Constant-current-to-constant-voltage power supply and control method

Abstract

The invention relates to a constant-current-to-constant-voltage power supply and a control method, and the power supply comprises a current bypass circuit which comprises a bypass switch and is used for bypassing the power supply from a main loop when the power supply fails; the DC / DC converter is used for converting the direct-current bus voltage into required output voltage; the direct-current bus capacitor is used for storing energy and maintaining the bus voltage to be stable; the control center is used for detecting output load power and calculating a required direct current bus voltage reference value Uref; the input end of the DC / DC converter is directly connected with the output end of the current bypass circuit, and the DC bus capacitor is bridged between parallel connection points; the control center calculates Uref according to the output load power and the input constant current value, and controls the on-off state of the bypass switch through a hysteresis control strategy so as to maintain the DC bus voltage within the range of Uref + / -delta U; the power supply does not comprise an independent constant-current-to-constant-voltage module.

Description

Technical Field

[0001] This invention belongs to the field of marine power supply technology, and particularly relates to a constant current to constant voltage power supply and control method. Background Technology

[0002] In marine observation, exploration, and engineering applications, constant current power supply is often used to power remote underwater equipment to achieve long-distance power transmission. Underwater equipment typically requires a stable DC voltage, thus necessitating a power supply device that can convert the constant current output from a shore-based constant current power supply into a stable DC voltage, i.e., a constant current to constant voltage (CC-CV) power supply.

[0003] Traditional underwater constant current to constant voltage power supplies typically consist of a current bypass circuit, a separate constant current to constant voltage module, a DC / DC converter, and a control center. Current bypass is an essential function of underwater constant current to constant voltage power supplies. Its purpose is to ensure that the power supply stops operating in case of a fault, thus avoiding the consumption of energy from the shore-based power source. After bypassing, the voltage on the constant current to constant voltage module will be 0V. The main function of the constant current to constant voltage module is to convert a constant input current into voltage to provide power for the downstream DC / DC converter. If the constant current is not converted to constant voltage, or if the converted voltage is 0V, even if a constant current flows through the module, there will be no power output at the input of the downstream DC / DC converter (P=U*I), resulting in no power output from the DC / DC converter. Therefore, the most critical step in a constant current to constant voltage power supply is how to convert the constant current into the required voltage. With a voltage U, combined with a constant current I input, the DC / DC converter input will have an input power of P=U*I. When a load is connected to the output of a DC / DC converter, if the power consumed by the load is less than the power at the input of the DC / DC converter, the output voltage is stable. However, if the power consumed by the load is greater than the power at the input of the DC / DC converter, the input power P=U*I does not increase. On the contrary, due to the increase in load, the input voltage is pulled down. In other words, the input power not only does not increase but decreases, further causing the input voltage to drop. This cycle continues until the input voltage reaches 0V, meaning the DC / DC input power is 0W. With no power at the input, there is no voltage output from the DC / DC converter. Therefore, for constant current to constant voltage power supplies, stabilizing the DC / DC input voltage is the most critical technology. There are various ways to stabilize the DC / DC input voltage (power), such as the power self-matching voltage stabilization method described in patent "CN202010217787.2". This method combines resistor-based voltage regulation with power matching circuitry. In short, it involves complex circuitry, numerous components, and complex control, significantly reducing the reliability and efficiency of the power supply.

[0004] For underwater power supplies, there are two key technical indicators: first, the reliability must be very high, because the cost of salvaging underwater power supplies is too high; second, the higher the efficiency, the better. Constant current power supply is used so that it can be transmitted over long distances. Higher efficiency can enable shore-based power supplies of the same power to carry more constant current to constant voltage power supplies.

[0005] Therefore, in view of the technical defects of existing underwater constant current to constant voltage power supplies, such as insufficient reliability, low conversion efficiency and complex circuits, there is an urgent need for a brand-new solution to simplify the circuit structure, reduce the number of components and avoid energy dissipation, so as to achieve high reliability and high efficiency at the same time and meet the stringent application requirements of the marine field. Summary of the Invention

[0006] The purpose of this invention is to overcome the technical shortcomings of existing underwater constant current to constant voltage power supplies, such as low reliability, insufficient conversion efficiency, and complex circuit structure. This invention provides a novel constant current to constant voltage power supply and control method, aiming to reduce potential failure points and improve the long-term operational reliability of the power system by optimizing the circuit topology, eliminating the need for a separate constant current to constant voltage module, reducing the number of electronic components, and simplifying the control logic. Simultaneously, by improving the energy conversion mechanism and avoiding the use of resistors for voltage regulation, higher energy conversion efficiency is achieved to meet the urgent needs of marine scientific research and engineering applications for high reliability and high efficiency in underwater power supply systems.

