Power conversion device and method for controlling same

Abstract

The invention provides a power conversion device and a control method thereof, and belongs to the technical field of power electronics. A primary side bridge arm in the power conversion device comprises a pair of complementary switch tubes, namely a first switch tube and a second switch tube, which are connected in series. The controller in the power conversion device can turn off the first switching tube at the second moment and then turn on the second switching tube at the third moment. And the integral value of the resonant cavity current in the power conversion device is a first integral threshold value in a time period between the second moment and the third moment (namely dead time). Wherein the integral value of the resonant cavity current is the first integral threshold value at the second moment and can represent that the voltage at the two ends of the second switching tube is smaller than the first voltage threshold value at the second moment. On the basis, the second switching tube is conducted at the second moment, so that self-adaptive dynamic adjustment of the dead time can be realized, and soft switching of the second switching tube can be ensured.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a power conversion device and a control method thereof. Background Art

[0002] A photovoltaic power generation system generally consists of multiple photovoltaic panels and multiple microinverters, where each photovoltaic panel can be connected to a microinverter. The microinverter can convert the direct current (DC) provided by the photovoltaic panel into alternating current (AC) and transmit this AC to the grid or load.

[0003] A micro-inverter typically includes: a primary bridge arm, a secondary bridge arm, and a transformer. The input end of the primary bridge arm is used to connect to a photovoltaic panel, the output end of the primary bridge arm is connected to the input end of the secondary bridge arm through a transformer, and the output end of the secondary bridge arm is used to connect to a power grid or a load. The primary bridge arm typically adopts an H-bridge structure, which includes two pairs of complementary switching tubes. The two switching tubes in each pair of complementary switching tubes need to be turned on alternately to avoid a short circuit at the input end of the primary bridge arm. Since the switching tube requires a certain amount of time to be turned on and off, a dead time needs to be inserted when each pair of complementary switching tubes switches between on and off states. During this dead time, both switching tubes in the complementary switching tubes are not turned on.

[0004] Because dead time is related to the microinverter's operating point (such as input voltage and output power), the microinverter can pre-store a mapping between the operating point and dead time. In actual operation, the microinverter can directly look up the table to obtain the corresponding dead time based on the current operating point. However, the dead time in this solution is fixed and lacks adaptive adjustment capabilities, which may prevent soft switching of the switch. Summary of the Invention

[0005] The present application provides a power conversion device and a control method thereof, which can solve the technical problem that power conversion devices such as micro inverters do not have the ability to adaptively adjust the dead time during operation, resulting in the inability to achieve soft switching of the switch tube.

[0006] In a first aspect, a power conversion device is provided, comprising: a primary bridge arm, a transformer, a secondary bridge arm, and a controller. The input end of the primary bridge arm is connected to a photovoltaic panel, the output end of the primary bridge arm is connected to the input end of the secondary bridge arm via a transformer, and the output end of the secondary bridge arm is connected to a power grid or a load. The primary bridge arm comprises a first switching transistor and a second switching transistor, which are connected in series between the positive and negative electrodes of the input end of the primary bridge arm, i.e., the first and second switching transistors form a pair of complementary switching transistors in the primary bridge arm. The controller is configured to control the first switching transistor to be turned on and the second switching transistor to be turned off at a first moment. The controller is further configured to control the first switching transistor to be turned off at a second moment, and to control the second switching transistor to be turned on at a third moment. The integral value of the resonant cavity current in the power conversion device during the period between the second moment and the third moment is a first integral threshold. The resonant cavity current is the resonant cavity current between the output end of the primary bridge arm and the primary side of the transformer, or the resonant cavity current between the secondary side of the transformer and the input end of the secondary bridge arm. Furthermore, at the third moment, the voltage across the second switch tube is less than the first voltage threshold.

[0007] It is understandable that after the controller turns off the first switch tube at the second moment, that is, after the dead time begins, the resonant cavity current in the power conversion device will begin to charge the capacitor connected in parallel at both ends of the first switch tube (such as the parasitic capacitance of the first switch tube), thereby causing the voltage across the first switch tube to gradually rise. Correspondingly, the resonant cavity current will discharge the capacitor connected in parallel at both ends of the second switch tube (such as the parasitic capacitance of the second switch tube), thereby causing the voltage across the second switch tube to gradually decrease. It can be seen that after the dead time begins, the voltage change across the switch tube is the result of the resonant cavity current charging and discharging the capacitor connected in parallel with the switch tube.

[0008] Since the integral of the resonant cavity current is a charge, and the change in charge on the capacitor corresponds to a change in the capacitor voltage, and thus corresponds to a change in the voltage across the switch tube, in this application, the voltage across the switch tube can be reflected by the integral value of the resonant cavity current. For example, the integral value of the resonant cavity current is a first integral threshold, which can characterize the change in the voltage across the second switch tube as the bus voltage or close to the bus voltage. Wherein, the bus voltage refers to the voltage of the DC bus, and the input end of the primary bridge arm is used to connect the photovoltaic panel through the DC bus. Based on this, when the controller detects that the integral value of the resonant cavity current reaches the first integral threshold at the third moment, it can be determined that the voltage across the second switch tube drops from the bus voltage to a value less than the first voltage threshold, for example, to 0. Accordingly, the controller controls the second switch tube to turn on at the third moment (that is, the dead time ends at the third moment), which can achieve soft switching of the second switch tube. Based on the above analysis, it can be seen that the solution provided by the present application can judge the change in the voltage across the switch tube according to the integral value of the resonant cavity current actually sampled, and can turn on the switch tube when the voltage across the switch tube is less than the first voltage threshold (for example, the voltage drops to zero). In this way, adaptive dynamic adjustment of the dead time is achieved, ensuring soft switching of the switch tube.

[0009] Optionally, the controller includes a current sampling circuit, an integration circuit, and a control circuit. The current sampling circuit is configured to sample the resonant cavity current and output the sample to the integration circuit. The control circuit is configured to control the integration circuit to integrate the resonant cavity current after the second moment, and to control the second switch to conduct at a third moment based on the integration value output by the integration circuit being a first integration threshold.

[0010] It is understood that a power conversion device is typically provided with a current sampling circuit for sampling the resonant cavity current, so as to protect the power conversion device based on the sampled resonant cavity current. In the present application, the current sampling circuit in the controller can reuse the existing current sampling circuit in the power conversion device to avoid increasing the structural complexity and hardware cost of the power conversion device. Furthermore, since the integration circuit has a relatively simple structure and low cost, using this integration circuit to integrate the resonant cavity current can also avoid increasing the structural complexity and hardware cost of the power conversion device.

[0011] Optionally, the integration circuit includes: an operational amplifier, a first resistor, a second resistor, an integration capacitor, and a switch. The inverting input of the operational amplifier is used to receive the resonant cavity current output by the current sampling circuit through the first resistor, the non-inverting input of the operational amplifier is used to receive the reference voltage through the second resistor, and the output of the operational amplifier is connected to the control circuit and is used to output the integration value to the control circuit. The integration capacitor is connected between the inverting input and output of the operational amplifier, and the switch is connected in parallel with the integration capacitor. The control circuit is used to control the switch to be turned off during the period between the second moment and the third moment, and to control the switch to be turned on before the second moment and after the third moment.

[0012] It can be understood that because the switch is connected in parallel with the integrating capacitor, when the switch is on, that is, before the second moment and after the third moment, the integrating capacitor is bypassed. At this time, the integrating function of the integrating circuit is not effective, or it can be understood that the integrating circuit does not have an integrating function. When the switch is turned off, the integrating capacitor begins to work, and the integrating function of the integrating circuit takes effect. It can be seen from this that the control circuit can achieve flexible control of the operating state of the integrating circuit by controlling the on and off of the switch, and the control logic is relatively simple.

[0013] Optionally, the switch may be a switching transistor. The switching transistor may be an insulated gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). The switching transistors in the primary bridge arm and the secondary bridge arm of the power conversion device may also be IGBTs or MOSFETs.

[0014] Optionally, the control circuit is configured to output a switch control signal to the switch. The switch control signal is at a low level between the second moment and the third moment, and is at a high level before the second moment and after the third moment. Accordingly, the switch is configured to be turned off under the control of the low-level switch control signal and turned on under the control of the high-level switch control signal.

[0015] Since the control circuit can control the on-off state of the switch and further control the working state of the integration circuit by controlling the level change of the switch control signal, the control logic of the control circuit can be effectively simplified.

[0016] Optionally, the integration circuit further includes a third resistor connected in series with the switch. It will be appreciated that when the switch is on, the third resistor is connected between the inverting input and output of the operational amplifier, bypassing the integrating capacitor. In this case, the integration circuit functions as an inverting amplifier, with a negative gain, and the absolute value of the gain equal to the ratio of the resistance value of the third resistor to the resistance value of the first resistor.

