Online uninterruptible power supply topological structure and control method

Abstract

The invention discloses an on-line uninterruptible power supply topological structure which is characterized in that commercial power input is electrically connected with a rectifying circuit and an inverter circuit in sequence through an input switch and then supplies power to a load through an output switch, the input side of a static bypass switch is electrically connected with the commercial power input, the output side of the static bypass switch is electrically connected with the load, the rectifying circuit topology is in a PFC + double-BOOST form, and the output side of the static bypass switch is electrically connected with the load. The positive half cycle and the negative half cycle of the alternating-current mains supply work in a staggered mode, boost output of the alternating-current mains supply is electrically connected with a high-voltage direct-current bus and charges a + BUS bus capacitor and a-BUS bus capacitor, the + BUS bus capacitor and the-BUS bus capacitor are electrically connected with the input end of the inverter circuit at the same time, the input end of the charging circuit is electrically connected with the high-voltage direct-current bus, and the output end of the charging circuit is electrically connected with the lithium battery pack. And the output end of the discharging circuit is connected with the high-voltage direct-current bus. The topological structure is simple and efficient, the overhead in the aspect of power device consumption is small, and better universality and maintainability are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply control, and in particular to an online uninterruptible power supply topology structure and a control method. Background Art

[0002] With the development of power control technology, the topology of uninterruptible power supply (UPS) has become more and more diversified. In pursuit of smaller size, lighter weight and higher conversion efficiency, UPS equipment has developed into high frequency. At the same time, based on the requirement of uninterruptible power supply, online UPS with inverter hot backup mode has been more applied and developed.

[0003] The existing small and medium power online UPS generally includes a rectifier circuit (AC / DC), an inverter circuit (DC / AC), a charging circuit, a discharge circuit, a bypass and a rechargeable battery. The topologies of the rectifier and inverter circuits are all various derivative forms of full-bridge or half-bridge, and the connection methods are basically the same. The input power passes through the rectifier circuit to form a DC bus (BUS) voltage, and the inverter circuit converts the DC bus voltage into an output voltage and sends it to the load. However, to obtain excellent conversion efficiency, it is often necessary to use more controllable switches, and the size of the DC bus voltage also determines the ability and efficiency of energy conversion and transmission; the bypass basically adopts a static switch control method; the rechargeable battery is generally a lead-acid battery or a lithium battery. The difference is that due to the different design standards of the DC bus voltage and the battery voltage, the topology and connection method of the charging and discharging circuits are also different. There are generally two forms. One is that the charging and discharging circuits are independent of each other. The discharge circuit uses DC / DC to boost to the DC bus, and the charging circuit input is taken from the AC input. The AC / DC is rectified first, and then the battery is charged through a flyback DC / DC conversion. This method has a low charging power and is not suitable for high-power charging requirements such as lithium battery charging. Another way is to integrate charging and discharging, and use the bidirectional flow of energy on the DC bus side and battery energy, such as bidirectional series resonance. This method is more advanced and has a high technical difficulty. In fact, the cost of switching and magnetic components for bidirectional flow is high, which is suitable for occasions with low battery voltage, while low battery voltage is not conducive to energy exchange with high-voltage DC bus. In addition, most existing UPS technology products are integrated circuits of rectification, inversion, discharge and charging, with low modularization, and poor maintainability and versatility.

[0004] Therefore, the above-mentioned existing UPS technology has the following disadvantages: (1) In order to obtain higher conversion efficiency, the dual conversion circuit switch cost of the existing online UPS is relatively high, which is not conducive to reliable control, and the cost is high and the overall design is complex. (2) When the UPS outputs small and medium power, the DC bus voltage is generally bipolar and high voltage, so the lower battery voltage and its charging and discharging circuit obviously cannot meet the requirements in terms of cost or power requirements. (3) The technical product modularity of the existing UPS is not high, and the maintainability and versatility are not strong. Summary of the invention

[0005] The purpose of the present invention is to provide an online uninterruptible power supply topology and implementation method thereof, so as to solve the problems of high cost of double conversion circuit switch of existing online UPS, complex overall design, and limited battery charging and discharging capacity in small and medium power conversion and transmission. At the same time, the modular UPS topology method has better versatility and maintainability.