[0007] To achieve the above objectives, the present invention provides a constant current to constant voltage power supply, comprising: A current bypass circuit, which includes a bypass switch for bypassing power from the main circuit in the event of a power failure. A DC / DC converter is used to convert the DC bus voltage into the required output voltage. DC bus capacitors are used to store energy and maintain stable bus voltage. The control center is used to detect the output load power and calculate the required DC bus voltage reference value Uref; The input terminal of the DC / DC converter is directly connected to the output terminal of the current bypass circuit, and the DC bus capacitor is connected across the parallel connection point; the control center calculates Uref based on the output load power and the input constant current value, and controls the switching state of the bypass switch through a hysteresis control strategy to maintain the DC bus voltage within the range of Uref±ΔU; the power supply does not include an independent constant current to constant voltage module.

[0008] Furthermore, the DC / DC converter is a half-bridge inverter structure, including two switching transistors and a transformer, used to convert the DC bus voltage into AC voltage and then rectify and output it after coupling through the transformer.

[0009] Furthermore, the control center calculates the output power by detecting the output current and voltage, adds the switching loss power, and divides it by the input constant current value to obtain Uref.

[0010] Furthermore, the power supply also includes a local redundancy structure, which includes: At least two identical power supply modules, A and B, are used, with the constant current input terminals of A and B connected in series. Each power module includes an independent current bypass circuit, DC bus capacitor, and DC / DC converter. The control power supplies of the two power modules are connected in parallel to supply power to the control center. When machine A is working normally, machine B is in bypass mode; when machine A malfunctions, machine B is put into operation.

[0011] Furthermore, the DC bus capacitor of the B unit obtains energy from the A unit through the magnetic circuit coupling of the transformer. After rectification by the switching diodes of the half-bridge inverter circuit of the B unit, it remains in a charging state to ensure that the control center can still work normally when the A unit fails.

[0012] A control method for the aforementioned constant current to constant voltage power supply is also provided, including the following steps: Detect the current and voltage of the output load and calculate the output power; Calculate the total power based on the output power and the preset switching losses; Calculate the DC bus voltage reference value Uref based on the total power and the input constant current value; The switching state of the bypass switch is controlled by a hysteresis control strategy to maintain the DC bus voltage within the range of Uref±ΔU.

[0013] Furthermore, the hysteresis control strategy includes: If the DC bus voltage is higher than Uref+ΔU, then open the bypass switch; If the DC bus voltage is lower than Uref-ΔU, the bypass switch is turned off and the half-bridge inverter of the DC / DC converter is paused. The inverter is restarted after the voltage recovers to Uref.

[0014] Furthermore, the method also includes a redundancy switching step: When the main power module fails, it automatically switches to the backup power module; The DC bus capacitor of the backup power module is pre-charged through the transformer coupling of the main power module to ensure uninterrupted control power supply.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) High reliability: It eliminates the need for a complex independent constant current to constant voltage module, significantly reduces the number of components in the main circuit, simplifies the circuit structure, thereby reducing the failure rate and improving the overall reliability of the power supply system.

[0016] (2) High conversion efficiency: The DC bus voltage is regulated by controlling the bypass switch and using the output load naturally, which completely avoids the method of using resistor energy consumption to stabilize the voltage, greatly reduces energy waste, and improves the conversion efficiency of the entire power supply system (including shore power supply).

[0017] (3) Low cost and small size: It effectively utilizes the inherent devices of constant current underwater voltage and achieves constant voltage output through clever control. No additional power processing hardware is required, which effectively reduces cost and size.

[0018] (4) Seamless redundancy backup: The proposed local redundancy design scheme only provides redundancy for the primary circuit on the high-voltage side, resulting in a compact structure. The backup module stores energy in advance through magnetic coupling and body diode rectification during standby, ensuring that the power supply to the control center is never interrupted and achieving seamless switching in case of failure, further enhancing the reliability of the system. Attached Figure Description

[0019] Figure 1 The electrical topology diagram of the constant current to constant voltage power supply is shown; Figure 2 The electrical simulation model was built. Figure 3 The waveforms of the output current, voltage, and bus voltage are shown. Figure 4 The diagram shows a partially redundant electrical topology for a constant current to constant voltage power supply. Figure 5 The electrical topology diagram shows two sets of modules jointly powering the control center. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1: Standalone System A conventional constant current to constant voltage power supply's main circuit consists of a current bypass circuit, a constant current to constant voltage module, and a DC / DC converter. The constant current to constant voltage power supply of this invention eliminates the need for a dedicated constant current to constant voltage module. Instead, it cleverly utilizes existing DC / DC converter circuits and constant current bypass switches to construct a constant current to constant voltage circuit. This not only significantly reduces the number of components in the main circuit but also improves the power supply's efficiency. Figure 1 As shown.