[0017] Optionally, the power conversion device further includes an inductive device connected between the secondary side of the transformer and the input end of the secondary bridge arm. A current sampling circuit in the controller can be used to sample the resonant cavity current flowing through the inductive device. The inductive device can be an inductor, also known as a resonant inductor.

[0018] Since a current sampling circuit is usually provided in a power conversion device for sampling the resonant cavity current flowing through the inductive device, the solution provided in the present application can reuse the current sampling circuit to sample the resonant cavity current to avoid increasing the structural complexity and hardware cost of the power conversion device.

[0019] Optionally, the controller is further configured to: at a fourth moment, control the second switching tube to turn off, and at a fifth moment, control the first switching tube to turn on. The integral value of the resonant cavity current during the period between the fourth moment and the fifth moment is a second integral threshold. Furthermore, at the fifth moment, the voltage across the first switching tube is less than a second voltage threshold. The second integral threshold may be equal to the first integral threshold. The second voltage threshold may be equal to the first voltage threshold, and both may be voltage values ​​close to 0, i.e., both voltage thresholds are voltage values ​​that enable the switching tube to achieve soft switching.

[0020] As previously mentioned, the integral value of the resonant cavity current can reflect changes in the voltage across the switching tube. Therefore, by properly setting the second integral threshold so that it represents a change in the voltage across the first switching tube equal to or close to the bus voltage, the controller can ensure that, when it detects that the integral value of the resonant cavity current reaches the second integral threshold at the fourth moment, it accurately determines that the voltage across the first switching tube has dropped from the bus voltage to a value less than the second voltage threshold, for example, to zero. At this point, the controller controls the first switching tube to conduct, achieving soft switching of the first switching tube.

[0021] Optionally, the controller is configured to integrate the resonant cavity current during different time periods using the same integration circuit. Because the first and second switching transistors are alternately turned on, the time period between the second and third moments, and the time period between the fourth and fifth moments, are non-overlapping time periods. Accordingly, the controller can integrate the resonant cavity current during different time periods using the same integration circuit and control the conduction of different switching transistors based on the integrated values ​​during different time periods. This effectively simplifies the controller structure and reduces hardware costs.

[0022] Optionally, the controller is configured to: control the first switch to be turned off based on the switching signal changing from a high level to a low level at a second moment; and control the second switch to be turned off based on the switching signal changing from a low level to a high level at a fourth moment. The switching signal is a square wave signal having a frequency equal to the switching frequency of the switch in the primary bridge arm and a duty cycle of one-half.

[0023] It can be understood that the square wave signal can be a driving signal generated by the controller through software to control the on and off of the first switch tube and the second switch tube, and the driving signal is an original driving signal that does not contain dead time. In the solution provided in the present application, the controller can directly control the switch tube to be turned off according to the square wave signal. For example, the first switch tube can be controlled to be turned off at the falling edge of the square wave signal, and the second switch tube can be controlled to be turned off at the rising edge of the square wave signal. In addition, the controller can control the conduction of the switch tube according to the integral value of the resonant cavity current. Or it can be understood that: the switch tube's turn-off signal (i.e., the falling edge of the driving signal) is directly generated by the software, and the switch tube's turn-on signal (i.e., the rising edge of the driving signal, i.e., the end time of the dead time) is generated by the delay of the integral circuit of the resonant cavity current.

[0024] In a second aspect, a control method for a power conversion device is provided. The method can be applied to the power conversion device provided in the first aspect, for example, to a controller in the power conversion device. The method comprises: at a first moment, controlling a first switching transistor in a primary bridge arm to be turned on and a second switching transistor to be turned off. The power conversion device comprises: a primary bridge arm, a transformer, and a secondary bridge arm, the primary arm being connected to the secondary bridge arm via a transformer, and the first switching transistor and the second switching transistor being connected in series between the positive and negative electrodes of the input terminal of the primary bridge arm. The method further comprises: at a second moment, controlling the first switching transistor to be turned off; and at a third moment, controlling the second switching transistor to be turned on. The integral value of the resonant cavity current during the period between the second moment and the third moment is a first integral threshold. The resonant cavity current is the resonant cavity current between the output terminal of the primary bridge arm and the primary side of the transformer, or the resonant cavity current between the secondary side of the transformer and the input terminal of the secondary bridge arm. Furthermore, at the third moment, the voltage across the second switching transistor is less than the first voltage threshold.

[0025] Optionally, the method further includes: at a fourth moment, controlling the second switch to be turned off; and at a fifth moment, controlling the first switch to be turned on. The integral value of the resonant cavity current in the period between the fourth moment and the fifth moment is a second integral threshold. Furthermore, at the fifth moment, the voltage across the first switch is less than the second voltage threshold.

[0026] Optionally, at the second moment, the process of controlling the first switch to turn off includes: controlling the first switch to turn off based on the switching signal changing from a high level to a low level at the second moment. At the fourth moment, the process of controlling the second switch to turn off includes: controlling the second switch to turn off based on the switching signal changing from a low level to a high level at the fourth moment. The switching signal is a square wave signal having a frequency equal to the switching frequency of the switch in the primary bridge arm, and having a duty cycle of one-half.

[0027] In a third aspect, a chip is provided, which includes a programmable logic circuit and / or program instructions, and when the chip is running, executes the control method provided in the second aspect.

[0028] In summary, the present application provides a power conversion device and a control method thereof. The primary bridge arm of the power conversion device includes a pair of complementary switching transistors connected in series: a first switching transistor and a second switching transistor. A controller in the power conversion device is capable of turning off the first switching transistor at a second moment and then turning on the second switching transistor at a third moment. During the period between the second moment and the third moment, the integral value of the resonant cavity current in the power conversion device is equal to a first integral threshold. It is understood that the period between the second moment and the third moment is the dead time, and the integral value of the resonant cavity current during this period can reflect the voltage changes across the second switching transistor. Because the controller can turn on the second switching transistor at the second moment when the integral value of the resonant cavity current reaches the first integral threshold, adaptive dynamic adjustment of the dead time is achieved. Furthermore, because the integral value of the resonant cavity current reaching the first integral threshold at the second moment indicates that the voltage across the second switching transistor is less than the first voltage threshold at the second moment, turning on the second switching transistor at the second moment ensures soft switching of the second switching transistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic structural diagram of a power generation system provided in an embodiment of the present application;

[0030] Figure 2 This is a schematic structural diagram of a micro-inverter provided in an embodiment of the present application;

[0031] Figure 31 is a schematic diagram of waveforms of the primary voltage, secondary voltage, and resonant cavity current in a micro-inverter provided in an embodiment of the present application;

[0032] Figure 4 1 is a waveform diagram of a resonant cavity current, a current before filtering, and a grid-connected current provided in an embodiment of the present application;

[0033] Figure 5 This is a schematic diagram of the corresponding relationship between the primary voltage and the switching state of the complementary switch tube provided by an embodiment of the present application;

[0034] Figure 6 1 is a waveform diagram of a driving signal and a capacitor voltage during a fully soft switching operation provided by an embodiment of the present application;

[0035] Figure 7 1 is a waveform diagram of a driving signal and a capacitor voltage during partial soft switching provided by an embodiment of the present application;

[0036] Figure 8 1 is a waveform diagram of a driving signal and a capacitor voltage during excessive soft switching provided by an embodiment of the present application;

[0037] Figure 9 1 is a waveform diagram of a driving signal of a switching tube provided in an embodiment of the present application;

[0038] Figure 10 This is a schematic diagram of the structure of a controller in a power conversion device provided in an embodiment of the present application;

[0039] Figure 11 1 is a waveform diagram of a driving signal of another switching tube provided in an embodiment of the present application;

[0040] Figure 12 This is a schematic structural diagram of a controller in another power conversion device provided in an embodiment of the present application;

[0041] Figure 13 1 is a waveform diagram of a driving signal of a first switching tube provided in an embodiment of the present application;

[0042] Figure 14 3 is a waveform diagram of a driving signal of a second switching tube provided in an embodiment of the present application. DETAILED DESCRIPTION

[0043] The power conversion device and control method provided by the embodiments of the present application are described in detail below with reference to the accompanying drawings. First, the key terms involved in the embodiments of the present application are introduced.

[0044] Inverter: Also known as a power converter, it is used to convert direct current (DC) power provided by photovoltaic panels (also known as photovoltaic modules or solar panels) or other DC power sources (such as energy storage batteries) into alternating current (AC).

[0045] Power grid: The whole power system consisting of substations and transmission and distribution lines of various voltages, also known as the public power grid.

[0046] Microinverter: An inverter connected directly to one or two photovoltaic panels, capable of achieving maximum power point tracking (MPPT) at the module level.

[0047] One-to-one micro-inverter: one photovoltaic panel is combined with one micro-inverter.

[0048] Resonant cavity current: the current generated by the resonance of an active device in a loop containing an active device (such as the inductor Lr and the capacitors Cr1 and Cr2 in the embodiment of the present application).

