Brake and booster integrated frequency converter of multiplexing switch device and control method

Abstract

The application relates to the technical field of frequency converters, in particular to a brake-boost integrated frequency converter using a multiplexing switch device and a control method thereof, which comprises a rectifier, an inverter and a direct current link, and further comprises: an electric reactor, one end of which is connected to a positive output end of the rectifier; a reconstruction unit, which comprises a switching switch, a freewheeling tube, a multiplexing switch and a braking resistor, the multiplexing switch being connected between a moving end of the switching switch and a negative bus, the switching switch having a first static end and a second static end, the first static end being connected to the other end of the electric reactor, the anode of the freewheeling tube being connected to the first static end, the cathode of the freewheeling tube being connected to a positive bus, and the second static end being connected to the positive bus through the braking resistor; and a controller, which is used for acquiring a bus voltage, controlling the moving end to be closed to the second static end and outputting a pulse width modulation signal to the multiplexing switch to make the braking resistor and the multiplexing switch form a chopper circuit when the bus voltage is higher than a preset braking threshold. The application can solve the defect that the load switching is easy to be straight-through, and realizes safe multiplexing of the device.

Description

Technical Field

[0001] This application relates to the technical field of frequency converters, and in particular to a brake-boost integrated frequency converter and control method that uses multiplexing switching devices. Background Technology

[0002] In industrial control, three-phase frequency converters based on AC-DC-AC topology are commonly used to drive motors. The system's front-end uses a rectifier bridge to convert AC power to DC bus voltage. The intermediate stage uses a DC reactor and bus capacitor for filtering and energy storage. The rear-end inverter bridge converts the DC power back to adjustable AC output. In actual continuous load operation, voltage dips or heavy loads can cause the DC bus voltage to be too low, requiring an active boost circuit to compensate for the bus level. When the motor is in a high-inertia deceleration state, the load's kinetic energy is converted into electrical energy and fed back to the DC bus in large quantities, causing a sharp rise in the voltage at the bus capacitor terminals. This necessitates a braking chopper circuit to dissipate the excess energy. Boost and braking conditions exhibit inherently mutually exclusive characteristics in terms of voltage state and operating environment.

[0003] Chinese invention patent application CN103684202A discloses a motor controller integrating drive and charging / discharging functions. This solution includes a bidirectional DC-DC converter, a three-phase bridge DC-AC bidirectional converter, and a mode switching device composed of switches. In motor drive mode, the switch is closed, the on-board battery is boosted by the bidirectional DC-DC converter and regulated to the DC bus, driving the subsequent inverter bridge to supply power to the motor. In parking charging mode, the switch is open, the AC power from the grid is rectified to obtain the bus voltage, and the bidirectional DC-DC converter switches to a step-down state to charge the battery pack with limited current. This architecture utilizes the switch to disconnect or close the physical connection, allowing the same set of power devices to be used in a time-division multiplexing manner between parking charging and vehicle driving modes.

[0004] The above solution relies on a mode switching device composed of mechanical switches for physical reconfiguration, which requires the motor to be stopped and the system to be in a static isolation environment. When facing dynamic conditions of continuous load operation of the frequency converter, transient voltage drops in the grid and high-frequency acceleration and deceleration of the motor cause a sudden alternation between boost demand and braking feedback demand within a very short time. Due to the inherent action delay and contact bounce characteristics of the physical switches, this execution structure cannot track the high-frequency transients of the bus voltage. If the contacts are forcibly switched directly in the main operating circuit with large-capacity bus capacitors and inductors, a high-energy arc and flyback voltage spike will inevitably be generated at the moment of load disconnection and closure. The discontinuous interruption of the high-frequency, high-current commutation path, coupled with the transient electrical response of the bus, can easily lead to a bus short circuit or breakdown failure of power semiconductor devices. Summary of the Invention

[0005] To address the issue of easy bypass during load switching and to achieve safe reuse of devices, this application provides a brake-boost integrated frequency converter and control method for multiplexing switching devices.

[0006] Firstly, the integrated brake-boost frequency converter with multiplexed switching devices provided in this application adopts the following technical solution: the integrated brake-boost frequency converter with multiplexed switching devices includes a rectifier, an inverter, and a DC link having a positive bus and a negative bus, wherein the negative output terminal of the rectifier is connected to the negative bus, and further includes: The reactor is connected at one end to the positive output terminal of the rectifier. The reconfiguration unit includes a switching switch, a freewheeling tube, a multiplexing switch, and a braking resistor. The multiplexing switch is connected between the moving end of the switching switch and the negative busbar. The switching switch has a first stationary end and a second stationary end. The first stationary end is connected to the other end of the reactor. The anode of the freewheeling tube is connected to the first stationary end, and the cathode of the freewheeling tube is connected to the positive busbar. The second stationary end is connected to the positive busbar via the braking resistor. The controller, connected to the switching switch and the multiplexer, is used to acquire the bus voltage. Internally configured with a preset boost threshold, a preset braking threshold, and a preset dead time, the controller controls the moving end to close to the first stationary end and outputs a pulse width modulation signal to the multiplexer when the bus voltage is lower than the preset boost threshold, so that the reactor, the multiplexer, and the freewheeling diode form a boost circuit. When the bus voltage is higher than the preset braking threshold, the controller controls the moving end to close to the second stationary end and outputs the pulse width modulation signal to the multiplexer so that the braking resistor and the multiplexer form a chopper circuit. Before changing the closed state of the moving end of the switching switch, the controller first turns off the multiplexer, and after controlling the switching switch to change the closed state of the moving end, it delays for the preset dead time before outputting the pulse width modulation signal to the multiplexer.