[0022] The power supply mainly includes a current bypass circuit, a DC bus capacitor C11, a DC / DC converter, and a control center (not shown separately in the figure). The current bypass circuit consists of a bypass switch Q13 and a diode D11. The DC / DC converter adopts a half-bridge inverter structure, consisting of switching transistors Q11 and Q12, a transformer T1, and a subsequent rectifier and filter circuit. The input terminals of the DC / DC converter (i.e., the positive and negative input terminals of the DC bus of the half-bridge inverter circuit) are directly connected in parallel with the output terminals of the current bypass circuit (i.e., the connection point between the cathode of diode D11 and bypass switch Q13). The DC bus capacitor C11 is directly connected across this parallel connection point and the negative input terminal. This topology omits the independent constant current to constant voltage module found in traditional power supplies.

[0023] When the power supply is first powered on, the control center closes the bypass switch Q13. A constant input current (e.g., 2A) flows through diode D11 to charge the DC bus capacitor C11. The voltage of capacitor C11 rises slowly. After reaching a certain value, the bypass switch opens, and the constant current stops charging capacitor C11, maintaining the voltage at the given value. When the bus voltage drops, the bypass switch closes again, and the constant current charges capacitor C11 again.

[0024] After the voltage across capacitor C11 stabilizes, the half-bridge inverter begins operation, generating AC current on the primary side of transformer T1. This AC current is then rectified and filtered on the secondary side of the transformer to produce DC output. The output voltage and current are used as feedback to control the duty cycle of the half-bridge inverter's switching transistors, outputting DC voltage according to the given output voltage value. For example, if the output voltage is DC 12V with a 1Ω load resistor, the output power is [value missing]. At this point, the power on the right side of the transformer must be >144W. If the constant current is 2A, the voltage at the DC bus on the primary side of the transformer must be >72V. If the DC bus voltage is less than 72V, the input power on the primary side of the transformer will be less than 144W. Since the load remains constant (1Ω), the DC output voltage will decrease, falling below 12V. For a voltage source, a constant voltage output must be maintained. Clearly, the current voltage output does not meet the requirements. Therefore, regardless of the output load, before the half-bridge inverter starts operating, the DC bus voltage must reach its maximum value before starting the inverter output. For example, if the maximum voltage reaches DC 120V, the input power on the primary side of the transformer will be P=U*I=240W. If the inverter is then turned on with a 1Ω load and the output voltage is DC 12V, the output power will be 144W. This does indeed meet the requirement of constant voltage output. However, this also brings another problem. When the load is very light, such as a 1000Ω resistor, the output voltage is DC 12V, and the output power is 0.144W. However, the input voltage is DC 120V, which will cause significant switching losses in the half-bridge inverter, wasting power and causing underwater equipment to overheat. Another issue with this power supply is that if the DC bus voltage drops, meaning the input power drops, and the output power is greater than the input power, the DC output voltage will be pulled down by the load, and the bus voltage will also be pulled down, creating a cycle that eventually leads to the DC bus voltage disappearing and failing to be re-established. To address the above issues, some products automatically match the DC bus voltage based on the output current, which does solve the problem. However, this results in complex circuitry, involving both resistive loads to regulate the bus voltage and power matching devices for adjustment. This complexity significantly reduces the power supply's reliability; furthermore, using resistor discharge to regulate voltage lowers the efficiency of the entire power system (including shore power supplies).

[0025] The underwater constant current power supply of the present invention makes full use of the bypass switch and the half-bridge inverter switch in the DC / DC converter. The control center detects the voltage and current values ​​at the power output terminal in real time, detects the load size at the DC output terminal, calculates the power required at the output terminal based on the load size, adds some power lost by switching, and obtains the total power. After dividing the total power by the input constant current value (2A), the voltage Uref required at the DC bus terminal is obtained.

[0026] To prevent frequent switching, a hysteresis voltage ΔU is designed here. The control center employs a hysteresis control strategy: When the voltage across capacitor C11 rises above (Uref + ΔU), the control center opens the bypass switch Q13. At this time, the constant current input is cut off, capacitor C11 stops charging, and the bus voltage is maintained by discharging to the DC / DC converter until the voltage drops to the required DC bus voltage Uref.