[0049] Hard switching refers to the situation where the voltage and current overlap when the switch is switching (i.e., when it is turned on or off). For example, when the switch is on, the current flowing through the switch rises rapidly, but the voltage across the switch has not yet completely dropped to zero. Alternatively, when the switch is off, the voltage across the switch rises rapidly, but the current through the switch has not yet completely dropped to zero. During hard switching, the voltage and current overlap of the switch result in higher switching losses.

[0050] Soft switching refers to the switching operation of a switch tube when the voltage or current of the switch tube is zero. Soft switching generally includes zero voltage switching (ZVS) and zero current switching (ZCS). ZVS means that the voltage drops to zero before the switch tube turns on, and ZCS means that the current drops to zero before the switch tube turns off. This application embodiment uses ZVS as an example for explanation.

[0051] Figure 1 This is a schematic diagram of a power generation system provided in an embodiment of the present application. The power generation system can be applied to residential power consumption scenarios or small industrial and commercial power consumption scenarios, and Figure 1 The power generation system using micro inverter is used as an example for explanation. Figure 1 As shown, the power generation system includes: a plurality of photovoltaic panels and a plurality of micro-inverters 10. Each photovoltaic panel is connected to a micro-inverter 10 and is used to provide direct current to the micro-inverter 10 to which it is connected. The micro-inverter 10 is used to convert the direct current into alternating current.

[0052] Alternatively, as Figure 1As shown, the power generation system may further include a load and / or a power grid, which may be an AC power grid. The multiple micro-inverters 10 may be connected to the load and / or the power grid and output AC power to the load and / or the power grid. For example, the multiple micro-inverters 10 may be connected to the load and the power grid, respectively, and may output AC power to the load and the power grid.

[0053] It's understandable that, compared to traditional inverters, microinverters can be directly connected to a single or two PV panels, achieving panel-level MPPT. Furthermore, with microinverters, the performance of a single PV panel doesn't affect the power generation of other PV panels in the system (i.e., the photovoltaic power generation system), resulting in high overall power generation efficiency and high power generation capacity.

[0054] The micro-inverter 10 generally includes a primary bridge arm, a transformer, a secondary bridge arm and a controller. The input end of the primary bridge arm is used to connect to the photovoltaic panel, for example, the photovoltaic panel is connected through a DC bus. The output end of the primary bridge arm is connected to the primary side of the transformer. The secondary side of the transformer is connected to the input end of the secondary bridge arm, and the output end of the secondary bridge arm is used to connect to the load and / or the power grid. Each bridge arm in the primary bridge arm and the secondary bridge arm includes a plurality of switching tubes, and the controller can provide drive signals to the plurality of switching tubes respectively to drive the plurality of switching tubes to work. The drive signal can be a pulse width modulation (PWM) signal. The switching tube is also called a power tube, which can be an IGBT or a MOSFET, etc.

[0055] The rapid development of switching transistors such as MOSFETs and IGBTs has gradually improved their loss performance, but switching losses remain a bottleneck for increasing system frequency and efficiency. As mentioned earlier, when voltage and current overlap during the switching process of the switch, hard switching losses will occur. The existence of hard switching not only limits the switching frequency and efficiency, but also prevents the size and weight of the filter inductor in the microinverter from being reduced. The filter inductor refers to the inductor in the filter circuit. Accordingly, soft switching (such as full soft switching) plays a key role in reducing heat generation in microinverters, improving operating efficiency, and reducing electromagnetic interference. Full soft switching means that the voltage across the switch is completely reduced to zero before the switch turns on. The implementation of full soft switching mainly includes the following two requirements: 1) current polarity constraint; 2) charge constraint. Current polarity constraint means that the current flowing through the switch is zero or negative before the switch turns off. Charge constraint means that the charge on the parasitic capacitance in the switch is zero before the switch turns on.

[0056] Figure 2 This is a schematic diagram of the structure of a micro inverter provided in an embodiment of the present application. Figure 2As shown, the primary bridge arm 11 of the micro-inverter 10 may be an H-bridge structure, which includes two pairs of complementary switching transistors, one pair of complementary switching transistors being S1 and S2, and the other pair of complementary switching transistors being S3 and S4. Figure 3 This is a waveform diagram of the primary voltage, secondary voltage and resonant cavity current in a micro inverter provided in an embodiment of the present application. Figure 3 The horizontal axis is time in seconds; the vertical axis is voltage in volts (V), and the vertical axis can also represent current in amperes (A). Figure 3 As shown, the primary voltage output by the primary bridge arm 01 may include three levels: Upv, 0, and -Upv. Among them, Upv is the bus voltage of the DC bus connected to the primary bridge arm 01, that is, the output voltage of the photovoltaic panel. The secondary bridge arm 13 in the micro-inverter can be a bidirectional half-bridge structure, and the secondary voltage output by it may include two levels: Ug and -Ug. The primary voltage and the secondary voltage work together to form the resonant cavity current i r . Resonant cavity current i r The cycle is consistent with the switching cycle of the switch tube in the micro inverter.

[0057] Figure 4 Schematic diagram of the waveforms of the resonant cavity current, the current before filtering and the grid current in a micro inverter provided in an embodiment of the present application. Figure 4 The horizontal axis is time in seconds, and the vertical axis is current in A. Figure 2 and Figure 4 , resonant cavity current i r Through the switch tubes (such as switch tubes S5 to S8) and capacitors (such as capacitor C r1 and C r2 ) work together to form the current before filtering i o The current before filtering i o The grid-connected current i is formed by the filter circuit 15. g .from Figure 4 It can be seen that the grid-connected current i g The frequency is 50 Hz, and the period is 0.02 seconds. Figure 3 and Figure 4 As can be seen from the horizontal axis, Figure 3 The voltage and current waveforms shown are those between 0.0024 seconds and 0.00243 seconds, i.e. Figure 3 The voltage and current waveforms are shown with the switching period of the switch tube as the time granularity, and the switching period is in microseconds. Figure 4 The current waveform shown is the waveform between 0 and 0.02 seconds, that is, Figure 4 The current waveform is shown with the period of the grid-connected current, i.e. the power frequency period (0.02 seconds) as the time granularity. Figure 3The resonant cavity current shown in can be the resonant cavity current between the primary bridge arm 11 and the primary side of the transformer 12, Figure 4 The resonant cavity current shown in can be the resonant cavity current between the secondary side of the transformer 12 and the secondary side bridge arm 13. Since the transformation ratio (also known as the turns ratio) between the primary and secondary sides of the transformer 12 is 1:N, the amplitude of the resonant cavity current on the primary side can be N times the amplitude of the resonant cavity current on the secondary side. N can be an integer greater than 1, for example, N can be equal to 5.

[0058] It is understandable that the conversion of the primary voltage output by the primary bridge arm 11 in the micro-inverter 10 between the three levels is the result of the complementary switching tubes in the primary bridge arm 11. Figure 5 As shown, Figure 5 The corresponding relationship between the primary voltage and the switching state of the complementary switch tube is shown in FIG. Figure 5 Drv3 is the driving signal of the switch tube S3 in the primary bridge arm 11, and Drv4 is the driving signal of the switch tube S4 in the primary bridge arm 11. Figure 5 It can be seen that the driving signal of the switch tube has two levels, 0 and 1, where 0 level (i.e. low level) is used to control the switch tube to turn off, and 1 level (i.e. high level) is used to control the switch tube to turn on. Figure 5 It can also be seen that during the operation of the microinverter 10, the complementary switches S3 and S4 are alternately turned on, allowing the primary voltage output by the primary bridge arm 11 to switch between different levels. Furthermore, because the switches require a certain amount of time to turn on and off, a dead time is inserted between the on and off states of each pair of complementary switches. During this dead time, both complementary switches are not conducting.

[0059] It is also understandable that if Figure 2 As shown, a freewheeling diode and a capacitor are connected in parallel at both ends of each switch tube in the micro-inverter 10. The freewheeling diode can be a parasitic diode (also called a body diode) of the switch tube, and the capacitor can be a parasitic capacitor of the switch tube, or can be an independently set capacitor element. During the dead time of the complementary switch tube, the resonant cavity current will charge and discharge the capacitor (such as parasitic capacitor) connected in parallel at both ends of the complementary switch tube. Take the complementary switch tubes S1 and S2 as an example for explanation, as shown in FIG. Figure 6 As shown, in the initial state, the driving signal Drv2 of the switch tube S2 is high, and the driving signal Drv1 of the switch tube S1 is low, corresponding to the switch tube S2 being turned on and the switch tube S1 being turned off. In addition, the voltage across the capacitor connected in parallel with the switch tube S2 is VC2 = 0, and the voltage across the capacitor connected in parallel with the switch tube S1 is VC1 = Upv. At time t1, Drv2 jumps to a low level, the switch tube S2 is turned off, and the resonant cavity current begins to charge the capacitor connected in parallel with the switch tube S2. VC2 begins to rise, and correspondingly VC1 begins to fall. Figure 6 As can be seen, the interval between t1 and t2 is the dead time, during which both switches S1 and S2 are off. Full soft switching occurs when the voltage VC1 across the capacitor connected in parallel with switch S1 drops to zero (equivalent to VC2 rising to Upv) (i.e., at t2), the dead time ends, Drv1 transitions to a high level, and switch S1 turns on.

