Permanent magnet brushless motor driving system having auxiliary charging and discharging circuit

Abstract

A motor driving system for a permanent magnet brushless motor, comprising: a pair of direct-current buses, having input ends connected to a single-phase alternating-current power supply by means of a rectification circuit, and output ends connected to a three-phase winding of the permanent magnet brushless motor by means of an inverter circuit; a direct-current bus capacitor provided between the pair of direct-current buses; and an auxiliary charging and discharging circuit arranged between the pair of direct-current buses alongside the direct-current bus capacitor. The auxiliary charging and discharging circuit comprises: a first branch and a second branch which are connected between the pair of direct-current buses, and an intermediate bridging branch connected between the first branch and the second branch; and a first capacitor and a first diode provided in the first branch, and a second capacitor and a second diode provided in the second branch. The auxiliary charging and discharging circuit has an auxiliary charging mode and an auxiliary discharging mode.

Description

Permanent magnet brushless motor drive system with auxiliary charging and discharging circuit Technical Field

[0001] This application relates to a drive system for a single-phase AC input permanent magnet brushless motor, which is equipped with an auxiliary charging and discharging circuit. Background Technology

[0002] Power tools using single-phase AC input to drive permanent magnet brushless motors are becoming increasingly common in the market. To meet harmonic requirements, most power tool drive systems use small DC bus capacitors. These small DC bus capacitors can lead to overvoltage problems. For example, when the mains voltage is unstable, the power tool lacks voltage spike suppression capabilities, causing electronic components to fail due to overvoltage after prolonged operation. In applications using generators as power sources, the voltage rises too quickly, leading to frequent overvoltage shutdowns. Furthermore, electronic components are prone to overvoltage failure during surge testing.

[0003] Summary of the Invention

[0004] This application aims to provide a drive system for a permanent magnet brushless motor with improved overvoltage suppression capability.

[0005] In one aspect, this application provides a motor drive system for a permanent magnet brushless motor, comprising:

[0006] A pair of DC buses, including a positive bus and a negative bus, wherein the input end of the pair of DC buses is connected to a single-phase AC power supply via a rectifier circuit, and the output end is connected to the three-phase winding of the permanent magnet brushless motor via an inverter circuit;

[0007] A DC bus capacitor disposed between the pair of DC buses; and

[0008] An auxiliary charging and discharging circuit is arranged parallel to the DC bus capacitor between the pair of DC buses, the auxiliary charging and discharging circuit comprising:

[0009] A first branch and a second branch connected between the positive busbar and the negative busbar, and an intermediate cross path connected between the first branch and the second branch; a first capacitor and a first diode disposed in the first branch, and a second capacitor and a second diode disposed in the second branch;

[0010] The auxiliary charging and discharging circuit has an auxiliary charging mode and an auxiliary discharging mode.

[0011] In the auxiliary charging mode, the auxiliary charging and discharging circuit constitutes an auxiliary charging circuit, wherein the first capacitor and the second capacitor are charged in series through the intermediate cross circuit.

[0012] In the auxiliary discharge mode, the auxiliary charging and discharging circuit constitutes an auxiliary discharge circuit, wherein the first capacitor discharges in parallel through the first diode and the second capacitor discharges in parallel through the second diode.

[0013] In one embodiment, when the DC bus voltage is higher than the sum of the voltages of the first capacitor and the second capacitor, the auxiliary charging and discharging circuit is in an auxiliary charging mode, which charges the first capacitor and the second capacitor until the sum of the voltages of the first capacitor and the second capacitor equals the DC bus voltage.

[0014] In one embodiment, during the power-on process of the drive system, the auxiliary charging and discharging circuit is in auxiliary charging mode, which charges the first capacitor and the second capacitor until the sum of the voltages of the first capacitor and the second capacitor equals the peak voltage of the input voltage input from the single-phase AC power supply through the rectifier circuit.

[0015] In one embodiment, after the drive system is powered on, the auxiliary charging and discharging circuit enters a silent state, wherein the pair of DC buses are charged and discharged only through the DC bus capacitor, the DC bus power supply is maintained at a voltage higher than that of the first capacitor and the second capacitor respectively, and the first capacitor and the second capacitor do not charge or discharge.

[0016] In one embodiment, when the DC bus voltage is lower than the voltage of the first capacitor and / or the second capacitor, the auxiliary charging and discharging circuit is in auxiliary discharging mode, causing the first capacitor and / or the second capacitor to discharge until the voltage of the first capacitor and / or the second capacitor is equal to the DC bus voltage.

[0017] In one embodiment, when the input voltage from the single-phase AC power supply is higher than the rated voltage, and the DC bus voltage is higher than the sum of the voltages of the first capacitor and the second capacitor and further increases, the auxiliary charging and discharging circuit enters the auxiliary charging mode, so that the first capacitor and the second capacitor are charged until the DC bus voltage reaches the voltage peak value, and the sum of the voltages of the first capacitor and the second capacitor is equal to the voltage peak value.

[0018] In one embodiment, when the DC bus voltage reaches its peak value and begins to decrease, the first capacitor and the second capacitor do not discharge and maintain their respective power supplies unchanged; then, when the DC bus voltage drops to the voltage of the first capacitor and / or the second capacitor and further decreases, the auxiliary charging and discharging circuit enters the auxiliary discharging mode, causing the first capacitor and / or the second capacitor to discharge.

[0019] In one embodiment, in the first branch, one end of the first capacitor is electrically connected to the positive busbar and the other end is electrically connected to the negative terminal of the first diode, and the positive terminal of the first diode is electrically connected to the negative busbar; in the second branch, one end of the second capacitor is electrically connected to the negative busbar and the other end is electrically connected to the positive terminal of the second diode, and the negative terminal of the second diode is electrically connected to the positive busbar.

[0020] In one embodiment, one end of the intermediate horizontal path is electrically connected to the first branch between the first capacitor and the first diode, and the other end is electrically connected to the second branch between the second capacitor and the second diode; a third diode is provided in the intermediate horizontal path, and the third diode is oriented to allow electrical energy to flow only from the first branch to the second branch and prevent reverse flow.

[0021] In one embodiment, the rated capacitances of the first capacitor and the second capacitor are equal.

[0022] In one embodiment, the rated capacitance of the DC bus capacitor is 30uF or less; the rated capacitance of the first capacitor and the second capacitor is more than three times the rated capacitance of the DC bus capacitor.

[0023] This application further relates to a power tool, including: a permanent magnet brushless motor; and a motor drive system configured to be connected to a single-phase AC power supply to power the permanent magnet brushless motor.

[0024] The single-phase AC power source can be the power grid or a generator, such as a diesel generator. The power tool may include a diesel generator as a single-phase AC power source.

[0025] According to this application, in the drive system of a permanent magnet brushless motor, an auxiliary charging and discharging circuit is added to the original DC bus capacitor, which improves the overvoltage suppression capability of the motor drive system, making it less prone to overvoltage failure and frequent overvoltage shutdown of equipment using the brushless motor and drive system, such as power tools. Attached Figure Description

[0026] Figure 1 is a circuit diagram of a drive system for a permanent magnet brushless motor according to one embodiment of this application;

[0027] Figure 2 shows the current situation in the charging mode of the auxiliary charging and discharging circuit of the drive system of this application;

[0028] Figure 3 shows the current situation in the discharge mode of the auxiliary charging and discharging circuit of the drive system of this application;

[0029] Figure 4 is a schematic diagram of the DC bus voltage and the capacitor voltage in the auxiliary charging and discharging circuit of the drive system of this application in the quiescent state under normal voltage after charging.

[0030] Figure 5 is a schematic diagram of the DC bus voltage and the capacitor voltage in the auxiliary charging and discharging circuit of the drive system of this application when the input voltage peak is raised. Detailed Implementation

[0031] Some embodiments of this application are described below with reference to the accompanying drawings.

[0032] This application aims to provide a motor drive system for a permanent magnet brushless motor, wherein the brushless motor is powered by a single-phase AC power supply. This brushless motor and motor drive system are particularly suitable for power tools, and the motor drive system will be described below using an application in a power tool as an example. However, this motor drive system can also be applied to other devices employing permanent magnet brushless motors.

[0033] A feasible circuit structure for the motor drive system is shown in Figure 1.

[0034] As shown in Figure 1, the permanent magnet brushless motor EC has three-phase windings U, V, and W. The motor drive system of motor EC includes a pair of DC buses, namely the positive bus L1 and the negative bus L2. The pair of DC buses are connected to a single-phase AC power supply AC through a rectifier circuit. The rectifier circuit includes an H-bridge circuit composed of first to fourth rectifier diodes S1 to S4, wherein the two ends of the AC power supply AC are respectively connected between the first rectifier diode S1 and the second rectifier diode S2, and between the third rectifier diode S3 and the fourth rectifier diode S4. The positive bus L1 is connected between the first rectifier diode S1 and the third rectifier diode S3, and the negative bus L2 is connected between the second rectifier diode S2 and the fourth rectifier diode S4, so that the AC power of the AC power supply AC is supplied to the pair of DC power buses in the form of DC power through the rectifier circuit.

[0035] An inverter is installed between the pair of DC buses and the three-phase windings U, V, and W of the motor EC. Its inverter circuit includes six switching transistors (e.g., IGBTs or MOSFETs). The following description uses MOSFETs as an example. In the example shown, the inverter circuit includes first to sixth MOSFETs Q1 to Q6. First MOSFET Q1 and second MOSFET Q2 are connected in series between the positive bus L1 and the negative bus L2. Third MOSFET Q3 and fourth MOSFET Q4 are connected in series between the positive bus L1 and the negative bus L2. Fifth MOSFET Q5 and sixth MOSFET Q6 are also connected in series between the positive bus L1 and the negative bus L2. The U-phase winding is connected between the first MOSFET Q1 and second MOSFET Q2. The V-phase winding is connected between the third MOSFET Q3 and the fourth MOSFET Q4. The W-phase winding is connected between the fifth MOSFET Q5 and the sixth MOSFET Q6. By controlling the on / off state of the first to sixth MOS transistors Q1 to Q6, the power supply from the pair of DC buses to the three-phase windings U, V, and W is switched sequentially, so that in each power supply cycle of the motor, one winding of the three-phase winding is connected to the positive bus L1, one winding is connected to the negative bus L2, and the other winding remains open.

[0036] It is understood that the above-mentioned rectifier circuit and inverter circuit can adopt various other forms known in the art, and other electrical components, such as power transformers, filter components, etc., can also be set in the motor drive system.

[0037] A DC bus capacitor C0 is installed between the rectifier circuit and the inverter circuit, between the positive bus L1 and the negative bus L2. One end of the DC bus capacitor C0 is electrically connected to the positive bus L1, and the other end is electrically connected to the negative bus L2, used to suppress voltage spikes generated during motor operation. This DC bus capacitor C0 can be a metal film capacitor, or it can be composed of a metal film capacitor and an aluminum electrolytic capacitor connected in parallel. To meet harmonic requirements, the capacitance of the DC bus capacitor C0 is relatively small, and the rated capacitance is usually selected to be below 30uF.

[0038] Furthermore, an auxiliary charging / discharging circuit is provided between the rectifier circuit and the inverter circuit, between the positive bus L1 and the negative bus L2. This auxiliary charging / discharging circuit is connected in parallel with the DC bus capacitor C0 and includes a first branch and a second branch connected between the positive bus L1 and the negative bus L2, as well as an intermediate cross path connected between the first branch and the second branch. In the first branch, a first capacitor C1 and a first diode D1 are provided, wherein one end of the first capacitor C1 is electrically connected to the positive bus L1, and the other end is electrically connected to the negative terminal of the first diode D1, and the positive terminal of the first diode D1 is electrically connected to the negative bus L2. In the second branch, a second capacitor C2 and a second diode D2 are provided, wherein one end of the second capacitor C2 is electrically connected to the negative bus L2, and the other end is electrically connected to the positive terminal of the second diode D2, and the negative terminal of the second diode D2 is electrically connected to the positive bus L1. A third diode D3 is placed in the middle horizontal path. The positive terminal of the third diode D3 is electrically connected to the first branch connection point between the first capacitor C1 and the first diode D1 on the first branch, and the negative terminal of the third diode D3 is electrically connected to the second branch connection point between the second capacitor C2 and the second diode D2 on the second branch. The orientation of the third diode D3 defines the current direction in the auxiliary charging circuit, that is, it only allows electrical energy to flow from the first branch to the second branch, prevents reverse flow, and avoids reverse surge current.

[0039] The rated capacitance of the first capacitor C1 and the second capacitor C2 is greater than the capacitance of the DC bus capacitor C0, for example, more than three times the capacitance of the DC bus capacitor C0, to ensure sufficient auxiliary charging and discharging capability. In the embodiments described below, it is assumed that the rated capacitance of the first capacitor C1 and the second capacitor C2 are equal, for example, their respective rated capacitances are selected between 100uF and 400uF.

[0040] The auxiliary charging and discharging circuit can realize the auxiliary charging mode and auxiliary discharging mode of the control system.

[0041] The auxiliary charging mode is shown in Figure 2. A first capacitor C1 and a second capacitor C2 are connected in series between the positive bus L1 and the negative bus L2 to form an auxiliary charging circuit. In this circuit, a third diode D3, located between the first and second capacitors C1 and C2, only allows energy to flow from the first branch to the second branch. The first diode D1 is oriented to prevent energy from flowing directly from the positive bus L1 to the negative bus L2 via the first capacitor C1. Therefore, energy flowing from the positive bus L1 through the first capacitor C1 can only flow to the second branch via the third diode D3. In the second branch, because the voltage on the negative side of the second diode D2 is higher than the voltage on the positive side, energy cannot flow to the positive bus L1 via the second diode D2; it can only flow to the second capacitor C2, and then to the negative bus L2. In this way, the electrical energy received from the power supply AC via the rectifier circuit on the positive bus L1 flows to the negative bus L2 through the first capacitor C1, the second diode D2, and the second capacitor C2 in the auxiliary charging circuit, and then returns to the power supply AC via the rectifier circuit, forming a complete auxiliary charging loop, as shown by the dashed line in Figure 2, where the direction of current flow is indicated by arrows. The auxiliary charging mode helps stabilize the DC bus voltage, i.e., the voltage between the positive bus L1 and the negative bus L2, during system boost. The system boost can originate from the power supply, such as generator power; or it can originate from the reverse current flowing from the motor to the DC bus when the inverter switch is turned off.

[0042] The auxiliary discharge mode is shown in Figure 3. A first capacitor C1 and a second capacitor C2 are connected in parallel between the positive bus L1 and the negative bus L2 to form an auxiliary discharge circuit. In this circuit, the first diode D1 and the second diode D2 are oriented to allow only the energy in the first capacitor C1 and the second capacitor C2 to flow to the positive bus L1, preventing reverse flow. Thus, the energy in the first capacitor C1 flows to the positive bus L1 via the first diode D1, and the energy in the second capacitor C2 flows to the positive bus L1 via the second diode D2. Specifically, the first capacitor C1 can only discharge through the first diode D1 in the first branch, and the second capacitor C2 can only discharge through the second diode D2 in the second branch. The current in the phase winding connected to the negative bus L2 flows through the first capacitor C1 and the second capacitor C2 connected in parallel in the auxiliary discharge circuit to the positive bus L1, and then to the phase winding connected to the positive bus, forming a complete auxiliary discharge loop, as shown by the dashed line in Figure 3, where the direction of current flow is indicated by arrows. The auxiliary discharge mode helps stabilize the DC bus voltage when the system is stepped down, while also creating conditions for the auxiliary circuit to recharge when the voltage rises.

[0043] The following describes an example of how the motor drive system operates.

[0044] The first step is the power-on process. The power-on process refers to the process after the power tool is started, the AC power supply is turned on, and the system voltage (which can be characterized by the DC bus voltage) rises to a stable state.

[0045] Before power-on, the initial system voltage is low, for example, zero. During power-on, the motor drive system receives power from the AC power supply, the DC bus voltage rises, and the DC bus capacitor C0 is charged and its voltage increases. Simultaneously, the auxiliary charging / discharging circuit is in auxiliary charging mode, causing the first capacitor C1 and the second capacitor C2 to also charge and their voltages increase. At the end of power-on, the voltage of the DC bus capacitor C0 rises to the peak voltage of the AC power supply; the series voltage of the first capacitor C1 and the second capacitor C2 rises to the peak voltage of the AC power supply, with each individual voltage being half of the peak voltage. The charging of the DC bus capacitor C0, the first capacitor C1, and the second capacitor C2 is complete. Assume the rated input voltage of the DC bus from the AC power supply is 220V, and the peak voltage is approximately 314V. At the end of power-on, the series voltage of the first capacitor C1 and the second capacitor C2 is approximately 314V, and the voltage across each of the first capacitor C1 and the second capacitor C2 is approximately 157V.

[0046] Next, after power-on, the auxiliary charging / discharging circuit enters a quiescent state under normal system voltage. As mentioned earlier, in discharge mode, the first capacitor C1 can only discharge through the first diode D1, and the second capacitor C2 can only discharge through the second diode D2. When the power tool is running under no-load or normal load, the load is low, and the DC bus capacitor C0 has a low degree of charging / discharging, causing the DC bus voltage to remain more than half higher than the peak voltage of the power supply AC. Since the DC bus voltage is higher than the voltages of the first capacitor C1 and the second capacitor C2, neither the first capacitor C1 nor the second capacitor C2 discharges; and the series voltage of the first capacitor C1 and the second capacitor C2 maintains the peak value of the DC bus voltage, so neither the first capacitor C1 nor the second capacitor C2 charges. Therefore, these two capacitors in the auxiliary charging / discharging circuit do not affect the tool characteristics under no-load and normal load conditions, and thus do not affect harmonics.

[0047] The changes in the DC bus voltage and the voltages of the two capacitors in the auxiliary charging / discharging circuit under quiescent conditions are schematically represented in Figure 4. In Figure 4, the horizontal axis represents time t, and the vertical axis represents voltage V. The line V_bus represents the DC bus voltage, i.e., the voltage between the positive bus L1 and the negative bus L2; ​​the line V_C1 represents the voltage of the first capacitor C1; and the line V_C2 represents the voltage of the second capacitor C2. It can be seen that the DC bus voltage varies (e.g., periodically) between a roughly horizontal straight segment (maintaining approximately 225V) and a rising curved segment (peak value approximately 314V). The voltages of the first capacitor C1 and the second capacitor C2 remain essentially constant at approximately 157V, without charging or discharging. Therefore, when the power tool is running under no-load or normal load, only the DC bus capacitor C0 is charged and discharged, and the first capacitor C1 and the second capacitor C2 remain quiescent without affecting the function of the DC bus capacitor C0.

[0048] Next, when the peak voltage of the AC power supply rises, the auxiliary charging and discharging circuit can absorb the voltage spike. Specifically, when the input voltage of the AC power supply unexpectedly increases (as is often encountered when using a generator as a power source) and the input power of the power tool increases simultaneously, the peak voltage of the DC bus will rise and exceed the peak voltage under normal system voltage, for example, exceeding 314V. As an example, assume the peak voltage of the DC bus reaches approximately 500V. In this case, the DC bus capacitor C0 alternately charges and discharges as the DC bus rises and falls, and the auxiliary charging and discharging circuit can also achieve alternating charging and discharging, suppressing DC bus voltage fluctuations. Figure 5 schematically illustrates this function. In Figure 5, the horizontal axis represents time t, and the vertical axis represents voltage V. The line V_bus represents the DC bus voltage, and the lines V_C1 and V_C2 represent the voltages of the first capacitor C1 and the second capacitor C2, respectively.

[0049] As shown in Figure 5, during the rising phase of one cycle of the DC bus voltage V_bus, the DC bus capacitor C0 is charged, and the first capacitor C1 and the second capacitor C2 are also charged simultaneously. The voltages V_C1 of the first capacitor C1 and V_C2 of the second capacitor C2 are in the charging phase CHG, that is, charging is achieved through the auxiliary charging circuit including the first capacitor C1, the third diode D3, and the second capacitor C2, thereby absorbing electrical energy and suppressing further increases in the DC bus voltage. The series voltage of the first capacitor C1 and the second capacitor C2 gradually rises to the peak voltage of approximately 500V. The voltages V_C1 and V_C2 of each individual capacitor rise to half of the peak voltage, which can be called the charging end voltage V1, approximately 250V.

[0050] During the process of the DC bus voltage V_bus starting to decrease after reaching its peak voltage, before it drops below the voltages of individual capacitors V_C1 and V_C2 (charging end voltage V1), the DC bus capacitor C0 discharges, but the first capacitor C1 and the second capacitor C2 do not discharge, and the voltages V_C1 and V_C2 remain approximately unchanged at the charging end voltage V1 (approximately 250V). When the DC bus voltage V_bus drops further below the voltages V_C1 and V_C2 (charging end voltage V1) of a single capacitor, the first capacitor C1 and the second capacitor C2 discharge simultaneously with the discharge of the DC bus capacitor C0. The voltages V_C1 and V_C2 of the first capacitor C1 and the second capacitor C2 are in the discharge phase DCH, which is achieved through an auxiliary discharge circuit containing the first capacitor C1 (and the first diode D1) and the second capacitor C2 (and the second diode D2) connected in parallel. The voltages V_C1 and V_C2 (and the voltage V_bus) gradually decrease to the discharge end voltage V2 (below the charging end voltage V1) and then remain approximately constant at V2. During the discharge phase DCH, the DC bus capacitor C0 discharges more extensively due to the high load. Simultaneously, since the first capacitor C1 and the second capacitor C2 begin discharging from the increased voltage (charging end voltage V1) during the discharge phase DCH, they discharge more easily and with a higher discharge amount than the DC bus capacitor C0. During the discharge phase DCH, the larger the load and the lower the discharge end voltage V2, the higher the discharge degree of the first capacitor C1 and the second capacitor C2.

[0051] Then, in the next cycle of the DC bus voltage V_bus, voltages V_C1 and V_C2 sequentially experience the charging phase (CHG) with voltage increase, the phase maintained at the charging end voltage V1, the discharging phase (DCH), and the phase maintained at the discharging end voltage V2, repeating this cycle. When the generator is the power source, the auxiliary charging and discharging circuit, by repeatedly charging and discharging in accordance with the periodic changes in the DC bus voltage, can suppress further increases in the DC bus voltage. When the grid is the power source, it can help absorb voltage spikes and improve the stability of the motor drive system during grid voltage instability and surges.

[0052] Next, when the power tool is operating at low speed under overload, the auxiliary charging and discharging circuit can discharge into the DC bus. Specifically, when the power tool is operating at low speed and high load, the DC bus voltage is low. At this time, the auxiliary charging and discharging circuit discharges, which can improve the load capacity of the power tool during low-speed operation. Therefore, the auxiliary charging and discharging circuit can improve the overload operation capability of the power tool.

[0053] Furthermore, when the brushless motor EC of a power tool operates without a position sensor, the DC bus voltage needs to be maintained at a certain level for terminal voltage detection. With a small DC bus capacitor C0, when the power tool is under low speed and high load, and the AC voltage is low, the DC bus capacitor C0 continuously discharges, causing the DC bus voltage to drop to near zero. If the DC bus voltage is too low, the terminal voltage detection condition is lost, and thus the position signal cannot be extracted. With the addition of the auxiliary charging and discharging circuit, when the DC bus voltage drops below half of the power supply peak voltage (e.g., approximately 157V), the auxiliary charging and discharging circuit discharges into the DC bus, thereby suppressing further drops in the DC bus voltage, maintaining the terminal voltage, improving the accuracy of position detection, and enhancing the current output capability at low speeds. This improves the load capacity under sensorless operation.

[0054] According to this application, an auxiliary charging and discharging circuit is added to the original DC bus capacitor in the drive system of a permanent magnet brushless motor. The auxiliary charging and discharging circuit includes a combination of two capacitors and corresponding diodes, so that in auxiliary charging mode, the two capacitors are connected in series between the positive and negative buses, and in auxiliary discharging mode, the two capacitors are connected in parallel between the positive and negative buses. The charging and discharging functions provided by the auxiliary charging and discharging circuit improve the overvoltage suppression capability of the motor drive system, making the power tool less prone to overvoltage failure and frequent overvoltage shutdowns.

