Cold start control method of uninterruptible power supply, controller and uninterruptible power supply

Abstract

The invention discloses a cold start control method for an uninterruptible power supply, a controller and the uninterruptible power supply, and the cold start control method comprises the steps: obtaining a voltage target value of the total voltage of a bus; performing boost control on a positive bus and a negative bus according to the voltage target value; an expected voltage is determined according to the voltage target value and a preset coefficient, and the preset coefficient is a proportionality coefficient of conversion between the voltage target value and the expected voltage; if the total voltage of the bus is continuously smaller than the expected voltage for a first preset time, cold start failure is judged, and shutdown power-off protection is executed; and if the bus total voltage is greater than the expected voltage, and the positive bus voltage and the negative bus voltage are respectively within a preset working voltage range, determining that cold start is successful, thereby improving the start stability of the bus in an unbalanced state.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the technical field of power supply, in particular to a cold start control method of an uninterruptible power supply, a controller and the uninterruptible power supply. BACKGROUND

[0002] An uninterruptible power supply (UPS) needs to undergo strict reliability verification before leaving the factory, including multiple battery cold start tests. For example, after discharging the system under load to the battery end of discharge voltage (EOD), the battery restart test is performed. In this process, the UPS first closes the rectifier and inverter, and then completes the shutdown power-off of the inverter. In actual application, if the UPS is deployed in a mountainous area or other outdoor or semi-outdoor environment, the fan may be blocked by insects, leaves and other foreign matter, triggering the fan fault protection mechanism. At this time, the system will also turn off the rectifier and inverter in turn, and finally perform the shutdown power-off operation.

[0003] However, in the above two types of shutdown processes, the inverter usually maintains a short running for a non-integer number of output cycles after the rectifier is turned off, in order to complete the current energy conversion cycle. This process will cause the energy consumption of the positive and negative bus capacitors to be inconsistent, resulting in a significant bus voltage imbalance at the moment of shutdown. Since the self-discharge rate of energy storage elements such as bus capacitors in the circuit is slow after the UPS is shut down, the voltage difference of the bus voltage often needs to be naturally attenuated to an acceptable range for several minutes. However, in actual operation, the on-site maintenance personnel may quickly trigger the cold start again after removing the fan foreign matter, or the factory test personnel may immediately perform the next round of battery cold start test after EOD shutdown, which will cause the battery to start cold under bus imbalance, easily leading to startup failure, affecting system reliability and user experience. SUMMARY

[0004] The present application provides a cold start control method of an uninterruptible power supply, a controller and the uninterruptible power supply to improve the stability of the startup.

[0005] In a first aspect, embodiments of the present application provide a cold start control method of an uninterruptible power supply, comprising:

[0006] obtaining a voltage target value of a bus total voltage of a current boost cycle and an actual voltage value of the bus total voltage;

[0007] boosting control is performed on both the positive bus and the negative bus according to the voltage target value;

[0008] determining an expected voltage according to the voltage target value and a preset coefficient, wherein the preset coefficient is a proportional coefficient for conversion between the voltage target value and the expected voltage;

[0009] If the actual voltage value of the bus total voltage continuously is less than the expected voltage for a first preset time, it is determined that the cold start fails, and a shutdown power-off protection is performed.

[0010] If the actual voltage value of the bus total voltage is greater than the expected voltage, and the positive bus voltage and the negative bus voltage are respectively within a preset working voltage range, it is determined that the cold start succeeds.

[0011] Optionally, a voltage target value of the bus total voltage in a current boosting period is obtained, including:

[0012] The positive bus voltage and the negative bus voltage at an initial time are obtained.

[0013] An initial voltage target value of the bus total voltage is determined according to the positive bus voltage and the negative bus voltage at the initial time, and the initial voltage target value is taken as a voltage target value of an initial boosting period.

[0014] The voltage target value corresponding to a subsequent boosting period is iteratively calculated based on the initial voltage target value and a preset first step length, wherein the voltage target value of each boosting period is obtained by superimposing the first step length on the voltage target value of a previous boosting period.

[0015] Optionally, the initial voltage target value is determined according to the current positive bus voltage and the current negative bus voltage, including:

[0016] An average value of the current positive bus voltage and the current negative bus voltage is calculated, and the average value is taken as the initial voltage target value.

[0017] Optionally, the positive bus and the negative bus are both subjected to boosting control according to the voltage target value, including:

[0018] A voltage error is determined based on a difference between the voltage target value and an actual voltage value of the bus total voltage, and a bus voltage difference is determined based on a difference between an absolute value of the positive bus voltage and an absolute value of the negative bus voltage.

[0019] A positive side control amount of the positive bus and a negative side control amount of the negative bus are determined according to the voltage error and the bus voltage difference, and the positive bus and the negative bus are subjected to boosting control based on the positive side control amount and the negative side control amount, so that the bus total voltage is boosted, and the voltage between the positive bus and the negative bus is balanced.

[0020] Optionally, the positive edge control quantity comprises a duty cycle control quantity of the positive edge, and the negative edge control quantity comprises a duty cycle control quantity of the negative edge; wherein the duty cycle control quantity of the positive edge is used to control the turn-on and turn-off of the first power switch tube on the positive bus side in the boost circuit, and the duty cycle control quantity of the negative edge is used to control the turn-on and turn-off of the second power switch tube on the negative bus side in the boost circuit, so as to realize bus voltage adjustment.

[0021] Optionally, the positive edge control quantity of the positive bus and the negative edge control quantity of the negative bus are determined according to the voltage error and the bus voltage difference, comprising:

[0022] The overall control quantity of the positive bus and the negative bus is determined according to the voltage error, and the overall control quantity is used to represent the basic control quantity of the total bus voltage energy demand;

[0023] The balance control quantity between the positive bus and the negative bus is determined according to the bus voltage difference, and the balance control quantity is used to represent the control quantity of voltage balance between the positive bus and the negative bus;

[0024] The duty cycle control quantity of the positive edge is determined according to the sum of the overall control quantity and the balance control quantity;

[0025] The duty cycle control quantity of the negative edge is determined according to the difference between the overall control quantity and the balance control quantity.