[0060] Correspondingly, Figure 7 The waveforms of the driving signal and capacitor voltage during incomplete soft switching are shown in FIG. Figure 8 The waveforms of the driving signal and capacitor voltage during excessive soft switching are shown in FIG. Figure 7 It can be seen that incomplete soft switching (also called partial soft switching) means that when the voltage VC1 across the capacitor connected in parallel with the switch tube S1 has not dropped to 0 (that is, when the voltage across the switch tube S1 has not dropped to 0), the dead time ends, Drv1 jumps to a high level, and the switch tube S1 is turned on. Figure 8 It can be seen that excessive soft switching means that the dead time ends a certain period of time after the voltage VC1 across the capacitor connected in parallel with the switch tube S1 drops to 0 (that is, the voltage across the switch tube S1 drops to 0), Drv1 jumps to a high level, and the switch tube S1 is turned on.

[0061] refer to Figures 7 to 9 As can be seen, when the complementary switches switch on and off, if the dead time is too short, it will result in incomplete soft switching, which will cause switching losses in the switches. If the dead time is set too long, it will lead to excessive soft switching, which will not only introduce losses in the freewheeling diode but also increase output voltage distortion. Therefore, by setting an appropriate dead time while ensuring current polarity, complete soft switching of the switches can be achieved, effectively reducing the switching losses of the one-to-one micro-inverter and improving efficiency.

[0062] In some embodiments, the duration of the dead time is related to the operating point of the microinverter, such as the bus voltage and output power. Therefore, the optimal dead time can be pre-calculated offline based on the operating point, and a mapping relationship between the operating point and the dead time can be established. This mapping relationship is stored in the chip in tabular form. In actual operation, the optimal dead time is directly obtained by looking up the table based on the current operating point. This solution is low-cost and does not require additional hardware circuits. However, since the dead time of this solution is fixed and lacks the ability to adaptively adjust, it is prone to incomplete soft switching and excessive soft switching.

[0063] In other embodiments, as described above, fully soft switching can be achieved by turning on the corresponding switch when the capacitor voltage of the capacitor connected in parallel across the switch drops to zero. Therefore, a capacitor voltage sampling circuit can be added to the microinverter. This capacitor voltage sampling circuit detects the capacitor voltage of the capacitor connected in parallel across the switch and adaptively controls the dead time based on this capacitor voltage. This solution can dynamically and adaptively adjust the dead time based on the actual operating conditions of the microinverter, achieving fully soft switching. However, this solution requires the addition of an additional capacitor voltage sampling circuit, which increases the structural complexity and hardware cost of the microinverter.

[0064] The present invention provides a power conversion device, which can be used in Figure 1 In the power generation system shown, the power conversion device can be a micro-inverter. Of course, the power conversion device can also be other types of inverters, and the embodiments of the present application are not limited to this. The power conversion device provided in the embodiments of the present application can achieve adaptive dynamic adjustment of the dead time with a relatively simple structure and low hardware cost to ensure complete soft switching of the switch tube, thereby effectively reducing the loss of the power conversion device and improving the working efficiency of the power conversion device.

[0065] The following describes the power conversion device provided by the embodiment of the present application by taking a micro inverter as an example. Figure 2 As shown, the power conversion device includes: a primary bridge arm 11, a transformer 12, a secondary bridge arm 13 and a controller 14. The input end of the primary bridge arm 11 is used to connect to the photovoltaic panel, for example, the photovoltaic panel is connected through a DC bus. The output end of the primary bridge arm 11 is connected to the primary side of the transformer 12, the secondary side of the transformer 12 is connected to the input end of the secondary bridge arm 13, and the output end of the secondary bridge arm 13 is used to connect to the power grid or load. The primary bridge arm 11, the transformer 12 and the secondary bridge arm 13 are used to convert the direct current provided by the photovoltaic panel into alternating current and output it to the power grid or load. Figure 2 The primary bridge arm 11 includes a first switch tube S1 and a second switch tube S2 , which are a pair of complementary switch tubes connected in series between the positive electrode and the negative electrode of the input end of the primary bridge arm 11 .

[0066] In an embodiment of the present application, the controller 14 is used to: at a first moment T1, control the first switch tube S1 to be turned on, and control the second switch tube S2 to be turned off. The controller 14 is also used to: at a second moment T2, control the first switch tube S1 to be turned off, and at a third moment T3, control the second switch tube S2 in the primary bridge arm 11 to be turned on. Among them, the integral value of the resonant cavity current in the power conversion device in the time period between the second moment T2 and the third moment T3 is a first integral threshold. The resonant cavity current is the resonant cavity current between the primary bridge arm 11 and the primary side of the transformer 12 (i.e., the primary resonant cavity current), or the resonant cavity current is the resonant cavity current between the secondary side of the transformer 12 and the secondary bridge arm 13 (i.e., the secondary resonant cavity current). It can be understood that the primary resonant cavity current is equal to N times the secondary resonant cavity current, and N is the transformation ratio of the primary side to the secondary side of the transformer 12.

[0067] Furthermore, at the third moment T3, the voltage across the second switch S2 is less than a first voltage threshold. The first voltage threshold can be a value close to 0, and is a voltage value that enables the second switch S2 to achieve soft switching. For example, after the second moment T2, the voltage across the second switch S2 gradually decreases until, at the third moment T3, the voltage across the second switch S2 drops to 0.

[0068] For example, refer to Figure 9 At the first moment T1, the controller 14 outputs a high-level drive signal Drv1 to the first switch S1 and a low-level drive signal Drv2 to the second switch S2. The first switch S1 is turned on, while the second switch S2 is turned off. At the second moment T2, the controller 14 outputs a high-level drive signal Drv1 to a low-level drive signal, turning off the first switch S1. At this point, the controller 14 outputs a low-level drive signal Drv2 to the second switch S2, and the dead time begins.

[0069] It can be understood that after the controller 14 turns off the first switch tube S1 at the second moment T2, that is, after the dead time begins, the resonant cavity current (such as the primary resonant cavity current) in the power conversion device begins to charge the capacitor connected in parallel at both ends of the first switch tube S1 (such as the parasitic capacitance of the first switch tube S1), thereby causing the voltage across the first switch tube S1 to gradually rise. Correspondingly, the resonant cavity current begins to discharge the capacitor connected in parallel at both ends of the second switch tube S2 (such as the parasitic capacitance of the second switch tube S2), thereby causing the voltage across the second switch tube S2 to gradually decrease. It can be seen that after the dead time begins, the voltage change across the first switch tube S1 and the voltage change across the second switch tube S2 are the result of the resonant cavity current charging and discharging the capacitor connected in parallel with the switch tube. Since the integral of the resonant cavity current is charge, and the change in charge on the capacitor corresponds to the change in capacitor voltage, and then corresponds to the change in voltage across the switch tube, in the embodiment of the present application, the integral value of the resonant cavity current can be used to reflect the change in voltage across the switch tube.

[0070] It can also be understood that after the second moment T2, the controller 14 can start to integrate the resonant cavity current. As the integral value of the resonant cavity current continues to rise, the voltage across the first switch tube S1 will continue to rise, and the voltage across the second switch tube S2 will continue to fall. Figure 9 As shown, until the third moment T3, the integral value of the resonant cavity current reaches the first integral threshold, indicating that the voltage across the second switch tube S2 drops to a value less than the first voltage threshold. For example, by reasonably setting the first integral threshold, it can be ensured that when the integral value of the resonant cavity current reaches the first integral threshold, the voltage across the second switch tube S2 drops from the bus voltage Upv to 0, and the voltage across the first switch tube S1 rises from 0 to the bus voltage Upv. At this time, the controller 14 can control the second switch tube S2 to conduct, for example Figure 9 As shown, the controller 14 can change the output drive signal Drv2 from a low level to a high level. Accordingly, the dead time ends. That is, the period between the second time point T2 and the third time point T3 is the dead time. Because the voltage across the second switch S2 drops to zero at the third time point T3, when the dead time ends, fully soft switching of the second switch S2 can be achieved.

[0071] It can also be understood that the above-mentioned first integration threshold can be determined based on the bus voltage Upv and the capacitance value of the capacitor connected in parallel at both ends of the first switch tube S1 (or the capacitance value of the capacitor connected in parallel at both ends of the second switch tube S2). For example, the first integration threshold can be equal to the charge required for the voltage of the capacitor connected in parallel at both ends of the first switch tube S1 to be charged from 0 to the bus voltage Upv (or close to the bus voltage Upv), that is, equal to the charge required for the voltage of the capacitor connected in parallel at both ends of the second switch tube S2 to be discharged from the bus voltage Upv to 0 or close to 0 (for example, the first voltage threshold). Alternatively, the first integration threshold can be equal to the product of the above-mentioned charge amount and a preset proportional coefficient. The proportional coefficient can be a coefficient generated by the controller 14 when sampling and integrating the resonant cavity current and performing proportional conversion on the resonant cavity current.