[0027] When the voltage on capacitor C11 drops below (Uref - ΔU) due to discharge, the control center shuts off bypass switch Q13 and half-bridge inverters Q11 and Q13. After the voltage rises to the required bus voltage value, bypass switch Q13 is shut off, and the half-bridge inverter restarts inversion.

[0028] By repeating this process, the DC bus voltage is stabilized within the range of Uref ± ΔU.

[0029] Once the DC bus voltage is established and stabilized, the control center controls the switching transistors Q11 and Q12 of the half-bridge inverter circuit to conduct alternately with a certain duty cycle, inverting the DC bus voltage into AC power. After coupling, isolation, and transformation by transformer T1, the AC power is then converted into a stable DC voltage (e.g., 12V) by the secondary rectifier and filter circuit. The control center uses the output voltage as feedback and maintains the stability of the output voltage by adjusting the duty cycle of the half-bridge inverter switching transistors.

[0030] Electrical simulation modeling, such as Figure 2 As shown, the DC output terminal is equipped with a dummy load R1=1000Ω, a load R2=1Ω, and R3=2.57Ω. At 2.15s, the hand shakes and closes the S1 switch, at 4.12s, the S2 switch closes, and at 8s, the S2 switch opens.

[0031] Output voltage and current waveforms are as follows Figure 3 As shown, the output current is very small before 2.15s, almost 0A, because the output load is 1000Ω, 12V / 1000=0.012A; after 2.15s, a 1Ω load is manually applied, and it can be seen that the DC output voltage drops instantly to about 10V. At this time, the DC bus voltage rises to about 82V. At 4.12s, switch S2 is closed, and another 2.57Ω load is applied. At this time, the DC output voltage drops rapidly to about 10V, and recovers to 12V in about 350ms. At this time, the DC bus voltage increases to about 110V. Then, at 8s, switch S2 is opened, the load decreases, the DC output current decreases, the output bus voltage remains unchanged at 12V, and the bus voltage drops to 82V again.

[0032] The simulation waveforms show that by cleverly controlling the bypass switch and the half-bridge inverter in the DC / DC converter, the constant voltage power supply can be output reliably and with maximum efficiency.

[0033] Example 2: Dual-machine system with partial redundancy For marine power supplies, due to the high cost of salvage, extremely high reliability is required. Therefore, redundant design is necessary, meaning that if one power supply fails, another can immediately take over.

[0034] If the entire power supply is designed with redundancy, it will inevitably result in a very large size. This invention addresses the weakness of such power supplies by designing a locally redundant underwater constant current to constant voltage power supply. Figure 1 As can be seen, the secondary voltage of transformer T1 is low, with only 12V output, which is a very low voltage environment, making it unlikely to malfunction and thus requiring no redundancy. Therefore, this invention only implements redundancy design on the primary side of the transformer. A winding identical to the original winding is added to the primary side of the transformer, and the same circuitry as the original primary side is connected to this new winding. The entire connection is as follows: Figure 4 The local redundancy design scheme is shown.

[0035] The redundant system consists of two identical power supply modules (MID-A and MID-B). The constant current input terminals of the two modules are connected in series. Each module includes all the circuits described in Example 1: its respective current bypass circuit (Q13, D11 / Q23, D21), DC bus capacitor (C11 / C21), and half-bridge inverter circuit (Q11, Q12, T1 / Q21, Q22, T1). Units A and B share a single control center. Units A and B communicate and coordinate their operation.

[0036] The switching process between working and redundant operations is as follows: During normal operation: The control center controls machine A to work normally (its bypass switch Q13 is open, and the half-bridge inverter is working), while machine B is in standby redundant state (its bypass switch Q23 is closed, bypassing the half-bridge inverter circuit of machine B, so as not to consume energy).

[0037] Redundant Power Supply Mechanism: There's a question of where the control center draws its power. If it draws power from capacitor C11 on module A, the control center will lose power if module A fails. Drawing power from capacitor C21 on module B also faces the same power loss problem. Once the control center loses power, the power supply cannot bypass the current, and with a constant current flowing continuously, further serious damage to the underwater power supply is inevitable. To address this, the DC bus capacitors (C11 and C21) of both modules share the power supply to the control center through a redundant circuit. Figure 5As shown. If the MID-A unit is working normally and the MID-B unit is bypassed, it consumes no power. However, if the MID-A unit malfunctions, or even if the half-bridge inverter arm short-circuits, the voltage on capacitor C11 will instantly disappear. The control center won't have time to bypass Q13 and disconnect Q23 before there's no power. Because the bypass switch Q23 of the MID-B unit won't be disconnected, capacitor C21 cannot be charged, leading to the control center being unable to operate due to power failure.