[0055] The permanent magnet brushless motor and its drive system of this application can be applied to various power tools, which can be connected to the power grid or a generator. When a diesel generator is used, the generator's output voltage (i.e., the input voltage of the DC bus) often exhibits instability. With the drive system of this application, fluctuations in the DC bus power supply can be reliably suppressed with the aid of an auxiliary charging and discharging circuit. Therefore, this application further relates to power tools employing the aforementioned permanent magnet brushless motor and its drive system, particularly power tools using a diesel generator as an AC power source. When using a diesel generator as the AC power source for a power tool, the diesel generator can be a separate unit, and the power tool's motor drive system can be connected to the diesel generator to obtain its output power; alternatively, the diesel generator can be integrated into the power tool itself, allowing the power tool to have its own built-in diesel generator as an AC power source.

[0056] The foregoing description of the drive system for the permanent magnet brushless motor of the power tool of this application, and in particular, a feasible implementation of its auxiliary charging and discharging circuit, is presented. Those skilled in the art, based on the principles of this application, can make adaptive modifications to the various details described above for specific applications.

[0057] For example, in the auxiliary charging and discharging circuit implementation described above, the rated capacitances of the first capacitor C1 and the second capacitor C2 are equal; however, in practical applications, even if the first capacitor C1 and the second capacitor C2 have different rated capacitances, the auxiliary charging and discharging circuit can still achieve similar technical effects.

[0058] For example, in the auxiliary charging and discharging circuit implementation described above, diodes D1 to D3 are used to control the series and parallel relationship of the two capacitors during the charging and discharging process; however, other electronic devices with polarity or current direction restrictions can be used to replace diodes D1 to D3, and the same series and parallel relationship of the two capacitors during the charging and discharging process can also be achieved.

[0059] Furthermore, in the auxiliary charging and discharging circuit implementation described above, a roughly H-shaped circuit containing two capacitors and corresponding diodes is used to realize the series and parallel relationship of the two capacitors during the charging and discharging process; however, other equivalent circuits that can realize this relationship can also be used here.

[0060] While this application has been described herein with reference to specific embodiments, the scope of this application is not limited to the details shown. Various modifications may be made to these details without departing from the basic principles of this application.

Claims

1. A motor drive system for a permanent magnet brushless motor, comprising: A pair of DC buses, including a positive bus (L1) and a negative bus (L2), wherein the input end of the pair of DC buses is connected to a single-phase AC power supply via a rectifier circuit, and the output end is connected to the three-phase winding of the permanent magnet brushless motor (EC) via an inverter circuit; The DC bus capacitor (C0) disposed between the pair of DC buses; and An auxiliary charging and discharging circuit is arranged side-by-side with the DC bus capacitor (C0) between the pair of DC buses, the auxiliary charging and discharging circuit comprising: A first branch and a second branch connected between the positive busbar (L1) and the negative busbar (L2), and an intermediate cross path connected between the first branch and the second branch; a first capacitor (C1) and a first diode (D1) disposed in the first branch, and a second capacitor (C2) and a second diode (D2) disposed in the second branch. The auxiliary charging and discharging circuit has an auxiliary charging mode and an auxiliary discharging mode. In the auxiliary charging mode, the auxiliary charging and discharging circuit constitutes an auxiliary charging circuit, wherein the first capacitor (C1) and the second capacitor (C2) are charged in series through the intermediate cross circuit; In the auxiliary discharge mode, the auxiliary charging and discharging circuit constitutes an auxiliary discharge circuit, wherein the first capacitor (C1) discharges in parallel through the first diode (D1) and the second capacitor (C2) discharges through the second diode (D2).

2. The motor drive system as described in claim 1, wherein, When the DC bus voltage is higher than the sum of the voltages of the first capacitor (C1) and the second capacitor (C2), the auxiliary charging and discharging circuit is in auxiliary charging mode, which charges the first capacitor (C1) and the second capacitor (C2) until the sum of the voltages of the first capacitor (C1) and the second capacitor (C2) equals the DC bus voltage.