[0072] For example, the first integration threshold can be obtained in advance through simulation or testing. During the simulation or testing, the controller 14 can integrate the resonant cavity current (primary resonant cavity current or secondary resonant cavity current) after the first switch tube S1 is turned off. When the voltage of the capacitor connected in parallel at both ends of the first switch tube S1 rises from 0 to the bus voltage Upv (or close to the bus voltage Upv), or when the voltage of the capacitor connected in parallel at both ends of the second switch tube S2 decreases from the bus voltage Upv to less than the first voltage threshold (for example, decreased to 0), the integral value of the resonant cavity current is detected and determined as the first integration threshold. Alternatively, the first integration threshold can be calculated based on the bus voltage Upv, the capacitance value of the capacitor connected in parallel at both ends of the switch tube, the parameters of each component in the sampling circuit of the resonant cavity current, and the parameters of each component in the integration circuit.

[0073] Based on the above analysis, it can be seen that in the solution provided by the embodiment of the present application, after the controller turns off the first switch tube at the second moment, it can start to integrate the resonant cavity current, and can turn on the second switch tube again at the third moment when it detects that the integral value of the resonant cavity current is the first integral threshold. The period between the first moment and the second moment is the dead time. In addition, the integral value of the resonant cavity current in this period can reflect the voltage change at both ends of the second switch tube, that is, the controller can accurately detect the voltage at both ends of the switch tube (that is, the capacitor voltage of the capacitor in parallel with the switch tube) based on the integral value of the resonant cavity current. Accordingly, the controller turns on the second switch tube when the integral value of the resonant cavity current is the first integral threshold, which can achieve adaptive dynamic adjustment of the dead time. In addition, since the integral value of the resonant cavity current reaches the first integral threshold at the second moment, it can indicate that the voltage at both ends of the second switch tube is less than the first voltage threshold at the second moment. Therefore, turning on the second switch tube at the second moment can ensure that the second switch tube is fully soft-switched.

[0074] Figure 10 This is a schematic diagram of the structure of a controller provided in an embodiment of the present application. Figure 10 As shown, the controller 14 includes: a current sampling circuit 141, an integration circuit 142, and a control circuit 143. The current sampling circuit 141 is used to sample the resonant cavity current and output it to the input end of the integration circuit 142. The output end of the integration circuit 142 is connected to the control circuit 143. The integration circuit 142 is used to integrate the received resonant cavity current and output the integrated value of the resonant cavity current to the control circuit 143. The control circuit 143 is used to control the integration circuit 142 to integrate the resonant cavity current after the second time T2, and to control the second switch S2 to turn on at a third time T3 based on the integrated value output by the integration circuit 142 being a first integration threshold.

[0075] For example, the control circuit 143 may include a logic judgment circuit and a PWM wave generating circuit. The logic judgment circuit is used to control the working state of the integration circuit 142 and to determine whether the integral value output by the integration circuit 142 reaches the first integral threshold. The PWM wave generating circuit is used to output a driving signal (i.e., a PWM signal) to the switch tube to control the on and off of the switch tube. For example, referring to Figure 10 , the PWM wave generating circuit can output a driving signal Drv1 to the first switch tube S1 and output a driving signal Drv2 to the second switch tube S2. Figure 9 As shown, at the first moment, the drive signal Drv1 is high and the drive signal Drv2 is low, turning the first switch S1 on and the second switch S2 off. At the second moment T2, the drive signal Drv2 remains low, and the second switch S2 remains off. The drive signal Drv1 then transitions from high to low, switching the first switch S1 from on to off. In other words, the first and second switches S1 and S2 enter the dead time at the second moment T2. Simultaneously, the logic circuit controls the integration circuit 142 to integrate the received resonant cavity current. At the third moment T3, the logic circuit detects that the integrated value of the resonant cavity current has reached the first integration threshold, confirming the end of the dead time and instructing the PWM generator circuit to transition the drive signal Drv2 from low to high, turning on the second switch S2.

[0076] It is understandable that a resonant cavity current sampling circuit is generally provided in a power conversion device. This sampling circuit is used to sample the resonant cavity current so as to protect the power conversion device based on the sampled resonant cavity current. In the embodiment of the present application, the above-mentioned current sampling circuit 141 can reuse the original resonant cavity current sampling circuit in the power conversion device. In this way, it is possible to effectively avoid increasing the structural complexity and hardware cost of the power conversion device. In addition, since the structure of the integration circuit is relatively simple and the cost is relatively low, it is also possible to avoid the structural complexity and hardware cost of the power conversion device being too high.

[0077] For example, the current sampling circuit 141 can be used to sample the primary resonant cavity current between the output end of the primary bridge arm 11 and the primary side of the transformer 12, or to sample the secondary resonant cavity current between the secondary side of the transformer 12 and the input end of the secondary bridge arm 13. If the secondary resonant cavity current of the transformer 12 is sampled, then because the voltage change across the switching tube in the primary bridge arm 11 is the result of the primary resonant cavity current, and the primary and secondary sides of the transformer 12 have a transformation ratio of 1:N, the above-mentioned proportionality coefficient must also take into account the transformation ratio N of the transformer 12.

[0078] Alternatively, as Figure 10 As shown, the integration circuit 142 includes: an operational amplifier A1, a first resistor R1, a second resistor R2, an integration capacitor C0, and a switch K. The inverting input terminal - of the operational amplifier A1 is used to receive the resonant cavity current output by the current sampling circuit 141 through the first resistor R1, the non-inverting input terminal + of the operational amplifier A1 is used to receive the reference voltage Vref through the second resistor R2, and the output terminal of the operational amplifier A1 is connected to the control circuit 143 and is used to output the integration value to the control circuit 143. The integration capacitor C0 is connected between the inverting input terminal - and the output terminal of the operational amplifier A1, and the switch K is connected in parallel with the integration capacitor C0. The switch K can be a switch tube, for example, a switch tube such as a MOSFET or an IGBT.

[0079] The control circuit 143 is configured to control the switch K to be turned off during a period between the second moment T2 and the third moment T3, and to control the switch K to be turned on before the second moment T2 and after the third moment T3.

[0080] It can be understood that since the switch K is connected in parallel with the integration capacitor C0, when the switch K is turned on, that is, before the second moment T2 and after the third moment T3, the integration capacitor C0 is bypassed. At this time, the integration function of the integration circuit 142 is not effective, or it can be understood that the integration circuit 142 does not have an integration function. When the switch K is turned off, the integration capacitor C0 starts to work, and the integration function of the integration circuit 142 takes effect. Based on the above analysis, it can be seen that the control circuit 143 can achieve flexible control of the working state of the integration circuit 142 by controlling the on and off of the switch K. The control logic of the control circuit 143 is relatively simple. Among them, after the integration function of the integration circuit 142 takes effect, the integration value V output by the integration circuit 142 at time t is out (t) Satisfy:

[0081]

[0082] Wherein, R represents the resistance value of the first resistor R1, C represents the capacitance value of the integral capacitor C0, V out (0) represents the initial output voltage of the integration circuit 142. Vin (t) represents the inverting input terminal of the integration circuit 142 receiving the input voltage at time t, which is obtained by the current sampling circuit 141 sampling the resonant cavity current.

[0083] It is also understood that the reference voltage Vref can be provided by a reference voltage generation circuit in the power conversion device. Furthermore, the reference voltage Vref can adjust the DC offset of the output voltage of operational amplifier A1, ensuring that the integration result output by operational amplifier A1 is within the linear operating range of operational amplifier A1. The second resistor R2 can be used to balance the input bias current of operational amplifier A1, and its resistance value can be equal to the resistance value of the first resistor R1.

[0084] Optionally, continue to refer to Figure 10 , the integration circuit 142 may further include a third resistor R3 connected in series with the switch K. Accordingly, when the switch K is turned on, the third resistor R3 is connected between the inverting input terminal - and the output terminal of the operational amplifier A1, and the integration capacitor C0 is bypassed. In this case, the integration circuit 142 functions as an inverting amplifier, and the gain of the inverting amplifier is negative, and the absolute value of the gain is equal to the ratio of the resistance value of the third resistor R3 to the resistance value of the first resistor R1. For example, the resistance value of the third resistor R3 can be equal to the resistance value of the first resistor R1, and accordingly, the gain of the inverting amplifier is equal to -1.

[0085] Optionally, continue to refer to Figure 10 , the control circuit 143 is used to output a switch control signal Rst to the switch K. The switch control signal Rst is also called a reset signal or a reset signal. Figure 9 As shown, the switch control signal Rst is at a low level between the second time T2 and the third time T3 to turn off the switch K. The switch control signal Rst is at a high level before the second time T2 and after the third time T3 to turn on the switch K.