[0007] Optionally, a pre-charge branch is connected in series between the first stationary terminal and the other end of the reactor, the pre-charge branch including a bypass switch and a current-limiting resistor connected in parallel; When the power is applied and the bus voltage is lower than the preset voltage threshold, the controller disconnects the bypass switch and forcibly shuts off the multiplex switch, allowing the current to flow to the DC link through the current limiting resistor and the freewheeling tube. When the bus voltage reaches the preset voltage threshold, the controller closes the bypass switch and releases the forced shutdown of the multiplex switch.

[0008] Optionally, the rectifier has an input terminal, and the controller internally stores the preset inductance, preset saturation current, and preset safety factor of the reactor; During the operation of the boost circuit, the controller acquires the real-time line voltage at the input terminal and the real-time current of the reactor. Based on the DC-side equivalent input voltage obtained from the real-time line voltage, the real-time current, the preset inductance, the preset saturation current, and the preset safety factor, the controller calculates the upper limit of the duty cycle. If the DC-side equivalent input voltage is lower than the preset minimum input voltage, the real-time current is greater than or equal to the product of the preset safety factor and the preset saturation current, or the current sampling is abnormal, the controller sets the upper limit of the duty cycle to zero and blocks the multiplexer. Otherwise, the controller clamps the actual duty cycle output to the multiplexer within the upper limit of the duty cycle.

[0009] Optionally, the switching switch is a solid-state switch, and the solid-state switch has an action delay time; The controller sets the preset dead time to be greater than the action delay time; and after controlling the switching switch to switch the closed state of the moving end and delaying the preset dead time, the controller outputs the pulse width modulation signal to the multiplexer after confirming that the moving end is in place based on the position feedback or conduction feedback of the switching switch.

[0010] Optionally, the reconfiguration unit includes a current sensing device connected in series with the multiplexing switch; the switching switch also has a preset safety neutral terminal that is not connected to the power circuit. The controller acquires the real-time current collected by the current detection device. When the real-time current is greater than a preset safety threshold, it forcibly shuts off the multiplexer and controls the moving end of the switching switch to disconnect from the first stationary end and the second stationary end, or switches to the preset safety stationary end.

[0011] Secondly, the control method for the integrated brake-boost frequency converter using multiplexing switching devices provided in this application adopts the following technical solution: The control method for the integrated brake-boost frequency converter using multiplexing switching devices includes: Obtain the bus voltage of the inverter, and obtain the preset boost threshold, preset braking threshold and preset dead time; If the bus voltage is lower than the preset boost threshold, the moving end of the inverter's switching switch is controlled to close to the first stationary end of the switching switch, and a pulse width modulation signal is output to the inverter's multiplexer to form a boost circuit; If the bus voltage is higher than the preset braking threshold, the moving end of the switching switch is controlled to close to the second stationary end of the switching switch, and the pulse width modulation signal is output to the multiplexer to form a chopper circuit. Before changing the closed state of the moving end of the switching switch, the multiplexer is turned off first, and after controlling the switching switch to switch the closed state of the moving end, the pulse width modulation signal is output to the multiplexer after a preset dead time.

[0012] Optionally, after forming the boost circuit, it includes: Obtain the real-time line voltage of the rectifier input to the frequency converter, and obtain the real-time current of the reactor of the frequency converter; Read the preset inductance, preset saturation current and preset safety factor stored in the controller of the frequency converter; The upper limit of the duty cycle is calculated based on the DC-side equivalent input voltage obtained from the real-time line voltage, the real-time current, the preset inductance, the preset saturation current, and the preset safety factor. If the DC-side equivalent input voltage is lower than the preset minimum input voltage, the real-time current is greater than or equal to the product of the preset safety factor and the preset saturation current, or the current sampling is in an abnormal state, the duty cycle upper limit is set to zero and the multiplexing switch of the frequency converter is blocked; otherwise, the actual duty cycle of the multiplexing switch output to the frequency converter is clamped within the duty cycle upper limit.

[0013] Optionally, after forming the boost circuit, it includes: If the bus voltage of the inverter reaches the preset boost exit threshold, the multiplexer of the inverter is first turned off, the moving end of the switching switch of the inverter is controlled to close to the second stationary end of the switching switch, and the preset dead time is delayed after switching the closed state of the moving end to keep the multiplexer in the off standby state.

[0014] Optionally, after forming the chopper circuit, the following is included: If the bus voltage of the frequency converter drops to a preset braking exit threshold, the multiplex switch of the frequency converter is turned off; Wherein, the preset braking exit threshold is less than the preset braking threshold.

[0015] Optionally, the switching switch of the frequency converter also has a preset safety neutral terminal that is not connected to the power circuit, and after forming the boost circuit or the chopper circuit, it includes: If the bus voltage of the frequency converter is greater than the preset overvoltage protection threshold or the state switching is abnormal, the multiplexing switch of the frequency converter is turned off, and the moving end of the switching switch is disconnected from the first stationary end and the second stationary end of the switching switch, or switched to the preset safe stationary end.

[0016] In summary, this application includes the following beneficial technical effects: 1. By configuring the switching switch, multiplexing switch and controller, the multiplexing switch is turned off before the switching switch changes the closing state of the moving end, and the pulse width modulation signal is output to the multiplexing switch after a preset dead time is delayed after the switching action is completed. This avoids the bus short circuit or power semiconductor breakdown failure caused by the direct switching of large current paths during the load switching process, and realizes the safe multiplexing of the same switching device between boost and braking conditions.

[0017] 2. By connecting a pre-charge branch consisting of a bypass switch and a current-limiting resistor in series between the first stationary terminal and the reactor, the bypass switch is disconnected and the multiplex switch is forcibly turned off when the power is on, so that the current charges the DC link through the current-limiting resistor and the freewheeling tube. The bypass switch is closed again after the bus voltage reaches the preset voltage build-up threshold, which reduces the impact current on the bus capacitor at the moment the frequency converter is powered on and improves the reliability of the system power-on.