[0006] The technical solution adopted by the present invention is an online uninterruptible power supply topology structure, the mains input is electrically connected to the rectifier circuit and the inverter circuit in sequence through the input switch, and then the load is powered through the output switch, the input side of the static bypass switch is electrically connected to the mains input, and the output side is electrically connected to the load, the rectifier circuit topology is a PFC+double BOOST form, and it works alternately in the positive half cycle and the negative half cycle of the AC mains, and its rectifier boost output is electrically connected to the high-voltage DC bus, and the +BUS bus capacitor and the -BUS bus capacitor are charged respectively, the ±BUS bus capacitors are electrically connected to the input end of the inverter circuit at the same time, the input end of the charging circuit is electrically connected to the high-voltage DC bus, and the output end is electrically connected to a lithium battery pack, the input end of the discharge circuit is electrically connected to the lithium battery pack, and the output end is connected to the high-voltage DC bus.

[0007] Preferably, the rectifier circuit is an active power factor correction (PFC) circuit, and the voltage and current on the AC input side are in phase.

[0008] Preferably, the inverter circuit adopts a three-level NPC inverter topology.

[0009] Preferably, at most only one of the charging circuit and the discharging circuit is in working state.

[0010] Preferably, the rectifier circuit and inverter circuit, charging circuit, discharge circuit, and lithium battery pack each include a controller, wherein the controllers of the rectifier circuit and inverter circuit modules serve as the master controller, and the controllers of other modules serve as slave controllers, and data exchange is performed between the controllers of each module in the form of a communication bus.

[0011] A method for controlling an online uninterruptible power supply, wherein a main controller detects in real time whether the AC voltage and frequency of the main power input are abnormal, and detects whether the rectifier circuit and the inverter circuit have double conversion abnormalities such as over-temperature and over-current. When the main controller detects that the main power and the double conversion are normal, the main controller commands the rectifier circuit and the inverter circuit to start working. If the main controller receives a charging request from a battery pack at this time, the main controller controls the charging circuit to work and the battery pack charging port to open until the battery pack is fully charged. If the main power is abnormal at any time, the main controller controls the rectifier circuit and the charging circuit to exit working, and commands the battery pack to close the charging port and open the discharge port, and controls the discharge circuit to work until the battery pack is powered off due to low power protection. When the main controller detects double conversion abnormalities at any time, the bypass is controlled to be turned on, and each module circuit is controlled to exit working state.

[0012] The beneficial effects of the present invention are as follows: the present invention is a single-input single-output online uninterruptible power supply, which can provide stable, reliable, high-quality electricity for precision electronic equipment loads in the case of poor power supply quality such as mains failure, over-voltage, under-voltage, frequency offset, voltage collapse, etc., and ensure uninterrupted power supply to the loads. The small and medium-power AC mains input is transformed into high-voltage DC through a rectifier circuit and the bus capacitor is charged, and then the high-voltage DC inverter output is used to supply power to the load, as well as the topological design of energy conversion and transmission between the DC bus and the lithium battery pack. The overall topological structure is simple and efficient, with low overhead in terms of power device usage, which is conducive to obtaining better power density. At the same time, the modular design of the circuit improves the versatility and maintainability of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a topological structure block diagram of the present invention.

[0014] Figure 2 It is a schematic diagram of the double conversion circuit of the present invention.

[0015] Figure 3 It is a schematic diagram of communication between the module controllers of the present invention.

