Illustrated guide to the terminal functions of inverters and inverter wiring

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Based on an explanation of the working principle of frequency converters, Changhui Instruments provides in-depth insights into the wiring of the power supply, motor, and main circuit of frequency converters, as well as the functions of various terminals on these devices, thereby helping electricians and instrument technicians gain a better understanding of frequency converters. The function of an inverter is to convert the mains AC power supply with a fixed frequency (50Hz or 60Hz) into an AC power supply with a variable frequency, which is then supplied to the motor; by changing the frequency of the AC power supply, speed control of the motor can be achieved. There are many types of frequency converters, which can be mainly divided into two categories: AC-DC-AC type frequency converters and AC-AC type frequency converters. An AC-DC-AC type inverter uses circuits to first convert the mains power supply into a direct current supply, and then converts that direct current supply into an alternating current supply with a variable frequency, which is subsequently supplied to the motor. By adjusting the frequency of the output power supply, the speed of the motor can be changed. http://yunrun.com.cn/upload/201810/25/201810251501142225.png Typical block diagram of an AC-DC-AC type inverter. An AC-AC type inverter uses circuits to directly convert the mains power supply into an alternating current supply with a variable frequency, which is then supplied to the motor; by adjusting the frequency of the output power supply, the speed of the motor can be changed. http://yunrun.com.cn/upload/201810/25/201810251522094662.png Typical structural block diagram of AC-AC frequency converters. Paperless recorders: yunrun.com.cn/product/. AC-AC frequency conversion circuits can generally only reduce the frequency of the input alternating current before outputting it; since the frequency of the mains power is already low, the speed control range of AC-AC frequency converters is quite narrow. Additionally, such converters require a large number of power electronic components such as thyristors, which results in a larger size and higher cost for the device. As a result, AC-AC frequency converters are not as widely used as AC-DC-AC frequency converters; therefore, Changhui Instruments mainly focuses on introducing AC-DC-AC frequency converters. General wiring diagram: Taking the Mitsubishi FR-A540 inverter as an example, the general wiring diagram is as follows: http://yunrun.com.cn/upload/201810/25/201810251526093475.png General wiring for the Mitsubishi FR-A540 inverter. The terminals of the inverter can be divided into main circuit terminals and control circuit terminals. ◆ Explanation of the main circuit terminals of the inverter: Terminal symbol, Terminal name, Description. R, S, T: AC power input – Connect to the mains power supply. However, when using a converter with a high power factor, make sure that these terminals are not connected. The U, V, W outputs of the inverter are connected to the three-phase squirrel-cage motor; the R1 and SI terminals are connected to the power supply for the control circuit, while the R and S terminals are connected to the AC power supply. When abnormal display and output are maintained or when a high power factor converter is used, remove the shorting strip between R-R1 and S-S1, and supply an external power source to terminals P and PR to connect the braking resistor. Remove the shorting strip between terminals PR and PX, and connect the optional braking resistor between P and PR. Connect P and N to the braking unit; connect the optional FR-BU type braking unit, power regeneration unit, or high power factor converter between them. Connect P and P1 to the DC reactor for improving the power factor. Remove the shorting strip between terminals P and P1, and connect the optional reactor for improving the power factor (FR-HC). Connect PR and PX to the internal braking circuit. When PX and PR are shorted together using a shorting strip (as per the factory setting), the internal braking device becomes active. Wiring: The enclosure of the frequency converter must be grounded by connecting it to the earth. ◆ Explanation of control circuit terminals. Wiring of the frequency converter’s main circuit: The terminal blocks for the main circuit of the frequency converter are shown in the figure below. The R, S, and T terminals on the terminal block are connected to a three-phase AC power supply; if connected to a single-phase AC power supply, the R and S terminals must be used for connection ； The U, V, and W terminals are connected to the motor ； The P1 and P terminals, RP and PX terminals, R and R1 terminals, as well as S and S1 terminals are connected using shorting strips ； The grounding terminal is connected and fixed to the ground wire using screws. http://yunrun.com.cn/upload/201810/25/201810251551542538.png Terminal block for the main circuit of the inverter. 