Voltage discharge method of energy storage converter, signal conversion device and energy storage system

Abstract

The invention discloses a voltage discharge method of an energy storage converter, a signal conversion device and an energy storage system.The voltage discharge method of the energy storage converter comprises the steps that when it is determined that the energy storage converter enters a turn-off shutdown state, a driving signal is provided for the energy storage converter so as to control the energy storage converter to be in an inversion state; the driving signal is a PWM signal formed by adding an initial alternating current signal and a common-mode alternating current signal. According to the technical scheme, the voltage discharge speed of the direct-current bus capacitor in the energy storage converter can be increased, and the safety of the energy storage converter is improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular, to a method for discharging the voltage of an energy storage converter, a signal conversion device, and an energy storage system. Background Art

[0002] In the current three-phase bridge power electronics conversion system, when the system shuts down, the DC bus capacitor still has a relatively high voltage. To avoid personal injury to equipment maintenance personnel caused by high voltage, it is necessary to discharge the voltage of the DC bus capacitor so that the voltage of the DC bus capacitor is discharged below the safe voltage within a certain period of time.

[0003] In the prior art, in order to discharge the capacitor voltage after the three-phase bridge power electronics conversion system shuts down, the following methods are usually adopted: ① Generally, a discharge circuit including a discharge resistor is connected in parallel at both ends of the DC bus capacitor. The more the number of discharge resistors, the faster the capacitor voltage discharge speed. However, the more the number of discharge resistors, the larger the occupied space, resulting in layout difficulties. ② Some operating loads in the conversion system can be electrically connected to both ends of the DC bus capacitor so that the operating loads consume the electrical energy in the bus capacitor, but there are no loads that can consume electrical energy in some conversion systems. ③ Using a cooling fan as a load to consume the electrical energy on the DC bus capacitor, but if the fan is used as a load for a long time, it will cause the fan to be fatigued and damaged. Therefore, how to improve the reliability of the electrical energy discharge of the DC bus capacitor has become an urgent technical problem to be solved currently. Summary of the Invention

[0004] The present invention provides a method for discharging the voltage of an energy storage converter, a signal conversion device, and an energy storage system to improve the voltage discharge speed of the DC bus capacitor in the energy storage system and improve the safety of the energy storage system.

[0005] In a first aspect, the present invention provides a method for discharging the voltage of an energy storage system, including:

[0006] Determining that the energy storage converter enters the shutdown state;

[0007] Providing a drive signal to the energy storage converter to control the energy storage converter to be in the inverter state; the drive signal is a PWM signal formed by adding an initial AC signal and a common-mode AC signal.

[0008] Optionally, the frequency of the initial AC signal is f1, and the frequency of the common-mode AC signal is f2;

[0009] Wherein, f1 ≤ f2 ≤ 320 * f1.

[0010] Optionally, the initial AC signal includes three-phase sine waves, and the common-mode AC signal includes square waves, sine waves, or sawtooth waves.

[0011] Optionally, the voltage amplitude of the initial AC signal is U0, and the voltage amplitude of the common-mode AC signal is U1;

[0012] wherein, 0.05*U0 ≤ U1 ≤ U0.

[0013] Optionally, after the energy storage converter enters the shutdown state, it further includes:

[0014] Obtain the first current voltage on the DC bus in the energy storage converter and the second current voltage on the AC side in the energy storage converter;

[0015] Judge whether the first current voltage is greater than the safety voltage and less than the first preset voltage, and whether the second current voltage is greater than the safety voltage and less than the second preset voltage;

[0016] If so, execute the step of providing a drive signal to the energy storage converter to control the energy storage converter to be in the inverter state.

[0017] Optionally, it further includes:

[0018] Obtain the first working voltage on the DC bus in the energy storage converter and the second working voltage on the AC side in the energy storage converter; the first working voltage is V01, the second working voltage is V02, the first preset voltage is V1, and the second preset voltage is V2;

[0019] wherein, V01*90% ≤ V1 ≤ V01*95%; V02*90% ≤ V2 ≤ V02*95%.

[0020] Optionally, the voltage discharge method further includes:

[0021] Real-time obtain the DC voltage on the DC bus in the energy storage converter;

[0022] Judge whether the DC voltage is less than or equal to the safety voltage;

[0023] If so, stop providing the drive signal to the energy storage converter.

[0024] Optionally, if the DC voltage is greater than the safety voltage, return to execute the step of providing the drive signal to the energy storage converter.

[0025] In a second aspect, the present invention provides a signal conversion device, including: an energy storage converter and a control module;

[0026] The control module is used to execute the voltage discharge method of the energy storage converter described in the first aspect.