[0026] In a second aspect, an embodiment of the present application provides a controller, which is used to execute the cold start control method in any of claims 1-6.

[0027] In a third aspect, an embodiment of the present application provides an uninterruptible power supply, comprising: a boost circuit and the controller in claim 7, wherein the first end of the boost circuit is connected with the controller, and the second end of the boost circuit is connected with the positive bus and the negative bus respectively;

[0028] The controller is used to acquire a voltage target value of the total bus voltage in a current boost cycle and an actual voltage value of the total bus voltage; and control the boost circuit to boost the positive bus and the negative bus according to the voltage target value;

[0029] The controller is further used to determine an expected voltage according to the voltage target value and a preset coefficient, wherein the preset coefficient is a proportional coefficient for conversion between the voltage target value and the expected voltage;

[0030] The controller is further used to execute shutdown power-off protection in a case where the actual voltage value of the total bus voltage continuously is less than the expected voltage for a first preset time.

[0031] Optionally, the voltage boosting circuit comprises a positive bus capacitor, a negative bus capacitor, a first power switch tube, a second power switch tube, a first inductor, a second inductor, a first diode and a second diode.

[0032] The positive pole of the battery is electrically connected to a first end of the first inductor; a second end of the first inductor is electrically connected to a first pole of the first power switch tube and an anode of the first diode respectively; a cathode of the first diode is connected to a first end of the positive bus capacitor, and a second end of the positive bus capacitor serves as a system midpoint; a second pole of the first power switch tube is connected to the system midpoint; a control pole of the first power switch tube is connected to the controller.

[0033] The negative pole of the battery is electrically connected to a first end of the second inductor; a second end of the second inductor is electrically connected to a first pole of the second power switch tube and a cathode of the second diode respectively; an anode of the second diode is connected to a first end of the negative bus capacitor; a second end of the negative bus capacitor is connected to the system midpoint; a second pole of the second power switch tube is connected to the system midpoint; a control pole of the second power switch tube is connected to the controller.

[0034] The controller is configured to determine a voltage error based on a difference between the voltage target value and an actual voltage value of the bus total voltage, and determine a bus voltage difference based on a difference between an absolute value of the positive bus voltage and an absolute value of the negative bus voltage.

[0035] The controller is further configured to determine a duty cycle control amount of a positive side of the positive bus and a duty cycle control amount of a negative side of the negative bus according to the voltage error and the bus voltage difference, wherein the duty cycle control amount of the positive side is used to control the turn-on and turn-off of the first power switch tube on the positive bus side in the voltage boosting circuit, and the duty cycle control amount of the negative side is used to control the turn-on and turn-off of the second power switch tube on the negative bus side in the voltage boosting circuit.

[0036] Optionally, the uninterruptible power supply further comprises a detection circuit.

[0037] The detection circuit is configured to detect an actual voltage value of the positive bus and an actual voltage value of the negative bus voltage.

[0038] The controller determines the actual voltage value of the bus total voltage based on the actual voltage value of the positive bus and the actual voltage value of the negative bus voltage.

[0039] The cold start control method of the uninterruptible power supply, the controller and the uninterruptible power supply provided by the embodiment of the present application, in the cold start voltage boosting process, take the bus total voltage as a unified control object, compare the real-time collected bus total voltage with the expected voltage obtained based on the voltage target value, and make a judgment in combination with time persistence, so as to ensure that the bus can be normally boosted to the expected voltage when the bus is unbalanced during cold start, and avoid the failure of soft start caused by bus voltage imbalance. The soft start failure protection is not entered due to the fact that the unilateral bus voltage does not reach the expectation at the beginning of cold start, the start stability is improved, and unnecessary downtime waiting is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A flowchart of a cold start control method of an uninterruptible power supply is provided for the embodiment of the present application;

[0041] Figure 2 A flowchart of a cold start control method of an uninterruptible power supply is provided for the embodiment of the present application;

[0042] Figure 3 A structure diagram of a voltage boosting circuit is provided for the embodiment of the present application;

[0043] Figure 4 A diagram of the duty cycle control amount of the positive and negative sides is provided for the embodiment of the present application;

[0044] Figure 5 A simplified circuit diagram in the first working state;

[0045] Figure 6 A simplified circuit diagram in the second working state;

[0046] Figure 7 A simplified circuit diagram in the third working state;

[0047] Figure 8 A flowchart of a cold start control method of an uninterruptible power supply is provided for the embodiment of the present application;

[0048] Figure 9 A structure diagram of an uninterruptible power supply is provided for the embodiment of the present application. DETAILED DESCRIPTION

[0049] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0050] During normal UPS operation, if the rectification function stops prematurely due to a fault on the rectifier boost side or other abnormal reasons, the inverter will typically continue to run for several or a non-integer number of output cycles before completely shutting down. During this transition phase, as energy continues to be output from the DC bus to the load, and the rectifier side can no longer replenish energy, the discharge paths of the positive and negative bus capacitors and the load characteristics may differ, resulting in a significant imbalance between the positive and negative bus voltages.

[0051] After power is off, the bus capacitor's self-discharge rate is slow, and this imbalance remains at a high level for a considerable period. If a rapid battery cold start is performed during this period, the actual bus voltage will exhibit an asymmetrical state with one side higher than the other. During startup, if a one-sided comparison is used, the difference between the higher voltage side and the target value will be significant, easily triggering a bus soft start failure, leading to cold start interruption, and impacting system availability and user experience.

