82results about How to "Reduce switching losses" patented technology

The invention discloses a totem-pole PFC circuit control method and device based on an improved SOGI-PLL, and belongs to the technical field of totem-pole PFC circuits, and the method comprises the steps: collecting the input voltage, input current and bus voltage of a totem-pole PFC circuit; synchronous phase information of the power grid voltage is obtained through an improved second-order generalized integral phase-locked loop; generating a current amplitude reference signal, and combining the current amplitude reference signal with the synchronous phase information to synthesize a current reference signal; generating a pulse width modulation signal for controlling a high-frequency switching tube; and a switching signal of the power frequency switching tube is generated based on the synchronous phase information, and the power frequency switching tube and the high-frequency switching tube are driven in combination with the pulse width modulation signal, so that the action time sequence is synchronous with the phase of the power grid voltage, and therefore, waveform tracking of the input current is realized, and current distortion at the zero crossing point is suppressed. Precise phase synchronization is realized based on the improved SOGI-PLL, totem pole PFC zero-crossing current distortion is effectively suppressed, and the power factor and waveform quality are improved.

The utility model discloses a charging voltage regulation circuit and a mobile power supply. The charging voltage regulation circuit comprises a charging interface module, an input rectification filtering module, a synchronous rectification module, an output filtering module, a protocol control module and a flyback control module. Wherein the protocol control module is electrically connected with the flyback control module and the charging interface module, the flyback control module is electrically connected with the input rectification filtering module and the synchronous rectification module, the synchronous rectification module is electrically connected with the output filtering module, and the output filtering module is electrically connected with the charging interface module. The synchronous rectification module is configured to adjust the input voltage input into the rectification filtering module, and the input voltage is output to the charging interface module through the output filtering module. According to the utility model, the drain-source voltage and switching loss of the synchronous rectification MOS can be reduced, and the stability and efficiency of the system are improved.

The application discloses a kind of modular multilevel converter thermal balance control method and system based on dynamic retention factor, for the thermal imbalance problem of flexible direct current transmission modular multilevel converter, propose thermal-electricity collaborative control method based on dynamic retention factor (DRF), break through the limitation of traditional capacitor voltage balancing strategy.Capacitor voltage tolerance boundary (rated value ±5%~10%) is set, combined with real-time temperature feedback to build dynamic weight adjustment mechanism, collect IGBT junction temperature to calculate normalized temperature deviation value, generate dynamic retention coefficient, and then obtain the corrected capacitor voltage, in charging mode, low-temperature module is preferentially put into in ascending order, in discharging mode, high-temperature module is preferentially put into in descending order;Further integrate model predictive control (MPC), based on thermal model rolling solution minimization temperature difference objective function, adjust dynamic adjustment coefficient ΔK.The scheme can effectively solve the problem of small-capacitor module thermal fatigue early decline, provide high reliability technical support for high-voltage high-power new energy grid-connected equipment.

The invention provides a switching power supply and a driving circuit and a driving method thereof, the driving circuit comprises a level shift circuit, a pulse generation circuit, a high-side driving circuit and a low-side driving circuit, an output signal of the level shift circuit is used for adjusting the potential of a first node in the high-side driving circuit, and an output signal of the pulse generation circuit is used for adjusting the potential of a second node in the low-side driving circuit. The high-side driving circuit drives the high-side switch unit to be switched on after the potential of the first node reaches a switching-on trigger potential, and the high-side driving circuit drives the high-side switch unit to be switched on after detecting that the driving signal of the low-side switch unit is changed into an invalid state and the high-side control signal is changed into an effective state; an additional potential adjusting path is established for the first node, so that the time for the potential of the first node to reach the turn-on trigger potential is shortened, namely the dead zone time from turn-off of the low-side switch unit to turn-on of the high-side switch unit is shortened, the switching speed of the high-side switch unit is increased, the reduction of dead zone loss and switching loss is realized, and the switching efficiency is improved. And the working efficiency of the switching power supply is improved.

The application belongs to the technical field of switching power supply, and an auxiliary circuit is added between two branches of a traditional two-phase Dickson converter; in a dead time when all main power tubes are closed, the auxiliary circuit can transfer the charge of one branch to another branch, realizes zero-voltage turn-on of all main power tubes, and reduces switching loss.

The application provides a semiconductor device manufacturing method and a semiconductor device. The method comprises the following steps: providing a semiconductor substrate, a first trench is formed in the semiconductor substrate, a field oxide layer is formed on the side wall and the bottom wall of the first trench, so that a space outside the surface of the field oxide layer in the first trench forms a second trench, and the first conductive material is filled in the second trench. The field oxide layer of the side wall of the first trench is removed to a first set depth to form a third trench. A barrier layer is formed on the bottom wall of the third trench, a gate oxide layer is formed on the side wall of the third trench, at least two separated gates are formed in the space outside the surface of the gate oxide layer in the third trench, the barrier layer is removed, and the gap between the separated gates is filled. Then, the space between the bottom of the separated gate and the upper surface of the field oxide layer forms an air layer. Due to the introduction of the air layer, the gate leakage capacitance and the gate-source capacitance are reduced, the switching loss and the conduction loss are reduced, and the opening rate of the device is improved.

This application provides a semiconductor structure and a method for forming the same. The semiconductor structure includes: a semiconductor substrate with a first insulating layer formed on its surface; a gate signal conditioning circuit and a virtual circuit disposed on the surface of the first insulating layer, wherein the gate signal conditioning circuit and the virtual circuit have identical structures; one end of the gate signal conditioning circuit is connected to a gate signal source, and the other end is connected to the gate of a device cell, wherein the gate signal conditioning circuit is used to adjust the resistance between the gate signal source and the gate of the device cell; one end of the virtual circuit is connected to a virtual gate monitoring signal terminal, and the other end is connected to a virtual gate monitoring ground terminal, wherein the virtual circuit is used to simulate the operation of the gate signal conditioning circuit and is monitored.

This invention discloses a phase-shifted full-bridge plasma power supply based on all SiC devices, belonging to the field of special power supply technology. It includes: a rectifier unit with a power factor correction circuit; an inverter unit containing a phase-shifted full-bridge topology composed of SiC power devices and an energy storage inductor, achieving zero-voltage switching through phase-shift control; a transformer unit; an output unit including an output filter capacitor; and a control unit that uses an incremental PID algorithm to generate phase-shift control signals. This invention analyzes the differences in zero-voltage switching between the leading and lagging bridge arms, utilizes the low output capacitance characteristics and dynamic dead-time adjustment of SiC devices, broadens the soft-switching range under light loads, effectively reduces output current ripple, and improves dynamic response speed and overall efficiency.

The application relates to the technical field of ocean exploration measurement, and discloses a Doppler log power supply control method and system based on hierarchical intelligent control, which comprises the following steps: acquiring and adaptively filtering original electrical and environmental signals by using a multi-parameter dynamic detection module; performing integration autoregressive moving average model identification based on load current sampling data by using a load adaptive adjustment module, and outputting predicted load current values; combining the prediction results to generate a feedforward instruction, so as to adjust the target switching frequency, duty cycle and working mode of a direct-current-to-direct-current conversion circuit; and using a stability verification layer to evaluate control loop indexes in real time based on a linear periodic time-varying Nyquist criterion, and sending an instruction change control parameter or a warning threshold at an instability critical point. The application improves the power conversion efficiency and dynamic response lag problem under a variable load environment, and improves the anti-disturbance capability and operation reliability of a Doppler log power supply system.

The utility model provides an IGBT driving circuit based on a push-pull structure, and relates to the technical field of power electronic device driving, and the IGBT driving circuit comprises an optocoupler isolation module which is used for receiving a control signal and providing electrical isolation output; the push-pull driving module comprises an NPN type triode Q1 and a PNP type triode Q2 which are complementary and symmetrical; the push-pull driving module is configured as follows: when the optocoupler is conducted, Q1 is saturated and conducted, Q2 is cut off, and a driving current charges an IGBT grid electrode through R2; when the optocoupler is turned off, the Q2 is saturated and turned on, the Q1 is turned off, and the driving current flows through the R3 to discharge the grid electrode of the IGBT. Bidirectional driving current is provided through a push-pull structure, the charge charging and discharging speed of the IGBT grid electrode is increased, the switching loss is reduced, bidirectional driving current is provided through a switch-on resistor R2 and a switch-off resistor R3, the resistance value of the switch-on resistor R2 is selected to be small, the purpose of reducing switch-on loss Eon is achieved, the resistance value of the switch-off resistor R3 is selected to be large, and the purpose of reducing switch-off Vce is achieved.

The invention discloses a double-MOS tube parallel drive control circuit and a control method, and relates to the technical field of power switch drive control, the circuit comprises an MOS tube Q1, an MOS tube Q2 and a comparator, the source electrodes and the drain electrodes of the MOS tube Q1 and the MOS tube Q2 are connected, the grid electrode of the MOS tube Q2 is connected to the output end of the comparator, the grid electrode of the MOS tube Q1 and the positive input end of the comparator are both connected with drive signals, and the positive input end of the comparator is connected with the output end of the comparator. The negative input end of the comparator is connected with a reference power supply, and the voltage of the reference power supply is equal to the conduction threshold voltage of the MOS tube Q1. The method comprises the following steps: a starting process: a driving signal is controlled to rise, an MOS tube Q1 is switched on, a comparator outputs a high level after being delayed, and an MOS tube Q2 is switched on; in the turn-off process, the driving signal is controlled to descend, the MOS tube Q1 is turned off firstly, the comparator outputs low level after being delayed, and the MOS tube Q2 is turned off. According to the invention, the switching loss when the double MOS tubes are connected in parallel can be effectively reduced.

The invention provides a multi-suspension shield grid MOSFET and a preparation method thereof, a shield grid is divided into a left part, a middle part and a right part, the left part and the right part are symmetrically distributed along the middle part, the upper part width of the middle part is larger than the lower part width, and the top of the middle part is higher than the tops of the left part and the right part. The middle part of the shield gate is connected with a source electrode, the left and right parts are floating, in a blocking state, the left and right floating shield gates can improve electric field distribution in the middle of a drift region, the thicker field oxide layer at the bottom can bear a higher electric field, and device breakdown at the bottom of the shield gate electrode is avoided. The output capacitance Coss contributed by the shield gate electrode is reduced while the reliability is improved, the switching loss is reduced, and the on-resistance is lower when the withstand voltage is the same.

The application belongs to the technical field of switching power supply, and relates to a cascaded switching capacitor converter. An auxiliary circuit is added between two branches outside a traditional cascaded converter. In a dead time when all main power tubes are closed, the auxiliary circuit can transfer the charge of one branch to another branch, realize zero-voltage turn-on of all main power tubes, and reduce switching loss.

This invention discloses a control device, an LLC switching power supply, and a control method thereof. The device includes: a control unit, which, when the LLC switching power supply is powered on, controls the current switching transistor in the upper and lower bridge switching transistors to turn on; and controls a set of rectifier switching transistors corresponding to the current switching transistor to turn on in advance; a control unit, which controls the current switching transistor to turn off, and controls the set of rectifier switching transistors corresponding to the current switching transistor to turn off; a detection unit, which detects the current on the resonant inductor to obtain a first detection signal, and detects the current on the magnetizing inductor to obtain a second detection signal; and a control unit, which, when the first and second detection signals are determined to be equal, outputs a control signal to control the set of rectifier switching transistors corresponding to the next switching transistor to turn on preferentially before the secondary side of the transformer is energized. This scheme reduces switching losses and improves power supply efficiency by prioritizing the switching transistors on the synchronous rectification side before the transformer conducts.

The invention relates to a high-integration-level and high-power-density module compatible with Econodual3 packaging. The high-integration-level and high-power-density module comprises a shell, two substrates arranged in the shell, a DC positive terminal, a DC negative terminal and an AC terminal. By overlapping the positive and negative terminals, the two connection regions on the substrate are adjacent and opposite in current, a proximity effect is generated to counteract a magnetic field, and stray inductance is reduced. And a wavy water channel is designed in the bottom plate, so that the cooling liquid is easier to generate vortex, and the heat dissipation efficiency is greatly improved. A driving signal loop is optimized to obtain low switching loss, heat resistance is reduced through copper paste sintering on the back faces of the chips and the substrate and DTS sintering connection on the front faces of the chips, parallel connection of 10 chips with the size of 6 mm * 7 mm and the total area of 420 mm < 2 > sic is achieved, a current sensor is further integrated in a shell, nanosecond-level overcurrent protection can be achieved, and the heat dissipation and control requirements of high-current and high-power-density application scenes are met. The overall structure is symmetrically designed, the high-voltage part is located on the outer side, the low-voltage signal control and acquisition part is located on the inner side, the wiring design of a PCB is facilitated, and the size of the module can be compatible and matched with Econodual3 packaging.