[0027] In a third aspect, the present invention provides an energy storage system, comprising: an energy storage converter, a battery, a DC control switch, an AC control switch, and a control device;

[0028] The energy storage converter includes a DC bus and a common grid access terminal; the DC bus is electrically connected to the battery and the DC side of the energy storage converter respectively; the DC control switch is located on the DC bus;

[0029] The AC control switch is electrically connected to the common grid access terminal and the AC side of the energy storage converter respectively;

[0030] The energy storage converter includes a plurality of switch control terminals, and the control device includes a plurality of switch signal providing terminals arranged in one-to-one correspondence with each of the switch control terminals; each of the switch control terminals is electrically connected to each of the switch signal providing terminals;

[0031] The control device is also electrically connected to the DC control switch and the AC control switch, and the control device is used to obtain the current state of the energy storage converter; the current state includes a conducting working state and a shut-down state; if the current state is the shut-down state; then a driving signal is provided to the energy storage converter to control the energy storage converter to be in an inverter state; the driving signal is a PWM signal formed by adding an initial AC signal and a common-mode AC signal.

[0032] Optionally, the DC bus includes a positive DC bus, a negative DC bus, and a zero-potential DC bus.

[0033] Optionally, the frequency of the initial AC signal is f1, and the frequency of the common-mode AC signal is f2;

[0034] wherein, f1 ≤ f2 ≤ 320 * f1.

[0035] Optionally, the initial AC signal includes three-phase sine waves, and the common-mode AC signal includes square waves, sine waves, or sawtooth waves.

[0036] Optionally, the voltage amplitude of the initial AC signal is U0, and the voltage amplitude of the common-mode AC signal is U1;

[0037] wherein, 0.05 * U0 ≤ U1 ≤ U0.

[0038] Optionally, the control device is configured to: after the energy storage converter enters the shutdown state, obtain a first current voltage on the DC bus in the energy storage converter and a second current voltage on the AC side in the energy storage converter; if the first current voltage is greater than the safety voltage and less than a first preset voltage, and the second current voltage is greater than the safety voltage and less than a second preset voltage; then execute the step of providing a drive signal to the energy storage converter to control the energy storage converter to be in an inverter state.

[0039] Optionally, the control device is specifically configured to: before the current state is the shutdown state, obtain a first operating voltage on the DC bus in the energy storage converter and a second operating voltage on the AC side in the energy storage converter; the first operating voltage is V01, the second operating voltage is V02, the first preset voltage is V1, and the second preset voltage is V2;

[0040] wherein, V01*90% ≤ V1 ≤ V01*95%; V02*90% ≤ V2 ≤ V02*95%.

[0041] Optionally, the control device is configured to: continuously obtain the DC voltage on the DC bus in the energy storage converter; if the DC voltage is less than or equal to the safety voltage, stop providing the drive signal to the energy storage converter.

[0042] Optionally, the control device is specifically configured to: if the DC voltage is greater than the safety voltage, return to execute the step of providing the drive signal to the energy storage converter.

[0043] The technical solution provided by the present invention provides a drive signal to the energy storage converter when the current state of the energy storage converter is the shutdown state to control the energy storage converter to be in an inverter state, and the drive signal is a PWM signal formed by adding an initial AC signal and a common-mode AC signal. In this way, the conduction duration of the switching tube during the inversion process can be increased, thereby increasing the voltage discharge speed of the bus capacitor and improving the safety of the energy storage system. Description of the Drawings

[0044] Figure 1 is a schematic structural diagram of an energy storage system provided by an embodiment of the present invention;

[0045] Figure 2 is a schematic circuit diagram of an energy storage converter provided by an embodiment of the present invention;

[0046] Figure 3 is a flowchart of a method for discharging the voltage of an energy storage converter provided by an embodiment of the present invention;

[0047] Figure 4Schematic diagram of the original waveform of a driving signal provided by an embodiment of the present invention;

[0048] Figure 5 Another schematic diagram of the original waveform of a driving signal provided by an embodiment of the present invention;

[0049] Figure 6 Flowchart of another method for discharging the voltage of an energy storage converter provided by an embodiment of the present invention;

[0050] Figure 7 Flowchart of yet another method for discharging the voltage of an energy storage converter provided by an embodiment of the present invention;

[0051] Figure 8 Schematic diagram of the structure of an energy storage system provided by an embodiment of the present invention;

[0052] Figure 9 Schematic diagram of the structure of a control device provided by an embodiment of the present invention. Detailed implementation manners

[0053] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the sake of description, only parts related to the present invention are shown in the drawings, rather than all the structures.

[0054] Figure 1 Schematic diagram of the structure of an energy storage system provided by an embodiment of the present invention, as Figure 1 shown, the energy storage system includes a battery 10, a DC bus, a DC control switch K1, an energy storage converter 20, an AC control switch K3, and a common grid access terminal 31. The DC bus is electrically connected to the battery 10 and the DC side of the energy storage converter 20 respectively; the DC control switch K1 is located on the DC bus; the AC control switch K2 is electrically connected to the common grid access terminal 31 and the AC side of the energy storage converter 20 respectively. The energy storage converter 20 includes a first bus capacitor C1 and a second bus capacitor C2 electrically connected to the DC bus.

