High-voltage brushless tool power system

Abstract

The utility model relates to the technical field of high-voltage brushless tool control, in particular to a high-voltage brushless tool power system. The device comprises a rectifier bridge, the positive electrode output end of the rectifier bridge is grounded through a filter module, the positive electrode output end of the rectifier bridge is adaptively connected with a brushless motor, and the filter module is used for rectifying and filtering voltage output by the rectifier bridge to form power supply voltage of the brushless motor so as to convert electric energy into mechanical energy. The circuit is characterized in that the filtering module is a valley-fill passive PFC, and the back electromotive force of the brushless motor is smaller than the rated valley voltage of the valley-fill passive PFC. By adopting the system, large burr current is avoided, and the problems of small motor output and low efficiency are solved.

Description

Technical Field

[0001] The utility model relates to the technical field of high-voltage brushless tool control, in particular to a high-voltage brushless tool power system. Background Art

[0002] The power system of high-voltage brushless electric tools uses a rectifier bridge to rectify and filter the AC power and then use it as a power supply to the permanent magnet brushless motor. The rectifier bridge converts one cycle of sinusoidal AC power into two half-wave DC power, and then filters the two half-wave DC power into nearly equal-amplitude DC power and transmits it to the brushless motor as the power supply voltage.

[0003] At present, the structure of the traditional power tool power system is as follows Figure 1 As shown in the figure, it uses a filter capacitor at the rear end of the rectifier bridge to filter the two half-wave DC into DC with nearly equal amplitude. The design of the filter capacitor at the rear end of the rectifier bridge is one of the difficulties of the system. If the filter capacitor at the rear end of the rectifier bridge has a large capacitance, this capacitor will filter the two half-wave DC into DC with nearly equal amplitude. At this time, the motor can run at full load at any time, with high output and high efficiency. However, this large capacitor makes the current output by the rectifier bridge a large burr current injected into the capacitor, such as Figure 2 As shown. This makes the power factor of the entire power system very low, which has an adverse impact on the power grid and is not conducive to the tool meeting the safety requirements of electromagnetic compatibility. If the filter capacitor at the rear end of the rectifier bridge has a small capacitance, the voltage input to the motor is close to two half-waves, and the amplitude oscillation is large, such as Figure 3 Therefore, when the half-wave voltage is high, the motor runs at full load, but when the half-wave voltage is low, the motor output is small and the efficiency is low. Even when the back EMF at the current running speed of the motor is higher than the half-wave voltage, the motor no longer outputs power. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide a high-voltage brushless tool power system, which will not cause large burr current, small motor output and low efficiency.

[0005] In order to solve the above problems, the following technical solutions are provided:

[0006] The utility model discloses a high-voltage brushless tool power system including a rectifier bridge, the positive output end of the rectifier bridge is grounded through a filter module, the positive output end of the rectifier bridge is connected to a brushless motor, and the filter module is used to rectify and filter the voltage output by the rectifier bridge to form a power supply voltage of the brushless motor, so as to convert electrical energy into mechanical energy. The utility model is characterized in that the filter module is a valley-filling passive PFC, and the back electromotive force amplitude of the brushless motor at the operating speed is less than the rated valley voltage of the valley-filling passive PFC.

[0007] The back electromotive force amplitude of the brushless motor at the operating speed is less than 95% of the rated valley voltage of the valley-filling passive PFC.

[0008] The valley-fill passive PFC comprises a diode D1, a diode D2, a diode D3, a capacitor C1 and a capacitor C2, the cathode of the diode D2 and the anode of the capacitor C1 are both connected to the anode output terminal of the rectifier bridge, the anode of the diode D2 is respectively connected to the cathode of the diode D3 and the anode of the capacitor C2, the cathode of the capacitor C1 is respectively connected to the anode of the diode D3 and the cathode of the diode D1, and the cathode of the capacitor C2 and the anode of the diode D3 are grounded.

[0009] The capacitances of the capacitors C1 and C2 are the same.

[0010] The capacitance of the capacitor C1 and the capacitor C2 is less than 180 microfarads.

[0011] A controllable switch is connected in series between the filter module and the positive output terminal of the rectifier bridge.

[0012] The positive output end of the rectifier bridge is connected to the brushless motor through an inverter, and the inverter is used to invert the rectified and filtered DC voltage into an AC voltage with a frequency related to the speed of the brushless motor to drive the brushless motor to rotate.