The application discloses a working mode detection method and circuit of an active clamp flyback converter, a main control chip, samples a drain end voltage VDS of a main power tube QL in a current period, detects a first voltage drop time of the main power tube QL after the main power tube QL is turned off, and determines the working mode of the current period of the active clamp flyback converter by judging the sequence of the first voltage drop time and a clamp tube driving time. Furthermore, based on the working mode determination result, the dead time of the active clamp flyback converter is accurately adjusted to be suitable for the detected working mode, the problem of mismatching between the dead time and the working mode is avoided, the main power tube QL of the active clamp flyback converter can keep realizing soft switching in a full load range, the switching loss of the active clamp flyback converter is greatly reduced, and the efficiency of the converter is improved.

The application discloses a bipolar high-gain Cuk DC-DC converter for a direct-current microgrid, and relates to the field of voltage converters.The bipolar high-gain Cuk DC-DC converter comprises a coupled input unit, a bipolar voltage boosting unit and an output unit which are adaptively connected.The coupled input unit comprises a switching tube S and a coupled inductor.The same name end of the primary winding L1 of the coupled inductor is connected with the first electrode of the switching tube S, the third electrode of the switching tube S forms the positive input end of the coupled input unit, and the non-same name end of the primary winding L1 of the coupled inductor forms the negative input end of the coupled input unit.The first electrode of the switching tube S is connected with the neutral point of the output unit through the bipolar voltage boosting unit, the negative input end of the coupled input unit is connected with the negative output end of the output unit through the bipolar voltage boosting unit, and the output voltage amplitude of the positive output end and the negative output end of the output unit relative to the neutral point is equal.The converter has the advantages of high gain, self-voltage equalization, no need of an additional clamping circuit, high efficiency and strong reliability.

The invention provides a preparation method of a silicon carbide step groove and a groove type silicon carbide device. The preparation method comprises the following steps: growing an etching mask layer on an epitaxial layer; carrying out photoetching process treatment on the etching mask layer; performing dry etching on the patterned etching mask layer to the upper surface of the epitaxial layer by taking the patterned photoresist as a mask to form a patterned etching mask layer, and etching the epitaxial layer by taking the patterned etching mask layer as a mask to form a first-stage groove; oxidizing a part of the etching mask layer into silicon dioxide by using a wet oxygen oxidation process, and removing the silicon dioxide by using a wet etching process to form a treated etching mask layer; and taking the processed etching mask layer as an etching mask, etching a part of the epitaxial layer close to two side walls of the first groove, forming a second-stage groove based on the first-stage groove, and obtaining a step-shaped groove. Thus, the overhigh electric field of the bottom gate oxide layer is improved, the breakdown phenomenon caused by tip electric field concentration is avoided, and the high-frequency switching circuit requirement of a new energy automobile is easily met.

This invention discloses a current-source wireless power transfer system topology and modulation method, relating to the field of current-source wireless power transfer system control technology. This circuit directly transmits electrical energy from the solar cell to the energy storage battery via wireless power transfer without the need for a step-up / step-down circuit, achieving single-stage wireless energy transfer with high efficiency. By designing a proprietary modulation method for this circuit, zero-current switching can be achieved, reducing switching current stress and losses. Through resonance and compensation circuits, switching can be achieved near the zero-crossing point of the inverter output voltage, achieving near-zero-voltage switching, further reducing switching voltage stress and losses, and realizing high-efficiency energy transfer. When the input is a photovoltaic cell connected through a filter circuit, the voltage of the photovoltaic cell can be controlled by phase shifting to achieve maximum photovoltaic power output and improve power generation efficiency.

The embodiment of the application discloses a control method and a switching power supply. The control method comprises the following steps: after the high-voltage starting of the switching power supply, and when the switching time interval of the second switch tube is equal to or smaller than the first preset value, the secondary side control module acquires the voltage waveform of the second connection point between the secondary side winding and the second switch tube; when the voltage waveform of the second connection point does not realize zero voltage switching, the secondary side control module adjusts the off current of the second switch tube until the voltage waveform of the first connection point between the primary side winding and the first switch tube is just zero; when the voltage waveform of the first connection point is just zero, the primary side control module controls the first switch tube to be turned on, so as to realize the zero voltage opening of the primary side. The embodiment reduces the switching loss of the switching power supply, and improves the EMI characteristics of the switching power supply.