[0055] Among them, the DC control switch K1 and the AC control switch K3 include switching devices such as relays or circuit breakers. The energy storage converter 20 includes a three-level topology or a five-level topology, which can be set according to actual needs and will not be specifically limited here. Exemplarily, Figure 2 Schematic diagram of the circuit structure of an energy storage converter provided by an embodiment of the present invention, as Figure 2As shown, the energy storage converter 20 has a three-level topology structure. The DC bus includes a positive DC bus C+ and a negative DC bus C-. The first end of the first bus capacitor C1 is electrically connected to the positive DC bus C+, the first end of the second bus capacitor C2 is electrically connected to the negative DC bus C-, and the second end of the first bus capacitor C1 is electrically connected to the second end of the second bus capacitor C2. The three-level topology structure includes a filter 32 on the AC side of multiple switching tubes. The filter 32 consists of an inductor and a capacitor. The filter in the A-phase line is composed of the first inductor L1 and the third capacitor, the filter in the B-phase line is composed of the second inductor L2 and the fourth capacitor C4, and the filter in the C-phase line is composed of the third inductor L3 and the fifth capacitor C5.

[0056] Specifically, the battery 10 is used to store or release DC electrical signals. The common power grid access terminal 31 includes an A-phase access terminal, a B-phase access terminal, and a C-phase access terminal, and the common power grid access terminal 31 can be electrically connected to the common power grid. When both the DC control switch K1 and the AC control switch K2 are in the on state, and the common power grid charges the battery 10 through the common power grid access terminal 31 and the energy storage converter 20, the energy storage converter 20 is in the rectification working state. The energy storage converter 20 is used to convert the AC electrical signal at the common power grid access terminal into a DC electrical signal and store it in the battery 10. When it is necessary to convert the DC electrical signal in the battery 10 into an AC electrical signal and transmit it to the common power grid access terminal 31, the energy storage converter 20 is in the inversion working state. However, when the DC control switch K1 and the AC control switch K2 change from the on state to the off state, the electrical energy in the bus capacitors (C1 and C2) in the energy storage converter 20 cannot be released in time, which may lead to an electric shock risk and low safety. Therefore, the embodiment of the present invention provides a method for discharging the voltage of the DC bus capacitor, which is specifically described below.

[0057] Figure 3 The flowchart of a method for discharging the voltage of an energy storage converter provided by an embodiment of the present invention is applicable to the situation of discharging the voltage of the bus capacitor when the energy storage converter changes from the inversion state or the rectification state to the open circuit state. This method can be executed by the energy storage system provided by the embodiment of the present invention, and the energy storage system can be implemented in the form of hardware and / or software. As Figure 3 shown, the method for discharging the voltage of the DC bus capacitor in the energy storage system includes:

[0058] S101. Determine that the energy storage converter enters the shutdown and stop state.

[0059] Specifically, the state of the control switch for controlling the conduction or cutoff of the energy storage converter can be obtained to determine the current state of the energy storage converter. For example, the on / off state of the DC control switch can be obtained through the state output terminal of the DC control switch, and the on / off state of the AC control switch can be obtained through the state output terminal of the AC control switch. Among them, the DC control switch is used to control the on / off state of the electrical connection path between the energy storage converter and the DC energy storage device, and the AC control switch is used to control the on / off state of the electrical connection path between the energy storage converter and the AC device. A detection circuit capable of detecting the current state is provided inside the DC control switch and the AC control switch. If both the DC control switch and the AC control switch are in the off state, it indicates that the energy storage converter is in the off and shutdown state. If both the DC control switch and the AC control switch are in the on state, it indicates that the energy storage converter is in the on and working state.

[0060] When the energy storage converter is in the on and working state, it indicates that the energy storage converter is in the inverter or rectifier state, and at this time, there is no need to discharge the voltage of the bus capacitor. If the energy storage converter is in the off and shutdown state, it indicates that the electrical connection paths between the energy storage converter and the DC energy storage device and the AC device are disconnected, and the energy storage converter stops working. At this time, a relatively high voltage will remain in the bus capacitor, and the voltage of the bus capacitor needs to be released to prevent personal injury to maintenance personnel when repairing the energy storage converter at this time, and improve the maintenance safety of the energy storage converter.

[0061] S102. Provide a drive signal to the energy storage converter to control the energy storage converter to be in the inverter state.

[0062] Among them, the drive signal is a PWM signal formed by adding the initial AC signal and the common-mode AC signal. When the energy storage converter is in the inverter state, the control signal provided to the control terminal of the switching tube is the initial AC signal, which can be a sinusoidal AC signal. When the energy storage converter is in the inverter state, the switches in the energy storage converter alternately conduct or cutoff, thereby converting the DC power with constant magnitude and direction into AC power with magnitude and direction changing periodically with time.