[0018] 3. By calculating the upper limit of the duty cycle based on the real-time line voltage, real-time current and the preset parameters of the reactor during the operation of the boost circuit, and clamping the actual output duty cycle within the upper limit, the upper limit of the duty cycle is set to zero and the multiplexing switch is blocked when the DC equivalent input voltage is too low or the real-time current reaches the saturation boundary. This avoids overcurrent failure caused by the magnetic saturation of the reactor and ensures the safe operation of the device under boost conditions. Attached Figure Description

[0019] Figure 1 A flowchart illustrating the control method of a brake boost inverter with multiplexed switching devices provided in this application embodiment; Figure 2 This is a schematic diagram of the main circuit topology of the brake boost inverter with multiplexed switching devices provided in the embodiments of this application. Figure 3 A schematic diagram of the circuit structure of the solid-state switching switch provided in the embodiments of this application; Figure 4 The circuit schematic diagram of the hardware shutdown channel provided in the embodiments of this application. Detailed Implementation

[0020] The following combination Figures 1-4 This application will be described in further detail.

[0021] Example 1

[0022] This embodiment discloses a brake-boost integrated frequency converter that reuses switching devices. This frequency converter is used in an AC-DC-AC drive system with three-phase AC input, DC bus energy storage, and inverter output. It can reuse the same power switching device to form a boost circuit when the DC bus voltage is low due to a grid voltage drop, and it can also reuse the same power switching device to form a braking chopper circuit when the DC bus voltage is high due to motor deceleration feedback. Thus, it achieves undervoltage compensation and overvoltage energy dissipation without the need for separate boost and braking switching transistors.

[0023] This frequency converter includes a rectifier, an inverter, a DC link, a reactor, and a reconfiguration unit. The rectifier's input terminal is connected to a three-phase AC power supply. Its positive output terminal outputs pulsating DC power, and its negative output terminal connects to the negative bus. The DC link has a positive bus and a negative bus, with a bus capacitor connected in parallel between them. This bus capacitor smooths the rectifier output and provides DC energy to the inverter. The inverter's DC input terminals are connected to both the positive and negative buses, and its AC output terminal is used to connect to the motor. One end of the reactor is connected to the rectifier's positive output terminal, and the other end serves as the reconfigurable main power feed-in terminal connected to the reconfiguration unit, allowing the rectifier's output energy to be directed to either the boost path or the standard bus path under different operating conditions.

[0024] The reconfiguration unit includes a switching switch, a freewheeling diode, a multiplexer, and a braking resistor. The multiplexer is connected between the moving end of the switching switch and the negative bus. The switching switch has a first stationary end and a second stationary end. The first stationary end is connected to the other end of the reactor. The anode of the freewheeling diode is connected to the first stationary end, and the cathode of the freewheeling diode is connected to the positive bus. The second stationary end is connected to one end of the braking resistor, and the other end of the braking resistor is connected to the positive bus. The multiplexer can be an insulated-gate bipolar transistor, a silicon carbide MOSFET, a silicon-based MOSFET, or a power semiconductor module with an anti-parallel diode. The power terminal of the multiplexer is connected in series between the moving end and the negative bus, and the control terminal of the multiplexer is connected to the isolation drive output terminal of the controller.

[0025] It is important to note that the freewheeling diode is not only the freewheeling device for Boost converters, but also continuously connected in series in the main power supply path of the inverter during non-boost periods (i.e., in the normal operating path of the inverter). It undertakes the series conduction task of supplying power to the positive bus from the rectified output under all operating conditions. Therefore, this freewheeling diode must be selected based on the continuous current rating of the inverter's full-load DC current, and a corresponding heat dissipation design must be configured to cope with additional conduction losses and temperature rise. In the normal power supply path during non-boost and non-braking states, the current needs to continuously supply power to the positive bus through the freewheeling diode; synchronous rectification can be used to reduce losses if necessary.

[0026] The freewheeling diode includes a diode-type freewheeling device or a controllable synchronous freewheeling device, specifically a fast recovery diode, a silicon carbide Schottky diode, or a synchronous rectifier switch. When a synchronous rectifier switch is used, it must be strictly turned off before the multiplexer is turned on. After the multiplexer is turned off, the synchronous rectifier switch must be turned on again after a shoot-through dead time. If abnormal conduction of the synchronous rectifier switch is detected, the multiplexer should be immediately blocked, and the direction of its body diode must allow the reactor to freewheel to the positive bus. The system uses a hardware interlocking mechanism to prevent it from forming a shoot-through between the positive and negative buses simultaneously with the multiplexer.

[0027] like Figure 2 As shown, in a typical connection configuration, AC power is supplied from the rectifier input terminal. The first power terminal of the multiplexer is connected to the moving terminal of the switching switch, and the second power terminal of the multiplexer is connected to the negative bus. The anode of the freewheeling diode is connected to the first stationary terminal, and the cathode of the freewheeling diode is connected to the positive bus. One end of the braking resistor is connected to the second stationary terminal, and the other end is connected to the positive bus. The first stationary terminal of the switching switch is connected to the reactor output terminal. Thus, when the moving terminal of the switching switch is closed to the first stationary terminal and outputs a pulse width modulation signal to the multiplexer, the current flows along the reactor, the moving terminal, and the multiplexer to the negative bus, and the reactor, the multiplexer, and the freewheeling diode form a boost circuit. When the moving terminal of the switching switch is closed to the second stationary terminal and outputs a pulse width modulation signal to the multiplexer, the current flows back from the positive bus through the braking resistor, the second stationary terminal, the moving terminal, and the multiplexer to the negative bus, and the braking resistor and the multiplexer form a chopper circuit. This reconfigured topology ensures that the reactor maintains a safe freewheeling path to the positive bus through the freewheeling tube, effectively reducing the risk of overvoltage caused by forced disconnection of a large inductor and effectively avoiding the serious safety hazard of short-circuiting the bus and discharging the braking resistor under normal control conditions during the boost state.