[0016] Figure 4 It is a control flow chart of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0018] like Figure 1As shown. The present invention is an online uninterruptible power supply topology structure and implementation method, including an input switch, a rectifier circuit, an inverter circuit, a bus capacitor, an output switch, a static bypass switch, a charging circuit, a discharge circuit, and a lithium battery pack. The rectifier circuit is an active power factor correction (PFC) circuit, which is connected to the AC mains input terminal to convert the AC voltage into a DC voltage, and the voltage and current on the AC input side are in phase to achieve green access to the grid. Its specific topology is the PFC+double BOOST form, which works alternately in the positive half-cycle and the negative half-cycle of the AC mains, combined with the power controllable switch tubes connected in parallel in the positive half-cycle and the negative half-cycle, and its boost output is respectively charged to the positive and negative DC bus (BUS) capacitors to form ±BUS DC bus voltages. The rectifier circuit certainly includes a PFC+BOOST capacitor pre-charging circuit (not shown) to avoid the PFC inductor from generating short-circuit current due to current saturation caused by the capacitor charging process when power is on. When the bus capacitor pre-charging process is completed, the pre-charging circuit exits the work. The bus capacitor is used for energy storage on the high-voltage DC bus, connecting the positive half-cycle output terminal +BUS and the negative half-cycle output terminal -BUS of the rectifier circuit to store the DC power converted by the rectification. The bus capacitor is also connected to the input terminal of the inverter circuit as the energy source of the inverter circuit. The inverter circuit, with the input terminal connected to the high-voltage DC bus, converts the high-voltage DC into AC. The inverter circuit adopts a three-level NPC inverter topology, and the voltage stress of the three-level bridge arm switch tube is small, which reduces the THD of the output AC voltage. The charging circuit, with the input terminal connected to the high-voltage DC bus and the output terminal connected to the battery pack, is responsible for stepping down the high-voltage DC bus voltage DC / DC to the charging voltage, and outputting the charging voltage and charging current requested by the battery pack. The discharge circuit, with the input terminal connected to the battery pack and the output terminal connected to the high-voltage DC bus, is responsible for stepping up the battery pack output voltage to the DC bus voltage via DC / DC. At most, only one of the charging circuit and the discharge circuit is in working state.

[0019] The rectifier circuit and inverter circuit (hereinafter referred to as rectifier inverter), the charging circuit, the discharge circuit, and the lithium battery pack are four circuit modules. Each module includes a controller (not shown) for modulation control, signal acquisition, and data transmission of each circuit module. The controllers of each module use a communication bus to exchange data. Specifically, it can be a CAN bus, RS485 serial port bus, etc. The communication bus mode with a high communication rate is conducive to the rapid control of the uninterruptible power supply. The rectifier inverter controller sends commands to each module and reads the data of each module through the bus, thereby scheduling the control and protection actions of the whole machine, and can provide telemetry and telesignaling data for the outside of the equipment. The input switch is connected to the AC input side at one end and the rectifier circuit at the other end. It is a controlled element. When the rectifier inverter controller detects that the quality of the AC mains is normal, the input switch is controlled to close, and the rectifier circuit and the inverter are put into operation successively. The output switch is connected to the output side of the inverter at one end and the load at the other end. It is a controlled element. When the rectifier inverter controller detects that the output AC meets the requirements, it controls the output switch to close, and the UPS works in normal mode. The energy obtained by the load is obtained through the double conversion process of rectification and inversion. The static bypass switch is connected to the mains input on the input side and the load on the output side. It is a semi-controllable element, generally a thyristor (SCR). When the UPS has a rectifier inverter fault, overload or overcurrent, or the internal ambient temperature is too high, the rectifier inverter controller turns on the static bypass switch under the control of the software control logic, and the input switch is disconnected from the output switch. The mains supplies power to the load through the path of the static bypass switch. At this time, the UPS works in the bypass state.

[0020] When the AC input voltage and frequency are within the allowable range, the input switch is closed, the static bypass switch is in the open state, and the rectifier circuit charges the bus capacitor to the target voltage ±vBUS after power factor correction and boosting. The total bus voltage is high voltage DC, and its level is generally 720V, 760V, 800V, etc. The voltage level can be designed and selected based on the software control method and the power switch tube device capabilities. The DC bus is connected to the inverter circuit, and the output switch is closed to convert DC power into AC power and send it to the user. If the lithium battery pack requests charging at this time, the lithium battery pack opens the charging port, and the charging circuit starts working, converting the energy stored on the DC bus into the charging voltage and current of the lithium battery, and charging the lithium battery pack until it is fully charged. The rated voltage of the lithium battery pack is generally 96V, and the number of lithium battery cells and the parallel capacity can also be selected according to the uninterrupted backup time. When the input AC voltage and frequency are not within the allowable range, including when the input AC power is disconnected, the rectifier circuit and input switch stop working, the discharge port of the lithium battery pack starts to output, and the discharge circuit starts working, boosting the output voltage of the lithium battery pack to the DC bus voltage in a short time to ensure that the bus capacitor does not lose power, the inverter circuit can continue to work, and the continuous power supply of the user load is not affected.

