part [2] mainly consists of a Schneider PLC, which collects various parameters and status of the scene in the PLC. The data collected by the PLC is transmitted to the dispatch center through the ADSL mode. Dispatching Center will return the user room temperature signal from the dispatch center back to the thermal station PLC. Realize the automatic operation of the thermal station according to the method of controlling the secondary water supply temperature and the water supply flow according to the indoor temperature of the end user. Whether the user's indoor temperature is up to the standard based on the temperature curve and the outdoor temperature released by the city heating office. 4 heat station function After a network of heat exchange through the heat exchanger, the second network of hot water to all users, the operation of the thermal station is superior and inferior mainly to the station end-user indoor temperature reaches the city's heating standard and heat Station operating costs, energy conservation as the standard, based on the above heating station heat mode on the use of qualitative and quantitative methods to achieve a combination of heating and energy conservation standards. Quality (1) is through the regulation of a network of water flow control valve to control the secondary network of water temperature. Quality control is simple, but less energy-efficient. The amount of adjustment (1) is in the circulating pump plus variable frequency control (3), by adjusting the secondary water flow to ensure end-user room temperature compliance, this way the energy saving effect is very good. We control the way is based on the amount of quality-based optimization of the control mode, this control mode can save 30% of electricity per year, through the circulating pump frequency and make up the pump frequency to improve the imbalance (3) can save 20% 30%. To ensure that the heat network end-user room temperature standards and the maximum degree of energy conservation, the economic benefits are impressive. 5 circulating pump control mode It is a square load application, the cost of ACS-510 is low and it has MODBUS communication function. We use MODBUS bus to control inverter, including inverter start, stop and speed AI Etc. The operating parameters of the inverter are transmitted to the PLC through the MODBUS bus and then to the dispatch center by the PLC. In this way, the control cabinet is easy to assemble due to less wiring and less auxiliary components with low failure rate, which achieves the control speed through the bus AIsubstation of district heat supply network given, its high precision, effective. Station set up two 37kW circulating pump, two pumps one main and one standby. Inverter with a delay of two. (1) Inverter debugging Inverter J2 is set to "off". Circulating pump drive not set to last address. Set 99 parameters 9901 to 0 by the control panel 9902 Set to "5" "HAND / AUTO" 9903 set to 380 9906 set to "1" 9907 set to "50" 9908 set to "2900" 9909 is set to "37" Set Communication Function 53 Group No. Set 5302 Set to "2" 5303 Set to 9.6kbits / s 5304 is set to "1" Set of 53 parameters should be the same as the protocol in the PLC. Set to "8", "1" "R" and address to "1" here. 98 group parameter setting JZ is set to "off" 9802 set to "1" to start the standard mod Corresponding method of inverter and PLC communication register Inverter register address Corresponding PLC address setting Remarks 1102 External control 1 / external control 2 selection 4001 8 1103 External Control 1 Given AI 4002 -32676 ~ 32676 Reference 1108 Set 0102 Speed ​​40102 0103 Output frequency 40103 0104 Current 40104 0301 Bus Status Word Bit 0 40301 Bit 0 Start-up method of the inverter The PLC sends data to the inverter 4001: Move 5 to 4001; Delay 100; Move 7 to 4001; Move 15 to 4001; Move 47 to 4001; Move 101 to 4001; At this moment the frequency changer starts, sends the rotational speed signal to the frequency changer AI 4001 through the main line. The speed signal of the inverter is controlled by the PLC according to the secondary network supply and return pressure difference of the thermal power station, that is, the secondary water supply flow rate signal, controlling the supply and return pressure difference to realize the real-time flow control. 6 make up pump control Replenishment Frequency inverter using ABB ACS-510 3kW fan pump load inverter, refueling inverter parameter setting and circulating pump is very similar, but its address is set to "3", the inverter J2 is set to "on", fill the water frequency The device is the last device on the Modbus bus. Replenishment speed control signal from the inverter to the drive by the PLC "4003" to ensure that the secondary network of constant pressure hot water. 7 Conclusion Through the heat station circulation pump plus inverter to realize the heat network volume adjustment shows that the ACS-510 inverter energy saving (3) the effect is very obvious, the use of ACS-510 inverter to control the water inverter to reduce heat network offset saves water. Using ACS-510's own modbus bus to control the operation of the inverter saves the investment of equipment in the thermal power station. Bus control reduces many external components, reduces the system failure rate and increases the reliability of the system. The operation of the ACS-510 inverter in the thermal station proves that the energy-saving effect of the inverter used in the circulating pump and the makeup pump of the heat network is very good, which is a very worthwhile promotion of the inverter application.