[0086] The above describes the process by which the controller 14 controls the second switching transistor S2 to turn on based on the integrated value of the resonant cavity current after controlling the first switching transistor S1 to turn off. It is understood that after controlling the second switching transistor S2 to turn off, the controller 14 can also control the first switching transistor S1 to turn on using the same method. Specifically, the controller 14 is further configured to: control the second switching transistor S2 to turn off at a fourth time T4; and control the first switching transistor S1 to turn on at a fifth time T5. The integrated value of the resonant cavity current during the period between the fourth time T4 and the fifth time T5 is a second integration threshold. Furthermore, at the fifth time T5, the voltage across the first switching transistor S1 is less than a second voltage threshold. This second voltage threshold can be equal to or different from the first voltage threshold. Furthermore, the second voltage threshold can be close to zero, that is, the second voltage threshold is a voltage value that enables the first switching transistor S1 to achieve soft switching. For example, after the fourth time T4, the voltage across the first switching transistor S1 gradually decreases until, at the fifth time T5, the voltage across the first switching transistor S1 drops to zero.

[0087] For example, refer to Figure 9 Before the fourth time T4, the drive signal Drv1 output by the controller 14 to the first switch S1 is at a low level, and the first switch S1 remains off. The drive signal Drv2 output by the controller 14 to the second switch S2 is at a high level, turning the second switch S2 on. At the fourth time T4, the drive signal Drv2 output by the controller 14 changes from a high level to a low level, turning the second switch S2 off. At this time, the drive signal Drv1 output by the controller 14 remains at a low level, and the first switch S1 remains off, and the dead time begins.

[0088] It is understood that after the controller 14 turns off the second switch S2 at the fourth time T4, i.e., after the dead time begins, the resonant cavity current in the power conversion device begins to charge the capacitor connected in parallel with the second switch S2 (e.g., the parasitic capacitance of the second switch S2), thereby gradually increasing the voltage across the second switch S2. Correspondingly, the resonant cavity current begins to discharge the capacitor connected in parallel with the first switch S1 (e.g., the parasitic capacitance of the first switch S1), thereby gradually decreasing the voltage across the first switch S1.

[0089] It is also understandable that after the fourth moment T4, the controller 14 can start integrating the resonant cavity current. As the integral value of the resonant cavity current continues to rise, the voltage across the second switch tube S2 will continue to rise, and the voltage across the first switch tube S1 will continue to fall. For example, Figure 9As shown, until the fifth moment T5, the integral value of the resonant cavity current reaches the second integral threshold, indicating that the voltage across the second switch tube S2 rises to the bus voltage Upv or is close to the bus voltage Upv, and the voltage across the first switch tube S1 drops below the second voltage threshold (for example, drops to 0). At this time, the controller 14 can control the first switch tube S1 to turn on. Figure 9 As shown, the controller 14 can jump the output drive signal Drv1 from a low level to a high level. Accordingly, the dead time ends. That is, the period between the fourth time point T4 and the fifth time point T5 is the dead time. By properly setting the second integral threshold, it can be ensured that the voltage across the first switch S1 drops to zero at the fifth time point T5, when the dead time ends, thereby achieving complete soft switching of the first switch S1.

[0090] It can also be understood that the above-mentioned second integration threshold can be determined based on the bus voltage Upv and the capacitance value of the capacitor connected in parallel at both ends of the second switch tube S2 (or the capacitance value of the capacitor connected in parallel at both ends of the first switch tube S1). For example, the second integration threshold can be equal to the charge required for the voltage of the capacitor connected in parallel at both ends of the second switch tube S2 to be charged from 0 to the bus voltage Upv (or close to the bus voltage Upv), that is, equal to the charge required for the voltage of the capacitor connected in parallel at both ends of the first switch tube S1 to be discharged from the bus voltage Upv to 0 or close to 0 (for example, the first voltage threshold). Alternatively, the second integration threshold can be equal to the product of the above-mentioned charge amount and a preset proportional coefficient. The proportional coefficient can be a coefficient generated by the controller 14 performing a proportional transformation on the resonant cavity current when integrating the resonant cavity current.

[0091] For example, the second integration threshold can also be obtained in advance through simulation or testing. During the simulation or testing, the controller 14 can integrate the resonant cavity current after the second switch S2 is turned off. When the voltage of the capacitor connected in parallel across the second switch S2 rises from 0 to the bus voltage Upv (or close to the bus voltage Upv), or when the voltage of the capacitor connected in parallel across the first switch S1 decreases from the bus voltage Upv to less than the first voltage threshold (for example, to 0), the integral value of the resonant cavity current is detected and determined as the second integration threshold. Alternatively, the second integration threshold can be calculated based on the bus voltage Upv, the capacitance value of the capacitor connected in parallel across the switch, the parameters of each component in the resonant cavity current sampling circuit, and the parameters of each component in the integration circuit. Since the device parameters of the first switch S1 and the second switch S2 are generally the same, the second integration threshold can be equal to the above-mentioned first integration threshold.

[0092] Optionally, because the first switching transistor S1 and the second switching transistor S2 are a pair of complementary switching transistors that are alternately turned on, the controller 14 can integrate the resonant cavity current in different time periods through the same integration circuit 142 and control the conduction of the first switching transistor S1 and the second switching transistor S2 based on the integration values ​​in different time periods. As a result, only one integration circuit is required to achieve switching control of the two switching transistors S1 and S2, thereby effectively simplifying the structure of the power conversion device and reducing costs.

[0093] For example, refer to Figure 9 and Figure 11 After either the first switch S1 or the second switch S2 is turned off, the control circuit 143 adjusts the switch control signal Rst to a low level, turning off the switch K and causing the integration circuit 142 to begin integrating the resonant cavity current. After the integrated value reaches the corresponding threshold, the control circuit 143 controls the corresponding switch to turn on and adjusts the switch control signal Rst to a high level, turning on the switch K. The integration circuit 142 stops integrating to prepare for subsequent steps.

[0094] Optionally, the controller 14 can also generate a switching signal S for the switch tube through software. The switching signal S is a square wave signal, and the duty cycle of the square wave signal can be one-half. The frequency of the square wave signal is the switching frequency of the switch tube. For example, the frequency of the square wave signal can be 100 kHz to 120 kHz. In addition, the frequency of the square wave signal can be a fixed frequency or an adjustable frequency (for example, it can be adjusted according to different operating points). The switching signal S can be understood as an original drive signal for controlling the on and off of the switch tube and does not include a dead zone. In an embodiment of the present application, the controller 14 can directly control the switch tube to be turned off based on the switching signal S, and control the switch tube to be turned on based on the integral value of the resonant cavity current. Alternatively, it can be understood that the switch tube's turn-off signal (such as the falling edge of the drive signal) is directly generated by the software, and the turn-on signal (i.e., the rising edge of the drive signal, or the dead zone time) is generated by the delay of the integration circuit of the resonant cavity current.

[0095] For example, refer to Figure 11 The controller 14 is used to: control the first switch tube S1 to turn off based on the switch signal S jumping from a high level to a low level at the second moment T2; and control the second switch tube S2 to turn off based on the switch signal S jumping from a low level to a high level at the fourth moment T4. It can be understood that Figure 11 As shown, the controller 14 can also generate a complementary signal of the switching signal S The complementary signal The switching signal S can be inverted, and the controller 14 can be based on the complementary signal Control the second switch S2 to turn off. Figure 11 , the controller 14 can control the first switch tube S1 to turn off at the falling edge of the switch signal S, and The falling edge of controls the second switch tube S2 to turn off.

[0096] It is understandable that the falling edge of the switch control signal Rst can also be caused by the switch signal S (or the complementary signal ) controls the generation of. For example, refer to Figure 11 When the switch signal S changes from high level to low level, the first switch tube S1 is turned off, and at the same time, the control circuit 143 controls the switch control signal Rst to change from high level to low level, and the integration circuit 142 starts to work. When the integral value output by the integration circuit 142 reaches the first integration threshold, the control circuit 143 controls the second switch tube S2 to turn on, and controls the switch control signal Rst to change from low level to high level, that is, the integration circuit 142 is reset (also called reset) to prepare for subsequent integration. Afterwards, when the complementary signal When the level changes from high to low, the second switch tube S2 is turned off. At the same time, the control circuit 143 controls the switch control signal Rst to change from high to low, and the integration circuit 142 starts working again.

[0097] It is also understandable that the controller 14 can also integrate the resonant cavity current in different time periods through different integration circuits, and control the conduction of different switching tubes based on the integration values ​​output by different integration circuits. Figure 12 The controller 14 may include two integration circuits 142a and 142b. The control circuit 143 is configured to control the integration circuit 142b to begin integrating the resonant cavity current after the first switch S1 is turned off, and to control the second switch S2 to turn on and control the integration circuit 142b to stop integration when the integration value 2 output by the integration circuit 142b reaches a first integration threshold. Furthermore, the control circuit 143 is configured to control the integration circuit 142a to begin integrating the resonant cavity current after the second switch S2 is turned off, and to control the first switch S1 to turn on and control the integration circuit 142a to stop integration when the integration value 1 output by the integration circuit 142a reaches a second integration threshold.