[0038] To address this, the DC bus capacitor of unit B is further configured to draw energy from unit A via magnetic coupling through a transformer. This energy is then rectified by the diodes in the switching transistors of unit B's half-bridge inverter circuit and kept charging to ensure the control center can operate normally even if unit A fails. Thus, even when unit B is bypassed, the AC current generated by unit A during operation, coupled through the magnetic coupling of transformer T1, induces a voltage on the primary winding of unit B. This voltage is rectified by the body diodes of the half-bridge inverter switching transistors (Q21, Q22) in unit B, continuously charging unit B's DC bus capacitor C21 and maintaining its voltage at a level similar to that of unit A's capacitor C11. Therefore, the power supply to the control center always has redundancy.

[0039] When a fault occurs in unit A (such as a short circuit), causing a momentary drop in the voltage of its capacitor C11, the control center will not lose power because it is still powered by capacitor C21. The control center can immediately detect the fault in unit A and then execute a switching operation: disconnecting the bypass switch Q23 of unit B and starting the half-bridge inverter circuit of unit B to take over the power supply to the load from unit A. Since capacitor C21 is always in a pre-charge state, this switching process can be completed instantaneously, achieving a seamless transition of the output voltage.

[0040] The redundant module of the present invention is in a bypass state, but is always in a state of sufficient energy, so it can be used without interruption, and the redundant control power supply does not lose power.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A constant current to constant voltage power supply, characterized in that, include: A current bypass circuit, which includes a bypass switch for bypassing power from the main circuit in the event of a power failure. A DC / DC converter is used to convert the DC bus voltage into the required output voltage. DC bus capacitors are used to store energy and maintain stable bus voltage. The control center is used to detect the output load power and calculate the required DC bus voltage reference value Uref; The input terminal of the DC / DC converter is directly connected in parallel with the output terminal of the current bypass circuit, and the DC bus capacitor is connected across the parallel connection point. The control center calculates Uref based on the output load power and the input constant current value, and controls the switching state of the bypass switch through a hysteresis control strategy to maintain the DC bus voltage within the range of Uref±ΔU.

2. The constant current to constant voltage power supply according to claim 1, characterized in that: The DC / DC converter is a half-bridge inverter structure, including two switching transistors and a transformer, used to convert the DC bus voltage into AC voltage and then rectify and output it after coupling through the transformer.

3. The constant current to constant voltage power supply according to claim 1 or 2, characterized in that: The control center calculates the output power by detecting the output current and voltage. The output power plus the switching loss power is divided by the input constant current value to obtain Uref.

4. The constant current to constant voltage power supply according to claim 1, characterized in that, A local redundancy structure is provided, the local redundancy structure including: Machine A and Machine B have two identical power supply modules, and the constant current input terminals of Machine A and Machine B are connected in series. Each power module includes an independent current bypass circuit, DC bus capacitor, and DC / DC converter. The control power supplies of the two power modules are connected in parallel to supply power to the control center. When machine A is working normally, machine B is in bypass mode; when machine A malfunctions, machine B is put into operation.

5. The constant current to constant voltage power supply according to claim 1, characterized in that: The DC bus capacitor of machine B obtains energy from machine A through the magnetic circuit coupling of the transformer. After rectification by the diodes of the switching transistors of the half-bridge inverter circuit of machine B, it is kept in a charging state to ensure that the control center can work normally when machine A fails.

6. A control method for a constant current to constant voltage power supply as described in any one of claims 1-5, characterized in that, Includes the following steps: Detect the current and voltage of the output load and calculate the output power; Calculate the total power based on the output power and the preset switching losses; Calculate the DC bus voltage reference value Uref based on the total power and the input constant current value; The switching state of the bypass switch is controlled by a hysteresis control strategy to maintain the DC bus voltage within the range of Uref±ΔU.

7. The control method according to claim 6, characterized in that, The hysteresis control strategy includes: If the DC bus voltage is higher than Uref+ΔU, then open the bypass switch; If the DC bus voltage is lower than Uref-ΔU, the bypass switch is turned off and the half-bridge inverter of the DC / DC converter is paused. The inverter is restarted after the voltage recovers to Uref.

8. The control method according to claim 6, characterized in that, It also includes a redundancy handover step: When the main power module fails, it automatically switches to the backup power module; The DC bus capacitor of the backup power module is pre-charged through the transformer coupling of the main power module to ensure uninterrupted control power supply.

Images