[0063] It should be noted that the energy storage converter includes a three-level converter or a five-level converter. Refer to Figure 2 , when the energy storage converter is a three-level converter, the energy storage converter includes 3 bridge arms, each bridge arm includes 4 switching tubes, and includes 12 control terminals, namely Sa1, Sa2, Sa3, Sa4, Sb1, Sb2, Sb3, Sb4, Sc1, Sc2, Sc3, Sc4.

[0064] Specifically, drive signals can be provided to the control terminals of the switching transistors in the energy storage inverter, so that the switching transistors are turned on in a time-sharing manner under the action of the drive signals, and the energy storage inverter is in an inversion state, enabling the voltage on the bus capacitors (C1 and C2) to be transmitted to the AC side through the switching transistors. Since there are parasitic resistances inside the switching transistors, during the transmission of the voltage of the bus capacitors, it will be consumed in the switching transistors and the transmission lines, and then released. In addition, by superimposing a common-mode AC signal on the initial AC signal, the conduction duration of the switching transistors within one cycle is increased, the energy discharge speed is increased, and the safety of the energy storage inverter is improved.

[0065] In the technical solution of the embodiment of the present invention, when the current state of the energy storage inverter is the off and shutdown state, a drive signal is provided to the energy storage inverter to control the energy storage inverter to be in an inversion state, and the drive signal is a PWM signal formed by adding an initial AC signal and a common-mode AC signal. In this way, the conduction duration of the switching transistors during the inversion process can be increased, and further the voltage discharge speed of the bus capacitors can be increased, and the safety of the energy storage inverter can be improved.

[0066] In an optional embodiment, Figure 4 is a schematic diagram of the original waveform of a drive signal provided by an embodiment of the present invention. As Figure 4 shown, the initial AC signal includes three-phase sine waves, and the common-mode AC signal includes a square wave d; the frequency of the initial AC signal is f1, and the frequency of the common-mode AC signal is f2. Among them, f1 ≤ f2 ≤ 320 * f1.

[0067] Specifically, the initial AC signal includes a0-phase sine AC signal, b0-phase sine AC signal, and c0-phase sine AC signal, and the phases of the a0-phase sine AC signal, b0-phase sine AC signal, and c0-phase sine AC signal differ by 120° respectively. When the frequency f2 of the common-mode AC signal is equal to the frequency f1 of the initial AC signal, the waveform after adding the a0-phase sine AC signal and the square wave d in the initial AC signal is waveform a1, the waveform after adding the b0-phase sine AC signal and the square wave d is waveform b1, and the waveform after adding the c0-phase sine AC signal and the square wave d is waveform c1. The PWM waves corresponding to waveform a1, waveform b1, and waveform c1 are the waveforms of the drive signal. Since the amplitudes of waveform a1, waveform b1, and waveform c1 after adding the common-mode AC signal increase, the conduction pulse widths of the corresponding PWM waves also increase. When the PWM waves are applied to the control terminals of the switching transistors, the conduction duration of the switching transistors can be increased. Refer to Figure 2 and Figure 4, during the positive half - cycle of waveform a1, the conduction time of some switching tubes related to the discharge of the first bus capacitor C1 increases, such that the voltage released by the first bus capacitor C1 is greater than the voltage released by the second bus capacitor C2, which is equivalent to the first bus capacitor C1 transferring energy to the second bus capacitor C2. During the negative half - cycle of waveform a1, the conduction time of some switching tubes related to the discharge of the second bus capacitor C2 increases, such that the voltage released by the second bus capacitor C2 is greater than the voltage released by the first bus capacitor, which is equivalent to the second bus capacitor C2 transferring energy to the first bus capacitor C1. Thus, by setting the common - mode AC signal to change between positive and negative signals, the voltage on the DC bus is repeatedly transferred between the first bus capacitor C1 and the second bus capacitor C2. During the transfer process, the electrical signal will generate losses on the transmission line and the parasitic resistance of the switching tubes, thereby enabling the release of energy, and the voltage will also be consumed on the bus capacitor and the capacitor in the AC filter 32 to increase the voltage discharge speed of the DC bus capacitor and improve the safety of the energy storage converter.

[0068] It should be noted that the above is only described by taking the common - mode AC signal as a square wave as an example. In other alternative embodiments, the common - mode AC signal can also be a sine wave, a sawtooth wave, etc., which can be set according to actual needs and will not be specifically limited here.

[0069] It can be understood that the above is only described by taking the frequency f2 of the common - mode AC signal equal to the frequency f1 of the initial AC signal as an example. Based on the fact that the frequency f2 of the common - mode AC signal is greater than the frequency f1 of the initial AC signal and less than or equal to 320 times the frequency f1 of the initial AC signal, the frequency f2 of the common - mode AC signal can also be other values, which will not be specifically limited here. Figure 5 The original waveform schematic diagram of another driving signal provided by the embodiment of the present invention is as Figure 5 shown. The frequency f2 of the common - mode AC signal can also be 3 times the frequency f1 of the initial AC signal. By increasing the frequency f2 of the common - mode AC signal, the transfer efficiency of the voltage between the first bus capacitor C1 and the second bus capacitor C2 can be improved, enabling the energy to be transferred multiple times in the transmission line, that is, consumed multiple times, thereby increasing the voltage discharge speed.