[0013] The above solution has the following advantages:

[0014] Since the filter module of the high-voltage brushless tool power system of the utility model is a valley-filling passive PFC, the back electromotive force of the brushless motor is less than the rated valley voltage of the valley-filling passive PFC. The use of valley-filling passive PFC for filtering and shaping will not cause the problem of large burr current. Moreover, setting the rated valley voltage of the valley-filling passive PFC to a value greater than the amplitude of the back electromotive force when the brushless motor is working will avoid the problem of low motor output and low efficiency, and will not cause the motor to stop outputting. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a circuit diagram of a high-voltage brushless tool power system in the background technology;

[0016] Figure 2 It is a schematic diagram of the current and voltage waveforms of the busbar after rectification of a high-voltage brushless tool power system using a large-capacitance capacitor in the background technology;

[0017] Figure 3 It is a schematic diagram of the current and voltage waveforms of the busbar after rectification of a high-voltage brushless tool power system using a small-capacitance capacitor in the background technology;

[0018] Figure 4 It is a circuit diagram of the high-voltage brushless tool power system of the utility model;

[0019] Figure 5 It is a schematic diagram of the brushless motor structure;

[0020] Figure 6 It is a back electromotive force comparison diagram of a high-voltage brushless tool power system using the utility model and a brushless motor whose back electromotive force is designed to be greater than the rated valley voltage of the valley-filling passive PFC;

[0021] Figure 7 It is a motor current and voltage waveform diagram of the high-voltage brushless tool power system using the utility model;

[0022] Figure 8 It is the motor current and voltage waveform diagram at the operating speed when the back EMF amplitude is greater than the rated valley voltage of the valley-filling passive PFC;

[0023] Fig. 9 yes Figure 6 Schematic diagram of the output of the two motors;

[0024] Fig.10 It is a comparison diagram of the motor power factor of the high-voltage brushless tool power system using the utility model and the high-voltage brushless tool power system in the background technology;

[0025] Fig.11 A schematic structural diagram of another embodiment of the high-voltage brushless tool power system of the utility model. DETAILED DESCRIPTION

[0026] The utility model is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0027] like Figure 4 As shown, the high-voltage brushless tool power system of the utility model includes a rectifier bridge 2, which is four diodes connected end to end. The specific structure of the rectifier bridge 2 belongs to the prior art and will not be repeated here. The positive input terminal and the negative input terminal of the rectifier bridge 2 are connected to the municipal power 1, that is, 220V AC power, and the negative output terminal of the rectifier bridge 2 is grounded. The rectifier bridge 2 performs full-wave rectification on the AC sinusoidal municipal power and converts it into two half-wave pulsating direct current. The positive output terminal of the rectifier bridge 2 is grounded through the filter module 3, which is responsible for filtering the two half-wave pulsating direct currents after rectification.

[0028] The filter module 3 is a valley-filling passive PFC, which contains a diode D1, a diode D2, a diode D3, a capacitor C1 and a capacitor C2. The cathode of the diode D2 and the anode of the capacitor C1 are both connected to the anode output terminal of the rectifier bridge, the anode of the diode D2 is respectively connected to the cathode of the diode D3 and the anode of the capacitor C2, the cathode of the capacitor C1 is respectively connected to the anode of the diode D3 and the cathode of the diode D1, and the cathode of the capacitor C2 and the anode of the diode D3 are grounded. When the voltage amplitude after rectification rises, the diodes D1 and D2 that are turned on in a single phase are closed, and the diode D3 is turned on. In this embodiment, the capacitance of the capacitor C1 and the capacitor C2 is the same. The capacitance of the capacitor C1 and the capacitor C2 is less than 180 microfarads. In this embodiment, the capacitors C1 and C2 are connected in series, and the rectifier circuit charges the two capacitors, and the voltage borne by the single capacitor is half of the voltage after rectification. After C1 and C2 are fully charged, diodes D1 and D2 are closed to play an isolation role. When the voltage drops from the peak value of the pulsating DC voltage to the valley value, the output voltage will drop accordingly. When the output voltage is lower than the voltage of the capacitor, capacitors C1 and C2 begin to discharge through their respective diodes D1 and D2 to fill the output voltage. At this time, diode D3 plays an isolation role. Capacitors C1 and C2 are charged in series, and the charging capacity is small; but capacitors C1 and C2 are discharged in parallel, and the discharge capacity is large. This charging and discharging method of the filter capacitor makes the voltage output after the rectifier bridge more stable, and changes the current that was originally a pulse peak waveform into a current waveform close to a sine wave, thereby achieving the purpose of correcting the power factor.

[0029] The positive output end of the rectifier bridge 2 is connected to the brushless motor through the inverter 4. The inverter 4 is used to invert the rectified and filtered DC voltage into an AC voltage with a frequency related to the speed of the brushless motor to drive the brushless motor to rotate. The brushless motor module is responsible for converting electrical energy into rotational mechanical energy for output work.

