Control method of portable power supply end voltage stabilization compensation power electronic transformer

Abstract

The invention discloses a control method of a portable power supply end voltage stabilization compensation power electronic transformer. The control method comprises the following steps: 1) connecting the power electronic transformer with a user end; a power line communication device PLC1 and a power line communication device PLC2 are arranged; 2) measuring the voltage u2 through the PLC1, measuring the voltage u1 through the PLC2, and calculating the current value i0 of the power cable; 3) setting a user side load voltage control loop PI1, a cable current control loop PI2 and a user side load voltage auxiliary control loop PI3; (4) when u2 is smaller than u2 *, the control loop PI1 stabilizes the user end voltage u1; when u2 is greater than or equal to u2 *, the voltage is controlled to be stabilized at u2 *; and when i0 is greater than or equal to id, the PI2 is combined with the PI1, and the user terminal voltage u1 is stabilized. The stability of user terminal voltage can be effectively improved, the electric energy transmission efficiency is improved, the size and weight of the cable are greatly reduced, and the power supply cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a control method for a portable power supply end voltage stabilization compensation power electronic transformer based on user end voltage accurate measurement and power line communication long-distance information feedback. Background Art

[0002] Low-voltage (220V / 380V) long-distance power supply mode is widely used for power supply guarantee in natural disaster rescue, emergency communication, field military activities, field operations, field camping and other field activities. However, the 220V / 380V low-voltage power distribution radius is generally only a few hundred meters, which cannot meet the demand for long-distance power supply in the field. Low-voltage long-distance power transmission has problems such as large voltage drop, large power loss, low transmission efficiency, severe cable heating, and too low voltage at the load end, which leads to unstable operation, performance degradation, damage or even burning of electrical equipment. Solving the problem of low-voltage long-distance power transmission in the field is urgent.

[0003] At present, there are three main technical routes to solve the problem of low-voltage long-distance power transmission. The first is to use thickened cables to reduce cable resistance, thereby achieving the purpose of reducing voltage drop and loss. This method can solve the problems of large voltage drop and loss in power transmission within a certain transmission distance and power, and the method is simple. However, this method is costly to use in the field, has large volume and weight, and is difficult to transport, carry, and lay cables in the field.

[0004] The second is to use the interval power transformation method. First, a step-up transformer is used at the power supply end to increase the transmission voltage. High-voltage power transmission can reduce energy loss. A step-down transformer is used at the user end to reduce the voltage to 220V / 380V low voltage to supply power to the user. This method can effectively reduce cable power loss and has the characteristics of stable voltage at the user end. However, this method has the problems of complex system structure, high cost, large size and weight of step-up and step-down transformers, inconvenient transportation, carrying, use and installation, etc. when used in the field, and has poor applicability.

[0005] The third method is to use cable voltage drop compensation at the user end. This method uses transformer winding boost to compensate for cable voltage drop or stabilized power supply to achieve voltage stabilization at the user end. However, this method has the disadvantages of large cable loss, low power transmission power, large coil volume and weight, and inability to accurately and stably output. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to solve the problems of poor stability of remote power use, high power consumption, large cable volume and weight, and high cost, and to provide a control method for a portable power supply-end voltage-stabilizing and compensating power electronic transformer, which can effectively improve the stability of the user-end voltage, improve the power transmission efficiency, and greatly reduce the volume and weight of the cable, and reduce the power supply cost.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a control method for a portable power supply end voltage stabilizing compensation power electronic transformer, characterized in that it includes the following steps:

[0008] 1) Connect the input end of the power electronic transformer to the power supply cable, and connect the output end to the user end through the power cable; and respectively set power line communication devices PLC1 and PLC2 at the output end of the power electronic transformer and the input end of the user end;