[0052] In view of this, Figure 1 This is a flowchart illustrating a cold start control method for an uninterruptible power supply (UPS) according to an embodiment of the present invention. This embodiment is applicable to cold start situations under UPS bus imbalance. The method can be executed by a cold start control device, which can be implemented in hardware and / or software. The method specifically includes the following steps:

[0053] S110. Obtain the target voltage value and the actual voltage value of the total bus voltage in the current boost cycle; wherein, the target voltage value is the expected total bus voltage value during cold start. For example, in the cold start boost phase, multiple boost cycles are typically set, and the target voltage value for each boost cycle can be different. Therefore, the target voltage value throughout the boost process is usually a dynamic voltage value. For instance, in the initial boost cycle, the target voltage value is set to the initial target voltage value. In the next boost cycle, the corresponding target voltage value can be obtained according to a preset first step length. The first step length of the target voltage values ​​in adjacent boost cycles can be the same, thus forming a smooth upward target trajectory until the final preset target voltage value of the system is reached. By setting a dynamic target voltage value, voltage overshoot and current surge during startup can be effectively suppressed, avoiding device stress or control instability caused by voltage mutations. The actual voltage value of the total bus voltage is the actual voltage value already reached by the total bus voltage during cold start. The actual voltage value of the total bus voltage can be expressed as the sum of the positive bus voltage and the negative bus voltage collected in real time. The positive bus voltage and the negative bus voltage can be obtained by sampling the bus capacitance.

[0054] S120. Perform voltage boosting control on both the positive and negative busbars according to the target voltage value;

[0055] Specifically, the voltage target value is essentially a target value of the bus total voltage, and thus the positive bus and the negative bus are regarded as a unified energy storage unit for cooperative voltage boosting. Exemplarily, the voltage boosting control can be implemented by a Boost-type voltage boosting circuit. According to a control instruction, the on and off of a power switch tube in the voltage boosting circuit are synchronously adjusted, the electrical energy can be transferred to the positive bus capacitor and the negative bus capacitor, and thus the bus total voltage is boosted.

[0056] In S130, an expected voltage is determined according to the voltage target value and a preset coefficient, where the preset coefficient is a proportional coefficient for conversion between the voltage target value and the expected voltage.

[0057] Specifically, the expected voltage can be represented as a product of the voltage target value and the preset coefficient. The preset coefficient is used to set a lowest reasonable threshold value that the bus voltage should reach in the soft start process. Exemplarily, the preset coefficient can be in a range of 0.5 to 1, and preferably in a range of 0.85 to 0.95. Considering different discharge resistance values in the bus loop, when the self-loss is slow, if the battery is immediately cold started after normal shutdown, since the duty cycle control of the on and off of the power switch tube in the voltage boosting circuit starts from 0 or a lower value and rises by a step, the voltage target value has an initial value. At this time, if a higher preset coefficient is used, the expected voltage will rapidly rise in the initial stage, a large deviation will be generated from the actual bus voltage, a voltage boosting abnormality can be misjudged, and even unnecessary protection actions can be triggered. Therefore, the preset coefficient can be used to lower the expected voltage in the initial stage according to the actual situation, so as to avoid large voltage boosting fluctuations.

[0058] In S140, it is determined whether the start is successful according to the bus total voltage and the expected voltage. If the actual voltage value of the bus total voltage is less than the expected voltage for a first preset time, it is determined that the cold start fails, and a shutdown power-off protection is performed. If the actual voltage value of the bus total voltage is greater than the expected voltage, and the positive bus voltage and the negative bus voltage are in a preset working voltage range, it is determined that the cold start is successful.

[0059] Specifically, if the actual voltage value of the bus total voltage is smaller than the expected voltage for a first preset time (for example, 100 ms), it indicates that the bus voltage rises slower than expected, and the UPS considers that the bus soft start fails, stops the bus voltage rising process, and performs shutdown protection to prevent device over-stress or oscillation; if the actual voltage value of the bus total voltage is greater than the expected voltage, and the positive bus voltage and the negative bus voltage are respectively within the preset working voltage range, it indicates that the bus soft start succeeds, the battery cold start ends normally, and it is determined that the cold start succeeds, the soft start phase is exited, the normal bus voltage closed-loop regulation mode is entered, and the inverter output is prepared to be started. It should be noted that the bus soft start failure protection mechanism cannot be simply discarded in exchange for a higher start success rate. This is because in some working conditions, even if the battery cold start phase has been completed, there may still be imbalance between the positive bus and the negative bus. In the imbalance state, the positive and negative half cycles of the inverter output sine wave will be asymmetric, resulting in uneven stress distribution of the device and affecting the normal work of the UPS, so the bus soft start failure protection cannot be directly deleted.

[0060] The cold start control method provided by the embodiment of the application takes the bus total voltage as a unified regulation object in the cold start voltage rising process, compares the real-time collected bus total voltage with the expected voltage obtained based on the voltage target value, and judges in combination with time persistence, to ensure that the bus can normally rise to the expected voltage when the bus is imbalanced during cold start, and to avoid unnecessary downtime waiting caused by entering the soft start failure protection when the single-sided bus voltage does not reach the expected value at the beginning of the cold start, thereby improving the start stability.

[0061] Optionally, in S110, the voltage target value of the bus total voltage of the current voltage rising period is acquired, and the method comprises the following steps.

[0062] In S111, the positive bus voltage and the negative bus voltage at an initial time are acquired, wherein the initial time is the first time point at which the uninterruptible power supply system is powered on from a complete power failure or a non-working state and starts to execute the start control logic.

[0063] In S112, the initial voltage target value of the bus total voltage is determined according to the positive bus voltage and the negative bus voltage at the initial time, and the initial voltage target value is taken as the voltage target value of the initial voltage rising period.

[0064] In S113, the voltage target value corresponding to a subsequent voltage rising period is iteratively calculated based on the initial voltage target value and a preset first step length, wherein the voltage target value of each voltage rising period is obtained by superimposing the first step length on the voltage target value of the previous voltage rising period.