[0070] It should be noted that by setting the frequency f2 of the common-mode AC signal to be greater than or equal to the frequency f1 of the initial AC signal, the voltage release states of the first bus capacitor C1 and the second bus capacitor C2 can be frequently switched, accelerating the voltage discharge speed of the bus capacitors. However, if the frequency f2 of the common-mode AC signal is greater than 320*f1, the voltage imbalance between the first bus capacitor C1 and the second bus capacitor C2 will increase, which is likely to damage the bus capacitors or accelerate the aging speed of the bus capacitors. Therefore, the frequency f2 of the common-mode AC signal is set between f1 and 320*f1 to ensure the reliability of the bus capacitors while increasing the voltage discharge speed of the bus capacitors.

[0071] In an optional embodiment, the voltage amplitude of the initial AC signal is U0, and the voltage amplitude of the common-mode AC signal is U1; where 0.05*U0 ≤ U1 ≤ U0.

[0072] Specifically, if the voltage amplitude U1 of the common-mode AC signal is less than 0.05*U0, it will cause the conduction time of the switching tube related to the discharge of the first bus capacitor to increase when the first bus capacitor discharges, but the increased time is short, resulting in less energy transferred from the first bus capacitor to the second bus capacitor; and when the second bus capacitor discharges, the conduction time of the switching tube related to the discharge of the second bus capacitor increases, but the increased time is short, thus resulting in less energy transferred from the second bus capacitor to the first bus capacitor, making the voltage release on the bus capacitors take a long time and the discharge speed slow. If the voltage amplitude U1 of the common-mode AC signal is greater than U0, it will cause the voltage transfer amount between the first bus capacitor and the second bus capacitor to increase, and the voltage imbalance between the first bus capacitor and the second bus capacitor to increase, reducing the service life of the switching tube. Therefore, setting the voltage amplitude U1 of the common-mode AC signal between 0.05*U0 and U0 can increase the voltage discharge speed of the bus capacitors and improve the reliability and service life of the energy storage converter at the same time.

[0073] It can be understood that based on the voltage amplitude U1 of the common-mode AC signal being between 0.05*U0 and U0, the voltage amplitude U1 of the common-mode AC signal can be set according to actual needs. In a preferred embodiment, U1 = 0.2*U0, and it can also be other values, which are not specifically limited here.

[0074] Optionally, Figure 6 is a flowchart of another voltage discharge method for the energy storage converter provided by the embodiment of the present invention. As Figure 6 shown, this voltage discharge method further includes:

[0075] S201. Obtain the current state of the energy storage converter.

[0076] Wherein, the current state includes a conducting working state and a turned-off shutdown state.

[0077] S202. Determine whether the current state is the off state; if so, execute S203.

[0078] S203. Obtain the first current voltage on the DC bus in the energy storage converter and the second current voltage on the AC side of the energy storage converter.

[0079] Among them, refer to Figure 1 or Figure 2 , the DC bus includes the positive DC bus C+ and the negative DC bus C-, and the first current voltage on the DC bus refers to the current voltage between the positive DC bus C+ and the negative DC bus C-. The second current voltage on the AC side refers to the current voltage amplitude of the three-phase electrical signals in the common power grid access terminal 31.

[0080] Specifically, the first current voltage on the DC bus can be obtained through a DC sampling circuit electrically connected to the DC bus, and the second current voltage on the AC side can be obtained through an AC sampling circuit electrically connected to the common power grid access terminal. The manner of obtaining the first current voltage on the DC bus and the second current voltage on the AC side can also be other, which is not specifically limited here.

[0081] S204. Determine whether the first current voltage is greater than the safety voltage and less than the first preset voltage, and whether the second current voltage is greater than the safety voltage and less than the second preset voltage; if so, execute S205.

[0082] Among them, the safety voltage, the first preset voltage, and the second preset voltage can be fixed values or non-fixed values, and can be determined according to actual needs. Exemplarily, the safety voltage is 36V, the first preset voltage is 950V, and the second preset voltage is 660V. It can also be other, which is not specifically limited here.

[0083] Specifically, if the first current voltage is less than the first preset voltage and the second current voltage is less than the second preset voltage, it indicates that the DC control switch and the AC control switch have been in the off state, and the energy storage converter stops working. Therefore, the first current voltage and the second current voltage will decrease.

[0084] Optionally, the first preset voltage and the second preset voltage can be determined based on the working voltages of the DC bus and the AC side. Specifically, it can include obtaining the first working voltage on the DC bus and the second working voltage on the AC side; the first working voltage is V01, the second working voltage is V02, the first preset voltage is V1, and the second preset voltage is V2; among them, V01*90% ≤ V1 ≤ V01*95%; V02*90% ≤ V2 ≤ V02*95%.