[0021] The battery pack has three states: charging, discharging, and standby. When the UPS is working in normal mode, if the battery pack BMS controller requests charging from the rectifier inverter controller, the rectifier inverter controller sends a charging instruction to the charging circuit, and the charging circuit starts to charge the battery pack; if the battery pack does not request a charging voltage from the rectifier inverter controller, the battery pack does not charge or discharge, and is in standby mode, waiting for charging or discharging instructions.

[0022] When the rectifier inverter controller detects that the quality of the AC mains power is abnormal, the internal software control logic disconnects the input switch and the rectifier circuit exits the working mode, and sends a discharge instruction to the charging circuit, the battery pack and the discharge circuit. At this time, whether the battery pack is in charging or standby state, it is terminated, the battery pack charging port is closed, the charging circuit stops working, and the battery pack discharge port maintains output. The discharge circuit raises the battery voltage to the voltage required by the DC bus to ensure that the DC bus does not lose power after the rectifier circuit exits. The inverter circuit converts the power supply energy required by the load into the battery pack. This process ensures the continuity of load power supply. At this time, the UPS works in battery mode.

[0023] Figure 2 is a schematic diagram of an online uninterruptible power supply double conversion circuit according to an embodiment of the present invention, which shows Figure 1 The main circuit is a specific circuit of rectification and inversion, while the charging circuit and the discharging circuit can adopt various cascade forms of forward and push-pull boost to realize the charging and discharging control of the lithium battery voltage and the high-voltage DC bus voltage, which will not be given in detail in the present invention. Figure 2 In the figure, the input switch S1, inductor L1, diodes D1 and D2, and switch tubes Q1 and Q2 form a PFC+double BOOST rectifier circuit. When the input AC is in the positive half cycle, the inductor L1, diode D1, and switch tube Q2 form a PFC+BOOST rectifier boost circuit to charge the bus capacitor C1 on the +BUS side. Conversely, when the input AC is in the negative half cycle, the inductor L1, diode D2, and switch tube Q1 form another PFC+BOOST rectifier boost circuit to charge the bus capacitor C2 on the -BUS side. The modulation mode of the switch tubes Q1 and Q2 can be controlled by dual closed-loop modulation according to the average current method based on the bus voltage feedback, input AC voltage feedback, and input AC current feedback. For the bidirectional characteristics of the switch tubes Q1 and Q2, the modulation conduction mode of the switch tubes Q1 and Q2 can be simplified, that is, Q1 and Q2 are turned on at the same time, and the conduction duty cycle is exactly the same. This method has a simple control method and reliable accuracy, and can greatly simplify the software and hardware costs of the power switch tube of the rectifier circuit. Figure 2In the embodiment, the switch tubes Q3, Q4, Q5, Q6, the diodes D3, D4, and the inductor L2 form an NPC type three-level inverter circuit. The positive of the bus capacitor C1, through the inductor energy storage path of the switch tubes Q3 and Q4 and the inductor L2, and the negative of the bus capacitor C1, through the inductor freewheeling path of the diode D3, the switch tube Q4 and the inductor L2, form the working sequence of the output AC positive half cycle. On the contrary, the inductor L2, the switch tube Q5, and the diode D4, through the positive of the bus capacitor C2, are the inductor freewheeling path of the output AC negative half cycle; the inductor L2, the switch tubes Q5 and Q6, and the negative of the bus capacitor C2 are the inductor energy storage path of the input AC negative half cycle. It is a common technology that the NPC inverter circuit uses SPWM adjustment technology to control the conduction of the switch tube, which will not be described in detail in the present invention. Figure 2 The specific circuit combining the rectifier circuit and the inverter circuit given can not only realize accurate and reliable conversion output, but also has low power tube usage cost, low heat loss, low software overhead, and easy topology implementation.

[0024] Combination Figure 4 The implementation method of the control flow details the embodiment of the present invention.