[0009] 2) PLC1 measures the voltage u2 at the output end of the power electronic transformer, PLC2 measures the voltage u1 at the user end, and feeds back the voltage value u1 measured by PLC2 to PLC1 in real time; the digital controller calculates the current value i0 of the power cable according to the voltage u2 at the output end of the power electronic transformer, the voltage u1 at the user end, and the impedance;

[0010] 3) Setting the user-side load voltage control loop PI1, by setting the voltage reference value u2* and the voltage value u1 of the remote end user side to form a voltage outer loop; setting the cable current control loop PI2, by setting the current reference value id and the cable line current value i0 to form a current inner loop; setting the user-side load voltage auxiliary control loop PI3, in parallel with the user-side load voltage control loop PI1, and capable of being switched by a conversion switch;

[0011] 4) Read the current voltage value u2 at the output end of the power electronic transformer and the current value i0 of the cable line, and compare them with the set voltage reference value u2* and the set current reference value id. When u2<u2*, use PI closed-loop control to adjust the input voltage of the power electronic transformer, and stabilize the user-end voltage u1 through the user-end load voltage control loop PI1; when u2≥u2*, switch to the user-end load voltage auxiliary control loop PI3 to control the voltage at the output end of the power electronic transformer to be stable at u2*; at the same time, when i0≥id, the cable current control loop PI2 is combined with the user-end load voltage control loop PI1 to stabilize the user-end voltage u1.

[0012] Further, the power electronic transformer includes a digital controller, an AC / DC module, a DC / AC module and a display screen, and the power line communication device PLC1 is connected to the digital controller to transmit the detected voltage value to the digital controller;

[0013] The power supply cable includes a three-phase power supply line and a neutral line, wherein the midpoint of each rectifier bridge arm of the AC / DC module is connected to the neutral line, and a relay switch S1 is provided between the front end of the neutral line and the connection between the rectifier bridge arm and the neutral line; the DC / AC module has four inverter bridge arms, wherein the midpoint of the inverter bridge arm is connected to the neutral line, and a relay switch S2 is provided between the connection between the rectifier bridge arm and the neutral line and the connection between the inverter bridge arm and the neutral line;

[0014] The digital controller is used to control the on and off of the relay switch S1 or S2.

[0015] Further, in step 4), the specific process is as follows:

[0016] S1: Read the current voltage value u2 at the output of the power electronic transformer and the current value i0 of the cable line;

[0017] S2: Compare the read voltage value u2 and current value i0 with the set voltage reference value u2* and current reference value id;

[0018] S3: When u2<u2*, the PI closed-loop control algorithm is used to adjust the PWM control signal to increase the on-time of the switch tube of the power electronic transformer, thereby increasing the voltage value u2 at the output end of the power electronic transformer until it stabilizes at the reference value u2*;

[0019] S4: When u2≥u2*, the protection function is started.

[0020] Furthermore, the display screen is an interactive display screen used for parameter setting and data display, and has a signal indicator light to display the current voltage output status.

[0021] Furthermore, it also includes a mobile terminal that can communicate with the power electronic transformer to perform parameter setting and data display.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. By controlling the voltage at the output end of the power electronic transformer, the voltage at the user end (remote end) can be controlled, rather than directly controlling the voltage at the remote user end. This can effectively improve the stability of the voltage at the user end and improve the efficiency of power transmission. In addition, by setting up an auxiliary control loop, the power electronic transformer equipment can be protected in extreme cases.

[0024] 2. Use power line communication devices to measure voltage and current and feedback the measured values. The power lines and communication lines are shared and no rewiring is required. Compared with wireless communication, it has a longer transmission distance and faster transmission rate, and has low cost, small size and light weight.

[0025] 3. The power supply voltage, load voltage, cable line current measurement, voltage regulation compensation and protection functions are integrated into the same hardware system. The cable line status can also be remotely monitored on the mobile phone. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the hardware system structure in this solution.

[0027] Figure 2 This is the circuit structure diagram of the power electronic transformer.