[0085] Specifically, before the energy storage converter enters the shutdown state, that is, when the energy storage converter is in the conducting working state, the energy storage converter may be in the rectification state or the inversion state. There is a relatively large first working voltage V01 on the DC bus, and a relatively large second working voltage V02 on the AC side. After the current states of the DC control switch and the AC control switch are converted from the conducting state to the off state, the voltage signals on the DC bus and the AC side will decrease, so that the voltage signal on the DC bus is less than the first working voltage V1, and the voltage signal on the AC side is also less than the second working voltage V2. By setting the range of the first preset voltage V1 to be 90% - 95% of V01, and the range of the second preset voltage V2 to be 90% - 95% of V02, when the first current voltage is greater than the safety voltage and less than the first preset voltage V1, and the second current voltage is greater than the safety voltage and less than the second preset voltage V2, it can be determined that the voltage signals on the DC bus and the AC side are decreasing, but the voltage values are relatively high, and the voltage in the energy storage converter needs to be discharged to improve the safety of the energy storage converter.

[0086] S205. Provide a drive signal to the energy storage converter to control the energy storage converter to be in the inversion state.

[0087] Wherein, the drive signal is the sum value of the initial AC signal and the common-mode AC signal.

[0088] The technical solution of the embodiment of the present invention, by obtaining the first current voltage on the DC bus and the second current voltage on the AC side when the current states of the energy storage converter are both off states, and determining that the energy storage converter is indeed in the off state when the first current voltage is less than the first preset voltage and the second current voltage is less than the second preset voltage, improves the reliability of the state judgment of the energy storage converter and the reliability of the voltage discharge of the DC bus capacitor, and avoids discharging the voltage of the DC bus capacitor when the energy storage converter is in the working state, thereby affecting the working stability of the DC / AC bidirectional converter.

[0089] In an optional embodiment, the embodiment of the present invention describes the situation after providing a drive signal to the energy storage converter. Figure 7 It is a flowchart of another voltage discharge method for the energy storage converter provided by the embodiment of the present invention. As Figure 7 shown, the voltage discharge method includes:

[0090] S301. Determine that the energy storage converter enters the shutdown state.

[0091] S302. Provide a drive signal to the energy storage converter to control the energy storage converter to be in the inversion state.

[0092] Among them, the drive signal is the sum value of the initial AC signal and the common-mode AC signal.

[0093] S303. Obtain the DC voltage on the DC bus in the energy storage converter in real time.

[0094] Among them, the reference Figure 1 or Figure 2 , the DC bus includes the positive DC bus C+ and the negative DC bus C-, and the DC voltage on the DC bus refers to the voltage between the positive DC bus C+ and the negative DC bus C-.

[0095] Specifically, the first current voltage on the DC bus can be obtained through a DC sampling circuit electrically connected to the DC bus. The method for obtaining the DC voltage on the DC bus can also be other, which is not specifically limited here.

[0096] S304. Determine whether the DC voltage is less than or equal to the safety voltage; if so, execute S305; if not, return to execute S302.

[0097] Among them, the safety voltage refers to the maximum voltage value that can avoid harm to the human body by the energy storage converter.

[0098] Specifically, after providing the drive signal to the energy storage converter to control the energy storage converter in the inverter state, the voltage on the DC bus can be discharged through the current-limiting resistor and the transmission line in the energy storage converter, so the voltage on the DC bus continues to drop. By obtaining the DC voltage on the DC bus in real time, when the DC voltage is greater than the safety voltage, the drive signal is continuously provided to the energy storage converter to make the DC voltage continue to drop until the DC voltage is less than the safety voltage, indicating that the DC voltage has reached the safety standard. At this time, the drive signal to the energy storage converter can be stopped, and the discharge process of the bus capacitor ends.

[0099] S305. Stop providing the drive signal to the energy storage converter.

[0100] The technical solution of the embodiment of the present invention, by obtaining the current state of the energy storage converter, when the current state of the energy storage converter is the shutdown state, providing a drive signal to the energy storage converter to control the energy storage converter in the inverter state, so that the voltage of the DC bus capacitor continues to discharge, and at the same time, obtaining the DC voltage on the DC bus in real time, so that when the DC voltage is less than or equal to the safety voltage, the drive signal to the energy storage converter is stopped, and the discharge process of the DC bus capacitor ends, reducing the working time of the energy storage converter and improving the service life of the internal components of the energy storage converter.

[0101] Based on the same inventive concept, the present invention also provides a signal conversion device, including an energy storage converter and a control module. The control module is used to execute the voltage discharge method of the energy storage converter provided in any embodiment of the present invention, and has the same beneficial effects as the executed method. Reference can be made to the above description and will not be elaborated here.

