JPH033601A - Power converter for electric car - Google Patents

Abstract

PURPOSE:To prevent the starting delay of a smoothing capacitor and to prolong the life of a contactor by operating a converter for a given period of time, when the DC side voltage of said converter lowers and the speed of an electric car increases and there is no operating command of said converter. CONSTITUTION:When PWM converter CONV interrupts operation, the voltage of a capacitor C1 starts lowering. In this case, when a rolling stock is coasting and its speed is higher than a certain value, the conditions of an AND circuit AND are satisfied if DC (VD) is lower than a set point corresponding to the peak value of AC voltage. Then, power is outputted from a one-shot timer T for a given period of time and the PWM converter CONV operates only for said period of time via a converter control circuit CONT to charge the capacitor C1 with electricity. At the time of starting said converter control circuit CONT and stopping said electric car, said conditions are not satisfied so that said operation is not performed.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention provides a converter in which a smoothing capacitor is connected to the DC side of a converter formed by bridge-connecting switching elements.
The present invention relates to a power conversion device for an electric vehicle that converts alternating current into direct current by controlling the switching element on and off to drive the electric vehicle.

(Prior art) Fig. 3 shows the main circuit of this type of power converter, in which the AC voltage taken in from the current collector PAN is supplied to the primary side of the main transformer T1, and the secondary side of this main transformer T1 is The AC voltage induced on the side is connected to the PWM converter C through a parallel connection circuit of contactor 1, contactor 2 and a series circuit of resistor R1.
Supplied to the DC side of 0NV. PWM converter C0N
In V, a diode is connected in a single-phase bridge, and a GTO Sirisk as a high frequency switching element is connected in antiparallel, and a rectified output is obtained on the DC side, which is converted into a smooth DC voltage by a smoothing capacitor C1. is converted to Next, this DC voltage is applied to the DC side of a VVVF inverter INV in which GTO thyristors are connected in a three-phase bridge and a freewheeling diode is connected in parallel to each GTO thyristor, and here, the variable voltage, iJ
Induction motor IMI is converted into alternating current with variable frequency.

1M2 is supplied.

In this Fig. 3, the GTO cyrisks constituting the PWM converter C0NV are controlled to turn on and off in a fixed order, so that the current flowing to the secondary side of the main transformer T1 has a sine wave shape, and the phase difference between the voltage and current is It is generally controlled so that the power factor becomes zero and the power factor becomes one.

By the way, in this power converter, the capacitor C
1 is used with a large capacity in order to smooth the pulsating current produced by rectifying the single-phase AC voltage. Therefore, when starting up this, if an AC power supply is directly connected to the PWM converter C0NV, a large inrush current will flow to the capacitor C1 through the diode bridge, making a protection circuit (not shown) that protects the input overcurrent of the PWM converter C0NV unnecessary. It will work.

Therefore, in order to limit this inrush current, a series connection circuit of 2 and resistor R1 is provided in the contactor, and at startup, 2 is first applied to the contactor to charge capacitor C1 through resistor R1, and then 1 to the contactor, and then control of the GTO thyristor is started.

(Problem to be solved by the invention) In the case of an electric vehicle, the main circuit does not operate continuously, but the PWM converter C operates in response to acceleration and braking between stations.
0NV must be started and stopped frequently. In this case, it takes time to charge the capacitor C1 whose voltage is low, and the contactor Kl is operated each time.

However, in this type of conventional power conversion device, there have been problems such as a start-up delay due to a voltage drop in a smoothing capacitor and a shortened lifespan of a contactor due to frequent operations.

This invention was made to solve the above problems, and is a power conversion device for electric vehicles that can eliminate startup delays caused by voltage drops in smoothing capacitors and extend the mechanical life of contactors. The purpose is to obtain.

[Structure of the invention]

(Means for Solving the Problems) In the present invention, a smoothing capacitor is connected to the DC side of a converter formed by bridge-connecting switching elements,
In the device for driving an electric vehicle by converting alternating current into direct current by controlling the switching element on and off, a first detection means detects that the direct current side voltage of the converter has decreased below a predetermined value; A logical product condition of a second detection means for detecting that the speed of the vehicle has increased above a set value, the outputs of these first and second detection means, and a signal indicating that there is no operation command for the converter is satisfied. The converter is characterized by comprising a logic circuit that determines whether the converter has been activated, and a timer that operates the converter for a predetermined period of time based on the output of the logic circuit.

(Function) PWM converter C0 that constitutes the above-mentioned power conversion device
The output voltage VDC of NV is as shown in Fig. 2(a),
It is higher than the peak value VACRP of the AC voltage. In addition, since the impedance of the current correction circuit including capacitor C1 is quite high, even if control of PWM converter C0NV is stopped, the voltage of capacitor C1 will not drop in a short time.
Declines relatively slowly.

On the other hand, capacitor C when starting PWM converter C0NV
An inrush current for 1 occurs only when the DC voltage VDC is lower than the peak value VACRP of the AC voltage, and does not occur when it is higher. Therefore, as shown in FIG. 2(b), the DC voltage VDC
It is sufficient if there is a means for operating the PWM converter C0NV for a certain period of time each time the AC voltage starts to become lower than the peak value VACRP of the AC voltage.