The invention discloses a bridge arm compensation modulation method suitable for a bridge arm multiplexing type modular multi-level high-voltage direct-current converter, and belongs to the technical field of high-voltage direct-current power transmission. The method comprises the following steps: firstly, generating respective quasi square wave reference voltage waveforms and quasi square wave reference current waveforms of a high-voltage bridge arm, a low-voltage bridge arm and a multiplexing bridge arm, then obtaining respective actual voltage reference values of the high-voltage bridge arm, the low-voltage bridge arm and the multiplexing bridge arm, then cooperatively adjusting the voltage of each bridge arm, generating a switching control instruction of each sub-module in each bridge arm, and finally switching the sub-modules in each bridge arm. And controlling the bridge arm current to complete quasi square wave commutation within a preset transition time, and completing bridge arm compensation modulation of the converter. The power transmission capacity, the dynamic response and the waveform quality are remarkably improved, meanwhile, the device is easily integrated into an existing bridge arm multiplexing type modular multi-level high-voltage direct-current converter, and the device is suitable for interconnection scenes of different direct-current voltage levels in a high-voltage direct-current power grid.

This invention provides a circuit topology and control method for high-power power conversion devices. This circuit topology exhibits low switching losses and high conversion efficiency in applications requiring high-frequency power switching. The invention also provides a power conversion device utilizing this circuit topology, outlining the device layout and transformer winding method. While meeting the requirements for high-power output, this further reduces the size and losses of the power conversion device, improving its steady-state and dynamic performance. Furthermore, this invention provides a voltage equalization control scheme to achieve voltage balancing between two high-voltage sub-circuits.

This application relates to an electronic starting relay, specifically within the technical field of relays. The electronic starting relay includes a bracket with a power supply terminal B+, an output terminal S, a signal input terminal, and a ground terminal E. The bracket integrates a control chip U1, a driver chip U2, an electronic switch Q1, and a power supply circuit. The input terminal of the power supply circuit is electrically connected to the power supply terminal B+, and the output terminal is electrically connected to both the control chip U1 and the driver chip U2. The signal input terminal is electrically connected to the control chip U1, and the control chip U1 is electrically connected to the driver chip U2. The input terminal of the electronic switch Q1 is electrically connected to the power supply terminal B+, the output terminal of the electronic switch Q1 is electrically connected to the output terminal S, and the control terminal of the electronic switch Q1 is electrically connected to the driver chip U2. This application enhances the vibration resistance and waterproof performance of the electronic starting relay, and provides overload and short-circuit protection, tooth top protection, timeout protection, secondary start protection, anti-drag protection, and a restart delay function.

The application discloses a kind of protection system and method of IGBT drive signal based on DSP and FPGA, belong to power electronics and power semiconductor control technical field.System includes signal acquisition unit, DSP master module, FPGA co-control module, IGBT drive circuit and IGBT power module;Signal acquisition unit acquires the operating state information of IGBT power module;DSP master module receives the control instruction and initial drive parameter of external system and carries out optimization to the parameter, handles fault signal and generates fault response instruction, sends control instruction, fault response instruction and optimized drive parameter to FPGA co-control module;FPGA co-control module generates PWM signal, generates fault signal and protection instruction according to the operating state information of IGBT power module when fault occurs;IGBT drive circuit receives PWM signal and protection instruction, generates IGBT drive signal;IGBT power module receives drive signal and responds, generates operating state information.The application can realize the real-time generation of IGBT drive signal, fault protection and dynamic optimization.

The invention discloses a passive auxiliary soft switching power amplifier based on hybrid ZVS (Zero Voltage Switching) / ZCS (Zero Voltage Switching). The passive auxiliary soft switching power amplifier comprises a double-direct-current voltage module, a double-resonant capacitor and resonant inductor passive soft switching network, a midpoint double-path parallel bridge arm, a double-switching tube high-frequency main power output bridge arm, a double-parallel auxiliary capacitor and an LC filtering output network. The passive auxiliary device adopted by the invention is simple, an additional auxiliary switch tube and a driving module are not needed, and the control complexity is greatly reduced; the design that the resonant inductor is connected in series with the midpoint bridge arm avoids the direct connection risk of the bridge arm fundamentally, dead time does not need to be set, and the operation reliability is improved; meanwhile, a hardware condition is created for realizing hybrid ZVS / ZCS for the full-switching tube, so that the switching loss is reduced, the heat loss of the whole machine is reduced due to the low-loss characteristic of the passive network, the heat dissipation design can be simplified, and the service life of the device can be prolonged; and the network structure is simple, small in size and easy to integrate.