3. The motor drive system as described in claim 1 or 2, wherein, During the power-on process of the drive system, the auxiliary charging and discharging circuit is in auxiliary charging mode, which charges the first capacitor (C1) and the second capacitor (C2) until the sum of the voltage of the first capacitor (C1) and the voltage of the second capacitor (C2) equals the peak voltage of the input voltage input from the single-phase AC power supply through the rectifier circuit.

4. The motor drive system as described in claim 3, wherein, After the drive system is powered on, the auxiliary charging and discharging circuit enters a silent state, wherein the pair of DC buses are charged and discharged only through the DC bus capacitor (C0), the DC bus power supply is maintained at a voltage higher than that of the first capacitor (C1) and the second capacitor (C2), and the first capacitor (C1) and the second capacitor (C2) do not charge or discharge.

5. The motor drive system as described in any one of claims 1-4, wherein, When the DC bus voltage is lower than the voltage of the first capacitor (C1) and / or the second capacitor (C2), the auxiliary charging and discharging circuit is in auxiliary discharging mode, which discharges the first capacitor (C1) and / or the second capacitor (C2) until the voltage of the first capacitor (C1) and / or the second capacitor (C2) is equal to the DC bus voltage.

6. The motor drive system as described in any one of claims 1-5, wherein, When the input voltage from the single-phase AC power supply is higher than the rated voltage, and the DC bus voltage is higher than the sum of the voltages of the first capacitor (C1) and the second capacitor (C2) and further increases, the auxiliary charging and discharging circuit enters the auxiliary charging mode, causing the first capacitor (C1) and the second capacitor (C2) to charge until the DC bus voltage reaches the voltage peak value, and the sum of the voltages of the first capacitor (C1) and the second capacitor (C2) equals the voltage peak value.

7. The motor drive system as described in claim 6, wherein, When the DC bus voltage reaches its peak value and begins to decrease, the first capacitor (C1) and the second capacitor (C2) do not discharge and maintain their respective power supplies unchanged; then, when the DC bus voltage drops to the voltage of the first capacitor (C1) and / or the second capacitor (C2) and further decreases, the auxiliary charging and discharging circuit enters the auxiliary discharging mode, causing the first capacitor (C1) and / or the second capacitor (C2) to discharge.

8. The motor drive system as described in any one of claims 1-7, wherein, In the first branch, one end of the first capacitor (C1) is electrically connected to the positive bus (L1), and the other end is electrically connected to the negative terminal of the first diode (D1). The positive terminal of the first diode (D1) is electrically connected to the negative bus (L2). In the second branch, one end of the second capacitor (C2) is electrically connected to the negative bus (L2), and the other end is electrically connected to the positive terminal of the second diode (D2). The negative terminal of the second diode (D2) is electrically connected to the positive bus (L1).

9. The motor drive system as described in claim 8, wherein, One end of the intermediate horizontal path is electrically connected to the first branch between the first capacitor (C1) and the first diode (D1), and the other end is electrically connected to the second branch between the second capacitor (C2) and the second diode (D2). A third diode (D3) is provided in the intermediate horizontal path. The third diode (D3) is oriented to allow electrical energy to flow only from the first branch to the second branch and to prevent reverse flow.

10. The motor drive system as described in any one of claims 1-9, wherein, The rated capacitances of the first capacitor (C1) and the second capacitor (C2) are equal.

11. The motor drive system according to any one of claims 1-10, wherein, The rated capacitance of the DC bus capacitor (C0) is less than 30uF; the rated capacitance of the first capacitor (C1) and the second capacitor (C2) is more than three times the rated capacitance of the DC bus capacitor (C0).

12. An electric tool, comprising: Permanent magnet brushless motor; The motor drive system as described in any one of claims 1-11 is configured to be connected to a single-phase alternating current (AC) power supply to power a permanent magnet brushless motor.

13. The power tool as claimed in claim 12, wherein, The single-phase AC power source is either the power grid or a generator.

14. The power tool as claimed in claim 13, wherein, The single-phase AC power supply is a diesel generator.

15. The power tool as claimed in claim 13, wherein, The power tool includes a diesel generator that serves as a single-phase alternating current (AC) power source.

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