[0028] The controller, as the main control actuator in this embodiment, connects to the switching switch and the multiplexing switch, and obtains the bus voltage between the positive and negative buses through a bus voltage sampling circuit. The bus voltage sampling circuit can employ a high-impedance voltage divider network with an isolation amplifier, or it can use a linear optocoupler isolation sampling circuit or an isolated Σ-Δ modulation sampling circuit. The sampling point is directly connected between the positive and negative buses, and the sampled signal is input to the controller after low-pass filtering, overvoltage clamping, and analog-to-digital conversion.

[0029] The controller is internally configured with preset boost threshold, preset braking threshold, and preset dead time, and includes a state machine, PWM generator, gate drive interlock unit, and fault latch unit. The preset boost threshold is lower than the preset braking threshold, with a voltage hysteresis range maintained between them. When the bus voltage is within the normal range (i.e., between the preset boost threshold and the preset braking threshold), the controller controls the multiplexer switch to turn off, and the moving end of the switching switch can remain at the second stationary end to form a braking standby state. At this time, the normal rectified power supply path is: rectifier output through reactor and freewheeling diode to the positive bus. This allows the system to maintain standard inverter operation and avoids frequent operation of the boost circuit and chopper circuit due to sampling ripple.

[0030] Taking a three-phase 380V AC input system as an example, the normal bus voltage is typically between approximately 510V and 560V. The preset boost threshold can be set to 430V to 480V, preferably 450V; the preset braking threshold can be set to 650V to 720V, preferably 680V; the preset boost de-energization threshold can be set to 500V to 540V, preferably 520V; the preset braking de-energization threshold can be set to 610V to 660V, preferably 640V; and the preset overvoltage protection threshold can be set to 730V to 780V, preferably 750V. These thresholds can be calibrated according to the AC input level, bus capacitor withstand voltage, inverter power level, and motor feedback energy. For a three-phase 220V AC input system, these thresholds can be scaled proportionally to the bus rated voltage; for a 690V AC input system, these thresholds can be recalibrated according to the device withstand voltage level and insulation margin.

[0031] When the inverter is powered on, the controller first performs pre-charge voltage build-up control. A pre-charge branch is connected in series between the first stationary terminal and the other end of the reactor. The pre-charge branch includes a bypass switch and a current-limiting resistor connected in parallel. When the system is first powered on and the bus voltage is lower than the preset voltage build-up threshold, the controller disconnects the bypass switch and forcibly shuts off the multiplexer switch. The rectifier output current flows sequentially through the reactor, the current-limiting resistor, the first stationary terminal, and the freewheeling tube to the DC link, charging the bus capacitor with a limited current. The voltage build-up threshold can be set to 70% to 90% of the rated DC bus voltage, preferably 80% of the rated DC bus voltage. When the bus voltage reaches the preset voltage build-up threshold and remains there for more than a preset confirmation time, the controller closes the bypass switch, bypassing the current-limiting resistor and releasing the forced shutdown of the multiplexer switch. If the bus voltage rise rate during pre-charge is lower than the preset lower limit or the current-limiting resistor temperature exceeds the temperature threshold, the controller keeps the multiplexer switch off and prohibits the switching switch from being put into operation.

[0032] In boost mode, if the bus voltage detected by the controller is lower than the preset boost threshold, this bus voltage serves as the boost determination input, triggering the controller to enter the boost preparation state. The controller first confirms that the multiplexer is off, then controls the moving end of the switching switch to close to the first stationary end, and delays for a preset dead time until the switching switch completes its operation. After the preset dead time expires and feedback from the switching switch's auxiliary contact or solid-state switch confirms that the moving end is connected to the first stationary end, the controller uses this confirmation signal as the boost PWM enable condition and outputs a boost PWM pulse to the multiplexer.

[0033] When the multiplexer is on, the rectifier output current flows to the negative bus through the reactor, pre-charge branch, first stationary terminal, moving terminal, and multiplexer, storing energy in the reactor. When the multiplexer is off, the reactor current cannot change abruptly. The induced voltage generated across the reactor and the rectified output voltage are superimposed and then released to the positive bus and bus capacitor through the first stationary terminal and freewheeling diode, thus boosting the DC bus voltage. Therefore, the input condition that the bus voltage is below the preset boost threshold reliably drives the switching switch into the first stationary terminal state. The confirmation output of the first stationary terminal state constitutes a necessary input condition for the boost PWM output, and the reactor freewheeling output after the boost PWM action becomes the direct source of the bus voltage boost.

[0034] During the operation of the boost circuit, the controller also acquires the real-time line voltage input to the rectifier and the real-time current of the reactor. The real-time line voltage can be directly acquired through the three-phase voltage sampling circuit, or indirectly estimated through the rectifier output voltage ripple and phase reconstruction algorithm. The controller internally stores the preset inductance of the reactor. Preset saturation current and preset safety factor The controller acquires the DC-side equivalent input voltage derived from the real-time line voltage in each control cycle. and the current real-time current acquired by the reactor And according to the switching cycle The upper limit of the duty cycle is derived and calculated. Based on physical formulas, the peak current of the reactor when energy storage is turned on is estimated as follows: To prevent magnetic saturation, the peak current must not exceed the allowable critical saturation boundary, i.e. Therefore, the formula for calculating the upper limit of the duty cycle is derived as follows: If the DC side equivalent input voltage The voltage is lower than the preset minimum input voltage, or the real-time current of the reactor is lower than the preset minimum input voltage. If the current sample size is greater than or equal to the product of the preset safety factor and the preset saturation current, or if an abnormal current sampling occurs, the controller will forcibly set the upper limit of the duty cycle to zero and lock the multiplexer.

[0035] If the operating conditions are normal, the controller will substitute the values ​​into the formula to calculate the result. The actual duty cycle is clamped within this upper limit, serving as the upper limit for the duty cycle, and the final output to the multiplexer is also clamped within this upper limit. A preset safety factor can be set from 0.65 to 0.85, preferably 0.75. If the closed-loop regulated duty cycle calculated using the conventional voltage / current loop is higher than the upper limit, the controller forcibly outputs the upper limit; if it is lower, it outputs the closed-loop regulated duty cycle. This limitation on the actual duty cycle directly constrains the reactor current slope, preventing overcurrent or power device failure due to reactor magnetic saturation.

[0036] The boost PWM can employ dual closed-loop control with an outer voltage loop and an inner current loop. The outer voltage loop uses a preset boost exit threshold or target bus voltage as a reference value, and the sampled bus voltage as feedback, outputting a reactor current reference value. The inner current loop uses the reactor current reference value as input, and the real-time current collected by a current sensing device as feedback, outputting the multiplexer duty cycle. The current sensing device can be a shunt resistor, Hall effect current sensor, fluxgate current sensor, or current transformer connected in series with the emitter or source circuit of the multiplexer. The output of the current sensing device is isolated, amplified, and filtered before being input to the controller, enabling the controller to update the current feedback in each PWM cycle.

[0037] When the bus voltage reaches the preset boost exit threshold, the controller uses this bus voltage as the exit input, first stopping the output boost PWM and turning off the multiplexer switch. After the multiplexer switch is turned off, the moving end no longer bears the main pulse current controlled by the multiplexer switch, and the switching current is significantly reduced. Combined with dead time, position feedback, and absorption protection, the risk of arcing or overvoltage during load switching can be reduced, thus reducing the need to wait for the residual current of the reactor to completely decay through the freewheeling diode. Subsequently, the controller controls the moving end of the switching switch to close to the second stationary end, and delays the closing state of the switching moving end for a preset dead time. After the preset dead time expires, the multiplexer switch remains in the off standby state, at which time the grid energy resumes to supply power to the DC link through the normal power supply path composed of the rectifier, reactor, and freewheeling diode.

[0038] During braking, motor deceleration or load driving causes the inverter to feed mechanical energy back to the DC link, resulting in a bus voltage higher than the preset braking threshold. The controller uses this bus voltage exceeding the preset braking threshold as the braking judgment input. It first shuts off the multiplexer, then controls the moving end of the switching switch to close to the second stationary end, and delays for a preset dead time. After the preset dead time expires and the switching switch confirms via conduction feedback or auxiliary contact feedback that the moving end is connected to the second stationary end, the controller outputs a braking PWM pulse to the multiplexer.

[0039] When the multiplexer is on, excess energy from the DC bus flows from the positive bus through the braking resistor, the second stationary terminal, the moving terminal, and the multiplexer to the negative bus. The braking resistor converts electrical energy into heat energy. When the multiplexer is off, the braking resistor branch is disconnected, and the bus capacitor continues to receive energy fed back from the inverter, which is then re-evaluated by the controller in the next cycle. Thus, the input condition that the bus voltage is higher than the preset braking threshold drives the switching switch to the second stationary terminal state. The second stationary terminal state confirmation output becomes the braking PWM enable input. The braking PWM controls the braking resistor to consume energy, and the energy consumption of the braking resistor causes the bus voltage to drop, forming a closed-loop feedback.

[0040] Braking PWM can employ a fixed-frequency duty cycle adjustment method. The controller calculates the duty cycle of the multiplexed switch based on the voltage deviation above a preset braking threshold as input. During braking, the controller internally uses a formula... Calculate the instantaneous power dissipation of the braking resistor, where This is the DC bus voltage. The value of the braking resistor. This refers to the actual duty cycle. The controller estimates the accumulated heat capacity based on the instantaneous power and the set average power limit of the braking resistor. When the estimated temperature reaches the derating threshold, the controller actively reduces the upper limit of the duty cycle. When the temperature reaches the maximum protection temperature threshold, the controller stops braking and shuts off the multiplexer, simultaneously triggering the inverter to execute torque limiting or load reduction commands. As an equivalent alternative, braking control can also employ a hysteresis comparison method or a lookup table correction method.

[0041] When the bus voltage drops to the preset braking exit threshold, the controller shuts off the multiplexer and stops the braking PWM output. The preset braking exit threshold is lower than the preset braking threshold, forming a braking hysteresis loop to prevent high-frequency fluctuations in the bus voltage near the threshold. If the bus voltage continues to rise during braking and exceeds the preset overvoltage protection threshold, the controller immediately forces the multiplexer to shut off, prohibiting the inverter from continuing to output torque, and controls the moving end of the switching switch to disconnect from the first and second stationary ends, or switch to the preset safe stationary end that is not connected to the power circuit. The preset safe stationary end is used to disconnect the boost or braking chopper branch involved by the multiplexer, and is not equivalent to completely cutting off the power supply path from the rectifier to the DC bus. For applications requiring uninterrupted motor control, the controller can also output a torque limiting signal to the upper drive algorithm, causing the inverter to reduce the amplitude of the regenerative current injected into the DC bus.

[0042] Before changing the closed state of the moving end of the changeover switch, the controller first turns off the multiplexer. After controlling the changeover switch to switch the closed state of its moving end, it delays for a preset dead time before outputting a pulse width modulation signal to the multiplexer. The changeover switch can be a mechanical contactor, a magnetic latching relay, a solid-state relay, a bidirectional thyristor assembly, an anti-series MOSFET assembly, or an anti-series IGBT assembly. For general dynamic requirements, mechanical contactors or relays can be used; however, when facing high-frequency transient reconfiguration or rapid dynamic switching requirements, mechanical contactors are difficult to adapt to high-frequency, rapid, and frequent switching, and solid-state switches are preferred.

[0043] After the multiplexer switches turn off before the switching switches, the moving end no longer bears the main pulse current, significantly reducing the switching current and lowering the safety risk of triggering a high-energy arc or flyback overvoltage. Therefore, the preset dead time does not need to take into account the arc extinguishing time; the preset dead time is set only according to the switching switch action delay time and the contact bounce duration. For mechanical contactors, the preset dead time can be set from 10ms to 80ms, preferably from 30ms to 50ms; for solid-state switches, the preset dead time can be set from 5μs to 500μs, preferably from 20μs to 100μs. If the switching switch is a solid-state switch, the controller sets the preset dead time to be greater than the solid-state switch action delay time. The starting point of the preset dead time is the moment the switching switch action command is issued, and the ending point is the moment when the output of the pulse width modulation signal to the multiplexer switch is allowed again.

[0044] like Figure 4 As shown, to improve switching safety, the controller can set a hardware shutdown channel in the gate drive circuit of the multiplexer K2. This hardware shutdown channel includes a comparator, a latch, logic gates, and a gate drive disable terminal. The current signal collected by the current sensing device is connected to the non-inverting input of the comparator, and a preset safety threshold is connected to the inverting input of the comparator. When the real-time current exceeds the preset safety threshold, the comparator outputs an overcurrent signal, the latch locks the fault state, and outputs a fast shutdown signal. This fast shutdown signal directly triggers the gate drive disable terminal, and after being combined with the PWM control signal issued by the MCU controller through logic AND gates and other circuits, it intercepts the underlying control pulses sent to the drive circuit, thereby immediately shutting down the multiplexer K2. The MCU controller subsequently obtains the status through the interface between control terminal 1 and control terminal 2, and controls the moving end of the switching switch to disconnect from the first and second stationary ends, or switch to the preset safety stationary end that is not connected to the power circuit. The preset safety threshold can be set to 70% to 80% of the rated pulse current of the multiplexer, preferably 75%. If a Hall current sensor is used, the reactor current and the braking resistor current can be monitored simultaneously; if a shunt resistor is used, the shunt resistor can be placed in the low-side circuit of the multiplexer and the real-time current can be transmitted through an isolation amplifier.

[0045] The detection channels and scenarios for state transition anomalies include: inconsistencies between the switching switch feedback status and control commands detected by the switching switch auxiliary contacts; errors in simultaneous short-circuiting of the first and second stationary terminals by the moving end, determined by voltage drop detection across the solid-state switch branch; failure of the moving end to reach the target stationary terminal within a specified delay time, identified by a timeout timer; abnormal multiplexer turn-off feedback obtained through the desaturation or isolation fault pin inside the gate driver; and abnormal rises in bus voltage during topology switching, identified by the bus voltage sampling channel. When the controller detects any state transition anomaly, it immediately shuts off the multiplexer and controls the moving end to disconnect from the first and second stationary terminals, or switches to a preset safe stationary terminal that is not connected to the power circuit. Simultaneously, it latches the fault code and outputs fault information to the host computer. After the moving end is disconnected or held at the preset safe stationary terminal, the reactor is no longer forcibly short-circuited, the multiplexer no longer experiences pulses, and the inverter avoids operation in unsafe conditions.

[0046] Combination Figure 1 This embodiment also discloses the control method of the above-mentioned frequency converter. The controller first obtains the bus voltage of the frequency converter through the bus voltage sampling circuit, and obtains the preset boost threshold, preset braking threshold and preset dead time, and compares the bus voltage with each threshold in a loop. If the bus voltage is lower than the preset boost threshold, the controller first turns off the multiplexer, controls the moving end to close to the first stationary end, and after a preset dead time delay, outputs a pulse width modulation signal to the multiplexer based on the DC side equivalent input voltage obtained from the real-time line voltage and the duty cycle limiting formula parameters, thus forming a boost circuit. If the bus voltage is higher than the preset braking threshold, the controller first turns off the multiplexer, controls the moving end to close to the second stationary end, and after a preset dead time delay, outputs a pulse width modulation signal to the multiplexer based on the bus voltage deviation, thus forming a chopper circuit. If the bus voltage does not trigger the boost and braking thresholds and is in the normal range, the judgment process directly returns to the monitoring step of obtaining the bus voltage, maintains the moving end closed to the second stationary end and shuts off the power pulse of the multiplexer, so that each component operates according to the normal power supply path.

[0047] Example 2

[0048] This embodiment, based on Embodiment 1, discloses a braking-boost integrated frequency converter and its control method that employs a solid-state switching device with rapid dynamic reconfiguration capability. This embodiment is applicable to servo drives, hoisting machinery frequency converters, centrifugal equipment frequency converters, and energy storage auxiliary drive systems where motors frequently accelerate and decelerate, bus voltage changes rapidly, and equipment size is limited.

[0049] The inverter in this embodiment includes a rectifier, an inverter, a DC link, a reactor, a pre-charge branch, a reconfiguration unit, and a controller. The rectifier input is connected to a three-phase AC power supply, the positive output of the rectifier is connected to one end of the reactor, and the negative output of the rectifier is connected to the negative bus. A pre-charge branch is connected in series between the first stationary terminal and the other end of the reactor. The pre-charge branch includes a bypass switch and a current-limiting resistor connected in parallel; the bypass switch can be a contactor or a solid-state bypass switch. The DC link includes a positive bus, a negative bus, and a bus capacitor bank connected in parallel between them. The inverter is connected to the positive and negative buses and outputs adjustable AC power to the motor.

[0050] Combination Figure 3 The reconfiguration unit includes a solid-state switching switch K1, a freewheeling diode, a multiplexer, a braking resistor, and a current sensing device. The solid-state switching switch K1 has a moving terminal, a first stationary terminal, and a second stationary terminal, as well as a preset safety stationary terminal that is independently suspended. Its specific structure includes a first solid-state branch and a second solid-state branch. The first solid-state branch includes two MOSFET sources connected in anti-series, connected between the moving terminal and the first stationary terminal, and connected to an external drive signal via control terminal 1. The second solid-state branch also includes two MOSFET sources connected in anti-series, connected between the moving terminal and the second stationary terminal, and connected to an external drive signal via control terminal 2. Each solid-state branch has an independent isolated gate drive. The two drive signals are prevented from conducting simultaneously by hardware interlocking logic. Each anti-series branch has an RC buffer absorption network or a transient voltage suppressor (TVS) connected in parallel on both sides to deal with stray current. Voltage spike. The power terminal of the multiplexer is connected between the moving terminal and the negative bus. The anode of the freewheeling diode is connected to the first stationary terminal, and the cathode of the freewheeling diode is connected to the positive bus. The braking resistor is connected between the second stationary terminal and the positive bus. The current sensing device is connected in series with the multiplexer and outputs real-time current to the controller.