A power conversion device according to an aspect of the present invention includes: a plurality of power conversion units connected in parallel via an inductance component; and a control unit that changes turn-on and turn-off timings of switching elements included in each of the plurality of power conversion units to control an output, in which the control unit alternately and repeatedly delays the turn-on timing of the switching elements included in the first power conversion unit and the turn-on timing of the switching elements included in the second power conversion unit.

The application discloses a single-phase photovoltaic energy storage converter and a control method thereof, relates to the technical field of photovoltaic charging and discharging control, and comprises a front-stage bidirectional power conversion unit, a rear-stage single-phase inversion unit, an integrated main control unit and a wide-voltage adaptation control unit. The input end of the front-stage bidirectional power conversion unit is used for being connected with a direct-current power supply, and the output end is connected with the direct-current bus end of the rear-stage single-phase inversion unit. The output end of the rear-stage single-phase inversion unit is used for being connected with a power grid or a load. The integrated main control unit is electrically connected with the front-stage bidirectional power conversion unit, the rear-stage single-phase inversion unit and the wide-voltage adaptation control unit respectively, and is configured to perform integrated collaborative control of double-mode switching, power conversion, battery management and energy scheduling. The wide-voltage adaptation control unit is connected with the front-stage bidirectional power conversion unit, and the front-stage bidirectional power conversion unit is configured to work in full-condition soft switching within a wide direct-current input voltage range.

A gate drive circuit adapted to high junction temperature environments, and its turn-on and turn-off methods, are disclosed. The gate drive circuit includes a main three-terminal transistor, a turn-off circuit, and an auxiliary circuit. The added auxiliary circuit generates an auxiliary current signal, either in the same direction or opposite to the control signal current, to the control electrode of the main three-terminal transistor during the turn-on and turn-off processes within a preset time period. This disclosure enables the generation of corresponding positive or negative auxiliary current signals at the control electrode of the three-terminal transistor. During the conduction process, the auxiliary circuit can generate a reverse auxiliary current signal at the control electrode of the three-terminal transistor during the current rise phase, reducing the drive current of the turn-on signal to decrease di. d / dt, suppressing the turn-on current; during the turn-off process, the auxiliary circuit can generate a unidirectional auxiliary current signal at the control electrode of the three-terminal transistor in the current-decreasing segment, increasing the drive current of the turn-off signal and accelerating the turn-off speed.

The disclosure provides a control method of an inverter system and an electronic device, and relates to the technical field of power electronics. The inverter system comprises a voltage conversion circuit and an inverter circuit. The control method of the inverter system comprises the following steps: acquiring an electrical parameter of the voltage conversion circuit; determining whether a control mode of the voltage conversion circuit meets a switching condition according to the electrical parameter; in the case where the control mode meets the switching condition, performing mode switching on the control mode, and the mode switching is used to realize mutual switching between a closed-loop control mode and an open-loop control mode; wherein, in the case where the control mode is the open-loop control mode, a switch tube of the voltage conversion circuit is driven at a fixed frequency and a fixed duty cycle, and in the case where the control mode is the closed-loop control mode, the switch tube of the voltage conversion circuit is driven at a variable frequency and a variable duty cycle. The embodiment of the disclosure can reduce the switching loss of the voltage conversion circuit and improve the overall conversion efficiency of the system.

A pulse width modulation control according to the present invention is performed such that, when changing a modulation rate when a sinusoidal wave is used as a waveform of a modulation wave, the modulation rate is continuously changed from a normal modulation region to an overmodulation region, and, in switching between the normal modulation region and the overmodulation region, the modulation rate in the normal modulation region is not discontinuous with the modulation rate in the overmodulation region. In the overmodulation region, limiting the modulation rate α prevents a jump phenomenon in pulse width from occurring and the continuity of the pulse width from disappearing due to the jump phenomenon. The upper limit αupper of the modulation rate α is a threshold at which the pulse width of a PWM pulse signal jumps to a duty ratio of 50 %, and limits the modulation rate α to less than the threshold.