[0098] For example, reference Figure 13 and Figure 14At the first moment T1, the drive signal Drv1 is at a high level and the drive signal Drv2 is at a low level, turning the first switch S1 on and the second switch S2 off. At the second moment T2, the control circuit 143 controls the drive signal Drv1 to transition from a high level to a low level based on the falling edge of the switch signal S, thereby turning off the first switch S1. Simultaneously, the control circuit 143 can control the switch control signal Rst2 to a low level based on the falling edge of the switch signal S, thereby turning off the switch K in the integration circuit 142b, thereby causing the integration circuit 142b to begin integrating the resonant cavity current. At the third moment T3, when the integral value 2 output by the integration circuit 142b reaches the first integration threshold, the control circuit 143 can control the drive signal Drv2 to transition from a low level to a high level, thereby turning on the second switch S2. At the same time, the control circuit 143 can control the switch control signal Rst2 to be high level to control the switch K in the integration circuit 142b to be turned on, thereby stopping the integration circuit 142b from integrating, that is, resetting the integration circuit 142b.

[0099] At the fourth moment T4, the control circuit 143 generates the complementary signal The falling edge of the control driving signal Drv2 changes from high level to low level to control the second switch tube S2 to turn off. At the same time, the control circuit 143 can be based on the complementary signal The falling edge of the control switch control signal Rst1 controls the switch control signal Rst1 to a low level to control the switch K in the integration circuit 142a to turn off, thereby causing the integration circuit 142a to start integrating the resonant cavity current. At the fifth moment T5, when the integral value 1 output by the integration circuit 142a reaches the second integration threshold, the control circuit 143 can control the drive signal Drv1 to jump from a low level to a high level to control the first switch tube S1 to turn on. At the same time, the control circuit 143 can control the switch control signal Rst1 to a high level to control the switch K in the integration circuit 142a to turn on, thereby causing the integration circuit 142a to stop integrating, that is, reset (reset) the integration circuit 142a. Afterwards, the control circuit 143 can be based on the switch signal S and the complementary signal The level changes and the above control process is executed cyclically.

[0100] Optionally, the control circuit 143 in the controller 14 may include a micro-controller unit (MCU), a complex programming logic device (CPLD) or a field programmable gate array (FPGA).

[0101] The following is an introduction to the circuit topology of the power conversion device. Figure 2As shown, the primary bridge arm 11 is an H-bridge structure, which includes two pairs of complementary switch tubes, each pair of complementary switch tubes including two switch tubes connected in series between the positive and negative electrodes of the input end of the primary bridge arm 11. Figure 2 Switches S1 and S2 form a complementary pair, and switches S3 and S4 form a complementary pair. One end of the primary side of transformer 12 is connected to the series node between switches S1 and S2, and the other end of the primary side of transformer 12 is connected to the series node between switches S3 and S4. In other words, the series node between switches S1 and S2 and the series node between switches S3 and S4 form the output end of primary bridge arm 11.

[0102] Continue to refer Figure 2 The secondary bridge arm 13 can be a half-bridge circuit, and the secondary bridge arm 13 includes: a switch tube S5, a switch tube S6, a switch tube S7 and a switch tube S8 connected in series between the positive and negative electrodes of the output end of the secondary bridge arm 14, and capacitors Cr1 and Cr2 connected in series between the positive and negative electrodes of the output end of the secondary bridge arm 14. The capacitance values ​​of the capacitors Cr1 and Cr2 can be equal. Figure 2 It can be seen that one end of the secondary side of the transformer 12 can be connected to the series node between the switches S6 and S7, and the other end of the secondary side of the transformer 12 can be connected to the series node between the capacitors Cr1 and Cr2. In other words, the series node between the switches S6 and S7 and the series node between the capacitors Cr1 and Cr2 constitute the input end of the secondary side bridge arm 13.

[0103] It is understandable that the secondary bridge arm 13 can also be a full-bridge circuit, that is, the capacitors Cr1 and Cr2 in the secondary bridge arm 13 can be replaced by four switches connected in series. Figure 2 As shown, capacitors may be connected in parallel at both ends of each switch tube in the primary bridge arm 11 and the secondary bridge arm 13 , and the capacitors may be parasitic capacitors of the switch tubes.

[0104] Alternatively, as Figure 2 As shown, the power conversion device may also include an inductive device Lr, which may be a resonant inductor. The resonant inductor Lr may be connected in series between the secondary side of the transformer 12 and the input end of the secondary side bridge arm 13. For example, one end of the resonant inductor Lr may be connected to one end of the secondary side of the transformer 12, and the other end of the resonant inductor Lr may be connected to the series node between the switch tubes S6 and S7 in the secondary side bridge arm 13. Accordingly, the above-mentioned resonant cavity current may refer to the current flowing through the resonant inductor Lr, that is, the secondary side resonant cavity current. It can be understood that the power conversion device may not need to separately set up a resonant inductor Lr, and the leakage inductance of the transformer 12 may equivalently form a resonant inductor Lr.

[0105] Optionally, continue to refer to Figure 2 The transformer 12 in the power conversion device provided in the embodiment of the present application may be a high-frequency transformer, and the turns ratio of the primary side to the secondary side may be 1:N, where N may be an integer greater than 1. Figure 2 L in m Represents the excitation inductance of the transformer 12. The power conversion device may also include a bus capacitor C bus And filter circuit 15. Among them, the bus capacitor C bus The filter circuit 15 is connected in parallel to the input end of the primary bridge arm 11. The filter circuit 15 is connected to the output end of the secondary bridge arm 13 and is used to filter the current i output by the secondary bridge arm 13. o Filter to get the grid-connected current i g The filter circuit 15 may be an electromagnetic compatibility (EMC) filter.

[0106] The above is based on the first switch tube Figure 2 The switch tube S1 in the primary bridge arm 11 is shown, and the second switch tube is the switch tube S2. It is understandable that the first switch tube can also be the switch tube S2, and the second switch tube can also be the switch tube S1. Alternatively, the first switch tube can also be Figure 2 The switch S3 in the primary bridge arm 11 is shown. Accordingly, the second switch S4 can be used. Alternatively, the first switch S4 can be used, and the second switch S3 can be used. This embodiment of the present application does not limit the first and second switches; it is sufficient that the two switches are a pair of complementary switches in the primary bridge arm 11.

[0107] Furthermore, it is also understood that the primary bridge arm 11 of the power conversion device includes two pairs of complementary switching transistors. For each pair of complementary switching transistors, the controller 14 can control the dead time when the pair of complementary switching transistors switches on and off based on the solution provided in the above embodiment. That is, for both switching transistors in each pair of complementary switching transistors, the controller 14 can integrate the resonant cavity current after one of the switching transistors is turned off, and control the other switching transistor to conduct when the integrated value of the resonant cavity current reaches a corresponding threshold. Accordingly, the controller 14 can include two integration circuits 142, one of which is configured to begin integrating the resonant cavity current after either switching transistor S1 or S2 is turned off, and the other integration circuit 142 is configured to begin integrating the resonant cavity current after either switching transistor S3 or S4 is turned off. Based on this, the control circuit 143 can control the dead time when switching transistors S1 and S2 switches on and off, and the dead time when switching transistors S3 and S4 switches on and off, respectively, through the two integration circuits 142. That is, the controller 14 can adaptively adjust the dead time of each pair of complementary switching tubes in the primary bridge arm 11 to ensure that each pair of complementary switching tubes can achieve complete soft switching, thereby effectively reducing the switching loss of the power conversion device.

[0108] It can also be understood that the switch tubes S5 and S7 in the secondary bridge arm 13 are a pair of complementary switch tubes, and the switch tubes S6 and S8 are a pair of complementary switch tubes. For each pair of complementary switch tubes in the secondary bridge arm 13, a corresponding integration circuit can also be provided in the controller 14, so that when each pair of complementary switch tubes switches between on and off states, the resonant cavity current is integrated based on the corresponding integration circuit, and the dead time is controlled based on the integration result. In other words, the controller 14 can also implement adaptive adjustment of the dead time of each pair of complementary switch tubes in the secondary bridge arm 13, ensuring that each pair of complementary switch tubes can achieve complete soft switching, thereby effectively reducing the switching loss of the power conversion device.