[0051] In addition to gate drive, each solid-state branch of the solid-state switching switch is equipped with a status feedback circuit based on branch voltage drop or optocoupler isolation detection. The controller only uses the turn-on feedback of the first solid-state branch as the boost PWM enable condition after a preset dead time delay and accurate receipt of the turn-on feedback; and only uses the turn-on feedback of the second solid-state branch as the braking PWM enable condition; if the corresponding turn-on feedback confirmation is not received, the controller will resolutely not output PWM pulses to the multiplexer.

[0052] The controller includes a bus voltage sampling channel, a line voltage sampling channel, a current sampling channel, a temperature sampling channel, a PWM output unit, a solid-state switching drive unit, and a protection logic unit. Internally, the controller stores preset boost threshold, preset braking threshold, preset dead time, preset boost exit threshold, preset overvoltage protection threshold, as well as preset inductance, preset saturation current, and preset safety factor for the reactor.

[0053] After the system powers on and pre-charge voltage is built up, the controller enters the bus voltage monitoring state. When the bus voltage is lower than the preset boost threshold, the controller first confirms that the multiplexer feedback has been turned off, shuts down the second solid-state branch, and confirms that the second stationary path is disconnected. Then, it turns on the first solid-state branch, causing the moving end of the solid-state switching switch to close to the first stationary end. After the preset dead time expires and the first solid-state branch is confirmed to be in the correct position based on the conduction feedback, the controller enables the multiplexer boost PWM.

[0054] During the boost control process, the controller uses a hardware current sampling channel to capture the real-time current of the reactor and a line voltage channel to obtain the DC-side equivalent input voltage derived from the real-time line voltage. Combining this with stored preset inductance, preset saturation current, and preset safety factor, the formula is applied... The controller calculates the upper limit of the duty cycle for each cycle in real time. If the DC-side equivalent input voltage is lower than the preset minimum input voltage, or the real-time current of the reactor is greater than or equal to the product of the preset safety factor and the preset saturation current, or a current sampling anomaly occurs, the controller will force the upper limit of the duty cycle to zero and lock the multiplexing switch. Under normal calculation conditions, when a large duty cycle is requested by the outer voltage loop due to a deep voltage dip in the grid, the controller will force the actual PWM duty cycle to be clamped to this limit. Within the specified range, the peak inductor current is strictly controlled to the lower limit of the saturation current after the safety factor is reduced, thus avoiding overcurrent or power device failure due to reactor magnetic saturation.

[0055] If the bus voltage reaches the preset boost exit threshold, the controller immediately cancels the PWM and turns off the multiplexer. After the multiplexer is reliably turned off and there is no large current in the branch, the controller shuts down the first solid-state branch and turns on the second solid-state branch. Since the moving end is in a passive state at the moment of disconnection, the reverse recovery and leakage current stress of the anti-series MOSFET body diode are greatly reduced. After the preset dead time expires and the second solid-state branch is turned on, the multiplexer enters the chopper standby state.

[0056] When the bus voltage exceeds the preset braking threshold, the controller establishes braking preparation conditions. First, it confirms the multiplexer is off, shutting down the first solid-state branch and enabling the second solid-state branch. After the preset dead time expires and the second solid-state branch confirms conduction based on conduction feedback, the controller enables braking PWM. When the multiplexer is on, it consumes bus energy in the braking resistor; when it is off, the braking circuit is blocked. When the bus voltage drops to the preset braking exit threshold, the controller shuts off the multiplexer and stops braking PWM.

[0057] The control method in this embodiment forms a closed causal chain of data flow detection, judgment, feedback, and action verification. The pre-confirmation of the multiplexer's off-state, the hardware interlock dead zone of the solid-state switching switch, and the feedback of action completion together form a strict safe switching handshake sequence. This architecture achieves safe and reliable power management under mutually exclusive threshold judgment conditions with low hardware redundancy costs, reducing the risk of shoot-through short circuits caused by unconfirmed actions.

[0058] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A brake-boost integrated frequency converter using multiplexing switching devices, comprising a rectifier, an inverter, and a DC link having a positive bus and a negative bus, wherein the negative output terminal of the rectifier is connected to the negative bus, characterized in that, Also includes: The reactor is connected at one end to the positive output terminal of the rectifier. The reconfiguration unit includes a switching switch, a freewheeling tube, a multiplexing switch, and a braking resistor. The multiplexing switch is connected between the moving end of the switching switch and the negative busbar. The switching switch has a first stationary end and a second stationary end. The first stationary end is connected to the other end of the reactor. The anode of the freewheeling tube is connected to the first stationary end, and the cathode of the freewheeling tube is connected to the positive busbar. The second stationary end is connected to the positive busbar via the braking resistor. The controller, connected to the switching switch and the multiplexer, is used to acquire the bus voltage. Internally configured with a preset boost threshold, a preset braking threshold, and a preset dead time, the controller controls the moving end to close to the first stationary end and outputs a pulse width modulation signal to the multiplexer when the bus voltage is lower than the preset boost threshold, so that the reactor, the multiplexer, and the freewheeling diode form a boost circuit. When the bus voltage is higher than the preset braking threshold, the controller controls the moving end to close to the second stationary end and outputs the pulse width modulation signal to the multiplexer so that the braking resistor and the multiplexer form a chopper circuit. Before changing the closed state of the moving end of the switching switch, the controller first turns off the multiplexer, and after controlling the switching switch to change the closed state of the moving end, it delays for the preset dead time before outputting the pulse width modulation signal to the multiplexer.

2. The integrated braking and boost frequency converter with multiplexing switching devices according to claim 1, characterized in that, A pre-charge branch is connected in series between the first stationary terminal and the other end of the reactor. The pre-charge branch includes a bypass switch and a current-limiting resistor connected in parallel. When the power is applied and the bus voltage is lower than the preset voltage threshold, the controller disconnects the bypass switch and forcibly shuts off the multiplex switch, allowing the current to flow to the DC link through the current limiting resistor and the freewheeling tube. When the bus voltage reaches the preset voltage threshold, the controller closes the bypass switch and releases the forced shutdown of the multiplex switch.

3. The integrated braking and boost frequency converter with multiplexing switching devices according to claim 1, characterized in that, The rectifier has an input terminal, and the controller internally stores the preset inductance, preset saturation current and preset safety factor of the reactor. During the operation of the boost circuit, the controller acquires the real-time line voltage at the input terminal and the real-time current of the reactor, and calculates the upper limit of the duty cycle based on the DC equivalent input voltage obtained from the real-time line voltage, the real-time current, the preset inductance, the preset saturation current and the preset safety factor; If the DC-side equivalent input voltage is lower than the preset minimum input voltage, the real-time current is greater than or equal to the product of the preset safety factor and the preset saturation current, or the current sampling is abnormal, the controller will set the duty cycle upper limit to zero and lock the multiplexer. Otherwise, the controller will output the actual duty cycle clamp to the multiplexer within the duty cycle upper limit.

4. The integrated braking and boost frequency converter with multiplexing switching devices according to claim 1, characterized in that, The switching switch is a solid-state switch, and the solid-state switch has an action delay time; The controller sets the preset dead time to be greater than the action delay time; and after controlling the switching switch to switch the closed state of the moving end and delaying the preset dead time, the controller outputs the pulse width modulation signal to the multiplexer after confirming that the moving end is in place based on the position feedback or conduction feedback of the switching switch.

5. The integrated braking and boost frequency converter with multiplexing switching devices according to claim 1, characterized in that, The reconfiguration unit includes a current detection device connected in series with the multiplexing switch; the switching switch also has a preset safety stationary terminal that is not connected to the power circuit. The controller acquires the real-time current collected by the current detection device. When the real-time current is greater than a preset safety threshold, it forcibly shuts off the multiplexer and controls the moving end of the switching switch to disconnect from the first stationary end and the second stationary end, or switches to the preset safety stationary end.

6. A control method for a brake-boost integrated frequency converter using multiplexing switching devices, applied to the brake-boost integrated frequency converter using multiplexing switching devices as described in any one of claims 1 to 5, characterized in that, include: Obtain the bus voltage of the inverter, and obtain the preset boost threshold, preset braking threshold and preset dead time; If the bus voltage is lower than the preset boost threshold, the moving end of the inverter's switching switch is controlled to close to the first stationary end of the switching switch, and a pulse width modulation signal is output to the inverter's multiplexer to form a boost circuit; If the bus voltage is higher than the preset braking threshold, the moving end of the switching switch is controlled to close to the second stationary end of the switching switch, and the pulse width modulation signal is output to the multiplexer to form a chopper circuit. Before changing the closed state of the moving end of the switching switch, the multiplexer is turned off first, and after controlling the switching switch to switch the closed state of the moving end, the pulse width modulation signal is output to the multiplexer after a preset dead time.

7. The control method for the integrated braking and boost frequency converter with multiplexing switching devices according to claim 6, characterized in that, After forming the boost circuit, it includes: Obtain the real-time line voltage of the rectifier input to the frequency converter, and obtain the real-time current of the reactor of the frequency converter; Read the preset inductance, preset saturation current and preset safety factor stored in the controller of the frequency converter; The upper limit of the duty cycle is calculated based on the DC-side equivalent input voltage obtained from the real-time line voltage, the real-time current, the preset inductance, the preset saturation current, and the preset safety factor. If the DC-side equivalent input voltage is lower than the preset minimum input voltage, the real-time current is greater than or equal to the product of the preset safety factor and the preset saturation current, or the current sampling is in an abnormal state, the duty cycle upper limit is set to zero and the multiplexing switch of the frequency converter is blocked; otherwise, the actual duty cycle of the multiplexing switch output to the frequency converter is clamped within the duty cycle upper limit.

8. The control method for the integrated braking and boost frequency converter with multiplexing switching devices according to claim 6, characterized in that, After forming the boost circuit, it includes: If the bus voltage of the inverter reaches the preset boost exit threshold, the multiplexer of the inverter is first turned off, the moving end of the switching switch of the inverter is controlled to close to the second stationary end of the switching switch, and the preset dead time is delayed after switching the closed state of the moving end to keep the multiplexer in the off standby state.

9. The control method for the integrated braking and boost frequency converter with multiplexing switching devices according to claim 6, characterized in that, After forming the chopper circuit, it includes: If the bus voltage of the frequency converter drops to a preset braking exit threshold, the multiplex switch of the frequency converter is turned off; Wherein, the preset braking exit threshold is less than the preset braking threshold.

10. The control method for the integrated braking and boost frequency converter with multiplexing switching devices according to claim 6, characterized in that, The switching switch of the frequency converter also has a preset safety static terminal that is not connected to the power circuit, and after forming the boost circuit or the chopper circuit, it includes: If the bus voltage of the frequency converter is greater than the preset overvoltage protection threshold or the state switching is abnormal, the multiplexing switch of the frequency converter is turned off, and the moving end of the switching switch is disconnected from the first stationary end and the second stationary end of the switching switch, or switched to the preset safe stationary end.

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