[0065] Specifically, when the user triggers the battery cold start instruction, the current positive bus voltage and negative bus voltage are collected. At this time, the system may be in the residual voltage state after complete power failure, and the bus capacitor still has some electric charge. The initial voltage target value is determined in combination with the collected current positive bus voltage and negative bus voltage. For example, in the embodiment of the application, the average value of the current positive bus voltage and the negative bus voltage is used as the initial voltage target value. Starting from the initial voltage target value, the voltage target value is gradually increased by a fixed first step length in a preset time period, so that the voltage target value of each voltage boosting period is correspondingly obtained, forming a smooth rising target trajectory, until the system reaches the final preset voltage target value. For example, the preset time period can be 20 ms, and the first step length is 0.05 V.

[0066] In the embodiment of the application, the voltage target value is not started from zero or a fixed value, but is determined according to the actual residual voltage state of the bus. From the existing residual voltage, the voltage is continued to be boosted, which can significantly reduce the time required to reach the preset target voltage, improve the starting efficiency, and also can avoid unnecessary repeated charging or overshoot excitation of the charged bus. The starting surge current can be effectively suppressed, and the starting reliability is improved.

[0067] Figure 2 A flowchart of another uninterrupted power supply cold start control method is provided for the embodiment of the application, as shown in Figure 2 , which comprises:

[0068] S210, obtaining the voltage target value of the bus total voltage and the actual voltage value of the bus total voltage of the current voltage boosting period;

[0069] S220, determining the voltage error based on the difference between the voltage target value and the actual voltage value of the bus total voltage, and determining the bus voltage difference based on the difference between the absolute value of the positive bus voltage and the absolute value of the negative bus voltage;

[0070] Specifically, in the starting process, the bus total voltage is taken as a unified control object, so that the difference between the voltage target value and the bus total voltage, i.e. the voltage error, can reflect the difference between the current bus total voltage and the voltage target value. The bus voltage difference can reflect the difference between the absolute values of the current positive bus and the negative bus.

[0071] S230, determining the positive side control amount of the positive bus and the negative side control amount of the negative bus according to the voltage error and the bus voltage difference, and performing voltage boosting control on the positive bus and the negative bus based on the positive side control amount and the negative side control amount, so that the bus total voltage is boosted, and the voltage between the positive bus and the negative bus is balanced.

[0072] Specifically, the bus total voltage is taken as a unified control object, and thus a basic control quantity for overall voltage boosting is generated based on a voltage error between the bus total voltage and a target voltage value, which can be synchronously applied to the positive bus and the negative bus, so that the bus total voltage can approach the target voltage value. A control quantity for eliminating imbalance is generated based on a bus voltage difference between the positive bus and the negative bus, and the control quantity is reversely applied to the basic control quantity of the positive bus and the negative bus, respectively, for example, if the bus voltage difference is positive, that is, the positive bus voltage is greater than the negative bus voltage, the positive-side control quantity of the positive bus and the negative-side control quantity of the negative bus can be determined by reducing the basic control quantity of the positive bus and increasing the basic control quantity of the negative bus, respectively.

[0073] In the start success judgment, based on the comparison between the bus total voltage and the expected voltage, the bus can be normally boosted to the expected voltage when the battery cold start is performed in the bus imbalance, and the soft start failure protection will not be entered because the unilaterally bus voltage rise does not reach the expectation at the beginning of the cold start, thereby causing the power-off shutdown.

[0074] Based on the above embodiment, optionally, the positive-side control quantity includes a duty ratio control quantity of the positive side, and the negative-side control quantity includes a duty ratio control quantity of the negative side; wherein the duty ratio control quantity of the positive side is used to control the conduction and the turn-off of the first power switch tube on the positive bus side in the boost circuit, and the duty ratio control quantity of the negative side is used to control the conduction and the turn-off of the second power switch tube on the negative bus side in the boost circuit, so as to realize the bus voltage adjustment.

[0075] Specifically, Figure 3 A structure schematic diagram of a boost circuit is provided for the embodiment of the application, and the embodiment can be applied to the cold start in the bus imbalance of an uninterruptible power supply. The boost circuit comprises a positive bus capacitor C1, a negative bus capacitor C2, a first power switch tube Q1, a second power switch tube Q2, a first inductor L1, a second inductor L2, a first diode D1 and a second diode D2.

[0076] Specifically, the positive electrode of the battery BAT is electrically connected to the first end of the first inductor L1; the second end of the first inductor L1 is electrically connected to the first electrode of the first power switch tube Q1 and the anode of the first diode D1, respectively; the cathode of the first diode D1 is connected to the first end of the positive bus capacitor C1, and the second end of the positive bus capacitor C1 is taken as a system midpoint. The second electrode of the first power switch tube Q1 is connected to the system midpoint; the control electrode of the first power switch tube is connected to the output end of the positive-side control quantity.

[0077] Accordingly, the negative terminal of battery BAT is electrically connected to the first terminal of the second inductor L2; the second terminal of the second inductor L2 is electrically connected to the first terminal of the second power switch Q2 and the cathode of the second diode D2; the anode of the second diode D2 is connected to the first terminal of the negative bus capacitor C2; the second terminal of the negative bus capacitor C2 is connected to the system midpoint. The second terminal of the second power switch Q2 is connected to the system midpoint. The control terminal of the second power switch is connected to the output terminal of the negative control quantity.

[0078] Therefore, the positive bus capacitor C1 and the negative bus capacitor C2 are connected in series between the positive bus BUS+ and the negative bus BUS- in a common midpoint manner. Bus voltage sampling points can be set at the first end of the positive bus capacitor C1 and the first end of the negative bus capacitor C2 to collect the positive bus voltage and the negative bus voltage.

[0079] In one embodiment, the first power switch Q1 and the second power switch Q2 are either insulated-gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field-effect transistors (MOSFETs). The control terminal of the first power switch Q1 receives the duty cycle control quantity D+ from the positive side, and the control terminal of the second power switch Q2 receives the duty cycle control quantity D- from the negative side, thereby regulating the bus voltage boosting process and balancing the positive and negative bus voltages. The duty cycle control quantities D+ and D- from the positive and negative sides can be output through a voltage outer loop control circuit. It should be noted that the voltage outer loop is a voltage control loop used to control the voltage in a circuit. By measuring and controlling the output voltage, it stabilizes the output voltage at a target value. Voltage control loops are widely used in power systems, electronic equipment, and industrial automation, and will not be elaborated further here.

[0080] In one embodiment, the boost circuit further includes a first controllable switching device SCR1 and a second controllable switching device SCR2. The first controllable switching device SCR1 is connected in series between the positive terminal of the battery BAT and the first inductor L1; the second controllable switching device SCR2 is connected in series between the negative terminal of the battery BAT and the first terminal of the second inductor L2. Specifically, during the initial cold start phase of the battery BAT, the first controllable switching device SCR1 and the second controllable switching device SCR2 can be controlled to close, thereby connecting the battery BAT. When not needed, the connection of the battery BAT can be disconnected to ensure safe system operation.

[0081] Based on the above embodiment, by sampling the voltage of the battery BAT, it is judged whether the voltage of the battery BAT is normal, if normal, entering the cold start starting stage of the battery BAT, controlling the first controllable switching device SCR1 and the second controllable switching device SCR2 to be closed, the battery BAT directly as the input source of the boost circuit, the first diode D1 and the second diode D2 can be used as the anti-reverse diode, for preventing the bus capacitor from discharging to the ground. In the cold start stage, taking the bus total voltage as the unified control object, through the PWM duty ratio control quantity output control of the conduction and turn-off of the first power switch tube Q1, that is, the duty ratio control quantity of the positive side, and the PWM duty ratio control quantity output control of the conduction and turn-off of the second power switch tube Q2, that is, the duty ratio control quantity of the negative side, the boost and balance of the positive bus BUS+ and the negative bus BUS- are realized.

[0082] wherein, Figure 4 A schematic diagram of the duty ratio control quantity of the positive and negative sides is provided for the embodiment of the application, referring to Figure 4 The duty ratio control quantity D+ of the positive side and the duty ratio control quantity D- of the negative side are PWM duty ratio control quantities. Exemplarily, the first power switch tube Q1 and the second power switch tube Q2 are turned off at a high level and turned on at a low level. Assuming that the positive bus voltage is greater than the negative bus voltage, the balance control quantity is greater than 0, indicating that the negative bus needs to be boosted. The duty ratio control quantity D+ of the positive side can be greater than the duty ratio control quantity D- of the negative side, that is, the first power switch tube Q1 is turned on for a longer time. The control quantity of the first power switch tube Q1 and the second power switch tube Q2 is simultaneously emitted, and three working states can be obtained.

[0083] Figure 5 A simplified circuit schematic diagram in the first working state is provided, referring to Figure 5 The first power switch tube Q1 and the second power switch tube Q2 are both turned on, the current path is the positive electrode of the battery BAT→the first controllable switching device SCR1→the first inductor L1→the first power switch tube Q1→the second power switch tube Q2→the second inductor L2→the second controllable switching device SCR2→the negative electrode of the battery BAT, the first inductor L1 and the second inductor L2 are charged, preparing for subsequent energy release.

[0084] Figure 6 A simplified circuit schematic diagram in the second working state is provided, referring to Figure 6 The first power switch tube Q1 is turned on and the second power switch tube Q2 is turned off, the current path is the positive electrode of the battery BAT→the first controllable switching device SCR1→the first inductor L1→the first power switch tube Q1→the negative bus capacitor C2→the second diode D2→the second inductor L2→the second controllable switching device SCR2→the negative electrode of the battery BAT, the negative bus capacitor C2 is charged, the energy is transferred from the positive bus BUS+ side to the negative bus BUS- side, and the degree of bus imbalance is reduced.

[0085] Figure 7 For the third working state, see the simplified circuit schematic diagram Figure 7 , the first power switch tube Q1 and the second power switch tube Q2 are both off, the current path is the positive electrode of the battery BAT→the first controllable switching device SCR1→the first inductor L1→the first diode D1→the positive bus capacitor C1→the negative bus capacitor C2→the second diode D2→the second inductor L2→the second controllable switching device SCR2→the negative electrode of the battery BAT, the positive bus capacitor C1 and the negative bus capacitor C2 are charged, and the energy of the whole bus is raised.

[0086] When the system detects that the negative bus voltage is greater than the positive bus voltage, the balance control quantity is less than 0, indicating that the positive bus needs to be boosted, and the duty cycle control quantity D+ of the positive side can be obtained to be less than the duty cycle control quantity D- of the negative side, that is, the second power switch tube Q2 is turned on for a longer time. For the case that the second power switch tube Q2 is turned on and the first power switch tube Q1 is off, the current path is the positive electrode of the battery BAT→the first controllable switching device SCR1→the first inductor L1→the first diode D1→the positive bus capacitor C1→the second power switch tube Q2→the second inductor L2→the second controllable switching device SCR2→the negative electrode of the battery BAT, the positive bus capacitor C1 is charged, the energy is transferred from the negative bus BUS- side to the positive bus BUS+ side, and the degree of bus imbalance is reduced.

[0087] S240, determining an expected voltage according to the voltage target value and a preset coefficient, wherein the preset coefficient is a proportional coefficient for conversion between the voltage target value and the expected voltage;

[0088] S250, judging whether the cold start is successful according to the bus total voltage and the expected voltage, wherein if the actual voltage value of the bus total voltage is less than the expected voltage for a first preset time, it is determined that the cold start fails, and shutdown power protection is performed; if the actual voltage value of the bus total voltage is greater than the expected voltage, and the positive bus voltage and the negative bus voltage are within a preset working voltage range, it is determined that the cold start is successful.