1. Principle of wiring the main circuit of the inverter: http://yunrun.com.cn/upload/201810/25/201810251601061912.png Schematic diagram of the main circuit wiring. The R, S, and T terminals are connected to the mains power supply, while they are also connected to the rectifier circuit of the inverter. The U, V, and W terminals are connected to a motor, while an inverter circuit is connected internally. A shorting piece (or a DC reactor to improve the power factor) is connected to the P and P1 terminals to link the rectifier circuit with the inverter circuit. Shorting strips are connected to the PX and PR terminals to link the internal braking resistor with the braking control device. If the braking effect of the internal braking resistor is not satisfactory, the shorting piece between the PX and PR terminals can be removed, and a braking resistor can be connected externally to the P and PR terminals. The P and N terminals are respectively the positive and negative ends of the internal DC voltage; to enhance the braking capacity during deceleration, the shorting piece between the PX and PR terminals can be removed, and a dedicated braking unit (i.e., a braking circuit) can be connected to the P and N terminals. The R1 and S1 terminals are internally connected to the control circuit; externally, they are connected to the R and S terminals via shorting links. The power from the R and S terminals is supplied to the control circuit as a power source through these shorting links via the R1 and S1 terminals. If it is desired that the control circuit can still function in the absence of mains power supply at terminals R, S, T, the shorting pieces between R and R1, as well as between S and S1, can be removed, allowing the two-phase mains power supply to be connected directly to terminals R1 and S1. 2. Connection of power supply, motor, and inverter: http://yunrun.com.cn/upload/201810/25/201810251619331756.png When making the connections, it is important to ensure that the power cables are not connected to the U, V, and W terminals; otherwise, it may damage the internal circuits of the inverter. Since the inverter may leak electricity during operation, it is necessary to connect the grounding terminal to the ground wire in order to discharge any leakage current from the inverter. 3. Connection of inverter options: There are many options available for inverters, including external braking resistors, FR-BU braking units, FR-HC rectifiers for improving the power factor, FR-RC energy recovery units, and DC reactors for enhancing the power factor. First, the connection of commonly used external braking resistors and DC reactors will be explained; for the connection of other options, refer to the user manual for the Mitsubishi FR-A540 frequency converter. ①Connection of external braking resistors: http://yunrun.com.cn/upload/201810/25/201810251628235353.png. To connect an external braking resistor to the inverter, first remove the shorting piece between the PR and PX terminals, and then use connection wires to link the braking resistor to the PR and P terminals. ②Connection of the DC reactor: http://yunrun.com.cn/upload/201810/25/201810251632105408.png. For connecting the DC power factor reactor, first remove the shorting strip between the P1 and P terminals, and then use connection wires to link the DC reactor to the P1 and P terminals. 4. Wiring for the external power supply to the control circuit: http://yunrun.com.cn/upload/201810/25/201810251641090831.png. The power terminals R1 and S1 of the control circuit are connected to the R and S terminals by default. During operation, if an abnormality occurs in the inverter, it may cause the circuit breaker (or contactor) at the power input terminal of the inverter to disconnect, which in turn cuts off the power supply to the inverter’s control circuit; as a result, the inverter is unable to send out any abnormality signals. To maintain power to the control circuit when needed, connect the R1 and S1 terminals of the control circuit’s power supply to the two-phase power lines on the input side of the circuit breaker. This way, even after the circuit breaker trips, the control circuit remains powered. Wiring of the inverter control circuit: 1. Control circuit terminal block; 2. Changing the control logic. The FR-A540 inverter comes with two types of control logic: leakage type and source type, with the leakage type logic being set by default at the time of manufacture. To change the control logic of the inverter to source logic, follow the steps shown in the figure below; the specific procedure is as follows: http://yunrun.com.cn/upload/201810/25/201810251644277549.png Remove the front cover of the inverter. http://yunrun.com.cn/upload/201810/25/201810251648283640.png Loosen the screws of the control circuit terminal block, then remove the terminal block ； On the back of the control circuit terminal block, remove the shorting piece from the control logic setting jumper and install it on another jumper nearby. In this way, the control logic of the inverter is changed from sink control to source control. http://yunrun.com.cn/upload/201810/25/201810251658289284.png Typical wiring diagram for an inverter operating under leakage-type control logic. In the diagram, the forward button is connected between the STF terminal and the SD terminal; when the forward button is pressed, current is generated in the inverter’s internal power supply and flows out from the STF terminal, passes through the forward button, and returns to the negative pole of the internal power supply via the SD terminal. The path of this current is shown in the diagram. Additionally, when