[0028] Figure 3 This is the control schematic diagram of this solution. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] Example: See Figure 1-Figure 3 , a control method for a portable power supply end voltage stabilizing compensation power electronic transformer, comprising the following steps:

[0031] 1) Establish a power transmission hardware system, that is, connect the input end of the power electronic transformer to the power supply cable (grid or generator set), and connect the output end to the user end through the (long-distance) power cable. Set power line communication devices PLC1 and PLC2 at the output end of the power electronic transformer and the input end of the user end respectively; wherein, the power line communication devices PLC1 and PLC2 communicate and transmit data through the carrier communication of the power cable, realize the sharing of power lines and communication lines, do not need to rewire, have a longer transmission distance and faster transmission rate, and have the advantages of low cost, small size and light weight.

[0032] 2) PLC1 measures the voltage u2 at the output end of the power electronic transformer, PLC2 measures the voltage u1 at the user end, and feeds back the voltage value u1 measured by PLC2 to PLC1 in real time; the digital controller calculates the current value i0 of the power cable according to the voltage u2 at the output end of the power electronic transformer, the voltage u1 at the user end, and the impedance; that is, i0 = (u2-u1) / Z, where Z is the impedance.

[0033] 3) Set the user-side load voltage control loop PI1, and form a voltage outer loop by setting the voltage reference value u2* and the long-distance end user side voltage value u1; set the cable current control loop PI2, and form a current inner loop by setting the current reference value id and the cable line current value i0; set the user-side load voltage auxiliary control loop PI3, which is connected in parallel with the user-side load voltage control loop PI1 and can be switched by a conversion switch.

[0034] 4) Read the current output voltage value u2 of the power electronic transformer and the current value i0 of the cable line, and compare them with the set voltage reference value u2* and the set current reference value id. When u2<u2*, use PI closed-loop control to adjust the input voltage of the power electronic transformer, and stabilize the user-end voltage u1 through the user-end load voltage control loop PI1; when u2≥u2*, switch to the user-end load voltage auxiliary control loop PI3 to control the voltage at the output end of the power electronic transformer to be stable at u2*, or stabilize the output u1 to 220V / 380V; at the same time, when i0≥id, add current outer loop control, combine the cable current control loop PI2 with the user-end load voltage control loop PI1, force the start of the protection function, and stabilize the user-end voltage u1.

[0035] The power electronic transformer includes a digital controller, an AC / DC module, a DC / AC module and a display screen, and the power line communication device PLC1 is connected to the digital controller to transmit the detected voltage value to the digital controller. During implementation, the power electronic transformer, the power line communication device PLC1, the (DSP) digital controller and the display screen are integrated into one.

[0036] The display screen is an interactive display screen, which is used for parameter setting and data display, and has a signal indicator light to display the current voltage output status. It also includes a mobile terminal that can communicate with the power electronic transformer to perform parameter setting and data display. During operation, the system's voltage (u1)-time (t), voltage (u2)-time (t), and current (i0)-time (t) data are displayed through the display screen, and the network can also be connected to a mobile terminal, such as a mobile phone on the user side, for remote monitoring. In normal mode, the green indicator light on the display screen is on; in protection mode, the red indicator light on the display screen is on, and it is displayed immediately on the mobile phone APP end to prompt the user of the current status and to take targeted actions.

[0037] The power supply cable includes a three-phase power supply line and a neutral line, wherein the midpoint of each rectifier bridge arm of the AC / DC module is connected to the neutral line, and a relay switch S1 is provided between the front end of the neutral line and the connection between the rectifier bridge arm and the neutral line; the DC / AC module has four inverter bridge arms, wherein the midpoint of the inverter bridge arm is connected to the neutral line, and a relay switch S2 is provided between the connection between the rectifier bridge arm and the neutral line and the connection between the inverter bridge arm and the neutral line.