[0030] The back EMF amplitude of the brushless motor's operating speed is less than the rated valley voltage of the valley-filling passive PFC. Further, the back EMF amplitude of the brushless motor's operating speed is less than 95% of the rated valley voltage of the valley-filling passive PFC. The back EMF amplitude of the brushless motor when operating under overload should be designed to be less than 95% of the rated valley voltage. The motor back EMF refers to the induced electromotive force generated by the rotation of the rotor magnetic field at the rated speed of the motor, which is one of the most important parameters when designing the motor. When a motor has a fixed lamination form, its back EMF at the rated speed is affected by the rotor magnetic steel grade, rotor magnetic steel length, rotor lamination length, stator lamination length, coil winding method (such as delta or star connection), and the number of coil turns, such as Figure 5 shown.

[0031] like Figure 6The back EMF amplitude of motor A when overloaded at 7500RPM (revolutions per minute) is 136V, which is lower than 95% of the rated valley voltage of 155.5V. The back EMF amplitude of motor B when overloaded at 7500RPM (revolutions per minute) is 170V, which is higher than the rated valley voltage of 155.5V. At the bottom of the voltage, current still flows through motor A, and the motor has torque output to the outside, such as Figure 7 However, at the bottom of the voltage, the current in motor B is very small, so the motor basically does not exert any force externally. Figure 8 The output characteristics comparison shows that the constant speed range of motor A is more than 25% larger than that of motor B, and the output power of motor A is significantly stronger than that of motor B. Fig. 9 And the power factor of motor A designed with this solution is significantly higher than that of the single capacitor filtering solution. Fig.10 Show.

[0032] In another possible implementation, a controllable switch 5 is connected in series between the filter module 3 and the positive output terminal of the rectifier bridge 2, which can control the access time of the PFC circuit in real time to further improve the power factor and motor output performance. Fig.11 The controllable switch can be a device such as a MOS tube, and the specific type can be selected by technicians in this field according to actual needs. It belongs to the existing technology and will not be described here.

[0033] When the filter module after rectification in this scheme uses a valley-filling passive PFC circuit, the back electromotive force amplitude of the motor design in this scheme during overload operation should be lower than 95% of the PFC rated valley output voltage. The rated valley voltage refers to half of the voltage amplitude after rectification, for example, for 220V AC, the rated valley voltage is 155.5V.

[0034] The utility model improves the power factor of the power system and at the same time improves the output capacity of the high-voltage brushless electric tool.

Claims

1. A high-voltage brushless tool power system, comprising a rectifier bridge, wherein the positive output end of the rectifier bridge is grounded through a filter module, the positive output end of the rectifier bridge is adaptively connected to a brushless motor, and the filter module is used to rectify and filter the voltage output by the rectifier bridge to form a power supply voltage of the brushless motor, so as to convert electrical energy into mechanical energy; characterized in that: The filtering module is a valley-filling passive PFC, and the back electromotive force amplitude of the brushless motor at the operating speed is less than the rated valley voltage of the valley-filling passive PFC.

2. The high-voltage brushless tool power system according to claim 1, characterized in that: The back electromotive force amplitude of the brushless motor at the operating speed is less than 95% of the rated valley voltage of the valley-filling passive PFC.

3. The high-voltage brushless tool power system according to claim 1, characterized in that: The valley-fill passive PFC comprises a diode D1, a diode D2, a diode D3, a capacitor C1 and a capacitor C2, the cathode of the diode D2 and the anode of the capacitor C1 are both connected to the anode output terminal of the rectifier bridge, the anode of the diode D2 is respectively connected to the cathode of the diode D3 and the anode of the capacitor C2, the cathode of the capacitor C1 is respectively connected to the anode of the diode D3 and the cathode of the diode D1, and the cathode of the capacitor C2 and the anode of the diode D3 are grounded.

4. The high-voltage brushless tool power system according to claim 3, characterized in that: The capacitances of the capacitors C1 and C2 are the same.

5. The high-voltage brushless tool power system according to claim 4, characterized in that: The capacitance of the capacitor C1 and the capacitor C2 is less than 180 microfarads.

6. The high-voltage brushless tool power system according to claim 1, characterized in that: A controllable switch is connected in series between the filter module and the positive output terminal of the rectifier bridge.

7. The high-voltage brushless tool power system according to claim 1, characterized in that: The positive output end of the rectifier bridge is connected to the brushless motor through an inverter, and the inverter is used to invert the rectified and filtered DC voltage into an AC voltage with a frequency related to the speed of the brushless motor to drive the brushless motor to rotate.

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