[0089] Figure 8 For another flowchart of the cold start control method of the uninterruptible power supply provided by the embodiment, see Figure 8 , which comprises:

[0090] S310, obtaining a voltage target value of a bus total voltage and an actual voltage value of the bus total voltage in a current boost period;

[0091] S320, determining a voltage error based on a difference between the voltage target value and the actual voltage value of the bus total voltage, and determining a bus voltage difference based on a difference between an absolute value of the positive bus voltage and an absolute value of the negative bus voltage;

[0092] S330, determining an overall control quantity of the positive bus and the negative bus according to the voltage error;

[0093] Specifically, the bus total voltage is taken as a unified control object, and thus an overall control quantity for overall voltage boosting is generated based on a voltage error between the bus total voltage and a target voltage value. The overall control quantity is used to represent a basic control quantity of bus total voltage energy demand, and can be synchronously applied to the positive bus and the negative bus, so that the bus total voltage can approach the target voltage value. In voltage outer loop control, a proportional-integral controller (PI controller) is usually used, the voltage error is taken as an input quantity, and the overall control quantity for adjusting the total bus voltage is output by using proportional and integral gains. The overall control quantity can be equivalent to a duty ratio control quantity, and can be synchronously applied to the first power switch Q1 and the second power switch Q2 on the positive bus and the negative bus, so that the bus total voltage can approach the target voltage value.

[0094] S340, determining an equalization control quantity between the positive bus and the negative bus according to the bus voltage difference;

[0095] Specifically, if the positive bus voltage is greater than the negative bus voltage, the negative bus needs to be boosted to reduce the difference. If the positive bus voltage is less than the negative bus voltage, the positive bus needs to be boosted to reduce the difference. Based on the bus voltage difference between the positive bus and the negative bus, an equalization control quantity for eliminating the imbalance is generated. For example, the equalization control quantity is determined according to the product of the bus voltage difference and an equalization coefficient. The equalization coefficient can be a normalized value between the unit bus voltage difference and the duty ratio control quantity. It needs to be noted that the equalization coefficient can be an engineering parameter obtained by system modeling or experimental calibration, which will not be described here. Therefore, the equalization control quantity can be used to represent a duty ratio control quantity for voltage equalization between the positive bus and the negative bus.

[0096] S350, determining the duty ratio control quantity D+ of the positive side according to the sum of the overall control quantity and the equalization control quantity, and determining the duty ratio control quantity D- of the negative side according to the difference between the overall control quantity and the equalization control quantity.

[0097] Specifically, the equalization control quantity is inversely applied to the overall control quantity, the duty ratio control quantity D+ of the positive side is represented as the sum of the overall control quantity and the equalization control quantity, and the duty ratio control quantity D- of the negative side is represented as the difference between the overall control quantity and the equalization control quantity. For example, when the positive bus voltage is greater than the negative bus voltage, the equalization control quantity is greater than 0, the duty ratio control quantity of the positive side is greater than that of the negative side, and the conduction time of the first power switch Q1 is longer. It can be obtained that the first power switch Q1 is turned on and the second power switch Q2 is turned off, so that the negative bus capacitor C2 is charged, the energy is transferred from the positive bus BUS+ side to the negative bus BUS- side, and the degree of bus imbalance is reduced.

[0098] When the positive bus voltage is less than the negative bus voltage, the balance control amount is less than 0, the duty cycle control amount of the positive side is less than the duty cycle control amount of the negative side, that is, the turn-on time of the second power switch tube Q2 is longer. The first power switch tube Q1 is turned on, and the second power switch tube Q2 is turned off, so that the positive bus capacitor C1 is charged, and the energy is transferred from the negative bus BUS- side to the positive bus BUS+ side, thereby reducing the degree of bus imbalance.

[0099] S360, determining an expected voltage according to the voltage target value and a preset coefficient, wherein the preset coefficient is a proportional coefficient for conversion between the voltage target value and the expected voltage;

[0100] S370, judging whether the cold start is successful according to the total bus voltage and the expected voltage, wherein if the actual voltage value of the total bus voltage is less than the expected voltage for a first preset time, it is determined that the cold start fails, and shutdown power-off protection is performed; if the actual voltage value of the total bus voltage is greater than the expected voltage, and the positive bus voltage and the negative bus voltage are within a preset working voltage range, it is determined that the cold start is successful.

[0101] The embodiment of the present application also provides a controller, which is used to execute the cold start control method of any embodiment of the present application.

[0102] The embodiment of the present application also provides a cold start control device of an uninterruptible power supply, Figure 9 A structure schematic diagram of an uninterruptible power supply provided by the embodiment of the present application, referring to Figure 9 , comprising: a boost circuit 120 and the controller 110 in the above embodiment, the first end of the boost circuit 120 is connected with the controller 110, and the second end of the boost circuit 120 is connected with the positive bus BUS+ and the negative bus BUS- respectively;

[0103] The controller 110 is used to acquire the voltage target value of the total bus voltage and the actual voltage value of the total bus voltage in a current boost period, and control the boost circuit to boost the positive bus and the negative bus according to the voltage target value;

[0104] The controller 110 is also used to determine an expected voltage according to the voltage target value and a preset coefficient, wherein the preset coefficient is a proportional coefficient for conversion between the voltage target value and the expected voltage;

[0105] The controller 110 is also used to perform shutdown power-off protection in the case that the actual voltage value of the total bus voltage is less than the expected voltage for a first preset time.

[0106] Specifically, the voltage target value is a voltage value expected to be reached by the bus total voltage during the cold start process. For example, during the cold start boost stage, the controller 110 can generally have multiple boost periods, and the voltage target value of each boost period can be different. For example, in the initial boost period, the voltage target value is set to an initial voltage target value, and in the next boost period, the corresponding voltage target value can be obtained according to a preset first step. The first step of the voltage target value of adjacent boost periods can be the same, so as to form a smooth target trajectory, until the system reaches the final preset voltage target value. By setting a dynamic voltage target value, the voltage overshoot and current impact during the start-up process can be effectively suppressed, and the device stress or control instability caused by voltage mutation can be avoided. The actual voltage value of the bus total voltage is the actual voltage value reached by the bus total voltage during the cold start process. The actual voltage value of the bus total voltage can be represented as the sum of the positive bus voltage and the negative bus voltage collected in real time, and the positive bus voltage and the negative bus voltage can be obtained by sampling the bus capacitor.

[0107] The controller 110 controls the boost circuit 120 to boost both the positive bus and the negative bus according to the voltage target value, and considers the positive bus and the negative bus as a unified energy storage unit for collaborative boosting. The boost circuit 120 adjusts the conduction and turn-off of the power switch tube in the boost circuit according to the control instruction output by the controller 110, so as to realize the transfer of electrical energy to the positive bus capacitor and the negative bus capacitor, thereby improving the bus total voltage.

[0108] The controller 110 determines the expected voltage according to the voltage target value and a preset coefficient, wherein the preset coefficient is a proportional coefficient for converting between the voltage target value and the expected voltage. The preset coefficient is used to set the lowest reasonable threshold value that the bus voltage should reach during the soft start process. For example, the preset coefficient can be in the range of 0.5 to 1, and preferably in the range of 0.85 to 0.95. Considering the different discharge resistance values in the bus loop, when the self-loss is slow, if the battery is immediately cold started after normal shutdown, since the duty cycle control of the conduction and turn-off of the power switch tube in the boost circuit starts from 0 or a lower value and rises by a step, the voltage target value has an initial value. At this time, if a higher preset coefficient is used, the expected voltage will rapidly rise in the initial start-up period, resulting in a large deviation from the actual bus voltage, which may be misjudged as abnormal boost, and even trigger unnecessary protection actions. Therefore, the preset coefficient can be used to lower the expected voltage in the initial period according to the actual situation, so as to avoid large boost fluctuations.

[0109] The controller 110 determines whether the starting is successful according to the bus total voltage and the expected voltage. If the actual voltage value of the bus total voltage is less than the expected voltage for a first preset time, it is determined that the cold starting fails, and the shutdown protection is performed. If the actual voltage value of the bus total voltage is greater than the expected voltage, and the positive bus voltage and the negative bus voltage are in a preset working voltage range, it is determined that the cold starting is successful.

[0110] Based on the above embodiments, combined with Figure 3 The boost circuit 110 includes a positive bus capacitor C1, a negative bus capacitor C2, a first power switch Q1, a second power switch Q2, a first inductor L1, a second inductor L2, a first diode D1 and a second diode D2.

[0111] Specifically, the positive electrode of the battery BAT is electrically connected to the first end of the first inductor L1. The second end of the first inductor L1 is electrically connected to the first electrode of the first power switch Q1 and the anode of the first diode D1, respectively. The cathode of the first diode D1 is connected to the first end of the positive bus capacitor C1, and the second end of the positive bus capacitor C1 is used as a system midpoint. The second electrode of the first power switch Q1 is connected to the system midpoint, and the control electrode of the first power switch is connected to the controller 110.

[0112] Correspondingly, the negative electrode of the battery BAT is electrically connected to the first end of the second inductor L2. The second end of the second inductor L2 is electrically connected to the first electrode of the second power switch Q2 and the cathode of the second diode D2, respectively. The anode of the second diode D2 is connected to the first end of the negative bus capacitor C2. The second end of the negative bus capacitor C2 is connected to the system midpoint. The second electrode of the second power switch Q2 is connected to the system midpoint. The control electrode of the second power switch is connected to the controller 110. The controller 110 is configured to determine a voltage error based on a difference between the voltage target value and the actual voltage value of the bus total voltage, determine a bus voltage difference based on a difference between the absolute value of the positive bus voltage and the absolute value of the negative bus voltage, and determine a duty cycle control amount of the positive side of the positive bus and a duty cycle control amount of the negative side of the negative bus according to the voltage error and the bus voltage difference. The boost circuit 120 is configured to adjust the positive bus voltage and the negative bus voltage based on the duty cycle control amount of the positive side and the duty cycle control amount of the negative side. The duty cycle control amount of the positive side is used to control the conduction and turn-off of the first power switch Q1 on the positive bus side in the boost circuit, and the duty cycle control amount of the negative side is used to control the conduction and turn-off of the second power switch Q2 on the negative bus side in the boost circuit.

[0113] Optionally, the uninterruptible power supply further includes a detection circuit 130.

[0114] The detection circuit 130 is configured to detect the actual voltage value of the positive bus and the actual voltage value of the negative bus voltage.

[0115] The controller 110 determines the actual voltage value of the bus total voltage based on the actual voltage value of the positive bus and the actual voltage value of the negative bus voltage.

[0116] Specifically, the actual voltage value of the bus total voltage is the actual voltage value that the bus total voltage has reached during the cold start process. The detection circuit 130 can obtain the positive bus voltage and the negative bus voltage by sampling the positive bus capacitor and the negative bus capacitor, respectively. The actual voltage value of the bus total voltage can be represented as the sum of the real-time collected positive bus voltage and negative bus voltage, therefore, the controller 110 can calculate the actual voltage value of the bus total voltage based on the actual voltage value of the positive bus and the actual voltage value of the negative bus voltage.

[0117] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A cold start control method of an uninterruptible power supply, characterized by, The method comprises the following steps: obtaining a voltage target value of a bus total voltage in a current boosting period and an actual voltage value of the bus total voltage; performing boosting control on both the positive bus and the negative bus according to the voltage target value; determining an expected voltage according to the voltage target value and a preset coefficient, wherein the preset coefficient is a proportional coefficient for conversion between the voltage target value and the expected voltage; if the actual voltage value of the bus total voltage is continuously less than the expected voltage for a first preset time, determining that cold start fails and performing shutdown protection; if the actual voltage value of the bus total voltage is greater than the expected voltage and the positive bus voltage and the negative bus voltage are respectively within a preset working voltage range, determining that cold start succeeds.

2. The cold start-up control method of an uninterruptible power supply according to claim 1, characterized by, The method for obtaining the voltage target value of the bus total voltage in the current boosting period comprises the following steps: obtaining a positive bus voltage and a negative bus voltage at an initial time; determining an initial voltage target value of the bus total voltage according to the positive bus voltage and the negative bus voltage at the initial time, wherein the initial voltage target value is used as the voltage target value of an initial boosting period; iteratively calculating the voltage target value corresponding to a subsequent boosting period based on the initial voltage target value and a preset first step, wherein the voltage target value of each boosting period is obtained by superimposing the first step on the voltage target value of a previous boosting period.

3. The cold start-up control method of an uninterruptible power supply according to claim 2, characterized by, The method for determining the initial voltage target value according to the current positive bus voltage and the current negative bus voltage comprises the following steps: calculating an average value of the current positive bus voltage and the current negative bus voltage, and taking the average value as the initial voltage target value.

4. The cold start-up control method of an uninterruptible power supply according to claim 2, characterized by, The method for performing boosting control on both the positive bus and the negative bus according to the voltage target value comprises the following steps: determining a voltage error based on a difference between the voltage target value and an actual voltage value of the bus total voltage, and determining a bus voltage difference based on a difference between an absolute value of the positive bus voltage and an absolute value of the negative bus voltage; determining a positive side control amount of the positive bus and a negative side control amount of the negative bus according to the voltage error and the bus voltage difference, and performing boosting control on the positive bus and the negative bus based on the positive side control amount and the negative side control amount, so that the bus total voltage is boosted and the voltage between the positive bus and the negative bus is balanced.

5. The cold start-up control method of an uninterruptible power supply according to claim 4, characterized by, The positive side control amount comprises a duty cycle control amount of the positive side, and the negative side control amount comprises a duty cycle control amount of the negative side; wherein the duty cycle control amount of the positive side is used to control conduction and turn-off of a first power switch tube on the positive bus side in a boosting circuit, and the duty cycle control amount of the negative side is used to control conduction and turn-off of a second power switch tube on the negative bus side in the boosting circuit, so as to realize bus voltage adjustment.

6. The cold start-up control method of an uninterruptible power supply according to claim 5, characterized by, The method for determining the positive side control amount of the positive bus and the negative side control amount of the negative bus according to the voltage error and the bus voltage difference comprises the following steps: determining an overall control amount of the positive bus and the negative bus according to the voltage error, wherein the overall control amount is used to represent a basic control amount of energy demand of the bus total voltage; determining a balancing control amount between the positive bus and the negative bus according to the bus voltage difference, wherein the balancing control amount is used to represent a control amount for voltage balancing between the positive bus and the negative bus; determining the duty cycle control quantity of the positive side according to the sum of the overall control quantity and the balance control quantity; determining the duty cycle control quantity of the negative side according to the difference between the overall control quantity and the balance control quantity.

7. A controller characterized by comprising: The controller is configured to perform the cold start control method of any one of claims 1-6.

8. An uninterruptible power supply, characterized by comprising: a boost circuit and the controller of claim 7, a first end of the boost circuit being connected to the controller, a second end of the boost circuit being connected to the positive bus and the negative bus respectively; the controller is configured to obtain a voltage target value of a bus total voltage in a current boost cycle and an actual voltage value of the bus total voltage; and, control the boost circuit to boost the positive bus and the negative bus according to the voltage target value; the controller is further configured to determine an expected voltage according to the voltage target value and a preset coefficient, wherein the preset coefficient is a proportional coefficient for conversion between the voltage target value and the expected voltage; the controller is further configured to perform shutdown protection in a case where the actual voltage value of the bus total voltage continuously less than the expected voltage for a first preset time.

9. The uninterruptible power supply of claim 8, wherein, The boost circuit comprises: a positive bus capacitor, a negative bus capacitor, a first power switch tube, a second power switch tube, a first inductor, a second inductor, a first diode and a second diode. A positive electrode of a battery is electrically connected to a first end of the first inductor; a second end of the first inductor is electrically connected to a first pole of the first power switch tube and an anode of the first diode respectively; a cathode of the first diode is connected to a first end of the positive bus capacitor, and a second end of the positive bus capacitor is used as a system midpoint; a second pole of the first power switch tube is connected to the system midpoint; a control pole of the first power switch tube is connected to the controller. A negative electrode of the battery is electrically connected to a first end of the second inductor; a second end of the second inductor is electrically connected to a first pole of the second power switch tube and a cathode of the second diode respectively; an anode of the second diode is connected to a first end of the negative bus capacitor; a second end of the negative bus capacitor is connected to the system midpoint; a second pole of the second power switch tube is connected to the system midpoint; a control pole of the second power switch tube is connected to the controller. The controller is configured to determine a voltage error based on a difference between the voltage target value and the actual voltage value of the bus total voltage, and determine a bus voltage difference based on a difference between the positive bus voltage absolute value and the negative bus voltage absolute value; The controller is further configured to determine a duty cycle control quantity of a positive side of the positive bus and a duty cycle control quantity of a negative side of the negative bus according to the voltage error and the bus voltage difference, wherein the duty cycle control quantity of the positive side is used to control the conduction and the turn-off of the first power switch tube on the positive bus side in the boost circuit, and the duty cycle control quantity of the negative side is used to control the conduction and the turn-off of the second power switch tube on the negative bus side in the boost circuit.

10. The uninterruptible power supply of claim 9, wherein, The uninterruptible power supply further comprises a detection circuit; The detection circuit is configured to detect the actual voltage value of the positive bus and the actual voltage value of the negative bus voltage; The controller determines an actual voltage value of the bus total voltage based on an actual voltage value of the positive bus and an actual voltage value of the negative bus voltage.

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