[0038] Relay switches S1 and S2 are switched by digital controllers through blocking corresponding power devices and relays to realize different circuit control strategy switching. In the voltage regulation / protection function modes, AC-DC always provides stable DC voltage for DC-AC and completes power factor correction. DC-AC controls and stabilizes the user-side voltage according to the set value during the voltage regulation function, and stabilizes its own output voltage during the protection function. In the case of three-phase four-wire output, the neutral line n is derived from the midpoint of the fourth bridge arm, and the output end of the power electronic transformer can withstand a large unbalanced component. S1 and S2 are used to control and change the circuit topology. When S1 is disconnected, the input is a three-phase three-wire system. When S1 is turned on, the input can use single-phase AC input or three-phase four-wire input, which improves compatibility. By setting switch S2, compatible multi-standard output can be achieved. This solution first converts AC power into DC power through AC-DC. The DC bus voltage udc can reach 500-1000V. DC-AC then converts DC power into controllable AC power. The output voltage can be adjusted in real time according to the settings. In the application scenario of long cables, the output voltage of DC-AC can be adjusted to reduce the loss on the output cable.

[0039] The digital controller is used to control the on and off of the relay switch S1 or S2.

[0040] In specific implementation, during voltage stabilization operation, PI1 is the remote load voltage control loop, which forms a voltage outer loop by setting the voltage reference value u2* (the reference value of 220V / 380V corresponding to the dq coordinate transformation) and the voltage value u1 at the remote end user side; PI2 is the cable current control loop, which forms a voltage outer loop by setting the current reference value i d The above two loops stabilize the voltage at the user end at 220V / 380V, and limit it to the maximum value when the current is too large to prevent the cable current from exceeding the tolerable range. Once the load power on the user side exceeds the limit, the voltage value u2 at the output end of the power electronic transformer will exceed the preset upper limit u2* of the power electronic transformer voltage value. At this time, it will automatically switch to the auxiliary control loop and enter the protection operation state. When the PI1 and PI3 control loops are switched transiently, the PI integral initial value will be initialized with the output value of the other party before the switch to prevent transient jumps.

[0041] Among them, the specific control process of the digital controller is as follows:

[0042] S1: Read the current voltage value u2 at the output of the power electronic transformer and the current value i0 of the cable line;

[0043] S2: Compare the read voltage value u2 and current value i0 with the set voltage reference value u2* and current reference value id;

[0044] S3: When u2<u2*, the PI closed-loop control algorithm is used to adjust the PWM control signal to increase the on-time of the power electronic transformer switch (i.e., the duty cycle PWM increases), thereby increasing the voltage value u2 at the output end of the power electronic transformer until it stabilizes at the reference value u2*. In this way, the output voltage u1 is stabilized by closed-loop control, so that no matter how long the cable is, it can be closed-loop controlled to ensure that the load end voltage is stable at 220V / 380V.

[0045] S4: When u2≥u2*, the protection function is activated. In order to prevent the inverter output voltage from being too high, a loop switching control mechanism is set. When the output voltage is too high, u2 is stabilized at the u2* voltage value to prevent the inverter voltage from being too high and damaging the DC-AC inverter. It is suitable for overvoltage protection during dynamic load unloading.