[0109] In summary, embodiments of the present application provide a power conversion device, wherein the primary bridge arm of the power conversion device includes a pair of complementary switching transistors connected in series: a first switching transistor and a second switching transistor. A controller in the power conversion device is capable of turning off the first switching transistor at a second moment and then turning on the second switching transistor at a third moment. During the period between the second moment and the third moment, the integral value of the resonant cavity current in the power conversion device is equal to a first integral threshold. It is understood that the period between the second moment and the third moment is the dead time, and the integral value of the resonant cavity current during this period can reflect the voltage change across the second switching transistor. Because the controller can turn on the second switching transistor at the second moment when the integral value of the resonant cavity current reaches the first integral threshold, adaptive dynamic adjustment of the dead time is achieved. Furthermore, because the integral value of the resonant cavity current reaching the first integral threshold at the second moment indicates that the voltage across the second switching transistor is less than the first voltage threshold at the second moment, turning on the second switching transistor at the second moment ensures soft switching of the second switching transistor.

[0110] The present application also provides a method for controlling a power conversion device, which can be applied to the power conversion device provided in the above embodiment. For example, the method can be executed by the controller 14 in the power conversion device. The method includes:

[0111] Step 101: At a first moment, control the first switch tube in the primary bridge arm to be turned on and the second switch tube to be turned off.

[0112] The power conversion device includes a primary bridge arm, a transformer, and a secondary bridge arm. The primary bridge arm is connected to the secondary bridge arm via a transformer, and a first switch tube and a second switch tube are connected in series between the positive and negative electrodes of the input end of the primary bridge arm.

[0113] Step 102: At the second moment, control the first switch tube to turn off.

[0114] Step 103: At a third moment, control the second switching transistor to be turned on. The integral value of the resonant cavity current during the period between the second moment and the third moment is a first integral threshold. The resonant cavity current is the resonant cavity current between the output end of the primary bridge arm and the primary end of the transformer, or the resonant cavity current between the secondary end of the transformer and the input end of the secondary bridge arm. Furthermore, at the third moment, the voltage across the second switching transistor is less than the first voltage threshold.

[0115] Optionally, the method further includes:

[0116] Step 104: At the fourth moment, control the second switch tube to be turned off.

[0117] Step 105: At the fifth moment, control the first switch tube to be turned on.

[0118] The integral value of the resonant cavity current in the period between the fourth moment and the fifth moment is the second integral threshold, and at the fifth moment, the voltage across the first switch tube is less than the second voltage threshold.

[0119] Optionally, step 102 may include: controlling the first switch to turn off based on the switch signal changing from a high level to a low level at the second moment. Step 104 may include: controlling the second switch to turn off based on the switch signal changing from a low level to a high level at the fourth moment. The switch signal is a square wave signal having a duty cycle of 1 / 2.

[0120] It is understood that the high level and low level in the embodiments of the present application refer to two level states of the signal, and the high level and low level are relative. The embodiments of the present application do not limit the voltage values ​​corresponding to the high level and low level respectively. In addition, the embodiments of the present application are all illustrated by taking the high level as the effective level (also called the conduction level or the turn-on level) and the low level as the invalid level (also called the turn-off level) as an example. Of course, the effective level can also be a low level, and the invalid level can also be a high level. For example, when the switch control signal is low, the switch is turned on, and when the switch control signal is high, the switch is turned off.

[0121] It can also be understood that the control method of the power conversion device provided in the above embodiment has basically the same implementation method and technical effect as the power conversion device described in the above embodiment. Therefore, for the purpose of brevity, the implementation method and technical effect of the control method of the power conversion device will not be repeated here.

[0122] In the embodiments of the present application, the terms "first", "second" and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "at least one" means one or more, and "a plurality" means two or more.

[0123] In the embodiments of this application, the term "and / or" is simply a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0124] The above are merely optional embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and such modifications or substitutions should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A power conversion device, characterized in that: The power conversion device includes: a primary bridge arm, a transformer, a secondary bridge arm and a controller; The input end of the primary bridge arm is used to connect to the photovoltaic panel, the output end of the primary bridge arm is connected to the input end of the secondary bridge arm through the transformer, and the output end of the secondary bridge arm is used to connect to the power grid or the load, and the primary bridge arm includes a first switching tube and a second switching tube, and the first switching tube and the second switching tube are connected in series between the positive electrode and the negative electrode of the input end of the primary bridge arm; The controller is used to: At a first moment, controlling the first switch tube to be turned on and the second switch tube to be turned off; At the second moment, controlling the first switch tube to turn off; At a third moment, the second switch tube is controlled to be turned on, and the integral value of the resonant cavity current in a period between the second moment and the third moment is a first integral threshold; In which, the resonant cavity current is the resonant cavity current between the output end of the primary bridge arm and the primary side of the transformer, or the resonant cavity current between the secondary side of the transformer and the input end of the secondary bridge arm; at the third moment, the voltage across the second switching tube is less than the first voltage threshold.

2. The power conversion device according to claim 1, characterized in that: The controller includes: a current sampling circuit, an integration circuit and a control circuit; The current sampling circuit is used to sample the resonant cavity current and output it to the integration circuit; The control circuit is used to control the integration circuit to integrate the resonant cavity current after the second moment, and to control the second switch tube to be turned on at the third moment based on the integration value output by the integration circuit as the first integration threshold.

3. The power conversion device according to claim 2, characterized in that: The integration circuit includes: an operational amplifier, a first resistor, a second resistor, an integration capacitor and a switch; The inverting input terminal of the operational amplifier is used to receive the resonant cavity current output by the current sampling circuit through the first resistor, the non-inverting input terminal of the operational amplifier is used to receive the reference voltage through the second resistor, and the output terminal of the operational amplifier is connected to the control circuit and is used to output the integrated value; The integrating capacitor is connected between the inverting input terminal and the output terminal of the operational amplifier, and the switch is connected in parallel with the integrating capacitor; The control circuit is configured to control the switch to be turned off during a period between the second moment and the third moment, and to control the switch to be turned on before the second moment and after the third moment.

4. The power conversion device according to claim 3, characterized in that: The control circuit is configured to output a switch control signal to the switch, wherein the switch control signal is at a low level during a period between the second moment and the third moment, and is at a high level before the second moment and after the third moment; The switch is configured to be turned off under the control of the switch control signal at a low level, and to be turned on under the control of the switch control signal at a high level.

5. The power conversion device according to any one of claims 2 to 4, characterized in that: The power conversion device further includes: an inductive device connected between the secondary side of the transformer and the input end of the secondary side bridge arm; The current sampling circuit is used to sample the resonant cavity current flowing through the inductive device.

6. The power conversion device according to any one of claims 1 to 5, characterized in that: The controller is also used for: At a fourth moment, controlling the second switch tube to turn off; At a fifth moment, the first switch tube is controlled to be turned on, and an integral value of the resonant cavity current in a period between the fourth moment and the fifth moment is a second integral threshold; Wherein, at the fifth moment, the voltage across the first switch tube is less than the second voltage threshold.

7. The power conversion device according to claim 6, characterized in that: The controller is used to integrate the resonant cavity current in different time periods through the same integration circuit.

8. The power conversion device according to claim 6 or 7, characterized in that: The controller is used to: Based on the switching signal changing from a high level to a low level at the second moment, controlling the first switching tube to turn off; Based on the switching signal changing from a low level to a high level at the fourth moment, controlling the second switching tube to turn off; The switching signal is a square wave signal, the frequency of the square wave signal is the switching frequency of the switch tube in the primary bridge arm, and the duty cycle of the square wave signal is one half.

9. A control method for a power conversion device, characterized in that: The method comprises: At a first moment, controlling the first switch tube in the primary bridge arm to be turned on and the second switch tube to be turned off, wherein the power conversion device comprises: the primary bridge arm, a transformer, and a secondary bridge arm, the primary bridge arm being connected to the secondary bridge arm via the transformer, and the first switch tube and the second switch tube being connected in series between the positive electrode and the negative electrode of the input end of the primary bridge arm; At the second moment, controlling the first switch tube to turn off; At a third moment, the second switch tube is controlled to be turned on, and the integral value of the resonant cavity current in a period between the second moment and the third moment is a first integral threshold; In which, the resonant cavity current is the resonant cavity current between the output end of the primary bridge arm and the primary side of the transformer, or the resonant cavity current between the secondary side of the transformer and the input end of the secondary bridge arm; at the third moment, the voltage across the second switching tube is less than the first voltage threshold.

10. The method according to claim 9, characterized in that The method further comprises: At a fourth moment, controlling the second switch tube to turn off; At a fifth moment, the first switch tube is controlled to be turned on, and an integral value of the resonant cavity current in a period between the fourth moment and the fifth moment is a second integral threshold; Wherein, at the fifth moment, the voltage across the first switch tube is less than the second voltage threshold.

11. The method according to claim 10, characterized in that At the second moment, controlling the first switch tube to turn off includes: controlling the first switch tube to turn off based on the switch signal jumping from a high level to a low level at the second moment; At the fourth moment, controlling the second switch tube to turn off includes: controlling the second switch tube to turn off based on the switch signal jumping from a low level to a high level at the fourth moment; The switching signal is a square wave signal, the frequency of the square wave signal is the switching frequency of the switch tube in the primary bridge arm, and the duty cycle of the square wave signal is one half.

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