[0102] Figure 8 FIG. is a schematic structural diagram of an energy storage system provided by an embodiment of the present invention, as Figure 8 shown. The energy storage system includes an energy storage converter 20, a battery 10, a DC control switch K1, an AC control switch K3, a public grid access terminal 31, and a control device 40. The energy storage converter 20 includes a DC bus 11. The DC bus 11 is electrically connected to the battery 10 and the DC side of the energy storage converter 20 respectively; the DC control switch K1 is located on the DC bus 11; the AC control switch K2 is electrically connected to the public grid access terminal 31 and the AC side of the energy storage converter 20 respectively; the energy storage converter 20 includes a plurality of switch control terminals S, and the control device 40 includes a plurality of switch signal providing terminals T arranged in one-to-one correspondence with each switch control terminal S; each switch control terminal S is electrically connected to each switch signal providing terminal T.

[0103] Optionally, the DC bus includes a positive DC bus C+, a negative DC bus C−, and a zero-potential DC bus C0, so that there are at least three power-offs on the DC bus of the energy storage converter to meet the connection requirements of multi-level ports.

[0104] Among them, the control device 40 is also electrically connected to the DC control switch K1 and the AC control switch K2. The control device 40 is used to obtain the current state of the energy storage converter 20; the current state includes a conducting working state and a shut-down state; if the current state is the shut-down state, a driving signal is provided to the energy storage converter to control the energy storage converter to be in an inverter state; the driving signal is a PWM signal formed by adding an initial AC signal and a common-mode AC signal.

[0105] Optionally, the initial AC signal includes three-phase sine waves, and the common-mode AC signal includes square waves, sine waves, or sawtooth waves. The frequency of the initial AC signal is f1, and the frequency of the common-mode AC signal is f2; where f1 ≤ f2 ≤ 320*f1.

[0106] Optionally, the voltage amplitude of the initial AC signal is U0, and the voltage amplitude of the common-mode AC signal is U1; where 0.05*U0 ≤ U1 ≤ U0.

[0107] Optionally, the control device 40 is configured to: after the current state is the off state, obtain the first current voltage on the DC bus in the energy storage converter and the second current voltage on the AC side in the energy storage converter; if the first current voltage is greater than the safety voltage and less than the first preset voltage, and the second current voltage is greater than the safety voltage and less than the second preset voltage; then perform the step of providing a drive signal to the energy storage converter to control the energy storage converter to be in the inversion state.

[0108] Optionally, the control device 40 is specifically configured to: before the current state is the off state, obtain the first working voltage on the DC bus in the energy storage converter and the second working voltage on the AC side in the energy storage converter; the first working voltage is V01, the second working voltage is V02, the first preset voltage is V1, and the second preset voltage is V2; wherein, 90%×V01 ≤ V1 ≤ 95%×V01; 90%×V02 ≤ V2 ≤ 95%×V02.

[0109] Optionally, the control device 40 is configured to: obtain the DC voltage on the DC bus in the energy storage converter in real time; if the DC voltage is less than or equal to the safety voltage, stop providing the drive signal to the energy storage converter.

[0110] Optionally, the control device 40 is specifically configured to: if the DC voltage is greater than the safety voltage, return to execute the step of providing the drive signal to the energy storage converter.

[0111] The execution function of the control device 40 has the same beneficial effects as the method for discharging the voltage of the DC bus capacitor in the energy storage converter provided by the present invention, and the same parts can be referred to the above description.

[0112] Specifically, Figure 9 is a schematic structural diagram of a control device provided by an embodiment of the present invention. As Figure 9 shown, the control device 40 includes a DQ / ABC transformation module 44, a common-mode AC signal providing module 45, and a PWM modulation module 46. By providing the initial modulation wave amplitude and modulation wave phase to the DQ / ABC transformation module 44, the DQ / ABC transformation module 44 outputs three-phase initial AC signals, including Vmod_a, Vmod_b, and Vmod_c. The phases of the three-phase electrical signals are 120° different from each other. The common-mode AC signal Vcom provided by the common-mode AC signal providing module 45 includes a square wave signal. The signals obtained by superimposing the three-phase initial AC signals and the common-mode AC signal Vcom are input into the PWM modulation module 45, so that the PWM modulation module 45 outputs corresponding PWM control signals to the switch signal providing end T according to the input three-phase electrical signals.

[0113] Note that the above is only a preferred embodiment of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein. Various obvious changes, re-adjustments, combinations with each other, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, it may also include more other equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A voltage discharge method for an energy storage converter, characterized in that Comprising: Determine that the energy storage converter enters the shutdown state; Provide a drive signal to the energy storage converter to control the energy storage converter to be in the inverter state; The drive signal is a PWM signal formed by adding an initial AC signal and a common-mode AC signal.

2. The voltage discharge method according to claim 1, characterized in that, The frequency of the initial AC signal is f1, and the frequency of the common-mode AC signal is f2; Wherein, f1 ≤ f2 ≤ 320 * f1.