[0046] Specifically: the digital controller starts running after power-on, system initialization, timer, AD sampling, PWM, CAN communication and other modules are initialized and assigned initial values. In one operation cycle, when running to the interrupt program, read the current voltage value u2 at the output of the power electronic transformer and the current value i0 of the cable line. By comparing with the set voltage reference value u2* and the set current reference value id, the PI closed-loop control algorithm is used to adjust the PWM control signal to adjust and stabilize the user-side voltage. In extreme cases, if the voltage value u2 at the output of the power electronic transformer exceeds the upper limit u2* of the pre-set voltage value of the power electronic transformer, the protection program is started, and the program uses the PI closed-loop control algorithm to stabilize the voltage value u1 at the output of the power electronic transformer, and the protection of the power electronic transformer system is realized by software. Finally, the AD conversion is started, the interrupt ends within one cycle, and the main program is entered to wait for the next cycle.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A control method for a portable power supply end voltage stabilizing and compensating power electronic transformer, characterized in that: The steps include: 1) Connect the input end of the power electronic transformer to the power supply cable, and connect the output end to the user end through the power cable; and respectively set power line communication devices PLC1 and PLC2 at the output end of the power electronic transformer and the input end of the user end; 2) PLC1 measures the voltage u2 at the output end of the power electronic transformer, PLC2 measures the voltage u1 at the user end, and feeds back the voltage value u1 measured by PLC2 to PLC1 in real time; The digital controller calculates the current value i0 of the power cable according to the voltage u2 at the output end of the power electronic transformer, the voltage u1 at the user end, and the impedance; 3) Setting the user-side load voltage control loop PI1, by setting the voltage reference value u2* and the long-distance end user side voltage value u1 to form a voltage outer loop; Set the cable current control loop PI2, and form a current inner loop by setting the current reference value id and the cable line current value i0; A user-side load voltage auxiliary control loop PI3 is set, which is connected in parallel with the user-side load voltage control loop PI1 and can be switched by a conversion switch; 4) Read the current voltage value u2 at the output end of the power electronic transformer and the current value i0 of the cable line, and compare them with the set voltage reference value u2* and the set current reference value id. When u2<u2*, use PI closed-loop control to adjust the input voltage of the power electronic transformer, and stabilize the user-end voltage u1 through the user-end load voltage control loop PI1; when u2≥u2*, switch to the user-end load voltage auxiliary control loop PI3 to control the voltage at the output end of the power electronic transformer to be stable at u2*; at the same time, when i0≥id, the cable current control loop PI2 is combined with the user-end load voltage control loop PI1 to stabilize the user-end voltage u1.

2. The control method of a portable power supply end voltage stabilizing and compensating power electronic transformer according to claim 1, characterized in that: The power electronic transformer includes a digital controller, an AC / DC module, a DC / AC module and a display screen, and the power line communication device PLC1 is connected to the digital controller to transmit the detected voltage value to the digital controller; The power supply cable includes a three-phase power supply line and a neutral line, wherein the midpoint of each rectifier bridge arm of the AC / DC module is connected to the neutral line, and a relay switch S1 is provided between the front end of the neutral line and the connection between the rectifier bridge arm and the neutral line; the DC / AC module has four inverter bridge arms, wherein the midpoint of the inverter bridge arm is connected to the neutral line, and a relay switch S2 is provided between the connection between the rectifier bridge arm and the neutral line and the connection between the inverter bridge arm and the neutral line; The digital controller is used to control the on and off of the relay switch S1 or S2.

3. The control method of a portable power supply end voltage stabilizing and compensating power electronic transformer according to claim 2, characterized in that: In step 4), the specific process is as follows: S1: Read the current voltage value u2 at the output of the power electronic transformer and the current value i0 of the cable line; S2: Compare the read voltage value u2 and current value i0 with the set voltage reference value u2* and current reference value id; S3: When u2<u2*, the PI closed-loop control algorithm is used to adjust the PWM control signal to increase the on-time of the switch tube of the power electronic transformer, thereby increasing the voltage value u2 at the output end of the power electronic transformer until it stabilizes at the reference value u2*; S4: When u2≥u2*, the protection function is started.

4. The control method of a portable power supply end voltage stabilizing and compensating power electronic transformer according to claim 2, characterized in that: The display screen is an interactive display screen used for parameter setting and data display, and has a signal indicator light to display the current voltage output status.

5. The control method of a portable power supply end voltage stabilizing and compensating power electronic transformer according to claim 4, characterized in that: It also includes a mobile terminal that can communicate with the power electronic transformer to perform parameter setting and data display.

Images