[0025] After the uninterruptible power supply is connected to the AC input, the internal auxiliary power supply is powered on to supply power to the circuit chips of each module. The uninterruptible power supply control circuit completes initialization and waits for the operator to give the power-on command before each module works. The specific control and implementation method is as follows: When the main controller detects that the voltage and frequency of the AC input are within the allowable range, the main controller controls the rectifier circuit and the inverter circuit to start working, and detects in real time whether the uninterruptible power supply has over-temperature, over-current, and abnormal rectification and inverter. If there is an abnormality, the double conversion is stopped, and the power supply channel for the user is switched to the bypass, that is, the static bypass switch is turned on, and the AC input directly supplies power to the load. On the contrary, the rectifier inverter continues to work, and the uninterruptible power supply works in normal mode. In normal mode, if the main controller receives a charging request signal from the BMS controller of the lithium battery pack, the main controller commands the lithium battery pack to open the charging port, and the charging circuit starts working. The charging circuit converts the DC bus voltage into the lithium battery charging voltage to realize the charging process of the lithium battery pack until the lithium battery pack is full, the charging circuit stops working, and the charging port of the lithium battery pack is closed. When the main controller detects that the voltage and frequency of the AC input are not within the allowable range, the main controller sends a discharge command to the communication bus, the input switch is disconnected, the rectifier circuit stops working, the charging circuit stops working, the lithium battery pack closes the charging port and opens the discharge port, the discharge circuit starts working, the DC bus energy is provided by the lithium battery pack, and the inverter circuit continues to ensure the power supply of the user's load. When the lithium battery pack is discharged to low power protection, the lithium battery pack BMS controller disconnects the discharge port, the main controller receives the low battery protection command, and starts to execute the shutdown operation. In normal mode, the operator executes the shutdown command to shut down the working circuit module.

[0026] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An online uninterruptible power supply topology structure, characterized in that: The AC input is electrically connected to the rectifier circuit and the inverter circuit in sequence through the input switch, and then supplies power to the load through the output switch. The input side of the static bypass switch is electrically connected to the AC input, and the output side is electrically connected to the load. The rectifier circuit topology is PFC+dual BOOST, and it works alternately in the positive half-cycle and the negative half-cycle of the AC AC power. Its rectifier boost output is electrically connected to the high-voltage DC bus, and the +BUS bus capacitor and -BUS bus capacitor are charged respectively. The ±BUS bus capacitors are electrically connected to the input end of the inverter circuit at the same time, the input end of the charging circuit is electrically connected to the high-voltage DC bus, and the output end is electrically connected to the lithium battery pack. The input end of the discharge circuit is electrically connected to the lithium battery pack, and the output end is connected to the high-voltage DC bus.

2. The online uninterruptible power supply topology structure according to claim 1, characterized in that: The rectifier circuit is an active power factor correction (PFC) circuit, and the voltage and current on the AC input side are in phase.

3. The online uninterruptible power supply topology structure according to claim 1, characterized in that: The inverter circuit adopts a three-level NPC inverter topology.

4. The online uninterruptible power supply topology structure according to claim 1, characterized in that: At most only one of the charging circuit and the discharging circuit is in working state.

5. The online uninterruptible power supply topology structure according to claim 1, characterized in that: The rectifier circuit and inverter circuit, charging circuit, discharging circuit and lithium battery pack each include a controller, wherein the controllers of the rectifier circuit and inverter circuit modules serve as the master controller, and the controllers of other modules serve as slave controllers, and data exchange is performed between the controllers of each module in the form of a communication bus.

6. An online uninterruptible power supply control method, characterized in that: The main controller detects in real time whether the AC voltage and frequency of the mains input are abnormal, and detects whether the rectifier circuit and the inverter circuit have double conversion abnormalities such as overtemperature and overcurrent. When the main controller detects that the mains and the double conversion are normal, the main controller commands the rectifier circuit and the inverter circuit to start working. If the main controller receives a charging request from the battery pack at this time, it controls the charging circuit to work and the battery pack charging port to open until the battery pack is fully charged. If the mains power is abnormal at any time, the main controller controls the rectifier circuit and the charging circuit to exit working, and at the same time commands the battery pack to close the charging port and open the discharge port, and controls the discharge circuit to work until the battery pack is powered off due to low power protection. When the main controller detects a double conversion abnormality at any time, it controls the bypass to be turned on, and controls the circuits of each module to exit working.

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