3. The voltage discharge method according to claim 1, wherein The initial AC signal includes three-phase sine waves, and the common-mode AC signal includes square waves, sine waves or sawtooth waves.

4. The voltage discharge method according to claim 2, characterized in that, The voltage amplitude of the initial AC signal is U0, and the voltage amplitude of the common-mode AC signal is U1; Wherein, 0.05 * U0 ≤ U1 ≤ U0.

5. The voltage discharging method according to claim 1, wherein After the energy storage converter enters the shutdown state, it further includes: Obtain the first current voltage on the DC bus in the energy storage converter and the second current voltage on the AC side in the energy storage converter; Judge whether the first current voltage is greater than the safety voltage and less than the first preset voltage, and whether the second current voltage is greater than the safety voltage and less than the second preset voltage; If so, execute the step of providing a drive signal to the energy storage converter to control the energy storage converter to be in the inverter state.

6. The voltage discharge method according to claim 5, characterized in that, It further includes: Obtain the first working voltage on the DC bus in the energy storage converter and the second working voltage on the AC side in the energy storage converter; the first working voltage is V01, the second working voltage is V02, the first preset voltage is V1, and the second preset voltage is V2; Wherein, V01 * 90% ≤ V1 ≤ V01 * 95%; V02 * 90% ≤ V2 ≤ V02 * 95%.

7. The voltage discharging method according to claim 1, characterized in that, It further includes: Real-time obtain the DC voltage on the DC bus in the energy storage converter; Judge whether the DC voltage is less than or equal to the safety voltage; If so, stop providing the drive signal to the energy storage converter.

8. The voltage discharge method according to claim 7, characterized in that, If the DC voltage is greater than the safety voltage, return to execute the step of providing the drive signal to the energy storage converter.

9. A signal conversion device, characterized in that, Comprising: An energy storage converter and a control module; The control module is used to execute the voltage discharge method of the energy storage converter according to any one of claims 1-8.

10. An energy storage system, characterized in that, Comprising: An energy storage converter, a battery, a DC control switch, an AC control switch, a common power grid access terminal and a control device; The energy storage converter includes a DC bus; the DC bus is electrically connected to the battery and the DC side of the energy storage converter respectively; the DC control switch is located on the DC bus; The AC control switch is electrically connected to the common power grid access terminal and the AC side of the energy storage converter respectively; The energy storage converter includes a plurality of switch control terminals, and the control device includes a plurality of switch signal providing terminals arranged in one-to-one correspondence with each of the switch control terminals; each of the switch control terminals is electrically connected to each of the switch signal providing terminals; The control device is also electrically connected to the DC control switch and the AC control switch. The control device is used to obtain the current state of the energy storage converter; the current state includes a conducting working state and a shut-down state; if the current state is the shut-down state, a driving signal is provided to the energy storage converter to control the energy storage converter to be in an inversion state; the driving signal is a PWM signal formed by adding an initial AC signal and a common-mode AC signal.

11. The energy storage system according to claim 10, wherein, The DC bus includes a positive DC bus, a negative DC bus, and a zero-potential DC bus.

12. The energy storage system according to claim 10, wherein The frequency of the initial AC signal is f1, and the frequency of the common-mode AC signal is f2; where f1 ≤ f2 ≤ 320 * f1.

13. The energy storage system according to claim 10, characterized in that, The initial AC signal includes three-phase sine waves, and the common-mode AC signal includes square waves, sine waves, or sawtooth waves.

14. The energy storage system according to claim 12, characterized in that, The voltage amplitude of the initial AC signal is U0, and the voltage amplitude of the common-mode AC signal is U1; where 0.05 * U0 ≤ U1 ≤ U0.

15. The energy storage system according to claim 10, wherein The control device is configured to: after the energy storage converter enters the shut-down state, obtain the first current voltage on the DC bus in the energy storage converter and the second current voltage on the AC side in the energy storage converter; if the first current voltage is greater than the safety voltage and less than the first preset voltage, and the second current voltage is greater than the safety voltage and less than the second preset voltage, then execute the step of providing a driving signal to the energy storage converter to control the energy storage converter to be in an inversion state.

16. The energy storage system according to claim 15, characterized in that, The control device is specifically configured to: before the current state is the off state, obtain the first working voltage on the DC bus in the energy storage converter and the second working voltage on the AC side in the energy storage converter; the first working voltage is V01, the second working voltage is V02, the first preset voltage is V1, and the second preset voltage is V2; where 90% * V01 ≤ V1 ≤ 95% * V01; 90% * V02 ≤ V2 ≤ 95% * V02.

17. The energy storage system according to claim 10, wherein, The control device is configured to: continuously obtain the DC voltage on the DC bus in the energy storage converter; if the DC voltage is less than or equal to the safety voltage, stop providing the driving signal to the energy storage converter.

18. The energy storage system according to claim 17, wherein The control device is specifically configured to: if the DC voltage is greater than the safety voltage, return to execute the step of providing the driving signal to the energy storage converter.

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