an external circuit is required at the open-circuit output of the transistor collector inside the inverter, the SE terminal must be used as the common terminal. The current from the external circuit flows in through the corresponding terminal (the RUN terminal in the diagram), passes through the transistor internally, and then flows out through the SE terminal. The path of the current is indicated by the arrows in the diagram; the diodes connected by dashed lines do not conduct under drain-type control logic. http://yunrun.com.cn/upload/201810/25/201810251744358957.png Typical wiring diagram for an inverter operating under source-control logic. The forward button in the diagram should be connected between the STF terminal and the PC terminal. When the forward button is pressed, current is generated by the inverter’s internal power supply; this current flows out from the PC terminal, passes through the forward button, and enters again at the STF terminal, returning to the negative pole of the internal power supply. The path of this current is shown in the diagram. Additionally, when an external circuit is required at the open-circuit output of the transistor collector inside the inverter, the SE terminal must be used as the common terminal; the current should flow in from the SE terminal, pass through the transistor internally, and then exit through the corresponding terminal (such as the RUN terminal in the diagram). The path of the current is indicated by the arrows in the diagram, and the diodes connected by dashed lines indicate that they cannot conduct under source-control logic. 3. Use of STOP, CS, and PC terminals ① Use of the STOP terminal: http://yunrun.com.cn/upload/201810/25/201810251704011756.png Wiring diagram for self-holding of the start signal (open-collector logic). This terminal is used when stop control is required. The stop button shown in the diagram is a normally closed button. When the forward button is pressed, current flows from the STF terminal; the path of this current is: from the STF terminal → the forward button → the STOP terminal → the stop button → and back into the SD terminal. The presence of current at the STF terminal indicates that a forward operation command has been received, and the inverter supplies power to the motor in forward direction, causing the motor to rotate forward. When the forward button is released, no current is output from the STF terminal, and the motor stops rotating. If the stop button is pressed, no current can be output from the STOP, STF, and STR terminals, and the motor cannot be started. ②Use of the CS terminal: The CS-SD terminals are shorted together; this terminal is used when instant power loss followed by restart is required, or when switching between the mains power supply and the inverter. For example, in leaky logic mode when performing an instant power loss restart, first short-circuit the CS-SD terminals, and then set parameter Pr.57 to a \"free-running time for instant power loss restart\" other than \"9999\". ③Use of PC terminals: When a PC or SD terminal is used to supply a DC 24V power supply, the PC serves as the positive pole of the power supply, while the SD serves as the negative pole (common terminal). The PC version can supply a DC voltage of 18V to 26V, with a permissible current of 0.1A. http://yunrun.com.cn/upload/201810/25/201810251709100872.png Connection of the PU interface; appearance of the PU interface and definitions of its pins. 1. Connection of the PU interface to a computer with an RS-485 interface: When connecting a computer to a single frequency converter, the connection of the PU interface is as shown in the figure below. During connection, both the computer’s RS-485 interface and the inverter’s PU interface use RJ45 connectors (commonly known as network plugs), while the connection cable used is a 10BASE-T cable (such as the twisted pair cables used for computer networking). Since pins ② and ⑧ of the PU interface are used to supply power to the operation panel, these pins are not utilized during RS-485 communication with a computer. http://yunrun.com.cn/upload/201810/25/201810251714233638.png Wiring methods for the PU interface and RS-485 interface. When connecting a computer to multiple inverters, the connection of the PU interface is as shown in the figure below. The function of the distributor in the diagram is to divide one signal into multiple signals. Additionally, due to transmission speed and distance, signal reflections may occur, causing communication issues; therefore, a terminal impedance resistor (100Ω) can be installed at the distributor connected to the last frequency converter. http://yunrun.com.cn/upload/201810/25/201810251722278162.png Computer connected to multiple inverters
http://yunrun.com.cn/upload/201810/25/201810251726483631.png Wiring method for connecting a computer to multiple inverters
2. Connecting the PU interface to a computer with an RS-232C interface
Since most computers do not have an RS-485 interface, while many computers are equipped with an RS-232C interface (serial port, also known as COM port), an RS-232C-to-RS-485 interface converter can be used to enable computers with an RS-232C interface to connect to the PU port. Source: In-depth guide with multiple images on the terminal functions and wiring of frequency converters – yunrun.com.cn/tech/2224.html