The present invention focuses on this, and the logic No. 15 indicates that the DC side voltage of the converter has fallen below a predetermined value, that the speed of the vehicle has exceeded the set value, and that there is no command to operate the converter. Since the converter is operated for a certain period of time when the product condition is satisfied, the voltage of the smoothing capacitor is maintained above a predetermined value, and the number of contactor operations is suppressed, thereby preventing startup delays. And the life of the contactor is extended.

(Embodiment) Figure 1 is a circuit diagram showing an embodiment of the present invention.
Elements that are the same as those in the figures are given the same number 0 and their explanations will be omitted. Here, the voltage detector PTI detects the secondary voltage of the main transformer T1 and outputs a voltage signal VA to the current detector CTI.
detects the secondary side current of the main transformer T1 and supplies the current signal 11, and the voltage detector PT2 detects the output side voltage of the PWM converter C0NV and supplies the voltage signal VD to the converter control circuit C0NT. Circuit C0N
T controls each excitation coil of contactor Kl and 2 under the condition of the presence of operation command Ps, and also controls PWM converter C0N.
Controls the CTO cyrisks that make up V.

In addition, a setting signal VACR corresponding to the peak value of the alternating current
An amplifier AMP 1 which uses A as one input and the voltage signal VD of the voltage detector PT2 as the other input, compares the two and detects that the DC voltage has decreased from the peak value of the AC voltage.
A setting signal VEL(') corresponding to a low speed of 5 Km/h fri degrees is inputted on one side, and an actual speed signal VEUI from a speed detector (not shown) is inputted on the other side.The two are compared and the speed of the vehicle is determined. an amplifier AMP2 that detects that the speed has decreased below a set speed; a negative circuit NOT that inverts the level of the operation command PS;
Human power, the output of the negative circuit NOT is connected to the second human power, amplifier AMP
The present invention includes an AND circuit AND which uses the output of the AND circuit AND as a third human power, and a one-shot timer T which gives an operation command to the converter control circuit C0NT for a fixed period of time based on the output of the AND circuit AND.

The operation of this embodiment configured as described above will be explained below.

First, the converter control circuit C0NT operates the contactor Kl on the condition that the operation command PS is given.

It controls the current in the coil of K2 and provides an appropriate signal to the gate of the GTO thyrisk that constitutes the pwhi converter C0NV. In this case, PWM converter C0N
When V is first started, the vehicle speed is zero and amplifier AMP2
Since the output of is rOJ, the condition of the logical product circuit AND is not satisfied, and the one-shot timer T does not output a signal, so the charging circuit using the contactor Kl, 2 and resistor R1 described earlier is activated. to start the PWM converter C0NV.

Next, when the PWM converter C0NV stops operating,
The voltage of capacitor C1 starts to drop, but at this time, if the vehicle is coasting and the speed is above a certain value, the DC voltage detection signal VD will be lower than the set value VACRP corresponding to the peak value of AC voltage. Now the AND circuit AN
Condition D is satisfied, and the one-shot timer T outputs an operation command for a certain period of time. This operation command causes PWM
Converter C0NV operates for a short period of time to charge capacitor C1 to a high DC voltage again.

In this case, the short-term operation of the PWM converter C0NV is so-called. Since the condition is close to no-load operation, P
There is no burden on the WM converter C0NV.

In addition, short-time operation of PWM converter C0NV is conditional on the speed exceeding a predetermined value, so when the electric car stops, the charge in capacitor C1 is discharged, preventing electric shocks during inspection. be able to.

Thus, according to this embodiment, control is performed in accordance with the principle explanatory diagram of FIG. suppressed.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is detected that the DC side voltage of the converter has decreased below a predetermined value, while it is detected that the speed of the vehicle has increased beyond the set value, and these detection signals are detected. , and a signal indicating that there is no operating command for the converter is established, and the converter is operated for a certain period of time. This prevents a delay in starting due to a voltage drop in the smoothing capacitor, and The mechanical life of the contactor can be extended.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
), (b) is a time chart for explaining the present invention in detail, and FIG. 3 is a diagram showing the main circuit for explaining a conventional power conversion device for an electric vehicle. C0NV...PWM converter, C1...capacitor, PTI, PT2...voltage detector, Kl, 2...
・Contactor, R1...Resistor, C0NT...Converter control circuit, AMPl, AMP2...Amplifier, NOT
...Negation circuit, AND...Logical product circuit, T...One-shot timer.

Claims (1)

[Claims] A smoothing capacitor is connected to the DC side of a converter formed by bridge-connecting switching elements, and the switching element is controlled on and off to convert AC to DC to drive an electric vehicle, wherein the converter is a first detection means for detecting that the DC side voltage has decreased below a predetermined value; a second detection means for detecting that the speed of the vehicle has increased above a set value;
a logic circuit that determines that an AND condition of the output of the detection means and a signal indicating that there is no operation command for the converter is satisfied; and a timer that operates the converter for a certain period of time based on the output of the logic circuit. A power conversion device for an electric vehicle, characterized by comprising: